Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924012212019 > ' Cornell University Library Q 113.A57 The scientific papers of the late Thomas 3 1924 012 212 019 SCIENTIFIC PAPERS THE SCIENTIFIC PAPERS OF THE LATE THOMAS. M^DEEWS, M.D., F.R.S. VICE-PRESIDENT AND PROFESSOR OF CHEMISTRY QUEEN'S COLLEOB, BELFAST MEMOIE o^ny'v li T pr- BY PTorTAIT, M.A., Sec.R.S.E.,and aTcRUM BROWN, M.D,, F.R.I PROFESSORS IN THE UNIVERSITY OF EDINBURGH LONDON MACMILLAN AND CO. AND NEW YORK 1889 All rights reserved PREFACE. Among the noted names which adorn the history of Britain during the last half century, one of the most brilliant groups is that of the Experimental Philosophers whose work lay, in great part, in the border-land between Chemistry and Physics. It is remarkable that each of the three kingdoms is represented in this group by at least one prominent member, England by Faraday and Joule, Scotland by Graham, Ireland by Andrews. The scattered papers of the three first-named have been collected and republished, so that they are now easily acces- sible. In the present work we have endeavoured to complete this series of reprints, so as to exhibit in a connected form the steps by which Andrews developed such grand subjects as Real of Combination, the Natitre of Ozone, and the Continuity of the Liquid and Gaseous States. Andrews' published papers have, with one or two unim- portant exceptions, been reprinted verbatim, and we have been able to obtain clieMs of most of the wood-cuts. To ensure accuracy in the plates, oi which the originals had long been destroyed, we have had them exactly reproduced by photo- lithography. Our task has been rendered comparatively easy by the zealous and efficient aid which we have throughout received from the daughters of Dr. Andrews. Not only have they made iv Preface. the very complete Index, and assisted with scrupulous care in the correction of the press, they have more than once called our attention to slips or inadvertences which had escaped our notice. Wherever anything of this kind has been discovered,, we have inserted [in square brackets] a Note containing the requisite correction, extracted if possible from the author's, laboratory books. The steel portrait has been engraved from an excellent photograph, taken at Paris in the summer of 1875. It repre- sents very faithfully the appearance of Dr. Andrews in his sixty-second year. In writing the brief Memoir which foUows, we have availed ourselves as far as possible of Dr. Andrews' own letters ; and have quoted occasionally from letters received by him, in par- ticular those dealing with scientific matters. Without seeking formal permission from the writers, or their representatives, we could not have made use of the mass of Dr. Andrews' corres- pondence ; especially that which relates to his official work, or to political questions such as those connected with the Supplemental Charter. Many of these questions perforce occupied Dr. Andrews' thoughts and time to the prejudice of his scientific inquiries ; but we have passed them over lightly. We have endeavoured to picture to the reader the Man, and especially the Man of Science ; — not the sorely-tried Vice- President of an Institution which was more than once treated as a sort of political shuttle-cock. P. G. Tait. Alex. Ceum Beown. College, Edinbubgh, December, 1888. CONTENTS. PAGE Memoir, ix I. — On the Action of a Flame urged by the Blowpipe on OTHER Flames, - 1 II. — On the Detection of Baryta or Strontia when in Union WITH Limb, 3 III. — Chemical Researches on the Blood op Cholera Patients, 7 IV. — On some Caves in the Island of Rathlin and the adjoin- ing Coast of the County op Antrim, 20 V. — On the Changes produced in the Composition of the Blood BY repeated Bleedings, 21 "VI. — On the Conducting Power of certain Flames and op Heated Air for Electricity, 25 VII. — On the Thermo-electric Currents developed between Metals and Fused Salts, 36 VIII. — On some singular Modifications op the Ordinary Action of Nitric Acid on certain Metals, 45 IX. — On the Influence of Voltaic Combination in Chemical Action, - - 47 X.^On the Action op Nitric Acid upon Bismuth and other Metals, - 49 XI. — On the Properties of Voltaic Circles in which concen- trated Sulphuric Acid is the liquid Conductor, - 57 XII. — On the Cooling Power of Gases, 66 vi Contents. PAGE XIII.— On the Heat developed dttrino the Combination op Acids and Bases, - '"■ XIV.— On the Heat developed DtiEiNa the Formation of the Metallic Compounds of Chlorine, Bromine, and Iodine, 90' XV. — Notice of some recent Determinations of the Heat developed during the Formation of certain Compounds OF Chlorine, - " ■'•"^ XVI.— On the Thermal changes accompanying Basic Substi- tutions, '■'^' XVII. — Note on the Irish species of Eobertsonian Saxifrages, IS* XVIIL— On the Heat disengaged during the Combination of Bodies with Oxtgen and Chlorine, - - 130 XIX. — On the Specific Heat of Bromine, - 161 XX. — On the Latent Heat of Vapours, ISS XXI. — On the Heat disengaged during Metallic Substitu- tions, - 1V9' XXII. — Report on the Heat of Combination, 19& XXIII. — Account of an Apparatus for determining the Quantity of Htgrometeic Moisture in the Air, 221 XXIV. — On a Method of obtaining a Perfect Vacuum in THE Receiver of an Air-pump, 223 XXV. — On THE Discovery of minute quantities of Soda by the action of Polarized Light, 228- XXVI.^On the Atomic Weights of Platinum and Barium, 22& XXVII. — On the Microscopic Structure of certain Basaltic AND MeTAMORPHIC RoCKS, AND THE OCCURRENCE OF METALLIC Iron in them, . 231 XXVIII. — On a new variety of Magnetic Iron Ore ; with Remarks upon the Application of Bicarbonate of Baryta to Quantitative Analyses, 234 Contents. vii PAQE XXIX.— On a new Aspirator, 235 XXX. — On a simple Instrument for Graduating Glass Tubes, 239 XXXI. — On the Constitution and Properties op Ozone, - 240 XXXII. — On the Polar Decomposition op Water by common AND atmospheric Elbctricitt, 258 XXXIII. — Note on the Density op Ozone, 262 XXXIV. — Second Note on Ozone, 264 XXXV. — On the Volumetric relations op Ozone, and the Action op the Electrical Discharge on Oxygen and other Gases, 267 XXXVI. — On the Eppect op Great Pressures combined with Cold, on the Six Non-Condensable Gases, 293 XXXVII. — On the Identity op the Body in the Atmosphere which decomposes Iodide op Potassium with Ozone, 294 XXXVIII.^ — On the Continuity op the Gaseous and Liquid States op Matter, 296 XXXIX.— On the Absorption-bands of Bile, 318. XL. — On the Heat developed in the Combination op Acids AND Bases. (Second Memoir), 319 XLL— On the Gaseous and Liquid states op Matter, 333 XLII. — Address to the Chemical Section op the British Association, - 344 XLIII. — On the Dichroism op the Vapour op Iodine, 359 XLIV. — On the Action op Heat on Bromine, 360 XLV. — ^Address on Ozone, 361 XLVI. — On the Composition op an Inflammable Gas issuing prom below the Silt-bed in Belfast, 381 viii Contents. PAOE XLVII. — Preliminary Notice of furthbr Eesbarches on the Physical properties op Matter in the Liquid and Gaseous states under varied conditions of Pressure and Temperature, 383 XLVIII. — Presidential Address, - XLIX. — On the Gaseous state of Matter, 393 418 L. — On the Properties of Matter in the Gaseous and Liquid states under various conditions of Temperature and Pressure, 457 LI. — Electro-Magnetic Machines and the recent Improvements IN THEM BY M. GRAMME, 472 LII. — On the Heat developed in the Combination of the Acids AND Bases, - 492 LIII. — On the Heat devklopbd in Chemical Reactions, 495 LIV. — Note on the Composition of Magnetic Oxide of Iron, AND on the Occurrence of that Mineral and of Metallic Iron in certain Igneous and Metamorphic Hocks, - 505 Index, 509 PLATE ILLUSTEATIONS. Portrait of Dr. Andrews, Plate I., - IL, IIL, IV., v., VI., Frontispiece. To face page 94 „ 130 235 „ 242 „ 270 „ 298 MEMOIE. Thomas Andrews was born at 3 Donegall Square, Belfast, on the 19th December, 1813. His grandfather Michael, eldest son of John Andrews of Comber, married a daughter of Dr. Meek of Campfield, near Falkirk. The eldest son, Thomas John Andrews, settled as a linen merchant in Belfast, where he married Elizabeth, daughter of James Stevenson, and grand- daughter of Adam Johnston of Glynn, Co. Antrim. They had six children, of whom Thomas, the subject of this memoir, was the eldest. Andrews was sent at an early age to the Belfast Academy, and thence to the Academical Institution, where he studied mathematics under Professor James Thomson, and classics under the Eev. Dr. Hincks, both men of mark in their respective departments. He acquired considerable proficiency in Prench under Monsieur D'Oisy, for whom he entertained a high regard. He was a diligent pupil, and gained several prizes. His most intimate companion was Thomas O'Hagan, afterwards Lord Chancellor of Ireland ; and the close friendship formed at school lasted uninterruptedly through life. From the Institution Andrews was transferred for a short period to his father's office, but left it in 1828 to study chemistry, under Dr. Thomas Thomson, at the University of Glasgow. He was described in a letter of introduction, from the well- X Memoir. known Belfast physician Dr. M'Donnell, to Dr. Thomson, dated 1st November, 1828, as a modest, silent boy, who had a great capacity for general knowledge, and who wished to study chemistry profoundly, not merely as being connected with his professional business, but as a great branch of human know- ledge. Andrews attended the Chemistry Class during the winter session 1828-9 : and Professor Meikleham certified that, in the Public Class of Natural Philosophy, which he attended at the same period, " he distinguished himself for ability." After this first coUege session, and while only fifteen, Andrews published his first scientific paper, " On the Action of the Blowpipe on Flame." This was shortly afterwards followed by a note " On the Detection of Baryta or Strontia when in union with Lime,'' characterized by the care and analytical skill so conspicuous in all his subsequent work. (See Nos. I. and II., below.) In a letter dated March 25th, 1830, Dr. M'Donnell suggests to Thomas Andrews, sen., that his son " should enter Dublin College, and return home from that, without pursuing the usual course of study there. He should at the same time be bound nominally to a surgeon, .... after which he should go to France and Italy, and remain there until he has satisfied his own mind; and, returning from_ thence, should attend as many terms in Dublin as would qualify him for taking the degree of Bachelor of Arts, and either or both the other degrees in Surgery and Physick ; taking care, in these pursuits, never to relinquish the, idea of becoming ultimately a merchant if it be- came his duty or interest to do so." This somewhat peculiar advice seems to have been acted upon, and in the summer of 1830 Andrews went by sea to Bordeaux, whence he made his way to Paris through the south and centre of France. In the Diary which he then kept there Metnoir. xi are notes describing the geological features of the Gave (Basses. Pyrenees), showing his early bent towards observational science ; and in later life he often spoke with interest of his visit on this occasion to Anvergne. On his arrival in Paris he wrote to his mother as follows, under date September 27th, 1830 : — None of the classes have commenced yet. I believe they will not open till November. At present Grovernment is remodelling the dif- ferent schools, as well as every other department. I have called on M. Th6nard twice, but without seeing him. I will positively see him to-morrow, and, if possible, will commence in a laboratory immedi- ately. . . . (29th). — I called yesterday morning on M. Th6nard, to whom M. D'Oisy had previously spoken about me. He told me that at present it was the vacation, but to call on him the 25th of next month, when he would give me a ticket which would enable me to attend and get a good place at all the lectures. . . . Mr. Hawden informed me that there was at present a course of lectures instituted expressly for the use of the students who may be at Paris during the vacation. He introduced me there himself, so that I shall now be enabled to study as well as during the winter. The lectures are upon Zoology, Chemistry in its application to the Arts, Botany and Vegetable Physics, and Mineralogy and Geology. . . . The Professor of Chemistry in the above Institution (M. Payen) is very celebrated, and his course is said to be very good. The only letter I have not yet delivered is that of M. Brongniart. The reason is that he does not live in Paris, but at Sfevres. I shall probably walk out there to-morrow ; but I do not believe any laboratory will be open before November. . . . (October 19th). — I called some time past on M. Brongniart at Sfevres. He received me with great civility, told me that he would make inquiry upon the subject of a laboratory, and write to me in a day or two. At the same time he gave me permission to see the porcelain manufactory of which he is the conductor. This was a thing of some importance, as it is, I believe, almost impossible to obtain an order to see it. I accordingly received a note from him two days after, in which he stated that, having consulted his son-in- law, M. Dumas, he had directed him to M. Sobeiran. I immediately xii Memoir. called on the latter, but he told me that his laboratory -was quite ele- mentary, and that I would not be able to find any laboratory in Paris like those of Berzelius or Stromeyer where analysis is practised. I was a good deal provoked at this intelligence, but resolved not to despair. I called immediately on Dumas (who is the Professor of Chemistry at the Eoyal College of France, and one of the ablest chemists here), and explained to him what I wanted. He received me with much courtesy, and said that he was not certain he would be able to accommodate me in his own laboratory, but he would speak to some of his friends. . . . This will be still more useful than any school. ... In addition to the lectures I before mentioned (two of which, however, have closed), I now follow an excellent course of chemistry applied to dyeing, by M. Chevreul, a chemist of the first rank, the director of the manufactory of the Gobelins. The regular winter course will not commence till Novem- ber. In short, I am as busy as I can be. . . . (October 21st). — But I quit public affairs to tell you of my good fortune \vith respect to a laboratory. I return at this moment from the laboratory of M. Dumas, where I have spent the morning, and in which he has permitted me to work. He is at present engaged in organic analysis. . . . He is exceedingly affable, and con- versed the whole morning with me on the state of chemistry, etc., in England. I cannot enter into particulars, but his opinions coin- cided exactly with the ideas I had on the subject. . . . There is only another young man in the laboratory — an American — but we all speak French. I cannot express to you how fortunate I consider myself in having succeeded thus ; .... I need not repeat that M. Dumas stands in the very first rank here. Besides, it is an admirable opportunity of acquiring the language. On that subject I did not find the least difficulty in following any of the lec- tures — indeed, I took as copious notes from the first lecture I attended as I could have done had it been delivered in English. ... If chemistry will be ever of any service to me scientifically, I am on the road both to acquire it well and to see the great men here who pursue it. I shall, of course, attend M. Dumas' course at the College of France, which is public. ... I never was in better health and spirits than at present — indeed, I must acknow- ledge to you that I was a little fagged and wearied in travelling. . . . . In fact, a companion is absolutely necessary ; besides, I must confess, I prefer the fumes of the laboratory to the air of the Memoir. xiii mountains — but of all this again. I have nothing more to say. Tell the doctor I shall bear in mind his request should I have the good fortune of meeting M. Gay-Lussac. ... I breakfast every morning at a Httle after seven, and from that time till nine o'clock at night I have not an idle moment. . . . In addition to his chemical work Andrews spent some time each day in the Hopital de la Pitie. But a severe attack of fever rendered it necessary for him to return home. After his return he passed a successful under-graduate course of four years in Trinity College, Dublin, where he dis- tinguished himself in classics as well as in science, and obtained several prizes, with certificates in lieu of others which the college rules against pluralities prevented his receiving. He attended at the same time lectures in the School of Physic in Ireland, in the Meath Hospital, and in the Eichmond Surgical Hospital. In November, 1832, he wrote as foUows to his father: — I received both your letters in due time, and having now had a little experience of the different studies in which I am engaged, I can form a more correct judgment of what I shall be able to execute as well as attempt. I first consulted with Mr. M'Clean as to reading with a tutor, and to this, as he had been always formerly, so now he was opposed ; indeed, the Fellows in general are very averse to grinders, conceiving that although they may enable an inferior scholar to gain a prize over a superior, yet in the end they are of more injury than use to those who read with them, since it is a very different thing to read and understand the matter of an examination, and to be made up on it as a child or parrot. It is for this reason chiefly that I think it will be better for me to end as I have begun, and gain what advantage I can from the college course. But another motive more immediately influences me, that if I gave another hour to attendance on a tutor I should have scarcely any time left for private study. I first attend morning lecture at six o'clock — then my medical studies occupy me till one or two — and on two days in the week Hamilton lectures from two to three on astronomy. This I am sure you will think full enough occupation, but should xiv Memoir. you however still wish me to read with a tutor I will do it. . . . Although I never spoke of my experiments to any one {except Apjohn) and the No. of the Phil. Mag. which I brought with me lies still untouched in my desk — yet Mr. M'Clean heard of them from rumour and told me he had read a paper of which I was the reputed author. However, though I mention these circumstances, yet it is no less my resolution to devote every moment I can spare from the medical studies to the college business. . . . A year later he writes to his mother as follows : — . . . I am greatly absorbed in my hospital and medical studies ; — indeed I begin to feel an enthusiasm similar to what I used to have for chemistry ; the diseases I see, the treatment, every- thing connected with them is the general object of my waking thoughts ; — and such a state of mind is one of the happiest. Dr. Graves has the peculiar talent of investing every object he touches on with a deep and stirring interest ; and for this alone I shall ever be indebted to him. I breakfast before seven o'clock, and, of course, by candle light ; my hospital occupies me from eight till eleven or twelve. Some days I have a lecture from eleven till twelve — then during the day I either read or dissect till three — another lecture till four : the rest of the evening is devoted to reading. In 1833 Andrews seems to have intended to become a student in the laboratory of Berzelius. He obtained for this purpose a letter of introduction from M. Dumas ; but the intention was not carried out, and the letter was sent in with his testimonials when Dr. Andrews applied for the Professor- ship of Chemistry in the Belfast Institution. M. Dumas says — " M. Andrews m'a paru z^le et capable, digne enfin de vos hauts enseignemens. J'ose espdrer que vous serez assez bon pour Taccueillir favorablement, et que vous en ^prouverez toute la satisfaction qu'il m'a procur^e, pendant son trop court s^jour auprfes de moi." In 1834 Andrews attended hospital and dispensary prac- tice in Belfast ; he spent the ensuing winter and summer sessions in Edinburgh, where he studied under Drs. Alison, Graham, John Thomson, Knox, and Turner. Memoir. xv In November of that year he wrote to his mother the follow- ing interesting details as to the Edinburgh Medical School: — As to lectures I am yet undecided — midwifery, surgery, clinical medifcine, and anatomy I must attend; I shall be examined on botany in March. The easiest way of preparing for this examination is to attend the lectures now, instead of in summer. So here are five classes besides the dissections — then I do not know whether Dr. Thomson's class must be attended by me till I see the Dean of Faculty ; and if it is not, I do not think I shall take his ticket. These are certainly too many lectures to attend, but as they do not call rolls I must omit those that are least useful. They are all absolutely required either for degree or diploma. As to myself I never felt in better health or spirits. . . . Again towards the end of the session he writes : — I am busily engaged in preparing for these examinations, although I feel no anxiety as to the result, yet examinations always keep one excited; besides it is here universally the custom to grind, but I do not think that it is necessary, or else I should not hesitate to do so. It is a great advantage to me that I have not to prepare chemistry, as this is the subject upon which students are in general most deficient and which they most fear at the examinations. Botany and anatomy occupy my attention especially at present. There are two examinations for the degree, but the first is the more important, and I expect to have it over as well as that for my diploma towards the end of April or beginning of May. The second examination for the degree will take place probably about June, but the degree is not granted till the 1st August, when I must be present, and I shall also have one class to attend during summer. Then, if all goes on well, the world will be open before me. . . . There is one great source of pleasure in the medical profession which few other pursuits afford in the same degree — the great and intense interest of the subject which affords one so much excitement; and although this is also too often a cause of great anxiety, yet I believe there are few medical men who would willingly exchange their pursuit for any other. . . . 27th March, 1835. — I was present to-day at a concluding lecture of Dr. Chalmers, which was certainly very eloquent and beautiful. xvi Memoir. He passed the warmest eulogium on the bishops of the Church of England, and said that the scholars, highly equipped and armed, which had issued from Oxford and Cambridge had done more for the cause of Christianity than any other body of men, and rendered the Established Church deserving of all her highest endowments. . . . You would have supposed that you had been listening to a laboured eulogium on the Church of England from some of her own prelates. ... I cannot say that I thought his style of reason- ing at all equal to his oratory. He spoke a great deal about New- ton — as in his work on astronomy — but he failed greatly in establish- ing a comparison between him and the peasant studying the Bible. It is curious that the whole lecture was occupied in defending a position which Dr. Bruce maintains in his sermons, and which was controverted by some of his opponents, viz., that an unlettered peasant is as capable of discovering the true system of theology as the ablest divine. He declared that a peasant was able to discover all the truths of religion and see the grounds of all creeds ; but that it required a man of the most extensive acquirements to be able to defend them. The following excerpt from a letter of April 5th, 1835, is of peculiar interest, though of a very different kind : — I dined twice from home last week rather against my wish, as I am at present engaged so much ^vith preparation. It was with Mr. Horner and Mr. Miller. I met young Kean at Mr. Horner's and was greatly pleased with his conversation and manner. We after- wards went to see him in the character of Shylock ; he is not, in my opinion, at all equal either to his father or to Young, but still he has very high powers and I think a greater command of countenance than any actor I have ever seen. He succeeded here last winter very indifferently, but during the whole of his present engagement he has performed to crowded houses, and with great simplicity he told us that his success had on this occasion been so unexpected that it had quite overpowered him, so that he scarcely slept for the first week which he spent in Edinburgh. He gave us a very interesting account of himself and his father, with whom he had often acted tlie part of father and son in tragedies. The excitement of acting Eichard III. he mentioned is so great that he has to be carried ofi" the stage and laid in bed nearly insensible— where he is muffled up till he recovers. It was very kind of Mr. Horner to afford me such an Memoir. xvii opportunity of seeing so interesting a person. Nothing, however, must induce me to go out again till my exams, are over. On the 25th April, 1835, Andrews obtained the Diploma of the Eoyal CoUege of Surgeons of Edinburgh, and on the 1st August of the same year the degree of M.D. of the University of Edinburgh. His thesis was entitled " On the Circulation and the Properties of the Blood." In 1 8 3 5 he was offered, and declined, the Chairs of Chemistry in the Eichmond School of Medicine and in the Park Street School of Medicine, Dublin. His own view of the matter is summarily expressed thus : — . . . Again I have kicked away the ball of fortune and preferred the humbler attractions of Dame Prudence to her more glittering rival. In plain language, I have declined the situation in the Park Street, and you may expect me in Belfast in a few days. . . . I have made a very beautiful discovery in toxicology. When I told Dr. Stokes of a consequence of it in a very simple case which every one imagines he understands, he seemed greatly surprised. " Is it new to you," I asked him. "Yes," he replied, "and to every one else : don't mention it to any one till you publish it." I intend therefore to show that it has not been incapacity which has made me shrink from this situation, by publishing a paper on this subject which will do me, I hope, some credit. In the same year, having settled in Belfast as a physician, he was the first Professor appointed to teach chemistry in the Eoyal Belfast Academical Institution, and during the next ten years he delivered extended courses of lectures, and gave instruction in practical chemistry, to a large number of students. A successful private practice left him little time for research, but during the immediately succeeding years he pro- duced several very valuable papers, chiefly connected with Voltaic Action and Heat of Combination. The latter of these were soon thoroughly appreciated by scientific men both at home " and abroad ; and Andrews became recognized as one of the most promising of the younger chemists. S( xviii Memoir. Dr. Andrews visited Paris again in 1836. He writes to his mother, on July 28th of that year: — It is La Piti6 that I shall attend principally, and 1 find that there are private courses such as I required. I have also ascertained that the other establishment will be open to me as having graduated, so that the principal objects of my journey will be accomplished. . . . This day being the anniversary of the Eevolution, there was funeral service in all the churches, both protestant and catholic, which were all in deep mourning on account of those who died during the three days. The music in the church of St. Eoch was very fine. There was both a military and a sacred band. Tomorrow there will be magnificent illuminations for the Eevolution, and the celebrated triumphal arch, which was commenced thirty years ago by Napoleon and is only now finished, will be opened. There was also to have been a review of 150,000, but in consequence of the discovery of some conspiracy, real or pretended, against the king's life, this will not take place. Dr. Chermside invited me to dine with him to-morrow and afterwards to go and see the illuminations I have not yet called upon Dumas. . . . . Do not write to me till the Phil. Magazine for August comes. . . . The last sentence is very suggestive. It obviously refers to the paper on the Conditcting Power of Flame, reprinted as No. VI., p.^25 below. A subsequent letter, dated 1st September, gives the following very interesting information : — . . . I happened to be at the meeting of the Institute last Monday week, when I was surprised by being accosted by Mr. Graham of Glasgow, who has come to Paris for a few weeks on his way to Germany. I was greatly delighted to see him, and this unexpected circumstance has afforded me an opportunity of seeing and conversing with most of the distinguished chemists here. M. Dumas had just returned, and was also at the Institute. After the meeting we spoke to him, and he invited us to breakfast with him. He recognized me at once and received me very kindly. He had heard of Mr. Graham's arrival and had been looking for him at the meeting, and it was pleasing to see with what distinction and attention he received the latter. On the day on which we break- Memoir. xix fasted with him he spent several hours in conversing with Mr. Graham, showed us the ficole Poly technique, and the Conservatoire des Arts, and we did not separate till nearly five o'clock. Next day we proceeded to visit, at the Gohelins, M. Chevreul, one of the most eminent chemists here, who also received Mr. Graham with much distinction, and explained to us some interesting researches in which he has heen engaged. We afterwards saw one of the most amiable and talented of the French chemists, M. Berthier, who has the direction of the School of Mines, and M. Jules Gay-Lussac. When we meet I will detail all that occurred at these interesting interviews. All these persons received Mr. Graham as a chemist of high reputation, and henc? the interviews did not consist of a few words of ceremony, but lasted for some hours. Of what use they have been to me you may judge from the circumstance that I shall have to-morrow an opportunity of witnessing a very important experiment in M. Berthier's laboratory, and that M. Jules Gay-Lussac has promised to introduce me to his father when he returns to town. I spent the whole week with Mr. Graham, and had an opportunity of telling him of my galvanic experiments, which appeared to interest him ; and he has also been so kind as to give me very flattering letters of intro- duction to Mr. Faraday, Dr. Turner, and Mr. Phillips, which I will deliver on my return. So you see I have thus attained nearly all my desires in this way. . . . It should be mentioned in this connection that Andrews became very intimate with Faraday, for whom he entertained a feeling of extraordinary regard. Unfortunately the correspond- ence between them, so far as it has been preserved, contains little of importance from the purely scientific point of view. A characteristic extract, however, will come in appropriately at its proper date. The letter proceeds to state that Andrews had ordered a thermo-multiplier and galvanometer, both of the most exquisite delicacy. I found that there is only one person here (or in the world) who can make them, M. Gourjon, whose name you may remem- ber I found mentioned in Dumas' work. On calling upon him I was both astonished and delighted at the perfection of his instru- ments. . . . He is not a common instrument maker, but a young XX Memoir. man enthusiastically fond of the subject, and whose repiitation is already great, so that this is not puflBng. Besides the instrument makers both in London and Paris, Dumas, and Becquerel in his work refer to him as the only person who can construct these beautiful pieces of apparatus. I must also tell you that I have a most important train of experiments in view in which they will be absolutely essential. . . . Apropos of this he says, September 19 th : — . . . You must not suppose that I have been neglecting medicine ; on the contrary, I have continued sedulously to attend the hospitals, and have derived a great deal of information, particu- larly on the use of the stethoscope. The advantages here of every kind are very great, and incomparably superior to what exist else- where — at least, where I have been. But, as I anticipated, the lectures are all closed, so that I have little to do during the day or evening. However, I do not think it would be worth while to return here again in summer, S,s the principal, indeed all the important, medical lectures are in winter, and both my lectureship and profession would prevent me from being absent during that period of the year. I hope our hospital will soon be completed, and in a state for the reception of patients. . . . During the next few years Andrews published a number of original papers connected with Voltaic circuits, and a very curious one " On the Thermo-electric Currents hetween Metals and Fused iSalts " (No. VII. below). He was elected a member of the Eoyal Irish Academy in 1839, and became an original member of the Chemical Society in 1841. In 1842 Dr. Andrews married Jane Hardie, daughter of Major "Wallcer, formerly of the 42nd Highlanders, who had served in Egypt and in the I'eninsula, and who afterwards joined the Eenfrewshire Militia. The wife of Major Walker was Penelope Leslie, the youngest daughter of Adam Johnston of Glynn, already mentioned as a maternal ancestor of Dr. Andrews. In 1843 Andrews received from Faraday the following highly characteristic letter : — Memoir. xxi Your hearty letter reached me yesterday, and there are two points in it which I cannot allow myself to leave unanswered, however un- worthy I am to write, or lazy I may be, or indisposed as I may think myself. .... Your kind invitation is most acceptable to me, though I have no idea when I can take advantage of it : — perhaps never, but the thought of your wishing it is itself refreshing, and I do sincerely thank you for your kindness. For your paper, too, I thank you, and though I agree with Rochefoucault in most things, yet my gratitude is something besides a keen sense of favours to come. As to the particular point of your letter about which you honour me by asking my advice, I have no advice to give, but I have a strong feeling on the matter, and will tell you what I should do. I have always felt that there is something degrading in offering rewards for intellectual exertion, and that Societies or Academies or even Kings and Emperors should mingle in the matter does not remove the degradation ; for the feeling which is hurt is a point above their condition, and belongs to the respect which a man owes to himself. With this feeling I have never, since I was a boy, aimed at any such prize, or even if as in your case they came near me, have allowed them to move me from my course, and I have always contended that such rewards will never move the men who are most worthy of re- ward. Still I think rewards and honours good if properly distributed, but they should be given for what a man has done, and not offered for what he is to do, or else talent must be considered as a thing marketable and to be bought and sold ; and thus down falls that high tone of mind which is the best excitement to a man of power, and will make him do more than any common-place reward. When a man is rewarded for his deserts, he honours those who grant the reward, and they give it not as a moving impulse to him, biit to all those who by the reward are led to look to that man for an example. If, I were you, therefore, I should go on my way and discover and publish (if I could) ; but having done that, I see no objection, as the time draws nigh, to send copies of the papers to the Academy or even such an account of them as may be considered fit — and, in doing so, I should think I was paying a fit mark of respect to the Academy, and giving them the opportunity of marking their sense of what had been done if they saw fit. But I would not depart from my own high position (I mean as respects feeling) for any reward they could give. Excuse my freedom. I have no time to dot i i, or cross 1 1, or punctuate. I hope you will find out the meaning. xxii Memoir. A Royal Medal was adjudged to Dr. Andrews in 1844, bv the Council of the Eoyal Society, for his paper entitled " On the Thermal Clmnges accompanyi-ng Basic Substitutions," printed as No. XVI., p. 107 below. Early in 1845 Dr. Andrews was informed of the wish of several of the Fellows of King's College, London, that he should come forward as a candidate for the Chair of Chemistry there. He declined however to do so, but in the autumn of the same year he resigned his connection with the Belfast Institution, and gave up his private practice, on his appointment to the Vice-Presidentship of the Northern College, now Queen's College, Belfast. The Presidents and Vice-Presidents of these new Irish institutions were appointed some years before the Colleges were opened, or the Professors elected, in order that the Government might have their advice and assistance in maturing the whole scheme. Andrews was thus associated with another justly-distinguished Irishman, Sir Eobeit Kane ; and it is mainly to their labours and foresight that the Queen's Colleges, when at last opened, appeared before the world in full working order. It had been understood from the first that Andrews was to be the Professor of Chemistry in Belfast, but he was required (as a matter of form, merely) to produce a few testimonials. These he obtained at once, in the highest terms, from such men as Graham, Humphrey Lloyd, MacCullagh, etc., and they need not be given here. But it may be interesting to show, as briefly as possible, the opinions of the two greatest of foreign chemists. Liebig wrote (Nov. 10th, 1845) as follows : Ich hege die voile Ueberzeugung dass der Platz um den Sie sich .... bewerben, keinen wiirdigeren Besitzer iinden diirfte. Sie haben viele Jahre hindurch mit den grossten Schwierigkeiten zu kampfen gehabt, um der warmen Neigung welche Sie fiir die Naturwissenschaften hegenNahrung zu geben, und wait entfernt dass Ihr Muth und Eiferdadurch gelahmt worden ware, haben Sie duroh Memoir xyni Ihre letzten wichtigen Arbeiten iiber die Warme bey chemischen Verbindungen dargethan, dass die Beschaftigniig mit der "Wissen- schaft ein Bediirfniss Ibres Geistes ist. Dumas (Xov. 29, 1845) wrote : — Tos titres a la nouvelle fonction a laquelle vous aspirez sont si claiis et si evidents, que je ne concevrais guere que vous n'y fassiez point appele . . . mais, tout en enseignant la chimie, n'oubUez pas que vous comptez au nombre des physiciens distingnes de votre pays. The rest of this letter is not personal, but refers to the im- possibility of separating chemistry from physics, and to the im- portant aid which each of these sciences constantly obtains from the other. In 1846 Dr. Andrews was elected honorary member of the " Societe des Sciences XatureUes du Canton de Yaud." He received a letter from the President, M. Elie "Wartmann, send- ing the Diploma, and referring to the researches on the " Heat of Combination." Xext year came the Irish Famine. Dr. Andrews took an active interest in raising a fond for the establishment of soup- kitchens. His exertions in behalf of the poor at this time, and during the epidemic of fever that followed, were indefatigabla In 1848 he paid a short visit to Paris, with ilrs. Andrews, but before he could renew his acquaintance with scientific friends, he was recalled home by illness in his family. Dr. Andrews was elected Fellow of the Koyal Society, June 7th, 1849. In this year the Queen's Colleges were opened, and Dr. Andrews was as successful in his professorship as he had formerly been as a physician. He soon gathered large classes, alike for general chemistry and for practical work. During the winter months, a select number of students were admitted to the laboratory by examination, and in their training he took especial interest ; and it is a gratifying fact that the great majority of Dr. Andrews' most trusted laboratory pupils xxiv Memoir. turned out successful men in after life. All his spare time, for the greater part of every working day, was spent in his private laboratory. Here he delighted to receive his scientific friends, and to engage eagerly in conversation with them, while his hands were busy with the steady, dehberate' construction or adjustment of apparatus for his next research. Henceforth the teaching of science, and his own private research, became the absorbing occupations of his life, and almost the only intervals of relaxation we have to record in the midst of the busy college sessions are occasional Saturdays and Sundays spent at Clande- boye with his intimate and valued friend. Lord Dufferin. These visits were sources of much pleasure, both from the sympathetic interest always shown by Lord Dufferin in science, and from the opportunities they afforded Dr. Andrews of meeting many of the leading statesmen and literary men of the day. In the same year an award of 1000 francs was made to Andrews by the Academy of Sciences for his Memoir on the determination of the quantity of heat disengaged in chemical combination (Fo. LIII. below). This was given a titre d'indem- niti, as the greater part of the contents had already been published. In 185,0, in the course of a tour on the Continent, in which he was accompanied by Mrs. Andrews, Dr. Andrews spent some time in Basle with Schonbein, and in Vienna with Schrotter. He also visited Verona, Venice, the quicksilver mines of Idria, and the caves at Adelsberg. He returned home by Prague, Dresden, Hanover, Cologne, and Brussels. In the summer of 1851 he made a tour through Connaught with Dr. Edgar. Three large Scottish houses had appointed agents for the sewed muslin manufacture in,Sligo and other places, so that the schools established by Dr. Edgar were no longer merely charitable institutions, but workshops supplying the trade in the regular way. " Bare walls marked the spots Memoir. xxv "where, previous to the famine, a numerous though wretched population had succeeded with difficulty in procuring a hare subsistence, but where now scarcely a human being is to be seen." In the following letter to Dr. Apjohn, one of his most inti- mate friends, Dr. Andrews describes his course for medical stiidents as it was carried on in 1851 : — " I have not printed any syllabus of my lectures, which embrace pretty nearly the same range of topics you were in the habit of discussing in your course at the College of Surgeons. . . . " I have always entered pretty fully into the subject of heat, including the physical subjects of expansion and radiation, as well as its more special relations to chemistry. I have also been in the habit of treating the subjects of electricity proper, galvanism, and electro-magnetism at considerable length ; but this year I postponed the discussion of the details of these subjects till the last term of my lectures, which occupies the month of May and part of Jtme. This term, I should remark, medical students are not required to attend, Edthough the lectures are open to them if they wish to avail themselves of the privilege. My reason for this arrangement was simply this, that many medical lecturers (such as Gregory in Edin- burgh) do not introduce these subjects into their courses at all, and I considered them to be of less practical importance to the medical student than pure chemistry. I gave, however, a short account of the leading facts of electricity during the winter course. " In chemistry I dwell particularly on the more important electro-negative elements and their binary compounds — ^not omitting cyanogen — then proceed to potassium and its com- pounds (which I treat pretty fully), as well as the compounds of sodium, calcium, magnesium, and aluminium. I then give an account of the manufactures of glass and porcelain, and xxvi Memoir. afterwards select the more important of the ordinary metals — such as iron, manganese, zinc, copper, mercury, silver, etc. " In organic chemistry I begin usually with oxalic and formic acid; next take up the amylaceous and saccharine bodies; then the ethyl, methyl, and amyl series, including the fermentations. After this I select some of the more iuteresting organic groups, such as the benzoic series, varying this part of my lectures from time to time ; next follow the vegetable acids and alkalis. " In animal chemistry I am obliged to be more brief. The so-called protein compounds are described, and the properties and chief constituents of the urine, bile, etc. On the urinary calculi I always dwell at length, both in my lectures and course of practical chemistry. " In the course of medical chemistry I first go through a systematic course of qualitative analysis, dwelling particularly on the modes of detecting poisons and of examining the princi- pal healthy and morbid secretions, following on this last point pretty closely Bird's recent work on medical chemistry. I then show the laethod of determining the quantities of each con- stituent in an ore or earthy mineral, but the time is too limited to enable me to pursue this part of the subject to any extent. Finally, we have some organic compound. . . . " "We have had Eose, Magnus, and Liebig here lately, all greatly delighted with this part of the country. The latter urged me strongly to resume my experiments on the Heat of Combination. Of those already published he has given a very long account in the Jahresbcricht. I have been of late worry- ing myself with ozone, and have made some progress, but not as much as I desired. " P.S. — Of course the general laws of chemistry are dis- cussed, as well as its more important applications to the Arts." At the British Association meeting in Belfast, in 1852, Dr. Andrews was president of the Chemical Section, where he read Mem.oir. xxvii three papers, besides one in the Geological Section. In the course of the year he made an excursion in Donegal, visited Horn Head, and ascended Erigal. He describes a large church, built of statuary marble, in the midst of a wilderness of bare rocks near Lake Dunlewy, in Donegal, the only edifice of the kind on this side of Milan. The marble was obtained from a quarry in the neighbourhood of Dunlewy Lake, which pro- mised, if fully worked, to be not greatly inferior to that of Carara. The hotel (Gweedore) at which Dr. Andrews stayed was built and maintained by Lord George HiU, " who had transformed the whole face of the coimty, and deserved aU the praise he had received." Shortly after this Andrews began the first series of elaborate researches on Ozone, which were communicated to the Eoyal Society in 1856, with the title "On the Constitution and Pro- perties of Ozone " (No. XXXI. below). Dr. Andrews spent the summer of 1854 at Heidelberg with Mrs. Andrews and his children. Here he had much pleasant intercourse with the Professors of the University, especially with Bunsen, Delffs, and Eau. He ^^sited liebig at Munich, where he also met Hofmann, and afterwards made a short tour through the Tyrol. In 1855 he read, before the meeting of the British Associa- tion, papers " On the Polar Decomposition of Water hy Common and Atmospheric Electricity" and "On the Allotropic Modifica- tions of Chlorine and Bromine analogous to tJie Ozone from Oxygen.'' Both Dr. Andrews' communications were specially noticed by the Duke of Argyll in his concluding address, while giving an account of the more remarkable papers read at the meeting. Dr. Andrews spent the summer of 1856 in Paris with his family. He took with him introductions to Wurtz and Despretz. He also saw Faraday frequently during a short Xxviii Memoir. visit the latter made to Paris. Dr. Andrews had much inter- course with Dumas, Despretz, Peligot, De Luca, and Chevreul ; cilso with Mr. (now Sir WUliam) Grove, with whom he afterwards made a tour in Normandy. Towards the end of this year he commenced his experiments for the determination of the volumetric relations of Ozone. He had satisfied himself that there is an increase of volume when electrolytic Ozone is destroyed by heat, before he asked his col- league, Tait, to join him in the inquiry. Their joint experiments were carried on, with but few intervals, till the commence- ment of 1860, when an account of them was published in the Philosophical Transactions (No. XXXV. below). Andrews then, almost immediately, commenced preliminary experiments on the compression of gases. Tait worked with Andrews at this new subject also, until he resigned his Chair in Belfast, in summer 1860. It is worthy of note that the first method employed for producing high pressures was the electrolysis of water in closed vessels. This method, though in other respects satis- factory, had to be abandoned in consequence of the explosions which occurred in the (necessarily) wider part of the tube, which contained the electrolyte, and which was subjected to internal pressure only. In August, 1858, Dr. Andrews wrote to Sir William Eowan Hamilton as follows : — Our Professor of Mathematics (author of a work on Dynamics and formerly a senior wrangler at Cambridge) has been directing his attention of late to Quaternions, and is anxious to be allowed to cor- respond with you on that subject. Mr. Tait is a young man of excellent abilities, and, I believe, a very good mathematician ; and I have therefore no hesitation in introducing him to you. The following is part of the answer : — Of course I accept it as a great compliment that Professor Tait should be pleased to desire to correspond with me upon the subject of Quaternions. ... I have been turning my attention to other Memoir. xxix and older subjects, especially to Differential Equations and Definite Integrals in connection with old but revived researches of my own. (I do not mean just now those which Jacobi enriched by his com- ments.) My hand must therefore be expected to be somewhat out. But I suppose that I cannot have forgotten the principles of the whole theory. Dr. Andrews, by the above letter, ^^^tually secured to science that great posthumous volume, the " Me-ments of Qimtemixms." For Hamilton wrote in January, 1859 : — It was useful to me . . . to have my attention recalled to the whole subject of the Quaternions, which I had been almost trying to forget — partly under the impression that nobody cared, or would soon care, about them. The result seems likely to be that I shall go on to write some such " Manual," not necessarily a very short one. . . In a letter of 1861 from M. Wurtz, who had the Ozone paper translated in the Amiales dc Chimie, the writer says :— " Je ne voulais pas vous dcrire avant de pouvoir vous informer que j'ai fait un extrait de votre travail pour I'inserer aux Annales. Je m'occiipe de cette tache dans ce moment et je suis frapp^ des r^sultats extraordinaires que vous avez obtenus. Je dirai presque que ces r^sultats sont de nature a nous troubler, parcequ'ils jettent de nouveau une certaine incertitude dans une question qui paraissait resolue par vos experiences anterieures. Dans tous les cas ce fait de la densite extraordinaire de I'ozone me parait bien etabli par vos minutieuses et ing^nieuses recberches, et ce fait me parait im des plus ^tranges et des plus- curieux de la chimie." The following extract from a letter of this period to an old student (J. W. Smyth, of the Bengal Ci^il Service, lately a Judge of the Chief Court of the Punjaub) shows how Andrews carried even into his lighter reading the habits of minute accuracy which are so conspicuous in his scientific work : — I have nearly completed my inquii-y regarding the implication of Elizabeth in the murder of Eizzio. Strange to say, Tytler relates all the events of the year in which it occurred as belonging to 1565, XXX Memoir. while all other writers refer them to 1566. They happened in the year 1565-6, supposing we call the first year of our era 0-1. But, according to our present system, the date is 1566, and the letter was written in the same year. In that year the 9th of March, o.S., fell ■on a Saturday ; aiid therefore three days intervened between the date of the letter from Randolph and Bedford (written at Berwick) and the commission of the murder. This interval of time was quite too short to enable Elizabeth to give warning of the conspiracy to Mary, much less to detain the Earl of Moray in London. The vindication of Elizabeth is complete, both from the internal language ■of the letter and from a comparison of the dates, and it ought to be made known, as the statement has since been repeated by Lingard and other popular writers. The points here raised were submitted by Andrews to his •colleague, the well-known Prof. G. L. Craik, and gave rise to an iuteresting correspondence ; the result being to confirm the conclusions quoted. In 1865, at the instance of Signor Matteucci, Dr. Andrews acted as juror for the Italian section of the Dublin Exhibition. The " Studium Gcnerale," an interesting pamphlet on Uni- versity constitution, was published in 1867. In the same year Dr. Andrews was President of the Education Section of the Belfast Meeting of the Social Science Congress. He delivered an address on Education, as President of this Section. He also read a paper entitled, " Suggestions for Checking the Hurtful Use of Alcoholic Beverages,"' which will be referred to later. Dr. Andrews' views on this subject were warmly supported by several persons of high authority, and drew forth many letters at a later period from prominent politicians. In 1869 Dr. Andrews published a pamphlet on the "Church in Ireland." In the same year his great paper on " The Continuity of the Liquid and Gaseous States of Matter" was selected by the Eoyal Society as the Bakerian lecture (No, XXXVIII. below). In a letter to Mrs. Andrews, Dr. Andrews, referring to the Memoir. xxxi above, writes: — "I really begin to think that Dame Nature has at last been kind to me, and rewarded me with a discovery of a higher order than I ever expected to make." In 1870 Dr. Andrews was elected Hon. Fellow of the Eoyal Society of Edinburgh to succeed Mr. Graham. The Hon. Degree of Doctor of Laws was conferred on him by the University of Edinburgh on 1st August, 1871. Dr. Andrews was President of the Chemical Section at the Edinburgh Meeting of the British Association, and delivered his address to the Section on the 3rd August, 1871. At this meeting. Professor Maskelyne described a green mineral, then recently found in Cornwall, which he named Andrewsite, in honour of Dr. Andrews. In 1872 the Board of Trinity College, Dublin, voted him the Hon. Degree of Doctor of Laws, which was conferred in the following year. In 1873, at a meeting of the Convocation of the Queen's University in Ireland, Dr. Andrews made a telling speech against extending the privileges of the University to women. In 1874 Clerk-Maxwell's attention was called to Andrews' experiments on the compressibility of mixtures of carbonic acid and nitrogen, and the effect of the admixture on the critical point. A characteristic letter on the subject will be given later. In 1875 Prof. Eijke procured one of Dr. Andrews' pressure apparatus for the University of Leyden. M. Janssen, a student of that University, spent some time in Dr. Andrews' laboratory studying the subject with a view to carrying on further original investigations. Dr. Andrews' subsequent letters to M. Janssen contain valuable practical details (sometimes of the minutest character) as to the mounting of the apparatus, and the precautions to be taken in using it. In 1875 Dr. Andrews made a tour on the Continent with two of his daughters. He joined the Geographical Congress xxxii Memoir. then being held in Paris ; he received a most gratifying recep- tion at the French Academy, and communicated a paper, pub- lished in the Compter Bcndus under the title " Expenences di, hauies jn-essions sur les Gaz." On this occasion he made the acquaintance of General Menabr^a, with whom he became intimate. At Nantes he assisted at the meeting of the French Association for the promotion of Science. He was made a Vice-President of the Ch'emical Section, and read two papers before it, " Experiences sur les Gaz a de hautes pressions ct d divcrses tcviperatures," and " Faits sur VOzonc, ct sur Ic Chlore electrise," published in the Compte JRcndii, de V Association Fran- caise pour V Avancement dcs Sciences, Nantes, 1875. Thence Brittany was visited, where Dr. Andrews was much interested in the stones of Carnac, the curious tumulus of Gavr Innis, and also in some recent excavations of Eoman remains. He then crossed France to Lyons, proceeded to Geneva, and, after a short tour in Switzerland, returned home by the Ehine. Shortly afterwards he received a letter from M. Dumas, introducing M. Cailletet and telling of Sir C. AVlieatstone's dangerous illness. This letter is of importance as well from the character and position of the writer, as from its contents. It runs as follows : — Paris, le 18— S"'", 1875. Cher M. Andrews, — Je saisis avec empressement Toccasion de vous remercier de votre bonne lettre Je vous 6cris le coeur bien attrist^. Sir Ch. "\^Tieatstone est bien malade. En passant k Paris, il a 6t4 surpris par una bronchite com- pUqu6e qui depuis huit jours le retient au lit, et qxii pendant deux jours nous a kisses sans espoir. II est encore en vie. Je I'ai vu dans la journ6e. Mais, son 6tat est des plus graves. Je suis bien affect6 do ce triste et grave evonemont. II y a quinze jours, il assistait k la S&rice de lAcadtoaie et tout le monde le com- phmentait sur sa bonne sant6. Elle semblait, en effet, s'gtre bien am6lior6e. Quelques jours plustard, sa mort (5tait imminente. Memoir. xxxiii Mes amis s'en vont. II est triste de vieillir. Faraday, Wheatstone, Graham, representaient pour moi la fleur de la vieille Angleterre. Vous appartenez ^ la jeune Angleterre, et vous vivrez longtems encore pour sa gloire ; mais je vous demande pendant que je suis encore de ce monde de vous souvenir que vous etes I'heritier des aflfections que j'avais contract6es dans votre pays. Avec mes voeux pour votre longue conservation et I'expression de mes sentimens les plus affectueux J.-B. Dumas. M. Wheatstone vient de mourir ! Grande perte pour I'Angleterre et pour la science ! Grand deuil pour ses amis ! ! Mardi, 19 — 8*'°, k deux heures. After a winter spent in making and reducing experiments, Dr. Andrews delivered as the Bakerian Lecture for 1876 his memoir, " On the Gaseous State of Matter," containing further developments of his discoveries on the continuity of the liquid and gaseous states (No. XLIX. below). He was President of the Glasgow meeting of the British Associ- ation, and delivered his presidential address on the 6 th September. One of the Evening Lectures was delivered by Professor Tait, who closed it by speaking of the Chairman in the following words : — I have done my best, under circumstances of time, place, and surroundings, all alike unpropitious. But the chance of being able to back up, however imperfectly, my old friend Dr. Andrews, in whose laboratory I first learned properly to use scientific apparatus, and whose sage counsel impressed upon me the paramount importance of scientific accuracy, and, above all, of scientific honesty — such a chance was one which no surroundings, however unpropitious, could have induced me to forego. The honorary degree of LL.D. was conferred on Andrews by the University of Glasgow, 1st May, 1877. Dr. Andrews resigned the offices of Vice-President and Professor of Chemistry in Queen's College, Belfast, on the 10th xxxiv Memoir. October, 1879. After resigning, lie lived in gi'eat retirement at Fort "William Park, Belfast. A Grace of the Senate of the Queen's University, Ireland, was passed on the 8th October, 1879, to confer on him the honorary degree of Doctor in Science. The degree was con- ferred on the 15 th of the same month. At a meeting held in December of the saine year, in Queen's College, Belfast, it was proposed to commemorate the services rendered to science and to education by Dr. Andrews. It was resolved that the IMemorial should consist iirstly, of a portnut or bust to be placed in the College, and a replica to be pre- sented to Dr. Andrews' family ; secondly, of a prize or scholar- ship to be founded in Queen's College, Belfast, and awarded for high attainment in those sciences in which Dr. Andrews had achieved his distinction. In 1883 the Andrews' Studentship for the promotion of the study of Chemical and Physical Science was established. Dr. Andrews' portrait now hangs in the Examination Hall of the College, and a replica has been presented to his family. In 1880, Dr. Andrews received a letter from the Duke of jMarlborough, then Lord Lieutenant of Ireland, offering him, by Her Majesty's gracious permission, the honour of ci\-il knight- hood. Dr. Andrews, though appreciating deeply the kindness of the proposal, declined the distinction on account of indif- ferent health. Later in the year, he for the same reason declined to preside over the Chemical Section at the Jubilee ileeting of the British Association held at York. In 1884 he was elected corresponding member of the Eoyal Society of Sciences of Gottingen. The grave debihty from whicli Dr. Andrews had long been suffering increased so much during the spring and summer of 1885, as to cause the greatest anxiety to his friends. In Sep- tember he was obliged from weakness to remain indoors, and Memoir. xxxv from the 2nd October was confined to bed. Even then he con tinned to take an interest in science, and in the course of public events. On the 1 3th of November he seemed to revive slightly, but no real strength returned. He sank gradually, and died most peacefully on the 26th November, surrounded by his family. His grave is in the Borough Cemetery, Belfast, where a granite obelisk now marks the spot. Mrs. Andrews survives her husband, with three daughters and two sons. The elder son is Major in the Devonshire Eegiment, and the younger a member of the Irish Bar. Andrews was not only a profound and original thinker, he was an experimenter of the very highest order, as patient as he was skilful. The writers have, like many others, seen and admired his confident manipulation of wide sealed tubes, half full of liquid carbonic acid, or even of sulphuric ether ; how he, knowing the soundness of his own glass-blowing, boldly heated such tubes in the flame of a Bunsen lamp till the liquid entirely disappeared, and pointed out with eager enjoy- ment the extraordinary phenomena presented as the contents cooled nearly to the critical temperature. The whole tube seemed, for a short time, to be filled with a substance present- ing, to an exaggerated degxee, the appearance of a mixture of water and strong brine before diffusion has sensibly operated. We have spoken of Andrews' remarkable skill in manipula- tion, and of his unwearied patience. But even these were eclipsed by the perfect calmness with which, though on the very verge of an important discovery, he attended to every point of minute and laborious detail ; so that his first success- xxxvi Memoir. ful experiment was as exactly carried out and recorded as was its future repetition. This was all the more remarkable in that he was, especially in public, a man of a highly nervous and excitable temperament. An excellent French and German scholar, he kept himself always well acquainted with the most recent progress of science, whether chemical or physical. He constructed his own divid- ing engine for the calibration of the exquisite thermometers which he made for his researches on heat ; and his air-pump (in which he took special delight) was furnished with numerous valuable improvements, all devised by him for particular applications. His laboratory books are models of ample, but not superfluous detail. He was, personally, a man of simple unpretending manner ; conscientious almost to an extreme, but thoroughly trustworthy and warm-hearted ; an excellent example of the true Christian philosopher. Dr. Andrews was deeply interested in public affairs, but very rarely took an active part in politics, and was quite free from party feeling. His only writings bearing in any way on political matters are " Chapters of Contemporary History." The first, entitled " Studium Generalc," and published in 1867,^ is a historical and critical discussion of the function of a University, with special reference to the Queen's Colleges. The immediate occasion of its publication was the issue of a supplementary charter to the Queen's University, completely changing the relations of the Colleges to the University, and enabling the senate of the University to confer degrees on any person who had matriculated in the University and was deemed ^Longmans, London. Memoir. xxxvil qualified by the senate, although he had not studied in any of the colleges. This step was taken by the ministry of Earl Eussell without consulting parliament (although both the Chancellor of the Exchequer and the Home Secretary had led everyone to believe that full opportunity for discussion would be given before any definite proceeding was taken) six days before they tendered their resignation — indeed the formal issue of the charter took place only one day before the resignation of the ministry was accepted. Dr. Andrews sketches the history of the University of London, the Queen's University, and the Catholic University in Ireland, specially comparing the constitution of the latter with that of the Catholic University at Louvain (founded in 1833). He gives a full and impartial account of the Supple- mental Charter, and of the events connected with its issue, pointing out the evils which in his opinion would result from it. But while the pamphlet deals primarily with what is now matter of ancient history, there is much in it of more than passing interest. Dr. Andrews had studied the question of the function of Universities, and of the duty of Governments to the higher education in no narrow or provincial way, and his opinions, founded on extensive observation and after mature deliberation, are specially worthy of consideration now, when it seems almost universally admitted that a great extension of University teaching is required, the only difficulty being in what way this should be provided. On this point Dr. Andrews' views were very clear. He regarded the system, which many English statesmen seem to think the only reason- able one, of grouping a number of teaching institutions and placing them under the care of a so-called University, as fatal to freedom and progress. Each centre of the higher teaching should be the site of a true and independent University. Here are his words on this subject : — xxxviii Memoir. The admirers of the institutions which have arisen in France, out of the wreck caused by the revolution of 1789, will not view with favour the proposal to establish a third university in Ireland, wholly distinct from the two already existing in that country. According to their views, the present institutions for higher education ought rather to be assimilated to one another, and combined into a national university, like the Imperial University of France. Con- sidering the great control over the education of the country such a system would give to the executive government, it is not surprising to find it regarded with favour in some influential circles. It may, perhaps, be said that it would afford facilities for the prevention of abuses, and for the introduction of new methods of teaching. But such advantages would be a poor compensation for the depressing influence a gigantic organisation of this kind would exert upon the free play of thought and action.^ The similarity of the universities of ' Sir J. Graham, while advocating one university for the Queen's Colleges in Ireland, instead of investing each of them with the power of granting degrees, was entirely opposed to the absorption of the University of Dublin in a national university. In the formal statement which he made on introducing the Colleges Act, he declared that he was decidedly of opiniou that neither policy nor justice permitted any interference with Trinity College, Dublin, as it existed at the time he spoke. — Annual Reginter for 1845, p. 144. The writer has had good opportunities, in early and later life, of acquiring from personal experience a knowledge of the actual working of different universities, both in these countries and on the continent of Europe. He was a member of the original Board of Colleges appointed by Sir J. Graham [supra, p. 29), and since that time he has been officially connected with one of the Queen's Colleges. He hopes he will, therefore, be excused from the charge of presumption if he ventures to express the opinion, as the result of his experience and observation, that the government of Sir R. Peel committed a serious mistake, when they departed from former precedent, in their scheme for extending higher education in Ireland. If, instead_ of the present ooinplioated arraugements, they had established two universities, one in the north and the other in the south of Ireland, on the same free principles as the Queen's Colleges, they would, in the opinion of the writer, have acted more wisely ; and they would also have laid the foundation of institutions, of whoso permanence there could be no reasonable dpubt The Board of Colleges used its best endeavours to mould the new scheme into a workmg form; but the writer, while claiming credit to the Queen's Colleges for what they have done, would be acting disingenuously if he expressed an approval of the peculiar features of tlie system of which they form a part. That that system has, at the same time, worked well on the whole and IS deserving of further trial, he hopes to have convinced every candid reader of these pages ; and, if the public expect to receive a return iii useful work for the large expenditure incurred, they ought to disoouraae any attempt unnecessarily to meddle with it, or to t^nper with its fundamental principles. The Queen s University is as much an integral part of the system of the Queen s Colleges as the Umversity of Dublin is of that of Trinity College. Even the Catholic prelates appear to have recognized the truth of this statement, and they accordingly demanded, not only that the original Memoir. xxxix Scotland, and the abolition of religious tests, are perhaps favourable to the introduction of the Imperial system into that country ; but the proposal has happily been received there with little favour ; and, for the sake of sound and free education, it is earnestly to be hoped that the Scottish universities ■will be able to maintain the independ- ence they have so long eiljoyed. Universities, if properly conducted, ought to be what they are in Germany — centres of intelligence scattered over a country — each shining brightly with its own peculiar light, and not coldly reflecting the rays of a distant luminary. The only considerations, which ought to limit their num- ber, are the requirements of the country, and the means of sustain- ing them in efficiency. From their nature, they must always be ■ costly institutions, for they will utterly fail in their object, and fall into disrepute, if conducted by inferior men, or with insufficient appliances. The two countries in Europe, where university educa- tion has been made most largely available to the middle classes, are Scotland and Germany. No one is ignorant of the influence the four universities of Scotland have had in promoting the material prosperity of that country; but few, except those conversant with the practical arts, are aware of the immense advantages England herself has derived from them, jjarticularly in her great northern seats of industry. It may indeed be said, without exaggeration, that England would long ago have been forced to establish universities, after the Scottish or German model, for the use of the middle classes, if the universities of Scotland and Germany had not furnished her with a large supply of men, well versed in the sciences connected with the useful arts."- In the present century, no country constitution of the colleges should be changed, but that a new university should be incorporated. The writer must give them credit for having acted throughout these proceedings with great boldness, if not altogether with candour ; but their present views are very different from those held by the legislature when it sanctioned the measure of 1845. The writer will scarcely be accused of having shown any reluctance to yield to the reasonable claims of the Catholic Church, but he does not think it should be permitted to have any control over institutions designed for the use of the whole population of Ireland. 1 The University of Glasgow, after the appointment of Dr. Thomson to the chair of chemistry, in 1818, began to educate a number of scientific and practical chemists, many of whom were afterwards scattered over Lancashire, and aided greatly in developing the manufactures of that district which are dependent on chemical skill. Dr. Turner, who long held the professorship of chemistry in University College, studied under Stromeyer, in the University of Gbttingen. His successor, the present Master of the Mint, who, with the illustrious Faraday, so long sustained the character of England in experimental xl Memoir. has laboured more sedulously, or more successfully, than Prussia in improving and extending her great universities, and she has been influenced in this course by the highest motives which can animate a nation.! The United States of America have followed in the same path, and have covered their vast territories with universities, some of which are already favourably known. Canada and Australia have likewise not failed in this respect to perform their duty, and have fully supplied their inhabitants with the means of university education. As regards the internal arrangements and methods of teaching, it is desirable, according to the writer's view, that they should, be as varied as possible in different universities. In the world we inhabit, we find everywhere unity of design with variety of execution, and this is true even of the communities into which mankind is divided. Education and training must form the foundation of civilized life in every country ; but how diversified in detail, yet how rich in results, science, was a student of the University of Glasgow, and was the first to teach practical chemistry in London, as Dr. Thomson had taught it in Glasgow. The genius of Liebig founded, about the same time, in the small University of Giessen, a school of chemistry destined, in modern times, to rival in celebrity and usefulness the school of the Stagyrite in ancient Athens. Wohler, at Gtittingen, and Buusen, first at Marburg and afterwards at Heidelberg, followed close upon the footsteps of Liebig. To one or other of these German universities, all the young chemists of England, for many years, repaired, in order to complete their education ; and Great Britain is, in this way, indebted to the universities of Germany for no inconsiderable portion of her material prosperity. It would be invidious to refer to individual names, where so many are dis- tinguished ; but I may be excused for giving expression to a feeling of regret that this country should have recently lost the ser-vices of one whom England and Germany are alike proud to claim. Had London possessed a university, such as the University of Berlin, the result would probably have been diflFereut, and the name of Hofmann, like that of Hersohel, might have been permanently inscribed on the rolls of British science. • " The University of Berlin, like her sister of Bonn, is a creation of our century. It was founded in the year 1810, at a period when the pressure of foreign domination weighed almost insupportably on Prussia ; and it will ever remain significant of the direction of the German mind, that the great men _ of that time should have hoped to develop, by high intellectual training, the forces necessary for the political regeneration of their country. " — Report on the Laboratories in the Universities of Bonn and Berlin, by A. W. Hofmann, p. 47. Previous to the late war, there were six universities in Prussia. The newly-acquired territories have added three to the list, viz. Kiel, Gottingen, and Marburg.— /rf. p. 1. The writer has ventured to suggest (supra, p. 29) that a university should be founded in Manchester, on a scale worthy of that great centre of intelligence and industry. Since the passage referred to was sent to the press, he has observed, with gratification, that a meeting was lately held in Manchester, for the purpose of giving a large extension to Owens College. He hopes that this movement, if it does not already embrace it,; will lead to the larger design of founding a Free University. Meinoir. xli will be manifest if the arts and industries of Western Europe are compared with those of Eastern Asia. The imperial institutions of France, from their magnitude and imposing form, may captivate the rulers, and even the people of a country ; but similar institutions were coincident with the decline of the Eoman Empire, and literature and art soon withered under their protection. The example of ancient Greece, or of modern Germany, is more worthy of imitation than that of imperial Rome or imperial France ; and the chief end of higher education, the cultivation of habits of accurate and independent thought, will be best attained by allowing the fullest freedom of action, to those who are engaged in the diflScult task, of training the youth of a country in the noble walks of literature and science. Holding these views, Dr. Andrews strongly advocated the foundation of a true teaching University for London and the conversion of the Owens College, Manchester, into a Univer- sity of the Scottish or German type. He proceeds thus : — Is it too late to hope that the recommendation made by the House of Commons so long ago as 1835, in a formal address to the Crown, may yet receive attention, at least in some modified form, and that the two great colleges of London (University and King's) may be in- corporated into one university — the University of London in fact as well as in name — which, recognizing the great principle, equally true now as in the days of ancient Greece, that on the efficient train- ing of its young men mainly rest the hopes of a nation, will be satisfied with modifying the arrangements which long experience has sanctioned in the old universities, so as to meet the wants of those for whom the new university is designed, instead of making a weak attempt to educate a nation through the sole agency of encyclopedic examinations ? If some such scheme as this were carried into effect, I feel very sure that, instead of a degree in arts being conferred upon fifty persons in one year, ten times that number of candidates would qualify themselves annually for this distinction, by passing through a well-digested undergraduate course, to the great advantage of the community, and the elevation of the middle class of English society. The success of the Scottish nation, in the face of few natural advantages, has been greatly due to the excellent training which its four universities have afforded, at a moderate cost, to a very large xlii Memoir. portion of the middle class of that country ; and the clergy in parti- cular of all the great churches in Scotland, enjoy the advantage of receiving a regular university education in arts, before they enter upon their special studies. The same remark cannot, I fear, be applied to a large number of the nonconforming clergy of England ; and e^ en in the Church of England itself there are too many cases, where the novitiate does not receive any university training. May I further add that the ancient city of Manchester, with its vast popu- lation, its scientific triumphs, and its Philosophical Society, publish- ing memoirs for upwards of half a century, is the only place in Europe, with similar pretensions, which is not the seat of a great university ? More than one name of European reputation now sus- tains in science the character of the town where Dalton lived, and it ought surely not to be too great an effort for Manchester, following the example of Brussels, to found and maintain a free university of its own.'' The foundation of the Victoria University has to some extent carried out this idea, but what Dr. Andrews wished was a University of Manchester without affiliated colleges, as he held that " any attempt " on the part of the new University " to follow the example of the University of London, either by affiliating colleges over the country or by substituting examina- tion for collegiate training, could only lead to the degradation of all high mental culture, whether scientific or literary." ^ Andrews would have welcomed a University of Liverpool, or of Leeds, well equipped with able teachers and good libraries ^A full account of the free university of Brussels will be found in the Rapport sur Vitat de V Instruction Supirieure en Belgique, par M. Nothomb, vol. ii. pp. 2133 to 2252. At its inauguration in 1834, M. Rouppe, chief magistrate of Brussels, referred in the following terms to the motives which led to this patriotic design : " De simples citoyens de Bruxelles, sans autre but que de concourir au progrfes des lettres et des sciences, saus autre d^sir que d'Stre utiles k la jeunesse studieuse, se r^unissent, s'imposent des sacrifices, en imposent a leurs amis, et tons ensemble fondent, au sein d'une population norabreuse, intelligente et active, un ^tablissement ou lis appellent, pour lea seconder, des personnes zel^es et d^vou^es comme eux au plus grand bien-Stre de la generation qui s'^lfeve : telle est I'origine de I'universit^ libre qui s'ouvre en ce moment." In 1842 it contained twenty-two ordinary and ten extraordi- nary professors, and in the first eight years of its existence, 2,530 students had been enrolled ou its books. 2 Letter on the proposal to erect the Owens College into a University. Memoir. xliii and museums ; but he would not have approved of the sub- ordhiation of Institutions, each fit to be an independent Uni- versity, to a central board : — however fully each of them might be represented on it. The second chapter of Contemporary History, " The Church in Ireland," was published in 1869, immediately after the pro- posal to disestablish and disendow the Church of Ireland. It contains a historical sketch of each religious body in Ireland, and the general character of the views expressed as to Church property may be seen from the passage (p. 55), part of which Dr. Andrews has talcen as the motto of the pamphlet. " The property of the Church is, in reality, the property of the nation, to be used for the spiritual benefit of the people at large. When the Church of the Reformation failed to enforce con- formity, and to establish herself as the Church of the whole nation, she ought, in common fairness, to have resigned a portion of the Church property." The views expressed in these two pamphlets received the hearty assent of Dr. Andrews' old friend Thomas Graham. We extract the following passages from two of Graham's letters, dated in 1867 and 1869 respectively : — I beg to congratulate you upon your lusty pamphlet — Studium Generale. Allow me to say that I found it most interesting, and that in few writings, political, moral, or scientific, do I sympathize more fully with the author. At the same time I do not see grounds for much apprehension of danger to the Queen's Colleges from the doubtful policy lately entered upon with regard to the Irish Univer- sity. They have already asserted their superiority over private teaching, and have little to fear from it. . . . I am delighted with your new pamphlet, which I have devoured at a single sitting. It is quite a relief to meet with a discussion of the Irish question, where ■ every paragraph, every sentence, conveys something positive and new after the wordy, unsubstantial discus- sions from the press and the hustings with which we have been oppressed. Your chivalrous defence of Maynooth I particularly xliv Memoir. admire. The permanent provision made for that institution was one of Peel's greatest achievements. But the English public, when it obtains time for reflection, will, I trust, recoil from the perpetra- tion of a great injustice for the sake of a fancied consistency. The moderate views you advocate must gradually force their way. Your publication could not be better timed, and will, I trust, receive the serious attention it deserves. A paper already referred to may perhaps be included among Andrews' political writings. In 1867 the Social Science Association visited Belfast, and Andrews was President of the Education Section. He took a great interest in social prob- lems, had thought much on the question of the improvement of the physical and intellectual condition of the people, and often talked to his friends on the subject. The paper there- fore which he communicated to the Association, entitled " Suggestions for Checking the Hurtful Use of Alcoholic Beverages hy the Working Classes," was not hastily drawn up for the occasion, but was the expression of his mature opinion on a matter which had long occupied his mind. He had no faith in prohibition ; he looked on it as wrong in itself, and certain to fail, but having satisfied himself as to the physical causes of the special bodily and mental damage suffered by the working classes from alcoholic indulgence, he set himself to discover how the present state of the law affects these causes, and what change of law would, without ' unduly interfering with liberty, place working men in a position more favourable to health. Among the working classes three causes especially aggravate this evil— insufficient food, impure air, and strong forms of alcohol. Even the skilled artizan of intemperate habits is rarely able, or, if able, inclined to piu^chase proper food ; and during a drinking carouse he usually takes no food whatever. In this way intoxica- tion and subsequently disease are produced by an amount of alcohol which would be comparatively harmless in the case of a well-fed man. The impure air of the confined apartments in which many Memoir. xlv trades are carried on acts, to some extent, like deficient nourish- ment, and by depressing the tone of the system renders it less capable of resisting the hurtful action of an excess of the alcoholic stimulant. The third source of aggravation, or the use of undiluted alcoholic beverages, is even more important than the others to which I have referred. Alcohol, taken in the form of brandy, gin, or whisky, unmixed with water, all of which contain about 50 per cent, of pure spirit or absolute alcohol, is a great deal too strong. It produces, when habitually used of this strength, a morbid craving which cannot be resisted, a state of disease from which recovery is hopeless. No one will be inclined to dispute that the public-house and gin palace, as they now exist, are an outrage to society and a disgrace to the country, and that the mischief they do to the working classes, as dens of intemperance, is incomparably greater than any advantage they afford as places of refreshment. With the view of abating this great evil, I propose in the first place, to have them changed into places truly of refreshment, the only purpose for which they ought to be licensed. No house should, according to my view, be licensed as a public-house for the sale of alcoholic beverages, unless it be provided with ample appliances for cooking and serving food, and the license should be withdrawn if it be found that these appliances are not made use of, and that the public-house is devoted solely to the sale of stimulants. My second proposal rests on the assumption that no one should be allowed to sell, for consumption on his premises, anything which is positively ruinous to the population. Gin, brandy, or whisky, taken undiluted, are fatal to a town population, very hurtful to any population. They contain, as commonly sold, from 50 to 55 per cent, of pure alcohol, and few men take them for any length of time undiluted with water, without falling eventually into intemperate habits. . . . My second proposal is, that no licensed publican should be allowed to sell, or keep in store, any liquor containing more than 17 per cent, of alcohol. I have taken the limit of 17 per cent, as being the strength of sherry, but I should hope to see the burgundy standard, or 12 per cent., eventually adopted. The police ought to have power to seize any spirit or wine of greater strength than 17 per cent, found in the public-house, or in any store-house con- nected with it. . . . xlvi Memoir. The object of my last proposal is not to put any undue restriction on the enjoyment or gratification of the working classes, but to pre- vent others from placing before them a dangerous beverage— one unfit for human use. No one, it appears to me, would have any valid ground for complaint, because he was restricted in the public- house to the use of a beverage of the strength of sherry, or even of buro-undy. I have little doubt that the skilled artizan, as well as the poor labourer, would soon give a hearty assent to such a measure. Andrews' first published paper on a chemical subject is on the " Composition of the Blood of Cholera Patients." He showed that it differed from normal blood only by having a smaller pro- portion of water. In his paper " On a New Variety of Magnetic Iron Ore," etc. (No. XXVIII. below), he recommended the use of a solution of bicarbonate of baryta instead of the precipi- tated carbonate for separating the protoxides and sesquioxides of the iron group. This method has not been so much noticed or used as it deserves : it is both elegant and accurate. Of great interest from a mineralogical point of view is his dis- covery of the wide diffusion of Magnetite, and of the frequent presence, along with it, of finely divided metallic Iron (Nos. XXVII. and LIV. below). Much more, important in itself, aiid as showing the bent of his mind to the borderland between Chemistry and Physics is a paper on " Galvanic Cells with Strong Sulphuric Acid," in which he showed that the composi- tion of the gas given off at the cathode varies in a remarkable manner with the temperature. This is quite in accordance with what we now believe as to the constitution and dissociation of strong sulphuric acid, but at the time the paper was written nothing was known which could lead anyone to suspect such a variation (No. XI. below). We now come to one of his great works — the determination of the " Heai Evolved during Chemical Action." In three series of Memoir. xlvii investigations he determined the heat given out in the forma- tion of neutral, acid, and basic salts, by the action of acid on base ; in the displacement of one metal in a salt by another ; in the formation of oxides ; and in the formation of chlorides, bromides, and iodides. In this great research we see the character of the man, his clear view of what was to be ob- served, his distinct recognition of the sources of experimental error, and the simple but effectual means he took to get his results free from the effects of such disturbing causes. Especi- ally worthy of note is his use of solutions so dilute that further addition of water produced no sensible thermal change. A few months before the publication of Andrews' first paper on the Heat of Combination, Hess of St. Petersburg, began a series of similar investigations. His first paper (1840) dealt chiefly with the heat evolved when sulphuric acid is diluted with water, but in subsequent papers he published an extensive series of determinations of the heat of neutralization of acids and bases. The results of the altogether independent work of Andrews and Hess agree very closely. It is remarkable that they drew quite opposite conclusions from them. Hess, looking only to the case of the alkalies and alkaline earths, supposed that the amount of heat given out in neutralization depended on the acid only, and was constant when the same quantity of a given acid was neutralized, whatever was the base ; a view quite untenable when we extend our observations to neutral- ization by such bases as oxide of silver. Andrews, taking a wider range of acids and bases, held that the heat given out depended on the base and not on the acid. He was quite aware that there were exceptions to this, and looked out for their causes. So far from overlooking these exceptions, or supposing them to be due to experimental error (as Hess thought he did), he drew special attention to them, as remarkable peculiarities of the substances requiring explanation. Thus, our knowledge xlviii Memoir. of the extraordinary amount of heat given out in the formation of mercuric cyanide by the action of dilute prussic acid on red oxide of mercury is due to Andrews, who pointed out how strikingly it contrasted with the heat of formation of the cyanides of the alkali metals from alkali and prussic acid. Andrews' direct determinations of the heat of formation of chlorides, bromides, and iodides have not been repeated, but we are able to judge of their accuracy by their very close agree- ment with the results obtained since by indirect means. Besides the papers on Heat of Combination, contributed to learned societies and scientific journals in this country, in which Dr. Andrews published his observations, we have included in the collection extracts from the paper sent to the Trench Academy of Sciences (No. LIII. below), because in it he explains more fully the reasons for some of the precautions taken in the experiments. The well-known experiments of Favre and Silbermann were published not long after Andrews' first papers on this subject. It is interesting to notice that where these differ from Andrews, subsequent investigations particularly those of Berthelot and of Thomsen, have shown that Andrews was right. In this connection we may refer to the latest criticism of Dr. Andrews' work on Thermal Chemistry by Professor Ostwald in his treatise on General Chemistry. Professor Ostwald speaks of the remarkable accuracy of Andrews' direct determinations of the heat of combustion of simple and com- pound substances in oxygen and in chlorine ; he seems, how- ever, to undervalue Andrews' early investigations on the heat produced by the action of acids on bases. He says that in these he gave merely the immediately observed changes of temperature. Now this is not the case. In his earliest paper Andrews gives the water value of the brass and glass of the apparatus, including the thermometer, and also the quantity of Memoir. xlix water in each experiment ; he uses chemical equivalents of the acting suhstances, and thus his results can be translated into any units that may be preferred. The heat required to raise 1 gramme of water through one degree Celsius is no doubt a more convenient unit (especially now that it is generally adopted) than the heat required to raise 3 grammes of water through one degree Fahrenheit, but it is not more philosophical. The only correction which Andrews did not introduce in stating his results is that depending on the difference between the specific heat of water and that of the very dilute solution the temperature of which was observed. He did not forget this source of error, but states that as it falls within the limits of observational error it need not be allowed for. In 1855 Andrews communicated to the Eoyal Society a paper of great importance and interest on " Ozone " (No. XXXI. below). This remarkable substance had been studied by Schonbein, its discoverer, Marignac, De la Eive, Berzelius, Williamson, Fr4my and Becquerel, and Baumert, but its nature still remained a mystery. Is ozone always the same thing, or are the ozone of electrolysis, that of the electric machine, and that formed during the slow oxidation of phosphorus, different bodies very like one another in pro- perties ? Some experiments seemed to show that ozone contained nothing but oxygen, others that it was an oxide of hydrogen containing a larger proportion of oxygen than water does. The question was exactly of the kind to attract Andrews and to call out his peculiar powers of investigation. By a series of experiments remarkable for simplicity and delicacy, and perfect adaptation to the purpose in view, he proved that " ozone, from whatever source derived, is one and the same body, having identical properties and the same con- d 1 , Memoir. stitution, and is not a compound body, but oxygen in an altered or allotropic condition." The investigation into the nature of ozone was continued by Andrews and Tait, and the results published (1860) in their paper " On the Volumetric Relations of Ozone and the Action of the Electrical Discharge on Oxygen and other Gases " (No. XXXV. below). These results led directly to the theory of the consti- tution of ozone now universally held ; indeed, that theory is distinctly stated by Andrews and Tait, although not further discussed on account of its supposed improbability. The following interesting letter was written (in English) by Schonbein, in acknowledgment of Andrews' paper (No. XXXVII. below) " On the Identity of the Body in the Atmo- sphere which decomposes Iodide of Potassium with Ozone." \ You have obliged me very much by the kind lines with which you were pleased to favour me the other day, and you may easily imagine, that with no small degree of attention I perused the highly interesting contents of your communication to the Royal Society. Having (in spite of the multifarious objections raised to my con- clusions) these last twenty-lBve years entertained no shadow of doubt about ozone being a constituent part of the atmosphere, I could not be much surprised at the results of your very ingenious experiments ; and the less so, that I had last year published myself a paper in which, I think, I have succeeded in proving by matter-of-fact evidence the correctness of my original views. As you are no doubt in the habit of reading German, I take the liberty to send you the paper alluded to, from which you will perceive that, by means entirely different from, those employed by you, I arrived at the same results. If you should happen to cross once more the Channel to take a trip to our fair land, which is quite as green as your Emerald Island, pray do not pass BS,le without favoring with a visit your old friend. None of Andrews' chemical papers can be read without some new idea being communicated to the reader, however well ac- quainted he may be with the subject. Memoir. li The investigation, however, by which Andrews is, and will continue to be, best known was that " On the Continuity of the Liquid and Gaseous States of Matter," which formed the subject of the Bakerian Lecture in 1869, and again in 1876. The results obtained by him were of such importance as to justify our going into some detail. One of the earliest of Faraday's researches was devoted to the liquefaction of gases, and he succeeded with all but a few, which were in consequence, till very recently, distinguished as " non condensable." But he expressed the conviction, founded on experiment, that even these could be liquefied by the con- joint action of sufi&cient pressure and sufficient reduction of temperature. Another extremely ingenious experimenter, Cagniard de la Tour, had approached the subject from the opposite side ; and had shown that liquids, such as water and sulphuric ether, could be changed into something which was certainly not liquid, by sufficient rise of temperature without any great increase in volume. Eegnault, also, had measured with his unrivalled precision the compressibility of various gases ; and had called attention to the curious differences which they show in their modes of divergence from Boyle's Law. And iTatterer, by employing pressures of some thousands of atmospheres, had arrived at other startling results. The whole subject was in that chaotic state which naturally precedes the advent of the Kepler who is to marshal, under a few general statements, each intrinsically simple, the mass of apparently irreconcilable phenomena. Andrews' classical researches completely effected this simpli- fication. Guided by some former results of Faraday and Eegnault, he selected carbonic acid as the substance whose behaviour was made the subject of exhaustive study through lii Memoir. wide ranges of temperature and of pressure. He devised an extremely ingenious form of apparatus for the purpose, had the coarser metallic parts constructed under his own eye by a remarkably skilful mechanic ; and himself made and calibrated the glass portions, purified with great care and skill the gas to be operated on, and finally fitted up the whole with unwearying patience. The simpler and more prominent results of this splendid research, which was made the Bakerian Lecture for 1869 (No. XXXVIII. below) may be briefly summed up as follows : (a) When carbonic acid is maintained at any temperature above 30°'9 C, it cannot even in part be condensed into liquid by any pressure however great. (b) If the temperature be below 30°-9 C, the gradual increase of pressure ultimately leads to liquefaction ; but the pressure of the vapour in presence of the liquid is less as the tempera- ture is lower. (c) A cycle of operations, in Carnot's sense, can be performed on liquid carbonic acid in such a way that, during the first stage of the expansion we have optical proof of the existence of liquid and gas side by side in the same vessel ; while, on cooling down to the original temperature and volume, the whole contents are once more liquid, though at no stage of the latter part of the operation is there any appearance of the joint presence of two different states of matter. It is this fact which suggested the title of the paper. (d) The key to the explanation of observed deviations from Boyle's Law is furnished by the study of the isothermals of carbonic acid at temperatures not much above 30°-9 C. For Andrews' measurements show that the product of pressure and volume (which, by Boyle's Law, should be constant) diminishes with increase of pressure to a minimum, and thereafter rises rapidly as the pressure is further increased. Memoir. liii Many other valuable results, such as the great compressi- bility of liquid carbonic acid, especially at temperatures near to that of the critical point, the alteration of surface-tension of the liquid, . and of its angle of contact with glass, as the temperature is raised, etc., appear as mere side issues of this investigation. The discovery of this critical temperature, or critical point, soon led to the liquefaction (and in certain cases even to the solidification) of the gases which had been called "non- condensable." Andrews' work had supplied all the necessary hints for the adaptation of his apparatus to such a purpose. In fact the main requisites were : (1) to work on a larger scale ; (2) to employ very low temperatures; and especially (3) to provide means of ensuring sudden relaxation of pressure. The work of Pictet, Cailletet, and v. Wroblewski, on this subject, followed as a natural and almost immediate consequence of that of Andrews. The study of the isothermals of various gases, especially in the form (naturally suggested by some of Andrews' results) of a relation between the pressure, and the product of pressure and volume, has since been effected in the most complete manner by Amagat. Andrews pushed his researches on this important subject much farther than is recorded in his first Balcerian Lecture. A preliminary notice of his new results was sent to the Eoyal Society in 1875 (E"o. XLVII. below). It deals with the pressure of liquefaction of carbonic acid at difi"erent tempera- tures (the pressure of the saturated vapour), and the expansi- bility of the liquid, or gas, at high pressures. It gives, in other words, precise data for the construction of the isothermals, and the steam-line. But it introduces an altogether new ques- tion, of an exceedingly interesting nature, the effect of an admixture of nitrogen on the critical temperature of carbonic liv Memoir. acid. In the course of this work Andrews discovered the singular change of volume which takes place when these gases, originally separated hy the liquefaction and re-vaporization of one of them, are allowed to diffuse into one another at constant (high) pressure. The details of the former of these subjects form the Bakerian Lecture for 1876 (No. XLIX. below); but those of the latter were only published posthumously in 1886 (No. L. below) : — though from the subjoined extract from a letter of Clerk-Maxwell to Andrews, it is evident that they must have been obtained in 1874, if not earlier, as the letter is dated in November of that year. What you told us at Belfast about the properties of a mixture of carbonic acid and nitrogen has been often in my thoughts, and appears to me exceedingly important for the theory of gases and liquids. The most obvious way of considering the matter appears to be to compare the observed facts with Dalton's law of evaporation. Conceive a vessel containing nitrogen at a given pressure and temperature. Now let a certain quantity of liquid carbonic acid be introduced. According to Dalton it will evaporate till the density of the gaseous carbonic acid has reached a value corresponding to the temperature, but if there is enough of room it will all evaporate. That is, it will all evaporate unless the total volume of the mixed matter is less than the volume of COj gas at its maximum density. Conversely, and even h fmiiori, COg gas will not liquefy till its density (independent of N,) is at least the maximum density. This is the hypothetical case founded on Dalton's law. If, in the real case, CO^ gas can exist when mixed with nitrogen in a vessel of a certain volume, whereas, if the nitrogen were removed from the vessel, part of the COj would liquefy, then the power of nitrogen to keep carbonic acid in the gaseous form is fully established. I should be greatly obliged to you if you will let me know when you publish the experiments in full, as the numerical results will be of great value in discriminating between different theories of gases. Memoir. Iv Are the numerical results of your former experiments on CO^ published anywhere except in the Fhil. Trans. ? I have just finished a clay model of a fancy surface, showing the solid, liquid, and gaseous states, and the continuity of liquid and gaseous states. I am afraid that even COj would not make a very compact model if worked truly to scale. But the data as to speciiic heat in the liquid and solid states are wanting as yet, and also the latent heat of fusion and evaporation. From another letter of Clerk-Maxwell's, written in 1876, we take the following extract : — I look forward to hear some good news about the constitution of matter when your Bakerian lecture is published. We are in sad perplexity about it at present. Boltzmann's theor- ems prove far too much. We are also perplexed by the electric conductivity of the warm air which rises from a flame, say of Bunsen's burner. I find that gases kept quiet inside a tube do not conduct even at a red heat. I have also tried mercury vapour and sodium vapour as well as steam, but all appear destitute of conducting power. Smoke conducts well by means of its solid particles. Dr. Andrews was intimately acquainted with the late Prof. Poggendorff, who translated all his papers and inserted them in the Annalen der Physik, so that they acquired an early and wide circulation among foreign scientific men. In addition to the papers which are reproduced below, Andrews seems to have printed little of a scientific character. Three brief accounts of parts of his Bakerian Lectures we have not thought it necessary to reprint, viz. : — " Experiences d, hautes pressions sur les gaz." Gomptes Rendus, August 9, 1875. " Uxp&iences sur les gaz d, de hautes pressions et h, diverses temperatures." Association Frangaise pour I'Avancement des Sciences. Congrts de Nantes, 1875. Ivi Memoir. " On the Continuity of the Liquid and Gaseous States of Matter." Royal Dublin Society, 1871. rroin the first of these we extract the following passages : — " Les deviations de la loi de Gay-Lussac que pr&ente I'acide car- bonique sous de hautes pressions ont un grand int^rSt. La valeur du coefficient d'expansion (a) augmente avec la pression d'une manifere vraiment remarquable. C'est ainsi qu'a une pression de 40 atmo- spheres et entre 6 degrfe et GS^e, j'ai trouv6 a = 0,00945, c'est-a-dire un peu plus que 2 J fois autant que sous lapression d'une atmosphere; mais ce qui est meme plus important, c'est que la valeur de a, d pres- sion constante, change avec la tempiraiure. II suffira, pour justifier cette proposition, de dire qn'k la pression cit^e de 40 atmosphferes la valeur de a entre 63°,6 et 100°,6, pour la meme unite de volume, s'abaisse k 0,00719. Une foule d'experiences sur ce sujet, faites k des pressions tres-variees, se sont montrees d'accord. " Quant a la methode k volume constant, mes experiences ne sont pas terminees, mais les resultats obtenus sont semblables a ceux qu'on observe par la methode k pression constante. En un mot, la valeur de a, comme coefficient de la force Uastique, s'accroit avec la pression et change avec la temperature. Pour la theorie dynamique des gaz, ce resultat est d'une haute valeur; je regarde done comme un devoir de multiplier les experiences sur cette partie du sujet et de lesvarierde toutes les manieres possibles. "A I'egard des gaz qui n'ont pas encore ete liquefies, o'est-k-dire des gaz dont les points critiques sont au-dessousdes temperatures les plus basses connues, je n'ai fait que des essais, mais ils ont donne un resultat remarquable. J'ai soumis simultanement I'hydrogene et I'azote en volumes egaux a des pressions croissantes ; d'abord I'azote, comme on aurait pu s'y attendre, diminue de volume plus vite que I'hydrogene ; mais, en augmentant la pression, la difference dans la contractilite des deux gaz diminue ; enfin I'hydrogene I'emporte sur I'azote et son volume diminue plus vite que celui de I'azote, de sorte que, vers 300 atmospheres de pression, les deux gaz occupent, pour la seconde fois, le meme volume. " Eeste k determiner les veritables pressions qui correspondent aux indications du manometre, soit k gaz hydrogene, soit k air. M. Natterer a aborde cette question il y a plus de quarante ans ; et M. Cailletet, dans les derniers temps, s'est occup6 du m(toe sujet. Ces Memoir. Ivii physiciens ont comprim6 les gaz dans des cylindres m6talliques et iriesur6 la pression par des moyens mecaniques. Comme point de depart, ces recherclies sont d'une haute valeur, mais je n'ai pu employer leurs r^sultats pour corriger les indications du manomfetre. La methode suivie par Arago et Dulong, et par M. Regnault, peut seule conduire k une solution vraie de cette question ; mais il est Evident que le proc6d6 simple, adopts par ces illustres physiciens, ne s'appliquerait pas a, des pressions de 500 ou de 1000 atmospheres. II serait assez difficile, en elTet, d'installer un tube de mercure de 380 metres de hauteur et presque impossible de le faire a une hauteur de 760 mtoes. Pendant trois ans j'ai 6tudi6 cette question avec soin, et la Soci6t6 Royale de Londres a bien voulu mettre a ma dis- position les moyens de faire des essais preliminaires. La question s'est presentee pendant longtemps k moi comme un problfeme suscep- tible de se resoudre, sans doute, par des methodes theoriquement parfaites, mais celles-ci offraient, en pratique, des difficultes qu'on pouvait croire insurmontables. C'est done avec plaisir que i'annonce que ces difficultes n'existent plus et que cette experience fondamentale pourra se faire d'une manifere qui ne laissera rien a desirer, soit a I'^gard de I'exactitude des mesures, soit a I'egard de I'importance des pressions. II est vrai, I'appareil aura des dimensions vraiment gigantesques, les frais de son installation seront un peu con- siderables, et le travail des observations pourra semblerp6nible; mais ces difficultes ne doivent point arreter quand il s'agit d'une haute question scientifique, et la bonte avec laquelle on a bien voulu accueillir mes travaux m'est un grand encouragement a faire de mon mieux dans la poursuite de cette recherche." Though Amagat has recently succeeded, in the most brilliant manner, in carrying out the measurement of pressures by means of a mercury column of 330 metres, and has constructed a manometer capable of giving accurate results up to at least 3000 or 4000 atmospheres, it would still be extremely interesting to know what was the method imagined by Dr. Andrews, of which he speaks so confidently in the extract above. Unfortunately he seems to have left no description of his proposed apparatus ; and the working drawing, which was prepared for the instrument maker, exhibits only a portion Iviii Memoir. of the whole. That mercury was to be employed seems evi- dent from the following extract from the second paper above named ': — Dans toutes ces experiences, les pressions ont 6te mesurees au moyen du manomfetre k air ou k hydrogfene. Ces indications doivent sans doute subir des corrections importantes ; de nouvelles experiences sont en preparation pour mesurer directement au moyen d'une colonne de mercure les effets de la compression sur les gaz ; elles permettront de pousser la pression jusqu'i 500 et 1000 atmo- spheres. Some MS. notes and small sketches by Professor James Thomson, who was consulted about details of the apparatus ; some statements by Mr. Taylor, the laboratory assistant ; the recollections of Professor Everett and of Dr. Crum Brown, to whom Andrews had spoken about it ; and the incomplete working drawing above mentioned ; all taken together make the following general conclusions almost certain. (a) The pressure- vessel was a doubly-connected space, which could be made singly-connected in two different ways, by clos- ing one of two conical valves and opening the other. This space was filled, partly with mercury, partly with water, as is shown in the rough sectional sketch annexed, where the shaded part represents mercury. When the valve D is open, but C closed, the pressures in A and B are equal ; but when C is opened after D is shut, the pressure in A exceeds that in B by a quantity which can be calculated from the difference of levels of the mercury in the two vertical tubes, and the specific gravities of mercury and of water at the average pressure in the vessel. A screw-plunger fitted in the wall of B enables the experi- menter to alter the pressure at pleasure, by altering the interior volume of the vessel. There seems also to have been provision made for adapting a mercury forcing-pump to B. (6) Connected with A are two tubes filled with the gases to Memoir. lix •ti ■ .. be operated on, and connected with B is a duplicate of one ai' them. This is the important feature of the apparatus. Thus at A there may be compression tubes with air and carbonic acid respectively, and at B another air-tube as nearly as possible equal and similar to that at A. Whatever be the law of compression of air, this arrangement obviously enables the experimenter to operate by means of an arithmetical series of increasing pressures. For he has only to make the air-tube in B indicate the same amount of compression L as that last reached by the air-tube in A, and " so on. There are special adjustments of smaller screw-plungers for making the difference of level of the mercury columns as nearly as possible the same every time that D is closed and C opened. (c) The column of mercury may be of any practicable height ; and it is clear that a connected series of vessels of this kind, of which the last has its B at atmospheric pressure, will (theoretic- ally) enable the experimenter to apply a measured pressure of an amount depending on the number of vessels. But it is also clear that the difficulties to be overcome in using such an apparatus, and especially in reducing its results, are extremely numerous and formidable. It is barely conceiv- able that they might be overcome even so far as to give accurate readings of pressure up to three or four hundred atmospheres. The ingenuity of the design is quite on a par with that of the Repeating Circle, but the advantages to be obtained by its employment are, in all probability, as visionary as those of Borda's celebrated device have proved themselves. From the third of these papers it is only necessary to make the following short extract, which shows how fully Andrews understood the bearing of his own results : — Ix Memoir. There can, however, be little doubt that all bodies, like mercury and water, are capable of existing in the three physical states. We may indeed live yet to see, or at least we may feel some confidence that those who come after us will see, such bodies as oxygen and hydrogen in the liquid, perhaps even in the solid state, and the ques- tion of their metallic or non-metallic nature thereby finally settled. Another little paper by Andrews, not now reprinted, appears in Pogff. Ann. CXLII., 1871, p. 320, with the title " Historische Notiz iiher das Eiscalorimeter." Its object is simply to call attention to the fact that the measurement of heat by the change of volume which takes place in thfe melting of ice had been suggested by Sir John Herschel. The only popular scientific article which, to our knowledge, was written by Dr. Andrews for an Encycloptedia, is to be found under the heading States of Matter, in a work called Chemistry as Applied to the Arts and Manufactures (London : William Mackenzie, no date). It contains a slight sketch of the con- tents of his Bakerian Lectures, with notices of the previous work of Faraday, Cagniard de la Tour, etc., on the same sub- ject. Dr. Andrews left in MS., besides the Diary of his trip through the south and centre of Trance, already mentioned, and one or two of his early lectures at the Eoyal Belfast Insti- tution, the following more or less nearly completed papers : — {a) On Electrical Conduction. (h) On the Discoveries and Writings of Faraday. (c) On the Ancient and Modern Views of the Constitution of Matter. (1865 ?) (d) Tlie Difficulties of France, their Cause and Renudy. (1874?) {e) Heidelberg. (1854 ?) (/) On the Action of Heat on Ozone, vnth some Observations on the Occurrence of that Body in the Atmosphere. (g) Notes of an Excursion to the "Long Brae Mountain" lying between the Diamond Bocks and Slieve Donard. Memoir. Ixi The first (a), is an early essay, undated, but obviously written shortly after Andrews made his experiments on Pused Salts (No. VII. below). The others (with the probable exception of the last named) are drawn up as semi-popular lectures, and were read before one or other of the literary or scientific societies in Belfast. "With the exception of (d) and (/), they contain, so far as we can see, little (due to Andrews himself) which is strikingly original, either in the sense of criticism or in the mode of presentation. Anything of the kind would have been foreign to their purpose. That marked (d) seems to have been, at one time, intended for publi- cation as a pamphlet, but the intention was not carried out. One lecture, indeed, of this class, on " Magneto-electric Machines," was published in Nature by Dr. Andrews himself. We have therefore (at the instance of Sir W. Thomson) included it, as No. LI., in the present collection. The others we do not think it necessary to publish. From the scientific point of view (c) is the most interesting. But it is incomplete, inasmuch as though the parts dealing with the Lucretian Atom, and with the ideas of Boscovich, are fully written out ; the rest is merely lecture notes, consisting of little more than headings. The contents of (/) are given, partly above, partly in the papers reprinted below. The last on the list {g), seems to have been drawn up for the instruction of the family circle and for private friends. It deals with the measurement of heights by means of an aneroid, and with some peculiar geo- logical features of the junction of granite and clay-slate in the Mourne mountains. Dr. Andrews' LaJboratory Note-books, which were made of four or five sheets of stout foolscap paper, once folded crosswise and sewed together, have been bound in seven thick volumes, and the series is complete. They contain, in addition to the materials for his published scientific papers, the results of an Ixii Memoir. uncompleted series of researches on the absorption of radiant heat by gases and vapours. These were commenced by him in 1864 in the Physical Laboratory of Edinburgh University, and taken up from time to time in subsequent years. It is worthy of note that Andrews seems to have at once seen the error in- volved in using tubes of a few inches in diameter; for his apparatus, constructed in tinned iron, was of gigantic dimensions. SCIENTIFIC PAPERS. I.— ON THE ACTION OF A FLAME URGED BY THE BLOWPIPE ON OTHER FLAMES. Philosophical Magazine, 1829, II., p. 366. To THE Editors of the Philosophical Magazine and Annals. Belfast, October 5, 1829. Gentlemen, — Although the action of the flame produced by the blast of the blowpipe has been tried upon almost every substance which could be exposed to it, yet its influence upon flame itself has never, I believe, been examined.^ I directed the flame of a candle urged by a mouth blowpipe upon that of another candle of equal size, so that the extremity of the reducing flame of the first candle played on the flame of the other, in the same manner as the orifice of a blowpipe. On applying the blast, the flame of the second or remote candle was inverted, and exhibited nearly the same appearances as a flame acted on immediately by the blowpipe. The reducing part of it terminated in a perfect conical shape, and beyond it the oxydizing part appeared of a similar form. The reducing flame, however, formed by this means was considerably larger than that formed by the blowpipe in the usual manner, and from some comparative experiments which I made, its heating power appeared to be scarcely so great. I approached the second candle to the first, till the reducing flame of the latter penetrated beyond the flame of the former. In this case the reducing flame was terminated by irregular points, and its outlines were indistinctly marked. On removing the flame of the second candle into the oxydizing part of the first, the former was inverted as in the other cases, but the reducing part of it terminated not in a point but in a luminous zone. ' In the case of the spirits of -wine eoliplle, the impetuosity with which the vapour of the spirits issues from the orifice of the tube prevents the action of the flames on each other from being observed. A 2 On the Action of a Flame urged by the Blowpipe. [i. This latter experiment will succeed even when the flames of the two candles are six inches distant, but beyond that point an irregular waving is only produced in the second flame. It is evident, however, that this poiut will vary according to the flame which is employed. Instead of two, I have placed six different flames in the same manner in succession, and the last of them seemed to be inverted equally with the first; from which it would appear that any number of flames might by this means be directed by a single blast. The action of the one flame in directing the others may be strikingly exemplified by removing the flame in immediate contact with the blowpipe during the blast, for the rest wiU be then affected only by an irregular unsteady motion. In like manner, if we fuse a small piece of metallic tin or lead in the reducing part of the remote flame, and then remove that flame, the metal will instantly be converted into an oxide. By inserting the above in the FMlosophical Magazine and Annals of Philosophy you will oblige. — Yours etc., (Signed) Thomas Andrews. II.— ON THE DETECTION OF BAEYTA OR STEONTIA WHEN IN UNION WITH LIME. Philosophical Magazine, 1830, I., p. 404. The best method which has yet been proposed to distinguish strontia when combined with lime, is perhaps that by which Stromeyer first succeeded in determining the composition of arragonite, and I believe it alone has been employed in the analyses that have been made by different chemists of the varieties of that mineral. It is founded upon the insolubility of nitrate of strontia in pure alcohol, which at the same time dissolves with facility the nitrate of lime. In theory the pro- cess is absolutely perfect, and, when properly conducted, it seems susceptible in practice of very great precision ; but it must at the same time be confessed that its failure in the hands of some of the most expert chemists proves it to be a far from satisfactory mode of analysis. As nitrate of baryta is insoluble in alcohol, baryta may likewise in this manner be separated from lime. Bucholz having endeavoured unsuccessfully to verify the analysis of Stromeyer, suggested another process, which, though he failed himself in executing, was afterwards performed by Gehlen. It consisted in separating the strontia from the greater part of the lime (the mixture being previously reduced to the pure state) by solution in boiling water, and afterwards distinguishing the presence of the former by the crystallization of its hydrate on allowing the solution to cool. It is evident that although in this way considerable quantities of strontia may be detected, yet when it exists in small proportion the process will entirely fail, in consequence of the solubility of strontia in cold water. If baryta be substituted for strontia, this method will be stUl more defective, since that earth is much more soluble in water than strontia. 4 On the Detection of Baryta or Strontia ["• Mr. Brande has proposed to precipitate directly the sulphate of strontia from a solution of the earths in nitric acid, and after washing it with repeated affusions of boiling water to determine its weight. This mode of analysis appears to me, with much deference to so high an authority, to be much more exception- able than any that has yet been proposed. I have in vain endeavoured to throw down sulphate of strontia in this manner, although present to the amount of 5 per cent., for when the solution was so dilute that no precipitate at first appeared on the addition of sulphate of soda, a voluminous deposit of crystallized sulphate of lime slowly formed, without any previous precipitation of sulphate of strontia. Nor will boiling water effect a separation of the sulphates of lime and strontia,, as it is nearly impossible to wash away any considerable quantity of ,the former sulphate by means of that liquid, while the latter is at the same time sensibly soluble in it. It is possible, however, that there may be some circumstance, on which the success of this experiment depends, of which I have, not been aware; for Mr. Brande obtained by this means a. precipitate which upon examination proved to be pure sulphate of strontia, and the weight of which corresponded exactly with the original quantity of carbonate of strontia that he employed. It will certainly be less liable to objection in the case of baryta, but it appears to me very doubtful whether it wUl effect a complete separation, or distinguish a small quantity, even of that, earth. The following method, which is merely an extension of that proposed by Bucholz, will be found not less sensible in its in- dications, whUe it is at the same time more easy of execution, and more certain in its results, than the process of Stromeyer. Dissolve the carbonates of lime and baryta or strontia in nitric acid, evaporate the solution to dryness, and decompose the nitrates by heat ; to the dry mass add boiling water (pure in the case of baryta, but saturated in the cold with sulphate of strontia in the case of that earth) and boil it for a few minutes, keeping the crucible at the same time loosely covered with its lid. Throw the whole on a covered filter, and to the liquid which passes through add sulphuric acid or a soluble sulphate ; a white powder will precipitate if either baryta or "•^ Wh^n in Union with Lime. • --'• 5 strontia be present, but if not,' the liquid will retain its trans- parency. ' ' \ I decomposed in this manner 99-75 grains of nitrate of lime and '25 grain of nitrate of ' baryta ; a white precipitate immediately appeared on the addition of sulphuric acid to the filtered liquid. A similar experiment, made with equal proportions of the nitrates of lime and strontia, was attended with the same result ; the precipitate, however, did not appear quite so soon as 'before. Hence it appeats that xoir part at least of baryta or strontia united to lime may be in this way rendered evident. It is almost unnecessary to add that when pure lime was treated in a similar manner, no precipitate fell, since. sulphate of lime is nearly four times as soluble in boiling water as lime itself If, however, the liquid be raised to the boiling point after the addition of the sulphuric acid, one or two crystals of sulphate of lime will sometimes form, but, as these are transparent and of a distinctly crystalline appearance, it is impossible to mistake them for the sulphate either of baryta or strontia. ■"■ In these experiments I have in general preferred the employment of sulphuric acid to that of a sulphate, as I have found it to be a rather more delicate test, particularly of the presence of strontia. It must, of course, be carefully purified from sulphate of lead. It is generally believed on the authority of Dr. Hope, that sulphate of strontia is sensibly soluble in water, so that the addition of a barytic salt or an alkaline carbonate to a solution of it, will indicate the presence of both its constituents, and this circumstance has been proposed as a distinguishing test between the sulphates of baryta and strontia. On the other hand, the late Mr. Smithson states that " water or solution of sulphate of soda, in which sulphate of strontia had long lain, did not produce the least cloud on the addition of what is commonly called sub- carbonate of soda"; and Dr. Thomson was unable to detect any trace of strontia in the supernatant liquid which remained after the mutual decomposition of solutions of sulphate of ^ I added to three different portions of lime-water saturated at 60°, sulphate of soda, sulphate of ammonia, and sulphuric acid ; no precipitate appeared at the end of some weeks in the first two liquids, but a large quantity of gypseous crystals was slowly deposited in the latter in the course of some days. 6 On the Detection of Baryta or Strontia. !"• soda and chloride of strontium. I digested for some hours sulphate of strontia, obtained by precipitation, in pure water, in a solution of sulphate of soda, and in water acidulated with sulphuric acid ; carbonate of soda was added to each liquid, and heat applied ; a precipitate appeared in all of them ; it was most considerable in the iirst, while in the last the opal- escence was scarcely perceptible ; 900 grains of the solution in pure water were evaporated to dryness, and left a residue of sulphate of strontia which weighed '25 grain; from which it follows that one part of sulphate of strontia requires about 3600 parts of water, at the temperature of 60°, for solution. It also appears that the presence of sulphate of soda and sulphuric acid (in small quantity) diminishes its solubility. I have not examined whether chloride of sodiiim would produce a similar effect, but the experiments of Dr. Thomson would lead to this conclusion. III.— CHEMICAL EESEAECHES ON THE BLOOD OF CHOLEEA PATIENTS. Philosophical Magazine and Journal of Science, 1832, II., p. 295. The discordancies in the various analyses which have been published of the cholera blood, rendering it desirable that the subject should be again investigated with precision, I availed myself of the opportunity afforded by the prevalence of the epidemic in Belfast to institute a new set of experiments. The iirst analysis of cholera blood that appeared in this country is Dr. Clanny's, from which, and a corresponding analysis of the blood in health, he inferred that the water, as well as the albumen and fibrin, are deficient in quantity, that the colouring matter and what he denominates free carbon, are greatly in excess, and that the saline constituents are entirely wanting. Dr. O'Shaughnessy is the next chemist who turned his attention to the subject; but he seems to have confined himself principally to the serum, of which he has published a very elaborate examination. He found its specific gravity increased in consequence of the deficiency of water, the animal matter considerably in excess, but a diminution of the salts, especially of the carbonate of soda, which in one case was absent, the serum being devoid of action on test paper. But the latest, and by far the most valuable researches on cholera blood are those of Dr. Thomson, which although they do not exhibit its true composition, yet furnish data from which it may be nearly calculated. He agrees with Dr. Clanny in the excess of colouring matter and deficiency of water, albumen, and fibrin (but he confesses that the deficiency of the latter may be doubted) in the blood ; while in the serum he found the albu- men increased, but the salts normal in amount and composition.^ 1 An abstract of Dr. O'Shaughnesay's results will be found in Phil. Mag. and Annals, N.S., vol. 11, p. 469. Dr. Thomson's researches on cholera blood were published in the same volume, p. 347. 8 Chemical Researches on the Blood of Cholera Patients, [m. A few of these different results may have arisen from varia- tions in the composition of the specimens of blood which were subjected to analysis, others can be referred only to errors of experiment; but the principal source of them is the diversity of the modes of analysis which were followed. It is for this latter reason that I shall enter with more minuteness than might otherwise be necessary into the details of the follow- ing experiments. Specimen 1. Choleka Hospital, Belfast. — This was ob- tained from a rapid case of cholera ; but I know nothing more of its history. The blood was taken from the vena cava immediately after death, and introduced into a vial, in which it afterwards coagu- lated. The serum was slightly tinged red, but perfectly trans- parent ; the crassamentum was not in this case darker than it often appears in healthy blood. Their relative proportions were — Serum, 41-6 Crassamentum, 58'4 100-0 But as the serum was merely drawn off, these . proportions do not admit of comparison with the healthy ratio of Berzelius. Serum,. — Specific gravity, 1-038, had an alkaline reaction. 32-518 grammes of it were evaporated to dryness ; and after being reduced to a coarse powder, dried till they ceased to lose weight on a warm bath, the temperature being prevented from rising too high by placing some shreds of cotton beneath the capsule containing the albumen. The dried mass weighed 4-078 grammes. This was now incinerated and washed repeatedly with boiling water, which was evaporated to dry- ness, and the saline matter thus obtained calcined, and found to weigh -243 gramme, to which adding -027 (obtained as we shall hereafter mention) we have the saline matter soluble in water equal to -27 gramme. About -02 gramme of this matter was carefully examined to determine its nature. By spontaneous evaporation it lit.] Chemical Resea/rches on the Blood of Cholera Patients. -9 yielded a set of crystals, which, examined by a microscope, proved to be principally cubes intersected by others of an aeicular form. Two or three of the largest and purest lof these cubes were dissolved in water ; the solution had a strongly alkaline reaction, and was precipitated by nitrate of silver, the precipitate being soluble in ammonia. The rest of the crystals were now dissolved in a drop of water ; pure ammonia was added to a minute portion of it, and a faint cloud appeared, indicating the presence of phosphoric acid. The remainder of the solution was divided into two portions ; to one of which tartaric acid was added, and to the other chloride of platinum. Evolution of gas took place in both cases, and in the one solution, numerous clusters of crystals (whose shape was a six-sided prism) appeared in a few seconds; while in the other a granular deposit of octohedral crystals was soon formed. To the remaining "25 gramme of saline matter, chloride of barium was added in excess ; a white precipitate fell, but the solution continued alkaline, and by evaporating it to dryness, a portion of insoluble matter remained, which had principally arisen during the evaporation, forming a thick crust on the surface of the liquid. The solution still continued slightly alkaline, and became opake on the surface. These experiments indicate the presence of uncombined alkali. The carbonate of baryta weighed and estimated for the whole saline matter was equal to '0972 gramme, equivalent to '0525 carbonate of soda. It dissolved with effervescence in nitric acid, leaving a residue of "012 of sulphate of baryta, equivalent to '008 of sulphate of potash. The nitric acid solution was precipitated by ammonia and prussiate of potash occasioned a faint white-cloud. In order to obtain the remainder of the saline matter from the incinerated mass, it was boiled in acidulated water, '050 gramme of saline matter was obtained, of which '027 gramme dissolved in water. The remainder was dissolved in nitric acid and precipitated by ammonia of a slightly red colour, then redissolved in nitric acid and precipitated by oxalate of ammonia ; but I could not detect any magnesia in it, probably from the minute scale on which the experiment was performed. The serum therefore contained — 10 Chemical Researches on the Blood of Cholera Patients, [m. Water, 874-59 Albumen, 116-40 Chlorides of sodiuin and potassium, with uncombined alkali. 6-69 Carbonate and phosphate of soda. 1-36 Sulphate of potash. •25 Phosphate of lime. •71 1000^00 Crassamentum. — 23-49 grammes were dried in the same manner as the albumen; they lost 16-472 grammes of water. This water arose from the serum in the crassamentum, and must have been united by its analysis to 2-360 grammes of albumen and salts. Hence the crassamentum consisted of 18-832 serum and 4-658 red globules and fibrin. 58-58 grammes of the same crassamentum were washed to separate the iibrin, but the process was very tedious, and after persevering for above a week, I did not succeed in render- ing the fibrin perfectly colourless. It was dried at the same temperature as the albumen and crassamentum. It weighed ■52 gramme and was of a dirty green colour. From these experiments the composition of the blood was — Water, Albumen and salts, Eed globules, Fibrin, 78-43 10-00 11-06 •51 100-00 Specimen 2. Cholera Hospital, Ballymacaeeett. — This specimen of blood was taken from a male patient (set. 50), who had been seized with cholera the same morning, and died early on the following day. From the commencement of the attack he had passed involuntary stools, and vomited copiously. The pulse was perceptible before he was bled, but afterwards became very faint and irregular. The blood flowed with difficulty, and was of a very dark colour, and -viscid consistence. ni.] Chemical Researches on the Blood of Cholera Patients. 11 It coagulated perfectly, the serum was yellow and pure, and the crassamentum much darker and more bulky than usual.^ Serum. — Specific gravity, 1-045; alkaline reaction; taste saline, similar to healthy serum. 14-377 grammes of it were analyzed in precisely the same maimer as the preceding speci- men. Its constituents were — Water, 847-02 Albumen, 144-36 Chlorides of sodium and potassium, with free alkali. 5-96 Carbonate and phosphate of soda, 1-62 Sulphate of potash. -22 Phosphate of Hme, with a trace of iron, -82 1000-00 73-11 13-21 13-38 -30 Crassamentum. — The blood weighed 77-94 grammes, and the crassamentum, with a considerable portion of impure serum, 58-27 grammes. The latter contained 47-604 grammes of serum, and -231 gramme of fibrin of a buff colour and pretty pure. The composition of the blood was therefore — Water, - Albumen and salts, - Eed globules, Fibrin, - 100-00 Specimen 3. Lunatic Asylum, near Belfast. — This was taken from a female patient (aet. 20) in the state of collapse, the radial pulse not being perceptible when the blood was drawn. It flowed in a continuous stream for a few seconds, but afterwards trickled with extreme difficulty. The patient died next day. The blood was black and thick ; it coagulated as usual. Sernmi. — Specific gravity, 1-040, of a pure yellow colour ; 1 In this, as well as in all the following cases, the blood was received into a, vial, which was immediately closed. This precaution was necessary, as serum exposed to the air evaporates with great rapidity. 12 Chemical Researches on the. Blood' of. Cholera JP(iUents. :[ni. 4'811 grammes left, by desiccation, '6 3 6 gramme of albumen and salts. It contaiaed therefore- — Water, - - ' 8-6 5-9 5' Albumen and salts, - - - 13 4* 05 1000-00 The saline matter was not weighed, but its solution was alkaline, and effervesced with acids. Crassamentum. — The proportion of serum to cr9.ssamentum was — ; Serum, - - 40*5 Crassamentum, - - 59'5 100-0 But the same observation applies to this as to the former determination. The crassamentum contained 68-55 per cent, of water ; it con- tained also -075 gramme of pure fibrin, equivalent to -^6 per cent., the blood weighiug 28-937 grammes. Hence it con- sisted of — Water, - - 74-93 Albumen and salts, 11-60 Eed globules, - 13-21 Fibrin, .. -26 100-00 Specimen 4. Lunatic Asylum. — This blood was drawn from the jugular vera of a female patient (aet. 20) who had rallied from collapse for about a day by artificial excitement, the blue- ness having disappeared, and the natural warmth having been restored. The blood was obtained six hours after death. It did not coagulate, but the red globules subsided, leaving the serum yellow and pure. Serum. — Specific gravity, 1-040. 9-940 grammes df it were subjected to analysis, and found to contain — - I"-] Chemical Researches on the Blood of Cholera Patients. 13 Water, 866-72 Mbtimen and salts, - 1 3 3 ■ 2 8 1000-00 The saline matter was found to be about 1-2 per cent., but the iexperimeiit was mat made with much precision : its solution in water was alkaline, effervesced with acids, and contained both potash and soda. The blood was found to contain — Water, - - ; - 76-07 Albumen and salts, 11-69 Eed globules, 12-24 100-00 There was no fibrin present. Having thus ascertained the composition of the blood in the severer stages of the complaint, I next proceeded to examine it in the incipient stages. Two of the first specimens I procured were from the Cholera Hospital, taken from patients affected with diarrhoea and vomit- ing, but who afterwards recovered. I did not see them myself, and therefore cannot be certain whether they were real cases of cholera • or not : the specimens resembled in every respect healthy blood. The specific gravity of the serum of one was 1-0243, and of that of the other 1-0232. The latter was subjected to analysis ; it contained — , Water,- r - 919-99 Albumen, 71-62 Salts, 8-39 1000-00 The serum was to the crassamentum in the ratio of 51-3 and .48-7, and the latter contained 74 per cent, of serum. Hence the blood was composed of — 14 Chemical Researches on the Blood of Cholera Patients. [™- Water, - - - 80-35 Albumen and salts, 6-99 Eed globules, - 12-66 100-00 Specimen 6. Ballymacaeeett Hospital. — This was taken from a female (at. 45), who had been affected with violent purging and vomiting. The pulse was feeble when the blood was drawn, but she did not fall into collapse. The blood coagulated as usual. &TOm.— Specific gravity, 1-031 ; very pure. It consisted of— Water,- - - 891-69 Albumen and salts, 108-31 1000-00 77-93 9-43 12-34 -30 Crassamentum. — The fibrin in this case was determined by agitating a separate portion of the blood with a network of iron wire, and was thus readily obtained pure, and found to be •296 per cent. The blood contained — Water, - Albumen, Eed globules, Fibrin, 100-00 In three other cases of incipient cholera the serum was found to have the following specific gravities — 1*027, 1*030, 1-033. The last was from a very well marked case. These experiments on the blood of incipient cases, though less numerous than I should have wished, seem to me to warrant the general con- clusion, that the composition of the blood does not differ from the normal state during the early stages of the disease. In order to show more clearly the changes induced in the blood by cholera, I shall collate the results of my own experi- ments with those obtained in the analysis of healthy blood. «!•] Ghemical Researches on the Blood of Cholera Patients. 15 SERUM. Health. Cholera. Sp. Gravity, Sp. Gravity, Sp. Gravity, 1-029. 1-03S. 1-045. Water, 900-00 874-59 847-02 Albumen, 90-80 116-40 144-36 Chlorides of sodium and potas- sium, - 6-60 6-69 5-96 Carbonate and phosphate of soda, 1-65 1-36 1-62 Sulphate of potash. •35 •25 •22 Earthy phosphates, •60 •71 •82 1000-00 1000-00 1000-00 The analysis of healthy blood is Dr. Mareet's, which closely agrees with those of Berzelius and Lecanu. A glance at this table is sufficient to show that in the serum of cholera blood, the albumen is in great excess, but that the salts are both qiuilitatively and quantitatively the same, the minute differences in their proportions being less than analysts have found in healthy blood.^ BLOOD. Cholera. Incipient Cholera. Health. Prevost and Dumas. 1 2 3 4 5 6 Water, Albumen and salts; Red globules. Fibrin, - 78-43 10-00 11-06 •51 73-11 13-21 13-38 -30 74-93 11-60 13-21 -26 76-07 11-69 12-24 80-35 6-99 12-66 77-93 9-43 12-34 -30 78-39 8-69 12-92 I shall venture to give one other table, because I believe its results have not been published in any English work, and they are essential to a correct knowledge of the composition of the blood. 1 It may not be uninteresting to observe here the striking analogy between these conclusions and those of Dr. Marcet, who found in the analysis of dropsi- cal fluids, that however great the variation of albumen, the proportion of salts was invariably the same as in the serum of blood. 16 Chemical Researches on the Blood of Cholera Patients, [ni. Male. Female. [ Max. MiD. Max. Min. j Water, Albumen and salts, Eeii globules and fibrin. .85:31 8-74 13-00 79-04 e-72 6-83 80-53 9-23 14-84 77-86 ■ 6-68 j 11-58 I The variation in cholera blood from the healthy standard is not so great as is generally supposed. The water is not only in every case below the mean of healthy blood, but belo\^ the minimum in the experiments of Lecanu, and the albumen is proportionally increased. In the analysis of Prevost and Dumas and of Lecanu, the fibrin was not separated from the red globules, nor do I know of any experiment worthy of con- fidence on the amount of the former constituent in healthy blood ; it is generally estimated at about five per cent., but I am inclined to believe that it is not one tenth of that quantity. Indeed, it is with dif&dence that I publish the results I have obtained from cholera blood, as I am satisfied that the process suggested by Dr. O'Shaughnessy is the only one susceptible of precision. It was, however, followed in the last experiment, and the results agreed with those obtained by the othei method. Another source of fallacy is this; — that the tempera- ture at which fibrin is decomposed seems much lower than that necessary to decompose other animal principles: but further experiments are necessary to elucidate this point. I shaU only further observe, that in the heart from which the specimen No. 1 was taken, scarcely a vestige of fibrin could be discovered. But the most interesting and important fact derived from these investigations is, that, contrary to the conclusions of former experimenters, and apparently in direct opposition to the evidence of the senses, the colouriag particles in black cholera blood exist in the same proportion as in the blood of health varying not more than a half per cent, from the normal standard; and as a much greater diversity is found in the blood of different individuals in health, we must conclude that these slight vari- ations are independent of, and unconnected with, its diseased state. in.] Chemical Researches on the Blood of Cholera Patients. 17 These results differ very much from preceding analyses, but it will not be difficult to reconcile them with the experiments of Dr. Thomson. In order to separate the globules, he merely washed the crassamentum (drained of its serum), and evap- orated the solution thus obtained ; but it is evident that in this way "a portion of serum containing albumen" which could never be appreciated, varying with the bulk of the coagulum, " would be added to the colouring matter, and have the effect of apparently increasing its quantity." In one experiment he found in this way the red globules to be 27'4 per cent., while the albumen and salts only amounted to 5-9 per cent. ; in another the red globules were 23-2 per cent., and the albumen 7'5. Fortunately, however, he has stated the water in the crassamentum, as well as its proportion to the serum, from which, and the composition of the serum, the relative proportion of the constituents of the specimens of blood which he analysed may readily be calculated as follows : Water, 70-76 67-96 Albumen and salts, - 13-53 15-83 Eed globules. 15-33 14-87 Fibrin, -38 1-34 100-00 100-00 These results do not perfectly agree with my own experi- ments, but the coincidence is sufficient to confirm the deduc- tions which I have made from them. The analysis of the serum by Dr. Thomson proves also that the salts are in every respect normal, and I cannot therefore avoid concluding that the experiments of Dr. O'Shaughnessy are inexact. Unless Dr. Cla'nny will publish with more detail the methods he has followed in analysing both healthy and diseased blood, it wUl be difficult to understand how he has arrived at his conclusions. It may be right, however, to observe, that the amount of residual carbon obtained by calcining albumen, globules, or any proximate principle will not depend on the organic matter itself, but on the salts, and especially on the phosphates which may be present, for these by fusing protect the carbon from combustion ; but if they are previously removed then the 18 Chemical Researches on the Blood of Cholera Patients, [m. " free carbon " of Dr. Clanny will speedily disappear by calcina- tion even in a covered crucible. If these experiments and those of Dr. Thomson can be relied upon, the principles upon which the saline treatment is founded are evidently false. To introduce a small quantity of inert saline matter into the stomach will certainly be as inefficacious in the cure of diseases as it is innocuous ; but it is a question of very great importance to determine, whether the addition of a large portion of salts to the blood by infusion into the veins (introduced with an intention of supplying a deficiency, but in reality occasioning an excess,) may not only be not beneficial, but positively injurious. It is not improbable that since so great a uniformity exists in the amount of saline ingredients in every variety of serous fluid, this quantity in the serum of blood may be essential to the due discharge of the functions of that fluid. An accurate examination of the blood in sea-scurvy might throw light on this obscure subject, for either the exhibition of saline remedies is an absurdity, or the serum of a scurvy patient is overcharged with salts. In dropsy the blood is drained of a fluid containing a much larger quantity of salts than the cholera evacuations (if the experiments of Dr. O'Shaughnessy on the latter be exact) ; yet who will pretend to discover in such patients or in their blood any of those marvellous effects which have been attributed to the absence of these matters ? The evacuations in cholera, containing little more than half the saline matter of the serum, ought to increase instead of diminishing its saline contents ; but I do not doubt that if these evacuations could be obtained in the same state in which they are separated from the serum, and unmixed with other fluids, they would contain nearly the same proportion of salts which is found in it. There is one circumstance indeed, which renders it improbable that even if a deficiency of salts could occur, it would produce any very injurious effect : the serum of a bullock, resembling in every other respect that of man, contains (according to Berzelius) less than half its saline ingredients, yet it is neither darker nor more difficult of arterialization. But we must not hence draw a hasty con- clusion, that either a deficiency or excess of salts in the blood would be harmless. 111.] Ghevnical Researches on the Blood of Cholera Patients. 19 The following are the general conclusions that appear to follow from these researches : That the only difference between the blood of cholera and of health consists in a deficiency of water in the serum, and a consequent excess of albumen. That the saline ingredients of the serum are the same as in healthy blood. That the red globules, and probably the fibrin also, are normaL That the want of fluidity ia the blood, the darkness of its colour, and the bulk of the crassamentum, are simple effects of the increased viscidity of the serum. I am at present engaged in further researches connected with this subject, but conceiving these results to be of some immediate interest, I have been induced to publish them in this detached state. 20 IV.— ON SOME CAVES IN THE ISLAND OF RATHLIN AND THE ADJOINING COAST OF THE COUNTY OF ANTRIM. From the Report of the British Association, Edinburgh, 1834. Of these caves six were examined by the author, viz., four in Eathlin, one in the rock called Carrick-a-rede, and one in the mainland near Ballintoy. In a cave in Eathlin, a thick layer of sea sand containing marine shells was found beneath the stalag- mite, near the termination of the cave ; and in another cave a different variety of water-worn sandstones was discovered in a similar situation, but no trace of shells could be seen. In an- other large cave at Eathlin, a rude piece of antiquity formed of iron and resembling the handle of a sword, was found quite close to the skeleton of a sheep. The length of the Eathlin caves varied from 150 to 250 feet ; the dimensions in other respects were very different. It seems obvious from these circumstances, from the position of the entrances to some of the caves and the narrowness of those of others, first, that many of the animals could not have entered them in their present position and state; second, that the sea must have formerly entered them at a much higher relative elevation than its present level. 21 v.— ON THE CHANGES PEODUCED IN THE COMPOSITION Of THE BLOOD BY REPEATED BLEEDINGS, Thomson's Records of Oenerai Science, vol. 1, 1835, p. 31. The object of the following experiments is to determine with precision, the changes which are produced in the composi- tion of the blood by repeated abstractions of large quantities of it from the general circulation. In the human subject, opportunities seldom occur of procuring proper specimens for examination, although the operation of venesection is so frequently performed, as in those cases where it requires to be repeated at short intervals the blood is generally in a morbid state. Instead of waiting for such casual occasions, I directed my attention to those animals in which the composition of the blood is nearly the same as in man, conceiving that similar results would in either case be produced. I selected the blood of calves for the purpose of experiment, and as it is the practice of butchers in this country to bleed these animals several times before they are slaughtered, I availed myself of this circumstance to procure suitable portions of blood. The animal is bled from a large orifice in the jugular vein, till symptoms of syncope appear, and the operation is in general repeated at intervals of twenty-four hours. It is once fed between each operation upon a mixture of meal and water, but this is often omitted before the last bleeding. The appearance of the blood becomes greatly altered by the successive abstractions ; the crassamentum is at first very large, and a portion of the red globules are unattached to it, but it progressively diminishes in bulk, while its consistency increases, till upon the fourth bleeding it appears a small contracted ball immersed in a large quantity of serum, adhering to the stopper of the vessel in which it is contained, and presenting on its external surface an exact cast of the interior of the vessel. 22 On the Changes Produced in the Composition [v. The following analyses were performed by the same method that I formerly employed in a set of experiments on the blood of cholera patients, which were published in the Fhilc- sopUcal Magazine for September, 1832. They are nearly all a mean of two separate analyses which seldom differed from each other more than 0-5 per cent. A calf was bled four times; between the first and second bleedings a week elapsed, but the rest took place at intervals of twenty-four hours, and the animal was fed between each operation. The composition of the serum and blood at each bleeding is exhibited in the following tables : SERUM. Water, - Albumen and salts, First. Second. Third. Fourth. 92-19 7-82 93-96 6-04 93-81 6-19 94-18 5-82 100-00 100-00 100-00 100-00 BLOOD. Water, - Albumen and salts, Eed globules and fibrin,- First. Second. Third. Fourth. 81-36 6-89 11-75 85-49 5-50 901 87-41 5-77 6-82 89-25 5-52 5-23 100-00 100-00 100-00 100-00 The serum had at the third bleeding a specific gravity of 1-020, and at the fourth, of 1-017. At the third bleeding the specific gravity of the blood itself was 1*0 31. The next calf whose blood was examined was' nine weeks old. I did not procure any blood from the first bleeding. The third bleeding was twenty-four hours after the second, and during that period, the animal was once fed ; twelve hours v.] Of the Blood hy Repeated Bleedings. 23 afterwards it was bled a fourth time, but it received no more food. SEEUM. Water, Albumen aud salts. Second. Third. 93-32 6-68 100-00 94-39 5-61 100-00 Fourtli. 94-59 5-41 100-00 BLOOD. Water, Albumen and salts, Eed globules and fibrin. Second. Third. Fourth. 82-05 5-85 12-10 89-14 5-29 5-57 88-92 5-06 6-04 100-00 100-00 100-00 The albumen and salts, it is e\'ident, decrease at each bleeding; the diminution is, however, very variable, and even after the fourth time does not amount to one per cent, and a half In the globules, the same diminution takes place, but to such a degree that they are at least reduced to less than one half their original quantity. To this principle, a remarkable excep- tion occurs in the composition of the blood taken at the last bleeding of the second calf, where the globules are slightly increased above the preceding analysis ; but it will be observed that the animal received no food during the intervening period, from which the blood might obtain a fresh supply of serum, while the tendency of the different excretions of the animal was to drain from the circulating mass its aqueous part, and thus to increase the apparent quantity of the globules. This explanation is confirmed by the following analysis. A calf three weeks old was bled twice before it was killed ; twelve hours elapsed between the two bleedings, during which time it obtained no food. 24 On the Glianges Produced by Certain Bleed/ings. [v. SERUM. "Water, Albumen and salts, First. Second. 92-48 7-52 93-35 6-65 100-00 100-00 BLOOD. Water, Albumen and salts, Globules, First. Second. 82-48 6-70 10-82 83-47 5-95 10-58 100-00 100-00 The globules have here, it is true, diminished at the second bleeding, but so slightly, that we may attribute this circum- stance to the unassimilated chyle which must have been present in the system. In the former case, the animal had been exhausted by previous depletions, and hence possessed no store from which the blood could derive even a small portion of serum, as in the latter instance. VI.— ON THE CONDUCTING POWER OF CERTAIN FLAMES AND OF HEATED AIR FOR ELECTRICITY. Philosophical Magazine and Journal of Science, 1836, II., p. 176. In some recent memoirs on electricity it has been assumed that the discharge of electricity through flame depends simply upon the temperature to which the air in the flame is elevated. Thus Dr. Eitchie observes that " the flame of a blowpipe is a hoUow cone containing highly rarefied air. The electric fluid will therefore glide along such a cone exactly as it does along the interior of a hollow cone of glass partially exhausted of air. We are therefore not to regard flame as a conductor of electricity in the ordinary sense of the term, when the only part it performs in the conduction is that of forming a partial vacuum." ^ These remarks refer to common electricity ; but Mr. Faraday likewise assumes that the relations of flame and heated air to electricity of low tension are the same, in his excellent paper on the " Identity of Electricities derived from different Sources." In order to prove that the latter variety of electricity may be discharged by heated air in the same manner as the former, he performed the following experiment. Having attached fine platina wires to the poles of a galvanic battery of 20 pairs of plates, and brought their extremities very close to each other, but without touching, he found that where they were heated to bright redness by the application of the side of a spirit-lamp flame, the current was freely trans- mitted. On putting the ends of the wires very close by the side of and parallel to each other, but not touching, the effects were, perhaps, more readily obtained than before. " These effects," he continues, " not hitherto known or expected under this form, are only cases of the discharge which takes place through air between the charcoal terminations of the poles of ^Philosophical Transactions for 1828, p. 376. 26 On the Conducting Power of Certain Flames [vi. a powerful (galvanic) battery when they are gradually separated after contact. Here the passage is through heated air, exactly as with common electricity."^ On the other hand, the celebrated experiments of Erman, which were repeated and extended by Biot, are opposed to this simple view of the subject, and tend to prove that in the power of conducting electricity of feeble tension flames present some remarkable properties which are different in flames of different kinds, and cannot therefore be identical with those of heated air. The experiments of Erman, however, refer only to flames ; and as the whole subject was involved in much obscurity, although connected with one of the most remarkable electrical properties that have yet been discovered, it appeared to be deserving of new investigation. To detect the passage of an electrical current, the test which I employed in the following experiments was the solution of the iodide of potassium, the extreme delicacy of which was first, I believe, pointed out by Faraday. A slip of bibulous paper moistened with this solution was placed on a platina plate, supported upon an insulating stand of glass. The negative pole of the battery was brought into contact with the platina plate, while a wire of platina attached to the positive pole rested on the moistened paper. The existence of the current was inferred from the deposition of iodine beneath the positive pole; and when no iodine was deposited, I have described the current as being interrupted. By this expression it is only to be understood that if a current did pass it was too feeble to produce any sensible decomposition of the solution of iodide of potassium. The extreme delicacy of this test, and the pre- cautions which must be employed in using it, wiU be evident from this simple experiment. If the positive pole of a battery, composed of a single pair of zinc and platina plates, be placed upon the paper of the decomposing apparatus, and the platina plate touched by the moistened finger, no effect will occur, pro- vided the negative pole be insulated ; but if that pole be brought into contact with the ground, a deposition of iodine will immediately take place beneath the positive pole. Here Philosophical Transactions for 1832, pp. 26, 27. VI.] And of Heated Air for Electricity. 27 the feeble current produced by a single pair of plates, after traversing a long extent of imperfect conductors, is still capable of being easily detected by the decomposition of the solution of iodide of potassium. A battery of 2 pairs of plates charged with common pump water was carefully insulated ; the poles were terminated by platina wires which were introduced into the flame of a spirit lamp, and a decomposing apparatus was interposed in the course of the circuit. The passage, of the current was proved by the deposition of iodine at the positive pole. This experiment was varied by placing the wires in different positions in the flame, but the result was the same, even when they were at the distance of an inch and a half from each other. When very fine wires were employed, and brought only into contact with the flame, the effect was diminished, although it was still distinct ; but by substituting slips of platina foil for the wires, and augmenting the surfaces of contact, the effect was greatly increased. A battery consisting of a single pair of plates of platina and amalgamated zinc charged with dilute sulphuric acid was now employed, and even the current produced by this simple voltaic arrangement was found to be capable of passing through the flame of alcohol, and of decomposing the solution of the iodide of potassium. It is evident from these results that, although the experiment of Paraday which has been described is perfectly accurate, yet it involves some conditions which are not essential, and others which are unfavourable to its success. The conclusions that are derived from it will on this account require to be modified. To ascertain whether other flames are capable of transmitting in a similar manner the electrical current, the same arrange- ment was adopted, and the larger battery charged with water again employed. The flames of coal gas, ether, hydrogen, and charcoal were tried, and the passage of the current through each of them was proved by the occurrence of decomposition. From the quantity of iodine deposited, the current appeared to pass with more facility through the flame of charcoal, and with less facility through the flame of coal gas than it passed through the flame of alcohol. As the flames were in very dif- 28 On the Conducting Power of Certain Flavnes [vi. ferent states, this circumstance may not afford an exact method of determining the relative conducting powers of these flames ; but even with a single pair of plates, so large a quantity of iodine was separated when the current passed through the flame of charcoal, as to leave no doubt that its conducting power is greatly superior to that of the other flames which were examined. The conducting power of the flame of charcoal was further illustrated by obtaining the other effects of electricity from a current passing through it. The poles of the battery of 20 pairs of plates, weakly charged with a mixture of dilute nitric and sulphuric acids, were introduced into the flame of a char- coal fire contained in a small furnace and urged by bellows. The diameter of the flame was about flve inches, and the poles were two inches apart from each other, and one inch and a half from the sides of the furnace. The current that passed between the poles thus situated deflected strongly the needle of a galvanometer, rapidly decomposed water, and communicated a slight shock to the tongue. AU these effects ceased when the flame was not in contact with the poles. As the flame of charcoal evidently holds a high rank in the list of imperfect conductors, it became an object of interest to determine whether it might be substituted for the liquid in the cell of a voltaic arrangement ; whether, in fact, it possesses the properties of an electrolyte. This did not appear to be the case; for on placing slips of platina and copper vertically opposite to each other in a charcoal flame, and connecting them either with a decomposing apparatus or a galvanometer, no evidence could be obtained of the existence of an electrical current, although the copper was rapidly oxidized. It is weU known that a wire of platina suspended above the flame of an Argand lamp will become heated to bright redness, showing that the air around it has reached at least as high a temperature. It was the conducting power of air heated to redness in this manner that I examined, from the facility of performing experiments upon it. Two platina wires were sus- pended from insulating supports above the flame of an Argand gas lamp, and connected with the poles of a battery of 20 pairs of plates on "WoUaston's construction in vigorous action, but no iodine appeared in the decomposing apparatus. The same VI.] And of Heated Air for Electricity. 29 negative result was obtained, whether fine platiua points approximated as closely as possible to each other, or broad slips of platina foil were employed as poles. From this experiment it appears to follow that air simply heated to redness does not conduct the current of a battery of 20 pairs of plates, but the singular facts which are now to be described will not admit of so easy an explanation. The negative pole of a battery of 2 5 pairs of plates charged with pump water was connected by metallic contact with the brass tube of an Argand gas lamp, at a distance from the orifices through which the gas issued, and a coil of platma wire suspended above, but not touching the flame, was attached to the positive pole. When the flame was suf&cienbly powerful to heat the coU to redness, the current passed freely, although the coil was at least one inch distant from the flame. But when the direction of the current was reversed, the negative pole being connected with the heated coU, and the positive pole with the base of the lamp, the passage of the current could no longer be detected. In the former case the solution of iodide of potassium was decomposed in a few seconds ; in the latter case no decomposition occurred, however long the contact was maintained, yet the direction of the current had alone been changed, the other conditions of the experiment remaining the same. Similar effects were obtained, when a piece of well-burned charcoal was substituted for the platina coil in the heated air. Nor were they different when a battery of 83 pairs of plates with double coppers, charged with a solu- tion of common salt, was used. These experiments were fre- quently repeated, and every source of error carefully avoided. This property of conducting and interrupting the same voltaic current when flowing in opposite directions is not peculiar to heated air. It also belongs to flames ; but in con- sequence of their higher conducting power, feeble voltaic com- binations must be employed to discover it. One pole of a battery of a single pair of plates, immersed m dilute sulphuric acid, was connected with the brass tube of an Argand gas lamp, and the other pole was attached to a coil of platina wire which rested upon the top of the flame. "When the latter pole was positive, the current passed ; when negative, 30 On the Oondudimg Power of Certain Flames [yi. it was interrupted. The same battery being employed, one pole was brought into contact with the ignited charcoal of a charcoal fire, and the other with the flame ; the current passed, whether the pole in the flame was positive or negative, but much more readily when it was positive. In the action of the magneto-electrical machine, as it is now constructed, the direction of the current is reversed at every semi-revolution of the soft iron armature; and from this circum- stance the elements of compound bodies that are decomposed by it cannot be obtained in a separate state. By substituting this machine for the galvanic battery, any difference in the transmission of two currents perfectly similar, but tending to move in opposite directions, could be observed without altering the arrangement of the apparatus ; and thus I expected not only to verify in a striking manner the preceding results, but also to obtain from the magnet the effects of a continuous electrical current flowing in one direction. The' electricity of the machine I employed had sufiicient tension to decompose water, to burn metallic leaves, and to cause considerable shocks, but it did not pass sensibly through heated air even when the most favourable arrangement was adopted. By substituting the flame of charcoal for heated air the peculiar property of flame in conducting voltaic electricity was found also to exist in the case of electricity obtained from the magnet. The points by which the sparks are usually procured from the machiae were replaced by a circular disk, and a copper wire was introduced into each of the cups of mercury in which the disks revolved. One of these was connected with a platina wire placed over a charcoal fire at such a distance, that when the fire was urged by bellows it became surrounded by the flame ; the other wire had a platina termination, and rested on a slip of paper moistened with the solution of iodide of potassium. The circuit was completed by inserting one extremity of a wire of platina into the side of the furnace so as to bring it into contact with the charcoal, while the other extremity was placed upon the slip of moistened paper. By this arrangement the currents developed by the rotation of the machine would be obliged to pass downwards through the flame to the charcoal "^i-l And of Heated Air for Electricity. 31 and in the reverse direction ; and, if equally transmitted, iodine would appear beneath each of the wires placed on the bibulous paper, as actually happens when the circuit is completed by a metallic communication. On urging the fire till the flame reached the upper pole, and turning at the same time the machine with moderate rapidity, iodine was deposited at one of the wires which rested on the moistened paper, while there was not the slightest discolouration beneath the other wire. From the wire at which the iodine was deposited, it followed that the current was transmitted when the pole in the flame was positive, and interrupted when the same pole was negative. The direction in which the machine was turned did not produce any difference in the result ; but by reversing the poles in contact with the flame and with the charcoal, iodine was deposited at the opposite wire. Here then was the most distinct proof of a free path being afforded to an electrical current passing in one direction, while a current, differing only in the direction in which it tended to move, was interrupted. When the machine was turned very rapidly, a slight deposi- tion of iodine took place at the wire, where there was none when the machine was turned more slowly ; and at the same time a great quantity of iodine was visible around the other wire. Both poles were now introduced into the charcoal flame and the machine worked rapidly ; iodine was deposited at both wires. When the poles were surrounded to the same extent by the flame, the deposition was apparently similar at each wire ; but when one pole was made just to touch the flame, while the other was brought extensively into contact with it, although iodine still appeared at both wires, it was no longer in the same quantity, showing that the current passed more freely in one direction than in the other. When the pole which only touched the flame was positive, the current passed with more facility than when the same pole was negative. That the current, whose effects disappeared or were dimin- ished, was actually interrupted and not neutralized by an opposite current developed during the combustion, it was easy to prove by connecting wires of platina with the flame and ignited charcoal, and completing the circuit through the solution 32 On the Conducting Power of Certain Flames [vi. of the iodide of potassium; but no decomposition occurred. The free electricity which Pouillet ascertained to be developed during the process of combustion exists in too small quantity to produce any chemical effects, and cannot therefore influence the results of these experiments. It is difficult to discover a satisfactory explanation of this property of flame and heated air. That the same current, when moving in opposite directions, will overcome with a different degree of facility any obstacle in its path appears, so far as our present knowledge of this subject extends, to be a general law of electricity. For illustrations of this priaciple, I may refer to the phenomena presented by the discharge of electricity of high tension across air ; to the interesting experiments of Davy, in which different effects were obtained in the discharge of a powerful b'atbery by reversing the terminations of its poles ; to those of Peltier on the alterations of the temperature of metallic junctions from the passage of feeble voltaic currents; and, finally, to the observations of Becquerel on the facility with which the positive electricity overcomes an obstacle when the two electricities are separated by the agency of heat in a closed metallic circuit. But even assuming the accuracy of this principle, we have still to inquire whether its cause can be discovered in particular cases. The unipolar property of the flame of alcohol, which was discovered by Erman, and which Biot has explained with so much precision and accuracy, furnishes an explanation of some of the preceding results, and may perhaps be applied to them aU. If heated air and the flames of charcoal and alcohol conduct with more facility the positive than the negative elec- tricity, and if the surface of contact of each pole with the heated air or flame be different, it is evident that the current will find the greatest difficulty in passing when it is the negative pole whose contact is least. This conclusion agrees perfectly with one of the experiments which have been described on the flame of charcoal. But it is more difficult to apply the same explanation to the other experiments, unless we assume that the contacts of the flame of coal gas with the metallic aperture from which the gas issues, of the flame of charcoal with the ignited charcoal itself, and of the heated air above an Argand '«'i-] And of Heated Air for Electricity. S3 lamp with the flame, are more intimate and perfect than can be obtained between the flame or heated air and a platina wire introduced directly into them. It does not appear to be im- probable that this is actually the case. Although the general conclusions that follow from these experiments agree with those of Erman, yet when they are minutely compared, an apparent discordance will be observed to exist between them. According to Erman, when the poles of a pile charged with a solution of common salt are introduced into the flame of alcohol, the divergence of the leaves of electro- scopes connected with each pole did not sensibly diminish, the flame in this case apparently insulating the current. That the insulation, however, was not perfect the experiments which have been before described clearly prove ; but I was anxious to establish the same fact from an examination of the state of tension of the poles. To ascertain the tension of the poles, I employed the gold-leaf electroscope of Bohnenberger, which presents peculiar advantages in experiments upon voltaic electricity. The pile usually employed consisted of 100 pairs of plates mounted with pump- water ; they were arranged in two columns and carefully insulated. Erman observed that if one pole of a voltaic pile be intro- duced into an alcohol flame, the other being insulated, and if the flame be touched by a wire in connexion with the ground, the tension of the pole which terminates in the flame will cease, while that of the insulated pole will increase. Here the flame conducts the electricity of the pole with which it is in contact. But when the insulation of the other pole was removed, I found that then the deviation of the leaf of the electroscope attached to the pole which had been introduced into the flame did not apparently diminish when the flame was connected with the ground. This does not arise from the flame insulating under these circumstances the electricity of the pole inserted into it, but from its conducting power being so feeble that it is incapable of removing the tension of that pole as rapidly as it is acquired. If the wire by which the flame is connected with the ground be insulated, and its free extremity placed on the cap of an electroscope, the deviation of the gold-leaf of the instrument will indicate the presence of the same kind of free electricity c 34 On the Conducting Power of Certain Flames [vi. as that of the pole in the flame. On the same principle, a feeble current may actually be conducted by the flame when the opposite poles of a battery are inserted into it, without any sensible diminution of the tension of its poles. By obstructing the passage of the positive electricity, so as to reverse the second part of Erman's experiment, the accuracy of this explanation was established. The surface of contact of the positive pole with the flame was rendered as small as possible by employing a very fine wire of platina, while on the negative side a coil of platina, exposing a far greater extent of surface, was suspended in the flame ; but on introducing a wire in communication with the ground into the flame, the tension of the positive pole ceased, while that of the negative pole increased. Fluid conductors were then interposed on the positive side, but the result was the same. -The following arrangement was next successfully adopted. A platina wire was hermetically sealed into one end of a glass tube about sV of an inch in diameter and 8 inches long, which was filled with common alcohol, and another similar wire was inserted into its open extremity. The positive end of the pile being connected with the first wire, the second wire became the positive pole, so that the column of alcohol formed part of the circuit. When the positive pole was placed in the flame of a ' spirit-lamp, and the flame touched by a wire in connexion with the ground, the deviation of the leaf of the electroscope attached to that pole ceased, while that of the electroscope connected with the negative pole increased. This showed that the positive electricity was freely transmitted through both the flame and the column of alcohol. When both poles were inserted into the flame, their tensions, as indicated by the electroscopes, did not sensibly diminish ; but when the flame was touched by a wire connected with the ground, the deviation of the leaf of the electroscope on the negative side diminished, while that of the electroscope on the positive side increased. The tendency appeared now no longer in favour of the positive but of the negative electricity, which proves that the flame always allowed a small quantity of the latter kind of electricity to pass, and did not perfectly insulate the poles of the voltaic pile. VI.] And of Heated Air for Electricity. So Although not connected with the subject of this paper, I take the opportunity of observing that by employing a similar contrivance on the negative side the tendency of alkaline soap to conduct negative electricity may be apparently reversed ; but for this purpose a column of alcohol -h of an inch in diameter and \ of an inch long is sufficient, while in the case of the flame of alcohol a similar column two or three inches long is required. From the experiments which I have detailed, it is evident that the conducting power of flames for electricity cannot be explained by the diminished elasticity of the gaseous matter which they contain ; nor does the conduction of a feeble current of electricity by the flame of alcohol appear to be a particular case of the discharge of a powerful battery between charcoal poles when separated after contact. The flame of alcohol conducts the electricity of a single pair ' of plates even when the poles are separated by a considerable distance, while with a battery of far greater power no sensible separation of the poles in air can be obtained without altogether interrupting the passage of the current. Electricity of feeble tension passes through flame, because flame is an imperfect conductor ; but electricity of high tension forces a passage across heated air, because the particles of the air are unable to resist its powerful repulsive action. In the one case the presence of the flame is essential to the result, in the other case the air presents only an obstacle to be removed, and the experiment will succeed better in a vacuum. It has only been on the authority of numerous and often repeated experiments that I have thus ventured to dissent from the conclusion of the eminent philosopher, by whose pro- found and varied researches the science of electricity has of late years been so much extended. Nor is the important question of the identity of common and voltaic electricity affected by the results which I have obtained. The similarity of the arch formed by the discharge of an electrical and galvanic battery between charcoal surfaces shows clearly that there is a perfect analogy in the passage of the voltaic and common electric currents across air. Belfast, June 22, 1836. 36 VII.— ON THE THEEMO-ELECTEIC CUEEENT8 DEVELOPED BETWEEN METALS AND FUSED SALTS. London and Edinburgh Philosophical Magazine and Joumod of Science, 1837, L, p. 43.3. The interesting discovery made by Faraday of the high con- ducting power of certain fused salts for voltaic electricity, led me to expect that electrical currents might be produced by bringing them into contact with the metals, analogous to the thermo-electric currents observed by Seebeck. Having easily succeeded in verifying this conjecture, and having observed that the currents thus produced exhibited some remarkable properties, I submitted them to a careful examination, the result of which forms the subject of the present paper. To detect the presence of the electrical current, a very delicate galvanometer, constructed for me by M. Gourjon of Paris, was employed, in which the copper wire made nearly 3,000 revolutions round the lower needle, and the system of needles was rendered as perfectly astatic as possible. A gal- vanometer having 20 or 30 coils, with astatic needles, will be found, however, sufficiently sensible to give decided indications of the passage of the principal currents which I shall have occasion to describe. Having taken two similar wires of platina (such as are used in experiments with the blow-pipe), and connected them with the extremities of the copper wire of the galvanometer that has just been described, I fused a small globule of borax in the flame of a spirit-lamp, on the free extremity of one of the platina wires, and introducing the free extremity of the other wire into the flame, I brought the latter, raised to a higher temperature than the former, into contact with the fused globule ; the needle of the instrument was instantly driven with great violence to the limit of the scale. The direction of the current, as indicated by the deflection of the needle, was ■^"•] On the Thermo- Electric Currents, etc. 37 from the hotter platina wire through the fused salt to the colder wire. A permanent electrical current in the same direction was obtained, by simply fusing the globule between the two wires, and applying the flame of the lamp in such a manner that, at the points of contact with the fused salt, the wires were at different temperatures. To discover whether the current had sufficient intensity to pass through acidulated water, a column of water (to which a few drops of sulphuric acid had been added), whose length was about half an inch, was interposed in the course of the circuit, the connecting poles in the water being formed of platina wires. On fusing the globule as before, the needle of the gal- vanometer was still deflected through an arc of 80° or 90°, but with less violence than when a complete metallic circuit was employed. When carbonate of soda was substituted for borax in these experiments, similar but more powerful currents were obtained. My first attempts to obtain chemical decompositions by means of these currents were unsuccessful when the common forms of apparatus were used ; but by employing poles exposing unequal surfaces, this object was finally attained.^ A piece of bibulous paper, exposing on each side a surface of one fourth of a square inch, was moistened with a solution of the iodide of potassium, and laid on a platina plate, which was in metallic connection ^ The influence of the surface of the poles, in rendering perceptible the separation of the elements of an electrolyte, is very remarkable. Faraday has observed that not a bubble of gas will appear on the surface of a pair of platina plates, immersed in dilute sulphuric acid, when made the poles of a voltaic combination, formed by a single pair of platina and zinc plates charged with the same dilute acid ; and hence that distinguished philosopher has inferred, that the tension of such a current is too low to effect the decomposition of water. On repeating and varying the conditions of this experiment, I found that if two fine wires were substituted for the platina plates the same negative result was obtained ; but that if a platina plate exposing an extensive surface to the liquid was used as one pole, and a fine wire of the same metal as the other, then a minute stream of bubbles of gas arose from the wire, which after continuing for some time, finally ceased to appear. An additional quantity of gas was, however, easily procured, either by increasing the surface of the broad pole, or by removing it and heating it to redness, or by reversing the direction of the current. The following appears to be a satisfactory explana- tion of these results. When the poles exposed on both sides equal surfaces, the gases were dissolved in the nascent state by the surrounding liquid ; but when the polar surfaces were unequal, the solution of the gas being greatly facilitated by the broader pole, the element of the water separated there was dissolved, while the other element was disengaged, in the gaseous state, at the 38 On the Thermo-Electric Currents Developed between [vii. with one of the platina wires used in the previous experiments. The extremity of the other platina wire in contact with the globule, was applied to the surface of the bibulous paper, and the flame of the lamp was so directed, that the latter was the colder of the wires between which the globule of borax or car- bonate of soda was fused. The platina plate in this arrange- ment therefore constituted the negative pole, and the extremity of the wire applied to the bibulous paper, the positive pole. Accordingly, when the circuit was completed, an abundant de- position of iodine occurred beneath the platina wire. When a similar wire of platina was substituted for the plate on the negative side, the effect was either none or scarcely perceptible. A compound arrangement was next formed by placing a series of platina wires on supports, in the same horizontal hne, and fusing between their adjacent extremities small globules of borax. The globules and wires were exactly similar to those that are used in blowpipe experiments. A spirit-lamp was applied to each globule, so as to heat unequally the wires in contact with it ; and the corresponding extremity of each wire being preserved at the higher temperature, the current was transmitted in the same direction through the whole series. By connecting the extremities of four cells of this arrangement with an apparatus for decomposing water, in which the opposite poles consisted of a thick platina wire and a guarded platina point (both being immersed in dilute sulphuric acid), very minute bubbles of gas soon appeared at the guarded point, and slowly separating from it ascended through the liquid. They wire which served as tlie opposite pole. Indeed, Becquerel had already cor- rectly inferred, from the circumstance of the plates acquiring polarity, that the water in this experiment of Faraday must have been decomposed. It is from the obstacle presented to the passage of the current by the acquired polarity of the platina plate, that the gas soon ceases to be formed in greater abundance than it can be dissolveil by the water ; and its reappearance under the circum- stances stated before, is an obvious consequence from the well-known properties of polarized plates. By employing a similar artifice, a solution of sulphate of soda may be decomposed by means of a single couple of platina and zinc plates, charged with a solution of chloride of sodium, and the presence of the free acid or alliali rendered evident by its action on litmus or turmeric paper. In order therefore to discover, in case of difficulty, whether an electrical current is capable of decomposing water or other substances, it is necessary to employ poles having very unequal surfaces ; and this will be effected in the most per- fect manner by opposing a thick wire or plate of platina to one of Wollaston's guarded points. VI1-] i/etoZs and Fused Salts. 39 were obtained in whichever direction the current was passed, but rather more abundantly when the point was negative and the wire positive. With only two cells, similar bubbles formed in a visible manner on the guarded point, but in such exceed- ingly small quantity that they did not separate from it. "With an arrangement containing 20 cells, a doubtful sensation was communicated to the tongue when the poles were applied to it ; but no spark was visible, although the current was passed through a helix of copper wire surrounding a bar of iron, and the contact was broken with great rapidity by means of a revolving apparatus. It is necessary to observe, however, that the lamps were unprotected, and that it was impossible to render the flames of such a number of spirit-lamps burning near each other, so steady as to heat at the same moment, in the required manner, all the globules and wires. With an enlarged and more perfect form of apparatus, there can be little doubt that a spark might be obtained. The extremities of the platina wires which were introduced into the globules of borax, after having been employed in these experiments, did not exhibit any appearanceof chemical action; their lustre was untarnished, and their edges presented a sharp and well-defined outline, without being in the least degree rounded away. To render still more certain the absence of any chemical action, a very fine wire of platina was used as the hottest wire, in contact with the fused borax, and the circuit being completed by a metallic wire, a continuous current was maintained for several hours ; but there was no apparent change either in the wires or the borax. With carbonate of soda instead of borax, the result was the same. When it is remembered that this current, if transmitted through a solution of the iodide of potassium, (in which case the greater part of the current is even interrupted,) would have produced in a few seconds a very perceptible deposition of iodine, it is impossible to imagine that the same current could continue, for a long space of time, to be produced from chemical action in one of the platina wires without any sensible alteration of the metallic surface. Besides, it is well known that under ordinary circum- stances there is no chemical action exercised by platina upon fused borax or carbonate of soda. 40 On the Thermo-Electric Currents Developed between [vii. It is certainly very iateresting to see powerful chemical affinities tlius overcome by simply bringing two metallic wires, at different temperatures, into contact with a fused salt, between which and the wires no [chemical] action takes place. The direction of the current is not influenced by the quantity of surface in contact with the wires, but depends altogether on the difference of temperature, as was ascertained by careful experiments. Similar results were obtained when other fused salts were substituted for borax, such as carbonate of potash, chloride and iodide of potassium, sulphate of soda, chloride of strontium, etc. Even with boracic acid, which Faraday has observed to be a very imperfect conductor of voltaic electricity, I succeeded in deflecting the needle of the galvanometer through an arc of 40°, the circuit being closed by metallic wires. The direction of the current was the same as with borax. To compare the intensity of these currents with those pro- duced by chemical action, the galvanometer and a hydro- electric couple were both interposed in the course of the circuit, and the connections were so adjusted, that the currents developed by the fused salt and in the voltaic cell should be in opposition to each other. In this case the deflection of the needle would indicate the current of superior intensity. On comparing these currents with various hydro-electric combin- ations, they appeared, when fuUy developed, to have a some- what superior tension to the currents produced by a couple of platina and silver plates immersed, in dilute sulphuric or nitric acid. If the nitric acid was so strong as to dissolve rapidly the silver, then the voltaic current became superior. The effect of substituting other metals for one or both of the platina wires still remained to be examined ; but here con- siderable difficulties often arose, from the fusibility and tendency to oxidation of many of the metals. When the platina wires were replaced by wires of palladium, currents in every respect similar were obtained. When platina was opposed to palladium, gold or silver, fused soda or borax being interposed, the current was always from the platina through the fused salt to the other metal, provided the platina was at a higher temperature. When the palladium VII-] Metals and Fused Salts. 41 was hotter than the platina, the current was reversed, or from the palladium to the platina. It was difficult to expose the gold or silver wire to a higher temperature than the platina without fusing it, when a globule of soda or borax was used ; but by substituting a more fusible globule, formed of a mixture of the carbonates of soda and potash, the current was readily obtained from the silver or gold to the platina, so long as the former metals were maintained at a higher temperature. These experiments prove that the position of the metals in the thermo-electric scale does not exercise any influence upon the direction of the current, which is altogether determined by the relative temperatures of the wires. When platina at a higher temperature was opposed to copper, fused borax or soda being interposed, the current in very numerous trials (with one or two rare exceptions) was from the platina through the salt to the copper. It was only when from the action of the flame a very rapid formation and solution of the oxide of copper occurred, that the reverse current was obtained ; but when the chemical action was not considerable the current was always from the platina. A current was also obtained in the same direction with boracic acid instead of borax. These results are the more interesting, as they prove most distinctly that chemical action cannot be the source of these currents, since in this example the platina would require to have been the metal attacked. On substituting iron for copper a violent chemical action took place, the borax or soda became dark and opake from dis- solving the oxide of iron, and the direction of the current was in general from the iron to the platina, even when the latter was at a much higher temperature than the former. However, by fusing a small globule of borax or soda on an iron wire in the reducing part of the flame, and bringing a hot platina wire into contact with it, I obtained a current from the platina to the iron ; but the experiment is difiicult to perform and will rarely succeed. When platina was opposed to the following metals, viz., antimony, lead, zinc, and tin, it was with some difficulty that even a mixture of the alkaline carbonates was maintained in a state of complete fusion, the platina being at a red heat. 42 On the Tliet'm.o-Electric Currents Developed between [vn. while the other metal was itself almost at the point of melting : the current was in every ease from the platina through the fused salt to the other metal. In these cases it was evidently impossible to reverse the temperature of the metals. When the interposed globule consisted of chlorate of potash, the current was always from the oxidable metal to the platina, but here the chemical action was very considerable. In the case of the noble metals, the direction of the current was the same with the chlorate of potash as with the other fused salts. It appears from the preceding experiments, that an electrical current is always produced when a fused salt capable of con- ducting electricity is brought into contact with two metals at different temperatures ; and that when chemical action does not interfere, the direction of the current is not influenced by the nature of the salt or metal, being always from the hotter metal through the fused salt to the colder metal. This current has an intensity inferior to that of the hydro-electric current developed by platina and zinc plates, but greatly superior to that of the common thermo-electric currents, and is capable of decomposing with great facility water and other electrolytes. The source of this current may probably be simply referred to the contact between the heated metal and fused salt, which appears to be capable of generating an electri- cal current, more intense as the temperature of the point of contact is more elevated. According to this view, opposite currents are developed at the point of contact of each metal with the fused salts ; but that which is produced at the point whose temperature is higher, having a superior intensity, overcomes the other, and its effects alone are exhibited ; just as happens when two similar metallic junctions in a closed metallic circuit are exposed to unequal temperatures. The superior intensity of this current to those obtained from the metals alone, depends probably on the greater obstacle pre- sented to the reunion of the two electricities, at the junctions where they are separated from the inferior conducting power of the fused salt. Hitherto I have only described the currents produced when the interposed salt is in a state of perfect fusion, but before the salt becomes actually fused, electrical currents are developed. ^"■] Metals and Fused Salts. 43 whose direction no longer follows the simple law, that has been before enunciated, but varies in the most singular and perplex- ing manner. After a long and tedious investigation, I have been completely baffled in my attempts to discover the essen- tial conditions upon which the directions of these currents depend, and I shall therefore describe at present only one or two experiments which will show the complicated nature of the inquiry, and may, perhaps, draw the attention of others to this curious part of electrical science. In the investigation of these currents a very sensible galvanometer must be employed. A small platina spoon was partly filled with fused carbonate of soda, and the end of a thick wire of the same metal was introduced into the fused salt, metallic contact being carefuUy avoided. When the salt had cooled, the wire and spoon were connected with the galvanometer. On applying a very gentle heat to the bottom of the spoon, by means of a small spirit- flame placed at a considerable distance, a current was obtained from the spoon to the wire, or from the hot. metal to the cold ; this current was very feeble, and could rarely be maintained beyond a few minutes. By increasing the temperature of the lower part of the spoon till the salt in contact with it entered into fusion, while the portion surrounding the cold wire was still in a solid state, a powerful current was obtained from the wire to the cup, or from the cold metal to the hot. When the temperature of the cup was still further raised so as to fuse the whole of the salt, the current was of course again reversed, being from the hot metal to the cold. It was interesting to observe the violent manner in which from this cause the needle of the instrument started from one extremity of its scale to the opposite, on the slightest movement of the flame. To the class of partially fused salts belongs heated glass, which accordingly presented similar changes in the direction of the current. Thus when a platina wire was covered with a very thin coating of glass, and another wire at a higher temperature brought into contact with the glass, the current was from the cold metal through the glass to the hot. If a thicker piece of glass was interposed, the first current was from the hot wire to the cold, but on raising the temperature a current was obtained in the opposite direction. M. Becquerel had already observed 44 On the Thermo- Electric Currents, etc. [vii. by means of a sensible gold leaf electroscope that when platina wires at unequal temperatures are separated by means of heated glass, they exhibit signs of free electricity, one of them being connected with the ground and the other with the electro- scope ; but the general conclusion which he attempts to deduce from the result of this single experiment is certainly inaccurate, as it is founded on the assumption that the colder wire will give always signs of positive electricity, which we have seen is only true when the glass is thick and at a certain temperature. The conditions, however, here stated are not the only circum- stances which influence the direction of the electrical currents with heated glass, but as my experiments do not lead to any definite result, I refrain from describing them. These currents may likewise be obtained by interposing certain minerals between unequally heated wires ; thus mica placed between platina wires and heated very strongly caused a deflection in the galvanometer needle of 7°, and the mineral called stilbite of 25° ; the current in both cases was from the hot platina to the cold. Belfast, April 11, 1837. 45 VIII.— ON SOME SINGULAE MODIFICATIONS OF THE ORDINAEY ACTION OF NITEIC ACID ON CERTAIN METALS. Read before the Liverpool Meeting of the British Association, 1837. Published in the Philosophical Magazine, 1837, II., p. 554. Bismuth in nitric acid of specific gravity 1-4, was rapidly acted upon, but this action immediately ceased when the bar was touched by platinum. On removing the platinum from the liquor, the bismuth will sometimes begin again to dissolve ; at other times, its surface wiU become covered with a black crust, which is soon removed by the acid ; but the metal, though now exhibiting a beautifully polished surface, is no longer acted upon by the acid, or, at least, is dissolved only with extreme slowness. Thus, a slip of metal, which, in its ordinary state will require only a few seconds to complete its solution, will, when thus slightly modified, resist for many hours the action of the same acid. Copper and tin present similar phenomena, but zinc, when treated in the same way, has its oxidation and solution not arrested, but merely retarded. Arsenic was found to present a singular anomaly when heated in nitric acid so as to give rise to effervescence : the contact of the platinum in the usual way did not produce any effect ; whereas, when an acidulous solution of silver is used, platinum exercised its usual influence. In the case of six metals, platinum checks the action of nitric acid, and three of them appear to be brought into a permanently peculiar state, opposed to chemical action. Platinum always separates any film of oxide as its initial function ; but after its separation, it exercises a polarizing action, for example, it brings the other metal into a peculiar state, which enables it to resist chemical action. 46 On the Action of J^itric Acid on Certain Metals, [vm. On the conclusion of this paper, the President [Mr. Faraday] drew the attention of the Section to the analogy between the facts detailed by Dr. Andrews, and the preserva- tion of iron by brass, as instanced in the communication of Mr. Hartley. In both cases, according to the known laws of electro-chemical action, effects, the very opposite of what are observed, should present themselves. The bismuth, copper, etc., should oxidize quickest when in contact with the platinum ; and if, as would seem demonstrated by Mr. Hartley, brass protects wrought and cast-iron, the brass itself should be acted upon with increased rapidity. The solution of these anomalies, he conceived to be quite within the range of science in its present state, and he urged upon the members of the Section the necessity of studying the phfenomena in question, as their explication would constitute a very valuable addition to the existing state of our electrical knowledge. 47 IX.— ON THE INFLUENCE OF VOLTAIC COMBINATION IN CHEMICAL ACTION. From the Report of the Newcastle Meeting of the British Association, 1838. In dilute sulphuric acid, composed of one atom of the dry acid and eight atoms of water, the solution of distilled zinc is permanently accelerated, by connecting it with a plate of platina immersed in the same liquid, so as to form a voltaic combination. In acid containing seven atoms of water the ordinary action is at first increased, and afterwards rather diminished, by contact with platina. But when zinc is heated in acid containing less than this quantity of water, the connexion with platina transfers the evolution of gas from the surface of the positive to that of the negative metal, and at the same time diminishes its quantity, and consequently retards the rate of solution of the zinc. The formation of a galvanic circle exerts, therefore, a reverse effect on the solution of zinc in sulphuric acid containing more or less than seven atoms of water. The principal circumstances which influence these results are the adhesion of the hydrogen gas to the surface of the zinc ; the formation of sulphate of zinc, which is greatly facilitated by the presence of seven atoms of water in union with each atom of acid (that being the number of atoms of water of crystalliza- tion contained in it) ; and, lastly, the proper action of the voltaic circle which tends to diminish the solution of the zinc. In dilute acid, the first circumstance retards the action on the zinc alone, and the second facilitates its solution ; then the platina surface enables the hydrogen to escape. But in the stronger acid the voltaic association impedes the solution of the zinc, partly from the evolution of gas being transferred to the platina, and thus the saturated liquid being allowed to accumu- late around the zinc plate, and partly from the real effect of the galvanic combination. That the proper tendency of a voltaic circle is to diminish the chemical action of the solution 48 Voltaic Combination in Cheviical Action. [ix. on the electro-positive metal, the author endeavoured to show, from the consideration, that in ordinary solution the electri- cities thus developed have only an indefinitely small portion of liquid to traverse, while in voltaic solution their reunion can only be effected by passing across a column of variable extent, and composed of an imperfectly conducting substance. And, as the action is greater the nearer the plates are to each other, that action ought to attain a maximum when the distance between the plates vanishes, provided this condition could actually be realized. 49 X.— ON THE ACTION OF NITRIC ACID UPON BISMUTH AND OTHER METALS. From the Pkilosophical Magazine, 1838, I., p. 305. To THE Editors of the " Philosophical Magazine and Journal." Gentlemen, — I am happy to find that the observations which I communicated to the British Association, on some singular modifications of the ordinary action of nitric acid upon certain metals, have attracted the attention of so distinguished a philosopher as M. Schoenbein, whose opinions upon this subject must be considered to be of peculiar value. As, however, the results of some of my experiments are at variance with those which M. Schoenbein has obtained, and would tend perhaps to modify his conclusions, and as the published notice of my paper is very brief and imperfect, I shall now endeavour to give as complete an account of this subject as my in- vestigations will enable me to do. In the following extract from the manuscript read at Liverpool will be found a complete description of the phee- nomena to which M. Schoenbein alludes, and which he supposes that I may not perhaps have remarked. "Having introduced a small fragment of bismuth into a large excess of nitric acid of sp. gr. 1'4, and afterwards brought a plate of platina, exposing an extensive surface to the liquid, into contact with the bismuth, the solution of the latter almost entirely ceased, while at the same time its surface assumed a peculiarly brilliant lustre. On removing the platina, the bismuth sometimes began to dissolve in its ordinary manner ; at other times, a dark film appeared upon its surface which soon afterwards dissolved away and the metallic surface again became visible. But the action of the acid on the bismuth was now no longer perceptible, and, although not altogether arrested, . yet it had become so feeble that a piece of bismuth weighing scarcely half a grain was not completely dissolved by D 50 On the Action of Nitric Acid upon [x. a large excess of acid at the end of two days. Yet during this period the acid was removed, and replaced by a fresh portion. Indeed, the more frequently the solvent was changed, the more slowly did the action proceed, — a result apparently paradoxical, but arising from the circumstance, that the metal in this peculiar state is less able to resist the action of an acid having a metallic salt in solution than that of a pure acid. "If the bismuth in this pecuUar state was touched by a platina wire, the only effect apparently produced was that of increasing, perhaps, the brilliancy of its lustre ; but when the contact with the platina was broken, the surface of the bismuth became at first covered with a dark film, then recovered its metallic aspect as before ; and this series of phsenomena always occurred when connection with the platina was made and broken. " Copper gave very similar results to bismuth. The contact of platina checked its solution in the same acid and maintained its surface bright. When the platina was removed its surface became covered with a black coat of oxide, which was afterwards very slowly dissolved by the acid, leaving the copper in the peculiar or slowly soluble state. But if the copper, while covered with the oxide, was raised from the liquid, the acid adhering to its surface instantly dissolved away the crust ; the copper was now, however, left in its ordinary state." It is obvious that the bismuth and copper, in the preceding experiments, are brought into the peculiar or slowly soluble state, -by being made the positive surfaces in a simple voltaic arrangement. I was therefore much surprised to observe that M. Schoenbein should have failed in producing the same effect by making the bismuth act as the positive pole of a pile, while it is well known that iron can be rendered inactive in both ways ; and that, from this difference in the bearing of the two metals, he should have concluded, that the peculiar condition of iron is not brought about by the same cause which occasions the inactivity of bismuth. The following experiments wiU, however, show that in this respect there is the most perfect similarity in the behaviour of iron and the other metals. When a small bar of bismuth, connected, as the positive pole. X.] Bismuth and other Metals. 51 with a battery composed of two pairs of amalgamated zinc and platina plates, was introduced into nitric acid of sp. gr. I'i at the temperature of 75° Fahr., its solution was instantly checked, and on breaking contact with the battery, the bismuth was found to be in the peculiar state. The acid in this experiment was contained in a platina capsule, which was connected with the other end of the battery and formed the negative pole. But on substituting for this feeble arrangement a battery of 20 pairs of double plates in moderate action, the bismuth con- tinued to dissolve at a sensible rate when the circuit was completed (although much more slowly and in a different manner than when alone), and the peculiar state was afterwards rarely developed. So far are these experiments from establishing a distinction in the manner of development of the peculiar states of iron and bismuth, that they will appear from what follows to show more clearly the identity of the two cases. The inactive state of iron is more readily produced by simply bringing it into contact with a platina surface than by making it the positive pole of a couronne des tasses: for in .the former case, the action of the acid may be arrested after it has already commenced,^ while in the latter case, it is essential that the iron should be connected with the battery before it is introduced into the acid.^ If a more powerful battery is employed, the iron acting as positive pole has been shown by Dr. Faraday to be actually oxidized and dissolved while the .Current is passing ; ^ but as M. Schoenbein attributes the trace of iron which he has himself sometimes discovered in the liquid, to the action of the acid vapours upon the part of the iron above the acid, and the conduction of the nitrate thus formed down into the acid by capillary attraction,* I thought it necessary to repeat the experiment in such a manner as to obviate this objection. This was easily effected by attaching a small piece of iron wire to a fine wire of platina, and immersing the former completely beneath the surface of the liquid, or by coating an iron wire with glass and exposing simply a section ^Faraday, Phil. Mag., vol. 9, p. 58. ^ Sclicenbein, ibid., p. 55. ^ Ibid., pp. 62, 63. '' See Phil. Mag., vol. 10, p. 173. 52 On the Action of Nitric Acid upon [x. of the wire to the acid. When the iron thus adjusted was made the positive pole of a battery of 20 pairs of plates in moderate action, it began to dissolve at a very perceptible rate (oxygen gas being, however, at the same time, evolved from its surface), and a black crust of insoluble oxide was usually formed, when the connection with the battery was broken. This result was obtained with different specimens of nitric acid from the sp. gr. of 1'47 to that of 1"5, yet such acids have no action whatever upon iron alone ; so that the passage of an electrical current of sufficient intensity is capable of becoming the cause of the solution of iron when acting as the positive pole. The manner of closing the circuit produced no difference in the result. It appears therefore from these observations that the passage of an electrical current of a certain intensity renders iron and bismuth inactive in acids capable of dissolving them, while the passage of a current of a higher intensity causes their solution in acids which otherwise have scarcely any action upon them. It is true that the required intensities of the currents for these objects are different for each metal, but this necessarily follows from the difference in their chemical relations to nitric acid. But although the peculiar state of the two metals thus appears to be developed by the same cause, it must be carefuUy observed, that while the chemical action of the acid upon iron is entirely destroyed, its action upon bismuth, and all the other metals which I have examined, except perhaps tin, is only greatly retarded. This distinction, important as it is, does not appear to me to be sufficient to prevent us from referring aU the phtenomena to the same general principle. As to the circumstance of the peroxide of lead not protecting bismuth while it protects iron, I have only to observe, that this substance has so little tendency to attach itself to the surface of bismuth, that I have never been able to succeed in coating properly that metal with it ; and when I endeavoured to employ iron coated with the peroxide to protect bismuth in nitric acid of sp. gr. 1-4, the peroxide generally separated leaving the surface of the iron exposed. Concentrated nitric acid immediately develops the peculiar state of bismuth, as well as of iron, and when a small portion X.] Bismuth and other Metals. 58 of bismuth is left in nitric acid of sp. gr. 1"5, its solution will occupy some weeks, just as happens when, in the peculiar state, it is kept in nitric acid of sp. gr, 1'4. But even in the same acid and at the same temperature, it is remarkable what apparently trivial circumstances are capable of determining these two states in bismuth, and the facts which I have now to describe are certainly among the most singular to which this inquiry has led. If a small fragment of bismuth (half a grain, for example,) is introduced into nitric acid of the sp. gr. 1'4, at the temperature of 40° or 50° Fahr., and allowed to remain at rest, it will usually dissolve in a few seconds, with the disengagement of orange fumes ; but sometimes, after the solution has proceeded to a certain extent, it will suddenly cease, and the bismuth will be found in the peculiar state. This latter effect will be more frequently obtained by agitating the liquid, so as to bring a fresh surface of acid into contact with the bismuth. But the peculiar state is never produced in this way till the original surface of the bismuth has been dissolved away, and a fresh surface exposed to the acid. It is easy, however, to procure a surface of bismuth, which will always be inactive, even when first introduced into acid of the above strength, not only at the temperature of 50° Fahr., but even at that of 80°, at which degree unattached fragments of bismuth always dissolve with great rapidity. For this purpose all that is necessary is to fill a glass tube about tV of an inch in diameter with fused bismuth and then to file it across, so as to expose a circular section of bismuth to the acid. The surface thus obtained was always found to be in the peculiar state on its first immersion in the acid. The greatest care was taken to render the surfaces of the unattached fragments perfectly similar by filing, and to bring all to the same temperature. Are we to suppose that in this case the glass acts the part of an electro-negative metal, and induces the peculiar state by developing an electrical current ? This supposition appears extremely improbable, and some experiments which I made in reference to this view were unfavourable to it. The influence of the glass is most probably mechanical, as the plain surface of the bismuth alone exposed to the acid opposes its solution. 54 On the Action of Nitric Acid wpon [x. and hhus develops the peculiar state. It must be acknowledged, ab the same time, that there is" some difficulty in supposing that so slight a mechanical difference should have the effect of arresting a powerful chemical action. The phsenomena presented by the other metals agree in their general features with those already described, although they differ slightly in some of the details. The peculiar state of tin closely resembles that of iron. Mtric acid of sp. gr. 1'5 exerts no action whatever upon tin ; at least I have preserved that metal in acid of this strength for several weeks, and its surface still remains untarnished.^ If a pencil of tin is dipped into nitric acid, sp. gr. 1"47, at 50" Fahr., it is immediately attacked, and its surface becomes densely coated with peroxide ; but if the acid is placed in a platina vessel, with which the tin has been connected before immersion, the acid will no longer act upon it, and on breaking contact the tin will be found to be inactive. This metal may also be rendered inactive, by being made the positive pole of a battery of a certain strength. It resists better the solvent action of a current of higher intensity, and opposes a greater obstacle to its passage than iron or bismuth. To the facts before stated in reference to copper, it may now be added that nitric acid of sp. gr. 1'5 develops in this metal also the peculiar state. In this state it is slowly soluble. When alone in acid of sp. gr. 1"47, there is at iirst violent action, then the copper acquires the peculiar state : when connected with platina it acquires at once that state; and so long as the contact with the platina is maintained, the copper retains a bright lustre ; but when it is broken, the surface of the metal becomes covered with a black film, which can only be partially dissolved by the acid or by renewing the connection with the platina. A permanently peculiar state cannot be produced in zinc ; but by connecting it with platina, or making it the positive pole of a pile, its solution may be greatly retarded, so long as the current continues to pass. ^InDumaa's Traiti[\o\. 1) it is stated that nitric acid of sp. gr. 1'5 acts violently upon tin, which is insoluble in acid of sp. gr. 1 -48. This is certainly a mistake, provided pure nitric acid is employed. X-] Bismuth and other Metals. 55 In taking a general view of this subject, it is necessary to distinguish the modification which the action of the acid undergoes, while the metal forms part of a voltaic arrangement, from the permanent modification which continues after its con- nection with the battery has been destroyed. Having extended my inquiries to other oxyacids, I find that the chemical action of those acids in a concentrated state upon the metals is diminished by voltaic associations. The effect of galvanic combinations upon chemical action may be thus generally stated. The contact of an electro-negative metal increases the ordinary action of an oxyacid upon an electro-positive metal, if the acid is so dilute that the latter lecomes oxidized from the decomposition of the water, and retards or arrests that action, if the acid is so concentrated that the metal is oxidized from the decomposition of the acid itself. ^ Thus, in the case of the sulphuric acid, if hydrogen gas is disengaged at the surface of the platina, in a voltaic combina- tion of zinc and platina, the ordinary solution of the zinc will be greatly accelerated by contact with the platina ; but if sulphurous acid is set free at the platina surface, then the solu- tion of the zinc will be, on the contrary, greatly retarded. The experiments by which the latter part of this law has been established are contained in a paper which will shortly be pre- sented to the Eoyal Irish Academy. In reference to the peculiar state of the metal in nitric acid, after it is separated from the voltaic influence, it may be useful to remark, that the more completely it is developed, and the more perfectly inactive the metal becomes, the brighter is the surface which it presents to the liquid; and as Faraday has shown that the remarkable properties of a platina plate, when polarized by acting as the positive pole of a battery, depend upon the absolute cleanness and purity of its surface, is it not probable that, in hke manner, the inactive states of these metals depend upon the pure metallic ^To the first part of this law an . exception, which is perhaps rather apparent than real, occurs in the action of some dilute acids upon iron under certain circumstances ; to the second part, which, I believe has not been before observed, I have yet met with no exception. 56 On the Action of Nitric Acid, etc. [x. surfaces which the voltaic action develops hy dissohdng away every trace of oxide, upon which surface, when thus more perfectly freed from all impurity than can he effected hy mechanical means, the acid has either no action or a greatly diminished action ? This is merely however stated as a simple conjecture, and I can offer no explanation of most of the particular facts which have heen described. — I am, Gentlemen, yours, etc., Thomas Andrews. Beuast, February 6, 1838. 57 XI.— ON THE PEOPEETIES OF VOLTAIC CIRCLES IN WHICH CONCENTRATED SULPHURIC ACID IS THE LIQUID CONDUCTOR. From the Tramactions of the JRoycU Irish Academy, vol. 18, p. 149, 1838. The remarkable discovery of Professor Schoenbein of Bale respecting the modification which the chemical action of nitric acid upon iron undergoes when they are brought into contact under certain voltaic conditions, has led me to examine the general phenomena which are exhibited by voltaic circles whose liquid conductor consists of a concentrated acid. In a paper read at the last meeting of the British Association, I showed that the solution of the oxidable metals in strong nitric acid is greatly retarded when they are voltaically associated with such metals as platina, upon which that acid has no action ; a result which is evidently the reverse of the ordinary effect of the passage of an electrical current. The object of the present communication is to extend the same principle to the action of concentrated sulphuric acid under similar conditions, and to investigate some of the circum- stances which influence the development of electrical currents in this way. When a piece of zinc is introduced into strong sulphuric acid (sp. gr. 1-847) at common temperatures, its surface becomes covered with a mass of gaseous bubbles, so fine that they might be almost mistaken for a white precipitate, which very slowly separate from the zinc, but by agitation, or the application of a gentle heat, may be easily removed. The gas thus disengaged is hydrogen in a state of perfect purity. On applying heat to the acid there is scarcely any further extrica- tion of gas, till the temperature has reached nearly 100° cent., when a very fine stream of gas begins to arise from the surface of the zinc. As the heat is raised, the quantity of gas becomes more considerable ; from 120° to 150° cent, there is a rapid 58 On the Properties of Voltaic Circles. [xi. effervescence, and at still higher temperatures vast quantities of gas, mixed with the vapours of sulphur, are disengaged. On examination, this gas was found to consist of a mixture of sulphurous acid and hydrogen gas. "When an excess of zinc was employed the hydrogen in the beginning of the process amounted to 20 per cent, of the whole, but towards the end it increased to nearly 40 per cent. A similar portion of zinc being connected with a platina wire, and the free extremities of each being introduced into the same acid, so as to form a voltaic circle, the fine bubbles before described now appeared chiefly on the surface of the platina. When removed they did not form again, unless a fresh surface of zinc was exposed. The gas thus obtained was found to be pure hydrogen. The acid was then heated, but there was no extrication of gas from the surface of either metal till the tem- perature reached 150° cent., and then only a few minute streams arose from the platina wire. At 190° the evolution of gas from the platina wire did not exceed that from the uncon- nected zinc at 140° or 150=. From 210° to 240° there was rapid effervescence. During the course of the experiment no gas appeared at the surface of the zinc, unless the temperature was very high, so that torrents of gas were disengaged from the platina, when by a close inspection some very fine streams might be perceived forcing a passage from certain points of the zinc surface. The gas extricated from the surface of the platina differed from that obtained when the zinc alone was dissolved, — in the small quantity of hydrogen which it contained, and in that quantity diminishing instead of increasing as the solution proceeded. In fact the hydrogen was found to amount to 9 per cent, in the commencement of the experiment, and towards the end it diminished to only 1 per cent., the rest of the gas being sulphurous acid. A quantity of sulphur was also separated, both when the zinc was alone and connected with the platina, which sometimes appeared in crystals in the acid, at other times became diffused through the mass of the liquid, so as to render it nearly opake, while at high temperatures it was disengaged in the state of vapour. Gold and palladium act in the same manner as platina. There was no apparent difference in these results, whether XI.] On the Properties of Voltaic Circles. 59 pure zinc, or the sheet zinc of commerce was used, and from the uniform surface which it exposes, the latter was employed in all the following experiments. To ascertain with precision the retarding influence of the platina upon the solution of zinc, similar portions of connected and unconnected zinc were exposed to the action of sulphuric acid of sp. gr. 1-845 at the same time and in the same vessel. The platina was placed opposite to both surfaces of the zinc, and at the distance of one-fourth of an inch ; it exposed to the liquid a surface which was about one-third of that of the zinc. The connexion was made above the liquid. The following table contains the results of a series of experi- ments made at different temperatures, in which the second column gives the ratio of the quantities of zinc dissolved from equal weights of that metal, when alone and when united to platina, assuming as unit the quantity dissolved in the latter case. No. of Experi- ment. Eatio of Zinc Dissolved. Temperature. Connected. Alone. 1 1 : 2-065 168° to 170° cent. 2 1 : 2-255 203° to 206° „ 3 1 : 2-347 221° to 233° ,, 4 1 : 3-000 238° to 240° „ ^ 1 • 3-208 242° 6 1 : 1-478 250° to 270° „ 7 1 : 1-335 265° „ Although the zinc was removed from the acid, and its loss ascertained, before its surface had undergone much alteration, yet as the connected zinc diminished less during the process of solution than the other, the surfaces became no longer precisely similar; and hence the differences exhibited by the table are less than they ought to be. From an inspection of the table, it appears that the greatest difference in the quantity of zinc dissolved occurs at the temperature of 242°, where the action of the acid is reduced to less than one third by the contact of the platina ; while at higher and lower temperatures the differ- 60 071 the Properties of Voltaic Circles. [xi. ence is less considerable. This circumstance may, perhaps, be explained by the following considerations. The rapidity of the solution of zinc, whether alone or connected, in- creases at a much faster ratio than the temperature, till it reaches a maximum point, when it can scarcely be augmented by farther increments of temperature. Now the effect of the contact of platina being to reduce the rate of solution of the zinc in the acid at a given temperature, (to what it is at 40° or 50° cent, lower than when unconnected,) it is evident that the difference will increase till they both attain such a temperature that they dissolve with the greatest possible rapidity when the difference will undergo a diminution. The effect of the distance of the platina and zinc plates from each other in the acid was next investigated. Two couples of platina and zinc, similar in every respect, except that in the one, the zinc plate and platina were in con- tact, and in the other, at the distance of '1 inch, were intro- duced into sulphuric acid, at the temperature of 225° cent. The quantity of zinc dissolved in the first couple was to that dissolved in the second as 1-587 : 1. When the distances be- tween the platina and zinc were •! and "o inch respectively, the quantities of zinc dissolved were as 1-441 : 1. The temperature in this case was 230°. The galvanometer needle was also more strongly deflected when the metals were near each other. The action of the acid on the zinc therefore increases with the proximity of the platina, as in common voltaic circles. This is further shown by the parts of the surface of the zinc which are nearest the platina dissolving most rapidly. Next the distance between the platina and zinc plates being the same, the extent of the platina surface in each couple was varied. The results obtained are exhibited in the following table, in which the second column shows the distance between the platina and zinc in the acid ; the third, the extent of the platina surface in each couple referred to that of the zinc as unit; the fourth, the ratio of the platina surfaces to each other ; the fifth, the ratio of the quantities of zinc dis- solved with the respective platina surfaces-; and the sixth, the temperature. XI.] On the Properties of Voltaic Circles. 61 No. of Experiment. Distance be- tween Platina and Zinc. Platina surface. Zinc = 1. Ratio of Platina sur. Ratio of Zinc dissolved. Tempera- ture. 1 2 3 4 5 6 J inch. i „ 2-3 4 •1 •1 ■13 1 3-4 12 •4 •7 2 9 1 1-5 3 4 7 15 1 9 •878 •890 •872 ■920 ■822 ■857 225° c. 230° 225° 220° 205° 18U° Although the variations in the extent of the platina surfaces, both when , compared to each other and to the surface of the zinc, are very considerable, yet the quantities of zinc dissolved present only slight differences, and do not appear to be in- fluenced by those changes in the platina surfaces. It must, however, be particularly observed, that there is invariably less zinc dissolved with the larger platina plate, — a result altogether at variance with the established laws of voltaic action. To ascertain whether this apparent anomaly depended upon some peculiarity in the mode of generation of these currents, or on the ordinary action of the acid on the zinc being more com- pletely checked by the broader platiiia surface, it appeared to be necessary to determine the quantity of electricity actually developed under these conditions. For this purpose a galvano- meter, composed of a pair of astatic needles, with a single silver wire between them, was interposed in the course of the circuit. As the needle of such an instrument can scarcely be maintained in a stationary position, but oscillates through an arc of two or three degrees round a fixed point, the most accurate method of ascertaining its deflection is to make five or more observations of the extremities of the arcs through which it vibrates, and to take a mean of the whole ; and this was the method followed in obtaining the deflections contained in the next table. As each degree of the scale occupied only one-fortieth of an inch, and was not subdivided into smaller parts, it was difficult to avoid an error of a quarter of a degree in making the observa- tions. The second column of the annexed table gives the extent of the surface of the platina exposed to the liquid, that of the zinc being represented by 1 ; and the third column, the 62 On the Properties of Voltaic Circles. [XI. deflection of the needle of the galvanometer. The temperature was 156° c. during the whole course of the experiment, and the distance between the zinc and platina siirfaces was one inch and a half. No. of Experiment. Platina Surface, Zinc being = 1. Deflection. 1 •8 30^1 2 ■2 29-8 3 ■08 30-1 4 •02 299 5 •01 27^4 6 •008 26 7 ■0008 14^2 The trifling differences in the deflections of the needle, in the first four experiments, certainly depended upon the unavoidable errors of observation and minute variations in the temperature of the acid. The current was therefore not perceptibly affected by altering the extent of the platina surface exposed to the liquid, unless that surface was reduced to less than -gV of the surface of the zinc ; and even when it amounted to tAt of the latter, the deflection of the needle was only one half less than with equal surfaces. This is very different from the well- known effect of similar changes in the extent of the surface exposed by the electro-negative metal in voltaic circles formed with the dilute acids. As a term of comparison, the platina surfaces used in experiments 1 and 4, being connected with similar zinc plates as before, and introduced into a mixture of dilute nitric and sulphuric acids, the deflections were 2o°^5 and 7" respectively. Although there was no visible disengagement of sulphurous acid gas from the zinc in the preceding experiments, except in No. 7, yet by comparing these results with those before obtained, it will appear that increasing the platina surface tends to arrest more completely the ordinary or local action of the acid on the zinc. When a slip of zinc in heated sulphuric acid was made the positive pole of a galvanic battery of twenty pairs of plates in XI.] On the Properties of Voltaic Circles. 68 moderate action, sulphurous acid ceased to be evolved from its surface, and the solution of the metal was greatly retarded. As a contrast with the preceding results, the influence of mercury, in connexion with zinc, upon the solution of the latter metal, may be mentioned. If these metals are heated separ- ately in concentrated sulphuric acid, till a gentle effervescence occurs at the surface of both, and then brought into contact, a very violent chemical reaction instantly occurs, an amalgam appears at first to be formed, and afterwards the zinc dissolves with the utmost degree of violence. It is the most remarkable example of increased chemical action from the formation of a voltaic combination with which I am acquainted. These facts are the more singular, as it thus appears that the influence both of amalgamation and of contact with platina on the solution of zinc is reversed in dilute and concentrated sulphuric acid. The general phenomena presented by the other metals capable of decomposing sulphuric acid were similar to these already described in the case of zinc, but in the details there were some important points of difference. Two similar m'ow wires, I and I', were placed in a glass tube containing concentrated sulphuric acid, I being alone, and 1' connected with a platina wire finer than itself. When first immersed in the acid the fine bubbles before described appeared at P and I, none at I'. On heating the liquid vast volumes of gas were extricated from I, but there was no gas I visible at P or I' till the liquid was raised nearly 1 to the point of ebullition, when there was some effervescence at P, and slight local disengagement of gas at I'. When pencils of tin, T and T', (T being unconnected, and T' connected with the platina P, and similar designations are used for the following metals,) were substituted for the iron wire ; the same phenomena occurred in the cold acid as with zinc and iron. Heat being applied to the acid, gas appeared at the same time at T and P ; but on raising the temperature a little higher, the action suddenly became so violent on T that it was impossible to observe the surfaces of T' and P. By heating T' and P in G4 On the Properties of Voltaic Circles. [xi. a separate tube, the quantity of gas at P became very consider- able, but far less than that before given off from T. There was also an obvious extrication of gas from T . With lismuth no gas appeared in the cold. On applying heat the surface of B became covered with a dark film, and soon afterwards that of B'. Continuing to apply the heat, gas was disengaged from P and B, but in much greater quantity from the latter. There was very little gas from B . Antimony gave precisely similar results to bismuth, except that there was ratlier more gas extricated from the metal con- nected with the platina when the temperature was high. With silver no gas appeared in the cold. On applying heat S and S' became dark nearly at the same moment ; as the heat was raised, gas was abundantly disengaged from S, and in smaller quantities from S' and P, but in the case of this metal the quan- tities of gas extricated from S' and P appeared to be equal. With arsenic and mercury there was no action in the cold. When the acid was heated the disengagement of sulphurous acid appeared to be scarcely, if at all, diminished, by connecting these metals with platina. The quantity of gas also extricated at the surface of the platina was very trifling. Taking a general view of these results, it will be observed, that the evolution of hydrogen gas, on immersion in the cold acid, occurred only with the metals, zinc, iron, and tin. 'The phenomena exhibited in this case by the platina and zinc couple afford a remarkable example of the cessation of a chemical action from the surface of the zinc acquiring a peculiar or pol- arized state. For although a large mass of bubbles appeared at first, yet by heating gently the liquid these not only were separ- ated, but not the least trace of gas afterwards appeared at either surface. There is a striking analogy in this, to the action of nitric acid of certain strengths upon some of the metals. In the cases of iron and ziac, the disengagement of gas was wholly transferred from the surface of these metals to that of the platina in connexion with them ; in those of bismuth, anti- mony, and tin, there was slight extrication of gas at the surface of the dissolving metal ; in that of silver, the quantity of gas was nearly the same from the platina and silver ; while in the cases of arsenic and mercury, scarcely any gas was given off XI.] Oil the Properties of Voltaic Circles. 65 from the platina, the action of the acid on the two latter metals not being perceptibly diminished by contact with platina. If these results are compared with those which have been already obtained with nitric acid, it wiU be evident that in the case of the concentrated acids the formation of a voltaic circle has in general the tendency to diminish chemical action. The following law will be found to be generally, although not uni- versally true, the exceptions to it being probably, however, rather apparent than real. The ordinary chemical action of an oxy-acid upon the metals soluble in it, is, in general, diminished when the acid is concentrated, hy voltaically associating them with certain electro-fositive metals ; hut on the contrary, is increased when the acid is dilute. In the preceding experiments the diminution of chemical action occurred in cases in which the acid itself suffered decom- position; while in common voltaic circles, where it is well kiiown that the action is increased, the elements of water alone are eliminated ; but how far this coincidence may be universal, must be determined by future investigations. 66 XII.— ON THE COOLING POWER OF GASES. From the Proceedings of the Royal Irish Academy, vol. 1, 1840, p. 465, Leslie observed long ago that a heated body cools more rapidly in hydrogen gas than in atmospheric air ; but Dalton and Davy were the first who attempted to estimate the cooling powers of the gases, by observing the times which a thermo- meter heated to the same point took to cool through the same number of degrees in different gases. So. difficult of execution, however, is this method, that their results difi'er in every respect most widely from each other ; thus, for example, Davy found that a thermometer cooled twice as fast in defiant gas as in nitrous oxide, while Dalton found the rate of cooling in both these gases to be the same. The subject appeared to be deserving of further investiga- tion, and the author has endeavoured to pursue it by a novel method, which may perhaps be susceptible of other applica- tions in inquiries connected with the science of heat. "When a fine metallic wire is placed in the circuit of a voltaic circle, it is well Tmown that it wUl become heated, and the temperature which it finally acquires (provided the length of the wire remain the same and the action of the battery continue constant) will depend upon the cooling power of the medium in which the wire is placed. If the current be of sufficient intensity to heat the wire to redness in air, the variations in its appearance, when placed in other gases, wiU. exhibit at a glance their relative cooling powers. But since the conducting power of wires for electricity diminishes as their temperature rises, a measure of the effect may be obtained by ascertaining the changes produced in the intensity of the current, which will increase or diminish according to the greater or less cool- ing power of the medium in which the wire is placed. The battery employed in the following experiments consisted of four large cells, on Daniell's construction, charged with his standard solutions ; and of a small cell, composed of an exterior XII.] On the CooUng Power of Gases. 67 cylinder of amalgamated zinc, and an interior plate of platina, the latter being separated from the former by a cylindrical membrane, and both immersed in dilute sulphuric acid. The ■hydrogen gas, disengaged from the platina plate, was collected in a graduated tube, and its volume taken as a measure of the intensity of the current. A platina wire, about 2-5 inches long, and T^TT in diameter, was stretched in the middle of a wide glass tube, by means of copper pincers, which were connected by thick wires of the same metal with the poles of the battery. The glass tube was so adjusted as to be easily traversed by a current of gas, which afterwards escaped from beneath a surface of mercury, and the connecting wires being passed through collars of caoutchouc, the whole apparatus was rendered perfectly air-tight. In making the observations, a current of the gas, carefully •dried, was passed in great excess through the apparatus, in order to sweep away as completely as possible the atmospheric air ; the current was then arrested, and, the connections with the battery being established, the appearance presented by the heated wire was noted, and the intensity of the current transmitted through it ascertained by collecting the hydrogen evolved in the small cell during the space of two minutes. The gas was next displaced by a current of dry air and the same experiment repeated. During these experiments the battery was always in a very constant state of action. The results are contained in the following table, in which the second column gives the quantity of hydrogen extricated at each experiment with the wire in air, the third with the wire in the gas, and the fourth column expresses the ratios of these numbers — those in the second being taken as unit : Name of Gas. Intensity : Wire in Air. Intensity : Wire in Gas. Eatio of Int. : that in Air=l. Muriatic acid, 65-9 63-1 0-958 Sulphuric acid, 69-2 66-9 0-967 Nitrogen, 67-3 67- 0-995 Carbonic oxide. 68-1 68-3 1-003 Cyanogen, 66-3 67- 1-010 Carbonic acid, 66-6 67-5 1-013 68 On the CooUng Power of Gases. [XII. Name of Gas. Intensity : "Wire in Air. Intensity : Wire in Gas. Ratio of Int.: that in Air= 1. Detitoxide of nitrogen. Protoxide of nitrogen. Oxygen, Olefiant gas. Ammonia, Hydrogen, 66-2 68-3 68-3 68-2 67-4 67-0 67-3 69-6 69-6 76-2 75-3 92-6 1016 1-019 1-019 1-171 1-118 1-382 As, however, the law which connects the intensity of a voltaic current traversing a wire with the temperature to which it raises the wire is unknown, these numbers do not furnish us with the means of determining the exact variations of temperature, sustained by the wire which was employed in these experiments. But, as a term of comparison, it may be mentioned that when the wire was immersed in distilled water which prevented its temperature from sensibly rising, the intensity of the current was almost exactly twice as great as when the wire was allowed to become heated in atmospheric air at the ordinary pressure. The appearances presented by the platina wire corresponded with the foregoing results. In atmospheric air, it exhibited a bright red heat ; in the muriatic and sulphurous acid gases, the redness was distinctly a shade brighter ; in cyanogen, carbonic- oxide, and hydrogen,^ there was no sensible difference ; in carbonic acid, oxygen, and the deutoxide of nitrogen, the wire,, so far as the eye could judge, appeared rather duller than in air ; while, in olefiant gas and ammonia, it was only raised to- a very obscure red heat, and in hydrogen, no redness whatever was visible, even in complete darkness. This method may, it is obvious, be extended to vapours ; and from some trials made with them, it appeared that the cooling powers of the vapours of alcohol and ether are considerably greater than the cooling power of air, and that of steam very slightly greater. On the other hand, the cooling power of all gases diminishes as they become rarefied ; so much so, that the platina wire used [Obviously a misprint for nitrogen. P. G. T.] XII.] On the Cooliing Power of Gases. 69 in the preceding experiments reached in vacuum nearly its point of fusion, while, at the same time, the intensity of the current considerably diminished. The gases may be conveniently arranged into the following groups, in reference to their cooling powers ; and it will be found on inspecting the table, that those arranged in each group differ little in this property from each other : — Group I. Gases whose cooling power is less than that of atmospheric air : sulphurous acid, muriatic acid. Group II. Gases whose cooling power is nearly the same : nitrogen, carbonic oxide, cyanogen, carbonic acid, deutoxide of nitrogen, protoxide of nitrogen, oxygen, vapour of water. Group III. Gases whose cooling power is greater : defiant gas, ammonia, vapours of alcohol and ether. Group IV. Hydrogen. 70 XIII.— ON THE HEAT DEVELOPED DUEING THE COMBINATION OF ACIDS AND BASES. From the Transactions of the Royal Irish Academy, vol. 19, p. 228, 1841. 1. It has been long known that chemical actions are m general accompanied by the evolution or abstraction of caloric. In most cases the change of temperature depends upon the result of the action of different causes, some of which tend to increase, and others to diminish the initial temperature of the reacting bodies. Thus, in the decomposition of a solution of carbonate of soda by concentrated sulphuric acid, the combination of the sulphuric acid with water and with the alcali are two distinct sources of heat, while the separation of the carbonic acid from the soda, and its evolution in the gaseous form, are equally distinct causes of a diminution of temperature. To estimate the influence of each of these circumstances in any particular instance is a problem of great difficulty ; and we can only expect to accomplish its complete solution, by confining our investigations, in the first place, to these simpler cases, where the variations of temperature are produced by the operation of one single cause. For this reason, I have confined myself, in this preliminary inquiry, to the examination of the calorific phenomena which occur during the combination of acids and bases with each other, under the most favourable circum- stances, for obtaiaing results free from complication. 2. The experiments to be hereafter described were all per- formed with very dilute solutions, by which means no correction was required for the heat evolved, when strong solutions of certa,in acids and alcalies are diluted. The method of operat- ing is easily described. In separate glass vessels solutions of determinate weights were prepared, one containing the quantity of alcali whose power of generating heat was sought, and the other, a little more than the equivalent of acid required to neutralize the alcali. After the liquids had acquired the same temperature, they were mixed together in the jar containing XIII.] On Heat Developed during Combination of Acids. 71 the alcali, and the increase of heat carefully observed by a delicate thermometer. This process was adopted from the facility of its execution and the uniformity of its results. It is, however, obvious, that a large portion of heat would be absorbed by the glass vessel ; and it was, therefore, necessary to establish, by a series of independent experiments, the cor- rections to be applied to the temperatures thus obtained, 3. As a basis to this whole investigation, the heat developed in ithe combination of nitric acid and potash was carefully deter- mined. But before describing the method employed, I must anticipate an observation which will be afterwards proved, viz., that the same amount of heat is developed when a given quantity of an alcali is united to an acid, whether the acid added be just sufficient to neutralize the alcali, or be consider- ably in excess.^ The addition of a slight excess of acid does not, therefore, in any way interfere with the results, except in so far as it renders them more unifoi-m and certain, by pro- ducing a rapid and complete neutralization of the alcali. 4. A cylindrical vessel of very thin brass was procured, capable of containing rather more than the quantity of liquid employed. Into this vessel was introduced the solution of caustic potash, the weight of which solution was about nine times greater than that of the dilute nitric acid destined to neutralize it. This vessel was so thin that we may assume, without any sensible error, its temperature to have been identical with that of its liquid contents. It weighed 6 "6 3 grammes, which, assuming the specific heat of brass to be '094, is equivalent to 0'623 gr. water. 5. As the weights of the glass and mercury in the bulb and immersed portion of the tube of the thermometer were both unknown, I was obliged to have recourse to a direct experi- ment, in order to ascertain their equivalent of water. For this purpose, 3 grammes of water (the quantity of Hquid usually employed) were introduced into the brass vessel, and the increase of its temperature carefully observed, when the ther- mometer, previously heated through a certain number of ^ These observations, as well as others of a similar kind in subsequent parts of this paper, refer always to dilute solutions, such as are employed in these experiments. 72 On the Heat Developed during the [xin. degrees, was suddenly cooled by immersion in it. Denoting by t tbe loss of heat sustained by the thermometer, and by t' the temperature gained by the liquid, I obtained in different trials the following numbers : 1. 2. 3. ^=59°-00 i; = 69°-00 i!=: 72-00 t'= 0°-90 t'= l°-00 t'= 1°-15 Hence, we deduce for the value of the thermometer in grammes of water, 1. 2. 3. Mean. 0-47 0-45 0-49 0-47 6. From the last two results we may therefore conclude, that the brass vessel and thermometer, taken together, are equivalent to r09 gr. water. 7. A very important source of error in this and other similar investigations, where the variation of temperature of a liquid requires to be observed with the utmost precision, arises from the cooling influence of the surrounding air during the time occupied by the observation, which, in the experiments I am about to describe, amounted to nearly l'. Where the increase of temperature does not exceed 2° or 3° Fahr., the common method of cooling the liquid before the experiment begins, as many degrees below the temperature of the air as it will after- wards rise above it, may be employed with success ; but for greater increments of heat, this process is liable to a serious error, which it is necessary to avoid. In fact, on mixing the liquids together, the thermometer attains, in a very few seconds, almost its ultimate point of elevation, and it occupies at least four-fifths of the entire time in rising through the last half degree. As, therefore, the mixture continues much longer in the upper than in the lower half of its range of temperature, the method just described will necessarily yield results sensibly below the truth.^ In practice, this error may be effectually obviated, by reducing the initial temperature of the liquid so far below the temperature of the air, that its final maximum may never reach higher than 2° F. above the same point. ^ A similar observation has been made by M. Eegnault in his recent and valuable memoir on the ' ' Specific Heats of Simple and Compound Bodies " {Ann. da Ohim., t. 6.S, p. 23) ; but the error thus induced he corrects by means, of an interpolating formula. o xin.] Combination of Acids and Bases. 73 8. The strongest nitric acid employed in these experiments contained 13-3 per cent, of real acid, and when one part of such an acid is diluted with nine parts of water, no sensible production of heat can be discovered by the most delicate thermometer. The corresponding solution of caustic potash, containing only 1'3 per cent, of alcali, was of course far beyond the limit of such sources of heat. That simple dilution exer- cised no influence on the result was further proved, by increasing the weight of the acid liquid, and diminishing that of the alcaline, while, at the same time, the quantities of acid and alcali in each, as also the total weight of both liquids, remained the same ; yet such variations in the form of the experiment produced no change whatever in the elevation of temperature observed on mixing them." 9. Having discussed the corrections arising from the form of apparatus, I now proceed to give the details of the funda- mental experiment, on the absolute amount of heat evolved in the union of nitric acid and potash. The general accuracy of these results was tested and confirmed by repeating the experi- ments in the form of a series, in which (the weight of the whole liquid remaining constant) the quantities of the com- bining substances were taken successively, in the proportions expressed by the numbers 1,2, 4 ; and it will be seen that the corresponding increments of temperature bear a similar ratio to each other. 1 0. Into the brass vessel before described, a solution of caustic potash, containing "0882 gr. of alcali was introduced. It weighed 27"3 gr., which, added to 1'09 gr., the equivalent in water of the vessel and thermometer (6), makes the whole equal to 28-39 gr. water. The acid solution, in a small glass tube, weighed 2-83 gr., and contained "106 anhydrous nitric acid. Thermometer in air stood at 38° F. Temp, of acid, - 38°-20 „ alcaline solution, 3 7°' 00 Mean temp, before mixture, 37°" 11 Temp, after mixture, 3 8 "■7 5 Increase in temp. (31-22 water), l°-64 74 On the Heat Developed during the [xm. 11. The last experiment repeated. Thar, in air 39°. Temp, of acid, alcaline solution, 39" ■00 37° •50 37° •64 39° •25 Mean temp, before mixture. Temp, after mixture. Increase (31^22 gr. water), 1°'61 12. Alcaline solution weighed 27"2 gr., and contained "1765 gr. of pure potash, or double that in the last experiments. Acid solution weighed 2 '8 5 gr. containing '212 anhydrous nitric acid. Ther. in air. 39°"5. Temp, of acid,- 39-00 „ alcaline solution, 37°'00 Mean temp, before mixture, 37°"18 Temp, after mixture, - 40°-40 Increase (31^14 water), - 3°^22 13. Alcaline solution 2 6 'So gr., containing "353 potash; acid liquid 3^25 gr., containing -424 anhydrous nitric acid. Ther. in air 39°-3. Temp, of acid, „ alcaline solution. 39" •70 34° ■30 34° ■86 41° ■45 Mean temp, before mixture. Temp, after mixture, - Increase (31-19 water), 6°^59 14. Eeducing these results to the quantity of alcali (-353 gr.) used in last experiment, and to 30 gr. of water, we obtain the following numbers : 1- 2. 3. 4. Mean. 6°-83 6°-70 6°-68 6°^85 6°-76 XIII.] Combination of Acids and Bases. I^y 1 5. This may be otherwise expressed, by stating that 1 gr. of potash, in combining with nitric acid, is capable of heating 85 gr. of water through 6°-76 of Fahrenheit's scale, or, which is the same thing, of heating 574"6 gr. of water through 1°. It must, however, be carefully observed, that in this experiment it is not pure water, but a weak solution of nitrate of potash, which is actually heated ; and the above numbers would there- fore require a further correction, in consequence of the difference between the specific heats of these liquids. This correction, however, must be extremely small, from the very dilute solutions obtained : it would probably be within the limit of the errors of observation. 16. Many of the subsequent experiments would have been performed with difficulty in a metallic vessel. I therefore substituted a pretty thick glass jar for the brass vessel, and both solutions were brought as nearly as possible to the tem- perature of the surrounding air, at the commencement of each observation. In this way numerous experiments were easily performed, which yielded results comparable with each other, although all below the truth. It was, therefore, necessary to ascertain the absolute loss of heat when the experiment was performed in this way, and whether it was proportional to the elevation of temperature. For this purpose, solutions were prepared containing the same quantity of potash and nitric acid as in the experiments with the brass cylinder. 17. Alcaline solution 27 gr., containing -0882 gr. potash ; acid solution 3 gr., containing 1'06 nitric acid. Temp, rose on mixture, 1°'45 Another experiment gave 1°'45 18. Alcaline solution 27 gr., containing -1765 potash; acid solution 3 gr., containing "212 nitric acid. Temp, rose on mixture, 2"-90 Another experiment gave 2°"9o 19. Alcaline solution 27 gr., containing -353 potash; acid solution 3 gT., containing '424 nitric acid. 76 On the Heat Developed during the [xm. Temp, rose on mixture, 5°'8 Another experiment gave 5°'8 20. Alcaline solution 24 gr., containing -353 potasli ; acid liquid 6 gr., containing -424 nitric acid. Temp, on mixture rose to 5 "9 21. Collecting these results, we obtain for the elevation of temperature of 3 gr. of water, in a glass vessel, by the com- bination of '3 5 3 gr. potash with nitric acid: 1. 2. 3. 4. 5. 6. Mean. 5°-8 5°-8 5°-8 5''-9 5°-8 5°-9 5°-83 This number differs by 0°-93 from the absolute quantity of heat before found, which is the loss of heat by this method of performing the experiment. It also appears from the coincid- ence of the results obtained with different proportions of alcali, that the loss of heat is proportional to the rise of temperature, and hence the necessary correction for this error is, in all cases, easily made. 22. When the base is insoluble in water, and slowly soluble in the acid, a new element enters into the observation, and requires to be estimated, viz., the cooling of the liquid during the prolonged duration of the experiment. In the observations last described, the thermometer attained its maximum in about 45" from the time the liquids were mixed, but in the solution of such substances, as magnesia or the oxide of zinc, not less than 2', or 2 J' will elapse before the liquid becomes transparent, and the thermometer stationary. Even to complete the solution within this period, the liquid requires to be constantly stirred with a glass rod. This circumstance renders these results less precise than those in which the combination occurs instan- taneously ; but the amount of error thus produced may be estimated, by repeating the same experiment in precisely the same manner, with a solution of caustic potash, containing exactly the quantity of alcali (as deduced by calculation from the foregoing experiments) which should produce the same elevation of temperature as had been obtained with the slowly soluble base. The difference between the increase of heat actually found, and that deduced from calculation, will. be equal xin.] Gomhination of Acids and Bases. 77 to the loss of caloric occasioned by the stirring, and length of the experiment ; and consequently the required correction for the number obtained by observation. The precise value of this correction will be given hereafter. 23. The general conclusions which I shall endeavour to establish in the subsequent part of this communication, may be enunciated in the form of the three following laws : Law 1 . — The heat developed during the union of acids and bases is determined by the base and not by the acid ; the same base producing, when combined with an equivalent of different acids, nearly the sarrie quantity of heat ; but different bases a different quantity. Law 2. — When a neutral is converted into an acid salt, by combining loith one or more atoms of acid, no change of tem- perature occurs. Law 3. — When a neutral is converted into a basic salt, by combining loith an additional proportion of base, the combination is accompanied with the evolution of heat. 24. To the first of these laws important exceptions are presented by the peroxide of mercury among the bases, and by the hydrocyanic, and probably the carbonic acid, among the acids ; and it is not improbable that more extended investiga- tions will lead to the discovery of other exceptions. The second law has been established by numerous experiments, and can scarcely be said to be liable to any well-marked exception ; but I feel much less confidence in enunciating the third, as a general principle, from the very limited number of cases of soluble subsalts in which it was possible to verify its accuracy. 25. In order to obtain results of as much uniformity as- possible, the standard alcaline solution was always mixed with rather a greater quantity of acid than was necessary to neutralize it.^ The combination was thus effected more rapidly and certainly, than if an attempt had been made to form an exactly ■• In the cases of the phosphoric and arsenic acids, the quantity of acid was just sufficient to convert the alcali into the common phosphate and arseniate ; that is, half an equivalent of acid for an equivalent of base. The reason of this will appear again (55). The number for chromic acid is only deduced from an indirect experiment upon the bichromate of potash. 78 On the Heat Developed during the [xni. neutral compound. That this excess of acid did not produce any sensible difference in the result, will be rendered evident, when the experiments are examined, which will be hereafter cited, in illustration of law second ; and, indeed, if no basic compound existed, the numbers obtained were identical, whether an equivalent of base was neutralized by an excess of acid, or a like equivalent of acid neutralized by an excess of base. I have arranged, in distinct tables, the increments of temperature obtained by combining an equivalent of each base with the acids. The equivalents taken were "3 5 3 gramme potash, •234 gr. soda, '129 gr. ammonia, '572 gr. barytes, "213 gr. lime, •154 gr. magnesia, •SOI gr. oxide of zinc, '834 gr. oxide of lead, -870 gr. oxide of silver, and •SIO gr. peroxide of mercury. The entire weight of the solution, after the mixture was made, amounted in every instance to 30 grammes. In the first four tables, the first column of numbers contains the elevation of the thermometer actually observed ; and the second, the result corrected for the loss of heat, occasioned by the mode of performing the experiment (21). 26. Table I. — Potash. Acid. Found. Corrected. Difference from Mean. Sulphuric, e°-3o 7°-32 + 0°-80 Nitric,- 5-83 6-76 + 0-24 Phosphoric, - 5-70 6-61 + 0-09 Arsenic, 5-70 6-61 + 0-09 Hydrochloric, 5-65 6-56 + 0-04 Hydriodic, 5-80 6-74 + 0-22 Boracic, 5-60 6-50 - 002 Chromic, 5-55 6-46 - 0-06 Oxalic, 5-70 e-6-T + 0-10 Acetic, 5-50 6-39 - 013 Tormic, 5-50 6-39 - 0-13 Tartaric, 5-25 6-10 - 0-42 Citric, - 5-25 6-10 - 0-42 i Succinic, 5-25 6-10 - 0-42 Mean, 6-52 XIII.] Combination of Acids and Bases. 27. Table II. — Soda. 79 Acid. Found. Corrected. Difference from Mean, Sulphuric, 6°-40 7°-44 + 0°-96 Nitric, 5'55 6-45 - 003 Phosphoric,- 5-55 6-45 - 0-03 Arsenic, 5-60 6-50 + 0-02 Hydrochloric, 5-80 6-74 + 0-26 Hydriodic, 5-70 6-62 + 0-14 Boracic, 5-80 6-74 + 0-26 Oxalic, 5-75 6-68 + 0-20 Acetic, 5-45 6-34 - 0-14 Tartaric, 5-10 5 '93 - 0-55 Citric, 5-10 5-93 - 0-55 Succinic, Mean, 5-10 5-93 - 0-55 6-48 28. Table III. — Barytes. Acid. Found. Corrected. Difference from Mean. Nitric, Hydrochloric, Hydriodic Acetic, Mean, 5°-90 5-85 6-00 5-50 6°-85 6-79 6-97 6-39 H-C-IO + 0-04 + 0-22 - 0-36 6-75 29. Table IV. — Ammonia, Acid. Found. Corrected. Difference from Mean. Sulphuric, 5°-45 e°-34 +0°-82 Nitric, 4-80 5-58 + 0-06 Arsenic, 4-90 5-69 + 0-17 Hydrochloric, 4-80 5-58 + 0-06 Hydriodic, - 4-80 5-58 + 0-06 Oxalic, 4-90 5-69 + 0-17 Acetic, 4-70 5-47 - 0-05 Tartaric, 4-40 5-11 - 0-41 Citric, 4-35 5-05 -0-47 Succinic, Mean, 4-40 5-11 -0-41 5-52 80 On the Heat Developed during the [XIII. 30. The remainder of the bases examined, being either in- soluble or very slightly soluble in water, were added in the solid state to the acid solution, whose weight was always so adjusted as, together with that of the base, to be equal to 30 grammes. The bases were all taken in the anhydrous state, except lime, which dissolves with extreme difficulty even in the dilute acids, unless previously converted into a hydrate. The experiments performed with these bases occupied from 80" to 100" longer than those with the soluble alcalies. This renders the application of a new correction necessary. The method of determining the amount of this correction has been already ex- plained (23). In the remaining tables, the first column contains the result as found by experiment ; the second, the duration of the observation ; the third, the correction applied for the heat lost thereby ; the fourth, the corrected result ; and the fifth, the difference from the mean. 31. Table V. — Magmsia. Acid. Found. Time. Cor. Time. Corrected. Difference from Mean. Sulphuric, Nitric, Hydrochloric, - Mean, ^"•oo 6-70 6-60 2' 2 2 0°'30 0-30 0-30 8°-48 8-13 8-11 -H0°-24 + 011 -Ul3 8-24 32. Table VI. — Idmc. Acid. Found. Time. Cor. Time. Corrected. Difference from Mean. Nitric, Hydrochloric, Agetic, Mean, 5°-95 5-85 5 '80 0°-25 0-25 0-25 7°-20 7-08 7-03 + 0°10 - 0-02 -0-07 710 XIII.] C@mbination of Acids mid Bases. 33. Table VII. — Oxide of Zinc. 81 Acid. Found. Time. Cor. Time. Corrected. Difference from Mean. Sulphuric, Nitric, - Hydrochloric, - Hydriodic, Mean, 4° -45 3-90 4-00 3-50 2' 2 2 4 0°-20 0-20 0-20 0-45 b'-40 4-76 4-88 4-59 + 0°-49 - 0-15 - 0-03 - 0-32 4-91 34. Table VIII. — Oxide of Lead. Acid. Found, Time. Cor. Time. Corrected. Difference from Mean. Nitric, Acetic, Mean, 3°-45 2-95 2' 3 0°-15 0-30 4°-18 3-78 + 0°-20 - 0-20 3-98 3 5. The oxide of silver gave, with nitric acid, an increase of temperature of 2°-7 corresponding, when corrected, to an actual elevation of 3°'23. 36. To render the numbers in each table strictly comparable with one another, would require a minute investigation of the in- fluence of every possible source of a variation of temperature in the experiments ; such are, differences in the specific heats of the solutions formed, alterations in the density of the liquids after mixture, etc. However, from very dilute solutions being employed, and also, from the results being identical when the strength of the solutions was greatly varied (9), it is probable that the errors arising from such causes could not amount, in most cases, to more than a few hundredths of a degree. Taking therefore the results as they appear in the tables, it will be found, on examination, that they are in accordance with Law 1, (24). If we refer to the first, second, and fourth tables, as being the most extensive, from the large number of soluble p 82 On the Heat Developed during the [xm. compounds formed by potash, soda, and ammonia, it will be ob- served, that the sulphuric acid develops from 0°"8 to nearly 1° more than the mean heat given by the other acids, while the tartaric, citric, and succinic acids fall from 0°'4 to 0°'55 short of the same. A minute investigation of the influence of the disturbing sources of heat will, no doubt, discover the cause of these dis- crepancies ; the high numbers for sulphuric acid are probably connected with that acid's well-known property of, developing much heat when combined with successive atoms of water. All the other acids develop very nearly the same amount of heat in combining with the same base ; the greatest divergences from the mean quantity being in the case of potash, -f 0°-24, and — 0°-13; in that of soda, -)- 0°-26, — 0°-14; and in that of ammonia, -(-0°"17 and — 0°-05. These differences are almost within the limits of the errors of experiment. In the other tables a similar agreement will be^ found to exist. Indeed the sulphuric acid does not exhibit in them so wide a discordance from the other acids as before. I must, however, remark that the numbers for the insoluble bases are scarcely so exact as those which are contained in the first four tables. i 37. Whether the base be soluble or insoluble in water, the increments of temperature obtained, by combining the same base with different acids, may be compared with each other ; but if we wish to discover the relations subsisting between the temperatures developed by different bases, it becomes necessary to take into consideration the heat absorbed by the insoluble bases, in passing from the solid to the fluid state. I am not at present acquainted with any method whereby the heat thus abstracted can be estimated. But the numbers for the insoluble bases, from this cause, will be all too low. "We may, therefore, arrange the bases in the following order, in respect to their power of developing heat when combining with the acids ; but this arrangement is liable to be disturbed when the value of the unknown quantities shall be determined. It must also be recollected that the potash, soda, barytes and lime were in the state of hydrates before mixture, while the magnesia, oxide of zinc, oxide of lead, and oxide of silver were anhydrous. XIII.] G'ombination of Acids and Bases. 83 Magnesia, Lime, Barytes, Potash, Soda,- Ammonia, - Oxide of Zinc, Oxide of Lead, Oxide of Silver, 8'24 + a; 7-10 +£k' 6-75 6-52 6-48 5-52 4-91+ a;" 3-98+ a;'" 3-23 +»"" 38. The peroxide of mercury has given results altogether at variance with the preceding. It develops with the nitric and acetic acids nearly the same quantity of heat, but with the hydracids the most singular anomalies occur, as will appear in the next table. 39. Table IX. — Peroxide of Mercury. Acid. Found. Time. Cor. Time. Corrected. Nitric, i-20 . 2 0-05 1-27 Acetic, 1-20 2 005 1-27 Hydrochloric, 3-80 2 0-20 4-65 Hydrocyanic, 5-85 2 0-25 7-10 Hydriodic, 9-20 3 0-60 11-40 40. To the last number some objection may be made, as a large excess of hydriodic acid was used to prevent the forma- tion of the insoluble periodide of mercury; but even if we omit it altogether, the other parts of the table exhibit singular discrepancies. It is probable that a , more extended investigation will discover other metallic oxides, resembling the peroxide of mercury, in yielding different quantities of heat, when they combine with the hydracids. 41. The hydrocyanic acid stands not less apart from the other acids than the oxide of mercury from the rest of the bases, in its development of heat when forming compounds ; and it is remarkable that no analogous property appears with the hydrochloric and hydriodic acids. The hydrocyanic acid used in these experiments was perfectly pure ; it was employed ^4 On the Heat Developed during the [xm. immediately after being rectified over chalk, and had no action on vegetable colours. I have collected together the elevations of temperature produced by it, and contrasted them with the mean quantities of heat given by the other acids with each Base. Hydrocyanic Acid. Mean of other Acids. Difference. Potash, Soda, - . Barytes, Ammonia, Peroxide of Mercury, r45 1-45 1-68 0-51 7-10 6-52 6-48 6-75 5-52 5-07 5-03 5-07 5-01 42. Thus the hydrocyanic acid develops with potash, soda, barytes, and ammonia, 5° less than the other acids. On the other hand, it yields no less than 7°"1 in combining with the peroxide of mercury, while the oxyacids produce with the same base, only l°-27. 43. I now proceed to cite a few experiments in illustration of Law 2 ; viz., that during the conversion of a neutral into an acid salt, no evolution of heat occurs. 44. 23 gr. of a solution of caustic potash, containing '353 gr. of alcali, were mixed with 7 gr. of a solution of oxalic acid, containing '271 gr. (or 1 equiv.) of acid. Temp, after mixture rose, 5°' 7. 45. 31 gr. of a solution of neutral oxalate of potash, contain- ing '624 gr. of the salt, were mixed with 9 gr. of a solution of oxalic acid, containing '271 gr. (1 equiv.) acid. Temp, after mixture rose, C'O. 46. The solution of binoxalate of potash, obtained in last experiment, was mixed with 18 gr. of the solution of oxalic- acid (2 equiv.). Temp, rose after mixture, 0°'15. After some time, crystals of quadroxalate of potash began to- form, which accounted for the slight elevation of temperature. 47. On adding to a solution of sulphate of potash a second atom of sulphuric acid, the temperature of the mixture rose only 0°*1, although the combination of the first atom had pro- duced 6°' 3 of heat. xni.] Combination of Acids and Bases. 85 48. Similar resultswere obtained with the oxalate, tartrate, and acetate of soda, when converted into the corresponding super- salts ; and by neutralizing these acid salts with the base, the same heat was invariably produced as if the excess of acid had existed in a free state. I may cite particularly the case of the bichromate of potash, which gave, when convertedinto the neutral chromate, a quantity of heat corresponding with that developed by the acids in general with potash, viz., 6° "4 5. In verifying this principle, care must be taken to select examples where all the compounds are soluble salts ; otherwise, the latent heat extricated by the solid precipitate would interfere with, and complicate the result. It is for this reason that the formation of the bitartrate of pota.sh is accompanied by heat, although none is evolved when the neutral tartrate of soda combines with a second atom of acid. 49. As a farther illustration of the same principle, I am unwilling to omit the description of an interesting experiment, although its corhplete explanation involves the consideration of a class of phenomena which I have carefully excluded from the present communication. Three solutions were prepared, each containing 2 5 gr. of liquid ; the first, holding in solution •353 gr. of pure potash ; the second, ■520 gr. of carbonate of potash; and the third, "683 gr. of bicarbonate of potash ; consequently the amount of real alcali the same in all. They were then separately neutralized by 5 gr. of a solution of nitric acid, containing a considerable excess of acid, and the two latter solutions were well stirred, to expel, as far "as possible, the carbonic acid gas before the final temperature was observed. The elevations of temperature were, for o Difference, Pure Potash, - 5-8 Carbonate of Potash, 1-7- 4-1 Bicarbonate of Potash, 0-4 1-3 5 0. Thus we see that the effect of separating the first atom of carbonic acid, in the gaseous state, from its combinations -with the alcali, was to caxise the disappearance of 4°'l of heat; while the separation of the second atom, and its complete 86 On the Heat Developed during the [xin- expulsion in the gaseous state, produced a further diminution of temperature of only 1°'3. In these observations, two distinct sources of an absorption of caloric exists ; one, the separation of the chemical compound into its constituents ; the other, the change of one of those constituents from the liqiiid to the gaseous state. Had both causes acted equally on the second as on the first atom of carbonic acid, we should have obtauied with the bicarbonate, as great a diminution of tempera- ture as had occurred with the carbonate, or the thermometer would have sunk 2°-4 instead of rising •4°. But the conver- sion of the second atom of carbonic acid into the gaseous state is completely effected, while a considerable portion of the first atom remains dissolved in the liquid ; and consequently, the striking difference in the result can only be accounted for, on the principle stated in the second law, that the combination, or separation of the second atom of carbonic acid is attended with no evolution or abstraction of heat. 51. The tribasic, phosphoric, and arsenic acids, iu their com- binations with the fixed alcalis, present a slight divergence from this law, and at the same time, give results closely coincident with each other. In the following table, the increments of temperature are exhibited which were observed, when solutions, containing the compounds denoted by the first and second members of the expression, were mixed together. The symbol NaO corresponds, as before, to '234 gr. soda, and the entire weight of the solution was 3 grammes. Found. Corrected. (NaO-hiPA)+iP205, 0°-40 0°-46 (NaO-h|PA) + iP205- 0°-30 0°-35 52. In other words, the combination of the common phos- phate of soda with half as much acid as it already contains pro- duces an increment of temperature of 0°"46 ; and its complete conversion into" the biphosphate, a farther increase of 0°"35. Similar numbers were obtained with the arsenic acid. Found. Corrected. (Na04-iAs205)-f-iAs206. O^'^O 0'-46 (NaO-f-iAs205)-|-JAs206. 0°'35 ()°-40 " XIII.] Combination of Acids and Bases. B7 54. The same acid gave with potash, Found. Corrected. (KO + iAs206) + |As205, 0°-80 0°'93 55. From these experiments it follows, that during the con- version of the common alcaline phosphates and arseniates into supersalts, a quantity of heat is evolved, which is about one seventh part of that produced during the formation of those salts themsielves. As, however, the alcaline phosphates and arseniates are not strictly neutral in composition, and their solutions have an alcaline reaction, it is, perhaps, scarcely correct to adduce them as exceptions to Law 2. The pyro- phosphoric acid, in similar circumstances, scarcely produces any heat ; resembling, in this and its other thermal properties, the ordinary acids. Denoting the pyrophosphoric acid by Pyr. we have. Found. Corrected. (NaO + iPyr A) + iPyr206, 0°-15 0°-17 (NaO + fPyrA) + iPyrA, - 0°-00 0°-00 55. The formation of the alcaline subphosphates and sub- arseniates, by the direct union of the common phosphates and arseniates, with an additional equivalent of base, is accompanied with a definite evolution of heat. On adding to solutions of these salts, containing the equivalents of alcali before referred to (NaO, "234 gr. KO, '3 5 3 gT.), alcaline solutions having half as much base as was already in the salts themselves, I obtained very uniform results. Found. Corrected. (NaO-|-jPA) + iNaO, l"-? l°-97 (NaO + iAs A) + iNaO, l°-7 l°-97 (KO + iAs205)-|-i^KO, l°-7 l°-97 (NaO + iPyraOs) + iNaO, 0°-l 0'^-12 5 6. That the heat produced was connected with the formation of the subsalt, appears distinctly from the circumstance, that a further addition of alcali was not attended with any increase of temperature. The absence of any heat in the case of the pyrophosphate of soda is easily explained on the same principle, as Graham has shown that no subpyrophosphate of soda exists. 57. The formation of these subsalts exercises a remarkablfe influence on the quantities of heat developed, when the base is 88 Qn the Seat Developed during the [xni. neutralized by successive portions of acid. In ordinary, cases, the heat evolved in this way is proportional to the quantity of acid added. Thus, on mixing a solution of pure potash vyith one fourth, one half, etc., an equivalent of nitric acid, the elevations of temperature v^ill be one half, one fourth, etc., of what is observed when the alcali is completely neutralized. And the same principle I find to hold good, when successive portions of the phosphoric (trihasic) and arsenic acids are added to solutions of the pure alcalis, till the subsalts are formed ; but, after that point, a very different law is followed, as will be seen in the next tables : Found. Corrected, I.-NaO + iPA, 4°-65 5°-40 (NaO + JPA) + ^P205). 0°-90 l°-04 II.— NaO + ^AsgOg, 4°-75 5°-51 (NaO + Hs205) + iAsA. 0°-85 0°-99 II.-KO + iAsA. 4.°-80 5°-57 (KO + lk.^fi,) + lksifi„ 0"-90 l°-04 58. Had the evolutions of heat corresponded with the additions of acid the second numbers would have been one half of the first in each set of experiments. Hence, the increments of temperature for equal portions of acid are nearly as 2"5 : 1, before and after the formation of the subsalt. The pyrophos- phoric acid, on the contrary, presents no similar irregularity, developing equal increments of heat, for equal additions of acid, till the pyrophosphate of soda (NaO + JPyrgOj) is formed. 59. It may, perhaps, be premature, from such imperfect and limited data, to offer any general observations on the preceding experiments ; but I shall, nevertheless, venture to show the accordance of laws second and third, with those general views of the constitution of the salts which have been so ably illus- trated by Graham. The conversion of a neutral into an acid salt being . in reality the formation of a double salt, is not accompanied by any disengagement of heat ; because such combinations as the latter do not evolve heat. No caloric is extricated when the tartrates of potash and soda unite ; and, consequently none ought to be given off, when the tartrate of spda is combined with the tartrate of water. But, on the xiii.] Gombination of Acids and Bases. 89 other hand, heat is disengaged when the base in the tartrate of water is replaced by soda ; because soda, in its combinations with the acids, evolves much more heat than water. How far the heat evolved in the formation of the different hydrated acids may be the same, is an interesting question not yet determined ; but there can be little doubt that water holds a very low rank among the bases, in reference to its power of generating heat when combining with the acids. On the same principles, and again referring to the observations of Graham, We can under- stand the cause of the evolution of heat during the conversion of the neutral phosphates and arseniates into basic salts. In reality, an equivalent of water is here again replaced by an equivalent of alcali, just as occurs in the direct combinations of the acids and alcalis.^ ' When the experiments detailed in the foregoing paper were almost completed, I received the 6th No. of Poggendorfi''s Annalen, for 1840, con- taining the first part of a valuable memoir, by M. Hess, entitled " Thermo- chemical Researches." The experiments detailed by M. Hess refer principally to the heat developed vi'hen sulphuric acid and water combine together — a subject not touched upon in the present paper. He has, however, extended his inquiry to the heat evolved during the combination of sulphuric acid with potash, soda, ammonia, and lime ; and also of hydrochloric acid with potash, soda, and ammonia. But the results obtained by M. Hess cannot be immedi- ately compared with those given in this communication, as his experiments were performed with stronger acids, which disengaged heat when diluted with water. The quantity of heat thus extricated, M. Hess has shown to be the same, whether the acid and water be mixed together in presence of a base or alone ; and he has likewise furnished accurate data, by means of which the heat derived from this source, in his experiments, may be estimated. 'Now, assuming with him, as a term of comparison, the number of grammes of water which would be heated through 1° centigrade, by saturating with each alcali 1 ■gramme of sulphuric acid, or the corresponding equivalent (0'908 pr. ) of hydrochloric acid — all taken in the state of very dilute solutions — we deduce from the foregoing tables the numerical results in the first of the following columns ; while those in the second are derived from the memoir of M. Hess : Tables. Hess. ( Potash, - 407 406 Sulphuric Acid with ] Soda, 413 411 ( Ammonia, 352 403 ( Potash, 364 362 Hydrochloric Acid with ] Soda, _ 373 368 ( Ammonia, - 310 318 It is very satisfactory to observe how closely these numbers agree with each other, with the single exception of that which expresses the heat evolved when sulphuric acid and ammonia combine. The cause of this discrepancy I have endeavoured in vain to discover ; but it probably depends upon some condition ill the experiment of M. Hess, which may have escaped my observation. 90 XIV.— ON THE HEAT DEVELOPED DUEING THE FORMA- TION OF THE METALLIC COMPOUNDS OF CHLOEINE, BROMINE, AND IODINE. From the Transactions of the EoyaJ, Irish Academy, 1842, vol. 19, p. 393. 1. In pursuance of the train of investigation commenced in a preceding Memoir, I propose, in the present communication, to advance to the consideration of the more complicated thermal phenomena, which are accompanied by alterations in the state of aggregation of the combining bodies. To deduce general conclusions from such inquiries is extremely difficult, as the variation of temperature measured by the thermometer is in every instance the resultant of more than a single cause, each of which must be separately eliminated, before the heat arising from the chemical union can be determined. It has been my endeavour to furnish as many data as possible, in the cases I have examined, for the solution of these interesting problems. 2. That we may be enabled to measure with precision the heat developed during a chemical combination, it is necessary that the reaction should be very quickly completed ; and the experiment is also greatly facilitated, when the action com- mences, by simple contact, without the application of external heat. These conditions are completely fulfilled, when chlorine, bromine, or iodine are brought into contact with zinc or iron, water being also present. To the success of the experiment the latter condition is indispensable, as these elementary bodies, at ordinary temperatures, and. in the dry state, have no action upon one another. '^ The relative proportion of water is also a 1 The description generally given in chemical works of the rapid manner iii which zinc, copper, antimony, etc. enter into combination with chlorine gas at common temperatures, is only true when the gas is in a moist state. Chlorine gas, when carefully dried, has no action whatever, at the ordinary temperature of the atmosphere, upon fine filings of zinc or iron, or upon copper reduced from its oxide by means of hydrogen gas, although the action, as is ^iv.] On Heat Developed, etc. 91 matter of importance. The quantity present must be sufficient to dissolve, with facility, the resulting compound, and it ought not greatly to exceed that amount. In the following experi- ments I usually employed about 2-4 gr. of water, for every 0'42 gr. chlorine, 0'9 gr. bromine, and 1"5 gr. iodine, which entered into combination. If this precaution be attended to, and the mixture briskly agitated, the whole reaction will be completed in the course of a few seconds. 3. As our object is to ascertain the heat due to the com- bination of the reacting bodies in an anhydrous state, and as we actually obtain the result of the combination in a state of solution in water, it is obviously necessary, in the first instance, to apply a correction for the heat arising from the solution. The amount of this correction is easily discovered, by determining the heat evolved during the solution of a corresponding weight of the dry compound in the normal pro- portion of water. If the combining bodies do not unite in more than one proportion, there only now remains to be deter- mined the heat evolved or absorbed during the changes of aggregation which occur in the course of the combination. Unfortunately we cannot attempt, by direct experiments, to discover the amount of this important correction. 4. If we now make A = heat evolved during the reaction of chlorine, zinc (in excess), and water, B = heat evolved during the solution of ZnCl in a like proportion of water, well known, is most energetic if moisture be present. On tlie contrary, the dry gas instantly combines with arsenic, antimony, and phosphorus. This striking difference appears to depend upon the circumstance that the compounds formed by chlorine with the former substances are solid at common temperatures and very fixed, while those formed with antimony and arsenic are fluid and volatile. The chloride of phosphorus is also very volatile. If, however, the chemical affinity be very intense, combination will take place, although the resulting compound be quite fixed and solid. Thus potassium inflames in dry chlorine gas, but the chloride which is formed terminates the action before the whole of the metal has entered into combination. The fluidity of the metal also exercises an important influence in determining the combination, — as in the case of mercury, which slowly combines with dry chlorine. The preceding remarks may be also applied to the behaviour of dry bromine when brought into contact with the metals. 92 On Heat Developed dui-img Formation of [-xiv. X = heat evolved or absorbed during the change of the constituents of ZnCl, from the state of aggrega- tion in which they exist, as gaseous chlorine and metallic zinc, to that state in which they exist in the dry chloride of zinc, X = heat due to the union of zinc and chlorine, we shall have the following general equation : ,)- = A — B±X. And, designating the corresponding values for bromine by a', b', x', ,v', and for iodine by a", b", x", x'\ we shall have ,/'=a'— B'±x', X =a — b ±x . 5. The class of metals forming more than one compound with chlorine, bromine, and iodine is very numerous ; but none of them present the same facilities for this investigation as iron, to which accordingly I propose to confine my attention in the present paper. It is usually stated in chemical works that when chlorine, bromine, or iodine act upon an excess of iron filings, suspended in water, a solution of protochloride, protobromide, or protoiodide of iron is formed. But such a description gives a very imperfect idea of the successive series of phenomena which actually take place. We have only, indeed, to watch carefully the progress of the experiment, in order to discover that a sesquicompound (FejClg, FcgBrg, Fejls) is formed in the first instance, which afterwards, by com- bining with an additional atom of iron, becomes converted into the protocompound (FcjClg -f- Fe, etc.). To prove this, we only require to filter the liquid before the reaction has terminated, when a red solution will be obtained, having all the properties of a solution of a sesquisalt of iron, and yielding by evapora- tion a red deliquescent mass. Whether the experiment be made with chlorine, bromine, or iodine, the same results will be obtained. An elegant illustration of a similar train of changes is afforded by the action of chlorine gas on metallic tin. If we agitate an excess of tin filings with a little water in a glass vessel of chlorine gas, till the colour of the gas has scarcely disappeared, and instantly filter, the liquid which passes through will .produce only a faint opalescence, when XIV.] Metallic Compounds of Chlorine, etc. 93 dropped into a solution of the bichloride of mercury ; but if the agitation be continued for only a few seconds after the disappearance of the chlorine, the filtered liquid will give a dense curdy precipitate when added to the same solution. 6. From these observations it follows, that the primary form of combination, into which the molecules of chlorine, bromine, and iodine enter with iron, is that represented by the formulas FegClg, FcgBrg, Fcals, and that the so-called protocompounds are, in reality, secondary combinations, formed by the union of the sesquicompounds with an additional atom of iron (FejClg + Fe, etc.). This conclusion is farther confirmed by the well-known fact, that when these substances unite at elevated temperatures, the red or sesquicompounds are always formed.^ 7. Let us now make c=:heat evolved during the reaction of chlorine, iron (in excess), and water. D = heat evolved during the solution of FejClg in a similar proportion of water. E = heat evolved during the combination of FcjClg in solution with Fe. . Y = heat evolved or absorbed during the change of aggregation of the constituents of FegClg. y = heat due to the union of Fcj with CI3. Let us also, as before, represent the corresponding values for bromine by c', d', b', y', y, and for iodine by c", d", k", y", y". The following equations will then give the values of y, y , and y: y =C — D — E ±Y, y =C — D — E ±Y, // fi II rr _L ir y =C — D — E ±Y . 8. Having thus endeavoured to lay down general formulas for the heat of combination, I proceed to describe the experi- ments by which the values of A, B, c, etc., have been determined. ^ If the view, which regards FeCl as the primary form of combination, be preferred, it will be necessary to suppose that tliree successive changes occur, — first, the formation of the compound Fej + Cl^; secondly, its con- version into FojClj by combining with 01 ; and thirdly, the reconversion of the latter into FejClj by its union with Fe. 94 On Heat Developed during Formation of [xiv. 9. The apparatus employed in these experiments consisted of several distinct parts. The combination was effected in a thin glass vessel of the form represented in fig. 1 [plate 1]. When chlorine was the subject of experiment, this vessel was filled with the gas in a moist state, and two very flimsy glass balls, such as those shown in fig.. 4, were afterwards cautiously introduced. One of these balls contained a large excess of the metal in the state of fine filings ; the other, a quantity of water, whose weight had been adjusted nearly in the propor- tions before described. On the other hand, when bromine and iodine were under examination, the metal and water were intro- duced into the vessel itself, whUe the bromine or iodine, carefully weighed, was contained in one of the little balls. The vessel was in all cases closed by a good cork, which was rendered air- tight by cement. A small stud of iron wire was inserted into the cork to maintain the glass vessel in its proper position in the interior of the apparatus. This vessel, thus prepared, was agitated for some time in water adjusted to the proper temperature, and then placed in the light copper vessel, fig. 2, which was immediately filled with water and its lid screwed on. In the top and bottom of the copper vessel, loops of copper wire were inserted, by means of which it could be suspended, without contact of the hand, in the centre of a cylindrical vessel of tin plate, fig. 3, having a detached cover above and below. The complete arrangement will be readily understood from an inspection of fig. 5. In the lids of the tin cylinder and copper vessel corresponding apertures existed, through which the bulb of a delicate thermometer could be introduced into the water in the interior of the latter. On withdrawing the thermometer the aperture in the copper vessel could be closed, in the course of two or three seconds without touching the vessel itself By this arrangement the copper vessel with its contents was suspended in a fixed position in the centre of, but not in contact with, an outer cylinder of tin plate, while at the same time the temperature of the water could be noted at any time without removing it from its situation. A larger cylindrical vessel, capable of being rapidly rotated round its shorter axis, completed the whole apparatus. It is shown in fig. 6. Missing Page xiv.] Metallic Compounds of Chlorine, etc. 95 10. "When an observation was made the copper vessel was suspended in the cylinder, the opening in its lid closed, and the apparatus placed in a horizontal position, and then cautiously agitated (lest the glass balls should break), till a perfectly uni- form temperature was established through the whole of the copper vessel and its contents. This being accomplished, the cylinder was again placed in the position represented in fig. 5, the temperature of the water carefully noted, and the cork replaced. It was then suddenly shaken, so as to rupture the glass balls within, and immediately afterwards secured in the interior of the larger cylinder, fig. 6, where the whole was rapidly rotated, for the space of five and a half minutes, from the time of observing the temperature. It was then removed, and the temperature of the water again observed. In the case of bromine and iodine, all that now remained to complete the experiment was to weigh the water in the copper vessel, but in the case of chlorine, the original volume of the gas had to be determined. For this purpose, the glass vessel was placed in a water-trough, and the cork withdrawn. From the quantity of water which rushed in, the bulk of the chlorine was easily estimated. It is almost unnecessary to add, that, in every instance, the whole of the chlorine had entered into combina- tion ; the small residue being atmospheric air, unavoidably introduced when the bulbs were inserted. 11. The accuracy of experiments of this kind greatly depends upon the heat which is gained or lost by the apparatus during the course of the experiment. In a vessel placed apart from other sources of heat, the losses and gains of heat will evidently be equal to one another for equal differences of temperature above and below that of the sorrounding air. But in the apparatus I have just described, from the proximity of the person of the observer, and the necessity of grasping the tin cylinder while placing it in, and removing it from, the rotating machine, this middle point is no longer the temperature of the air, but 1°'4 above that point. Direct experiments also showed that the water had nearly attained its maximum point in 45", from the time when the glass balls were ruptured, and 1 5" usually elapsed from the observation of the first temperature to the latter moment. We may, therefore, assume that the water is at the 96 On Heat Developed during Formation of [xiv. maximum temperature during 4|', and at the minimum during 1 5". If we put 6 for the excess of the final temperature above the air, e for the difference between the initial temperature and the same, and e and e' for the corrections to be applied for the cooling and heating of the apparatus, during periods of 4J' and 15" respectively, we shall have E=+(6-l°-4)x 0-049, e'= -(e+ 1°-4) X 0-003 + 0°-03. 12. The constant quantity 0°-03 is added to the correction for simple heating, as an allowance for the heat, transmitted by the hand through the apparatus, while rupturing the balls. The temperature of the water being generally so adjusted, that the mean poiijt between the initial and final temperatures was from half a degree to one degree above that of the air, the entire correction required was in all cases very small. 13. The value in water of the different parts of the apparatus was estimated with as much precision as possible. The specific heat of the copper and brass of the copper vessel was assumed to be 0-095, that of the glass of the glass vessel and balls was determined by a careful experiment to be 0-140. The leather, cork, and cement were found to be nearly equivalent to 1-1 gr. of water, and the specific heat of the solution formed in each experiment was also determined. 14. In the description of the experiments I have used the following abbreviations: Bar. — The height of the barometer. Th. air. — The temperature of the air. T\ — The initial temperature of the water in the copper vessel. T^ — The final temperature of the same. Inc. c. — The increment of temperature corrected for heating and cooling, according to the formulas given before. Aq. — The weight of the water in the copper vessel. Sn. — The weight of water equivalent to the solution of the compound formed. This is found by multiplying the absolute weight of the solution by its specific heat, which is also given. Vss. — The weight of water equivalent to the vessels and other solid substances used in each experiment. XIV.] Metallic Compounds of Chlorine, etc. 97 15. The temperatures are given in the degrees of Fahren- heit's scale ; the height of the barometer in English inches ; the volume of the chlorine in cubic centimetres ; and the weight of the water, etc. in grammes. The volume of the chlorine gas requires to be corrected for moisture, as well as for temperature and pressure, and I have assumed the weight of 100 cubic centimetres of the dry gas at 32°, and under a pressure of 2 9 '9 2 in. to he 0'317 grammes. COMPOUNDS OF ZIKC, 1 6. Zinc and chlorine, Zn + CI + Aq. Bar. Th. air T'. T'. Inc. c. Aq. Sn.(sp.heat076) 2-4 Vss. CI. Heat of comb. Mean heat referred to chlorine as unit, 2811°. Mean heat referred to zinc as unit, 3086°. The first number indicates the number of degrees through which a portion of water, equal in weight to the chlorine, would be raised by the heat extricated during the combination; the second, the corresponding number of degrees for a portion of water equal in weight to the zinc. 1 7. Zinc and bromine, Zn + Br + Aq. Th.air 63°-40 64°-10 68°-3 T'. - Cl°-30 62°-07 66°12 T^. - 66°-94 66°-91 7r-12 Inc. c. 5°-70 •l°-87 5°03 Aq. 152-8 gm. 155-0 gm. 158-4 gm. Sn. (sp. heat 0-62) 2-3 2-0 2-1 Vss. 19-4 19-4 19-4 29-47 in. 29-07 in. 29-97 in. 50°-70 48°-50 50°-80 47°-97 45°-22 49°-08 55°-20 52°-18 54°-14 7°-34 7°-03 5°-12 136-6 gm. 143-0 gm. 143-6 gm. ) 2-4 2-4 1-7 21-3 21-3 21-3 141-4 c.c. 141-0 c.c. 100-4 c.c. 2802° 2820° 2811° 98 On Heat Developed during Formation of [xiv. Br. 0-936 0806 0-847 Heat of comb. 1063° 1066° 1068° Mean heat referred to bromine as unit, 1066°. Mean heat referred to zinc as unit, 2586°. 18. Zinc and iodine, Zn + I + Aq. Th. air 64°-0 63°-80 ■38°-4 . T'. - 61°-08 60°-50 • ■36°-74 T'. 66°-72 67°-67 ■'42°=42 Inc. c. 5°-66 7°-24 6°-77 Aq. 159-5 gm. 161-lgm. 129-1 gm. Sn. (sp. heat 0-56) 3-8 4-9 3-2 Vss. 19-7 19-8 21-6 I. 2-372 3-084 2-000 Heat of comb. 436°-7 436°-2 444°-0 Mean heat referred to iodine as unit, 439°. Mean heat referred to zinc as unit, 1720°. 19. To ascertain in the preceding cases the heat due to the solution of the compound, portions of each, carefully dried, were introduced into the thin glass balls, and the weight accurately- ascertained, while the normal proportion of water for their solution was placed in the glass vessel. 20. Chloride of zinc and water, ZnCl + Aq. Th. air 36° -90 37°-20 T'. 35°-71 36°-05 T^. 39°-00 38°-72 Inc. c. 3°-29 2°-63 Aq. 1314 gm. 129-9 gm. Sn. (sp. heat 0-76) 10-6 8-4 Vss. 21-7 21-7 ZnCl 3-516 2-750 Heat of comb. 292° 292° Mean heat referred to chlorine as I init, 292°. Mean heat referred to zinc as unit. , 320°. 21. Bromide of zinc and water, ZnBr4- Aq. Th. air o4°00 55°-50 Ti. 53°-86 55°-35 XIV.] Metcdlio Compounds of Chlorine, etc. 99 T'. 56°-36 57°-41 Inc. c. 2°-51 2°-06 Aq. - 153-9 gm. 154-9 gm. Sn. (sp. heat 062) 9-1 7-7 Vss. - 19-4 19-4 ZnBr 5077 4-310 Heat of comb. 127° 122° Mean heat referred to bromine as unit, 124°-5. Mean heat referred to zinc as unit, 302°. 2. Iodide of zinc and water, Znl + Aq. Th. air 58°-60 59°10 38°-4 T'. 58°-02 59°-12 37°-58 T'. 59°-07 60°-21 40°-12 Inc. c. 1°02 1-06 2°-52 Aq. 1591 gm. 159-6 gm. 125-6 gm. Sn. (sp. heat 0-56) 4-8 5-0 10-7 Vss. 19-1 19-6 21-6 Znl 3o2 3-92 8-42 Heat of comb. 66°-5 62°-6 59'"3 Mean heat i-eferred to iodine as unit, 62° •8. Mean heat referred to zinc as unit, 246°. COMPOUNDS OF lEON. 23. Iron and chlorine, Fe^ + CI3 + Aq + Fe. Bai-. 30-07 in. 29-97 in. 29-08 Th. air 50°-50 50°-50 48°00 T'. 47°-47 47°-67 45°-78 T'. 53°-78 54°-08 51°-93 Inc. c. 6°-36 6°-47 6°-23 Aq. 133-8 gm. 143-9 gm. 143-9 gm Sn. (sp. heatO -74) 2-2 2-4 2-4 Vss. 21-1 21-3 21-4 CI. 131-7 c.c. 1415 ac. 1415 c.c. Heat of comb. - 2503° 2534'' 2505° Mean heat referred to chlorine as unit, 2514°. Jlean heat referred to iron in Fe, 1 as unit, 4921 100 On Heat Developed during Fwrnation of [xn-. 24. It must be carefully observed that the unit here taken is not the ^vhole of the iron dissolved, as in the case of zinc, but only two-thirds of it ; because the remaining third does not enter directly into combination with the chlorine, as has been already explained. 25. Iron and bromine, Fe^ + Brj + Aq + Fe. Th. air 64°10 49"-00 T'. 61'-81 47^-52 T^. 66°-89 53-55 Inc. c. 5-10 6°14 Aq. 155'3 gm. 147-4 gm. Sn. (sp. heat 60) 2-4 2-7 Vss, 19-4 19-4 Br. 0-994 1145 Heat of comb. 909° 909° jNIean heat referred to bromii 16 as unit, 909°. Mean heat referred to iron ir I Fca as unit, 3933°. 6. Iron and iodine, Fe. + Is + Aq + Fe. Th. air 63°-40 63°-20 38°10 T'. 61^04 60°-30 :i6°-32 T'. 6o°-99 65°-83 41-44 Ina e. 4'-97 5 55 o°-17 Aq. 157-7 gm. 162-1 gm. 12G1 gm, Sn. (sp. heat 0-54) 4-2 4-8 3-6 Vss. 19-6 19-5 21-6 I. 2-752 3151 2-360 Heat of comb. S27''-8 ; 528-3 331°-5 Mean heat referred to iodine as unit, 329-2. Mean heat referred to iron in Fe.> as unit, 2299°. 27. The object of the experiments detailed in the three following tables was to determine the heat evolved, when solutions of the sesquichloride, sesquibromide, and sesquiiodide of iron are converted into solutions of the protocompounds by agitation with an excess of iron. The sesquichloride of iron, obtained by the action of dry chlorine gas upon heated iron, was dissolved in water (the quantity being adjusted as usual) XIV.] Metallic Compounds of Chlorine, etc. 101 in the glass vessel, and an excess of iron filings was placed in one of the small balls. But I was obliged to have recourse to a different method in order to procure determinate quantities of the sesquibromide and sesquiiodide of iron in solution, from finding it impossible to obtain these compounds in the dry state. At first I attempted to add an excess of bromine or iodine to solutions of known strength of the protocompounds ; but, on endeavouring to expel the excess by heat, I found it difficult, even in the case of the sesquibromide of iron, to avoid the decomposition of the sesquicompound itself, when the solution was concentrated. The object in view was finally effected in a very complete and easy manner, by adding weighed quantities of bromine or iodine to solutions of the protobromide or protoiodide of iron, containing more than twice as much bromine or iodine, as the quantity added. The object of employing a larger proportion of the protosolutions than the bromine or iodine added would be capable of converting into the state of sesqui compounds, was to prevent the possibility of any free bromine or iodine being present ; and, as the results were the same, whether the excess of the protosolution was greater or less, it evidently in no way interfered with the success of the experiment. In reducing the results, we have therefore, to remember that the sesquicompound formed, con- tains three times the quantity of bromine or iodine added, designated in the tables by Br x 3 and I x 3. 2 8. Sesquichloride of iron and iron, FejClgAq + Fe. Th. air T'. T'. Inc. c. Aq. Sn. (sp. heat 0-73) 30 Vss. Fe.Cl, Heat of comb. Mean heat referred to chlorine in CI3 as unit, 40 2°' 5. Mean heat referred to iron in Fcj as unit, 788°. 61°-80 62°-50 43°-00 61°-85 61°-3o 41°-21 63°-34 64°-29 45°-4.5 r-46 2°-92 4°-25 132-8 gm. 144-3 gm. 151-4 gm. 30 6-8 10-4 21-8 21-4 19-9 0-8.56 1-895 2-900 406° 402° 402° 44° -40 46'70 47°-20 44°-46 46''-23 45°-77 46°-68 49°02 50°-84 2°-23 2°-81 5°-14 152-6 gm. 152-4 gm. 1521 gm. 6-3 7-3 12-9 19-6 19-6 19-6 2163 2-739 5-199 l84°-0 183°-9 182°-5 102 On Heat Developed during Formation of [xcv. 2 9. Sesquibromide of iron and iron, FegBrjAq + Fe. Th. air T'. T'. Inc. c. Aq. Sn. (sp. heat 0'60) Vas.- Brx3 Heat of comb. Mean heat referred to bromine in Brg as unit, 183° Mean heat referred to iron in Fej as unit, 794". 30. Sesquiiodide of iron and iron, FSgljAq+Fe. Th. air T'. - T. Inc. c. Aq.- Sn. (sp. heat 0-54) Vss. 1x3 Heat of comb. Mean heat referred to iodine in Ig as unit, 112°-1. Mean heat referred to iron in Fe.2 as unit, 783°. 31. To complete this part of the inquiry, it only remains to determine the heat evolved during the. solution of the ses- quichloride, sesquibromide, and sesquiiodide of iron in water. This I have been able to accomplish only in the case of the sesquichloride of iron, from having failed, as has been already remarked, in all my attempts to obtain the other two compounds in a dry state. Even a concentrated solution of the sesqui- bromide of iron allows bromine to escape during the process of evaporation. If the evaporation be carried to dryness, and the dry mass heated just to the point of fusion, a red substance remains, which is composed of one atom of the protobromide and one atom of the sesquibromide of iron (Fe4Br5). An approximation, however, may be made to the heat which would 47°-40 47°-00 51°-10 46°-41 46°-87 50°-15 49''-22 49°-24 54''-66 2° -80 2°-38 4'-58 151-2 gra. 150-5 gm. 146-8 gm. 1 9-1 6-8 17-7 200 19-9 19-8 4-497 3-741 7-596 L12°-3 112°-8 111°1 XIV.] Metallic Compounds of Chlorine, etc. 103 be developed during the solution of these compounds, by assum- ing that it will bear the same relation to the heat developed during the solution of the sesquichloride of iron, which has been already ascertained to exist in the case of the analogous compounds of zinc (20, 21, 22). 32. Sesquichloride of iron and water, Fe^Clj-J- Aq. Th, air - 60°-5 41°-4 T. - 60°-2 41°02 T'. - 61°-93 42°10 Inc. c. l°-68 l°-04 Aq. 132-8 gm. 120-4 gm. Sn. 2-7 1-6 Vss. 21-7 19-3 Fe.CIj 0-856 0-504 Heat of comb. - - 466° 441° Mean heat referred to chlorine in CI, as unit, 453°. Mean heat referred to iron in Fe, as unit, 887°. 33. On the principle just stated, we may infer, as a rude approximation, that the heat disengaged during the solution of the sesquibromide of iron would be (referred to the iron as unit) 837°; and that disengaged during the solution of the sesquiiodide, 682°. 34. If we now substitute the numerical values, obtained by the preceding experiments, for the known quantities in the equations given before, we shall obtain X = 3086° - 320° ± X (1 6, 20) a;' = 2586° - 302° ± x' (17, 21) x"= 1720°- 246° ±x" (18, 22) 2/ = 4921 ° - 887° - 788° ± t (23, 32, 28) y' = 3933° - 837° - 794° ± t' (25, 33, 29) y"= 2299° - 682° - 783° ± y" (26, 33, 30) From these equations we deduce X orZn + Cl = 2766° ±x x' or Zn + Br= 2284° + x' a;"orZn + I = 1474°±x" y orFe,+ Cl3= 3246° + t y' or Fe, + Brg = 2302° ± Y y" orFe.+ Ij = 834° +t" 10-t On Heat Developed duriivg Formation of [xiv. 35. It must be remembered that each of the letters x, X, etc. represents two unknown quantities ; first, the change of temperature due to the alteration of aggregation of the particles of the metallic elements, in passing from their ordinary form to that form in which they exist in the dry salt ; and, secondly, the change of temperature arising from the like alteration of aggregation of the particles of the electro-negative element. The actual value of these quantities cannot be determined by direct experiments, but it is probable that for the combinations of the same metal, the differences between x, x', and x", and between Y, Y*, and Y" will arise chiefly from the alterations of aggregation of the electro-negative, and not of the metallic element. Now, as the heat arising from the condensation of chlorine from the gaseous to what may perhaps be termed the saline solid state, must be far greater than that arising from the change of fluid bromine, or solid iodine, to the same state, it would be an object of great interest to determine the heat evolved or abstracted during the changes of these bodies from one physical condition to another, which would enable us to compare the heat of combination of each body in the same physical state. This I have only attempted yet to effect for the case of the solidification of bromine ; and, as the result of a very imperfect experiment, it may be stated, that the heat evolved during the passage of that substance from the fluid to the solid state, would be sufficient to raise an equal weight of water through 24°. This amount of heat is evidently far too small to account for the difierences observed in the values of x' and so'', and of y and y" ; from which it follows, that bromine and iodine, in the same physical state, evolve very different quantities of heat when combining with the metals. 36. On comparing the numbers deduced from the foregoing experiments (28, 29, 30) for the heat developed during the conversion of the sesqui-compounds of iron into the correspond- ing proto-compounds, by combining with half as much iron as they already contain, the very interestiag general principle results, that, referred to the combining iron as unit, the heat evolved in all these cases of combination is the same. In fact, we have Fe.CljAq-f-FerrTSS". Fe,Br3Aq-t-Fe=794°. FeJ, Aq-|-Fe=783°. XIV.] Metallic Compounds of Chlorine, etc. 105 The slight differences between these numbers are fuLy within the limits of the unavoidable errors of experiment, and leave no doubt of the truth of the principle just enunciated. 37. On a future occasion I hope to have an opportunity of describing a more extended series of experiments now in pro- gress, on the heat developed during the combination of other elements with chlorine, bromine, and iodine ; and, till that opportunity occurs, I shall reserve any further observations of a general character upon the preceding results. Meanwhile they may be thus recapitulated : 1. The heat developed during the combination of a given quantity of zinc with chlorine gas is sufficient to raise an equal weight of water through 2766°, while that evolved during the combination of the same metal with bromine, in the fluid state, is 2284° ; and with iodine, in the solid state, 1474°. 2. The heat developed during the combination of iron with chlorine, bromine, and iodine (which always takes place under the form FejClg, Fe^Brg, Fejg) is sufficient to raise an equal weight of water through 3246°, 2302°, and 834° respectively. 3. When solutions of the sesquichloride, sesquibromide, and sesquiiodide of iron become converted into proto-compounds by combining with iron, the heat evolved in all is the same for the same quantity of iron dissolved. 106 XV.— NOTICE OF SOME EECENT DETERMINATIONS OF THE HEAT DEVELOPED DUEING THE FORMATION OF CER- TAIN COMPOUNDS OF CHLORINE. From the Proceediiirjt of the Boyal Irish Academy, 1S43 : vol. 2, p. 404. The present results were obtained by a similar method to that described in the last volume of the Transactions of the Academy. The chlorine, however, was employed in the dry state, and the compounds being formed without the presence of water, the heat of combination was deduced from a single direct experi- ment. In the case of potassium, an important modification of the apparatus was required, which wiU be described when the full details of the experiments are communicated to the Academy. The numbers in the first column are the immediate results of experiments, and express, in degrees of Fahrenheit's scale, the heat produced during each reaction, in reference to the chlorine as unit, that is, the degrees through which a weight of water equal to that of the combining chlorine would be raised by the heat developed in the formation of each com- pound. The numbers in the second column express the same heat, referred to the combining metal as unit, and are deduced by calculation from the others. K-I-Cl Sn-t-Cl„ Sb„-f-Clg As.-fClg 5379° 5954' 1621° 1346' 1570° 1145' 1268° 898' 107 XVI.— ON THE THEEMAL CHANGES ACCOMPANYING BASIC SUBSTITUTIONS. From the Philosophical Transactions of the Boyal Society of London ; part 1, 1844, p. 21. In a communication made to the Eoyal Irish Academy, nearly three years ago, I described a series of experiments on the heat evolved during the mutual reaction of acids and bases upon one another, from which the general conclusion was deduced, that when the influence of all extraneous circumstances is eliminated, the heat is determined by the basic and not by the acid element of the combination. Nearly at the same time an important memoir was published by M. Hess on thermo-chemistry, in which an opposite result was arrived at, deduced however from a very limited number of experiments, and merely announced by its author, as a probable generalization, the accuracy of which could only be determined by further researches. The principle, as stated by M. Hess, is this, that different bases dis- engage the same quantity of heat in combining with the same acid.^ In the present state of chemical knowledge we cannot attempt the resolution of this problem by direct experiments on the anhydrous acids and bases, even if we adopt the hypo- thesis, no longer universally admitted by chemists, that the proxi- mate constituents of neutral salts are the ordinary acids and bases. Experiments performed with the concentrated acids are not adapted to yield simple results, since the mere circum- stance of dilution with water produces the evolution of large quantities of heat in the case of some acids, and none, or a very slight variation of temperature, in the case of others. It is for this reason that when an alkaline solution is neutralized by the addition of an equivalent of nitric acid, the heat disengaged is ' Poggendorflf's Amialen, Bd. 52, 107, or Phil. Mag. v. 20, p. 1. 108 On the Thermal Changes [xvi. very different, according to the state of concentration of the acid ; while the same circumstance produces little or no effect, when the tartaric acid is employed. If we institute a further comparison between the results, it will be found that while no simple relation exists between the temperatures obtained with different acids in a concentrated state, there is a very close approximation to an equal development of heat when the same base is neutralized by any dilute acid. In many apparently simple reactions it is difficult to ascer- tain with certainty all the combinations and decompositions which occur, and our thermal results become proportionally diiE- cult to interpret. Even to deduce the heat due to the combina- tion of an anhydrous acid and alkali from that evolved when their solutions are mixed together, is a question of very great difficulty, requiring the previous determination of many data, all of which are in few instances capable of being discovered by experiment. The liquids before mixture are, in fact, solu- tions of the acid and alkali in the state of hydrates, and as large quantities of heat were evolved during the formation of these hydrates, and generally also during their subsequent solu- tion, an equal absorption of heat will take place when these combinations are destroyed. A further allowance is also re- quired for the effect of the solution of the resulting compound. After making all these corrections it is doubtful whether the result finally obtained would not be a theoretical or imaginary number. If we adopt the view, now generally admitted by chemists, that the hydrated acids are in reality compounds of the pure acids with water performing the functions of a base, the heat produced when a dilute acid is neutralized by a base will arisi' from the latter displacing an equivalent of basic water,' and the general result, before referred to, may be thus expressed. " When the same base displaces water from any of its acid combinations, the heat disengaged is nearly the same." If for basic water we substitute any base, the law will receive a very general form as follows : — WJien one base displaces another from any of its neutral com- ^ Transactions of the Royai Irish Academy, v. 19, 247. XVI.] Accompanying Basic Substitutions. 10& binations, the heat evolved or abstracted is always the same, what- ever the acid element may he, provided the loses are the same. The following experiments were undertaken for the purpose of determining the accuracy of this principle. The base selected to displace others was the hydrate of potash, and it was always employed in a state of dilute solution. The strength of the solution was ascertained by neutralizing a determinate quantity with sulphuric acid of known strength. The required quantity was weighed in a thin brass vessel of a long cylindrical form, coated externally with copal varnish. The latter precaution effectually protected it from the action of all metallic solutions. The equivalent solution of the salt to be decomposed was contained in a thin glass jar, supported within a larger one, by means of a projecting rim. The whole was so adjusted that when the brass vessel with its contents was cautiously placed in the saline liquid it was sufficiently buoy- ant to float, and, at the same time, it extended through nearly the entire depth of the liquid. The weight of the two liquids taken together was 1000 grains, of which the saline solution formed about 700 grains. To bring the two liquids to the same temperature, a rapid rotatory motion was given to the inner vessel, by moving a light glass stirrer round in it. In the outer vessel a very delicate thermometer with a long cylin- drical bulb was suspended. As soon as a perfect equilibrium of temperature was established between the two fluids, the position of the thermometer was carefully observed. The edge of the brass vessel was then grasped with pincers, and its con- tents quickly added to the saline solution. The mixture was now rapidly stirred and the new position of the thermometer noted. The brass vessel was not again introduced into the liquid after the mixture had taken place. The heat evolved, except in a few instances, did not exceed '.}" ; and it was so arranged that the final temperature of the liquid was from 0°"3 to 1° higher than that of the surrounding air, according to the total amount of heat. When a diminution of temperature occurred the adjustments were accordingly modified.. » To this method of operating several objections will at once occur, but numerous trials have satisfied me that it gives very 110 On the Thermal Changes [xvi. accurate results when the variations of temperature are not considerable. The important condition of bringing the two liquids precisely to the same temperature in a short space of time is completely attained. The principal source of error is the heating or cooling of the alkaline solution during the moment of being transferred into the outer vessel, and, if the difference between the initial temperature of the fluid and that of the air had been considerable, this would have been a serious objection to the process. The difference in question rarely exceeded 2°. As a few drops of the alkaline solution remained adhering to the interior of the vessel, an excess of 3 grains was taken, which I found to be an exact allowance for the loss. A similar portion of the saline solution adhered to the outer surface of the brass vessel, but as both liquid and salt were carried off together, the error from this cause did not in any instance amount to more thaa a fraction of a hundredth of a degree. The exposure to the air of the caustic solution during the few minutes occupied in equalizing the temperatures induced no sensible error. The strength of the solution was such, that when a sulphate was employed, the entire fluid after mixture contained one per cent, of anhydrous sulphuric acid. Hence the required quantity of any salt was obtained by dividing its atomic weight by the atomic weight of sulphuric acid. The alkaline liquid con- tained from rro to o-Jrr of potash more than was sufficient to decompose the salt. The thermal value in water of the bulb of the thermometer employed was 6 grains ; that of the glass vessel and stirrer (the specific heat of the glass being 0'140) 68 grains ; making the entire value of the vessels 74 grains. The brass vessel being removed altogether after the temperatures were adjusted is of course not included. The corresponding value of the vessels in terms of the liquid obtained is 76 grains. The temperatures found are therefore corrected for the vessels by multiplying them by 1*076. Finally, a further correction is required for the specific heats of the solution* and precipitates obtained. But as the accurate determination of the specific heat of any substance requires great care and much time, I did not attempt to examine XVI.] Accompanying Basic Substitutions. Ill separately the specific heat of the product of every operation. I determined, however, very carefully the specific heats of the four principal solutions formed, and estimated the specific heats of the precipitated oxides (their weights taken in the anhydrous state) from the experiments of M. Eegnault. The liquids examined were solutions (of the normal strength) of the sulphate, nitrate, and acetate of potash, and of the chloride of potassium, and their specific heats were found to be respectively 0-973, 0-975, 0-971, and 0-97l.i I have collected the experimental results into separate tables. The first column of each table contains the name of the salt which was decomposed ; the second, its weight ; the third, the change of temperature found by experiment; the fourth, the same corrected for the vessels or referred to 1000 parts of the resulting mixture ; and the fifth, the same referred to 1000 parts of water. SALTS OF LIME. Salt. Weight. Found. Ref. to liquid. Ref. to water. CaO.NOj 20-6 -0-34 -6-37 -6-36 CaO.NOs 20-6 -0-32 -0-35 -0-34 CaO . SA . 6H0 32-7 -0-35 -0-38 -0-37 CaO.SA.6HO 32-7 -0-31 -0-34 -0-33 CaCl 13-9 -0-34 -0-37 -0-36 CaCl 13-9 -0-36 -0-39 -0-38 CaO . A . Aq 22-2 -0-35 -0-38 -0-37 CaO.A.Aq 22-2 -0-35 -0-38 -0-37 The nitrate was cautiously dried on a sand-bath ; in one experiment the solution was neutral; in the other, it had a slight alkaline reaction. The chloride was dried at a low red heat, but not fused. Its solution was distinctly alkaline, as this salt undergoes slight decomposition from the gentlest ignition. Of the acetate, dried in a warm atmosphere, 22-64 grains yielded 12-70 grains carbonate of lime, from which the required quantity, as given in the table, was calculated. ' See Note at the end. 112 On the Thei'Vial Glianges [XVI. The negative sign indicates that when potash displaces the base in these salts, a diminution of temperature takes place. The accordance of the results within the limits of the errors of experiment is perfect. SALTS OF MAGNESIA. The salts of magnesia are very imperfectly precipitated in the cold by caustic potash, and therefore the change of tem- perature indicated by the thermometer is only a part of that produced by the substitution of potash for magnesia. A depression of temperature occurred with these salts as with the preceding, amounting to between 0°"10 and 0°'15, in experiments made with the sulphate and chloride and an equivalent of potash. With a larger proportion of the latter, a greater depression of temperature occurred, but the substitu- tion appeared to be still incomplete. SALTS OF BARYTES AXD STEONTIA. In numerous experiments with the nitrates of barytes and strontia, and with- the chlorides of barium and strontium, no change of temperature occurred. The solutions were taken so dilute that a mere cloud appeared on mixture, consisting chiefly of a trace of carbonate. It is true that we have no positive proof that decomposition occurs unless stronger solutions are employed and a precipitate formed, but the comparative insolu- bility of these bases renders it very probable that in all cases substitution does take place. SALTS OF SODA. Salt. Weight. Found. NaO . NO5 21-4 + 0-14 NaO . NO5 21-4 + 0-13 NaO.SO3.lOHO 40-3 + 0-06 NaO.SO3.lOHO 40-3 + 0-07 NaCl 14-6 + 0-04 NaCl 14-6 + 0-05 NaO.CO^.lOHO 35-8 + 0-07 NaO.CO2.lOHO- 35-8 +0-05 XVI. ] A ccompanying Basic Substitutions. 113 SALTS OF AMMONIA. Salt. ■Weight. Found. Eef. to liquid. Kef. to water. AclH2O.SO3.HO- AdHjO . NO5 AdH^.Cl AdH2O.C2O3.HO AdHaO.CiHA-HO - 18-74 19-98 13-33 17-72 25-24 + 0-70 + 0-69 + 0-70 + 0-70 + 0-69 + 6-75 + 0-74 + 0-75 +0-75 + 0-74 + 0-73 + 0-72 + 0-73 + 0-73 + 0-72 These experiments repeated with another thermometer gave the following results, all corrections being made — sulphate, 0°-76 ; nitrate, 0°-77 ; muriate, 0°-76 ; oxalate, 0°-75 ; and tartrate, ,0°"76. These numbers agree perfectly with one another, but their average is 0°-03 higher than the above. Before examining the thermal relations of these salts, it is necessary to ascertain that their solutions are quite neutral, as the slightest excess of acid would altogether derange the results. I attempted to prepare a solution of the hydrocyanate of ammonia, by mixing together solutions containing an equivalent of hydrocyanic acid and an equivalent of ammonia. On decom- posing this liquid by potash, an elevation of temperature occurred in different trials of 0°-87 and 0°-90, which approxi- mates to the preceding results. The anomalies presented by the hydrocyanic acid in combining with the alkalies render this fact of some importance. The so-called neutral phosphate and arseniate of ammonia are salts anomalous in composition, and on theoretical grounds ought to differ in thermal properties from the other ammoniacal salts. If a second equivalent of ammonia (in dilute solution) be added to a solution of the ordinary neutral salts of ammonia, no change of temperature occurs ; but the same addition to the neutral phosphate produced an elevation of temperature of 0°-18. The latter salt, however, loses a part of its ammonia during evaporation with so much facility, preserving always its alkaline reaction, that I am not sure whether this is a property of the salt when of normal composition, or arose from its having lost a portion of its base before solution. When the same salt was decomposed by potash, the results were not uniform; in one experiment the heat amounted to 0°-98 ; in H 114 On the Thermal Changes [XVI. another, made with the same salt, after exposure for a very short time to a warm dry atmosphere, the heat was 1""60 ; and in a third, performed with a solution of the latter previously saturated with ammonia, the thermometer rose 1°'00. If we assume the heat produced during the decomposition of potash to he 0°-99, and subtract from this 0°-18, we shall have for the heat produced by the substitution of potash for ammonia 0°-81, which is nearly the same result as before. The thermal pro- perties of all the alkaline phosphates and arseniates are very compUcated, and will require further investigation. SALTS OF JIANGAXESE. Salt. Weight. Found. Eef. to Liquid. Eef. to "Water. MnO.SOs, MnO . SO3, Mna.Aq, MnCl.Aq, MnO . S . Aq, 18-9 18-9 24-9 249 30-7 -1-roo + 1-00 + 1-00 + 1-01 + 1-11 + 1-08 + 1-08 + 1-08 + 1-09 + 1-19 + 1-04 + 1-04 + 1-04 + 1-05 + 1-15 The composition of the chloride and succinate was determined by converting them into sulphates. 17"05 grains of the chloride gave 12 -9 4 grains of sulphate, and 11-24 grains of succinate gave 6'91 grains of the same, from which the above quantities were calculated. The succinate, it will be observed, produces a little more heat than the other salts. It is probable indeed that all these numbers are rather above the truth from the rapidity with which the precipitate absorbs oxygen. This produces a slight but distinct evolution of heat for some minutes after the precipitation takes place. PROTO-SALTS OF IRON. Salt. "Weight. Found. Eef. to Fluid. Eef. to "Water. FeO.SO3.7HO, FeCl . 4H0, FeC1.4H0, 34-6 24-6 24-6 + 1-52 + 1-57 + 1-53 + 1-64 + 1-69 + 1-65 + 1-58 + 1-63 + 1-59 The same observation applies to these results as to the preceding. xvt.] Accompanying Basic Substitutions. SALTS OF ZINC. 115 Salt. ■Weight. Found. Ref. to Liquid. Eef. to 'Water. ZnO.SOj, 20-06 + 1-73 + 1-86 + 1-79 . ZnO.SOj, 20-06 + 1-76 + 1-89 + 1-82 ZnO.NO5.Aq, 29-56 + 1-68 + 1-81 + 1-74 ZnO.NO5.Aq, 29-56 + 1-65 + 1-78 + 1-71 ZnO.NO5.Aq, 29-56 + 1-69 + 1-82 + 1-76 ZnCl, 16-87 + 1-65 + 1-78 + 1-71 ZnCl, 16-87 + 1-68 + 1-81 + 1-74 ZnCl, 16-87 + 1-67 + 1-80 + 1-73 ZnBr, 27-57 + 1-65 + 1-78 + 1-71 Znl,- 39-54 + 1-68 + 1-81 + 1-74 The sulphate was rendered anhydrous by cautious ignition. The nitrate was evaporated till it became a solid mass on cool- ing. 20*17 grains of the hydrated salt left 6-85 grains of the oxide on ignition. The chloride was cautiously fused and weighed in a covered crucible. The bromide and iodide were dried on a hot sand-bath, but not fused. The three latter compounds are slightly decomposed by the heat required to deprive them of all moisture. Hence the increments of heat obtained with them must be a little below the truth. All the above salts of zinc were precipitated by an exact equivalent of potash, and the precipitate thus formed was found to consist ■of the hydrated oxide. But when the acetate of zinc is treated in the same manner, the precipitate which falls is a subsalt. The supernatant liquid stiU contains a portion of the salt of zinc, and the addition of more potash produces a further precipitate. For this reason on precipitating an equivalent of this salt by an equivalent of potash, the thermometer rose only 1°-31. On attempting to effect a more complete decom- position by using a double equivalent of potash, the heat obtained was rather less ; but it is doubtful whether the additional quantity of alkali effected a more perfect substitu- tion, while the precipitate was, at the same time, to a great extent redissolved. This is an interesting example of an apparent exception to the law of equibasic heat arising from a •corresponding anomaly in the chemical reaction. 116 On the Thermal Changes [XVI. SALTS OF MEECUEY. The only salt of mercury adapted to these inquiries is the chloride. Half the usual equivalent of it (17"1 grains) and of the potash solution gave, in three experiments, 0°"90, 0°"86, and 0°'89, which, all corrections made and the final results doubled, correspond to 1°'89, 1°'81, and 1°'87. I have not been able to confirm this result by precipitating the oxide from any other salt. The bromide has too little solubility in cold water. The cyanuret is not decomposed by potash, and accordingly, no- heat is produced when their solutions are mixed. That the potash has not decomposed the salt is further proved by the circumstance, that on neutralizing it with an acid, the same increment of temperature occurred as if the alkali had been in a free state. The sulphate and nitrate are both decomposed when their solutions are diluted. It has, indeed, been lately asserted that a solution of the neutral nitrate may be obtained by precipitating the chloride with nitrate of silver. This is a mistake, as the usual decomposition occurs in this case. In fact, the solution of the supposed neutral nitrate, instead of the acid reaction of the cliloride from which it is formed, intensely reddens litmus paper. If a similar experiment be made with other metallic chlorides, capable of forming neutral nitrates, no perceptible change of reaction will be found to occur. These observations fully explain the anomalies which I formerly pointed out in the action of the dUute acids on the red oxide of mercury. SALTS OF LEAD. Salt. ■Weight. Found. Eef. to Liquid. Eef. to Water. PbO.NOs, 41-34 + 2-77 + 2-98 + 2-83 PbO.NOs, 41-34 + 2-77 + 2-98 + 2-83 4(PbO.NO,), 20-67 + 1-39 + 1-49 + 2-90 J(PbO.NO,), 20-67 + 1-37 + 1-47 + 2-86 4(PbO.A.3HO), 23-64 + 1-32 + 1-42 + 2-77 4{PbO.A.3HO), 23-64 + 1-33 + 1-43 + 2-80 In the last four experiments half quantities were taken, but the results are all reduced to the common standard in the XVI.] Accompanying Basic Substitutions. 117 fifth column. After the precipitate had subsided, the clear solution above was found to be highly alkaline, capable of precipitating freely the salts of lead, and containing at the same time a small quantity of lead in solution. These facts are well known, and prove that the preceding numbers represent only a part of the heat due to the substitution of potash for the oxide of lead. Their accordance shows that the salts of lead, when similarly treated with caustic potash, give equal quantities of heat. SALTS OF COPPER. Salt. Weight. Found. Ref . to Liquid. Ref. to Water. CuO.SOa, 19-90 + 2-86 + 3-08 + 2-97 CuO.SOj, 19-90 + 2-86 + 3-08 + 2-97 CuO.NO5.Aq, 30-53 + 2-86 + 3-08 + 2-97 CuO.NO5.Aq, 30-53 + 2-86 + 3-08 + 2-97 CuCl, 16-72 + 2-81 + 3-02 + 2-91 CuCl, 16-72 + 2-84 + 3 05 + 2-94 CuCl, 16-72 + 2-80 + 3-01 + 2-90 CuO. A.HO, - 24-87 + 3-08 + 3-30 + 3-18 CuO.A.HO, - 24-87 + 3-02 + 3-25 + 3-12 CuO . A . HO, - 24-87 + 3-06 + 3-29 + 3-16 The sulphate and chloride were weighed in the anhydrous state. The nitrate was taken in the state of moist crystals, and their composition determined by calcination, 8-73 grains yielding 2-83 grains oxide by calcination. The result with the acetate showing a small excess of heat, I endeavoured to discover whether it could be referred to some peculiarity in the precipitate, or in the composition of the salt. The precipitate obtained in the first experiment was collected and found to weigh 10-01 grains, or 1 per cent, more than the theoretical quantity, which, supposing an equal excess of caustic potash to have been present, could only have produced an error of 0°-03. Of the crystals employed in the last experiment, 9-40 grains being digested with nitric acid and afterwards calcined, yielded 3-74 grains oxide, which is exactly the theoretical result. It appears, therefore, that the acetate of copper, when decomposed by potash, produces about y-g- more heat than the other salts of copper. 118. On the Thermal Changes [xvi. SALTS OF SILVEE. The nitrate is the only salt of silver I have examined, and the experiment was performed in order to ascertain the position of the oxide of silver as a thermal base. The full equivalent 42"48 grains decomposed by potash, gave 3°'88, or referred to the resulting liquid 4°'17, or to water 3°"95. Two similar experiments with half an equivalent gave nearly similar results, viz., 3°*90 and 3°"94, all corrections being made and the final results doubled to bring them to the ordinary standard. SESQUISALTS OF IRON. The bases hitherto examined being all of the form MO, it was of importance to determine how far the same principle would apply to bases of the form MjOg. The sesquisalts of iron appeared to be the best adapted for experiment, but it is difficult to procure them in a neutral state. The most certain method of effecting this object, is to pass a current of chlorine gas to saturation through solutions of the protosalts, expelling afterwards the excess of chlorine by heat. In this way a solution of sesquichloride may be easily procured from the proto- chloride, and a mixture of sesquisulphate and sesquichloride from the protosulphate. But as the resulting sesquicompounds require one half more potash for decomposition than the proto- compounds from which they are derived, it was necessary, in order to preserve the usual quantity of potash, to take only two thirds of an equivalent of the latter. Accordingly 16 '40 crystallized protochloride of iron, converted into sesquichloride and decomposed by potash, gave, in different experiments, 3°*83, 3°'75 and 3°"74, which, all corrections made, correspond to 3°-97, 3°-89 and 3°-88. Of the crystallized protosulphate, 23'00 grains, treated in the same way, gave 4°'09, 4°"11 and 4°-12, corresponding to 4°-25, 4°-27 and 4°-28. These results, although not identical, present a sufficiently close approxima- tion, particularly when the uncertainty of the original composi- tion of the crystallized salts, and the difficulty of expelling without decomposition all the excess of chlorine, are considered. Another circumstance, whose influence it is difficult to appreciate, but which will tend to modify these results, is this, that the precipitate obtained always contains potash united by so strong XVI.] Accompanying Basic Substitutions. 119 an affinity to the hydrated sesquioxide that the action even of hot water produces only a partial separation. It is very probahle that this may occur to a different extent with different salts, and hence may be one source of variation in the thermal effects. On reviewing the foregoing results it will be observed, that while the effect of the substitution of potash for different bases produces thermal changes, varying from— 0°-34 to +4°'28, the greatest uniformity prevails in those obtained with the salts of each separate base. It is true that in some instances slight differences do manifest themselves, but these differences, I apprehend, are in general not greater than occur in the chemical reactions. It is of course essential to a perfect uniformity of result, that exact equivalents of the salt and base should be employed, and that a complete substitution should take place. But these conditions can rarely be fulfilled. It is important, however, to remark that with one or two excep- tions, the observed deviations are in the same direction which theory would indicate. The difficulty of obtaining most of the metallic salts in a perfectly neutral condition, and in a definite state of composition, is well known ; and in the case of deliquescent compounds, a separate analysis of the specimen can rarely be employed with advantage. The variable nature of the precipitate arising from imperfect substitutions is a fertile source of divergences in the results, and the tendency to this is further increased by the necessity of performing all the experiments without the application of external heat. The formation of a subsalt produces less heat than the precipitation of the hydrated oxide, for the obvious reason that in the former case an imperfect substitution takes place. A remarkable example of this has been already cited in the action of potash on the acetate of zinc, where a great deviation from the usual development of heat is distinctly shown to depend upon the precipitate beiug a subsalt. The same cause, no doubt, frequently interferes with the accuracy of the result in other cases, where only a small portion of subsalt is formed. In other examples, part of the original base still remains in solution, and in others again, portions of the substituting base are carried down along with the precipitate. When we take 120 On the Thermal Changes [xvi. into consideration all these sources of error, the numerous instances of perfect agreement with, as contrasted with the few examples of slight deviation from, the general law of the heat of substitution being equal for the same bases, appear to be sufficient fully to establish its accuracy. It may be hei-e observed that the accuracy of this principle will not be in any way affected whatever views may be adopted, as to the exact changes which occur when one base displaces another. Whether we consider the final result to arise from the simple substitution of one base into the position oceupied by another, or from a series of distinct chemical changes, each producing a certain thermal effect, the general facts now estab- lished will not be the less rigorously true. The separation of most of the bases in a solid form, will of course tend to produce heat, and as this will vary with different precipitates, the numbers for the insoluble bases cannot be exactly compared with one another. The amount of the latent heat due to precipitation is unknown, but it must be the same whenever the same precipitate is formed. The correction for this cause will, therefore, be a constant quantity for the salts of the same base, and if applied, could not affect the equality of the foregoing groups of numbers. It is important to observe, that, notwithstanding the heat due to the formation of the pre- cipitates, a diminution of temperature occurs when potash is substituted for lime or magnesia. On a first view this last fact appears to prove that potash is a less powerful thermal base than lime or magnesia, but a closer examination will show that it is at least premature to draw such a conclusion. It must be remembered that we are imperfectly acquainted with all the chemical changes which accompany the substitutions under consideration. We know that the substituting base existed in the state of a hydrate before mixture, and that after mixture the displaced base is also obtained in the same state. But we have no means of discovering with certainty in what state these bases exist in the solutions of their neutral combinations. If we assume that they exist in the state of hydrates, then the numbers given before will express exactly the heat arising from the chemical substitutions. But if we suppose that the potash separates XVI.] Accompanying Basic Substitutions. 121 from its combination with water, and the lime on the other hand unites with water during the course of the experiments, then these numbers will be the general result of a series of complicated changes. Other suppositions may be made, but we cannot prove the truth of any of them. One thing is certain, that whatever these unknown changes may be, they will be precisely similar when the bases employed are the same. Hence the foregoing experiments are sufficient to prove that with the same bases, the heat arising from basic substitutions is always the same, although the numbers may not express the entire change of temperature due to that cause. Among the circumstances which may perhaps be supposed to influence these results, are the changes of temperature arising from the solution of the saline compounds in water, — a subject recently investigated by Mr. Graham. But although it is true that a different salt remains in solution after substitution from that which was present before, yet it must be observed, that neither salt during the process assumes the solid state, and the changes of temperature in question are essentially dependent on that condition. For this reason, it appears to me that the thermal effects arising from solution are not in any way brought into action in the course of these experiments. The same general principle will be found to include nearly all the thermal results I formerly described, as arising from the action of bases and dilute acids upon one another, and upon solutions of neutral salts. In cases where the same base (as before mentioned) displaced water from any of its combinations with the acids, the heat evolved was nearly (but not exactly) the same. On the contrary, where no basic substitution occurred, there was either none, or a very slight variation of temperature. As examples of the latter, I may refer to the absence of any variation of temperature when solution's of a neutral salt and hydrated acid, capable of combining to form an acid or double salt,' are mixed. Mr. Graham has indeed lately made the observation, that the formation of certain acid sulphates is attended with a diminution of temperature, but the change of temperature so produced is of small amount compared with that arising from basic substitutions. It is difficult to prove that combination actually takes place when solutions 122 On the Thermal Changes [xvi. containing the proximate constituents of an acid or double salt are mixed. But, as far as I have investigated the subject, the thermal properties of the solutions thus formed are identical with those of solutions prepared by dissolving the crystallized acid or double salt in water. Thus, if we prepare solutions of crystallized binoxalate and quadroxalate of potash, and add to them exactly the quantity of potash required for neutralization, the usual heat due to the substitution of potash for water will be obtained. I have formerly shown that there is a definite evolution of heat when solutions of the common alkaline phosphates and arseniates are mixed with a solution containing an additional equivalent of base, while no change of temperature occurs when a solution of the pyrophosphate of soda is similarly treated. In the former case, it has been shown by Mr. Graham that an atom of basic water is displaced by an atom of alkali ; in the latter case, no basic water is present. In the preceding observations it has been assumed, that if the union of two substances be attended with the evolution of a certain definite quantity of heat, their separation will be attended with the absorption of the same quantity of heat. Although this proposition in the abstract is very probable, it requires to be demonstrated by direct experiment, and it is the more important to do so, as it will furnish, if true, a means of verifying the accuracy of our results. The reactions now described enable us to test it by experiment in one particular set of cases. In fact, if we take three bases, such as potash, oxide of copper, and water, capable of displacing one another in the above order, and if we measure the changes of temperature produced when the first and second, first and third, and second and third bases displace one another, then the change of tem- perature arising from the first substitution should be equal to the difference between the changes of temperature produced by the two latter. A few examples will illustrate this point. The numbers expressing the heat developed when the nitrate of water is decomposed by potash and lime are 6°-76 and 7''"20. The difference of these numbers is — 0°'44, indicating that a depression of temperature to that amount ought to take place when the former base is substituted for the latter. We have before seen that the result of the direct experiment is — 0°'37. XVI.] Accompanying Basic Substitutions. 12.3 In this and the following cases, the temperatures corrected only for the vessels are adopted, because I have not determined the specific heats of the metallic solutions. The error in the comparison from this circumstance is wholly insignificant. The heat produced in two experiments in which sulpha1;e of water was decomposed by potash was 7°'24 and 7°"22. The same compound decomposed by ammonia gave in different trials 6°-40, 6°-53 and 6°-51. The difference of the means of these numbers is + 0°'74. The direct experiment gave in one experiment + 0°-7 5, in another +0°"78. The corresponding number which expresses the substitution of oxide of zinc for water in the sulphate of water is 5°'40, and this taken from 7°"22 leaves 1°'82 for the heat due to the dis- placement of oxide of zinc by potash. The direct experiment gave l°-87. Two experiments were made to determine the heat arising from the substitution of oxide of copper for the base in the nitrate of water. In one of these experiments the hydrated oxide was taken ; in the other, the anhydrous oxide, obtained by precipitating a hot solution of the sulphate of copper by caustic potash. The results agreed closely with one another, being 3°'52 and 3°'53. Taking the mean of these numbers from 6°'76, we have 3°-23 to express the heat due to the substitu- tion of potash for oxide of copper. The result of the direct experiment was 3°'08. A similar comparison cannot be made with the salts of magnesia or lead, because an imperfect substitution takes place when their solutions are precipitated by potash. If we compare in like manner the other results contained in the paper before referred to, it will be found that the differences between theory and experiment rarely exceed 0°'3, — a close approximation when the defective method of investigation formerly employed, and the great difficulty of obtaining accurate results with the insoluble bases are considered. It may be remarked that there is no notable difference in the heat developed during the solution of the oxides of zinc and copper in the hydrous and anhydrous states, which makes it probable that the heat due to the combination of those bases with water is not considerable. 124 On the Thei^mal Changes [xvi. The preceding experiments appear to me to be sufficient to establish the accuracy of the general principle already stated, that when one base displaces another from any of its neutral combinations (all being taken in the state of dilute solution) the heat is always the same with the same bases, but in general different with different bases. The small deviations from this law in the case of the ordinary bases are not greater than we observe in other investigations connected with heat ; and I have before pointed out many circumstances which tend to account for some of these deviations. The results obtained during the decomposition of the salts of water present more remarkable anomalies, as I have formerly shown. Of these, the greater development of heat during the neutralization of the dilute sulphuric acid by alkaline solutions deserves particu- lar notice, and stiU remains unexplained. The anomalies pre- sented by the oxide of mercury and hydrocyanic acid, I have partly traced to their source. But the other results approxi- mate too closely to one another to leave any doubt that the same principle applies to the decomposition of the salts of water as well as to that of the salts of other bases. I have not succeeded in connecting the thermal develop- ments, as given by experiment, with any other property of the bases. In the following list I have arranged the bases hitherto examined in the order of the thermal results, attaching to each the number expressing the change of temperature produced when its salts are decomposed by potash. CaO, -0-36 ZnO, + 1-74 BaO, 0-00 HgO, + 1-86 SrO, 000 PbO, -|-2-82-f NaO, -I-0-08 CuO, + 300 AdH,0, -FO-74 AgO, -1-3-93 MnO, - + 1-07 Fep, -h4-09 FeO, -{-1-60 SUPPLEMENTARY NOTE ON THE DETERMINATION OF THE SPECIFIC HEATS OF FLUIDS. The accurate determination of the specific heats of fluids is of so much importance in all inquiries connected with the heat XVI.] Accompanying Basic Substitutions. 125 of combination, that I liave taken some pains to introduce greater simplicity and accuracy into the methods hitherto em- ployed for that purpose. The process I am about to describe is a modification of that adopted by M. Eegnault in his valu- able researches on the specific heats of simple and compound bodies, and I am also indebted to the same accurate philosopher for a knowledge of the most important precautions to be taken in inquiries of this kind. The general principle of the following method is to compare the increments of temperature produced by the cooling of a hot body in. water and in the fluid under examination. But instead of taking, as is usually done, a ball of heated metal, whose temperature at the moment of immersion cannot be known with absolute precision, I employed a thermometer with a very large reservoir, and so adjusted that the mercury does not appear in the stem till it is heated to nearly the boiling point of water. The cylindrical reservoir is about two inches long, and half an inch in diameter. A mark is placed on the stem corresponding to 201° Fahr., which point is situated about an inch and a half from the reservoir. This instrument is easily heated by means of a very simple apparatus till the mercury rises a little above the mark. The first step of the process is to determine accurately the thermal value of the reservoir with a small portion. of the stem adjacent to it in terms of water. For this purpose, a certain weight of water is placed in a cylindrical vessel of thin brass, which is suspended within a larger vessel of tin plate. A very delicate thermometer, with a long cylindrical bulb (capable of being read with ease to ts part of a degree) is suspended in the water, and the whole is so arranged that the initial tempera- ture of the fluid is about 5° below that 'of the surrounding air. The observer, previously agitating with a very light glass stirrer the water in the brass vessel, reads the temperature to an assistant, who notes it down and also marks the time. The former then removes the large thermometer from the heating ap- paratus (the disturbing influence of which is carefully prevented by a wooden screen), and, holding it at a suitable distance from the water, watches the descent of the mercury till it reaches the mark, when he instantly immerses it. The time of immersion 126 On the Thermal Changes [xvr. is again noted, and the whole is gently agitated for 3^^ minutes in the fluid. The temperature of the latter having now always attained a maximum, the new position of the thermometer is observed. The final temperature is never allowed to be more than 2° higher than the air. The corrections for the heating and cooling influence of the air are very small when all the above conditions are fulfilled. They must not, however, be neglected. The rate of heating for each degree of depression per minute was found to be 0°"01, and as from 12 to 20 seconds usually elapsed between the observation of the initial temperature and the immersion of the heated instrument, the correction for that period of the obser- vation was easily made. It was assumed that during the minute subsequent to the immersion, the heating and cooling processes counterbalanced one another ; and the correction for the last 2\ minutes was made on the hypothesis that the fluid during that period was at the final maximum. The rate of cooling was found to be about 0°'012 per minute, for each degree of excess, the fluid being kept in constant agitation. Knowing the weight of the water, the value in terms of water of the different parts of the apparatus, the temperature gained by the water and lost by the instrument, we possess all the data necessary to calculate the thermal value of the latter in terms of water. By repeating the same experiment with an equal bulk of the liquid whose specific heat is required, we obtain the thermal value of the same instrument in terms of the liquid. From these values the specific heat may be calculated. An equal bulk of the liquid is employed in order to have the instrument immersed in all cases to precisely the same depth, and, for a similar reason, it ought to be always introduced in a perpen- dicular direction into the fluid and maintained in the same position during the agitation. Before calculating the final result, it is necessary to obtain an approximate one, in order to find the thermal value of the brass vessel, etc., in terms of the liquid. In actual practice this is easily effected without in- volving any sensible error. If the specific heat of the liquid differ considerably from that of water, the correction for the heating and cooling influence of the air must also be modified. XVI.] Accompanying Basic Substitutions. 127 The weights of the different parts of the apparatus and their value in water are as follows : Mercury in bulb of thermometer by which the increment of temperature was measured, 300 gr.x 0-033, - 9-9 Glass in bulb and immersed portion of stem, 24 gr. X 0-14, - 3-3 Glass stirrer, 20 gr. x 0-14, - 2-8 Brass vessel, 420 gr. x 0'094, 39-5 Value of entire apparatus, 5 5 "5 The value of the apparatus in terms of the following solu- tions is 57'0 grains. If we now make — D. the difference between 201° and the iinal temperature of the liquid, or the heat lost by the instru- ment ; e. the excess of the final temperature above the air ; I. the increment of temperature observed ; Ic. the increment corrected ; F. the weight of the fluid ; Vss. the value of the apparatus in terms of the fluid ; X. the value of the instrument in terms of fluid. DISTILLED WATER. I. II. IIL IV. V. D. 132-0 131-7 132-8 132-5 132-8 e. VI 0-3 0-4 1-4 2-2 I. 6-38 6-45 6-46 6-40 6-40 Ic. 6-39 6-44 6-45 6-43 6-45 F. 1234-5 1234-5 1234-5 1234-5 1234-5 VSB. 55-5 55-5 55-5 55-5 55-5 X. 62-45 62-60 62-65 62-60 62-65 Mean value iu terms of water, 62-59. SOLUTION OF SULPHATE OF POTASH. (100 Parts contain 218 Salt.) I. II. III. D. 131-8 132-2 132-4 e. 1-3 1-1 1-0 I. 6-38 6-42 6-45 Ic. 6-41 6-43 6-46 F. 1264-5 1264-5 1264-5 Vss. 57-0 67-0 57-0 X. 64-27 64-28 64-48 Mean value in terms of solution, 64-34. Specific heat, 0-973 128 Thermal Changes in Basic Substitutions. SOLUTION OF NITRATE OF POTASH. (100 Parts contain 2-53 Salt.) I. II. III. D. 135-8 135-5 135-7 e. 11 1-4 1-0 I. 6-59 6-56 6-57 Ic. 6-60 6-59 6-58 F. 1264-5 1264-5 1264-5 VsP. 57-0 57-0 57-0 X. 64-23 64-27 64-08 Mean value in terms of solution, 64-19. Specific heat, 0-975. SOLUTION OF CHLORIDE OF POTASSIUM. (100 Parts contain 1-86 Salt.) II. III. IV. D. 132-8 132-4 132-3 132-4 e. 1-6 1-6 1-6 1-6 I. 6-45 6-43 6-42 6-43 Ic. 6-48 6-46 6-45 6-46 P. 1264-5 1264-5 1264-5 1264-5 Vss. 57-0 57-0 57-0 57-0 X. 64-48 64-48 64-43 64-48 [xvi. Mean value in terms of solution, 64-47 Specific heat, 0-971. SOLUTION OF ACETATE OF POTASH. (100 Parts contain 2-45 Salt.) I. n. III. D. 133-5 132-9 133-1 e. 1-8 2-1 1-8 I. - 6-46 6-44 6-46 Ic. 6-50 6-49 6-50 P. 1264-5 1264-5 1264-5 Vs.«. 57-0 57-0 57-0 X. 64-34 64-53 64-54 Mean value in terms of solution. 64-47. Specific heat, 0-971. 129 XVII.— NOTE ON THE lEISH SPECIES OF EOBERTSONIAN SAXIEBAGES. Beport of the British Association, Cambridge., 1845. The author having studied the Irish saxifrages and compared them with those of the Pyrenees, had come to a different con- clusion from Mr. Babington, and believed that there were only two true species in Ireland, the Saxifraga umbrosa and the S. Geum. The other species described by Mr. Babington in his " Manual " he regarded as varieties of one or other of these forms. 130 XVIII. — ON THE HEAT DISENGAGED DURING THE COMBINATION OF BODIES WITH OXYGEN AND CHLOEINE. From the Philosophical Magazine, 1848, I., p. 321. Extracted from a memoir communicated to the Academy of Sciences of Paris in March, 1845. I. COMBINATION OF OXYGEN WITH THE PERMANENT GASES. The determination of the c[uantity of heat, evolved during the combination of oxygen with hydrogen has occupied at different periods some of the most distinguished cultivators of chemical science, among whom we may cite the names of Crawford, Lavoisier, Dalton, Davy, and in more recent times, of Despretz and Dulong. The heat produced in other cases of gaseous combination has been made the subject of investigation by Dalton, Davy and Dulong ; but the methods employed by the two former were so defective as to render their results of comparatively little value. The experiments of Lavoisier were performed with his calori- meter, an instrument capable of yielding accurate results in certain cases, and when all due precautions are taken, but for obvious reasons now rarely, if ever, employed in investigations of this kind. Of the method employed by Despretz no detailed description, so far as I am aware, has been published. From the brief notice given by M. Cabart, we are made acquainted with the general form of apparatus employed by Dulong. It is evident from this description that Dulong's mode of operating must have been entirely different from that adopted in the present investigation. This circumstance should be kept in mind in comparing the results. In the following experiments, the mixtures of the gases, pre- pared in the same manner as for a common eudiometric experi- ment, were introduced into a copper vessel (Plate II., figs. ?> and 4), whose capacity was about 380 cubic centimetres. A vessel made of thin sheet copper will resist the force of AiudTgws' Papers Platell. xvm.] Heat Disengaged during Gomhination, etc. 131 the explosion of this quantity of even a mixture of defiant gas and oxygen. It was closed by a screw as shown in the figure, the head of which is perforated with a conical aperture (the apex towards the outside) to admit a very tightly-fitting cork. Through this cork a silver wire a a passes, and another h, is soldered to the side of the screw; these wires, as shown in the figure, are connected by a very fine platina wire. When the vessel is closed (fig. 3), the first silver wire is brought into contact with a narrow band of copper c c, which surrounds the upper edge of the vessel, but is at the same time insulated from it. The vessel containing the mixed gases, and adjusted in the manner described, was introduced into another of larger capacity, which was then filled with water at the proper tem- perature. The latter was suspended in a cylinder having a moveable cover at both ends, and the whole was finally intro- duced into an outer vessel, also of a cylindrical shape, and which was capable of being rapidly rotated round its shorter axis. The whole arrangement will be understood by inspecting fig. 5, in which the several parts of the apparatus are represented. Before observing the initial temperature, the apparatus was rotated for some time in order to establish a complete uniformity of temperature through all its parts. The apparatus being fixed in the position shown in fig. 5, the thermometer was next introduced through the apertures shown in the lids, and the temperature observed. On the removal of the thermometer, the exterior of the apparatus was brought into contact with one pole of a voltaic battery, while the other pole was passed through the water till it came into contact either with the central silver wire, or with the copper band (c c, fig. 3). The position of the wires at this period of the experiment is shown in fig. 5. By this arrangement the circuit was completed through the fine platina wire, which, becoming instantly ignited, caused the mixture to explode. The orifice of the calorimeter was then quickly closed with a good cork, the lid of the outer vessel shut down, and the whole rotated for thirty-five seconds, in which short space of time the heat produced by the combination was found to be uniformly distributed through the apparatus. 132 Heat Disengaged during Combination of [xvm. This rapid distribution of the heat was greatly facilitated by the presence of a small quantity of water in the inner vessel. The thermometer, previously brought as nearly as possible to the expected temperature of the liquid, was again introduced, and the increment of heat observed. The duration of the experiment was so short, that scarcely any correction for the cooling and heating influence of the air was required. The temperature of the air was in general a little above the mean between the initial and final temperatures of the apparatus : the heat, however, was given out so rapidly, that the latter must have been nearly at the final temperature during the greater part of the time. After each experiment, the apparatus was again rotated for a period of thirty-five seconds, and the loss of heat from cooling observed. I have assumed one half of this loss to be the required correction, except in the case of olefiant gas, when the initial tempera- ture was a little lower than usual. The correction so applied, it will be seen, never exceeded 0°-005 C. The thermal values of the different parts of the apparatus in terms of water were as follows :— Copper ] 70 grms. x 0'095, 16-1 5 Brass 111 „ x 0-094, 10-43 Solder 15 „ x 0-043, 0-64 Leather, cork, etc. 048 Thermal value, 27-70 The amount of water was always determined by weighing the apparatus with its contents after each experiment, and deducting the weight of the same when dry. HYDEOGEN AND OXYGEN. The hydrogen gas was purified, according to the method of M. Dumas, by passing it through a series of tubes in which it was successively exposed to solutions of the acetate of lead, sulphate of silver, and hydrate of potash. It was afterwards collected over water in a graduated vessel. In this way it became contaminated with a small quantity of atmospheric air, the amount of which it was necessary to ascertain with precision. This was effected by an independent experiment, in which the XVIII.] Bodies with Oxygen and Chlorine. 133 gas was collected in exactly the same manner. In the case of- other gases, the true volume was inferred from the diminution which occurred after the explosion. The difficulty of obtaining accurate results in experiments upon gases collected over water (which for obvious reasons could not be avoided in this inquiry) is so well known to chemists, that I deem it unnecessary to dwell upon this point. I have endeavoured in every case to determine by experiment, and to apply the necessary corrections for absorption, etc., but at the same time I have always given the results immediately obtained by observation. In the following table, H represents the volume of the hydro- gen gas in cubic centimetres as obtained by observation ; He, the same corrected for admixture of air, absorption by water, etc.; B, the height of the barometer in English inches reduced to 0° C; T, the temperature of the hydrogen gas in centigrade degrees ; E, the excess of -the final temperature of the water in the calorimeter above the air ; I, the increment of temperature found ; Ic, the same corrected ; W, the weight of the water in the calorimeter expressed in grammes ; and V the thermal value of the vessels. 2. 222-9 CO. 226-7 C.C. 30-16 in. 19°-8 0°-9 2^-063 2°-068 278-7 grms. 27-7 grms. Hence we have for the heat evolved during the combination of one litre of dry hydrogen gas measured at 0° C, and under a pressure of 29-92 in. (0-76 m.) with oxygen,- — 1. 2. 3. 4. 3025 3043 3052 3025 Taking the mean of these numbers, we deduce for the heat produced during the combination of — One litre hydrogen with oxygen 3036 One litre oxygen with hydrogen 6072 One gramme oxygen with hydrogen 4226 One gramme hydrogen with oxygen 33808 1. H 229-3 c.c. He 226-8 c.c. B 30-17 in. T 19°-7 E 0°-9 I 2° -074 Ic 2° -079 W 275-7 grms. V 27-7 grms. 3. 4. 229-1 C.C. 229-5 C.C. 226-6 C.C. 227-0 C.C. 3004 in. 29-97 in. 19° -3 20°-0 0°-8 0°-9 2°-071 2''-074 2° -075 2°-079 277-9 grms. 273-4 grms. 27-7 grms. 27-7 grms. 134 Heat Disengaged during Combination of [xvm. The unit to which these numbers are referred is the same as that adopted by Dulong, viz. the amount of heat required to raise, through one degree centigrade, one gramme of water taken at the temperature at which the experiment is performed. The above results fully confirm the accuracy of Dulong's experiments, the mean of which gives 3107 units for the heat produced by the combustion of one litre of hydrogen gas. The heat obtained in the union of oxygen and hydrogen arises from two distinct causes ; one the chemical combination, the other the condensation of the vapour formed by the combination. The latter is an accidental complication, which would not have interfered with the result if the experiment had been performed at a temperature superior to 100° C. If we assume the latent heat of steam at 20° to be 611 units, the heat evolved by the condensation of 1'125 grm. steam will be 687, which, taken from 4226, leaves 3539 for the true heat due to the chemical combination of 1 grm. oxygen with hydrogen ; and a similar correction may be applied to the other numbers. CARBONIC OXIDE AND OXYGEN. The carbonic oxide was prepared by the action of sulphuric acid on oxalic acid, the carbonic acid formed during the process being absorbed by a solution of caustic potash. To ensure complete combustion, an excess of oxygen was always employed. The residual gas, after being deprived of its carbonic acid, was measured, and the original volume of carbonic oxide was deduced from the reduction of volume of the mixture after combustion. As before, I have endeavoured to correct the volumes actually found for the errors inevitable to eudiometric experiments performed over water. A small allowance was also made for the air extracted from the water (about 20 grms.), which was always left in the inner vessel. In the subsequent tables, M designates in cubic centimetres the volume of the gaseous mixture before combustion ; Mc, the same corrected for absorption by water during the transference from one vessel into another, etc.; E the volume of the residue (consisting chiefly of the excess of oxygen) after combustion and removal of the carbonic acid ; Ec, the same corrected. The other letters have the significations already explained. M 1. 362-2 C.C. Mc 361-3 C.C. R 24-2 C.C. Ec 24-3 CO. B 30-09 in. T 15° -7 E i°-o I 2°-148 Ic 2°-153 W V 270-7 grms. 27-9 grms. 3. 362-0 C.C. 4. 361-8 C.C. 361-1 C.C. 360-9 c.e. 23-3 CO. 23-9 CO. 23-4 C.C. 24-0 C.C. 30-08 in. 30-04 in. 15°-5 15''-7 0°-9 l°-0 2°-151 2°-167 2°-156 2°-172 271-0 grms. 27-7 grms. 266-6 grms. 27-7 grms. XVIII.] Bodies with Oxygen and Chlorine. 135 2. 362-5 O.C. 361-6 CO. 24-2 0.0. 24-3 cc 30-09 in. 15°-8 0°-9 2°-132 2°-137 272-0 grms. 27-9 grms. The heat evolved during the eombustion of one litre of dry carbonic oxide gas, measured at 0° and under a pressure of 29-92 inches, is therefore — 1. 2. 3. 4. 3063 3053 3060 3051 Hence we have for the heat evolved during the combination of— One litre carbonic oxide with oxygen 3057 One litre oxygen with carbonic oxide 6114 One gramme oxygen with carbonic oxide 4255 One gramme carbonic oxide with oxygen 2431 The mean of Dulong's experiments is 3130 for the com- bustion of one litre of carbonic oxide. ' MAESH GAS AND OXYGEN. The marsh gas was obtained from a stagnant pool. It contained an unusually large proportion of nitrogen. A large excess of oxygen was employed to burn it. M- 360-2 cc 359-0 cc 360-0 cc Mc- 359-3 cc. 358-1 cc 359-1 CO. E 105-0 cc 108-5 ex. 125-2 CO. Ee 105-8 c,c 109-4 cc. 126-1 cc B 30-10 in. 30-10 in. 30-10 in. T 15°-8 15°-7 14°-1 E i°-o r-0 l°-0 I 2°-504 2°-457 2°-3l7 Ic 2°-509 2°-462 2°-322 W -268-1 grms. V 28-1 grms. 1. 9413 268-7 grms. -28-1 grms. 2. 9431 268-7 grms. 28-1 grms. 3. 9420 136 Heat Disengaged during Combination of [xvm. We have, therefore, for the heat evolved during the combina- tion of — One litre marsh gas with oxygen 9420 One litre oxygen with marsh gas 4716 One gramme oxygen with marsh gas 3277 One gramme marsh gas with oxygen 13108 A single experiment with the gas prepared artiiiciaUy from the acetate of potash, gave 9171 units for the heat produced by the combustion of one litre. The gas however was not free from empyreumatic odour. If we apply a similar correction for the heat produced by the condensation of the vapour of water to that employed before in the case of the combustion of hydrogen, we shall obtain for the true heat due to the combination of one gramme of oxygen with marsh gas 2931 units. OLEFIANT GAS AND OXYGEN. The olefiant gas, prepared and purified by the usual processes, was still found to contain 6-4 vols, of carbonic oxide in every 100 vols., in accordance with the observation first made by Dr. J. Davy. It is necessary, in reducing the results, to take into account the heat produced by the combustion of this portion of carbonic oxide. In order to insure the complete combustion of the gas, and at the same time to diminish the force of the explosion, nearly four and a half volumes of oxygen were taken for every volume of olefiant gas. M 364-8 c.c. 364-0 C.C. 364-2 c.c. Mc 363-9 C.C. 363-1 C.C. 363-9 C.C. R 110-3 C.C. 106-4 C.C. 110-4 CO. Ec 111-2 C.C. 107-3 C.C. 111-3 CO. B 30-15 in. 30-23 in. 30-23 in. T 13°-6 13° -3 13°-7 E 0°-8 l°-0 l^-O I 3° -015 3° -163 3°-033 Ic 3° -01 7 3°-166 3° -036 W V 265-3 grms. 28-] grms. 1. 255-7 grms. 28-1 grms. 2. 264-2 grms. 28-1 grms. 3. 15056 14979 15012 xviii.] Bodies with Oxygen and Chlorine. 137 Hence we obtain for the heat evolved during the combina- tion of — One litre olefiant gas with oxygen 15016 One litre oxygen with olefiant gas 5005 One gramme oxygen with olefiant gas 3483 One gramme olefiant gas with oxygen 11942 The experiments of Dulong vary from 15051 to 15576 for one litre of olefiant gas. Corrected for the heat produced by the condensation of the vapour of water, the number 3483 given above becomes re- duced to 3252, and the other numbers in the same proportion. II. COMBINATION OF OXYGEN WITH SOLID AND FLUID BODIES. A considerable modification of the apparatus was required for the determination of the heat produced during the combina- tion of solid and liquid substances with oxygen. The slowness of the combustion in most cases made it necessary to operate upon a larger scale; and as the apparatus could no longer be inverted, it was also necessary to distribute the heat by a different method. Fig. 1 exhibits the general form of the apparatus. The combination took place in a copper vessel of about four litres capacity. The combustible was placed in a platina cup, shown in fig. 2, which is suspended from the lid of the copper vessel by means of platina wires. A fourth wire, also of platina, but insulated by being surrounded by a glass tube, descends through an opening in the lid, and is connected below with the platina cup through the medium of a very fine platina wire, and above with a circular disc of copper, which is seen detached in fig. 2, and in its proper position in fig. 1. Before the commencement of an experiment, this disc was firmly fixed to the lid of the copper vessel, but it was also carefully insulated from it. Thus by bringing the disc and any other part of the copper vessel into contact with the opposite poles of a voltaic battery, the fine platina wire could be instantly ignited. In performing an experiment, the copper vessel was first filled with pure oxygen gas, the lid carrying the platina cup, etc. then introduced into its place, the copper disc attached to 138 Heat Disengaged during Combination of [xvm. the lid, and its metallic connexion with the insulated wire c carefully secured. The whole was next placed in the calori- meter, which contained the proper quantity of water previously cooled to the required temperature, and weighed. The inner vessel was secured in its place by the vertical rod a a. The calorimeter was covered with a lid containing apertures for the vertical rod and the thermometer, and the whole was surrounded by an outer vessel of tin plate to prevent the effects of radia- tion. The details of the arrangement will be obvious from an inspection of iig. 1. By means of the horizontal arm cc, the inner vessel could be agitated through the water in the calori- meter. A pin shown at h restrained the motion of the vertical rod within such limits that the inner vessel was never permitted to rise during the agitation above the surface of the water in the calorimeter. Upon the sides and bottom of the inner vessel small hollow knobs were placed, which maintained at all times a certain distance between the two vessels. Previous to the commencement of an experiment, the inner vessel was gently moved up and down till every part of the apparatus had acquired the same temperature. The ignition was effected by a similar method to that already described in the previous section, by bringing the vertical rod and the copper disc respectively into contact with the terminal wires of a gal- vanic arrangement. The same aperture in the lid served for the introduction of the thermometer and afterwards of the galvanic wire. After the combination had begun, the inner vessel was gently moved up and down within the calorimeter for a sufficient period of time to allow, not only the combustion to be completed, but the heat thereby produced to be uniformly distributed through the whole of the apparatus. In every experiment, after the observation of the iinal temperature, th$ agitation was again repeated during two minutes, in order to ascertain positively that the whole of the heat had been ob- tained. The longer period of time occupied in these experiments rendered the corrections for the cooling and heating influence of the air of more importance than in the former observations. To determine with absolute accuracy the value of these correc- tions, under the varying circumstances of each experiment. XVIII.] Bodies with Oxygen and Chlorine. 139 would have been extremely difficult. It has therefore been my endeavour so to arrange the experiments, that the amount of correction to be applied in each case may be very small; so small, indeed, that the application of an im- perfect approximation may be practically sufficient. From the effects of friction, the proximity of the person of the observer and other causes, the rate of heating was always greater than the rate of cooling for equal differences between the tempera- ture of the air and of the apparatus; and for the same reasons, the latter was found to maintain a stationary temperature only when the thermometer in it indicated a temperature about 0°'3 C. higher than that of the surrounding air. If we repre- sent by a the difference between the temperature of the air and of the apparatus, the correction V for the gain or loss of heat sustained by the apparatus during m minutes, will be expressed by the formula, V=+m(a + 0°-3)0°-0025. The values of V given by this expression agree within the ranges of temperature which occurred in these experiments, very closely with the direct results of observation. The usual time which elapsed between the observation of the initial and final temperatures was sixteen minutes ; and in such cases it was assumed that the apparatus was at the minimum temperature during one and a half minute, at the maximum during eight minutes, and during the intermediate period at the temperature of the air. In other cases, where the combination took place more quickly, the corrections were made on the assumption that the apparatus was at the minimum point during one minute, and at the maximum during one half of the whole time occupied by the experiment. CAEBON AND OXYGEN. The carbon was employed in the form of wood-charcoal. It was purified by the method of M. Dumas from aU oxidable matters; first by ebullition in strong nitro-muriatic acid, and afterwards by exposure for several hours at a strong red heat to the action of dry chlorine gas. To expel all volatile com- pounds, it was finally exposed to a strong white heat under a 140 Heat Disengaged during Combination of [xvm. layer of charcoal. The earthy impurities, together with a cer- tain portion of carbon (which, notwithstanding the great excess of oxygen, always escaped combustion) remained in the platina dish after each experiment. By deducting the weight of this residue from that of the carbon originally taken, the weight of the carbon consumed was immediately obtained. To obtain with accuracy the weight of the charcoal, it was introduced in the state of fine powder into the platina cup already referred to ; and after being heated nearly to ignition, the latter was enclosed in a copper box, which, when covered by its lid, com- municated with the external air only by a very small aperture. The whole was then allowed to cool in vacuo over sulphuric acid; and when cold, a stream of dry air was admitted into the receiver. The aperture in the lid being now closed, the weight of the entire was determined. To obtain complete combustion, a very large excess of oxygen was employed ; but even with this precaution, carbonic oxide was discovered in the residual gas in several of the following experiments. In the subsequent tables, M designates the weight of the substance burned ; T, the temperature of the air, and the other letters the same quantities as before. 1. 2. 3. 4. M 1-088 grm. 1-177 gnn. 0-980 grm. 0-957 grra. T 10°-6 10°-4 9°-6 10°-3 E 0°-3 0°-5 0°-7 0°-5 I 2°-473 2°-648 2°-238 2°-194 Ic 2°-464 2°-644 2°-239 2°-191 W 3183 grms. 3214 grms. 3176 grms. 3193 grms. V 180 grms. 180 grms. 180 grms. 180 grms. 3. 6. 1. 8. M 0-974 grm. 0-550 grm 0-540 grm. 0-626 grm. T 10°-0 9°-8 9°-0 9°-0 E 0°-5 0°-9 0°-3 0°-8 I- 2°-153 l°-438 l°-430 l°-627 lo 2°-150 l°-447 l°-425 l°-633 W 3229 grms. 2768 grms. 2728 grms. 2723 grms. V 180 grms. 174 grms. 174 grms. 174grms. 1. 2. 3. 4. 5. 6. 7. 8. 7616 7624 7667 7722 7825 7760 7658 7557 xviii.] Bodies with Oxygen and Chlorine. 141 We have, therefore, for the heat evolved during the combin- ation of — ■ One gramme carbon witli oxygen 7678 One gramme oxygen with carbon 2879 One litre oxygen with carbon 4137 These numbers cannot be considered perfectly accurate, but are probably a little below the truth, in consequence of the formation of the small quantity of carbonic oxide to which reference has already been made. The results of M. Dulong differ from one another still more than the preceding ; no doubt from the operation of the same cause, namely the formation of variable quantities of carbonic oxide. His numbers for one litre of oxygen consumed vary from 3770 to 4004 units, the mean result indicating 7288 units for the heat produced during the combustion of one gramme of carbon. The number given by Despretz for the same is 7912 units. The ancient experiments of Lavoisier present a remarkable coincidence with the results now obtained; and considering the form of apparatus employed, and the infant state of the science at the time they were performed, are deserving of special reference, as furnish- ing a singular example of the accuracy and ability by which so many of the works of that eminent philosopher are distin- guished. He found that 1 lb. of carbon in burning melted 9 6 '5 lbs. of ice, which corresponds to 7624 units. In de- ducing the latter number, the latent heat of water has been taken to be 79° in accordance with the experiments of Provost- aye and Desains. The results of Crawford and Dalton on the heat evolved during the combustion of charcoal are altogether erroneous.''- ^ Since the above was written, tlie results of an extended inquiry into the same subject have been communicated to the French Academy by MM. Fabre and Silbermann {Comptes Sendus, xx. 1565, and xxi. 944). They find that the development of heat is considerably affected by the physical state in which the carbon exists before combustion. Thus the mean quantity of heat disengaged, according to their experiments, by the diamond, amounts to 7824 units, by natural graphite to 7796, by artificial graphite to 7760, and by wood-charcoal to 8080 units. In these experiments, the quantity of carbonic oxide formed during each combustion was determined, and the result obtained by direct experiment was corrected accordingly. Considering the great importance of the subject, I have long intended to resume the inquiry, and have indeed already obtaiaed some new results, but they are still in a very imperfect state. From a rude estimate of the quantity of carbonic oxide which was formed in 142 Heat Disengaged during Combination of [xviii. SULPHUR AND OXYGEN. The sulphur was employed in the state of flowers of sulphur deprived of the acid with which they are always contaminated by washing. A small quantity of earthy residuum remained, the weight of which was determined at the end of each experiment, and deducted from the original weight of the sulphur. During the combustion, a small quantity of sulphuric acid (corresponding to about 3 per cent, of the sulphur) was formed, for which reason the experimental results must indicate a little more than the true quantity of heat due to the conversion of sulphur into sulphurous acid. The heat in these experiments was given out in the course of eight minutes. M T 1. 3-087 grms. 10°-4 2. 3-089 grms. 12°-8 3. 3-240 grms. 8°.0 4. 3-114 grms. 8°-7 B l°-0 l°-0 l°-5 0°-9 I 2°-510 2°-436 2°-467 2°-461 le 2°-512 2°-438 2°-476 2°-462 W V 2699 grms. 175 grms. 1. 2338 2739 grms. 175 grms. 2. 2300 2818 grms. 175 grins. 3. 2287 2737 grms. 175 grms. 4. 2302 the experiments described in the text, I inferred at the time that the true quantity of heat disengaged during the conversion of carbon into carbonic acid amounts to about 7900 units, or nearly the number already obtained by Despretz. On repeating these experiments, I found that if the charcoal be sus- pended in a cage formed of fine platiua wire instead of being placed in a cup, the combustion proceeds with such vivacity that not more tnan -j^-j part of the carbon is converted into carbonic oxide. In a single experiment per- formed in this way with wood-charcoal {not however perfectly purified), I obtained 7860 units of heat, which, corrected for the carbonic oxide formed, would correspond to 7881 units, as expressing the entire heat produced by the conversion of carbon into carbonic acid. This nearly agrees with the experi- ments of ITabre and Silbermann on the combustion of the diamond and graphite, but differs from their experiments with wood-charcoal itself. Further re- searches are required to settle this difficult question. At present I will only venture to direct attention to the apparently anomalous circumstance in Fabre and Silbermann's results, that while wood-charcoal extricates so much more heat in combining \vith oxygen than graphite or the diamond, the two latter yield very nearly the same quantity of heat. The analogy of the specific heats of these three forms of carbon is at variance with such a result, as will im- mediately appear from the following comparison : — Specific Heat (Regnault), Diamond, 0-147 Graphite, - 0-201 Wood-ohareoal, - - 0'242 Thus, while wood-charcoal has both a higher specific heat, and gives more heat of combination than graphite, the latter, with a higher specific heat, pro- duces less heat of combination than the diamond. Heat of Combination (Fabre and Silbermann). 7824 7778 8080 xvm.] Bodies with Oxygen and Chlorine. 143 We have, therefore, for the heat evolved during the combination of — One gramme sulphur vs^ith oxygen 2307 One gramme oxygen with sulphur 2307 One litre oxygen with sulphur 3315 Dulong's experiments indicate from 2452 to 2719 units of heat for each gramme of sulphur burned. ALCOHOL AND OXYGEN. The alcohol employed was perfectly pure. Its density at 15° was 0-7959, and it was always redistilled from a large excess of pure lime immediately before being used. The principal difficulty in examining the heat produced by the combustion of this substance, was to complete all the pre- liminary arrangements after its introduction into the oxygen gas so as to ignite it before any appreciable quantity had evaporated. The shortest time in which I was able to accompUsh this was seven minutes ; but there can be little doubt that any portion of alcohol which might rise into the state of vapour during this time would become ignited along with the rest. The duration of each experiment was iive minutes. 2. 3. 4. 0-890 grm. 0-943 grm. 0-962 grm. 10°-1 9°-8 9°-5 O"-? l°-2 l°-0 2°-040 2°-204 2°-288 2°-039 2°-206 2°-289 2773 grms. 2742 grms. 2745 grms. 174 grms. 174 grms. 174 grms. 2. 3. 4. 6752 ■ 6821 6946 We have, therefore, for the heat evolved during the combination of — One gramme alcohol with oxygen 6850 One gramme oxygen with alcohol 3282 One litre oxygen with alcohol 4716 In two experiments, Dulong found the heat produced during the combination of one litre of the vapour of alcohol with 1. M 1-063 grm. T 9°-4 E l°-4 I 2°-555 Ic 2'"-558 W 2686 grms. V 174 grms. 1. 6883 I44i Heat Disengaged during Combination of [xvnr. oxygen to be 14310 and 14441 units. The corresponding number deduced from the preceding experiments is 14156. PHOSPHOEUS AND OXYGEN, The inner vessel was fiUed with dry oxygen gas by displace- ment. A shallow dish of thin Dresden porcelain was substi- tuted for the platina cup, as platina enters into combination with phosphorus at the elevated temperature at which the latter burns in oxygen gas. The experiment occupied ten minutes, from the slowness with which the porcelain dish gave out its heat. M. 0-764 grm. 0-773 grm. 0-729 grm. T. 4° -5 4° -8 4°-l E. l°-2 l°-4 l°-7 I. 2°-504 2°-498 2''-321 Ic. 2°-511 2°-509 2°-336 W. 1644 giras. 1659 grms. 1658 grms. V. 117 grms. 117 grms. 117 grms. 12 3 5788 5764 5688 Hence we have for the heat evolved during the combination of— One gramme phosphorus with oxygen, 5747 One gramme oxygen with phosphorus, 4509 One litre oxygen with phosphorus, 6479 ZINC AND OXYGEN. The zinc employed in the following experiments was carefully distilled from the purest varieties of the metal in commerce. It was scarcely attacked in the cold by dilute sulphuric acid. It still however contained 0-0005 lead ; but this trace of impurity could exercise no influence on such experiments as the present. To prevent the agglutination of the fine parts of the zinc during the combustion, it was mixed in the state of very fine filings with one-half its weight of pulverized quartz. The ignition of the zinc was effected by the assistance of a small portion of phosphorus (about O'OOS grm. in each experiment), which was inflamed in the usual way by the voltaic battery. In cal- culating the results, the heat produced by the combustion of the phosphorus was estimated and deducted. XVIII.] Bodies wiifi. Oxygen and Chlorine. 145 In the- case of -this metal, it would have been manifestly impossible to collect the oxide formed by the combustiion; nor was it practicable to ascertain the weight of metallic zinc which had escaped oxidation, as an alloy was formed in every experi- ment between the zinc and platina. To protect the platina cup from being rapidly destroyed "by the latter action, it was even found necessary to place a thin sheet of platina below the zinc, and this required to be renewed after every experiment. For these reasons, no alternative remained but to measure the oxygen consumed in each experiment. This was effected by ascertaining, after the increment of temperature had been observed, the volume of gas which had disappeared. There was some difJficulty in making' this determination with accuracy, but every possible precaution was taken to avoid error. In the next two tables, M is the volume of oxygen consumed. It was measured in a moist state. M. 715 C.C. 793 C.C. 697 c.c. B. 30-16 in. 30-14 in. 30-10 in. • T. 6°-7 6°-9 7°-4 E. l°-7 2°-3 l°-3 I. 3°-077 3°-436 3°-027 Ic. 3°-099 3°-471 3°-041 W. 1617 grms, 1599 grms. 1611 grms. v. 117 grms. 117 grms. 117 grms. 1. 2. 3. 7717 7728 7684 From these data we obtain for the heat evolved during the combination of — One gramme zinc with oxygen, 1301 One gramme oxygen with zinc, 5366 One litre oxygen with zinc, - - 7710 Dulong found from 7378 to 7753 for the heat given out during the combination of one litre of oxygen gas with zinc. IRON AND OXYGEN. The experiments with this metal were performed in the same manner as the preceding, with this difference, that no quartz was , added to the finely divided metal. The ignition was effected by means of 0"001 grm. phosphorus. K 146 Heat Disengaged during Combination of [xvm. M. 957 c.c; ■ 982C.C. 859 C.C. B. 30-21 ill. 30-06 in. 30-01 in. T. 7°-9 7°-4 8°-6 E. .l°-4 l°-2 0°-8 I. 3°-180 3°-272 2°-821 Ic. 3°-193 3°-281 2°-822 W. 1610 grma. 1611 grms. 1615 grms. V. , 117 grjns. 117 grms. 117 grms. 1 2. 3. 5935 5970 5914 We have, therefore, for the heat evolved during the combma^ tion of — One gramme oxygen with iron, 4134 One litre oxygen with iron, 5940 TIN AND OXYGEN. In the experiments with this and the remaining metals, the amount of oxygen was ascertained by debermining the increase of weight of the metal after the combustion was finished. The tin was mixed with half its weight of pulverized and recently ignited quartz, and the weight of the mixture carefuUy deter- mined both before and after the experiment. To produce ignition, only O'OOl grm. phosphorus was required. The heat evolved by the combustion of this weight of phosphorus is nearly six units ; but as a part entered into combination with the tin and thus escaped combustion, I have taken only four units from the final results as a correction. The same small quantity of phosphorus was found to be sufficient in all the subsequent experiments with oxygen. In some instances, indeed, its presence might have been wholly dispensed with; but as it rendered the success of the experiment in all cases very certain, and at the same time introduced a very trifling correction, 1 always employed it. In the tables which follow, M designates the weight of oxygen absorbed by the metals or oxides. I.. 2. 3. M. 1-574 grm. 1-256 grm. 1-072 grm, T. Q'-l 10° -3 7° -6 E. 2°-4 r-2 0°-9 I. 3°-815 3° -060 2°-611 Ic. 3° -850 3° -072 2°,-615 XVIII.] Bodies with Oxygen and Chlorine. 147 w. V. 1. 1616 grms. 117 grms. 2. 1620 grms. 117 grms. 3. 1611 grms. 117 grms. 1. 4235 2. 4244 3. 4210 We have, therefore, for the heat evolved during the combination of — One gramme oxygen with tin. One litre oxygen with tin, 4230 6078 PROTOXIDE 01' TIN AND OXYGEN. The protoxide of tin was prepared, according to the directions of Fr^my, by boiling the hydrated oxide in a dilute solution of hydrate of potash. It was afterwards dried at a low red heat in a current of dry carbonic acid gas. The experiment was performed in the same manner as the last. The whole of ihd heat was given out in sixteen minutes. 1. 2. 3. M. 1-716 grm. 1-213 grm. 1-085 grm. T. 8°-0 9°-3 ll°-3 E. 2''-8 r-5 l°-6 I. 4°-286 3°-013 2°-723 Ic. 4°-329 3° -029 2°-744 W. 1611 grms. 1618 grms. 1610 grms. V. 117 grms. 117 grms. 117 grms. 1.' . 2. 3. 4353 4328 4364 We have, therefore, combination of— for the heat evolved during the One gramme oxygen with protoxide of tin, 4349 One gramme protoxide of tin with oxygen, 521 One litre oxygen with protoxide of tin, 6249 COPPER AND OXYGEN. The copper employed was obtained by reducing the pure oxide by means of hydrogen gas. The experiment was in all respects similar to the two last. 148 Heat Disengaged during Combination of [xvm. 1. 2. 3. M. 1.-629 grm. 2-040 grms. 2-387 grms. T.' 8°-9 9°-2 9°-6 E. 0°-3 0°-4 l°-4 I. 2°-310 2°-834 3°-258 Ic. 2°-302 2'-826 3°-272 W. 1603 grms. 1613 grms. 1609 grms. "V. 117 grms. 117 grms. 117 grms. 1. 2. 3. 2427 2393 2362 We have, therefore, for, the heat evolved during the combinatiou of — One gramme oxygen with copper, 2394 One litre oxygen with copper, 3440 PROTOXIDE OF COPPER AND OXYGEN. The protoxide of copper was obtained by the action of glucose at the boiling temperature upon a solution of sulphate of copper to which caustic potash had been added. The oxide thus obtained was dried, first in the air at a temperature not exceeding 100°, and afterwards at a low red heat in a current of dry carbonic acid gas. It was burned in the usual manner ; but the results in different trials did not agree well with one another, and the combustion proceeded so slowly that nearly half an hour was occupied in each experiment. It was assumed in correcting for the cooling influence of the air, that the apparatus was at the maximum temperature during twenty- two minutes. 2. 3. 1-785 grm. 1-814 grm. io°-3 ir-o 0°-9 0°-9 2°-338 2°-437 2°-365 2°-464 1603 grms. 1614 grms. 117 grms. 117 grms. 2. 3 2275 2347 We obtain, therefore, for the heat evolved during the com- bination of — One grarnme oxygen with protoxide of copper, 2288 One gramme protoxide of copper with oxygen, 256 One litre oxygen with protoxide of copper, 3288 M. T. 1. 1-289 grm. 9°-2 E. 0°-9 I. l°-662 Ic. l°-690 W. - V. ■ 1. 2243 1597 grms. 117 grms. XVIII.] Bodies with Oxygen and Chlorine. 149 The last four sets of experiments are favourable to the view proposed, I believe, by Dulong, that the quantities of heat produced by the combination of a metal and of its oxide with oxygen are the same for equal quantities of oxygen absorbed. Thus in the case of tin and its protoxide, 'we have for one gramme of combining oxygen the numbers — 4230, 4349; and for copper and its protoxide — 2394, 2288. The experiments of Dulong on tin and its protoxide agree with this conclusion. I may remark, however, that the results now obtained with the protoxide of copper can only be con- sidered to be approximations; and that further researches will be necessary to discover whether the above differences will disappear when the true numbers are exactly ascertained, or be increased. The principle will in any case only apply to metals, such as tin and copper, which are capable of forming oxides inferior to those produced by their combustion in oxygen gas. Among the gaseous combinations, the heat evolved by the combustion of. equal volumes of hydrogen and carbonic oxide is nearly the same, viz. 3036 for one litre of the former, and 3057 for the same volume of the latter; but this agreement is more apparent than real, and would entirely disappear if the experiments were made under strictly identical circumstances, that is, in such a way as to obtain the resulting compounds in both cases in the aeriform state. In fact, if we correct the number expressing the heat due to the combustion of hydrogen for the latent heat of the vapour of water, ■ it will become reduced to 2540, a number which is far from identical with 3057. It has been inferred from the experiments of Dulong, that the heat evolved in the combustion of a compound gas is the same as that evolved in the combustion of its constituents. This principle would lead to the very improbable conclusion, that the separation of the elements of the compound gas is not: 150 Heat Disengaged during Combination of [xviii. attended with any thermal change. But whether this be the case or not, the principle itself certainly does not follow as a legitimate consequence, either from the experiments of Dulong, or from those contaiued in this paper. If, on this hypothesis, we attenipt to deduce the heat evolved in the combustion of one litre of the vapour of carbon from the results obtained with marsh gas and defiant gas, we are led in the two cases to very different numbers. Thus, . . Dulong. Author. One litre marsh gas gives 9588 9420 Two litres hydrogen give .- 6212 6072 One litre vapour of carbon should give - 3376 3348 One litre olefiant gas gives 15338 15014 Two litres hydrogen give - 6212 6072 One litre vapour of carbon should give - 4563 4471 The experimental results when interpreted in this way lead therefore to two very different numbers to express the heat due to the conversion of the vapour of carbon into carbonic acid. \ .- III. COMBINATIONS 0^ CHLOEINE. Most of the experiments to be described in this section were performed with dry chlorine gas. The combining substance, included in a hermetically sealed and very fragile glass ball, was first introduced into the glass vessel destined to contain the gas. The latter was then filled by displacement with pure and dry chlorine, and was afterwards closed by a dry cork, which was traversed by a small glass tube terminating exter- nally in a capillary point. After the chlorine had attained the temperature of the external air, the capillary orifice was hermetically sealed. During this period the surface of the cork was attacked by the chlorine; but careful experiments proved that the amount of gas afterwards absorbed by the cork was quite insignificant, at least during the length of time -occu- pied by the experiment. The glass vessel thus prepared was introduced into another of copper, which served as a calorimeter, and was similar to that employed in the experiments on the combination of the gases, but of smaller size. The calorimeter was suspended, as xv-m.]' Bodies with Oxygen and: Ghlorme:^'"- l3l before, in a cylindrical vessel of tid plate. The temperature of the water in the calorimeter was taken before introducing the apparatus into the rotating cylinder. The whole- apparatus was then quickly shaken in order to rupture the glass ball, and immediately placed in the rotating cylinder, in which it was agitated for five minutes and a half. After the final tempera- ture had been observed, the agitation was repeated for one minute more, and the experiment was not considered accurate unless the thermometer afterwards indicated a slight loss of heat. Finally, the glass vessel was inverted under water, the capillary point of the tube broken, and the weight of the water that rushed in (the levels having been duly adjusted) ascertained. The residual air did not, in general, amount to more than one or two per cent, of the whole, and was in all cases free from the slightest odour of chlorine. The determination of the heat evolved during the combina- tion of potassium with chlorine involved experimental difficulties, which for some time appeared likely to prove insuperable, but were finally overcome by the employment of a somewhat novel form of apparatus. The chief source of difficulty arose from the intensity of the heat produced by the combination, which was such that no glass vessel could resist it without breaking Having formerly observed that chlorine gas, if perfectly dry, has not the slightest action in the cold on copper or zinc, it occurred to me that the experiment might perhaps succeed, if a brass vessel were substituted for the glass one to contain the chlorine. On making the trial with the requisite precautions, it succeeded perfectly. The chlorine must, however, be dried with the greatest care, and the lid of the brass vessel closed by ground metallic surfaces without the interposition of leather. The apparatus is represented in Plate II. fig. 6. The lid h has attached to it two copper tubes, by means of which the vessel is filled with chlorine. It is fixed in its place by means of the coupling screw c. As soon as the air has been swept away by the current of chlorine, the ends of the copper tubes are closed by small pins of the same metal, which are secured in their places by caoutchouc covers. While filling the brass vessel with gas, two similar glass vessels were connected with it, one on each side, so as to be filled by -the same stream of 152 ReatPismgaged dunng Combination of [xvm. gas; and the purity of the clildrihe eontained in the intermediate brass vessel was ascertained by analysing the gas in the other two vessels. The combining substance was in all cases employed in con- siderable excess ; and from the constant agitation, the whole of the chlorine entered into combination in the course of a very short time. The formula deduced from direct observation to express the correction required in this apparatus for the heating and cool- ing influence of the air, during m minutes (a, as before, being the difference between the temperature of the apparatus and of the air), was the following : Y = + m {a ± 0°'5) . 0°-01. In applying this formula, it was assumed that the apparatus was. at the initial .temperature during one minute, and at the final temperature during three minutes. POTASSIUM AND CHLORINE. In the following tables, M designates the volume of chlorine (dry) in cubic centimetres. 80-4 e.c. 80-6 c.c. 80-4 c.c. 29-63 in. 29-48 iu. 29-12 in. 12°-4 12°-8 10°-8 V-b l°-9 l°-6 2°-95 2°-92 2°-86 2°-96 2°-95 2°-88 218-3 grma. 218-4 grms. 220-4 grms. 23-8 grms. 23-8 grms. 23-8 grms.. 3. 4. 9380 9344 We have, therefore, for the heat evolved during the combina- tion of — One litre chlorine with potassium, - 9329 One gramme chlorine with potassium, 2943 One gxamme potassium with chlorine, 2655 One equivalent chlorine with potassium, 13008 The assumed equivalent of chlorine is its atomic weight, that, of oxygen being =1. M. 80-3 c.c. B. 30-00 in. T. 8°-6 E. r-5 I. 3°-00 Ic. 3°01 "W. 215-4 grms. V. 23-8 grms. 1. .2. 9218 9374 xvm.] Bodies with Oxygen and Chlorine. 153 TIN AND CHLOKINE. 1. 2. 3. 4. M. 132-2 C.C. 143-1 c.c. 135-1 c.c. 140-4 c.c. B. 30-03 in. 30-03 in. 30-03 in. 29-90 in. T. 10°-6 10°-8 12°-2 13°-2 E. 0°-9 r-3 l°-3 l°-3 I. 2°-21 2'''47 2°-34 2°-28 Ic. 2°-20 2°-48 2°-35 2°-29. W. 144-4 grms. 136-0 grms. 132-9 grms. 144-4 grms. V. - 22-5 grms. 22-5 grms. 22-5 grms. 22-5 grms. 1. 2. 3. 4. 2874 2843 2803 2857 Hence we obtain for the heat evolved during the combina- tion of— One litre chlorine with tin, - 2844 One gramme chlorine with tin, 897 One gramme tin with chlorine, 1079 One equivalent chlorine with tin, - 3966 The compound . formed in this reaction was the bichloride SnClj. ANTIMONY AND CHLOEINE. M. 1. 126-3 C.C. 2. 149-6 C.C. 3. 137-6 C.C. 4. 131-5 c.c. B. 29-09 in. 30-28 in. 30-06 in. 30-08 in. T. 4°-5 6°-7- 9°-l 8°-l E. l°'l r-9 l°-4 l°-4 I. 2°-21 2°-74 2''-40 2°-32 Ic. 2°-21 2°-77 2°-41 2''-33 W. V. I. 2739 128-6 grms. 21-8 grms., 2. 2748 124-8 grms. 21-9 grms. 3. 2680 127-6 grms. 21-1 grms. 4.- 2743 131-6 grms, 19'5 grms. The compound formed in these experiments was a crystalline, easily fusible solid. On the addition of water, a white insoluble precipitate was formed ; but when a solution of tartaric acid was substituted for the water, the precipitate which at first appeared was completely redissolved. It was therefore the terchloride of antimony SbClg. The ■ perchloride (SbClj) described' by M. Eose was- not prodticed in any appreciable c[uantity. We. obtain, therefore, for the! heat evolved during the'com- bination of — ' . . ..-1 154 Heai Disengaged duHng Combination of [xvin. One litre chlorine with antimony. One gramme chlorine with antimony, One gramme antimony with chlorine, One equivalent chlorine with antimony, 2726 860 707 3804 ARSENIC . AND CHLORINE. M. 1. 138-7 C.C. 2 3 145-1 C.C. 150-0 C.C. 4. 134-1 CO. B. 29-40 in. 29-45 in. 29-92 in. 30-08 in. T. 6°-9. 7°-o. e°-3 10°-6 E. l°-7 l°-7 l°-4 0°-8 I. l°-90 r-93 2°-06 l°-78 le. l°-93 l°-96 2°-07 l°-77 W. V. 132-6 grms. 21-1 grms. 1. 2. 2230 2271 140-2 grms. 134-9 grms. 21*1 grms. 21-1 grms. 3. 4. 2202 2227 141-8 grms. 22-5 gnus. The compound formed was fluid, and when added to water, was converted into the hydrochloric and arsenious acids, with- out the formation of a trace of arsenic acid. It was, therefore, the terchloride of arsenic AsCls. We have, therefore, for the heat evolved during the combin- ation of — One litre chlorine with arsenic,. 2232. One gramme chlorine with arsenic, 704 One gramme arsenic with chlorine, 994 One equivalent chlorine with arsenic, 3114 MERCURY- AND CHLORINE. This metal combines taore slowly with chlorine than any of the preceding. Ten minutes of agitation were required to obtain the whole of the heat extricated during the combination. M. 1. 119-2 C.C. 2. 120-1 C.C. 3. 139-5 C.C. B. 29-64 in. 29-64 in. 29-25 in. T. ir-6 ll°-7 ll°-5 E. -- - 0°-9 0°-9 1°-1 I. - 1°-81 . i^-ss 2°-01 Ic. - l°-83 r-9o 2°-04 W. V. 1. 2611 -139-1 grms. 22-6 gnus. 2. 2658 137-0 grms. 22-6 grms. 3. 2547 140-8 grms. 22-6 grms. )SPHOEUS AND CHLORINE. 1. 2. 145-4 C.C. 144-6 O.C. 29-85 in. 29-85 in. • ir-5 ll°-3 0°-6 l°-3 l°-62 i°-e2 1°-61 l°-63 XVIII.] Bodies with Oxygen and Chl6ri/ne. 155 The primary compound formed in this" reaction is probably the chloride HgCl ; but by the action of the excess of mercury, a portion of it is afterwards converted into the subchloride HgjCl. We have, therefore, for the heat evolved during the combination of- — : One litre chlorine with mercury, . 2605 One gramme chlorine with mercury, - 822 One equivalent chlorine with mercury, - 3633 M. - B. T. .- E. I. Ic. W. - 143-2 grms. 140-5 grms. V. - 23-2 grms. 23-2 grms. 1. 2. 1924 1926 The compound formed was the solid perchloride, PCI5, accompanied by a small quantity of the terchloride, PCI3. These experiments with phosphorus and chlorine can only be considered to be imperfect approximations. We obtain, therefore, for the heat evolved during the com- bination of — r One litre chlorine with phosphorus, 1925. One gramme chlorine with. phosphorus, - 607 One gramme phosphorus with chlorine, 3422 (?) One equivalent chlorine with phosphorus, 2683 ZINC AND CHLORINE. As dry chlorine gas has no action upon zinc at ordinary temperatures, it was necessary to introduce a little water into the vessel in which the; reaction took place. In the experi- ment, however, when thus arranged, two distinct sources of heat existed ; one, the combination of the zinc and chlorine, the other, the solution of the compound formed. To determine the amount of the latter, ah independent experiment was made ; and by subtracting it from the whole quantity of heat at first 156 Heat Disengaged during Combination of [xvm. obtained, there remained the increment of temperature due to the chemical combination. A small quantity of subchloride of zinc was always formed by the action of the excess of ^inc upon the solution. This would tend to render the results a little too high ; but its precise effect I had no means of ascertaining. The quantity of chlorine which entered into combination in each experiment, was determined by precipi- tating the solution (previously acidulated with nitric acid to dissolve the subchloride) by nitrate of -silver and weighing the chloride of silver. The apparatus was considerably larger than that employed in the foregoing experiments. In the next table, M designates the weight of the chloride of silver. M. T. 1. 2-911 grms. ie°-i 2. 3-140 grms. 15°-0 3. 2-793 grms. 14°-2 E. r-0 r-7 l°-3 I. 2°-79 3°-10 2° -60 Ic. 2°-78 3°-12 2°-60 W. V. 380-0 grms. 27'5 grms, 1. 2. 1577 1580 365-3 grms. , 27-5 grms. 3. 1610 399-7 grms. 27-5 grms. In two experiments, the number 162 was obtained for the heat arising from the solution of the chloride of zinc, which being deducted from the mean number 1589, there remains 1427 for the heat of combination. We have, therefore, for the heat, evolved during the com- bination of — One litre chlorine with zinc, 4524 One gramme chlorine with zinc, 1427 One gramme zinc with chlorine, 1529 One equivalent zinc with chlorine, 6309 ^ COPPER AND CHL0KINE.2 The experiments with copper were in all respects similar to those with zinc, except that the chlorine was estimated by volume and not by weight. ^ These results are almost identical with those which I obtained formerly by a process diflfering slightly from that now described. ( Trarmactions of the Royal Irish Academy, xix. p. 406.) ' ^ These experiments were not in the original paper. XVIII.] Bodies with Oxygen and Chlorine. 157 M. 1. 246-0 C.C. 2. 241-5 C.C. 3. 233-5 C.C. 4. 246-4 c.c. B. 29-53 in. 29-73 in. 29-56 in. 29-56 in. T. 17°-8 18°-9 18°-4 19°-3 E. 0°-6 0°-6 0°-7 0°-7 I. 1°-71 l°-62 l°-63 l°-67 Ic. r-71 l°-62 l°-63 l°-67 W. V. 1. 3037 371-3 grms. 27-3 grms. 2. 2927 382-1 grms. 27-3 grms. 3. 3061 382-8 grms. 27-3 grms. 4. 2950 382-7 grms. 27-3 grms. The heat due to the solution of the compound, referred to one litre of chlorine as unit, was found to be 260 units. We have, therefore, for the heat evolved during the combin- ation of — One litre chlorine with copper, 2734 One gramme chlorine with copper, 859 One gramme copper with chlorine, 961 One equivalent chlorine with copper, 3805 The results of the foregoing experiments are contained in the following table. I have adopted the number 7900, for the reasons given in the note, to express the heat produced during the combustion of carbon ; and have also added, from a former publication, the numbers which correspond to the heat evolved during the combination of chlorine and iron. COMBINATIONS OF OXYGEN. Of Oxygen. Of Substance. 1 grm. 33808 2431 Hydrogen Carbonic oxide 1 litre. 6072 6114 1 grm. or equiv. 4226 4255 Marsh gas 4716 3278 13108 defiant gas 5005 3483 11942 Alcohol 4716 3282 6850 Carbon 4256 2962 7900 Sulphur Phosphorus Zinc 3315 6479 7710 2307 4509 5366 2307 574T 1301 Iron 5940 4134 Tin 6078 4230 Protoxide of tin - 6249 4349 521 Copper Protoxide of copper - 3440 3288 2394 2288 256 158 Heat Disengaged duHng Combination of [xviii. COMBINATIONS OF CHLORINE. Of Chlorine. Of Substance. 1 grm. 1 litre. Igrm. 1 equiv. Potassium 9329 2943 13008 2655 Tin 2844 897 3966 1079 Aiitimony 2726 860 3804 707 Arsenic - 2232 704 3114 994 ■ Mercury - 2605 822 3633 Phosphorus 1925 607 2683 3422 (?) Zinc 4524 1427 6309 1529 Copper 2734 859 3805 961 Iron 2920 921 4072 1745 From a cursory inspection of the above numbers, it will be evident that the quantities of heat evolved during the combin- ation of different metals with chlorine or oxygen are very different, varying, in the case of the compounds of chlorine, from 13008 to 3114 units for each equivalent of chlorine. On the other hand, there is a general resemblance between the amounts of heat obtained when the same metal combines with oxygen and chlorine. Thus iron yields 4134 units with oxygen, 4072 with chlorine; antimony, 3817 with oxygen (Dulong), 3804 with chlorine; tia, 4230 with oxygen, 3966 with chlorine. In the case of zinc there is less agreement, and in that of copper, the results differ considerably ; but this may perhaps arise from the compounds of chlorine with those metals being obtained after each experiment in the state of aqueous solutions. The determination of the heat evolved during the combustion of potassium in oxygen gas would throw much light on this question. The only non-metallic element examined is phosphorus, and it gave nearly twice as much heat in combin- ing with oxygen as with chlorine. It may be interesting to inquire whether the thermal effects described in the foregoing extract can be connected with those obtained when compounds formed of the same bodies react upon one another by the moist way. Such a comparison is difficult and liable to much uncertainty, from the many intermediate reactions that occur during the formation of these compounds. But there are two cases that admit to some extent of this com- parison, and it may be interesting briefly to refer to them. xviii.] Bodies with Oxygen and Chlo7^e. 159 I have elsewhere shown, that when one and the same base displaces another from any of its neutral combinations, the same development of heat occurs^ ; and in a paper lately read before the Eoyal Society, I^ have endeavoured to extend a similar principle to the substitutions of metals for one another, and have also measured the quantities of heat evolved in many reactions of this kind. For my present object, it is only necessary to refer to two of these results, viz. the heat due to the substitution of an equivalent of oxide of zinc for oxide of copper (353 units), and that due to a like substitution of metallic zinc for metallic copper (3435 units). Now on the common view of the constitution of salts and of their solutions, the heat evolved during the precipitation of metallic copper by zinc should be equal to the difference of the quantities of heat disengaged during the combination of zinc and copper respec- tively with oxygen, added to the heat due to the substitution of oxide of zinc for oxide of copper. This assumes the truth of the principle (which I have in other inquiries endeavoured to illustrate, and is indeed almost self-evident), that when, in the course of any chemical reaction, thei constituents of a com- pound are separated from one another, there is a quantity of heat thereby absorbed, equal to that which would have been evolved if the same substances had entered into combination. Applying the numerical quantities, we have — Zn-f-0, 5366 Cu-l-0, 2394 (Zn-f-O)-(Cu-f-O),' 2972 Substitution of ZnO for CuO in salts of latter, 353 3325 This number 3325 should, therefore, represent the heat due to the substitution of metallic zinc for copper. The result actually obtained by direct experiment was 3435, an excellent approximation when all the varying circumstances of the particular experiments are taken into consideration. 1 Philosophical 7'ransactions for 1S44, p. 21. 160 Heat Disengaged during Combination, etc. [xvm. On the other hand, in the combination of chlorine with zinc and copper, we have — Compound dry. Compound in solution. Zn + Cl, 6309 7025 Zn + Cu,i 3805 4167 2504 2858 Neither of these numbers agrees with that first given for the heat produced by the substitution of zinc for copper. The thermal effects are therefore not favourable to the hypothesis that the metallic chlorides' exist, as such, in solution. In making these observations, I do not wish to attach to them more importance than they deserve. I am fully aware of the uncertainty of conclusions derived from a new and difficult inquiry. But as the heat developed in chemical reactions may be taken as a measure of the forces brought into play, I deemed it proper to refer to the foregoing cases, if only for the purpose of directing attention to the intimate relations which inquiries of this kind have with some of the most interesting questions of molecular chemistry. ^ [Obviously a misprint for Cu + Cl. A. 0. B.] 161 XiX.— ON THE SPECIFIC HEAT OF BROMINE. From the Quarterly Journal of The Chemical Society of London, Vol. I., p. 18. Nov. 15, 1847. Bromine being the only liquid member at ordinary tempera- tures of the class of bodies to which it belongs, it appeared important to ascertain its specific heat with reference to the law of Dulong and Petit. The low temperature at which bromine boils, and its feeble specific heat, rendered the deter- mination of the latter difficult. The method adopted was to heat bromine, contained in a small glass flask, to about 10° C. {18° F.) below its boiling point, by means of a water-bath, which was maintained at a very steady temperature. It was then quickly transferred into a glass tube, which had been previously immersed in a copper vessel filled with water, and the increment of temperature in the water was carefully observed. The details of the experiment are the same as those usually followed in such investigations. The bromine employed was carefully purified, and its purity tested by ascertaining its atomic weight, from the silver salt, previous to the experiment. It boiled at a temperature of 58° C. (137°'5 F.) imder a pressure •of 2 9 '9 inches. In the experiments the temperature of the air was about 11° C. (52°!".), and the bromine was heated to about 45° C. (1 13° F). Br. represents the weight of the bromine ; T the increment or gain of heat of the water ; T' the heat lost by the bromine ; and Sp.H. the specific heat. I. II. III. IV. V. Br. 25-08 grms. 26-13 grms. 24-.q8 grms. 24-69 grms. 24-18 grma. T l°-208 (C) I°-31o (C) r-263 (C) 1°-213 (C) 1°-184(C) T' 32° 32° 32°-7 31°-9 32°-4 Sp.H. 0-1053 0-1097 0-1083 0-1078 0-1044 Mean specific heat, 0-1071. Dr. Andrews concludes from these results that, in accordance with the views of Berzelius, the atomic weight usually ascribed L 1G2 On the Specific Heat of Bromine. [xix, to bromine in this country, as also those of the elements of the class to which it belongs, should be halved, in which case, sUver being taken at 1350, bromine, from the author's experi- ments, would be -^^ or nearly i^^, and i^,"-^ x 0-1071 = 53-55 would represent the atomic heat of bromine. According to the experiments of M. Eegnault, however, the atomic heats of the simple bodies vary between the limits of 38 and 42, and bromine would thus form an exception to the law of Dulong and Petit, as its atomic heat is about one-fourth higher than that required by theory. This discrepancy is- attributed by Dr. Andrews to the specific heat being, necessarily determined in the liquid state, and he considers that bromine would agree with the law of Dulong and Petit, and its specific heat be about 0-08, if this could be ascertained with the solid substance. 163 XX.— ON THE LA.TENT HEAT OF VAPOURS. From the Quarterly Journal of the Chemical Society of London, Vol. I., p. 27. Since the period when Black first explained his celebrated doctrine of Latent Heat, and showed the general method of measuring the quantities of heat evolved or abstracted during the changes of bodies from one physical state to another, the subject has attracted the attention of several distinguished inquirers both in this country and on the continent. It would be foreign to my present purpose to enter into a detailed account of their methods or results, which is indeed the less necessary, as a very complete history of the subject, accom- panied by critical remarks, will be found in an able memoir, published a few years ago in Poggendorff's Annalen,^ by Dr. Brix, of Berlin. More recently, two important communica- tions on this subject have been made to the Academy of Sciences of Paris ; one by M. Eegnault, on the Latent Heat of Steam when generated under different pressures ; the other by MM. Pavre and Silbermann, on the Latent Heat of the Vapours of several Organic Liquids. My object in entering upon this inquiry was not to attempt a new determination of the latent heat of aqueous vapour, but to extend the investigation to the vapours of other bodies differing widely from one another in chemical composition, with the view principally of ascertaining whether any fixed relation exists between the latent heat and the other physical properties of vapours. In this inquiry, I have been preceded by Ure, Despretz, Brix, and Pavre and Silbermann. Their results are, for the most part, remarkable for accuracy, but, with the exception of those of the last-named experimentalists, extend only to a very small number of substances. Even their experiments, however, only embrace compounds of oxygen, hydrogen, and iBd. LV. s. 341. 164 On the Latent Heat of Vapours. [XX. carbon. By employing a very delicate glass apparatus, I have been enabled to supply, in some measure, this deficiency, and to extend the inquiry to one simple substance, and a small number of inorganic compounds. The apparatus employed in these experiments is represented in Fig. 1. The fluid to be converted into vapour is placed in a Flo. 1. small glass flask, the neck of which has a very short bend, as shown in the figure. Into this the end of the receiver is inserted, by means of a small cork. The form of the receiver is shown in Fig. 2. It consists of a very thin bulb of German glass, terminating in a spiral tube of the same material. The glass receiver is fixed by a cork in a light copper vessel (Fig. 3), from which it can be easily removed at the end of XX.] On the Latent Heat of Vapours. 165 the experiment. The copper vessel, which is open above, is filled with water, cooled from 1° to 2° C. (l°-8 — 3°-6 F.) below the temperature of the air. The whole is surrounded by an outer vessel of tin-plate, fitted with a moveable lid in which are three openings, one for the thermometer, another for the extremity of the spiral tube of the receiver, and a third for the stirrer, which is formed of a very light and hollow glass tube. An additional screen, as shown in the figure, is interposed be- tween the lamp by which the liquid is heated, and the rest of the apparatus. The thermometer employed is very delicate, and the greatest pains were taken to insure its accuracy. The diameter of the reservoir is not greater than that of a thin thermometer tube, and it occupies the entire depth of the calori- pm. 3 meter. It is attached to an arbitrary metallic scale, divided into fiftieth parts of an inch. The errors of calibre were determined by two dis- tinct measurements of columns of mercury of different lengths ; the freezing point was ascer- tained by direct observation, and another point situated near 25° C. (77° F.), by comparison with an accurate thermometer, constructed by Greiner. It was easy from these data to prepare a table, showing the degree corresponding to each abritrary division of the scale, and also the multiplier, required to reduce an increment observed at any part of the scale, into true degrees. Two independent tables were constructed from the separate measurements, and they were found to differ nowhere more than 0°-01 C. (0°-018 F.). Within the ordinary limits of atmospheric temperature, the difference of the expansion of a metallic or glass scale for increments of a few degrees is so slight, that it may be neglected. The correction for the mercury in the stem of the thermometer is more important. The multipliers for the divisions of the arbitrary scale were corrected accordingly. 166 On ike I^ateni Heat of Vapours. [xx. The increments of temperature, as obtained, by observation, were carefully corrected for the cooling and heating influence of the surrounding air. From one to two minutes were occupied in raising the liquid to the point of ebullition ; and during this period, the thermometer remained nearly at the same point. While the ebullition contiuued, the thermometer rose very steadily and uniformly, but it did not attain the maximum point till about two minutes after the ebullition had ceased. For the heat gained and lost during these periods, a correction, deduced from direct experiments with the calorimeter alone, was applied. The agitation was continued for five minutes after the thermometer had reached the maximum, and the difference between the loss of heat observed, and that indicated by calculation, was added as a further correction to the result. This last is frequently omitted in inquiries such as the present, but it generally amounts to an appreciable quantity, and in accurate experiment ought never to be neglected. To prevent the mercurial column from becoming heated by the person of the observer, the divisions were read through a powerful magnifier, which was fixed on a moveable support. In addition to the causes of error already referred to, others exist of not less importance, but the effect of which it is much more difficult to estimate. If the liquid be boiled too slowly, a portion of the vapour will be condensed in the tube of the receiver just before it enters the calorimeter, and a considerable loss of heat will occur. On the other hand, if the ebullition is carried on very rapidly, an undue pressure will be produced in the interior of the retort, the temperature of the vapour will be raised above the ordinary boiling point, and too large an increment finally obtained. A portion of uncondensed but partially cooled vapour will also escape, particularly at the commencement of the operation, before the air has been expelled. On this part of the subject, an elaborate mathemati- cal investigation will be found in the memoir of Dr. Brix, to which reference has already been made ; but it may be doubted whether the experimental data are yet sufficiently precise to admit of the useful application of formulas derived from the higher branches of analysis. To ascertain, as far as possible. sx.] On the Latent Heat of Vapours. 167 the limits of error to which the apparatiis now described is liable, I made two series of experiments with water and alcohol ; in the first, the ebullition occupied from one and a half to two minutes ; in the second, from three and a half to five minutes. In order to complete the operation in the shortest period, the liquid was made to boil very violently, and there can be no doubt that the vapour was generated under a higher pressure than that of the atmosphere. In the other case, the ebullition proceeded at a gentle rate, and all the causes of error tended to render the results too low. The mean number given by the experiments of the first series for the latent heat of water, was 541°-4 C. (1038°'5 F.); and by those of the second, 532"y C. (1023° F.). The mean of the whole was 535°-9 C. (1030'-75 F.). This latter number agrees very closely with the mean of the results obtained by Despretz, Dulong, and Brix, and is almost identical with that recently arrived at by il. Eegnault.^ From these observations, it follows that when the operation was purposely so performed as to exaggerate to the utmost the errors occasioned by the apparatus, the result does not diverge more than Touth part from the true number. The experiments with alcohol lead to the same conclusion ; the mean of the series, in which the •ebullition occupied the shortest period, being 205°-0 C. (40 1° F.), and of that in which it occupied the longest period 202°'4 C. {396'-3 F.); so that the difference here was even less than in the experiments with water. In determining the latent heat of other bodies, the fluid was made to boil as fast as was possible, without producing increased pressure on the interior of the apparatus. In the case of a few hquids, it was found difficult to complete the vaporization in the ordinary time, and hence the results expressing their latent heats are probably a little below the true numbers. This remark applies particidarly to the iodic and oxalic ethers, and to the iodide and acetate of methyl. The weight of the condensed vapour was ascertained by weighing the glass receiver (Fig. 2) at the end of the experi- ment, and deducting the weight of the same when empty. Their numbers are, 531, Despretz ; 543, Dulong ; 540, Brix ; 536'4, Eegnault. 168 On the Latent Heat of Vapours. [xx. The boiling points of all the liquids operated on were determined with great care. This is often attended with considerable difficulty, and even distinguished chemists have committed serious mistakes in examining the boiling points of volatile iiuids. The numbers given in this paper were obtained by heating the liquid with a very small spirit flame in a glass retort, the thermometer being immersed in the vapour, at a short distance above the surface of the liquid. A quantity of mercury was placed in the retort, except in the case of liquids which attacked that metal. The results given by observation were corrected for the portion of mercury in the stem of the thermometer, which was not heated in the vapour, and also for the variations of the barometer. In making the latter correction, it was assumed, as a sufficient approximation, that the boiling points of other liquids were raised or depressed to the same extent as that of water by the same changes in the height of the barometer. The specific heats of several of the liquids were deterniined by direct experiment. The liquid raised to the boiling point was quickly introduced into a thin glass tube immersed in water, and the gain of heat of the latter observed. The re- sults iu general agreed very closely with those of Eegnault. In other cases, I have employed the numbers given by the same accurate observer, which were in general deter- mined by observing their rates of cooling. A slight error may thus be produced, in consequence of the specific heat of the liquid not being the same at different temperatures, but for the liquids actually employed, this difference is probably unimportant. Finally, every precaution was taken to operate on perfectly pure chemical substances. This is of much more importance in such inquiries as the present, than even in analytical investiga- tions, from the great differences in the specific heats of the same weight of different liquids. Thus, the presence of only j-hth part by weight of aqueous vapour would induce an error of iVth part in the determination of the latent heat of the vapour of ether. The weight and thermal value, in terms of water, of the different parts of the apparatus were as follows : XX.] On the Latent Heat of Vapours. 169 Copper vessel, 49 '5 grms. X 0'095 Glass receiver, 13-7 „ x0183 2-5 Thermometer, stirrer, and cork, 0"5 4'7 grms. 7 '7 grms. Thermal equivalent of apparatus. In stating the results, I have used the following abbreviations : Bar. : the height of the barometer reduced to 0. Air : the temperature of the air in centigrade degrees. Ex. : the excess of the final temperature of the water in the calorimeter above the air. Inc. : the increment of temperature, as obtained by observa- tion. T : the time of ebullition. T' : the time from the observation of the initial temperature tUl the thermometer attained its maximum. V : the weight of condensed vapour. W : the weight of the water in the calorimeter, exchisive of the thermal value of the vessels. L.H. : the latent heat corrected. Water. — Specific heat I'OO. Boiling point, under a pressure of 29-92 inches, at 100° C. (212° F.). FIEST SERIES. I. II. III. Bar. 29^52 in. 30^43 30^14 Air. 6°^50 8° -60 9°^90 Ex. 2°^69 2° -00 1°^97 Inc. 4°^083 3°^411 3°-761 T. 1', 20" 1', 35" r, 50" T'. 3', 45" 3', 30" 5', 0" V. 1-860 gm. 1-573 gm. 1 -766 gm. W. 2792^2 grms. 282-3 grms. 286^2 grms. L.H. 542^9 543-4 537^9 Mean latent heat ,, 54V4. SECOND SERIES. I. 11. III. IV. v. Bar. 29 •70 in. SO^IO in. 30-10 in. 30-15 in. 30^09 in. Air. 11° •30 10°^10 10°-44 9' '•55 10° -20 Ex. 2° ■08 r^87 2°-20 1° •83 ^•78 luc. 3° •772 3° -833 4° -078 4' ■•039 3°^822 170 On the Latent Heat of Vapours. [XX. I. II. III. lY. T. T. 4', 35" 4', 0" 3', 15" 3', 35" 5',0" T. 7', 10" 6', 15" 5', 45" 5', 40" 6', 55" V. 1-780 gm. 1-829 gm. 1-980 gm. 1-921 gm. 1-833 gm. VV. 285-1 grins. 287-8 grms. 2938 grm.=i 287-7 grms. 286-7 grms. L.H. 536-8 531-9 532-2 531-6 530-8 Mean latent heat, 532-7. Mean of whole series, 535-9. Alcoliol. — The alcohol was purified by repeated distillations from lime in a vapour-bath. It was deprived of essential oil by charcoal. It boiled at 78°-3 C. (ITS^-O F.) under a pressure of 30-3 in.; and hence its true boiling point, under a pressure of 29-9 in., is 77°-9 C. (l72"-3 F.). The mean of three experiments gave for its specific heat, 0-617. Bar. Air. Ex. Inc. T. T. V. W. L.H. FIEST SERIES. I. II. III. 29-75 in. 29-75 in. 29-73 in. 14°-20 14°-95 14°-55 l°-50 2° 00 2°-29 3°-467 3°-367 3°-633 1', 55" 2',0" 1', 45" 4', 25" 4', 40" 4', 40" 4-202 gms. 4167 gms. 4-418 gms. 286-0 gms. 289-4 gms. 286-S gms. 204-8 203-9 206-2 Mean latent heat, 205-0. SECOND SERIES. I. II. III. IT. V. Bar. 29-90 in. 29-90 in. 29-91 in. 29-91 in. 29-90 in. Air. 11°-10 11°-10 10°-80 ]0°-70 10°-60 Ex. 2°-38 l°-90 l°-56 r-92 l°-72 Inc. 4°-417 3°-833 3°-533 3°-878 3°-567 T. 4', 25" 4', 35" 3', 40" 3', 50" 4; 25" T'. 6', 40" 6', 4o" 4,55" 5', 25" 6', 0" V. 5-381 gms 4-785 gms . 4-402 gms . 4-830 gms. 4-430 gms. "W. - 286-3 gms. 292-2 gms. 293-0 gms. 29 1-4 gms. 289-0 gms. L.H. -201-7 201-4 201-5 199-7 199-7 Mean latent heat, 200-8. Mean of whole series, 202-4. XX.] On the Latent Heat of Vapours. 171 Bromine. — Pure bromine, according to my experiments, boils under a pressure of 29-9 in. at 58° C. (136°-6 F.) and its specific heat is 0-107.^ I. II. III. IV. Bar. 30-01 in. 29-99 in. 29-70 in. 29-70 in. Air. 6°-30 6°-50 5°-70 5°-70 Ex. I'-SS r-28 I'-SS l°-55 Inc. 2°-659 2°-708 2° -568 2°-975 T. 2', 45" 3', 30" 3', 55" 2', 55" T'. 5', 30" 6', 30" 6', 45" 6', 15" V. 14-983 gms. 15-291 gms. 14-638 gms. 16-910 gms. w. 279-8 gms. 279-2 gms. 279-3 gms. 279-2 gms. L.H. 45-95 45-62 45-28 45-56 Mean latent heat, 45-60. Protochloride of Phosphorus. — The protochloride was pre- pared by the action of dry chlorine gas on phosphorus. It was afterwards digested for several days with an excess of phosphorus, and purified by repeated distillations. It was perfectly limpid and colourless, and under a pressure of 30-20 in., it boiled at 78°-5 C. (173°-4 F.). I have taken Eegnault's number (0-209) for its specific heat. I. II. III. Bar. 29-54 in. 29-29 in. 29-49 in. Air. 4° -90 7°-16 10° -33 Ex. l°-67 2°-ll 2° -21 Inc. 2° -556 3°-0l7 3''-733 T. 2', 30" 2', 35" 3', 5" T'. 5', 30" 5', 30" 6', 0" V. U-245 gms. 13-122 gms. 16-531 gms. W. 280-0 gms. . 276-5 gms. 278-0 gms. L.H. 51-11 51-77 51-39 Mean latent heat, 51-42. Bichloride of Tin. — This compound was prepared by the action of dry chlorine on tin, and after being deprived of the excess of chlorine by digestion with tin filings, was purified by repeated distillations. It boiled at 112°-5 C. (233°-9 F.) under a pressure of 29-60 in. Its specific heat was assumed to be 0-148. ^ See preceding paper, p. 161. 172 On the Latent Heat of Vapoui's. [xx. I. II. III. Bar. 30-12 in. 30-12 in. 30-17 in. Air. 6°-10 6°-10 6°-40 Ex. l°-64 l°-55 l°-28 Inc. 2°-578 3°-006 2°-700 T. 2', W" 2', 0" 2', 45" r. &, 30" 5', 30" 6', 0" V. 16-232 grms. 18-555 grms. 16-924 grms. w. 278-8 grms. 278-8 grms. 278-8 grms. L.H. 30-37 31-02 30-21 Mean latent heat, 3053. Sulphuret of Carton. — This liquid was digested with chloride of calcium, and distilled. It boiled, under a pressure of 30-30 in., at 46°-2 (115° F.). Specific heat assumed to be 0-31^ (Eegnault). I. II. III. Bar. 29-92 in. 30-27 in. 30-27 in. Air. 9°-10 9°-05 8-94 Ex. a'-ss 3°-00 3° -44 Inc. 4° -422 4°-467 4°-761 T. 3', 30" 3', 0" 3', 45" T'. 5', 55" 5', 30" 6', 25" V. 13-465 grms. 13618 grms. 14-548 grms. W. 276-7 grms. 276-8 grms. 277-1 grms. L.H. 86-72 86-56 86-72 Mean latent heat, 86-67. Sulplmoric Ether. — This ether was purified in the usual manner. It boiled under a pressure of 29*61 in., at 34°' 9 C. (94°-73 F.). Specific heat, 0-517. I. II. III. Bar. 30-18 in. 30-16 in. 30-16 in. Air. 2°-30 8° -10 8° -10 Ex. r-78 l°-94 2° -11 Inc. 3° -783 3° -572 3° -806 T. 4', 15" 3', 50" 3', 50" T'. 6', 25" 6', 10" 6', 20" V. 10-477 grms. 9-812 grms. 10-473 grms. w. 277-0 grms. 277-1 grms. 276-5 grms. L.H. 89-89 90-94 90-50 Mean latent heat, 90-45. XX.] On the Latent Heat of Vapours. 173 Iodic Ether. — This ether was prepared by takmg 14 grms. phosphorus and 70 grms. alcohol, sp. gr. 0-816, and adding in small portions 46 grms. iodine, waiting between each addition of iodine till the liquid became clear. It was then distilled at a gentle heat, washed with water, and allowed to digest for forty-eight hours with an excess of chloride of calcium. It was again distilled at a temperature of from 70^ to 75° (158°-167° F.). The purification was finally completed by another digestion with chloride of calcium, and distillation. Its boiling point was found to be 7l°'3, (160°-36 F.), under a pressure of 29'9 in. I. II. III. IV. Bar. 29'53 in. 29-39 in. 29-40 in. 29-40 in. Air. 7°-70 7°-05 7°-90 8"" -05 Ex. 2°'39 l°-72 2° -28 2° -44 Inc. 3° -939 3° -294 3° -7 17 4° -256 T. 5', 35" 6', 5" 6', 0" 6',0" T. 8', 20" 9', 20" 8', 55" 9', 30" V. 20-974 grms. 17-504 grms. 19-590 grms. , 22-170 grms W. 289-6 grms. 292-1 grms. 285-2 grms. 283-7 grms. L.H. 46-94 46-78 46-83 46-94 Mean latent heat, 46-87. Oxalic Mher. — The oxalic employed in the following experi- ments, boiled at 184°"4 (396° F.), under a pressure of 30-7 in. Specific heat, 0-457. I. II. III. Bar. 30-66 in. 30-60 in. 30-60 in. Air. 6''-20 7°-50 7°-60 Ex. 2''-89 l°-50 2°-89 Inc. 4°-744 3°-772 4°-333 T. 3', 10" 5', 35" 3', 15" T'. 7', 25" 9', 50" 8', 30" V. 9-177 grms. 7-335 grms. 8'461 grms. W. 284-3 grms. 288-5 grms. 284-8 grms. L.H. 73-33 72-61 72-22 Mean latent heat, 72-72. Acetic Ether. — This ether, carefully purified, was found to boil at 74°-6 (166°-36 F.), tinder a pressure of 30 in. Its specific heat in two trials was found to be 0-471 and 0-477 ; mean, 0-474. 17-t On the Latent Heat of Vapours. Ixx. I. II. III. IV. Bar. 2.9-92 iu. 29-90 in. 29-90 in. ' 29-89 in. Air. 10°-20 10°-50 10°-90 11°-10 Ex. 2°-33 l°-94 l°-56 l°-78 luc. 4°-500 4''-012 3°-967 3°-711 T. 5', 55" 3', 50" 3', 10" 3', 35" r. 8', 35" 6', 45" 5', 45' 6', 30" V. 10-804 grms. 9-524 grms. 9-468 grms. 8-761 grms. w. 283-0 grms. 283-7 grms. 281-3 grms. 279-6 grms. L.H. 92-22 93-72 92-00 92-78 Mean latent heat, 92-68. Formic Ether. — The easiest method of procuring formic acid for the preparation of this ether, is by distilling rapidly hydrated oxalic acid. On neutralizing the acid liquid which passes over with carbonate of soda, the greater part of the oxalic acid precipitates in the form of oxalate of soda, and by evaporation, the formiate of soda, mixed with a little oxalate, is obtained. This may be etherified without further purification, as the formic ether is easily and completely separated from the oxalic by distillation. Formic ether thus obtained, probably furnishes the easiest means of procuring formic acid and its salts in a state of purity. Formic ether boils under a pressure of 30 in. at 54°-3 (129°-9 F.). In three experiments its specific heat was found to be 0-485, 0-487, and 0-490 ; mean, 0-485. I. II. III. IV. Bar. 29-83 iu. 29-57 in. 29-57 in. 29-57 in. Air. ll°-Oo 9°-20 9°-67 9°-55 Ex. l°-94 2°-00 l°-78 2° -28 Inc. 4° -006 3°-572 3°-439 4°-061 T. 2', 45" 3', 50" 3', 5.5" 1', 40" r. 5', 30" 6', 20" 6', 25' 4', 10" V. 9 -323 grms. 8-508 grms. 8-092 grms. 9-379 grms. w. 281-9 grms. 288-4 grms. 283-6 grms. 282-6 grms. L.H. 105-3 105-0 104-2 106-7 Mean latent lieat, 105-3. Methylic Alcohol. — The pyroxylic spirit of commerce was rectified several times over a water-bath from an excess of lime, the first and last portions being rejected. It was after- wards combined with chloride of calcium, and purified according to the method of Kane. It boiled at 65°-8 (150°-72 R), XX.] On the Latent Heat of Vapours. 175 under a pressure of 30 '2 in. In two experiments the numbers obtained for its specific heat were 0"611 and 0"615 ; mean, 0-613. I. II. III. Bar. 29-72 iu. 29-72 in. 29-71 in. Air. 11°-10 ll°-.90 12° -20 Ex. 2° -50 1°-61 2°-61 Inc. 4° -089 4°-539 4° -8011 T. 4', 5" 3', 15" 2', 35" T'. 6', 35" 5', 50" 4', 55" V. 4 '039 grms. 4-451 grms. 4-743 grms. W. 281-5 grms. 281-3 grms. 282-4 grms. L.H. 264 '0 ' 262-4 264-6 Mean latent heat, 263-7. Iodide of Methyl. — This compound was prepared by taking 5 grammes of purified wood-spirit and 1 grammes of phos- phorus, and adding iodine in small quantities as long as it was dissolved. The quantity of iodine taken up by the liquid was about 6 9 grammes. The liquid was then distilled at a tempera- ture varying from 70° to 90° (158°-196° F.) the distillate washed with ice-cold water, and added to a large excess of chloride of calcium with which it was allowed to digest for three days. It was afterwards rectified three times from chloride of calcium. It boiled at 42°-2 (108°?.) under a pressure of 29-6 in. Specific heat assumed to be 0-158. I. II. III. IV. Bar. 29-71 in. 29-70 iu. 29-81 in. 29-81 in. Air. 9°-50 9°-45 8°-80 9°-20 Ex. 2°-06 2° -33 l°-56 l°-83 Iqc. 3°-689 3°-883 3''-417 3°-761 T. 5', 15" 4', 50" 4', 50" 5', 55" T'. 7', 40" r, 20" r, 25" 8', 30" V. 21-465 grms. 22-446 grms. 20-011 grms. 21-460 grms. w. 288-0 grms. 286-9 grms. 291-0 grms. 282-0 grms. L.H. 46-06 46-39 46-00 45-83 Mean latent heat, 46-07. Acetate of Methyl. — The impure acetate of methyl, obtained by distilling a mixture of purified wood-spirit, acetate of soda, and sulphuric acid, was digested with milk of lime, and 170 On the Latent Heat of Vapours. [xx. chloride of calcium afterwards added in excess. After allowing the mixture to stand for twenty-four hours, the ether was decanted and digested for several days with chloride of calcium, and finally distilled in a water-bath, whose temperature never exceeded 65° (149° R). It boiled, under a pressure of 30 in., at 55° (131° ¥.). Specific heat assumed to be 0-47. I. II. III. Bar. 29-77 in. 29-78 in. 29-78 in. Air. io°-oo io°-io 10°- 60 Ex. l°-44 2° 06 r-94 Idc. 3° -806 3°-633 3° -578 T. 4', 35" 4', 40" 4', 35" T'. T, 35" 8', 5" 7', 25" V. 8-485 grma. 8-158 grms. 8-040 grcas. W. 283-8 grms. 284-2 grms. 284-1 grma. L.H. 110-0 110-3 '110-2 Mean latent heat, 110-2. Formiate of Methyl. — It was prepared and purified by a process analagous to that last described. It boiled at 32°-9 (91°-2 F.), under a pressure of 29-6 in. Specific heat assumed to be 0-47. I. II. III. IV. Bar. 30-07 in. 30-07 in. 30-06 iu. 30-06 ill. Air. 12°-70 13° 05 13° -00 13° -30 Ex. 1°-17 l°-28 0°-94 l°-40 Inc. 2° -289 2°-272 2°-417 2° -739 T. 3', 45" 3', 10" 3', 15" 3', 20" T'. 6', 5" 5', 15" 5', 25" 5', 30" V. 5-380 grms. 4-090 grms. 5-736 grmif. 6-272 grms. w. 289-0 grms. 291-4 grms. 294-5 grms. 282-7 grms. L.H. 116-7 116-7 117-7 117-3 Mean latent heat, 117 1. I have collected the foregoing results in the following table. The first column contains the latent heat for 1 gramme of each vapour ; the second for 1 liter, taken at the temperature of the point of ebullition of the vapour, and under the mean barometric pressure at which the experiments were performed. XX.] On the Latent Heat of Vapours. 177 For 1 Gramme. For 1 Liter. Bromine, 45 60 269-6 Protochloride of phosphorus, 51-42 244-4 Sulphuret of carbon, 86-67 254-9 Bichloride of tin, 30-53 253-5 Water, - 535-90 318-3 Sulphuric ether, 90-45 268-2 Alcohol, 202-40 324-2 Methylic alcohol. 263-70 303-5 Iodic ether. 46-87 254-7 Iodide of methyl. 46-07 252-8 Acetic ether, 92-68 287-9 Acetate of methyl, 110-20 303-6 ■Formic ether. 105-30 290-3 Formiate of methyl, 117-10 282-8 Oxalic ether. 72-72 291-4 It is obvious, from a cursory inspection of this table, that there exists some general relation between the volume of the vapour and its latent heat, but many other elements would require to be taken into consideration, before the precise nature of this relation can be determined. It has, indeed, been concluded, from a comparison I believe of the latent heats of water and alcohol, that the latent heat of equal volumes of different vapours is the same ; but the experimental results now obtained do not support so very simple and general a relation. It is not improbable, however, that under certain physical conditions, the proposition may be correct, but until these are realized, and the result established by direct experiment, we cannot be justified in drawing so general a conclusion. It may be well to remark, that in the above table, the latent heats of equal volumes of each vapour taken at the respective boiling points of the fluids are compared ; but in order to make the comparison more perfect, it would have been necessary to have examined equal volumes of the vapours taken at the same temperature. This could not, it is obvious, have been done, without operating under very different pressures, and thus introducing another source of complication into the results. Another circumstance, to which I may also refer, as connected with this subject, is the uncertainty that prevails as to the molecular constitution of some vapours near the temperatures at which they condense. The M 178 On the Latent Heat of Vapours. [xx. recent experiments of Cahours leave, it is true, little doubt that the densities of the vapours of the alcohols and of most of the compound ethers correspond with theory at all temperatures, but the singular anomalies presented by the acetic, formic, and sulphuric acids, and by the perchloride of phosphorus and some essential oils, show with what circumspection we must adopt the theoretical number as truly representing the density of any vapour near its point of condensation. Some of the irre- gularities in the results now given, may perhaps be traced to this cause. 179 XXI.— ON THE HEAT DISENGAGED DURING METALLIC SUBSTITUTIONS. From the Philosophical Transactions, 1848, Part I., p. 91. In the present comiminication I propose to give an account of some new investigations on the heat disengaged in chemical actions, which may be considered a continuation of my former inquiries on the same subject.^ The greater number of the experiments to be detailed in this paper were made some years ago, and the conclusion at which I arrived was briefly announced in the Philosophical Magazine for August, 1844. More recently, I have taken an opportunity to repeat many of my former experiments and to add new ones on the same subject, all of which confirm the general results formerly obtained. Having originally observed that although a very limited number of bases (potash, soda, barytes and strontia) develope nearly the same quantity of heat, when a chemical equivalent of each enters into combination with an acid, yet that the greater number of bases differ most widely from one another, when so treated, while on the other hand, that different acids {taken in the state of dilute solution) produce with the same base nearly the same amount of heat, I ventured to draw the general inference that the thermal effects produced are more intimately connected with the basic, or electro-positive, than with the acid, or electro-negative, element. In conformity with this view, it appeared probable that in the decomposition of solutions of neutral salts by the addition of bases or metallic bodies, the nature of the acid or electro-negative element of the compound would exercise no special influence on the result. I have already endeavoured to establish by experiment the truth of this principle in the case of basic substitutions, and, in ' Transactimis of the Boyal Irish Academy, vol. xix., pp. 228, 293. Also Philosophical Transactions for 1844, p. 21. 180 On the Heat Disengaged [xxi. •the present memoir, I propose to extend the same general law to the other case, in which one metallic element replaces, or is substituted for another. Few chemical actions are more simple in their final results, or admit more easily of being varied without changing the general type of the reaction, than those which form the subject of the present inquiry. "When a neutral solution of any salt of the black oxide of copper, as, for example, the sulphate, the chloride, or the acetate, is precipitated by metallic zinc, the final result is the substitution of an atom of zinc for an atom of copper in the solution, and the precipitation of an atom of copper. If the physical and chemical properties of equivalent solu- tions of different salts of copper be compared, they wO be found to present almost a complete identity, and the same remark applies to the solutions of the salts of zinc which remain after the reactions are finished. We have, therefore, every con- dition favourable to the production of simple thermal results. For the present object, it is not necessary to inquire in what state the metallic element exists in an aqueous solution of its salts, or what changes actually occur between the first addition of the zinc and the final precipitation of the copper ; it is enough to know that the final result is the same, whether we employ a solution of an oxy-salt, or of a haloid salt. The general result of the whole investigation may be stated in the following terms : — When an equivalent of one and the same metal replaces- another in a solution of any of its salts of the same order, the heat developed is always the same ; hut a change in cither of the metals produces a different development of heat. By the expression " solution of a salt of the same order" is. understood, a solution in which the same precipitate is produced by the addition of an alkali, or, on one view of the composi- tion of such salts, in which the metal exists in the same state of oxidation. SALTS OF COPPER WITH ZINC. Two distinct series of experiments were made with the salts of the black oxide of copper and metallic zinc. In the first series, concentrated solutions were taken and introduced into a small glass vessel, in which was XXI.] During Metallic Substitutions. 181 also placed a glass tube, open above, and containing pure zinc in a state of fine subdivision. The glass vessel, carefully- closed, was introduced into a larger vessel of copper furnished ■with a lid. The latter was filled with water adjusted to the proper temperature and suspended in an outer vessel of tin- plate, and the whole introduced into a cylinder closed with a lid and capable of being rotated.^ After all parts of the appar- atus had acquired the same temperature, a very sensible ther- mometer was introduced into the water contained in the copper vessel through a small orifice in the lid, and the position of the mercury in the tube observed. The thermometers having been removed and the orifice closed with a cork, the lid of the outer vessel was shut down, and the rotating wheel moved through half a revolution, by which means the metallic zinc was brought into contact with the copper solution. The rotation was afterwards continued for five minutes and a half, which was found to be sufficient not only to complete the precipitation of the copper, but also to diffuse the heat arising from the reaction uniformly through the apparatus. The temperature of the water was so adjusted as to render the corrections required for the heating and cooling influence of the air very inconsiderable ; their amount was, however, ascertained in each experiment and the results altered accordingly. To remove all uncertainty as to the strength of the solutions, a considerable quantity of each salt was dissolved in water, and a portion of the solution carefully analysed by precipitating the oxide of copper. The solutions were all employed in a per- fectly neutral state. In the second series of experiments, more dilute solutions were taken, and the increment of temperature observed directly in the solution in which the precipitation occurred. The zinc, cooled to the same degree as the liquid, was introduced after the temperature of the former had been observed, and the whole rotated for a period of one minute and a half. After the final temperature was taken, a few drops of the liquid were quickly withdrawn for future examination, and the apparatus was again ' For a description and representation of a similar apparatus, see Transae- itlons of the Royal Irish Academy, vol. xix. 182 On the Heat Disengaged [xxi. rotated for a period of one minute and a half. On again intro- ducing the thermometer, the temperature of the liquid was always found to be a few hundredths of a degree higher thanat the preceding observation, although the whole of the copper had been previously precipitated, and on repeating the same opera- tion several times, nearly the same development of heat occurred on each occasion. This secondary evolution of heat arose from two distinct causes, the oxidation of the precipitated metal by the air contained in the upper part of the glass vessel, and the voltaic circle formed by the precipitated copper with the zinc in excess. The influence of the former circumstance was clearly proved by repeating the experiment with the vessel as nearly filled as possible with the solution, which considerably diminished the amount of the secondary development of heat. But without entering into a minute discussion of the efficient causes of this rise of temperature, it is sufficient for the present object to observe that the same causes must have been in operation, even in a more intense degree, during the greater part of the first period of agitation, and would render the incre- ment then observed too high. The application of the required correction is very difficult, and the uncertainty on this point prevents absolute accuracy being attained in the following numerical results. As the most probable estimate, I assumed the correction to be equal to the increment observed during the second period of rotation, without applying any correction to this increment for the cooling influence of the air. The amount of this correction was usually about 0°'l C. It should be carefully remembered that the precipitation was in every experiment proved to be complete at the end of the first agita- tion, by removing a few drops of the solution and afterwards carefully testing it. In the first series of experiments with the salts of copper, no correction was applied for this secondary development of heat, because it was impossible to ascertain its amount, which, however, was probably less than in the experi- ments of the second series. FIRST SERIES. Sulphate of Copper and Zinc. — The solution of sulphate of copper weighed 43'3 grms., and contained I'lOO grm. oxide of XXI.] During Metallic Substitution a. 183 copper. The specific heat of the solution of sulphate of zinc which was formed, was found by direct experiment to be 0-935, and consequently its thermal equivalent 40 '5 grms. water. The apparatus in contact with the fluids contained 92 grms. copper, 20 grms. brass, and 43 grms. glass, besides the cork, etc. Its thermal equivalent, the excess of zinc included, was 17 "4 grms. water. The degrees are those of the centigrade scale. I. Air 13°-4. Increment found 2°-54, corrected 2°-53. Water 242-6 grms. Solution and vessels (equi- valent to) 57'9 grms. II. Air ll°-8. Increment found 2°-53, corrected 2°-53. Water 243-5 grms. Solution and vessels 57-9 grms. III. Air 12°-0. Increment found 2°-51, corrected 2°-52. Water 243-5 grms. Solution and vessels 57-9 grms. IV. Air 15°-4 Increment found 2°-51, corrected 2°-50. Water 243-6 grms. Solution and vessels 57-9 grms. Hence we have for the heat of combination referred to 1 grm. of metallic copper as unit, I. II. III. IV. Mean. 866° 868° 865° 858° 864° Chloride of Copper and Zinc. — The solution of chloride of copper weighed 43-3 grms. and contained 1-100 grm. oxide of copper. The specific heat of the solution of chloride of zinc was found to be 0-946. I. Air 13°-5. Increment found 2°-50, corrected 2°-51. Water 243-3 grms. Solution and vessels (equivalent to) 58-3 grms. II. Air 14°-0. Increment found 2°-52, corrected 2°-52. Water 238-3 grms. Solution and vessels 58-3 grms. III. Air 14°-9. Increment found 2°-49, corrected 2°-50. Water 244-8 grms. Solution and vessels 58-3 grms. IV. Air 13°-6. Increment found 2°-49, corrected 2°-50. Water 241-1 grms. Solution and vessels 58-3 grms. We have, therefore, for the heat of combination referred to the same unit as before, I. II. III. IV. Mean. 862° 851° 863° 852° 857° 184 On the Heat Disengaged [xxi. Acetate of Copper and Zinc. — The solution of acetate of copper weighed 43"3 grms., and contained 1'092 grm. oxide of copper. The solution of acetate of zinc formed during the reaction had a specific heat of 0'930. I. Air 16°-7. Increment found 2°-43, corrected 2°-44. Water 242*8 gi-ms. Solution and vessels (equivalent to) 5 7" 6 grms. II. Air 16°-7. Increment found 2°-43, corrected 2°-44. Water 24 3 '6 grms. Solution and vessels 57"6 grms. III. Air 15°-5. Increment found 2°-40, corrected 2°-41. Water 242-8 grms. Solution and vessels 57'6 grms. I. II. III. Mean 841° 843° 830° 838° SECOND SERIES. Sulphate of Copper and Zinc. — The solution of sulphate of copper weighed 100 grms., and contained 0'360 grm. oxide of copper. The specific heat of the solution of sulphate of zinc was ascertained by experiment to be 0"989. A large excess of zinc (4"5 grms.) in the state of fine filings was taken, in order to complete the action in the shortest possible time. The ziac had been carefully distilled, and contained not more than O'OOOS of impurity, which was chiefly lead. The glass vessel in which the experiment was performed, weighed 50 grms., and the thermal value of the entire apparatus with its contents was 106'3 grms. The whole of the copper was precipitated in the course of one minute and a half of agitation. I. Air 17°-9. Increment found 2°-48, corrected 2°-35. II. Air 17°-8. Increment found 2°-50, corrected 2°-37. III. Air 17°-5. Increment found 2°-48, corrected 2°-35. In these experiments the glass vessel was not entirely filled with the solution, and the correction for the secondary develop- ment of heat amounts, it will be observed, to 0°'13. In the two foUowiug experiments, a much smaller quantity of air was left iu the vessel, and the correction was thereby reduced to 0°'05. The solution now weighed 130-0 grms., and contained 0'468 grm. oxide of copper. The thermal equivalent of the whole apparatus was 136"3 grms. XXI.] During MetalUo Substitutions. 185 IV. Air 15°-5. Increment found 2°-40, corrected 2°-35. V. Air 16°-0. Increment found 2°-42, corrected 2°-37. I. II. III. IV. V. Mean. 869° 876° 869° 857° 867° 868° Chloride of Copper and Zinc. — The solution contained the same weight of oxide of copper, and the zinc solution had the same specific heat as the preceding. The last experiment was adjusted in the same manner as the fourth and fifth of the fore- going series. I. Air l7°-2. Increment found 2°-43, corrected 2' "•31. II. Air l7°-0. Increment found 2°-46, corrected 2° •34. III. Air 17°-6. Increment found 2°-46, corrected 2° ■34. IV. Air l7°-8. Increment found 2°-44, corrected 2° •32. V. Air 16°-1. Increment found 2°-40, corrected 2° ■35. I. II. III. IV. V. Mean. 8 54° 865° 865° 858° 857° 860° I. II. III. Air 17°^ 3. Air 17°^3. Air 18°^0. I. 875° Acetate of Copper and Zinc. — 100 grms. of a solution of this salt containing 0"360 grm. oxide of copper were taken. Specific heat of zinc solution 0^987. Thermal value of the whole 106'1 grms. Increment found 2°-49, corrected 2°^37- Increment found 2°'50, corrected 2°^38. Increment found 2°'5G, corrected 2°^38. TI. III. Mean. 878° 878° 877° Formiate of Gopher and Zv/ic. — The solution of this salt corresponded in all respects with that of the sulphate of copper. I. Air l7°-8. Increment found 2°-43, corrected 2°-36. II. Air 17°^6. Increment found 2°-41, corrected 2°-34. I. II. Mean. 873° 865° 869° Collecting the foregoing results, we find for the heat of com- bination from the first series, Sulphate of copper, 864° Chloride of copper, 857 Acetate of copper, 838 186 On the Heat Biseiigaged [xxi. And from the second series, Sulphate of copper, 868 Chloride of copper, 860 Acetate of copper, 877 rormiate of copper, 869 The agreement among these numbers is as close as can be expected in experiments of this kind, in which other disturbing sources of heat are present, whose precise influence it is difficult to estimate. It is very plain that the heat developed is wholly independent of the acid with which the metal is combined. The results obtained in the two series, in which solutions of very different strengths were employed, differ little from one another, but an accurate comparison cannot be made, as no correction for the disturbing thermal effects was applied to the numbers of the first series. AVe may, however, conclude that, within the limits of these experiments, the heat developed by the same amount of metallic substitution is nearly the same in solutions of different strengths. It is probable that this observation wiU not be found strictly to apply to very con- centrated solutions. It is almost unnecessary to remark that if, in the course of the reaction, any chemical change occurs besides the displace- ment of one metal by another, the heat evolved wiU no longer be the same. On this account, solutions of the metallic nitrates, especially if concentrated, are not adapted for this investigation. If we take the mean of the numbers in the second series, and adopt .S'96 as the atomic weight of copper, we shall have for the heat extricated during the displacement of C. F. 1 grm. copper by zinc, - 868° or 1562° 1 equiv. copper by zinc, 3435° or 6183° SALTS OF COPPER WITH lEOX. Two distinct series of experiments similar to the preceding were made on the precipitation of the salts of copper by iron. In the first series, the apparatus and solutions were in aU respects the same as in the experiments with zinc. A large quantity (from 12 to 13 grms.) of the precipitating metal was required. XXI.] During Metallic Substitutions. 187 FIRST SEEIES. Sulphate of Copper and Iron. I. Air 14°-7. Increment found l°-68, corrected l°-68. Water 246-4 grms. Solution and vessels (equivalent to) 59'1 grms. II. Air 14°-9. Increment found l°-68, corrected l°-68.. Water 244'3 grms. Solution and vessels 59'1 grms. III. Air 14°-4. Increment found l°-65, corrected l°-68. Water 2 43 '5 grms. Solution and vessels 59'1 grms. Hence we have for the heat of combination referred to 1 grm. copper as uni t, I. 584° II. 580° III. 579° Mean. 581° Chloride of Copper and Iron. T. Air 15°'5. Increment found 1°'77, corrected 1°'77. Water 243'1 grms. Solution and vessels 5 9 '5 grms. II. Air 14°-2. Increment found l°-77, corrected l°-77. Water 2 42 '5 grms. Solution and vessels 5 9 '5 grms. I. 11. Mean. 609° 610° 609°-o The greater amount of heat in the latter experiments arose from the proto-chloride of iron absorbing oxygen more rapidly than the proto-sulphate. In the next series this source of error was avoided, and the results agree better with each other. SECOND SERIES. In these experiments the salts were dissolved in recently boiled water, and a small bubble of air only was left in the containing vessel. Each solution weighed 126'7 grms. and contained 0'456 grm. oxide of copper. Sulphate of Copper and Iron. I. Air 15°-5. Increment found l°-64, corrected l°-62. Heat of combination 593°. Chloride of Copper and Iron. I. Air 15°-5. Increment found l°-64, corrected 1°-61. Heat of combination 590°. 188 On the Heat Disengaged [xxi. Taking the mean of the last experiments, we obtain for the heat extricated during the precipitation of C. F. 1 grm. copper by iron, - 592° or 1066° 1 equiv. copper by iron, 2342° or 4216° SALTS OF COPPER "WITH LEAD. Acetate of Copper and Lead. — As before, 100 grms. of a solution of acetate of copper containing 0"360 grm. oxide were taken. A large excess of lead (15 grms.) was required for complete precipitation. The thermal value of the entire was 106'0 grms. I. Air 21°-5. Increment found 0°-89, corrected 0°-77. II. Air 21°-5. Increment found 0°-89, corrected 0°77. I. ir. Mean. -' 284° 284° 284° Formiate of Copper wnd Lead. — The solution was adjusted as before. I. Air l7°-2. Increment found 0°-82, corrected 0°-72. II. Air 17°-1. Increment found 0°-8.3, corrected 0°-71. III. Air 16°-0. Increment found 0°-80, corrected 0°-70. I. II. III. Mean. 265° 269° 259° 268° Hence we have for the heat evolved duriug the precipitation of C. F. 1 grm. copper by lead, 268° or 482° 1 equiv. copper by lead, 1061° or 1909° SALTS OF SILVER WITH ZINC. The salts of silver are easUy reduced by agitating their solutions with finely divided zinc. The sulphate and acetate were selected for experiment, and the results will be found to afford a further illustration of the general principle laid down in the commencement of this paper. The secondary development of heat was also clearly manifested, and continued for a con- siderable period of time, but gradually diminished in intensity. The two following observations will exhibit the amount of this XXI.] Luring Metallic Substitutions. 189 heat, which, in the case of the salts of silver, must be chiefly ascribed to voltaic action. The annexed numbers give the increments of heat observed at intervals of two minutes, during each of which the agitation was continued in precisely the same manner. A few drops of the liquid having been removed after the first period of agitation, gave afterwards not the slightest opalescence with chloride of sodium, showing that the metallic precipitation was then finished. Sulphate of Silver. Acetate of Silver. First increment, l°-96 l°-94 Second increment, 0"14 0'12 Third increment, 0-12 012 Fourth increment, O'lO 0-08 Fifth increment, 0-09 0-06 Sixth increment, 0-04 0-06 The final temperature of the hquid was about 0°'7 above that of the surrounding air. The existence of a considerable amount of voltaic action was clearly shown by the evolution of hydrogen gas from the surface of the precipitated silver. Sulphate of Silver and Zinc. — The weight of the solution taken was 100 grms. An equal portion of the same solution yielded, on analysis, 0'600 grm. chloride of silver, correspond- ing to 0"452 grm. metallic silver. The thermal equivalent of the solution of sulphate of zinc obtained after precipitation was 99"6 grms. water, and of the vessels, etc. 6-8 grms. I. Air 16°'6. Increment found 1°"96, corrected 1°'82. II. Air 15°-2. Increment found l°-93, corrected l°-80. III. Air 15°-2. Increment found l°-92, corrected l°-79. I. II. III. Mean. 428° 424° 421° 424° In another set of experiments a weaker solution was employed, which gave, on analysis, 0-571 grm. chloride of silver. The thermal value of the whole was now 106-7 grms. Increment found l°-80, corrected l°-72. Increment found l°-80, corrected l°-72. Increment found 1°-81, corrected l°-73. II. III. Mean. 427° 429° 428° I. Air 18°2. II. Air 18°-0. III. Air I. 427° 18°-1. 190 On the Heat Disengaged [xxi. Acetate of Silver aind Zinc. — 100 grms. of the solution gave €•600 grm. chloride of silver. I. Air 16°-4. Increment found 1°'94, corrected 1°82. II. Air 15°-2. Increment found l°-93, corrected 1°-81. III. Air 15°-0. Increment found l°-9.3, corrected l°-80. I. II. III. Mean. 428° 426° 424° 426° This result is identical with the mean number deduced from the experiments with the sulphate. We have, therefore, for the heat evolved during the precipitation of C. F._ 1 grm. silver by zinc, 426° or 767° 1 equiv. silver by zinc, 5747° or 10345° It has been . already remarked that the nitrates do not in general yield the same thermal results as other salts, in con- sequence of the tendency of the nitric acid to decompose, which introduces other chemical actions in addition to the metallic precipitation. Approximate results were, however, obtained with the nitrate of silver. 100 grms. of a solution of nitrate of silver, containing 0'711 grm. of the dry salt, gave in three trials 2°-12, 2°'13 and 2°-ll, as increments, without any correction being applied. On continuing the agitation for periods of two minutes, and observing the temperature at the end of each period, the increments followed a singular law, being at first very small, and afterwards suddenly increasing. The march of the thermometer wUl be readily understood by inspecting the following numbers, which give the temperatures observed at the end of every two minutes of agitation : First increment. 2-12 213 211 Second increment, 0-03 0-06 0-07 Third increment, 003 002 0-03 Fourth increment, 014 0-11 017 Fifth increment, 0-23 0-17 0-25 Sixth increment. 018 016 0-20 Seventh increment, 013 015 0-23 Eighth increment. Oil Oil 016 XXI.] Buri/ng Metallic Substitutions. 191 The sudden increase in the amount of the increment which took place after the agitation had continued for six minutes is very remarkable, and it occurred uniformly in all the experi- ments. It plainly shows that some new voltaic or chemical action occurred at that time, with the nature of which I am not precisely acquainted. No analogous irregularity occurred with any of the other salts of silver which were examined. SALTS OF SILVEK WITH COPPER. All the solutions of silver in these experiments contaiaed the same quantity of silver. 100 grms. of each, precipitated by hydrochloric acid, gave 0"600 grm. chloride of silver. The copper had been reduced from the oxide by hydrogen, and about 2 grms. were taken in each experiment. Sulphate of Silver and Copper. I. Air 13°-9. Increment found 0°73, corrected 0°-68. II. Air 13°-7. Increment found 0°-71, corrected 0°-6y. III. Air 12°-7. Increment found 0°-76, corrected 0°-71. I. II. III. Mean. 159° 161° 166° 162° Acetate of Silver and Copper. I. Air 13°-4. Increment found 0°-68, corrected 0°-67. II. Air 12°'8. Increment found 0°'71, corrected 0°66. III. Air 12°-8. Increment found 0°-71, corrected 0°'66. I. II. III. Mean. 157° 155° 155° 156° nitrate of Silver and Copper. I. Air 13°-8. Increment found 0°-74, corrected 0°-70. II. Air 13°0. Increment found 0°-75, corrected 0°-70. III. Air 12°-8. Increment found 0°-77, corrected 0°-72. I. II. III. Mean. 164° 169° 169° 166° In this case the numbers obtained with the nitrate agree with the others. Hence we have for the heat developed during the precipitation of C. F, 1 grm. silver by copper, 161° or 290° 1 equiv. silver by copper, 2176° or 3917° 192 On the Heat Disengaged [xxi. SALTS or LEAD WITH ZINC. Acetate of Lead and Zinc. — The precipitation of lead from its solutions by metallic zinc is difficult to complete in a short space of time. A large excess of zinc (8 grms.) was required and four minutes of agitation. The results on this account are only approximations. The solution weighed 130 grms. and contained 1"305 grm. oxide of lead. The thermal equivalent of the whole was 136'0 grms. water. I. Air 17°-8. Increment found l°-63, corrected l°-60. II. Air 16°'5. Increment found 1°'68, corrected 1°"65. I. II. Mean. 180° 185° 182°-5 Formiate of Lead and Zinc. — 0*433 grm. of the salt employed gave 0'324 grm. oxide of lead. 100 grms. of the solution contained 1'35 grm. of the formiate. I. Air 12°'7. Increment found 1°"74, corrected 1°'61. I. 181°-5 Hence we have for the heat evolved during the precipitation of C. F. 1 grm. lead by zinc, ... 182° or 327° 1 equiv. lead by zinc, - 2357° or 4243° SALTS OF MERCURY WITH ZINC. Chloride of Mercury and Zinc. — This is the only salt of mer- cury which was examined. The result, however, is sufficient to determine the thermal position of mercury among the metals. 100 grms. of a solution containing 1'240 grm. chloride of mercury were taken. The thermal value of the whole was 106'4 grms. water. In this case no further development of heat occurred after the precipitation was completed, nor was there any disengagement of hydrogen gas. The excess of zinc, in fact, became amalgamated, which effectually prevented both oxidation and voltaic action. I. Air 16°-6. Increment found 2°-86, corrected 2°-86. II. Air 16°-5. Increment found 2°-85, corrected 2°-88. III. Air 16°-4. Increment found 2°-88, corrected 2"-88. I. II. III. Mean. 332° 334° 334° 333° XXI.] During Metallic Substitutions. 193 "We have, therefore, for the heat disengaged during the dis- placement of C. F. 1 grm. mercury by zinc, 333° or 600° 1 equiv. mercury by zinc, 4166° or 7499° SALTS OF PLATINUM WITH ZINC, Soda-Chloride of Platinum andZinc. — Of thesaltsof platinum, the double chloride of sodium and platinum is best adapted for this investigation. The complete precipitation of platinum by zinc is more difficult, and requires a longer time than that of any of the metals hitherto examined. This renders the corrections larger and the final results less exact. To ascertain the com- position of the salt employed, 0'692 grm. carefully dried were precipitated by muriate of ammonia and the precipitate ignited; 0'298 grm. metallic platinum were obtained. The solution employed in each experiment weighed 100 grms., and contained 0'721 grm. of the dry salt. I. Air 15°-4. Increment found 2°-94, corrected 2°-64. II. Air 16°-2. Increment found 2°-93, corrected 2°-62. I. II. Mean. 902° 896° 899° Hence we have for the heat disengaged during the precipita- tion of C. F. 1 grm. platinum by zinc, 899° or 1618° F. 1 equiv. platinum by zinc, 11085° or 19953° It would have been very interesting to have extended this investigation to other cases of metallic substitution, so as to have been able to present in one complete view the quantities of heat developed in all such cases ; but the facility with which some metals are oxidized, and the difficulty of precipitating others in a short space of time from their solutions, prevenied me from further extending the foregoing results. Tor con- venience, I have collected in the following table the numerical quantities already obtained : — Of precipitated metal. Igrm. 1 equiv. 868° 3435° 592 2342 268 1061 426 5747 161 2176 182 2357 333 4166 194 On the Heat Disengaged [xxi. Salts of copper and zinc, Salts of copper and iron, Salts of copper and lead, - Salts of silver and zinc. Salts of silver and copper. Salts of lead and zinc, Salts of mercury and zinc. Salts of platinum and zinc, - 899 11085 To prevent mistake, it may be right here to state that the numbers in the first column express the degrees centigrade through which one gramme of water would be heated by the precipitation of one gramme of the metal from a solution of any of its salts ; and that those in the second column express the degrees through which the same weight of water would be raised by the precipitation of an equivalent (oxygen = 1) of the same metal. If three metals. A, B, C, be so related that A is capable of displacing B and C from their combinations, and also B capable of displacing C ; then the heat developed in the substitution of A for C will be equal to that developed in the substitution of A for B, added to that developed in the substitution of B f or C ; and a similar rule may be applied to any number of metals similarly related. Several illustrations of this principle are afforded by the preceding table. Thus 1 eqiiiv. lead displaced by zinc, 2357° 1 equiv. copper by lead, - 1061 1 equiv. copper by zinc, - 3418 The experimental result for the last case is 3435°, which in such inquiries ,may be considered to be identical with the theoretical number. Again, 1 equiv. copper by zinc, 3435° 1 equiv. silver by copper, - 2176 1 equiv. silver by zinc, - 5611 XXI.] During Metallic Substitutions. 195 The experimental result is 5747°, which differs Ard part from theory. This difference only corresponds to an error of about 0°'04 among the three experiments, and the agreement may therefore be considered satisfactory. By applying the same principle, we can easily deduce the amount of heat developed in other cases of metallic substitution. Thus an equivalent of mercury displaced by zinc should give 731 units of heat, of platinum displaced by copper 7650 units, by mercury 6919 units, &c. 196 XXII.— REPOKT ON THE HEAT OF COMBINATION. From the Re/port of the British Association, 1849, p. 63. Theke are few molecular changes in the condition of matter which are not accompanied by the evolution or absorption of heat. The quantity of heat which is thus set free or absorbed, bears always a definite relation to the amount of the mechanical or chemical action, and its determination in each particular case is a problem of considerable interest as affording a measure of the forces in action. If we consider the great number of phae- nomena, mechanical, electrical and chemical, among which the production of heat forms the only bond of connexion which has- hitherto been clearly ascertained, although there may be strong, grounds for suspecting them to be only modified forms of the action of the same force, the importance of investigations of ithis kind to the future progress of physical science will become 'at once apparent. The object of the present Eeport is to give a general view of the actual state of knowledge on the subject of thermo-chemistry, under which we may conveniently include a Sescnption of the thermal effects that occur in chemical actions of every kind. A few new experiments wiU be described in their proper places. These will be given in some detail, but when referring to experi- ments already published, all numerical quantities will, as far as possible, be avoided. Before entering upon the consideration of chemical combin- ations and decompositions properly so called, it may be useful briefly to refer to the thermal changes which accompany solution. The earlier experiments on this subject having been made solely with the object of discovering frigorific mixtures, do not furnish quantitative measures p4-any scientific value. But of late years the inquiry has been pursued in a more useful XXII.] Report on the Heat of Combination. 197 way by Gay-Lussac, Thomson, Karsten, Chodnew and Graham. The salts examined have been chiefly the soluble sulphates, nitrates and chlorides, and the solvents pure water and saline and acid solutions. The principal results of these investiga- tions I have endeavoured to express in the following proposi- tions: — 1. The solution of a cystallized salt in water is always accompanied by an absorption of heat. 2. If equal weights of the same salt be dissolved in succes- sion in the same liquid, the heat absorbed will be less on each new addition of salt. 3. The heat absorbed by the solution of a salt in water, holding other salts dissolved, is generally less than that absorbed by its solution in pure water. 4. The heat absorbed by the solution of a salt in the dilute mineral acids, is generally greater than that absorbed by its solution in water. As the subject is of great extent, and the inquiry has hitherto embraced only a small number of cases of solution, it is not unlikely that some of these conclusions will require hereafter to be modified. From some experiments by Graham on the solution of salts belonging to certain isomor- phous groups, there is reason to suspect the existence of a ■connexion between isomorphism and the absorption of heat in solution. The foregoing remarks apply only to the solution of crystal- lized salts. If, however, we take a salt which crystallizes with water and make it anhydrous before solution, the thermal results will be altogether different. The anhydrous salt, when added to an excess of water, will first combine with its ordinary equivalent of water of crystallization, and the new compound will then dissolve. The change of temperature observed is therefore a complex quantity arising from the heat of combin- ation due to the union of the anhydrous salt with water, and the heat absorbed by the solution of the hydrous salt. From a comparison of the results obtained on dissolving the same salt in the anhydrous and hydrous states, Graham has endeavoured to deduce the amount of heat due to the combination of the dry .^alt with its water of crystallization. According to his experi- 198 Report on the Heat of GombiTiation. [xxn. ments, the sulphates of water, copper and manganese, disengage the same quantity of heat iu combining with the first atom of water. The sulphates of magnesia and ziac also disengage equal quantities of heat in their complete hydration. The same simple relation is not however observed to hold between the quantities of heat evolved in the complete hydration of the first set of salts, or in the combination of the second set with the first atom of water. Neither does it apply to the other sulphates of the magnesian series. None of the experiments hitherto published furnish all the requisite data for calculating with precision the absolute quantities of heat set free or absorbed in these cases of chemical action. The weights of the water and of the salt are given, and sometimes the weight and form of the vessel, and the material of which it is composed ; but these data are not sufficient to enable us to deduce the true numbers from the observed incre- ments or decrements of temperature. Knowing the weight and composition, of the containing vessel, we may, it is true, calculate its thermal value in water. But other corrections, such as those for the heatiag and cooling iafluence of the surrounding air, can only be ascertained by special experiments performed under similar conditions to the original observations. Neither have any experiments of sufficient accuracy been made to determine the specific heats of the solutions formed. To complete an investigation which would furnish all these elements, woidd be a work of very great labour, and will pro- bably scarcely be undertaken till our instruments and means of observation are greatly improved. As a first step to such an inquiry, I may here describe a few preliminary experiments on the specific heats of some saline solutions, and on the quantities of heat absorbed in the solution of successive portions of the same salt. To obtain results approaching to accuracy in experiments on the specific heats of saliue solutions is extremely difficult, as the errors of experiment are often of nearly the same order of magnitude as the whole differences to be observed. The correc- tions for the cooling and heating action of the air and for the effects of radiation, cannot be estimated with any certainty by the application of general formulas founded on experiments XXII.] Report on the Heat of Combination. 199 made at a different time;i and the most careful examination of the calibre of the thermometer tube will fail to render different parts of the scale accurately comparable with one another to a five-hundredth part. The general method pursued in the deter- mination of the following specific heats was the same which I described some years ago;^ but to avoid the uncertainties just referred to, alternate experiments were made with pure water and with the solution under conditions as nearly as possible identical, and these were repeated till accurate means were ob- tained. By this mode of operating, a very great degree of precision may be given to experiments of this kind. The only salts whose solutions have yet been examined are the nitrate of potash, the nitrate of soda and the chloride of sodium. They were all chemically pure. The density of each solution compared with water at the same temperature was also determined. The first solution of nitrate of potash contained for every 100 parts of water 25-29 parts of the salt. The thermal values of the thermometer with large reservoir described in the paper already referred to, in terms of this solution and of water, were found in alternate experiments to be — Solution I. Water. 5044. 4095 5047 4107 5050 4116 Mean, - 5047 4106 The temperature of the air during these experiments varied only from 18° C. to 18°- 5 0. The second and third solutions contained respectively 1 2 "6 4 5 and 6 '3 2 2 parts of nitrate of potash for 100 parts water. Air from 18°-5 to 18°-9. ^ If the vessel be uncovered, changes in the hygrometric stateof the atmosphere produce a very marked inflvience on the rate of cooling, -when the excess of temperature above the air amounts only to a few degrees ; and even in a close apartment the increased agitation of the air on a windy day sensibly increases the rate of cooling. ^Philosophical Transactions for 1844, p. 34. 200 Report on the Heat of Combination. [xxn. Solution II. Solution III. Water. 4600 4393 4118 4620 4387 4105 4605 4385 4108 4610 Mean 4610 4387 4110 From these data the specific heats of these solutions at the temperatures at which the experiments were performed, as com- pared with water at the same temperatures, may be easily com- puted. I have given them in the following table, as also the specific gravities of the liquids. I. II. III. Specific heat 0-8135 0-8915 0-9369 Specific gravity - 1-1368 1-0728 1-0382 The solutions of nitrate of soda contained 42-49, 21-245 and 10-622 parts respectively of nitrate of soda for 100 parts of water. The temperature of the air ranged from l7°-5 to 18°-8 during these experiments. Solution I. "Water. Solution II. Water. Solution III. Water. 5261 4107 4775 4116 4499 4116 5234 5117 4782 4098 4498 4098 5247 4119 4787 4100 4488 4100 Mean a 5247 4114 4781 4105 4495 - 4105 Specific heat Specific gravity - I. 0-7838 1-2272 II. III. 0-8585 0-9131 1-1256 1-0652 Of chloride of sodium two solutions were examined, the first containing 29-215, the second 14-607 chloride of sodium for 100 water. The air was nearly steady between 17°-9 and 18°. Solution I. Water. Solution II. Water. 5107 4111 4740 4111 5127 4106 4733 4106 5128 4731 Mean 5121 4108 4735 4108 I. II. Specific heat 0-8018 0-8671 Specific gravity 1-1724 1-0942 XXII.] Report on the Heat of Combination. 201 It may be not uninteresting to compare these numbers with those deduced by calculation from the specific heats of the salts in the dry state. The latter have been made the subject of experiment by Avogadro and Eegnault, but their results do not agree well with each other. I have adopted Eegnault's num- bers in my calculations. Solution. Nitrate of potash by 1. Decific heat experiment. 0-8135 Mean spec, heat of dry salt and water. 0-8463 }i it - 2. 0-8915 0-9145 jt )» 3. 0-9369 0-9566 Nitrate of soda 1. 0-7838 0-7847 33 >3 2. 0-8585 0-8736 _,, » 3. 0-9131 0-9307 Chloride of sodium 1. 0-8018 -0-8224 // w - 2. 0-8671 0-9000 It is obvious that the specific heat of the solution is, in every instance, less than the mean of the specific heats of its com- ponent parts, and that serious errors would be committed, if we should attempt to calculate on this principle of the thermal values of solutions which may be formed in the course of our experiments. I have made a short series of experiments on the quantities of heat absorbed during the solution of nitrate of soda and of nitrate of potash, when added in successive portions to the same liquid. The results fully confirm those previously obtained by Graham, but as the experiments were only preliminary trials to a more extended investigation, it is not necessary to describe them in detail. I may briefly state, tliat on dissolving 12-22 grammes of nitrate of soda in 250 grammes of water and repeating the experiment with each new solution, till the water was nearly saturated, the following decrements of temperature were found : — „ „ 1. 2-80 C. 6. 1-60 C. 2. 2-43 7. 1-47 3. 2-11 8. 1-39 4. 1-89 9. 1-33 5. 1-75 10. 1-^7 11. 1-21 202 Report on the Heat of Combination. [xxu. By the aid of the specific heats already determined, and knowing the thermal value of the vessel in which the experi- ments were performed (4'3 grms.), I have calculated for experi- ments 1, 4 and 9 the following numbers, which express the degrees Centigrade through which one part of water would be raised by the heat absorbed in the solution of one part of the salt. 1. 2. 3. 590 407 309 On dissolving 7 '9 9 grms. nitrate of potash in 250 grms. water, and repeating the operation as before, the successive decrements of temperature observed were, — 1. 2-65 C. 5. 2-06 C. 2. 2-49 6. 1-97 3. 2-34 7. 1-87 4. 2-22 8. 1-75 Combination of Sulphuric Acid with Water. — In an elaborate memoir on thermo-chemistry, which was published in Poggen- dorfF's 'Annalen,' Hess made the first systematic attempt to reduce the quantities of heat disengaged in the formation of the hydrates of sulphuric acid to definite laws. His experiments were made by two distinct methods, which however did not give exactly the same results. In the first or indirect method of operating, equivalent quantities of SO^, SO3HO, SO32HO, &c., were respectively mixed with a large excess of water and the increments of temperature observed in each case. The difference between the increments observed on mixing any two compounds with water, was assumed to correspond to the heat due to the combination of the first compound with the number of equivalents of water necessary to convert it into the second. Thus, if SO3HO added to jcHO gave a units of heat, and SO^SHO added to the same xHO gave & units, a-h was supposed to represent the number of units which would be obtained on combining SO3HO and 2H0. In the second, or direct method, each compound was combined with the quantity of water exactly required to convert it into the succeeding compound, and the heat measured by observing the increment of tempera- 6 xxii.] Report on the Heat of Combination. 20S ture of a determinate quantity of water surrounding the vessel in which the combination took place. These experiments have since been repeated by Graham, Abria, and Fabre and Silber- mann, but their results do not generally agree with the state- ments of Hess. The fundamental principle laid down by the latter is, that there exists a simple relation between the numbers which ex- press the quantities of heat set free in the formation of the suc- cessive hydrates of sulphuric acid. If we designate by 2a the heat disengaged in the combination of SO^HO with HO, then, according to Hess, the heat set free in the formation of the other hydrates will be SO3 + HO 8a SOjHO-fHO - 2a SO32HO + HO a SO3.3HO + 3HO - a SO36HO-I-CCHO - a In an early part of his memoir, Hess gives 3 8 "8 5 for the value of a, but this he afterwards changes to 46'94, still maintaining however the accuracy of the ratios. It is difficult to see how this can be correct. The only experiment described by Hess on the combination of the anhydrous acid with water gave the number 305, which bears to 46'94, not the ratio of 8:2, but nearly that of 6-5 to 2. Abria obtained a still lower number for the combination SO3 with HO. There can therefore be little doubt, if the experiments may be relied on, that the first ratio is too high. It remains to be seen how far the others have been confirmed by subsequent investigations. The multipliers of a for the three latter combinations given in the preceding table are, according to Graham's experiments, 0-72, 1-35 and 1'18. These numbers agree with Hess's state- ment only so far as to indicate that the heat evolved in the combination of SO^HO with HO is nearly the same as that evolved in the combination of SO32HO with 4H0. The experiments of Abria were performed by the direct method and with a similar apparatus to that employed by Hess. Adopting the views of Hess as to the quantities of heat in the cases of combination being in simple relations to one another. leory. Experiment. 6a 602a 2a 2-OOa a 0-95a ia 0-57a ia 0-35a |(Z 0-22a 204 Report on the Heat of Combination. [xxii. he arrives nevertheless at very different numbers for the ratios. In the next table I have given Abria's theoretical whole num- bers, as also the exact numbers which result from his ex- periments. SO3-I-HO SOjHO-fHO SO32HO-I-HO SOgSHO-hHO S034HO-t-HO SO^oRO + RO In the three latter cases, the simple relations iu the second column are scarcely borne out by the experimental numbers. The only agreement with the ratios given by Hess is in the combination SO32HO with HO, which, according to both experimenters, sets free exactly half as much heat as the com- bination SO3HO with HO. The value of a, given by Abria, is 39-33. The latest experiments on this subject are those of Fabre and Silbermann, from which I have calculated the following multipliers for a : — SO3HO-I-HO 200a S032HO-f-HO 0-93a SOgSHO-l-HO 0-53a SO34HO + HO 0-32a SOgSHO-fHO - 0-26a Hess has also attempted to express by simple multiple relations the quantities of heat disengaged in the formation of the hydrates of nitric acid, but for the details of his results I must refer to the original memoir. Combination of Acids and Bases.- — In the same memoir Hess describes an extensive set of experiments on the heat evolved during the union of certain bases with acids of different degrees of concentration. These experiments serve to illustrate the general principle, that in the formation of a chemical compound the heat developed is a constant quantity, being the same in amount, whether the combination takes place directly at one time or indirectly at repeated times. Thus he finds that on XXII.] Report on the Heat of Combination. 205 neutralizing an aqueous solution of ammonia with sulphuric acid, containing one, two, three and six atoms of water, there is a different development of heat in each case ; but by adding to the results found by experiment in the three latter cases the quantities of heat due to the combination of the monohydrated acid, with one, two and five atoms of water respectively, the same number is obtained in each case as in the direct combin- ation of the monohydrated acid itself. This principle is correct, but it is almost self-evident and scarcely required so elaborate a proof. The bases examined by Hess were potash, soda, ammonia and lime, which he combined in different ways with the sul- phuric, nitric and hydrochloric acids. The conclusion at which he arrives is, that the same acid in combining with equivalents of different bases produces the same quantity of heat, but at the same time he expresses some doubt as to the applicability of this principle to all similar cases of combination. Indeed, his own experiments with lime and ammonia do not accurately agree with it ; I refer particularly to his experiments with ammonia, which, when properly interpreted, appear to me to prove clearly that that base in combining with acids develops less heat than potash or soda, although I am aware that Hess himself has drawn from them a different conclusion. About the time of the publication of the first part of Hess's memoir, I had completed an investigation of the same subject, but instead of employing strong solutions of the acids and bases, I diluted all the liquids largely with water previous to exam- ining their thermal reactions. In this way I hoped to avoid the complex effects that arise when successive combinations and decompositions of different kinds occur in the same chemical action, and the result fully realized my anticipations. The general conclusion deduced from this investigation may be briefly expressed, by stating that the heat developed during the union of acids and bases is determined iy the base and not by the acid. The following special laws will be found to comprehend the greater number of cases of chemical action to which the foregoing principle can be made to apply. 1. An equivalent of the same base, combined with different acids, produces nearly the same quantity of heat. 206 Report on the Heat of Combination. [xxii. 2. An equivalent of the same acid, combined with different hases, produces different quantities of heat. 3. When a neutral salt is converted into an acid salt by ■combining with one or more equivalents of acid, no disengage- ment of heat occurs. 4. When a double salt is formed by the union of two neutral salts, no disengagement of heat occurs. 5. When a neutral salt is converted into a basic salt, the ■combination is accompanied by the disengagement of heat. 6. When one and the same base displaces another from any •of its neutral combinations, the heat evolved or absorbed is always the same whatever the acid element may be. As some of the bases (potash, soda, barytes and strontia) form what we may perhaps designate an isothermal group, such bases will develop the same, or nearly the same heat in com- bining with an acid, and no heat will be developed during their mutual displacements. These laws are not intended to embrace the thermal changes which occur during the conversion of an anhydrous acid and base into a crystalline compound. The steps by which such a conversion is effected are generally very complicated, and involve successive combinations and decompositions. We can- not combine, at ordinary temperatures, a dry acid and a dry base ; and when combination takes place in presence of water, hydrates of the acid and base are first formed, which are after- wards decomposed, and the crystalline salt finally obtained is sometimes anhydrous, sometimes combined with water. To expect simple results where so many different actions must produce each its proper thermal effect, would be altogether vain, and to introduce the consideration of some of these actions without the whole would only render the numbers empirical. In the experiments from which the foregoing laws were deduced, the acids and bases before combination, and the com- pounds after combination, were as nearly as possible in the same physical state. The only change which occurred was the combination of the acid and base, and the heat evolved must therefore have arisen from the act of combination. Such changes of temperature as are produced by solution are not in any way concerned in producing these thermal effects, as none XXII.] Report on the Heat of Combination. 207 of the reacting bodies assumed at any time the solid state. The insoluble bases form, it is true, an unavoidable exception to this statement, and in the experiments with them, the results would require to be corrected for the heat due to the change of the base from the solid to the fluid state. As this correction, however, although unknown, must be a constant quantity for the same base, it would not, if applied, interfere with the direct proof of the first law. In an inquiry of this kind, it is important, while endeavour- ing to generalize the results of experiment, to point out at the same time the differences which occur in particular cases between those results and the numbers deduced from the theory. In the whole range of the science of heat, scarcely a single general principle has yet been discovered which is strictly in accordance with all the results of experiment ; and from the application of improved methods of experimenting, discrepancies of this kind have of late years been found to exist where they had not before been suspected. In the original experiments from which the first of the fore- going laws was deduced, the mean heat developed by the nitric, phosphoric, arsenic, hydrochloric, hydriodic, boracic, chromic and oxalic acids being 6°*61, the greatest deviation from the mean on either side amounted only to 0°'15 ; and a similar remark may be made with respect to the combinations of soda, barytes and ammonia. On the other hand, sulphuric acid dis- engaged about 0°"7 more than the mean quantity, and the citric, tartaric and succinic acids about 0°'5 less. To ascertain whether these discrepancies depended on the state of dilution of the solutions, I repeated these experiments lately with solutions of only half the strength, but although only half the heat was obtained, similar differences were still found to exist. If, instead of taking just the quantity of sulphuric acid required to neutralize the base, we employ a large excess, the heat given out during combination will be nearly 0°'2 less, which reduces the anomaly presented by this acid to about 0°"5. The sulphurous acid not having been formerly examined, I have lately made some experiments on its thermal relations to the bases, the results of which are very interesting. Although one of the feeblest acids, it agrees almost exactly with sulphuric 208 Report on the Heat of Combination. [xxn. acid in the heat developed by its combination with potash. In several carefully conducted experiments the increments of tem- perature did not differ more than 0°'0o. Combining this with the fact that acids differing so much in composition and pro- perties as the nitric, boracic and oxalic, also disengage almost exactly the same amount of heat in the act of combination, there wUl, I conceive, be little hesitation in attributing the deviations already mentioned to the influence of extraneous causes, and in acknowledging the truth of the principle, that the heat of combination depends upon the neutralization or combination of the base, and not upon the nature of the acid by which the base is neutralized. That other causes of change of temperature, of feeble power, do actually exist, may be proved by the following fact. If we add an excess of sulphuric acid to the neutral solution after combination has taken place, a slight fall of temperature, amounting to about 0°'l, will occur ; if we make the same experiment with sulphurous acid, an increase of temperature .of about equal amount will be observed, while with oxalic acid there will be no thermal change of any kind. Now it is very probable that the same causes which produce these slight thermal effects are in opera- tion during the original combination of the acid and base, and if so, they would introduce anomalies into the quantities of heat then developed. There is one important condition, which, as far as my investi- gations extend, requires to be fulfilled in order that the first law may hold good ; viz. the acid must have the power of neutralizing the alkaline reaction of the bases. It is for this reason that the hydrocyanic, carbonic and arsenious acids do not develop the same quantity of heat in combining with potash as the other acids. The sparing solubility of the arsenious acid in water prevents an accurate examination of its thermal reactions ; but on repeated trials I obtained 0°'25 F., on combining with it the same quantity of potash which under similar conditions gave 0°'34 with nitric acid. Although a considerable excess of arsenious acid was taken, as proved by the fact that further additions produced no new development of heat, the solution still exhibited an alkaline reaction. The same is also well known to be true of the hydrocyanic and car- xxiT.] Report on the Heat of Combination. 209 bonic acids. In the case of bases, such as the oxide of copper, whose salts have all an acid reaction, this criterion will not apply ; but the exceptional acids are so few, and their peculi- arities so well marked, that they give rise to little difficulty in the experimental investigation. The quantities of heat developed by different bases in com- bining with the same acid are so different, that it is unneces- sary to refer particularly to the proofs of the second law. In this case, neutralizing power has no apparent influence on the results, as oxide of silver, which forms salts neutral to test paper with the strongest acids, is one of the feeblest bases if measured by its thermal power. It develops, in ^ fact, little more than one-third of the heat which potash does in combin- ing with the acids. The more recent experiments of Graham and of Favre and Silbermann, confirm the accuracy of the facts from which the second and third laws were deduced, that no heat is developed on mixing solutions of neutral salts or of a neutral salt and acid.^ It is difficult however to obtain, as Graham has remarked, positive proof of the occurrence of combination, when such solutions are brought into contact. . JFavre and Silbermann indeed are of opinion that acid salts cannot exist in the state of solution. JDouble Decompositions. — When solutions of two neutral salts are mixed and a precipitate formed from their mutual decom- position, there is always a disengagement of heat, which, though not considerable, is perfectly definite in amount. It does not altogether arise from, the components of the precipitate having changed from the fluid to the solid state — as it is not always the same for the same precipitate — but it is chiefly connected with the latent heat of the precipitate. If the latter contains water of crystallization, the heat given out is much greater than when an anhydrous precipitate is formed. Experiments of this kind appear at first view to be extremely simple, but it is often difficult to obtain exact results, from the length of time ' Slight changes of temperature may however occasionally be detected ; but iu some cases a development, in others, an absorption of heat occurs. These thermal effects evidently arise from causes altogether distinct from those which produce the combination of acids and bases. O 210 Report on the Heat of Combination. [xxn. during which the heat continues to be disengaged, even when the combination is aided by brisk agitation. The precipitation of the salts of barytes and lead by a soluble sulphate appeared to present favourable conditions for investi- gation, and accordingly I made an extensive set of experiments with these classes of salts. This is indeed the only part of the inquiry which I have been able to complete. A few other examples of double decomposition will however be noticed. Chloride of Barium and Sulphate of Magnesia. — Of chloride of barium carefully purified and dried immediately before the experiment at a low red heat, 16 '9 4 grms. were taken in each experiment, equivalent to 19'00 grms. sulphate of barytes. The weight of sulphate of magnesia (dry) was 10'3 grms., which is a little more than sufficient to decompose completely the chloride of barium. The entire weight of the water employed to dis- solve the salts was 234 grms., of which one-third was taken to dissolve the sulphate of magnesia, and two-thirds to dissolve the chloride of barium. The solutions were contained in vessels of thin copper, the smaller of which, when filled with its solution, floated in the larger, and could be rapidly rotated, so as to pro- duce in a short time a perfect equilibrium of temperature throughout the whole apparatus. The thermometer attained a maximum about 8' after the solutions were mixed. I have elsewhere indicated the precautions to be taken in such experi- ments, and shall therefore not refer to them here. In the fol- lowing statements I have given the temperature of the air, the increment actually observed in Centigrade degrees, and the number of degrees through which 1 grm. of water would be raised by the precipitation of 1 grm. and 1 equiv. (oxygen— 1) of the precipitate. In calculating the latter numbers, all the usual corrections were applied to the observed increments of temperature : — Temperature of air, - 18"-3 14°-4 Increments observed, 1°'95 1°*96 Heat for 1 grm. BaO, SO3, 25°-4 2o°-2 Heat for 1 equiv. BaO, SO,, 368°-9 Chloride of Barium and Sulphate of Soda. — The same weight of chloride of barium taken as before, and an equivalent weight of sulphate of soda. XXII.] Report on the Heat of Combination. 211 Temperature of air, 20°-2 18°-7 Increments observed, l°'o7 l°'5o Heat for 1 grm. BaO, SO3, 20°-4 20°-l Heat for 1 equiv. BaO, SO3, 294°-5 Chloride of Barium and Sulphate of Zinc. Temperature of air, 19°-7 19°-6 Increments observed, l°-69 l°-72 Heat for 1 grm. BaO, S03, - 22°-2 22°-4 Heat for 1 equiv. BaO, SO^, 32o°-l Chloride of Barium and Protosulphate of Iron. Temperature of air, 18°'8 Increment observed,- 1°'99 Heat for 1 grm. BaO, SO3, 25°-6 Heat for 1 equiv. BaO, SO3, 373°-2. Chloride of Barium and Sulphate of Copper. Temperature of air, 17°-5 l7°-6 Increments observed, 1°'85 1°'85 Heat for 1 grm. BaO, SO,,- 24°7 24°-6 Heat for 1 equiv. BaO, S63, 359°-4 Chloride of Barium and Sulphate of Ammonia. Temperature of air, ll°-3 11°1 Increments observed, 1°*85 I°'84 Heat for 1 grm. BaO, SO3, - 24°-2 24°-l Heat for 1 equiv. BaO, SO3, 352°-l Nitrate of Barytes and Sulphate of Magnesia. — As the nitrate of barytes is sparingly soluble in water, 10 '6 grms. only were taken, which is equivalent to half the quantity of chloride of barium used in the foregoing experiments. The other salts were reduced in the same proportion. Temperature of air, - 13°- 9 14°-4 Increments observed, 0°-82 0°-82 Heat for 1 grm. BaO, SO3, 22.°-2 21°-2 Heat for 1 equiv. BaO, SO,, 3 1 6'^-4 212 Report on the Heat of Combination. [xxii. Nitrate of Barytes and Suljphate of Soda. Temperature of air, 14°'4 Increment observed, 0°'75 Heat for 1 grm. BaO, SO3, 2 0°- 5 Heat for 1 eqniv. BaO, SO^, 298°-9 Nitrate of Barytes and Sulphate of Zinc. Temperature of air, 13°-9 14°-1 Increments observed, 0°'83 0°"83 Heat for 1 grm. BaO, S03, 22°-0 22°-0 Heat for 1 equiv. BaO, SO3, 3 2 0°-7 Nitrate of Barytes and Sulphate of Copper. Temperature of air, 14°-4 14°-4 Increments observed, 0°-88 0°-91 Heat for 1 grm. BaO, SO3, 23°-0 24°-5 Heat for 1 equiv. BaO, SO3, 3 4 6°-2 The salts of lead were next examined. The precipitation of the sulphate of lead took place with the same facility as that of the sulphate of barytes, the thermometer attaining the maximum in eight minutes. Acetate of Lead and Sulphate of Magnesia. — The acetate of lead was pure and in crystals, 4" 17 grms. precipitated by oxalate of ammonia gave 2 '4 5 4 grms. oxide of lead, which exactly agrees with the theoretical composition of the salt. In each of the following experiments, 30'80 grms. acetate of lead were taken, corresponding to 2 4' 6 3 sulphate of lead : — Temperature of air. Increments observed. Heat for 1 grm. PbO, SO3, Heat for 1 equiv. PbO, SO3, Temperature of air, - Increments observed. Heat for 1 grm. PbO, SO3, Heat for 1 equiv. PbO, SO3, 12= •7 12° •3 1^ ■•01 0° •97 9= '•9 9° •9 187° •6 ate of Soda. 12° •3 12= ■•2 0° •84 0= •86 8° •3 8= '•5 159°' 2 XXII.] Report on the Heat of Gomhinaiion. 213 Acetate of Lead and Sulphate of Zinc. Temperature of air, - 12°-3 13°-9 Increments observed, 0°-41 0°-37 Heat for 1 grm. PbO, SO^, 4°'l 3°-7 Heat for 1 equiv. PbO, SO3, 73°'9 In the last experiment the precipitation was so slow that the thermometer did not attain the highest point for thirteen minutes after the solutions were mixed. When the salts of lead are precipitated by a neutral oxalate, the heat disengaged is much greater than when they are pre- cipitated by a sulphate. I have not examined in detail the increments of temperature in this class of precipitations, but in one experiment, in which the acetate of lead was precipitated by the oxalate of potash, 3 6" 2 units of heat were obtained for each gramme of oxalate of lead. In the experiments next to be described, a dilute acid was substituted for one of the neutral solutions. Chloride of Barium and Sulphuric Acid. — The same quanti- ties of chloride of barium and of water were taken as in the experiments with the neutral sulphates. A slight excess of sulphuric acid was employed to secure complete precipitation. Temperature of air, l7°-8 18°-4 15°-1 .9°-8 Increments observed, 3°-44 3°-46 3°-38 3°-42 Heat for 1 grm. BaO, SO3, 45°-6 45°-6 44°-0 44°-2 Heat for 1 equiv. BaO, SO3, 6 54°- 6 Nitrate of Barytes arid Sulphuric Acid. — -As in the former experiments, half the usual equivalents only were taken. Temperature of air,- 15°-0 lo°-3 Increments observed. l°-50 l°-49 Heat for 1 grm. BaO, SO3, 40°-4 39°-2 Heat for 1 equiv. BaO, SO3, 580°-2 Acetate of Barytes and Sulphuric ; Acid. — Half equivalents were taken in this case also. Temperature of air,- 12°-3 12°-5 Increments observed, l°-90 1°-91 Heat for 1 grm. BaO, SO3, 49°-5 49°-3 Heat for 1 equiv. BaO, SO3, 720''-2 214 Report on the Heat of Combination. [xxn. Acetate of Barytes and Oxalic Acid. — 11-2 grms. of acetate of barytes, and 5 '3 3 grms. oxalic acid taken. Temperature of air,- 12° -'6 12°'8 Increments observed, 1°'19 1°-19 Heat for 1 grm. BaO, C2O3, 22°-l 21°-8 Heat for 1 equiv. BaO, Gfi^, 309°0 Acetate of Lead and Sulphuric Acid.- — Of the acetate 30 '8 grms. taken and an equivalent of the acid. Temperature of air,- 14°"9 14°'l Increments observed, 2°-84 ' 2°-86 Heat for 1 grm. PbO, SO.,, 28°-0 29°-2 Heat for 1 equiv. PbO, SOg, 542"-0 Nitrate of Lead and Sulphuric Acid. — Of nitrate of lead 2 6 "2 6 grms. taken. Temperature of air,- 9°-8 10°-3 Increments observed, 1°'63 1°'66 Heat for 1 grm. PbO, SO3, 16°-3 16°-4 Heat for 1 equiv. PbO, SO,, 309°-8 Acetate of Lead and Oxalic Acid. — 15*4 grms. of acetate of lead were taken. Temperature of air.- 9°'8 Increment observed, 2°*12 Heat for 1 grm. PbO, C^Og, 4°-3 Heat for 1 equiv. PbO, C2O3, 792°-9 These experiments can only be regarded as introductory to an extended and interesting subject of inquiry. "With such limited data, it would be premature to attempt to draw any general inferences. Solution of Metals in Nitric Acid. — Every chemist is familiar with the violent action of nitric acid on zinc and copper, and the abundant evolution of gas which accompanies it. But the facility with which the gases may be condensed by the acid solution is probably not so generally known, and when the experiment is made for the first time cannot fail to excite surprise. If a small vessel of thin German glass, of about the capacity of half a fluid ounce, be half-filled with nitric acid of XXII.] Report on the Heat of Gomhination. 215 density 1-4, and a slip of zinc be suspended in the upper part so as not to touch the acid, the flask hermetically sealed, and finally inverted while surrounded with cold water, a very violent action will occur, but without bursting the vessel. Having ascertained these facts, there was little difficulty in measuring the heat disengaged durmg the solution of the metals in nitric acid. The metal was weighed in a glass tube open at one end, which was introduced into a thin glass vessel containing nitric acid of specific gravity 1-4. The latter was then carefully closed and introduced into a copper vessel filled with water, and suspended in a metallic cylinder which was capable of rotation. On inverting the apparatus, the metal and acid came into contact, and the solution was com- pleted in a few seconds. The rotation was afterwards continued for five minutes, which was sufficient to diffuse the heat dis- engaged through every part of the calorimeter. Solution of Zinc in Nitric Acid. I. II. III. IV. Temperature of air,- 4-5 6-2 8-0 5-8 Increment found, 2'66 2-78 2-83 2-71 Increment corrected, 2'65 2-77 2-82 2-71 Weight of zinc, 0-587 grm. 0-600. grm. 6-615 grm. 0-604 grm. Weight of water, 294-8 284-4 289-3 294-6 Value of acid, - 7 "4 6-9 6-5 6-6 Value of vessels, 14-3 14-3 14-3 14-3 Heat of combination, 1429 1411 1422 1420 Hence we have for the heat disengaged during the solution in nitric acid of — 1 grm. zinc. 1420 1 equiv. zinc, 5857 Solution of Copper in Nitric Acid. I. II. III. ly. Temperature of air,- 8-9 6-8 7-8 8-5 Increment found, 2-56 2-58 2-58 2-57 Increment corrected, 2-55 2-56 2-57 2-56 Weight of copper, 1-202 grm. 1-204 grm . 1-206 grm. 1213 grm. Weight of water, 274-2 273-2 273-3 275-4 Value of acid, - 14-5 16 8 15-6 15-5 Value of vessels, 16-8 16-8 16-8 16-8 Heat of combination, 648 652 651 650 216 Report on the Heat of Combination. [xxir. We have therefore, for the heat disengaged during the solution in nitric acid of — 1 grm. copper,- - - 650 1 equiv. copper, 2578 I made several attempts to determine the amount of heat disengaged in the solution of iron in nitric acid, but although acids of different strengths were employed, I was unable to obtain satisfactory results, as the iron always assumed the passive state before a sufficient quantity was dissolved to raise the temperature of the water in the calorimeter through 1°. Silver, bismuth and other metals were also tried, but the solu- tion did not proceed with sufficient energy. The numbers 5857 and 2578 obtained above, are very nearly iu' the same ratio as 5366 and 2394, which, accord- ing to my experiments (and their results differ little from those of Dulong), express the quantities of heat set free by the combustion of zinc and copper in oxygen gas. This shows clearly that the oxidation of the metals is the principal cause of the heat produced during their solution in nitric acid. Other causes of thermal change however exist, which must exercise a considerable influence. Such are the combinations of the oxide with the nitric acid, the separation of the elements of a portion of the nitric acid during the solution, and the condensation of the oxygen gas during the combustion. From these and other circumstances, it is not unlikely that the numbers expressing the quantities of heat disengaged in these reactions will not be found in all other cases to be so nearly in the same ratio as in the foregoing examples ; but it may be presumed that the general results will be the same, and that those metals which produce a greater amount of heat by their combustion in oxygen will also produce a greater amount of heat when dissolving in nitric acid. The heat produced by the solution of copper in nitromuriatic acid is, according to the result of a single trial, about -fth less than that produced by its solution in nitric acid. Metallic substitutions. — I have lately treated this part of the subject at so great length in a paper published in the Philo- sophical Transactions, that I shall here only transcribe the general result of the investigation. It is thus expressed : — XXII.] Report on the Heat of Combination. 217 "When an equivalent of one and the same metal replaces an- other in a solution of any of its salts of the same order, the heat developed is always the same; but a change in either of the metals produces a different development of heat." This is evidently an analogous law to that already stated for the thermal changes which accompany basic substitutions. The numerical results are however entirely different in their details. Combustions in Oxygen Gas. — Since the time when Lavoisier published his celebrated experiments on the heat produced by combustion, the subject has frequently engaged the attention of chemists. But few results were obtained of any scientific value, till the posthumous publication of Dulong's valuable researches, which have formed the basis of all subsequent inquiries. More recently, Grassi and Favre and Silbermann have examined the same subject, and I liave myself lately published a set of experi- ments upon it, which were made some years ago. With the exception of some of Grassi's results, the numbers obtained by the different experimenters agree very nearly with each other, and we may therefore consider the quantities of heat developed by the combination of oxygen with the more important simple bodies and with some of their compounds to be determined with considerable precision. Favre and Silbermann have also ex- amined the combustion of carbon in the protoxide of nitrogen. A tabular view of nearly all the numerical results hitherto obtained, will be found in the edition of Gmelin's Hand-book of Chemistry recently published by the Cavendish Society. I shall here therefore confine myself to a few general observations. The following bodies in their ordinary physical states, viz. hydrogen, carbonic oxide, cyanogen, iron, tin and antimony, disengage nearly the same amount of heat in combining with an equal volume of oxygen. The numbers which express the heat of combination in these cases do not' in fact differ from one another more than -^th part of the whole quantity, — a differ- ence which is nearly within the limit of the errors of experi- ment. This observation applies only to the quantities of heat actually obtained by experiment. But if we apply corrections for the heat due to the changes of physical state which occur in some of these reactions, the same agreement wUl no longer be observed. Thus in the combustion of carbonic oxide, the 218 Report on the Heat of Combination. [xxn. resulting compound is obtained in the gaseous state, while in the combustion of hydrogen it is condensed during the course of the experiment into a liquid; and if, from the entire quantity of heat evolved in the latter case, we deduct that arising from the con- densation of the vapour of water, the result will no longer agree with the quantity of heat obtained in the former case. Protoxide of tin may probably be added to the foregoing list, and perhaps also phosphorus, which disengages however a little more heat than the other bodies. Sulphur, copper and the protoxide of copper, disengage, during their combustion in oxygen gas, a little more than half the quantity of heat evolved by the preceding class of bodies. Carbon occupies an intermediate position, while zinc gives out a larger quantity of heat than any of the bodies already enumer- ated; and potas,sium a still larger quantity than zinc. The combustion of a large number of carbo-hydrogens, alcohols, sethers and organic acids has been examined by Pavre and Silberniann. Their results prove the opinion to be erroneous, that if we subtract the oxygen in the form of water, the remaining elements give the same amount of heat as in the free state. In the reduction of oxide of iron by hydrogen gas, no per- ceptible evolution of heat occurs, while in the reduction of the oxide of copper by the same gas, it is well known that ignition takes place, unless the experiment is conducted very slowly. These phaenomena are at once explained by the fact, that in combining with oxygen, hydrogen gas disengages nearly the same quantity of heat as iron, and twice as much heat as copper. Pavre and Silbermann have observed that the heat of combustion is influenced to a considerable extent by the physical state in which the combustible exists before combin- ation. According to their experiments, carbon in the form of the diamond disengages 7824 units of heat during its com- bustion in oxygen gas; in the form of graphite 7778 units; and in that of wood-charcoal 8080 units. According to my own experiments and those of Despretz, the combustion of wood-charcoal produces only about 7900 units. Pavre and Silbermann have also supposed that they were able to detect xxii.] Report on the Heat of Combination. 219 differences in the quantities of heat disengaged by sulphur in its different allotropic states. The same chemists have also made the remarkable observation, that a much larger quantity of heat is evolved by the combustion of carbon in the protoxide of nitrogen than in oxygen gas. From this it should follow that in the separation of the elements of the protoxide of nitro- gen, heat would be set free. Accordingly, by passing the protoxide of nitrogen through a platina tube heated to redness by burning charcoal in a suitable apparatus, it was found that a larger quaiitity of heat was actually evolved than could be accounted for by the weight of charcoal burned. Combustions in Chlorine Gas. — Some years ago, I published the results of an investigation on the quantities of heat evolved in the combination of zinc and iron with chlorine, bromine and iodine; and I have lately given an account of a set of experiments on the combustion of potassium, tin, antimony, mercury, phosphorus and copper in chlorine gas. So far as I am aware, the only other experiments on this subject are those described by M. Abria on the combustion of hydrogen and phosphorus in chlorine. From a comparison of the results, it appears that in several cases the quantities of heat evolved during the combustion of the same metal in oxygen and chlorine are nearly the same. This observation applies particularly to the cases of iron, tin and antimony. Zinc however disengages a greater quantity of heat with chlorine (6309 units) than with oxygen (5366 units), and copper nearly twice as much (3805 and 2394 units). Phosphorus, on the contrary, gives less heat with chlorine than with oxygen (2683 and 4509 units). On comparing the quantities of heat disengaged by different bodies in combining with the same volume of chlorinej it will be found that potassium disengages a larger amount of heat than any other body hitherto examined, twice as much as zinc, and nearly four times as much as tin, antimony, or copper. Combinations of Bromine and Iodine. — The heat disengaged by the same body in combining with bromine is less than with chlorine, and with iodine less than with bromine. The greater development of heat in the case of chlorine is at least partly due to that element being in the gaseous state before combin- ation. In some early experiments, I observed that the 220 Report on the Heat of Combination. [xxn. quantities of heat developed on converting equivalent solutions of the sesquichloride, sesquibromide and sesquiiodide of iron into the corresponding proto-compounds were equal. When a solution of protochloride of iron is converted into sesquichloride by agitation with chlorine gas, a definite disengagement of heat occurs, as also in the formation of the sesquibromide of iron by the combination of the protobromide and bromine; but in the corresponding reaction between the protoiodide of iron and iodine, no change of temperature can be observed. 221 XXIII.— ACCOUNT OF AN APPARATUS FOK DETERMINING THE QUANTITY OF HYGEOMETEIC MOISTURE IN THE AIE. From the Report of the British Association for 1851, p. 29. The object of the author was to contrive an apparatus capable of giving directly the amount of moisture in the air by the un- erring indications of the balance, and which might, at the same time, be easily employed in the physical cabinet, or other place devoted to meteorological observations. For this purpose, accord- ing to a method long known to chemists, a given volume of air is drawn through a weighed U-tube filled with some substance retentive of moisture ; but the author proposes certain modifi- cations in the apparatus hitherto employed which are designed to render it applicable in the hands of persons not familiar with chemical operations, or who may not have the convenience of a laboratory within reach. "With this object in view, he found it necessary to reject both sulphuric acid and chloride of calcium as desiccating agents, in consequence of their being either too troublesome in the preparation, or unsafe in the vicinity of valuable instruments ; but an excellent substitute presented itself in calcined sulphate of lime or gypsum, which he ascertained by numerous experiments to be capable of removing every trace of moisture from air passed even in a tolerably rapid current through tubes containing it. The sulphate of lime was employed in small fragments prepared by moistening powdered alabaster, as commonly used by plasterers and moulders, and spreading the moistened mass into the form of thin plates, which were afterwards rendered perfectly anhy- drous by being placed on an iron plate heated nearly to obscure redness. The aspirator consists of a gasometer whose bell is attached as a counterpoise to the weight of a Dutch clock, sufficiently heavy to work it, by which simple contrivance 222 Apjparatus'for Determining Hygrometric Moisture, [xxm. a known volume of air may be drawn at a uniform rate, and in any required time, through the desiccating tube. The quantity of moisture in the air may, in this way, be determined to almost any degree of accuracy, either for short periods, as half an hour, or for longer periods, as 8, 12 or more hours, in which latter cas'e the apparatus becomes a sort of integrating hygrometer, by which the total amount of moisture in the air for a given period is indicated. 223 XXIV.— ON A METHOD OF OBTAINING A PERFECT VACUUM IN THE RECEIVER OP AN AIR-PUMP. From the Philosophical Magazine, 1852, I., p. lOi. The space left vacant in the upper part of a long glass tube, which after being filled with mercury is inverted in a basin of the same metal, affords the nearest approach to a perfect vacuum which has hitherto been obtained. It is true that it contains a little mercurial vapour at the ordinary temperature of our summers, and probably also at lower temperatures ; but the quantity is exceedingly small, and its influence in depressing the barometric column must be altogether inappreciable. Besides the mercurial vapour, a trace of air may generally be detected even in tubes which have been carefully filled, and in which the air interposed between the glass and mercury has been expelled by ebullition. This is best observed by inclining the tube tUl the mercury comes into contact with the upper end, when any air that may have been diffused through the vacuum will be seen collected in a small bubble, but greatly rarefied. It is easy to calculate approximately the depression of the mercurial column produced by this residual air. For this purpose the tube must be inclined till the bubble is exposed to a pressure of a few inches of mercury, measured in a vertical direction. In this position its apparent diameter is measured, as also the pressure to which it is exposed. For the object in view, the volume of the bubble may be calculated on the assumption that it is a sphere.^ The space occupied by the vacuum must also be estimated ; and with these data, the depression of the mer- curial column may easily be calculated. Let V be the volume of the space above the mercury when the tube is vertical ; ^ [This asaamption is unwarrantable. The true volume is very much leas, so that the vacuum is more nearly perfect, than is stated in the text, — P. G. T.] 224 On a Method of obtaining a Perfect Vacuum [xxiv. p, the pressure under which the diameter of the bubble of air has been measured ; r, the semi-diameter of the bubble ; X, the depression of the mercurial column. Then 3 ' ^ If the diameter of the bubble 2r be 0'02 inch, the pressure^ 2 inches, and "the space V 1'2 cubic inch, the value of x is nearly O^OOOOl inch; or the depression of the mercury, in consequence of the vacuum not being absolutely perfect, amounts only to j^j^dth of an inch. It is easy in actual practice to realize this close approximation to a perfect vacuum. The quantities now stated apply, in fact, to a barometric tube em- ployed in an experiment which will be subsequently described. The Torricellian vacuum leaves therefore scarcely anything to be desired in point of completeness ; but it is - unfortunately applicable to very few physical investigations. No instrument of any kind can be introduced into it, nor even any substance which is acted on by mercury. The vacuum obtained by the exhausting pump is not liable to these objections ; but even with machines of the most perfect construction, and in the best order, a very imperfect approach can be attained to a complete exhaustion. A good ordinary pump with silk valves seldom produces an exhaustion of 0'2 inch ; and it is very rare indeed, if the manometer is properly constructed, to have it carried to O'l inch. In his " Etudes Hygrom^triques " {Ann. de Chim. 3rd Series, vol. xv. p. 190), M. Eegnault has given the follow- ing method for pushing the exhaustion further after the valves have ceased to act. In a large glass globe of from 20 to 25 litres capacity (4|- to 5 J English gallons), he places an her- metically sealed capsule of glass containing from 40 to 50 grms. of sulphuric acid. He also introduces into the globe 2 or 3 grms. of water, and exhausts till the water has entirely disappeared and the machine ceases to act. By agitating the globe, the capsule is ruptured ; when the sulphuric acid coming into contact with the vapour of water, which has displaced nearly all the residual air in the receiver, condenses it and leaves a vacuum nearly perfect. This globe thus exhausted is & XXIV.] In the Receiver of an Air-Pump. 225 next placed in communication with the apparatus in which a very perfect vacuum is desired, taking care to remove the air from the , interior of the connecting tubes. On opening the stop-cocks, the air becomes uniformly diffused through the two spaces ; and if the capacity of the globe is considerable com- pared with that of the other vessel, the elastic force of the air may be reduced to a small fraction of a millimetre. If, on the contrary, the capacity of the latter is considerable, this opera- tion must be repeated several times. This ingenious process is not adapted to give a very perfect vacuum in the second vessel, unless the operation be repeated several times, which would be exceedingly laborious. It is also liable to other difficulties in the execution, which will at once occur to any one accustomed to experiments of this kind. Besides, it does not afford the means of obtaining a vacuum, which, as far as the indications of a mercurial manometer can be observed, is perfect ; as in M. Eegnault's observations, the elastic force of the air was still capable of measurement, al- though only amounting to a small fraction of a millimetre. By using the necessary precautions, a vacuum may be ob- tained by the following process, with very little trouble, in the ordinary receiver of an air-pump, so perfect that the residual air exerts no appreciable elastic force. Even after this limit has been reached, the exhaustion may be pushed still further, till it must become at last not less complete than the Torri- cellian vacuum ; while at the same timiC, by suppressing the manometer, the existence of mercurial vapour may be altogether prevented. The manipulations required to arrive at this result will not interfere with the presence of the most delicate in- struments in the receiver. Into the receiver of an ordinary air-pump, which is not required to exhaust further than to 0-3 inch, or even 0'5 inch, but which must retain the exhaustion perfectly for any length of time, two open vessels are introduced, one of which may be conveniently placed above the other ; the lower vessel contain- ing concentrated sulphuric acid, the upper a thin layer of a solution of caustic potash, which has been recently concentrated by ebullition. The precise quantities of these liquids is not a matter of importance, provided they are so adjusted that the P 226 On a Method of Obtaining a Perfect Vacuum [xxiv. acid is capable of desiccating completely the potash solution without becoming itself notably diminished ia strength, but at the same time does not expose so large a surface as to convert the potash into a dry mass in less than five or six hours at the least. The pump is in the first place worked till the air in the receiver has an elastic force of 0'3 or 0'4 inch, and the stop- cock below the plate is then closed. A communication is now established between the tube for admitting air below the valves and a gas-holder containing carbonic acid, which has been care- fully prepared so as to exclude the presence of atmospheric air. After all the air has been completely removed from the con- necting tubes by alternately exhausting and admitting carbonic acid, the stop-cock below the plate is opened and the carbonic acid allowed to pass into the receiver. The exhaustion is again, quickly performed to about the extent of half an inch or less. If a very perfect vacuum is desired, this operation may be again repeated ; and if extreme accuracy is required, it may be per- formed a third time. It is not likely that anything could be gained by carrying the process further. On leaving the apparatus to itself, the carbonic acid which has displaced the residual air is absorbed by the alkaline solution, and the aqueous vapour is afterwards removed by the sulphuric acid. The vacuum thus obtained is so perfect, that even after two opera- tions it exercises no appreciable tension. To give a clear conception of the progress of the absorption, I wUl describe in detail one observation iu which the tension was measured simultaneously by a good syphon-gauge and by a mano- meter, formed of a barometric tube 0'5 inch in diameter, inverted in the same reservoir of mercury as a similar tube communicating with the interior of the receiver. The barometer had been care- fully filled, and the depression of the mercury estimated by the method already described at less than i^^^dth of an inch. Previous to the admission of the carbonic acid, the exhaustion was carried only to 0'4 inch ; it was again carried to 1 inch ; and a third time to 0'5 inch, after which the apparatus was left to itself. Tlie manometer indicated a pressure in — 15' of 0-25 inch. 30' „ 0-17 „ 80' „ 0-10 „ 200' „ 0-02 „ 3fxiv.] In the Receiver of an Air-Pump. 227 In twelve hours the difference of level was just perceptible, when a perfectly level surface was brought down behind the tubes till the light was just excluded. In thirty-six hours not the slightest difference of level could be detected. The vacuum has remained without the slightest change for fourteen days. It is evident that the only limit to the completeness of the vacuum obtained by this process, arises from the difficulty of preparing carbonic acid gas perfectly free from air. This may be very nearly overcome by adopting precautions which are well known to practical chemists. When an extreme exhaustion is required, the gas-holder should be fiUed with recently boiled water, and the first portions of carbonic acid that are collected in it should be allowed to escape. The substitution of phosphoric for sulphuric acid would re- move the possibility of either aqueous or acid vapours being present even in the smallest amount, but such a refinement will rarely be found necessary. In the experiment just described, the theoretical residue of air would be j-^„dth part of the entire quantity in the receiver, which would cause a depression of ^dtli of an inch. This re- sult must have been nearly realized. If the exhaustion had been carried at each time to 0'2 inch, the residue by theory would have been only jia^j-oooth part. But the experimental results will not continue to keep pace with such small magnitudes. Qtteen's College, Belfast, January 7, 1851. 228 XXV.— ON THE DISCOVERY OF MINUTE QUANTITIES OF SODA BY THE ACTION OF POLARIZED LIGHT. From the Report of the British Association, 1852, p. 33. The double chloride of potassium and platinum crystallizing in regular octahedrons, exercises, when placed in the dark field of the polariscope, no depolarizing action ; and the same remark applies to the bichloride of platinum in consequence of its im- perfect crystallization. On the other hand, the chloride of sodium and platinum in thin crystalline plates is remarkable for its depolarizing power, and a trace of this salt, which is invisible to the naked eye, may be at once detected by the brilliant display of prismatic colours which it exhibits under the action of polarized light. The author applies this property to the detection of soda in the following way. The other bases having been removed by the ordinary methods, and the alkalies con- verted into chlorides, a drop of the solution is placed on a glass slide, and a very small quantity of a dilute solution of the bichloride of platinum added, avoiding as far as possible an excess of that reagent. The drop is then evaporated by a gentle heat till it begins to crystallize, and afterwards placed in the field of a microscope furnished with a good polarizing apparatus. On turning the analyser till the field becomes per- fectly dark, and excluding carefully the entrance of light laterally, the crystals remain quite invisible if either potash alone or no alkali whatever be present ; while the presence of the slightest trace of soda is at once indicated by the depolarizing action of its platinum compound. With a drop of solution of chloride of sodium, weighing 0"0015 gTamme, and containing y uooo of its weight of chloride of sodium, a very distinct effect was obtained. The quantity of soda thus detected was only i a u o^o o o o of a gramme, or about loooooo of a grain. 229 XXVI.— ON THE ATOMIC WEIGHTS OF PLATINUM AND BAEIUM. From the Report of the British Association, 1852, p. 33. ISTo determination of the atomic weight of platinum having been made since the recent revision of atomic weights, and the number adopted by chemists for that metal resting on the authority of a single experiment of Berzelius, the author considered it of importance, on practical as well as theoretical grounds, to institute some new experiments on the subject. The salt of platinum selected was the double chloride of potassium and platinum, which, after being dried m vacuo at. a temper- ature of 105° C, was decomposed by digestion with metallic zinc and a small quantity of water, the action being assisted by the application of heat towards the end of the process. After the complete precipitation of the platinum and the formation of chloride of zinc from the decomposition of the double salt, the excess of zinc was removed by the addition, first of acetic and subsequently of nitric acid. The precipitated platinum was then removed by means of a small and carefully washed filter, and the amount of chlorine in the solution of chloride of zinc ascertained by Gay-Lussac's process, which has been of late so successfully applied by Pelouze to the determination of several other atomic weights. The double chloride of potassium and platinum was found to retain T-g- o'ooo dths of its weight of moisture, even when dried at a temperature considerably superior to the boiling point of water. In three experiments performed by this process, the numbers obtained were 98'93, 98'84, and 9 9 '06; the mean number 9 8 '9 4 expresses therefore the atomic weight of platinum. For the atomic weight of barium, the author obtained from two closely-accordant experiments the number 6 8 '7 8 9, and concluded with some general observations as to the importance of a systematic series of experiments to settle, if possible, 230 AtoTTiic Weights of PlatinuTii and Barium. [xxvi. definitively, whether the law of Prout, that the atomic weights of all bodies are multiples of that of hydrogen, be universally true. He concluded by reading an interesting extract from a letter which he received from Baron Liebig: — -"It is not certain that Prout's law may not be true for oxygen, nitrogen and carbon, without it being necessary to assume as a consequence, that other bodies behave similarly; that is, their atomic weight must be exactly multiples by whole numbers of the atomic weight of hydrogen. The law is certainly not true of all bodies, but it may be true of certain groups, whose members, in respect to atomic weight, stand in a simple numerical relation to each other. The atomic weights of silicium, cobalt, strontium, tin, arsenic and lead, are in the same ratio as the numbers 1:2:3: 4:5:7. We do not see the necessity of this relation, but only the possibility. Why should fractional numbers only occur, and not whole numbers also ? I consider these relations only as facts; the law of the numbers themselves is quite unknown to us — as unknown as the absolute weights of the atoms." 231 XXVI r.— ON THE MICROSCOPIC STRUCTUEB OF CERTAIN BASALTIC AND METAMOEPHIC ROCKS, AND THE OCCUR- RENCE OF METALLIC IRON IN THEM. From the Report of the British Association, 1852, p. 34. If a thin splinter of basalt is viewed by reflected light in the field of a good microscope, it is seen to consist of a semitransparent granular mass, containing occasionally opake crystals of the magnetic oxide of iron and of iron pyrites. The former are easUy recognized by their dark colour, metallic lustre, and the triangular and striated facets of the regular octahedron ; the latter, by their yellow colour and cubical form. The semitrans- parent portion which forms the great mass of the stone evidently consists of two distinct minerals ; one having a resinous lustre, and in microscopic characters closely resembling crystallized augite ; the other, colourless and with a glassy lustre, might be referred to certain varieties of felspar or of zeolite. These remarks apply to the compact varieties of basalt. The metamorphic rock of Portrush — an indurated clay-slate containing the characteristic fossils of the lias formation, and in external characters closely resembling Lydian stone — exhibits under the microscope a very different appearance. It is formed, iu fact, of a semitransparent paste of homogeneous structure, everywhere thickly studded with innumerable microscopic cubes of iron pyrites. These crystals are very perfectly formed, but so minute that twenty of them may frequently be counted in the space of rrrrdth part of a square inch, the sides of the crystals being on an average not more than ao^oo dth of an inch in length. If a portion of any of these rocks be reduced, in a porcelain mortar, to a tolerably fine but not impalpable powder, and a magnet be passed several times through the powder, magnetic particles will be found adhering to the magnet, in greater or less abundance, according to the nature of the rock. On removing these magnetic particles and placing them in the 232 Microscopic Structure of Certain [xxvii. field of the microscope, they exhibit distinct polarity and all the other characters of the magnetic oxide of iron. This mineral may be separated by the above simple process not only from basalt, but from granite, clay-slate, primitive limestone, hardened chalk, magnesian limestone, and many metamorphic rocks. In short, it is one of the most widely-diffused minerals in nature, occurring in almost every rock which exhibits evidence of igneous action. The author was only able however to discover a doubtful trace in roofing-slate, serpentine and marble. After referring to the few instances in which metallic iron, not of meteoric origin, is alleged to have been observed, the author proceeded to describe the process by which he has succeeded in showing that native iron is by no means an uncommon constituent of basaltic rocks. The stone is first reduced to powder in a porcelain mortar, the use of metallic tools being carefully avoided in every part of the operation. The magnetic portions are then removed, as in the process for separating the oxide of iron, and placed in the field of the microscope. While in the field, they are moistened with an acid solution of sulphate of copper, which produces no change on the oxide, but immediately indicates the presence of the slightest trace of metallic iron by a deposition of metallic copper. On making this experiment, a deposit of copper occasionally occurred in irregular crystalline bunches, perfectly opake, and with the characteristic colour and lustre of that metal. With neutral solutions of the copper salt this deposit very rarely occurred, indicating either that the iron is covered with a film of oxide, or that it is analogous in properties to the meteoric alloy which precipitates copper from acid, but not from neutral solutions. If instead of the copper solution dilute sulphuric acid be added to the magnetic particles, a slight effervescence at particular points frequently indicates the pres- ence of the metallic iron ; and on adding solution of copper while the disengagement of gas continues, the latter is suddenly arrested, and a. bright deposit of metallic copper appears at the same points. The largest deposit of copper obtained was about Tcth of an inch in diameter. The most abundant indications of metallic iron were obtained from a coarse-grained variety of basalt, which forms the hill of Slieve Mish in Antrim, XXVII.] Basaltic and Metamorphic Bodes. 233 and also occurs at the Maiden Eocks and other localities. Indications of its presence in the basalt of the Giant's Cause- way, the lias slate of Portrush, and the trachyte of Auvergne have also been obtained. This experiment is liable to the ambiguity that nickel and cobalt, in a state of very fine subdivision, also precipitate copper, and would also be extracted from a powder containing them by passing a magnet through it. The extreme improb- ability of either of these metals being present is such, that the author considers it scarcely to weaken the conclusions at which he has arrived. 234 XXVIII.— ON A NEW VAEIETY OF MAGNETIC IRON ORE ; WITH REMARKS UPON THE APPLICATION OP BICAR- BONATE or BARYTA TO QUANTITATIVE ANALYSES. From the Report oj the British Association, 1852, p. 41. This mineral occurs in the schist rocks of the Mourne Moun- tains, near their junction with the granite. In external characters it resembles somewhat the common magnetic oxide ; but its lustre is inferior. It occurs both in the amorphous state and in imperfectly-formed octahedrons. Its composition was found to be, — Sesquioxide of iron, 71 "41 Protoxide of iron, 2 1 • 5 9 Magnesia, 6"45 The formula of this mineral is evidently 'Se^O^ + (FeO, MgO), a part of the protoxide of iron being replaced by magnesia. Although not mentioned in any of the published analyses of magnetic oxide of iron, magnesia appears to be a constant constituent of this mineral. The author gave the results of analyses of magnetic oxide in which 2'00, 0'7l, and 0'09 per cent, of magnesia had respectively replaced an equivalent amount of the protoxide of iron. It is remarkable that not a trace of lime could ever be detected in any specimen of magnetic oxide. Oxide of manganese is usually also present, but in minute quantity. In this analysis a solution of the bicarbonate of baryta was employed to separate the sesquioxide of iron from the magnesia. A solution of this compound, which is readily prepared by passing a current of carbonic acid into water con- taining recently precipitated carbonate of baryta in suspension, the author finds to effect a very complete separation of the sesquioxide of iron from the oxide of manganese and from magnesia, and considers that it may be very usefully employed in quantitative analyses for effecting the separation of the bases just mentioned, presenting many advantages over the insoluble carbonate of baryta, as well as over the other reagents usually employed for the same purpose. FLauIII. I 235 XXIX.— ON A NEW ASPIEATOE. From the Philosophical Magazine, 1852, II., p. 330. In this aspirator the current of air is produced by raising a cylindrical vessel A (Plate III.), open at bottom and immersed in water contained in the outer vessel B. The tube com- municates with the inner and upper part of A. The cords gg are attached to weights which counterpoise A. In short, the construction is precisely the same as that of the gasometers which are used in the preparation of gas for illuminating pur- poses on the large scale. In order to raise A, it is connected by means of the brass rod fh with the free end of the chain of a common one-day German clock, whose weight, Ic, is increased so as to enable it both to move the machinery of the clock and also to overcome the resistance of A. By this means the cylinder A is elevated at a perfectly uniform rate, and which may be varied at pleasure by augmenting or diminishing the length of the clock's pendulum. When the cylinder has at- tained the proper height, its motion is arrested by the nut /, the clock being at the same time stopped. To prepare for a second operation, the clock weight k is removed, the stopcock cl closed and e opened ; and by applying a gentle pressure to the top of A, or laying a small weight upon it, A is made to descend till the lower edge rests upon B. ^ is a thermometer having its bulb inserted in A. It is very easy to determine by experiment the precise volume of air which enters the receiver A during its ascent ; and if the apparatus be carefully constructed, no appreciable error will arise from inequalities in the volume of air entering A in different observations. And knowing the height of the barometer and the temperature of the air in A, which gives at the same time the tension of the aqueous vapour, it is easy to calculate the volume of air at a standard temperature and pressure which has passed through the apparatus. If the 236 On a New Aspiratoi\ [xxix. aspirator be applied to the determination of the amount of aqueous vapour, or other absorbable constituent in the atmos- phere, it will be necessary to find also the mean temperature and pressure of the air during the course of the experiment. With these data, a simple calculation will give the exact weight or volume of the aqueous vapour in the air. It is unnecessary to point out the many applications which an aspirator affording an absolutely uniform current of air may receive. In the chemical laboratory it will frequently be found a very convenient instrument of research, and may even be applied in some cases to quantitative experiments. But it is chiefly in atmospheric inquiries that this aspirator will find its applications ; and in the determination of the amount of oxygen, carbonic acid, aqueous vapour, and even ammonia in the air, it wUl prove, if I am not mistaken, a useful addition to the meteorological observatory. Por these various objects its size and form will require to be modified ; and it will be necessary where large quantities of air are operated on, to enlarge con- siderably its dimensions and employ more powerful clock- machinery than I have found necessary. The capacity of A in the apparatus I employed was 21'623 litres, or nearly 1320 cubic inches. With a pendulum of the ordinary length, six hours were required for its ascent ; but by reducing the length of the pendulum, the same operation was completed in an hour and a half. In the latter case, a current of air at the rate of 240 cent. cub. (14'6 cub. in.) per minute passed through the apparatus, and under these conditions I made a few experiments on the relative desiccating powers of certain substances, the results of which I will now very briefly state. With carefully dried gypsum in T, and fragments of pumice moistened with sulphuric acid in T', the latter underwent no change of weight after the passage of the first measure of the aspirator ; but in the next experiment (the same tubes being employed) it gained 0'056 grm. (086 grain); and in a subse- quent trial, after two hours had been allowed to elapse in order to allow the moisture to be imbibed by the gypsum, there was still a gain of 0-034 grm. (0-52 gr.). With fused chloride of calcium in T, and sulphuric acid in T', XXIX.] On a New Aspirator. 237 .the gains of T' in three consecutive experiments were respec- tively 0-033, 0-040, and 0-040 grm. Dry sulphate of lime appears therefore to be superior to fused chloride of calcium, but neither desiccates the air -with sufficient energy to be employed in these experiments. With sulphuric acid in T as well as in T', the latter experi- enced no change of weight till sixteen measures of the aspirator had passed through the tubes, but afterwards it began rapidly t*o increase in weight. "With well-dried, but not fused, chloride of calcium, as recom- mended long ago by Liebeg for organic analysis, in T, and sulphuric acid in T', some interesting results were obtained. To ascertain whether the absorption of moisture by T' was complete, a ■ third tube containing sulphuric acid was placed between it and the aspirator. Sixty measures of the aspirator were passed in succession through this series of tubes, which were only removed from time to time for the purpose of being weighed. The gain of tube T after this operation amounted to no less than 12-252 grms. (189-08 grs.) ; that of T' to 0-141 grm. (2-17 grs.); and of the tube next the aspirator to 0-21 grm. (0-32 gr.). It is important to remark that the gain of T' was a uniform quantity from the beginning to the end of the experiment ; its average increase of weight for each elevation of the aspirator from the first to the twenty-fifth time being 0-0024 grm. (0-037 gr.), and from the twenty-fifth to the sixtieth time 0-0023 grm. (0-035 gr.). The gain of the third tube is quite insignificant, not amounting to ^iirdth part of the whole quantity of aqueous vapour, and probably arising from moisture derived from the air in the aspirator, or from some accidental cause. The experiment in this case was continued till the stream of air was arrested by the liquefaction of the chloride of calcium in the further end of T from the aspirator ; yet the desiccating power of the chloride of calcium in the other limb continued unimpaired tiU the end. It appears, then, that the whole of the moisture may be absorbed from 1296 litres (or nearly 80,000 cubic inches) of atmospheric air in its ordinary state in this country by means of a chloride of calcium tube weighing about 90 grms. (1400 grs.), aided by a supplementary tube containing sulphuric acid, and of about half the weight. 238 On a New Aspirator. [xxix. As these tubes may be placed at the same time on the balance, no additional trouble is incurred by employing them both. Further experiments are, however, required to determine whether the small increase of weight sustained by the sulphuric acid tube arose actually from the absorption of aqueous vapour, or whether it may not have been due to the absorption by the sulphuric acid of a part of the carbonic acid existing in the air.^ If this latter view prove to be correct, dry chloride of calcium should be substituted for sulphuric acid in the tube T. A slight modification of the appiuatus would give the quan- tity of moisture in the air for shorter intervals of time ; and there can be no doubt that the tubes would continue to absorb all the moisture from air passing with much greater velocity than in the experiment just described. By increasing, if neces- sary, the length of the U-tubes, it would not be difficult to collect from 0'5 to 1 grm. (7 to 14 grains) of water from the air in periods of an hour, or even half an hour ; and thus the amount of aqueous vapour might be determined accurately to T^dth part of the whole quantity, instead of an uncertain approxima- tion to -jth or xVth of the same, which is perhaps all that can be attained by the methods now generally in use. QnEEN's College, Belfast, September 28, 1852. ^ See the observivtions on this subject of Prof. Rogers iu the Chemical Oasette, vol. vii. p. 477. 239 XXX.— ON A SIMPLE INSTRUMENT FOE GRADUATING GLASS TUBES. From the Seport of the British Association, 1853, p. 37. This instrument is intended to supply the chemist with a means of accurately graduating his glass measures of capacity. The divisions admit of being varied in- length to the j^^dth of an inch, so as to allow the graduation to be adapted to the changes in calibre of the vessel. They are obtained by the action of a micrometer-screw, one inch long, on a wooden block on which a standard scale is firmly fixed ; but the details of the construction could not be rendered intelligible without a figure. Scales exceeding three feet in length may be divided by means of this instrument, which the author has very suc- cessfully employed in the construction of thermometers for delicate investigations. The dividing instrument itself, and a thermometer graduated by its aid, were exhibited to the Section. 240 XXXI.— ON THE CONSTITUTION AND PROPEBTIES OF OZONE. From the Philosophical Transcbctions, part 1, 1856, p. 1. Among the many interesting bodies which the researches of modern chemists have brought to light, few are more- remark- able than the substance to which the name of ozone has been given, whether we consider its many singular and anomalous properties, or its intimate relations with the most important and widely-diffused element in nature. For the first recogni- tion of ozone and description of its properties, we are indebted to the sagacity of Schonbein, to whom the entire merit of the discovery unquestionably belongs. His earlier experiments were, however, chiefly directed to the elucidation of its pro- perties, and of the conditions under which it is formed; but not being accompanied by quantitative determinations, they did not throw any clear light on its actual constitution. The subject has also attracted of late years the attention of several very distinguished physical and chemical inquirers, among whom I may particularly mention Marignac, De la Eive, Berzelius, Williamson, Fremy and Becquerel, and Baumert. Schonbein has shown that a body having a peculiar and highly characteristic odour and very similar properties is formed under the three following conditions : — 1. When electrical sparks are passed through atmospheric air. 2. When pure water, or water holding certain acids or salts in solution, is decomposed by the voltaic current, the new sub- stance appearing, along with the oxygen gas, at the positive pole. 3. When certain bodies, and particularly phosphorus, are slowly oxidized at common temperatures in atmospheric air. Two distinct questions here arise for consideration. Is the same substance produced under these different conditions, or has Schonbein included under the name of ozone substances XXXI.] On the Constitution and Properties of Ozone. 241 having different compositions, although agreeing in some of their properties ? And next, what is the composition of ozone, or, if there be more ozones than one, how are they respectively constituted ? The experiments of Williamson ^ indicated the production of water, when ozone obtained by electrolysis was decomposed by being passed over heated copper, and Baumert^ obtained similar results when he passed a stream of electrolytic oxygen through a tube containing anhydrous phosphoric acid, which was heated at one point to redness. These experiments were not, however, adapted to yield quantitative results, but they led to the general conclusion that this variety of ozone is an oxide of hydrogen containing more oxygen than water. But from another and very important experiment, to which I shaU have occasion hereafter very fully to refer, Baumert has concluded that it is a teroxide of hydrogen, HO3. On the other hand, the experiments of De la Eive and of Fremy and Becquerel* have shown, that pure and dry oxygen gas may be converted by the electrical spark into ozone. I am not aware of any experiments on ozone obtained by the action of phosphorus on atmospheric air, which throw any distinct light on its constitution. Marignac passed a stream of this ozonized air through a solution of iodide of potassium, till the whole of the iodide was converted into iodate of potassa, and concluded that ozone produced in this way must be either oxygen in a peculiar state, or a peroxide of hydrogen. According to the results, therefore, of the most recent in- vestigations, it would appear, — That the substances comprehended under the name of ozone are not identical ; That the ozone obtained by the action of the electrical spark on oxygen gas is oxygen itself in an altered or allotropic state ; That the ozone obtained by the electrolytic decomposition of water is an oxide of hydrogen, having the formula HO3 ; and ^ Memoirn of the CliemicaZ Society, vol. ii. p. 395. ^ Poggendorff's Annalen, Band Ixxxix. S. 39. ' AnncUes de Chimie, 3^™^ s^rie, xxxv. p. 62. Q 242 On the Constitution and Properties of Ozone. [xxxi. That the ozone obtained by the action of phosphorus on oxygen is either oxygen itself, or a compound of oxygen and hydrogen.^ Tlie subject of ozone has at intervals engaged my attention during the last four or five years, and I was actually occupied with a series of experiments on the production of ozone by the electrical spark, when the appearance of Fremy and Becquerel's able researches induced me for the moment to lay aside the inquiry. The publication of Baumert's memoir led me subse- quently to resume it, as bis results were not in accordance with those which I had previously arrived at. But the method proposed by that physicist to determine whether ozone is an oxide of hydrogen, or oxygen in an allotropic condition, ap- peared to be so well suited to the purpose, that on resuming the inquiry, I considered it necessary in the first instance carefully to repeat his experiments. The results which I at first obtained were so far in accordance with those of Baumert, that they showed that the increase in weight of the apparatus was always more than the weight of the ozone, as deduced from its chemical action, but the relative proportion of these quantities was not in accordance with his results ; nor, on re- peating my own experiments, did they agree with one another. It was evident, therefore, that some disturbing cause existed which complicated the reaction, and, on further investigation, I not only found that such a cause did really exist, but succeeded in ascertaining its nature and the means of avoiding it. The experiments, on being now repeated, gave results very consistent with one another, and altogether at variance with the view that hydrogen is a constituent of ozone. The apparatus which I employed was arranged as follows: — A is a vessel (Plate IV. Fig. 1) of about two litres capacity, con- taining a mixture of one measure of pure and strong sulphuric acid, and seven measures of distilled water. The cylinder B, which is filled with a similar solution, is closed below with a diaphragm of bladder, so as to prevent effectually any mixture of the gases evolved at the two poles. A platina wire, pp, traverses ^ For a very complete account of all that is kno-wn on this subject, see the Article " Ozon" in the Handworterbuch dcr Chemie, Band v. S. 835 (Braun- schweig, 1853). iindrews' Papers . « Plal&JV. .w XXXI.] On the Constitution and Properties of Ozone. 243 and is fused into a short glass tube, fitted by grinding into the tubulated neck h : this wire terminates below in a bunch of fine platina wires, which form the positive pole of a voltaic arrangement. The negative pole is a platina plate, p', immersed in the liquid of the outer vessel. The vessel A was placed in a larger vessel containing cold water, to which ice was in some experiments added. This vessel has been omitted in the draw- ing for the sake of distinctness. CC'C" is a continuous tube, united by fusion with the larger neck of B, and filled from C to C with fragments of pumice, moistened with pure sulphuric acid. The length of the desiccating column was nearly one metre. D is a Liebig's apparatus, to the ends of which glass tubes were fused, which had previously been fitted by grinding, the one into the neck c of CC'C", the other into a tube, which was in like manner fused to a second Liebig's apparatus, E. The connexions c and e were, therefore, formed by glass surfaces carefully ground. In my earlier experimfents these connexions were made by means of small and dry corks, which, on the whole, are more convenient than ground-glass joints, and are quite unobjectionable, as, when the surface is small and the cork dry, the amount of ozone destrdyed by contact with the cork is wholly inappreciable. Caoutchouc connectors of any kind are altogether inadmissible ; they are attacked with such energy by ozone, even when diluted with 1000 times its volume of other gases, that the tube becomes perforated in the course of a few minutes. The vessel D contained a solution of iodide of potassium, acidulated with a little hydrochloric acid, and the vessel E, concentrated sulphuric acid. The U-tube F, filled with pumice moistened with sulphuric acid, prevented any moisture from passing backwards into E. The oxygen evolved was collected in the graduated glass vessel G-, inverted over water. The volume of the oxygen gas was determined only for the purpose of ascertaining its relation to the ozone produced. The mixture of oxygen and ozone, having been perfectly ■desiccated in its passage through the long tube CC'C", enters the vessel D, where the ozone is decomposed, iodine being set free and caustic potassa formed, which latter, combining with the free hydrochloric acid, forms chloride of potassium. If a 244 On the Constitution and Properties of Ozone. [xxxi. neutral solution of iodide of potassium is employed, the reaction is more complicated ; for, while the greater part of the iodine is set free as before, and dissolves in the excess of iodide of potassium, iodate of potassa and caustic potassa are at the same time formed. Whether the solution be taken in an acid or neutral state, the final result is in this respect always the same, that the active oxygen enters into a chemical combina- tion in the vessel D, and increases the weight of the liquid contained in that vessel. The increase in weight of the vessels D and E will give the entire weight of the ozone, whether that body be allotropic oxygen or an oxide of hydrogen. On the former supposition, the decomposition of the iodide of potassium will result in the substitution of oxygen for iodine, both remaining in D, while the sulphuric acid in E will retain the moisture which would otherwise be swept away by the current of dry gas ; on the latter, ozone will become resolved into water and oxygen, both of which will be retained in the vessels D and E. Now by determining the amount of free iodine in the iodide of potassium solution at the end of the experiment, the amount of active oxygen by which it has been displaced may be easily calcu- lated ; and on comparing this with the increase in weight of the vessels D and E, it will at once be seen whether ozone be a peroxide of hydrogen yielding water in its decom- position. Two experiments of this kind were performed by Baumert;. in the first, the increase in weight of the apparatus amounted to 0"0133 grm., and the weight of the oxygen, as calculated from the iodine set free, to O'OOSl grm.; in the second, the same quantities were respectively 0'0149 grm. and 0'00989 gi-m. The iodide of potassium was employed in the state of a neutral solution, and the iodate of potassa was subsequently decom- posed by the addition of a little hydrochloric acid. It was from these results that Baumert inferred that the ozone which accompanies oxygen obtained by the electrolysis of water, is an oxide of hydrogen having the formula HO3; and this conclusion, deduced from experiments which were devised with great skill and executed with care, has, in Germany at least, received very general assent. XXXI.] On the Constitution and Properties of Ozone. 245 Having, as already mentioned, found, on a repetition of these experiments, that a different expression resulted for the com- position of ozone from every new trial, I instituted a diligent search into all the circumstances of the experiment, and at last succeeded in referring the irregularities to the presence of a small, but appreciable quantity of carbonic acid, which, unless very great precautions be taken, is always present in electrolytic oxygen. When baryta water was substituted for the solution of iodide of potassium in D, a precipitate of carbonate of baryta appeared in the course of a few minutes. "With caustic potassa in the same vessel, the increase in weight, for the same volume of oxygen gas, was considerably greater than with the solution of iodide of potassium, and at the end of the experiment it was found that carbonate of potassa had been formed. Now as a small quantity of free potassa is always produced during the action of ozone on a neutral solution of iodide of potassium, it appeared not improbable that this would seize upon a portion of the carbonic acid just referred to, and thus the augmentation in the weight of the apparatus would depend upon two distinct causes, — the ozone reaction, and the absorption of carbonic acid. To prevent the occurrence of the latter, it was only necessary to acidulate the solution of iodide of potassium, so as to prevent the formation of free potassa, or to boil for some time the liquid subjected to electrolysis. The acidulation of the solution alone was found to be sufficient to prevent the carbonic acid from being absorbed, for when this precaution was attended to, the results were the same, whether the electrolyte was boiled immediately before the commencement of the experiment or not. "With this modification, the irregu- larities previously observed in different trials disappeared, and the simple and interesting result was obtained, that the increase in weight of the apparatus was exactly equal to the amount of oxygen deduced by calculation from the iodine set free. I will now describe the chief precautions which I adopted to avoid, as far as possible, all sources of error in the following experiments, the delicacy of which will at once be apparent, if we consider that not more than 40 milligrammes of ozone are 246 Oti the Constitution and Properties o/ Ozone. [xxxi. contained, under the most favourable cu-cumstances, in 1 litres of electrolytic oxygen ; and that it was necessary to have the arrangements so perfect, that this large quantity of gas (supposed to be free from ozone) should traverse the apparatus without producing any appreciable change in the united weight of the vessels D and E. The solution of iodide of potassium employed in all the experiments had the same composition, although the quantity of ozone obtained in some cases was three times greater than in others. It consisted of 2 grms. of iodide of potassiimi dissolved in 22 J grms. of a weak solution of hydrochloric acid, containing 2 per cent, of pure acid. As it is difficult to procure iodide of potassium entirely free from iodate of potassa, I always prepared, at the commencement of each experiment, two similar solutions, of which one was introduced into D, and the other preser\ed in a ground stoppered ^'ial, till the experiment was finished. The amount of free iodine in both was deter- mined at the same time, and the difference taken to represent the exact quantity of iodine due to the ozone reaction. The correction for the iodate of potassa in the original solution, when reduced, rarely represented more than O'OOl grm. oxygen, but quantities of this magnitude must not be neglected in these experiments. Previous to weighing the vessels D and E, one litre of atmospheric air, deprived of carbonic acid and carefully desiccated, was passed through the apparatus. The object of this precaution was to bring every part of the apparatus into the same state at the beginning of the experiment, in which it would be at the end. The same volume of dry air was passed through the apparatus at the conclusion of each experiment. It is rarely necessary in chemical investigations to apply a correction to the direct indications of the balance for chansjes in the temperature and pressure of the atmosphere, during the interval between two successive weighings. By preserving the apartment at a pretty uniform temperature, the corrections for thermometric changes may be confined within very narrow limits, but the movements of the barometer are not under our control ; and when, as in these experiments, a period of two and XXXI.] On the Constitution and Properties of Ozone. 247 sometimes of three days elapsed between the first and second weighings, it occasionally happened that the change in the atmospheric pressure was considerable, and an appreciable error (amounting in some instances to nearly 0-002 grm.) would have occurred, if no correction had been applied.^ To ascertain how far the action of the apparatus might be relied on, one or two preliminary experiments were made, which gave very satisfactory results. The vessel D, containing pure water, E, sulphuric acid, and another Liebig's condenser, also containing sulphuric acid, having been interposed between E and F, 3'5 litres of oxygen gas not containing ozone, followed by 1 litre of atmospheric air, were passed through the apparatus. The time occupied in the passage of the gas was about five hours. The vessel D lost 0-0311 grm., while E gained 0-0315 grm., the third vessel not sustaining any appreciable change of weight. If, therefore, D and E had been weighed together, the change of weight would have been only 0-0004 grm. In another experiment, in which a solution of strong caustic potassa was placed in D, the loss of D was 0-0175 grm., and the gain of E 0-0172 grm., the difference being less than one- third of a milligramme. Other experiments of the same kind, with different solutions in D, gave similar results. It is evident, therefore, that at the rate at which the gas traversed the apparatus, the whole of the moisture carried off from the liquid in D was retained by the sulphuric acid in E. To determine whether a notable quantity of iodine would be carried over by the current of the gas from D to E, a solution ^ This correction was calculated as follows : — To the volume in cubic centi- metres of the solution of iodide of potassium in D and of sulphuric acid in E, was added the volume of the glass of which the vessels D and E were formed. From this was deducted the volume of the weights employed. Let V be the diflference of the volumes so found in cubic centimetres ; p and p', the atmos- pheric pressures in English inches at the first and second weighings ; t and t', the corresponding temperatures in Centigrade degrees ; x, the weight, in grammes, of a volume of air equal to V, measured under the pressure p, and at the temperature t ; x\ the weight of the same volume of air atp' and t'. Then, since 1 cub. cent, air, at 0°, and under a pressure of 29-92 inches, weighs 0-00129 grm., *'~^=^Vl-t-0-00367«''29^~l-l-0003lJ7.«"29^P'^"^^^- The value of a/ — x is to be added to, or subtracted from, the increase of weight, B& found by direct experiment, according as it is a positive or negative quantity. 248 On the Constitution and Properties of Ozone. [jcxxi. of iodide of potassium containing a large quantity of free iodine was introduced into D, and a solution of pure iodide of potassium into E. After passing 4 litres of air through the apparatus, E was found to contain O^OOIS grm. iodine. This is equivalent to one-tenth of a milligramme of oxygen, and, from the large excess of iodine in the first solution, must be a greater quantity than could have been carried over in any of the subsequent experiments, although in some of them larger volumes of gas were passed through the apparatus. The free iodine was determined according to the very deKeate method first, I believe, proposed by Bunsen. A dilute solution of sulphurous acid was prepared, and its strength determiaed, immediately before analysing the liquid in D, by ascertaining how many measures of it were required to destroy a known weight of free iodine in a solution of iodide of potassium. A corresponding experiment was made with the solution in D, from which the quantity of free iodine in it was deduced by a very simple calculation. I. 10'2 litres of electrolytic oxygen containing ozone were passed through the apparatus at the rate of about three-quarters of a litre per hour. At the first weighing, the barometer was 29'85 in. and the thermometer, 5°"9 C; at the second weighing, the barometer was 2 9 '9 8 in. and the thermometer, 5°-3. The value of V (see preceding note) was 47 cub. cent. The gain in weight of the double apparatus D and E was 0"0375 grm., which gives, when corrected for atmospheric changes, for the true gain, 0-0379 grm. The free iodine in the solution contained in D, was neutralized by 11 2 '7 measures of a dilute solution of sulphurous acid. The other solution of iodide of potassium, which had been prepared at the same time as the first, and to which the same amount of acid had been added, required 0"8 measure of the same solution of sulphurous acid for neutralization. Hence the iodine eliminated by the action of the ozone was equivalent to lll'Q measures. Next, 0"o341 grm. pure iodine was added, together with 2 grms. of iodide of potassium, to a few drops of water, and when both were dissolved, the solution was diluted till it occupied exactly 100 cub. cent. From the mean of two XXXI.] On the Constitution and Properties of Ozone. 249 experiments which closely agreed with one another, it appeared that 100 measures of the solution of sulphurous acid neutral- ized 9 5 "9 6 cub. cent, of this solution, and hence 1 measure of the former corresponded to 0-00512 grm. iodine. From these data it follows, by an easy calculation, that the iodine disen- gaged by the ozone amounted to 0'609 grm., and the equivalent of oxygen to 0-0386 grm. II. 2-72 litres of electrolytic oxygen were passed through the apparatus at the same rate as before. At first weighing, barometer 29-60 in., thermometer 5°-8 0. ; at second weighing, barometer 29-60 in., thermometer 6°-0 C. Gain of weight of D and E 0-0107 grm., corrected, 0-0107 grm. The free iodine in D, after deducting the iodine due to the small quantity of iodate of potassa in the original solution, was neutralized by 30-2.3 measures of a solution of sulphurous acid, of which, as ascertained by direct experiment made at the time, 1 measure neutralized 0-00521 grm. free iodine. Hence the oxygen due to the displacement of iodine was 00100 grm. III. 2-86 litres of the same gas as in the preceding experi- ments were passed through the apparatus. At first weighing, barometer 30-06 in., thermometer 6°-6 C. ; at second weighing, barometer 30-20 in., thermometer 6°-l C. Gain of weight of D and E 0-0152 grm., corrected, 001 54 grm. The free iodine in D, corrected as before, was neutralized by 41-52 measures of a solution of sulphurous acid, of which 1 measure neutralized 0-00525 grm. iodine ; hence the weight of oxygen, as deduced from the weight of iodine set free, was 0-0138 grm. IV. 6-45 litres of electrolytic oxygen were passed through the apparatus. At first weighing, barometer 29-96 in., thermometer 6°-8 C; at second weighing, barometer 29-29 in., thermometer 7°-8 C. Gain of weight of D and E 0-0303 grm., corrected, 0-0288 grm. The free iodine in D was neutralized by 1 00-4 measures of a 250 On the Constitution and Properties of Ozone. [xxxi. solution of sulphurous acid, of whicli 1 measure neutralized 0'00441 grm. iodine ; hence the weight of oxygen deduced in this way was 0-0281 grm. V. 6" 8 litres of electrolytic oxygen passed. At first weigh- ing, barometer 30'53 in., thermometer 9°'8 0.; at second weighing, barometer 30 '44 in., thermometer 10°'4 C. Gain of weight of D and E 00254, corrected, 00251 srm. The free iodine in D neutralized 107"9 measures of a solution of sulphurous acid, of which 1 measure was equivalent to O'OOSoS grm. iodine ; hence the weight of oxygen deduced from the iodine set free was 0-0273 grm. Collecting these results and adding them together, so as to obtain the mean of the whole, we have Ozone deduced from the increase Ozone deduced from in weight of the apparatus. the iodine liberated. I. 0-0379 grm. 0-0386 grm. 00100 grm. II. 00107 grm. III. 0-0154 grm. IV. 0-0288 grm. V. 0-0251 grm. 0-0138 grm. 00281 grm. 0-0273 grm. 0-1179 grm. 01178 grm o* The agreement is complete, and proves unequivocally that water is not a product of the decomposition of ozone, which therefore does not contain hydrogen as a constituent. If its composition were HOj, the apparatus would have increased 0'1841 grm. in weight, instead of 0-1179 grm. The amount of ozone formed in these experiments was tolerably uniform. For 1 litre of oxygen the following weights of ozone were obtained : — Mean I. 0-0038 grm. II. 0-0037 grm. III. 0-0046 grm. IV. 0-0043 grm. V. 0-0040 grm. 0-0041 grm. XXXI.] On the Constitution and Properties of Ozone. 251 In the arrangement above described, the oxygen gas derived from the electrolytic decomposition of water was therefore accompanied by about nhx^h of its weight of ozone. In order to remove every possible doubt from these results, I fitted up an apparatus from every part of which organic sub- stances were excluded. No diaphragm was used, and all the connexions were made, either by fusing the ends of the con- necting tubes together, or by means of ground glass joints. The arrangement is represented in fig. 2. Two platina wires (fig. 3) were fused into the end of a glass tube, which was fitted by grinding to the tubulated neck h of the vessel A. The tube BB'B" was connected at a with the vessel A by a ground joint, and with C by fusion. It contained pumice moistened with sulphuric acid. The vessel C was also filled with sulphuric acid, and was connected by a ground glass joint with the iodide of potassium vessel D. The vessel E contained, as before, sulphuric acid. In this experiment, both the hydrogen and the oxygen traversed the apparatus, the accuracy of which was thus exposed to a very severe test. Twenty-two litres of the mixed gases were passed througli the apparatus. The gain in weight of D and E was 0"0135 grm., the respective heights of the barometer at the first and second weighings having been 28'96 in. and 29"57 in., and the temperatures 11°"1 and 10°-0. Tlie correction for change of pressure and temperature is therefore -|- 0'0014 grm., and the true gain 0-0149 grm. The free iodine in D, due to the action of the ozone, neutralized 62'65 measures of a solution of sulphurous acid, of which 1 measure corresponded to 0'00373 grm. iodine. The weight of ozone deduced from the iodine set free is therefore 00148 grm. The identity of these results is very satisfactory, when it is considered that this small weight of ozone was separated from 22 litres, or nearly five gallon measures of the mixed gases. The relative quantity of ozone to the amount of water decom- posed is less than in the former experiments, arising perhaps partly from a single platina wire having been in this case employed as the positive pole. In this experiment, great care 252 On the Constitution and Properties of Ozone. [xxxi. was taken to exclude both carbonic acid and nitrogen from the electrolyte. My next object was to determine, by careful quantitative experiments, whether water is really formed, as Williamson and Baumert have stated, when ozone is decomposed by heat. For this purpose, the same general arrangement was employed as in the first series of these experiments ; but the first Liebig's apparatus D, instead of being filled with a solution of iodide of potassium, was now empty, and placed in the upper part of a metallic cylinder (fig. 4 HH), where it was raised to a tempera- ture of about 400° C, by a current of heated air from a LesHe's burner. To the sulphuric acid apparatus E, was permanently attached and weighed along with it, a small U-tube G, contain- ing anhydrous phosphoric acid, so as to secure the condensation of the last trace of aqueous vapour, if any were present. The oxygen gas was collected and measured as in the former experi- ments. Two experiments were made. In the first, 6"8 litres of oxygen containing 0"027 grm. ozone were passed through the apparatus; in the second, 9-6 litres containing 0"038 grm. ozone. The compound sulphuric and phosphoric acid apparatus was found, aU corrections having been made, to have increased, in the one case one-third, and in the other case one-half of a milligramme in weight. Such quantities can only be referred to the unavoidable enors of experiment. If ozone were a com- pound body having the constitution HO3, the apparatus would have gained in the first experiment 10, and in the second 14 milligrammes. That ozone cannot contain nitrogen will appear from the following experiment. Two platina wires were hermetically sealed into the bottom of a small flask, into which water, con- taining a little sulphuric acid, was introduced and made to boil rapidly for some time. While the water was in a state of ebidlition, the wires were connected with the poles of a voltaic arrangement, so as to disengage the mixed gases along with the vapour of water. So long as the ebullition continued, no ozone made its appearance ; but on allowing the liquid gradually to cool, without arresting the current, its presence soon became manifest from its odour and action XXXI.] On the Constitution and Properties of Ozone. 253 on iodide of potassium paper. The ebullition and the current of the mixed gases must have rendered the presence of nitrogen here impossible. One question still remains to be answered. Does ozone, besides oxygen, contain any other constituent which is not absorbable by any of the reagents employed ? Although the gas which escaped from the apparatus, after the separation of the ozone, appeared to be pure oxygen, yet it would be rash to assert that it might not have contained some unknown body amounting to TxsWth of its weight, and having no very salient properties. This question appeared to me to admit of solution in another way. It will be seen, in a subsequent part of this paper, that there can be no doubt of the formation of ozone from pure and dry oxygen by the action of the electrical spark, and nothing is easier than to convert the whole of a given volume of oxygen into ozone in presence of a solution of iodide of potassium. The next step in the inquiry was therefore to ascertain whether ozone derived from electro- lysis, from the action of the electrical spark, and from the oxidation of phosphorus, exhibited a perfect identity in all its properties. One of the most remarkable properties of ozone is its destruc- tion by heat, or rather its conversion by heat into ordinary oxygen. To ascertain the temperature at which this change occurs, the vessel D, fig. 4, was placed in a bath of mercury, and the gas examined as it escaped, without previously passing it through the rest of the apparatus. On heating the mercurial bath, the amount of ozone, as determined by its action on iodide of potassium paper,i did not notably diminish till the tempera- ture attained 230" C. It still continued, however, very intense till the thermometer rose to 235°. Between that point and 240° the ozone reactions entirely disappeared, when the ozone was in a very dilute state ; but when more concentrated, slight traces of ozone could still be discovered, which no doubt would ^ Bibulous paper which has been dipped into a solution of iodide of potassium of moderate strength and afterwai'ds allowed to dry, but still retaining its liygrometrio moisture, is the most convenient test of ozone. If it be exposed to a continuous current of dry air, it should be removed from time to time and its hygrometrio moisture restored. 254 On the Constitution and Properties of Ozone. [xxxr. have also disappeared if the current of gas had been passed very slowly. Time is in fact an element in this action. Even at the temperature of 100° C. ozone is slowly destroyed. Two similar tubes were filled, at the same time, and by the same process, with ozone diluted as usual with oxygen, and afterwards hermetically sealed. One of these tubes was maintained for three hours in a vapour bath at 100° C, the other was not exposed to heat. On examining both tubes at the end of the time, it was found that the ozone in the tube which had been exposed to heat was perceptibly less than in the other. I have no doubt that, even at the common temperature of the air, ozone preserved in an hermetically sealed glass tube would gradually change into common oxygen. I made an experiment of this kind two or three years ago, which resulted in the dis- appearance of the ozone, but I do not remember the source from which the ozone was derived, nor what precautions were taken to dry the gas. On the other hand, ozone brought directly into contact with the vapour of water at the boiling-point is instantly destroyed. To obtain a continuous stream of ozone from the action of the electrical spark, a current of pure oxygen gas, obtained from the decomposition of the chlorate of potassa, and purified and dried by passing through tubes containing hydrate of potassa and sulphuric acid, was exposed to a rapid succession of electri- cal sparks. To obtain a sufficient stream of electricity, an electrical machine, firmly screwed down to the floor of the apartment, was connected by a belt with a heavy cast-iron wheel, 40 inches in diameter, contained in a frame which was also firmly secured to the floor. By this arrangement, the machine could be worked for any length of time continuously, the plate performing about 360 revolutions per minute. It was of course necessary to apply very frec[uently a hand rubber covered with amalgam to the plate, and it required the co- operation of three persons to permit the work to be easily performed. On passing the gas through the apparatus at nearly the same rate as in the experiments already described, an abundant stream of ozone was obtained, which enabled me to institute a very exact comparison between its properties and those of ozone obtained by electrolysis. XXXI.] On tJie Constitution and Properties of Ozone. 255 When heated in the mercurial bath, ozone prepared in this way was rapidly destroyed at the temperature of 237° C, which is the same temperature at which electrolytic ozone was also destroyed. The vapour of boiling water, in like manner, caused all the ozone reactions to disappear. The action of water at common temperatures and of alkaline solutions upon ozone is very remarkable. It is commonly stated that caustic potassa absorbs ozone, but that pure water, and solutions of lime, baryta, and ammonia, have no action upon it. This statement is far from being accurate. Pure water does not absorb ozone, and a stream of air containing ozone may be passed for any length of time through water without producing any change in the properties of the water. I have also preserved ozone for several days in a stoppered vial containing a little distilled water, and although the vessel was agitated from time to time, the ozone did not disappear. On the other hand, pure water has the property of destroying a small quantity of ozone. If ozone, obtained by the electrolysis of water, or by the action of the electrical spark, or by means of phosphorus, be largely diluted with atmospheric air, it will entirely disappear, if an attempt be made to collect it in a jar inverted over water. The following experiment is more precise. A flask provided with a ground glass stopper, of the capacity of half a litre, was filled with equal volumes of water and atmospheric air and inverted in the pneumatic trough. The ozone in a single bubble of electrolytic oxygen, passed quietly through the water into this volume of air, could easily be detected ; but on agitating the water briskly, even four or five bubbles were deprived of their ozone. The same gas, agitated with twice its volume of lime water, or one-third of its volume of baryta water, also ceased to exhibit the reactions of ozone. In like manner, the action of caustic potassa is also limited. A strong solution of that alkali in a Liebig's apparatus deprived one litre of electrolytic oxygen of its ozone, after which the ozone passed freely through it. These phenomena are singular and characteristic, and are the same with ozone from whatever source it is derived. Peroxide of manganese destroys ozone, affording an interest- ing example of what is commonly called catalytic action. 256 On the Constitution and Properties of Ozone. [xxxi. The oxide of manganese does not increase in weight, nor is water formed. Ozone from the three sources gives the same results. The odour of ozone, from whatever source derived, is the same. The same remark applies to its property of bleaching, without producing at first an acid reaction. Iodide of potassium is decomposed with the formation of iodate of potassa, and oxidable substances in solution, as the protosulphate of iron, are raised to a higher state of oxidation by all the varieties of ozone. It would not be difficult to extend this comparison, but enough has been shown, I conceive, to establish the absolute identity in properties of ozone in whatever way it may be pre- pared. Any difference which, on a superficial examination, may appear to exist, wiU be found on further inquiry to arise from the ozone being in a more or less dilute state. That ozone is formed by the action of the electrical spark on perfectly dry oxygen, is placed beyond all doubt by the follow- ing experiment. The curved tube a, fig. 5, having two platina wires, pp, hermetically sealed into it, was inverted over mercury and carefully filled with pure oxygen, after which a little sulphuric acid was introduced into one end (6). The whole was allowed to remain for twenty-four hours, when the oxygen was considered to be perfectly dry. Electrical sparks were now passed for some time between the platina wires, after which a solution of iodide of potassium was introduced into the other end of the tube. It became immediately coloured from the formation of free iodine, and the colour continued slowly to increase as the ozone was gradually absorbed. Again, a solution of iodide of potassium may be made to absorb the whole of the oxygen in a narrow tube, by the passage of electrical sparks. This experiment has been described by Fremy and Becquerel, and I have myself repeatedly verified its accuracy. With a thermometertube two inches long, the whole of the oxygen may be made to disappear in the course of one minute. The solution becomes always red from the decomposi- tion of the iodide of potassium. We have already seen that neither hydrogen nor nitrogen can be constituents of ozone, whether it be obtained from XXXI.] On the Constitution and Properties of Ozone. 257 electrolysis, or from the action of the electrical spark on oxygen ; and further, that all the supposed varieties of ozone exhibit in all respects identical properties. Connecting all these facts together, it clearly follows, — That no gaseous compound having the composition HO^ is formed during the electrolysis of water ; and That ozone, from whatever source derived, is one and the same body, having identical properties and the same constitu- tion, and is not a compound body, but oxygen in an altered or allotropic condition. 258 XXXII.— ON THE POLAR DECOMPOSITION OF WATER BY COMMON AND ATMOSPHERIC ELECTRICITY. From the Report of the British Association for 1855. In the fine experiment first made by two Dutch chemists, and afterwards modified and extended by Wollaston, water was decomposed by a succession of disruptive discharges produced by the common electrical machine. But in this experiment, as Wollaston himself has correctly remarked, we have only an imitation of the galvanic phtenomena, and the essential difiCer- ences between its results and true electro-chemical decom- position have been pointed out by Faraday with his usual clearness and ability. "The law which regulates the transference and final place of the evolved bodies," the latter remarks, " has no influence here. The water is decomposed at both poles, and the oxygen and hydrogen evolved at the wires are the . elements of the water existing the instant before in those places."^ The same distinguished experimentalist obtained only uncertain results when he attempted to procure the true polar decomposition of water by common electricity, that is, to decompose it so that the oxygen might be evolved at one pole and the hydrogen at the other. " "When what I consider the true effect only was obtained," he says, " the quantity of gas given off was so small that I could not ascertain whether it was, as it ought to be, oxygen at one wire and hydrogen at the other. Of the two streams, one seemed more copious than the other ; and on turning the apparatus round, still the same side in relation to the machine gave the largest stream. But the quantities were so small, that on working the machine for half an hour, I could hot obtain at either pole a bubble of gas larger than a grain of sand." '[This quotation is absurdly misprinted in the B.A. Report. It has now been corrected from Faraday's Experimental Researches, § 328. — P, G. T.] xxxn.] On the Polar Decomposition of Water, etc. 259 On repeating this experiment with wires of different lengths and thicknesses, I obtained the same uncertain results, although I had at my command &■ stream of electricity of great power, and which could be maintained without intermission for many hours. But while engaged in some experiments on the conver- sion of oxygen, contained in fine thermometer tubes, into ozone, the tubes being inverted in water, I found to my surprise that the gas in certain cases steadily augmented in volume, and on further inquiry I found that the augmentation of volume arose from the water having undergone polar decomposition. The conditions under which the gases arising from the polar decomposition of water might be obtained were now quite manifest, as was also the cause of no appreciable amount of gas having been obtained in former investigations. The quantity of gas produced in fact in a given time from the electrolysis of water, by means even of a powerful electrical machine, is so small, that the gases are dissolved in the liquid as quickly as they are formed, if the poles, whether they be large or small, be freely exposed to the action of a large mass of the liquid ; but if the bulk of liquid around each pole be made to corre- spond to the volume of the gases evolved, the latter will not be dissolved to a greater extent than in ordinary eudiometric experiments conducted over water. To attain this object it is only necessary to employ thermometer tubes, having fine platina wires hermetically sealed into their upper ends, as the tubes for receiving the gases. The wires may be so long as to extend- through the entire length of the thermometer tubes ; but it will be sufficient if they only project a short way into the tubes, as the film of liquid which covers the interior of the tube is sufficient to conduct electricity of such high tension as that produced by the electrical machine. That the gases were evolved very nearly in the proportion of 1 vol. oxygen to 2 vols, hydrogen, will appear from the following examples : — Hydrogen, 6-85 4-00 3-35 Oxygen,- 3-45 2-10 1-55 The electrolyte employed in these experiments was water containing 1 per cent, of sulphuric acid. The gases collected 260 On the Polar Decomposition of Water by [xxxn. in these tubes were thus proved to be oxygen and hydro- gen:— 1. Electrical sparks passed through the hydrogen tube exhibited the characteristic red colour which electrical flashes produce in that gas. 2. On introducing a solution of iodide of potassium into the oxygen tube, and passing sparks through it, the oxygen was converted into ozone, and absorbed in the course of about one minute. 3. On reversing the connexions with the electrical machine and the ground, the relative volumes of the gases were reversed ; and after passing the current for the same time as before, and afterwards a spark through the mixed gases, they combined together in both tubes with explosion. Each of the above divisions contained O'OOOOS cent, cub., and an electrical machine, in good order and performing 240 revolutions each minute, produced about I'l division of oxygen gas in the same time. A column of acidulated water, 1 feet long, and having a section equal to the internal calibre of a fine thermometer tube in which it was contained, presented no sensible resistance to the passage of this current ; but a similar column of distilled water 1 foot in length reduced the current to ith of its original amount. On passing the electrical current through a series of sixty pairs of thermometer tubes charged with acidulated water, and fitted with platina wires as already described, decomposition proceeded with the same facility, and the same amount of oxygen and hydrogen was collected in each pair of tubes as when only a single couple was interposed in the circuit. The same apparatus enabled me to decompose water without difficulty by means of atmospheric electricity. To collect the electricity, I employed an electrical kite which carried a fine brass wire attached to its cord. The experiments were all performed on fine clear days, when the air exhibited no unusual symptoms of free electricity. On connecting the platina wire of one of the thermometer tubes with the insulated wire of the kite, and that of the other tube with the ground, the decom- position proceeded slowly but steadily at the rate of 0-9 div. or about '000054 cub. cent, oxygen per hour. Hence about XXXII.] Common and Atmospheric Electricity. 261 0-000000085 gramme water was decomposed hourly, or nearly r ooo^ouo gramme, or ,o„\„„ of a grain. The wu-e of the kite gave small sparks, varying in length according to the amount of movement in the kite, from one-tenth to half an inch in length. The shocks were moderately strong ; and the needle of a galvanometer of 2000 coils was sensibly deflected. In the Philosophical Transactions for 1831, Mr. Barry describes an experiment, in which he supposes that he collected the gases produced by the decomposition of water by the action of atmospheric electricity ; but from the form of apparatus which he employed, I consider it very improbable that he could have succeeded in collecting any visible quantity of either of the gases. 262 XXXIII.— NOTE ON THE DENSITY OF OZONE. (In conjunction with Prof. Tait.) From the Proceedings of the Royal Society, 1857, vol. 8, p. 498. It is known that Ozone can only be obtained mixed with a large excess of oxygen. In a former communication by one of the authors of this note, it was shown that in the electrolysis of a mixture of 8 parts of water and 1 of sulphuric acid the mean quantity of Ozone does not exceed '0041 gramme iu a litre of oxygen, or -jiirth part. By using a mixture of equal volumes of acid and water, the relative quantity of Ozone may be doubled ; but even with the Ozone in this more concentrated state, the ■ordinary methods of determining the density of a gas are plainly inapplicable. The difficulty of the problem was farther increased by the rapid action of Ozone on mercury, which rendered it impossible to collect or measure the gas over that metal ; and the tension of aqueous vapour, as well as the gradual destruction of Ozone by water, prevented the use of the latter. After numerous trials, the method finally employed was to measure the change of volume which occurs in exposing a gaseous mixture containing Ozone to a temperature of 230° C, or upwards. The volume of the gas after this treatment was invariably found to have increased ; and by eliminating the effects of alteration of temperature and pressure during the course of the experiment, by the aid of a similar vessel to that containing the Ozone, the authors succeeded in estimating the change of volume which took place to an extremely small frac- tion of the entire amount. The vessels employed in different experiments varied in capacity from 200CC. to 600CC., and terminated in tubes of about 2 millimetres iu diameter, bent in a U-form and contain- ing sulphuric acid. The amount of Ozone was ascertained by passing a stream of the gas through two other vessels, one placed on each side of the vessel to be heated, and afterwards analysing their contents by the method described in the com- munication already referred to. It was easy to measure with XXXIII.] Note on the Density of Ozone. 263 certainty a change of pressure amounting to To^Tnrtli of the whole ; but on account of the ordinary fluctuations of atmos- pheric pressure between two consecutive observations of the primary and auxiliary vessels, it was rarely possible to work to this degree of accuracy. The experimental data have not yet been completely reduced, and some slight corrections have yet to be investigated ; but the general result of the inquiry, which has been a very pro- tracted one, gives — on the assumption that Ozone is oxygen in an allotropic condition — for its density as compared with that of oxygen, nearly the ratio of 4 to 1. The following approximate formulfe were employed in the reduction of the experiments. They are sufficiently exact for the purpose of calculation on account of the smallness of the quantities observed. 1. To reduce the change of level observed in the auxiliary vessel during the interval of the experiment to the equivalent quantity for the primary vessel — 2. To deduce from the corrected change of level in the primary vessel the relative density of Ozone and oxygen — =m(-4--rj °*n- e \a HJ In these formulae a is the barometric pressure in terms of the sulphuric acid in the U-tubes. H, the length of a tube of the same diameter as the U-tube of the primary vessel, and whose capacity is eqiial to that of the same vessel measured to the mean level of the acid in the U-tube. J7j, the same quantity for the auxiliary vessel. 8x^, one-half of the change in the difference of levels in the U- tube of auxiliary vessel. Bx, the corresponding quantity for the primary vessel. Bx half the observed change in the primary vessel corrected by the quantity Sx. m, the ratio of the weights of oxygen and Ozone in the gaseous mixture. (', the relative density of Ozone and oxygen. 264, XXXIV.— SECOND NOTE ON OZONE. (In conjunction with Prof. Tait.) From the Proceedings of the Eoyal Sodeiy, 1859, vol. 9, p. G06. Since the publication of tlieir " Note on the Density of Ozone " (Proceedings of the Eoyal Society, June 1857), the authors have been occupied with an extended investigation into the nature and properties of that body. The inquiry having proved more protracted than they anticipated, they have thought it proper to send to the Eoyal Society a brief notice of some of the more important facts which they have already observed, reserving a description of the methods employed, and of the details of the experiments, for a future communication. The commonly received statement, that the whole of a given volume of dry oxygen gas contained alone in an hermetically sealed tube can be converted into ozone by the passage of electrical sparks, is erroneous. In repeated trials, with tubes of every form and size, the authors found that not more than To^TT part of the oxygen could thus be changed into ozone. A greater effect was, it is true, produced by the silent discharge be- tween fine platina points ; but this also had its limit. In order to carry on the process, it is necessary to introduce into the appara- tus some substance, such as a solution of iodide of potassium, which has the property of taking up, in the form of oxygen, the ozone as it is produced. After many trials, an apparatus was contrived in the form of a double U, having a solution of iodide of potassium in one end, and a column of fragments of fused chloride of calcium interposed between this solution and the part of the tube where the electrical discharge was passed. The chloride of calcium allowed the ozone to pass, but arrested the vapour of water ; so that, while the discharge always took place in dry oxygen, the ozone was gradually absorbed. The experi- ment is not yet finished, but already one-fourth of the gas in a tube of the capacity of 1 cubic centimetres has disappeared. XXXIV.] Second Note on Ozone. 265 To produce this effect, the dischare from a machine in excellent order hab been passed through the tube for twenty-four hours. When oxygen is thus converted into ozone, a diminution of volume takes place. The greatest contraction occurs with the silent discharge, and amounts to about ^-^ of the volume of the gas. The passage of sparks has less effect than the silent dis- charge, and will even destroy a part of the contraction obtained by means of the latter. If the apparatus be exposed for a short time to the temperature of 250°C., so as to destroy the ozone, it will be found that the gas on cooling has recovered exactly its original volume. This observation proves, unequi- vocally, that if ozoiie be oxygen in an allotropic condition, its density is greater than that of oxygen. Experiments still in progress indicate that the density of ozone obtained by the electrical discharge must, on the above assumption, be represented by even a higher number than that deduced by the authors from their experiments on ozone prepared by electrolysis. When mercury is brought. into contact with dry oxygen, in which ozone has been formed by the electrical discharge, it loses to a great extent its mobility, and may be made to cover the interior of the tube with a fine reflecting surface resembling that of an ordinary mirror. It is remarkable that this great change in the state of the mercury is not accompanied by any further diminu- tion of the volume of the gas. The apparatus employed by the authors would have enabled them to estimate with certainty a change of volume amounting to xaooo part of the whole. On the contrary, on allowing the apparatus to stand, the gas begins slowly to expand ; and in thirty hours, when the ozone reactions have disappeared, the expansion amounts to a little more than one half of the contraction which had previously taken place. Dry silver, in the state both of leaf and of filings, has the property of entirely destroying ozone, whether prepared by electrolysis or by the electrical machine. If a stream of elec- trolytic ozone be passed over silver leaf or filings contained in a tube, the metal becomes altered in appearance where the gas comes first into contact with it ; but no appreciable increase of weight takes place, however long the experiment may be con- tinued. The volumetric results are similar to those already described in the case of mercury. 26G Second Rote on Ozone. [xxxiv. Arsenic also destroys dry ozone, but, as it likewise combines with dry oxygen, its separate action on ozone cannot be observed with precision. Most of the other metals examined, such as gold, platina, iron, zinc, tin, &c., are without action on dry ozone. Iodine, brought into contact with oxygen contracted by the electric discharge, instantly destroys the ozone reactions, and a yellowish solid is formed: no change of volume accompanies this action. Peroxide of manganese and oxide of copper have, it is well known, the property of destroying ozone, apparently without limit. The authors have found that these oxides undergo no sensible increase of weight, even after the destruction of 50 or 60 milligrammes of ozone. The same oxides, when brought into contact with oxygen contracted by the spark, restore it to nearly its original volume. Hydrogen gas, purified with care, and perfectly dry, was not changed in volume by the action either of the electrical spark, or of the silent discharge. A similar negative result was obtained with nitrogen and the silent discharge ; but with the spark a very slight alteration of volume appeared to occur, the cause of which is still under in- vestigation. In the experiments now described, the electrical sparks and dischargewere always obtainedfrom the common friction-machine. The .discharge from the induction coil, even when passed through two Leyden jars, produces very insignificant ozone effects. The heat which always accompanies this discharge, and its compara- tively feeble tension, sufficiently explain its want of energy. All the results recently obtained by the authors fuUy confirm the former experiments of one of them,^ that in no case is water produced by the destruction of ozone, whether prepared by electrolysis or by the electrical discharge. They reserve any further expression of their views as to the true relations which exist between ozone and oxygen, till they shall have an opportunity of laying the results of this inquiry in a more complete form before the Society. ^Phllomphical Transactions for 1856, Part I. 2Q'i XXXV.— ON THE VOLUMETRIC EELATIONS OF OZONE, AND THE ACTION OF THE ELECTRICAL DISCHARGE ON OXYGEN AND OTHER GASE3. (In coDiunotion with Prof. Tait.) From the Philosophical Transactions, 1860, Part I. §1- The molecular changes produced by the electric current, or discharge, in certain compound bodies through which it is transmitted, furnish some of the most interesting examples of the action of a decomposing force that have been discovered in later times. The discharge of the Leyden jar, through fine v?ires or thin metallic leaves, exhibited long ago the heating power of the current, and the interesting experiments of the Dutch chemists afterwards showed that the disruptive discharge has the power of splitting up compound bodies into their con- stituent parts. The great invention of the pile of Volta, by furnishing an abundant supply of electricity of moderate tension, led subsequently to the important discovery of the polar decom- position of water and of other compound bodies. In the case of gases, it has been known, since the time of Priestley and Caven- dish, that the spark discharge has the apparently antagonistic properties of causing decomposition in some cases and combina- tion in others. Finally, in our own day, Schonbein made the fine observation that a new substance (ozone), alike remark- able for the activity of its properties and for the facility with which it is destroyed, is formed by the action of the spark on pure oxygen gas, in the electrolysis of water, and in certain cases of slow oxidation. Our object in the present communication is to continue the investigation, already begun by one of us,^ of the properties of ^ Philosophical Transactions, 1856, p. 1 [AiM, p. 240]. 268 Voluw.eti'ic Relations of Ozone, and Action of [xxxv. ozone, by subjecting it under varied conditions to a series of careful volumetric experiments. We hoped, in this way, to throw some new light on the relations of this singular body to oxygen, by determining whether any, and what, change of volume occurs in its formation. Our expectations in this respect have not been disappointed. We have ascertained that when oxygen changes into ozone, a great condensation takes place ; so great indeed, that it is almost incompatible with the exist- ence of ozone as an allotropic form of oxygen in the gaseous state. This investigation has naturally extended itself to an examination of the effects produced by the electrical discharge upon other gases, simple as well as compound ; and although, from its great extent, this part of the inquiry has as yet been only partially entered into, some of the results already obtained are of considerable interest, and will be referred to in the present communication. Before proceeding further, we must draw attention to the difference of action which, in many cases, we have found to exist between the spark, or spark discharge, and the glow, or silent discharge. When the former terms are employed in this paper, they indicate a succession of brilliant sparks between two tine platinum wires, usually at the distance of 20 millims. (0"8 inch) from each other, and hermetically sealed into the tube con- taining the gas under observation. This form of discharge was obtained by connecting the free end of one of the platinum wires with an insulating stand, provided with a brass ball which was brought within a short distance of the prime conductor of an electrical machine in high order, while the free end of the other platinum wire was in connexion with the ground. The silent discharge presented no visible character except a faint glow, not visible by daylight, at each metallic point, and was obtained by connecting the iirst platinum wire, not with the insulator, but directly with the prime conductor. To avoid the mixture of the " brush " with the silent discharge, it was accessary to establish the connexion firmly both with the con- ductor and with the earth wire ; and, in some cases, where a full effect was required, the machine had to be turned very slowly. The electrical machine employed was a small plate one (18 inches in diameter), screwed down firmly to the floor of the XXXV.] Electrical Discharge on Oxygen and other Gases. 209 apartment, opposite to an open fire. On the prolongation of the axis of the plate, a wheel, 6 inches in diameter, was fixed, from which a belt passed to an iron wheel, 40 inches in diameter, revolving in a wooden frame, which was also fastened to the floor. By this arrangement, the machine could be easily made to turn at the rate of 350 revolutions per minute. To maintain a regular and powerful stream of electricity at this rapid rate of motion, it was found necessary, in addition to the ordinary cushions, to hold with the hand against the plate a rubber covered with amalgam. When in ordinary working order, the machine gave above 600 sparks per minute, and in decomposing water produced in the same time 0'0002 cub. cent, of the mixed gases.^ The ordinary forms of eudiometrical apparatus were found to be wholly inapplicable to this inquiry. We failed in discover- ing, by their means, whether even a change of volume occurs, when ozone is produced from oxygen. To increase the difficulty, the experiments could not be carried on in presence of mercury or water, as the former is immediately attacked by ozone ; and the latter not only destroys it rapidly by contact, but intro- duces a disturbing cause, in the form of aqueous vapour, ex- ceeding in general the whole effect to be measured. In the apparatus now to be described these difficulties were overcome, and very minute changes of volume determined with certainty. In Plate V. figs 1 and 2, the vessel in which the oxygen was contained is represented of different forms. It consists of a cylindiical tube ai, having two fine platinum wires hermetically sealed in opposite sides, and terminating in a capillary tube ode, of the form represented in the figure. The liquid in the limbs d, e is hydrated sulphuric acid (HO, SO^), and it is by the changes in the level of this liquid that the alteration in the volume of the gas in abc is determined. In order to make the necessary corrections for changes of tempera- ture and pressure, during the interval between two observa- tions, a vessel filled with dry air, of the same form and size as that employed in the experiment, was read along with it ; the reservoirs of both vessels being immersed in a large calori- ^ Reports of the British Association for 1855, Trans, of Sect. p. 46 [Anti, p. 258]. 270 Volumetric Relations of Ozone, and Action of [xxxv. meter, as shown in fig. 3. To the first of these vessels, we usually gave the name of primary vessel, and to the second that of auxiliary vessel. In order to correct for any slight differ- ence in the size of the vessels, or in the diameters of the capillary tubes, simultaneous readings of both were made at different temperatures, and a coefficient thus determined, by means of which the indications of the two vessels could be afterwards accurately compared. When the reservoirs were large, the corrections so to be applied were frequently less than the errors of observation. The extreme delicacy of this apparatus will be evident from the following considerations. If we take the case of a vessel with a large reservoir (fig. 1), the changes in volume of the con- tained gas, supposing the temperature to remain constant, will be nearly proportional to the changes of pressure indicated by a barometer filled with sulphuric acid. As the height of such a barometer, at the mean pressure of the atmosphere, would be about 5500 millims., an alteration of 1 millim. in the differ- ence of levels of the acid in the siphon tube {de, fig. 1) would correspond to a change of volume of about .^^^th of the entire gas ; but, as it was easy to read to O'O millim., or even to 0'25 millim., the apparatus in this form enabled us to estimate a change of volume not exceeding one-half, or even one-fourth of that quantity. "With a smaller reservoir (fig. 2), the indica- tions of the apparatus were, it is true, not quite so delicate, and a careful set of comparative readings with the auxiliary vessel was always required ; but even here, a change of volume, amounting to not more than ^^h of the whole could be determined with certainty. The absolute change of volume of the gas, corresponding to a given change in the levels of the acid in the siphon tube (corrected in the first instance by the aid of the auxiliary vessel), was estimated in two ways ; first, by observing the change of level produced by raising or lowering the temperature of the water in the calorimeter through a small number of degrees ; and secondly, by accurately determining, at the end of the experiment, the capacity of the reservoir and that of the capillary tube. The form of apparatus now described can only be employed Andrews' Pa,pers PMeV. n v_Z __ .. V ir"~ - "''^ 'v7>T -■■""'\ -^ ^ )::;) /' '--Kim^^-^^mMi^^- \ \ % % XXXV.] Electrical Discharge on Oxygen and other Gases. 271 when the entire change of volume of the gas does not amount, in the course of the experiment, to more than about one-tenth of the whole. When large changes of volume occur, the free end of the siphon tube must be hermetically sealed, so as to include a certain quantity of air, from whose subsequent change of volume that of the gas in the reservoir can be readily cal- culated. This modification of the apparatus we have found to be very convenient in experiments upon the action of the spark and silent discharge on the compound gases. §2. The oxygen gas employed in the following experiments was prepared from fused chlorate of potash, and, to purify and dry it, was passed through two U-tubes ; the first containing frag- ments of marble moistened with a strong solution of caustic potash, the second, fragments of glass moistened with sulphuric acid. The potash tube was sometimes suppressed. In order to remove every trace of nitrogen, the whole apparatus was placed in connexion with a good air-pump, and a vacuum produced to the extent of at least half an inch, while the gas was still being evolved from the fused chlorate (fig. 4). When the process of exhaustion was dis- continued, the gas soon filled the apparatus, and was expelled through the mercury at the lower end of the long gauge. The operation of exhausting and refilling the vessel was per- formed three times in every experiment. Supposing the con- nexions of the apparatus to have been perfectly air-tight, the nitrogen remaining, after this triple exhaustion, could not have amounted to more than 2oo!ooo th of the whole. This degree of accuracy was not, it is true, realized in practice, but the oxy- gen gas, prepared in this way, did not contain xinnrth of its volume of nitrogen. The connexion with the air-pump at a having been broken (the gas still continuing to pass freely over), the end of the tube was softened in a lamp and bent downwards at an obtuse angle, so as to allow it to dip into sulphuric acid contained in a small dish, as shown in fig. 5. The current of gas was now arrested, by removing gradually the lamps from the chlorate of potash, so as to allow the apparatus to cool slowly. When the acid had ascended a short way 272 Volumetric Relations of Ozone, and Action of [xxxv. in a c, the vessel was sealed hermetically at b, and after the acid had ascended to about the point c, the vessel was removed, and placed in the upright position represented in figs. 1 and 2. It was sometimes necessary to expel a bubble or two of gas, in order that the column of acid in the siphon tube might be in a convenient position when the vessel was placed in the calori- meter. Previous to filling the vessels, they were always cleaned by means of boiling nitric acid, and subsequent washing with distilled water. They were afterwards carefully dried. To the success of several of the following experiments, this precaution was indispensable. An auxiliary vessel having been filled in the same manner, either with air or with oxygen, the two vessels were placed in the calorimeter (fig. 3), and the difference of the levels of the acid in each carefully read. In our earlier experiments we generally used a cathetometer for this purpose, but latterly we found it more convenient and sufficiently accurate to apply to the limbs of the siphon tubes a scale divided into millimetres. From the rapidity indeed with which the readings were thus made, the results were found to be fully as trustworthy as those obtained with the cathetometer. When quantitative determina- tions were required, the temperature of the water in the calori- meter and the height of the barometer were carefully noted. After the levels were read, the free ends of the siphon tubes in both vessels were hermetically sealed. The primary vessel was then I'emoved from the calorimeter and placed in connexion with the electrical machine, to be exposed to the action either of the spark or silent discharge. When this operation was finished, the vessel was replaced in the calorimeter, the siphon tubes were opened, and the levels of the acid in the two vessels again read. In order to examine the effects of heat, the reservoir of the vessel was placed in a sort of air-bath, formed by suspending a long copper cylinder above a Leslie's gas-burner, the siphon tube being outside the cylinder, fig. 6. In this way a tem- perature of 300° C, which was sufficient to destroy in a short time all the ozone reactions, was readily obtained. This tem- perature was estimated without difficulty, by observing the amount of compression of the air in the outer leg of the siphon XXXV.] Electrical Discharge on Oxygen and other Oases. 273 tube. Our apparatus, with a slight modification, might, in fact, be employed as a thermometer for all temperatures below that at which glass begins to soften. It will probably tend to perspicuity, if we state, before going further, some of the general results of our experiments on the action of the electrical discharge on pure oxygen. I. When the silent discharge is passed through pure and dry oxygen, a contraction taJces place. This contraction pro- ceeds, at first rapidly, but afterwards more slowly, till it attains a limit, which, in one of our experiments, amounted to Ytth of the original volume of the gas. II. // a fetu electrical sparks be passed through the gas in this contracted state, it expands till it recovers about three- fourths of the contraction ; but, however long the sparks are passed, the gas never recovers its original volume. III. When electrical sparks are passed through pure and dry oxygen, it contracts, but to a much smaller extent than when acted on by the silent discharge. The oxygen is, in fact, brought to the same volume as when electrical sparks are passed through the same gas, previously contracted by the silent dis- charge. IV. When oxygen, contracted either by the silent discharge or by sparks, is exposed for a short time to the temperature of 270° C, it is restored to its original volume, and, on opening the vessel, the ozone reactions are found to have disappeared. The following experiments, taken from a large number which gave similar results, wiU serve to illustrate the foregoing statements. a. In a vessel, whose reservoir had a capacity of 5 cub. cent., sparks were passed for ten minutes, and produced a contraction of 5' 9 mUlims., as measured by the change of levels of the acid in the siphon tube. By heating the vessel after- wards to 300° C, the levels were restored to within O'l miUim. of their original position. With the silent discharge in the same vessel, a contraction of 39'5 millims. (corresponding to about one- thirtieth of the volume of the gas) was obtained in ten miuutes. Of this con- traction heat restored 3 8*7 millims. This slight difference of S 274 Volumetric RdaMons of Ozone, and Action of [xxxv. 0*8 millim. is probably due to distortion of the vessel produced by heat. Again, the sileut discharge gave in ten minutes a contraction of 3 7 6 millims., of which sparks, subsequently passed for seven minutes, destroyed 29'7 millims., leaving 7"9 millims. undestroyed. ^. In another vessel, having a reservoir of the capacity of 0"8 cub. cent., active sparks gave, in fifteen minutes, -4 miUims. of contraction. After fifteen minutes more of sparks there was no additional contraction. The silent discharge was now passed for fifteen minutes, and increased the contraction to 20 millims. ; in fifteen minutes more, the entire contraction was 31 millims. Four strong sparks reduced this to 2 2 '5 millims,, six or seven more to 16 mUlims., seven more to 11 millims., and sparks, continued for ten minutes, left 4 millims. of permanent contraction. y. In a third vessel, of about the same capacity as the last, sparks gave a final contraction of 7"5 millims. ; while the sUent discharge, pushed to its limit, increased the contraction to 90 millims., corresponding to about one-twelfth of the entire volume of the gas. This contraction was almost exactly destroyed by heat. Before leaving this part of the subject, we should mention that, when a fuU contraction is obtained by means of the silent discharge, it wUl be found very slowly to diminish from day to day. "\Ye have not ascertained whether, at the end of a very long period of time, the original volume of the gas would be recovered. At 100° C, the contraction diminishes much more rapidly than at ordinary temperatures. Thus it appears that the state produced by the electrical discharge is not permanent, even at common temperatures, and that it becomes more unstable as the temperature rises, till at 270° C, it is rapidly destroyed. § 3- We next proceeded to examine the volumetric changes which occur when oxygen, contracted by the electrical discharge, is brought into contact with other bodies. The first body we tried was mercury, the physical changes produced on which by ozone are known to be very remarkable. XXXV.] Electrical Discharge on Oxygen and other Gases. 275 When a capsule containing this metal is broken in a tube of oxygen gas through which the silent discharge has been passed, the mercury instantly loses its mobility, and, if gently shaken, covers the interior of the tube with a brilliant mirror. As the action continues, the mirrored surface breaks up, and the coat- ing becomes converted into a blackish semipulverulent sub- stance. Unless the tube be very violently shaken, the ozone reactions will not be entirely destroyed, until the mercury has been for some hours in contact with the gas. To determine the volumetric changes, a thin capsule, filled with pure mercury, and hermetically sealed, was placed in a vessel with a large reservoir of the usual form (fig. 1'), which was afterwards filled with dry oxygen. After the levels had been read, the silent discharge was passed until a considerable con- traction was obtained. The corrections for changes of tem- perature and pressure were, as in other cases, furnished by an auxiliary vessel. The free end of the siphon tube having been sealed, the primary vessel was removed from the calorimeter, and the capsule broken by a sudden jerk. The breaking of the capsule, in this and other experiments, was greatly facilitated by introducing into the vessel a small piece of thick glass tube, which fell on the capsule when the vessel was shaken (fig. 1', k). Viewing ozone as an allotropic form of oxygen, in the gaseous state, we expected that when mercury came into con- tact with it, a contraction would take place, equal to the volume of the ozone which entered into combination with the metal. This anticipation has not been realized. After the rupture of the capsule, the vessel was immediately replaced in the calorimeter and the levels read. Not the slightest diminu- tion of volume was observed in any one of a large number of experiments; on the contrary, an increase, corresponding to a change of 1 millim. in the levels, generally occurred. On allow- ing the vessels to remain in the calorimeter, and reading the position of the acid in the siphon tubes from time to time, the gas was found to expand steadily, but slowly, for some hours, tiU from two-thirds to five-sixths of the contraction produced by the discharge was recovered. If the vessel was opened at any time. while this expansion was going on, the ozone reactions 276 Volu7netric Relations of Ozone, and Action of [xxxv. were always manifest; but, when the expansion was at an end, the ozone reactions had also ceased. If the mercury, instead of being allowed tranquilly to act upon the gas, was violently agitated after breaking the capsule, a much smaller portion of the contraction was restored ; in some cases not more than one-sixth. Metallic silver, in the state both of leaf and of filings, gave similar results. The surface of the silver was partially blackened, about three-fourths of the original contraction was recovered, and the whole operation much more quickly terminated. As the above reactions were evidently complex, the mercury and silver partly entering into combination with the gas, while the compounds formed appeared to exercise a catalytic action, we endeavoured to find an elementary body which would instantly destroy the ozone reactions, and at the same time he without action on dry oxygen. After some trials, we found that iodine possessed the required' properties. We first ascer- tained that its vapour, although visible at common tempera- tures, has no appreciable tension. When a small capsule, con- taining pure and dry iodine, was broken in a vessel of the usual form filled with oxygen, the levels of the acid in the siphon tube were not altered. So slight also is the affinity of iodine for oxygen, that, on heating the reservoir so as to volatilize a considerable portion of the iodine, and afterwards allowing it to cool, the volume of the gas underwent no change. On the other hand, if ozone be present, the iodine is immediately attacked, a greyish-yellow compound is formed, and all ozone reactions are instantly destroyed. The experiment already described with mercury was now repeated substituting iodine for that metal. On breaking the capsule, the levels of the acid scarcely changed 1 millim., although the original contraction amounted to 50 millims. Ko> subsequent expansion took place, and, on opening the vessel, the ozone reactions had entirely disappeared. On the allotropic hypothesis, these experiments, and par- ticularly the last, lead to the conclusion that ozone must have a density at least fifty times as great as that of oxygen. This conclusion is indeed unavoidable from the experiments just described, unless it is assumed that at the same moment that XXXV.] Electrical Discharge on Oxygen and other Gases. 277 one portion of the ozone combines with the iodine, another portion changes back into oxygen, and that these quantities are so related to one another, that the expansion due to the one is exactly equal to the contraction arising from the other. Such a supposition can, however, not be considered probable. §4. In order to subject this remarkable property of ozone to a further examination, two additional series of experiments were undertaken, to a description of which we now proceed. In the first series, a primary and an auxiliary vessel with large reservoirs were filled with pure and dry oxygen, small capsules hermetically sealed, and containing portions of the same solution of iodide of potassium, having been previously placed in each. The silent discharge was passed through the primary vessel so as to produce a considerable contraction, amounting in different experiments to from 40 millims. to 80 millims. The levels of the acid in the siphon tubes of both vessels having been carefully read while the vessels were in the calorimeter, the ends were sealed, and the vessels shaken so as to break the capsules in both. In the primary vessel, the iodide ■of potassium solution became instantly coloured dark brown from the iodine set free, while that in the auxiliary vessel did not change. On replacing the vessels in the calorimeter, and opening the ends of the siphon tubes, the change in the levels indicated a considerable expansion in both. In the auxiliary vessel, this expansion was due to the tension of the vapour of the solution of iodide of potassium alone ; in the primary vessel, the expansion ought to have been less than this, on account of the absorption of ozone, if the volume of that body were capable of measurement. In the following Table, which contains the results of five very careful experiments made in this way, the first column gives the amount of contraction produced by the silent dis- charge in the primary vessel, previous to the breaking of the capsules ; the second, the temperature ; the third and fourth, the respective expansions in the primary and auxiliary vessels; and the fifth, the differences of the numbers in the third and fourth columns. 278 VoluTnetric Relatioois of Ozone, and Action of [xxxv. I. 81-5 11-OC. 68-5 70-0 — 1-5 II. 62-2 13-5C. 79-5 80-0 — O-o III. 72-2 8-7C. 50-7 52-0 — 1-3 IV. 63-5 12-2C. 71-5 73-0 — 1-5 V. 45-5 16-20. 87-0 89-2 — 2-2 The capacity of the vessels employed in these experiments was about 30 cub. cent., and the. primary and its auxiliary were found, in each experiment, by careful comparative observations, to work accurately together. The solution of iodide of potassium was purposely employed of different strengths in the several experiments. In I. it contaiued -jwth part of iodide of potassium ; in II. a^^th ; in III. |-rd ; and in IV. and V. ^th. In the two last the solution was sHghtly acidulated with hydrochloric acid, in the others it was neutral. The capsules contaiued each about 0-7 grm. of these solutions. The agreement in the results of these experiments, made with solutions of iodide of potassium so widely differing, is very remarkable. We ought also to observe that direct experiments, performed with great care, showed that the iodine set free by the ozone in the primary vessel did not affect the tension of the vapour of the solution. Taking the mean of the above numbers, the density of ozone, as compared with that of oxygen, must be expressed, on the allotropic hypothesis, by about the number 60 ; in other words, ozone must be a gas only about six times lighter than the metal lithium. If the small differences in the fifth column be due, wholly or in part, to accidental causes, which is far from improbable, a still higher number must, on the same hypothesis, be taken to express the density of ozone. In the last series of experiments, the amount of iodine set free in the solution of iodide of potassium was determined by analysis, and the weight of oxygen deduced therefrom compared with the weight of oxygen, calculated from the volumetric change which had occurred in the formation of the ozone. We shall describe these experiments with some detail, particularly as the methods employed will be found applicable XXXV.] Electrical Discharge on Oxygen and other Gases. 279 to other cases of gas analysis, wliere small changes in a given volmne of gas have to be estimated. Before filling it with oxygen, a sealed capsule containing a solution of iodide of potassium was introduced into the primary vessel, while the auxiliary contained the dry gas only. The silent discharge was passed through the former, and the contraction carefully observed. The capsule was then broken, and the solution agitated in the primary vessel for a few seconds. The siphon tube was next cut off, and the liquid carefully washed out and analysed by means of a weak solution of sulphurous acid, the exact strength of which had been immediately before determined by observing the amount required to decolorize a solution containing a known weight of iodiae. In some of the experiments the solution of iodide of potas- sium was slightly acidulated, iu the others it was neutral. In the latter case it was acidulated before being analysed. The results were the same, whether the solution was taken in the neutral or in the acid state. For, although oxygen gas acts upon an acid solution of iodide of potassium, the action requires time, and the contact in this case was only contiaued for a few seconds.^ The formula by which we calculated the residts of these experiments may be thus investigated. Let /, ff (fig. 1) be the mean level of the acid in the legs of the siphon tube ; d, e the levels at any time, t being the temperature, and II the barometric pressure corrected for temperature. Let also ge =^fd = x, and let H be the length of a tube similar to the siphon tube, and whose capacity is equal to that of the reservoir and of the siphon tube to /. Let a be the height of a barometer containing the liquid in the siphon ^Baranert has objected on this ground to some of the eirperiments in a former commnnication made by one of ns to the Society. We have foond that, in the circumstances in which those experiments were performed, abont one-twentieth of the effect was due to this cause ; but as the oxygen acting on the solution of iodide of potassium set free its equivalent of iodine, the equality of the numbers given in that paper could not be disturbed by this action. We have, since that time, by additional experiments, fuUy confirmed the statement that no water is produced in the destruction of electrolytic ozone by heat. 280 Volumetric Relations of Ozone, and Action of [xxxv. tube, p the pressure of the gas in the vessel, and V the volume of the gas reduced to 0° C. and 760 millims. Then, evidently, ^ -crl+af But ^=n(^+f V(l+alt) hence n(H+a;)(n-^) is a constant quantity. Taking the logarithmic differential, we have 28x 2xSa Q_SY aSt STL Sx _ a ~ a' V+l + af n R+x ^_^2x a -Now — =YF is multiplied by — , a quantity rarely exceeding 2W- To this degree of approximation, then, at least. If V^, H^, Xj represent for the auxiliary vessel the quantities corresponding to V, H, x in the primary, we have, since aSt STL , /2 1\ ._. If H^=:H, i.e. if the primary and auxiliary vessels be of similar dimensions, we have at once, from (1.) and (2.), 't=(^--Sx){1+^) .... (3.) If the vessels be not similar, let then instead of (3.) we have r=(^x-Sx„)(l+^) (4.) Formula (3.) or (4.) gives the change of volume in the gas, as deduced from the observed change in the levels in the siphon tube. XXXV.] Electncal Discharge on Oxygen and other Gases. 281 For the estimation of the portion of the gas (S^Y) taken up as ozone by the solution of iodide of potassium, let C be the capacity of the primary vessel to / in litres, s the number of measures of sulphurous acid required to decolorize the solution when washed out of the vessel, S the number required to decolorize I grm. of iodine. Then we have, evidently, as a sufficient approximation. Is (5,V J5-8S il+at)7(iO If we suppose ozone to be allotropic oxygen, with a relative density e : 1, then S,Y of oxygen contracts to -^— on being changed into ozone. Hence, on this hypothesis, SJ e ~SY~e-r In order to verify this method, two similar vessels were filled with pure oxygen, one containing a capsule filled with a neutral solution of iodide of potassium, the other a capsule filled with an acidulated solution of the same salt, and of precisely the same strength. The neutral solution was also introduced into the siphon tubes of both vessels. After break- ing the capsules, the levels were read, and the vessels set aside for some days ; at the end of which time it was found that a portion of oxygen gas had been absorbed in the primary vessel which contained the acid solution, while no change had occurred in the other. The levels were now read again, and the solution in the primary vessel analysed. The weight of the oxygen absorbed, as calculated by the foregoing formulae from the volumetric change, was 0'0002188 grm., while its weight deduced from the analysis was 0"0002181 grm. The close agreement between these numbers shows that the method is susceptible of considerable accuracy. The following Table contains the results of six experiments made in the manner above described. The primary and auxiliary vessels were carefully constructed of similar dimen- 282 Volumetric Relations of Ozone, and Action of [xxxv. sions, and were found, on trial, to work accurately together, so that formula (3.) was directly applicable. I. II. HI. IV. V. VI. mm. mm. mm. mm. mm. mm. 2^,. 31-6 - 3-0 -18-5 -48-5 51-0 39-0 2{x, + Sx^). 31-0 18-0 - 2-25 - 6-5 - 9-75 - 8-25 2x. 4-0 38-5 - 0-5 16-5 72-5 65-0 2(x + Sx). -78'0 - 2-75 -55-25 - 5-0 -39-0 -27-5 C. 0-0338 0-0306 0-0288 0-0279 0-0269 0-0346 s. 9-1 5-4 5-7 5-1 4-5 4-5 grm. grm. grm. grm. grm. grm. I. 0-0268 0-0684 0-0442 0-0674 0-0446 0-0621 S. 22-6 47-95 30-85 49-5 36-8 44-43 mm. mm. mm. mm. mm. mm. n. 777-0 772-5 7630 751-0 747-2 751-0 t. ll'-OC. 13°-450. 9°-lC. 9°-8C. 14°-0C. 14°-7C. 1 a- 0-000025 0-000024 0-000025 0-000026 0-000027 0-000036 0-932 0-938 0-947 0-927 0-952 0-933 On comparing these experiments with the foregoing, it will be observed that they do not give exactly the same result. Interpreted as they stand, they indicate a density for ozone, if we may use the expression, more than infinite, inasmuch as the quantity of oxygen deduced from the analysis is less than that corresponding to the contraction observed. But, although every precaution was taken to avoid all sources of uncertainty, it is not improbable that this difference between the amount of oxygen deduced from the contraction and from the analysis may arise from a slight defect in some of the data, particularly as it would only involve an error of the order of ao^oo th of the entire gas. Taking the mean result of the three series of experiments as they stand, it gives, on the allotropic hypothesis, almost exactly an infinite density for ozone. § 5. The commonly received statement, that the whole of a given volume of dry oxygen gas can be converted into ozone by the passage of electrical sparks, is erroneous. In repeated trials, with tubes of different forms and sizes, we found that not more that one-twelfth of the oxygen could, under the most favourable circumstances, be converted into ozone, even by the silent discharge, and a much smaller proportion by the action of sparks. But if the ozone is removed as fast as it is produced, XXXV.] Electrical Discharge on Oxygen and other Oases. 283 the conversion may be carried on indefinitely. An apparatus was constructed of the form shown in fig. 7. At a, I two fine platinum wires ■ were hermetically sealed into the glass ; at c there was a solution of iodide of potassium, and de was fiUed with fragments of fused chloride of calcium which allowed the ozone to pass freely, but arrested the vapour of the solution ; so that while the discharge always took place in pure and dry oxygen, the ozone was gradually absorbed. The volumetric change was measured by the readings of the sulphuric acid in the siphon tube fg sealed at g. The experiment was continued till five-twelfths of the oxygen (whose entire volume was about 12 cub. cent.) was absorbed, and the action was still going on. It was not considered necessary to persevere further, as the labour of turning the machine was very great. To produce the effect just mentioned, the discharge from the machine in excellent order had to be passed through the tube for twenty-four hours. When the electrical discharge is passed through rarefied oxygen, the phenomena are apparently the same as with the gas at the common pressure of the atmosphere. We filled a vessel with oxygen and exhausted it till the pressure was equal to 1 inch of mercury, in the hope that in this rarefied state a larger portion of the oxygen might be converted into ozone than under gTeater pressures, but this did not prove to be the case. We intend on a future occasion to pursue this part of the inquiry, and to examine particularly the effects of the electrical discharge on oxygen in different states of rarefaction and condensation. Ozone, obtained by electrolysis, gave results nearly similar to those already described. As the volume of the oxygen gas from which the ozone was derived could not, in the case of electrolytic ozone, be observed directly, it was estimated indirectly by placing three vessels in line and passing the same stream of electrolytic oxygen through them all. By heating the first and last vessels to 300°C., and observing the expansion produced in each, it was easy to calculate the expansion which would have occurred in the middle vessel, if it had been exposed to similar treatment. This expansion was assumed to be equal to the contraction which occurs when ozone is produced 284 Volumeti'ic Relations of Ozone, and Action of [xxxv. from oxygen by means of the electrical discharge. Finally, the actual amount of ozone in the middle vessel was determined by introducing a solution of iodide of potassium, and ascertaining by analysis the amount of iodine set free. The individual experiments with electrolytic ozone did not agree so well with one another as those performed with ozone prepared by the discharge. This arose partly from the very small quantity of ozone in electrolytic oxygen, but chiefly from the irregularity in that quantity at different times, even when the current was passing very steadily, which made it difficult to ascertain with certainty the expansion due to the ozone in the middle vessel. Our earlier results, indeed, gave a measurable volume for ozone, and as a first approximation we obtained the number 4 as expressing its density.^ But, by multiplying our experiments, and taking all possible precautions to ensure accuracy, we found that electrolytic ozone, like that produced by the discharge, has no appreciable volume. Ozone is not condensed at common pressures by the cold produced by a mixture of solid carbonic acid and ether. A stream of electrolytic oxygen, passed very slowly, first through a U-tube surrounded by snow and salt, and next through a spiral tube immersed in the carbonic acid and ether bath ( — 76° C), underwent no change. The ozone reactions, as the gas issued from the tube, after exposure to this low temperature, were as strong as before it entered the bath. §6. Hydrogen, prepared with care by the action of dilute sul- phuric acid recently boiled, on zinc, and purified by passing through three U- tubes containing corrosive sublimate in solu- tion, hydrate of potash, and sulphuric acid, respectively, and finally, in order to remove the last trace of oxygen, through a tube filled with metallic copper heated to redness, was found not to be altered in volume, either by the sparks or by the silent discharge. It appears to be a much better conductor of elec- tricity than oxygen. ^ Proceedings of the Royal Society, vol. viii. page 498, and vol. ix. page 606. [Anli, pp. 262, 264.] XXXV.] Electncal Discharge on Oxygen and other Gases. 285 With Nitrogen, prepared in the usual way by depriving atmospheric air of its oxygen by means of heated copper, the results were also negative. Among the compound gases, Carbonic Acid is rapidly decom- posed by the spark, slowly by the silent discharge ; in both cases expansion takes place. Cyanogen is at once decomposed by the spark with deposition of carbon (?) ; but presents so great a resistance to the passage of electricity, that the action of the silent discharge could not be ascertained with certainty. Protoxide of Nitrogen is readily attacked by the spark, with the formation of hyponitric acid, whose characteristic red colour is distinctly seen. The primary result of the spark action is expansion, but on allowing the gas to stand, it gradually contracts, in consequence of the absorption of the hyponitric acid gas by the sulphuric acid in the siphon tube. ' It is im- possible to determine the precise amount of the first expansion, as a certain amount of absorption occurs at the same time; but, in one imperfect trial, the ratio between the expansion and the subsequent contraction was nearly that of 1:2. This corre- sponds to the conversion of 8 vols, of protoxide of nitrogen into 4 vols, of hyponitric acid gas and 6 vols, of nitrogen. The silent discharge appears to produce the same resulb as the spark, but as the action is slower, the absorption interferes with any attempt to determine accurately the primary expansion. Deutoxide of Nitrogen presents the interesting example of a compound gas, which, under the influence both of the spark and silent discharge, undergoes, like oxygen, a diminution of volume. This is independent of the subsequent absorption of the hypo- nitric acid formed. This gas is remarkable for the facility with which it is decomposed by both forms of discharge. The pas- sage of sparks for two minutes, through a tube containing about 5 cub. cent., produced a contraction of the gas to nine-tenths of its original volume, followed after some time by a contraction not quite double of the former, from the absorption of the hypo- nitric acid gas. On continuing to pass sparks till the decom- position was finished, and waiting till the hyponitric acid gas was completely absorbed, the residue amounted to a little more than one-fourth of the original gas. This residue consisted of 286 Volumetric Relations of Ozone, and Action of [xxxv. a mixture of 1 1 vols, nitrogen and 1 vol. oxygen. It is evident that the final result is a little complicated, but there can be little doubt that the action of the spark is to convert 8 vols, of deutoxide of nitrogen into 4 vols, of hyponitric acid gas and 2 vols, of nitrogen. This decomposition may be due to the im- mediate action of the discharge ; or the deutoxide of nitrogen may, in the first instance, be resolved into equal volumes of nitrogen and oxygen, the latter combining as it is formed with undecomposed deutoxide. Carbonic Oxide has given results of great interest, the investi- gation of which has already occupied a considerable time, although it is not yet completed. The principal facts have, however, been already ascertained, and as they present some remarkable analogies to those already described in the case of oxygen, we shall briefly allude to them here, reserving the complete investigation for a future communication. The carbonic oxide was prepared by heating oxalic acid with an excess of sulphuric acid, and absorbing the carbonic acid by means of a strong solution of hydrate of potash. The gas, as it escaped from the end of the apparatus, did not produce the slightest turbidity in lime or baryta water, and was completely absorbed by an ammoniacal solution of the subchloride of copper. On exposing this gas to the action of the silent discharge, a steady contraction took place, and the surface of the positive platina wire became covered with a continuous deposit of a bronze colour. After some time, a trace, but only a trace, of the same deposit appeared at the point of the negative wire. If, after a contraction of 50 millims. or 60 mUlims. of the siphon tube had been obtained, a few electrical sparks were passed through the gas, the greater part of the contraction was, as in the case of oxygen, destroyed. Heat acted in the same direc- tion, but did not restore the gas altogether to its original volume. On continuing to pass the silent discharge, the gas continued to contract, and the deposit to increase on the positive wire. Portions of the same deposit were also scattered about the sides of the tube, being probably thrown off from the same wire. The experiment was in some cases continued till the gas had XXXV.] Electrical Discharge on Oxygen and other Gases. 287 contracted to about one-third of its origiaal volume. To effect this contraction, the machine had to he worked for sixty hours. The residual gas consisted of carbonic acid, oxygen, and unde- composed carbonic oxide. A similar deposit was obtained when the discharge took place between gold instead of platinum wires. This deposit appeared to be soluble in water. Its quantity was so small that direct analysis was altogether impossible. Its composition may, however, be determined by fixing with pre- cision the ratio of the volumes of the carbonic acid and oxygen produced. We have succeeded in devising a method by which this analysis may be effected even with less than 0"5 cub. cent, of the mixed gases, but this part of the investigation is still unfinished. Atnwspheric Air is the only gaseous mixture which we have exposed to the action of the silent discharge. Like pure oxygen, it undergoes a diminution of volume; but the operation is more quickly terminated and the contraction is less than with that gas alone. If, after the passage of the discharge, the vessel be set aside for some hours, the contraction will be found to augment ; and if the gaseous mixture be now again exposed to the action of the discharge, a further contraction will take place. On the other hand, heat destroys a portion only of the contrac- tion at first produced. All these facts are easily explained from the simultaneous formation of ozone and one of the higher oxides of nitrogen, and the marked influence of the latter, when formed, in arresting the formation of the former. To the same cause we have succeeded in referring an apparently anomalous state of oxygen, produced by passing a stream of strong electri- cal sparks, for some minutes, through that gas containiug a trace of nitrogen. The oxygen becomes by this treatment incapable of contracting or of changing into ozone under the action of the silent discharge, and only recovers its usual condition by exposure to heat or by standing for some hours. If the nitro- gen amounts to not more than wij-th of the entire volume, this condition cannot be produced more than two or three times. At first we supposed it to be a new (passive) state of oxygen, but we have now no hesitation in referring it to the presence of a trace of hyponitric acid gas produced by the electrical sparks. 288 Volumetric Relations of Ozone, and Action of [xxxv. It is perhaps premature to attempt a positive explanation of the facts now described regarding ozone. The foregoing inves- tigation into its volumetric relations has, for the moment, rather increased than diminished the difficulty of determining the true nature of that body. To reconcile the experimental results with the view that ozone is oxygen in an allotropic form, it is necessary to assume that its density immensely exceeds that of any known gas or vapour; being, as we have seen, according to the first and second series of experiments (§§ 3 and 4), from fifty to sixty times that of oxygen, and according to the third series (§ 4) absolutely infinite. Even the former results would make it only six times less dense than the metal lithium, and would place it rather in the class of solid or liquid bodies than of gaseous. The question may then be fairly proposed, — Can this singular body, at common temperatures, be actually a solid or liquid substance, whose particles, in an extremely fine state of subdivision, are suspended in the oxygen with which it is always mixed ? This question will scarcely, we think, admit of an af&rmative answer. Not only does ozone, mixed as usual with oxygen, pass through several U-tubes containing fragments of pumice moistened with sulphuric acid, but it exhibits its characteristic reactions when left for many hours in tubes of this kind. Besides, there is not the slightest cloud visible in a tube filled with oxygen, even when one-twelfth of the gas has been converted into ozone, nor does any deposit appear after long standing. Ozone may be formed under conditions which exclude the possibility of its containing, as a constituent, any element except oxygen, or the elements of oxygen, if that body should hereafter be shown to be compound. As has been before stated, our ex- periments may be reconciled with the allotropic view and an ordinary density, but still one greater than that of oxygen, if we assume that when ozone comes into contact with such substances as iodine, or solutions of iodide of potassium, one portion of it, retaining the gaseous form, is changed back into common oxygen, while the remainder enters into combination ; and that these are so related to one another, that the expansion due to the former is exactly equal to the contraction arising from the XXXV.] Electrical Discharge on Oxygen and other Gases. 289 latter. We do not, however, consider this supposition to be by any means probable, nor can it be easily reconciled with the results (§3) obtained when mercury acts on ozone. If we consider the conditions under which ozone is formed, we shall find them to be different from those which produce allotropic modifications in other cases. Such elements, for example, as phosphorus or sulphur, are modified by the action of heat, and not by the electrical discharge. It is true, at the same time, that the destruction of ozone, or, on the allotropic view, its reconversion into oxygen, by exposure to a tempera- ture of 270° C, is apparently analogous to that action of heat whereby common phosphorus is converted into the red variety. Without rejecting the allotropic constitution of ozone, although the results of our volumetric experiments are certainly difficult to reconcile with it, it may not be uninstructive to consider whether the facts already known admit of a different explanation. As ozone is formed from pure and dry oxygen by the electrical discharge, if it is not an allotropic form of oxygen, the latter must be either a mechanical mixture of two or more gases, or it must be a compound gas. It is perhaps scarcely necessary to consider the former hypothesis, according to which, oxygen, in its ordinary state, would be a mechanical mixture, as atmospheric air is a mixture of nitrogen and oxygen. The con- traction, which occurs when the electrical discharge is passed through oxygen, is at first sight indeed favourable to such a supposition, inasmuch as the combination of gases is usually accompanied either by a diminution, or no change of volume. But we have not been able to discover, in its other reactions, any facts which countenance this otherwise improbable view of the constitution of oxygen gas. Finally, it remains to be considered, whether in the formation of ozone, oxygen does not undergo a more profound molecular change than is involved in an allotropic modification, whether, .in short, this supposed element may not be actually decomposed. If, for the moment, we confine our attention to the phenomena which present themselves when the electrical discharge is passed through oxygen, this attractive hypothesis will be found to furnish a simple and plausible explanation of them all. It will be observed, at once, that the conditions under which ozone is T 290 Volumetric Relations of Ozorve, and Action of [xxxv. formed from oxygen by the electrical discharge, are precisely those under which other gases, known to be compound, are decomposed. The electrical current is one of very high intensity, and therefore very favourable to decomposition : when passed in the form of the silent discharge, a large contraction takes place in the volume of the gas, which is partially destroyed by a few electrical sparks, and wholly by heat. With nitrogen and hydrogen no similar effects are observed, the volume of these gases being quite unaffected by either form of discharge. The behaviour of carbonic oxide, when exposed to the action of the silent and spark discharge, corresponds remarkably to that of oxygen ; the latter form of discharge, while producing itself only a limited contraction in carbonic oxide, destroying a part of the contraction produced by the former, ^gain, when deutoxide of nitrogen is exposed to the action of the same agents, an immediate contraction takes place without any solid or liquid product being formed, showing that in certain cases of gaseous decompositions, the resulting gases occupy a smaller volume than the original compound. If we assume that oxygen is resolved by the electrical dis- charge into a new compound (ozone), containing the same constituents as the oxygen itself, but in a different proportion, and into one of the constituents themselves, in the same man- ner as carbonic acid is resolved into carbonic oxide and oxygen, or nitric oxide into hyponitric acid and nitrogen, the results of our experiments wiU admit of an easy explanation. One of the simplest suppositions we can make for this purpose is, that two volumes of oxygen consist of one volume of U and one volume of V, united without condensation (U and V being the supposed constituents of oxygen), and that one volume of ozone consists of two volumes of U and one volume of V; and further, that by the action of heat, iodine, etc., ozone is resolved into U and oxygen. The appearance of ozone at the positive pole in the electro- lysis of water, and its formation by the agency of so active a body as ordinary phosphorus, do not seem unfavourable to its being the result of decomposition. But the same observation will not apply to its production by the action of acids on such bodies as the peroxide of barium. We certainly should not xxxv.] Electrical Discharge on Oxygen and other Gases. 291 have expected to see a body derived from the decomposition of oxygen" produced under the latter circumstances, and, although the facts connected with its production in these cases have not been studied with precision, yet there appears to be no doubt that ozone is actually formed. We must in conclusion add, that the few attempts we have made to isolate either of^the supposed constituents of oxygen have failed. A^-^**"^^*^ ^ We are still continuing ( ^-proseeu^ this inquiry, and hope on a future occasion to lay before the Society the results of further experiments which are now in progress. Note, added July 12, 1860. It having been suggested that a certain amount of the contraction produced by the passage of the electrical discharge through tubes containing oxygen might arise from the action on that gas of the platinum wires, or of finely divided platinum, which, as in Mr. Gassiot's experiment, might be thrown off by the action of the discharge, we have made the following experi- ment, in order to ascertain whether such an action could have occurred in the conditions under which we operated. Before describing the experiment, it may be proper to state, that in the passage of the discharge of the electrical machine, there is no visible separation of metallic platinum, as in that of the dis- charge from the induction coil, nor other evidence of the wires being acted on; on the contrary, both the wires and tube retain their original appearance after having been frequently exposed to the alternate action of the discharge and of heat. A vessel, of the form represented in the annexed figure, was filled with pure and dry oxygen. It differs from the tubes ■usually employed only by having the lower end of the reservoir drawn out into a capillary tube a h. The platinum wires were inserted as usual, and an auxiliary vessel of the same size and form was filled with dry air. After determining the compara- tive range of the two vessels, their reservoirs were exposed, in the apparatus before described, to a temperature of 300° C, in order to bring them as exactly as possible into the same condition. When they had cooled, the levels of the acid in the siphon tubes were again read, and the silent discharge was / 292 Volumetric Relations of Ozone, etc. [xxxv. afterwards passed through the primary vessel till a contraction of twenty-seven millims. was obtained in its siphon tube. The extremity of the capillary tube of the reser- \^ voir was next cut off at a, and the end of the siphon tube d, which had the form repre- ^ sented in the figure, was dipped under sul- phuric acid. The open end at a was now connected with an apparatus, which sup- plied a slow stream of carefully dried air, and this was allowed to pass tiU. the ozone /4 01 ^^cl oxygen originally contained in the tube were entirely displaced by the dry air. It is obvious that by this arrangement the ozone was removed, whUe the platinum wires and the inner surface of the tube were left in precisely the same state as after the passage of the discharge. The tube was next sealed off at c, by the application of the point of a fine blowpipe flame, the current having been arrested, so as to leave the usual column of sulphuric acid in the siphon tube. In sealing it, care was taken not to allow the air in e to become heated. The vessel was again placed, along with the auxiliary, in the calorimeter, and the levels read. The ends of the siphon tubes hav- ing been first sealed, the reservoirs were exposed to 300° C. An expansion should have taken place in the primary vessel, if the platinum had retained oxygen capable of being disengaged at 300° C; but this was not found to be the case. The change of level in its sulphuric acid siphon (corrected by the auxiliary) did not amount to 0"2 millim., a degree of accuracy rarely attainable in these experiments. [Note to xxxvi., opposite. — In Dr. Andrews' Laboratory Book the numerical data for carbonic oxide are given as 1/310, and 1/382, respectively. The 1/278 belongs to a different stage of the experiment, and seems to have been quoted inadvertently.— P. G. T.] 293 XXXVI.— ON THE EFFECT OF GREAT PRESSURES COMBINED WITH COLD, ON THE SIX NON-CONDENSABLE GASES. From the Report of the British Association, 1861, p. 76. In this communication the author gave an account of some results already obtained in a research, with which he is still occupied, on the changes of physical state which occur when the non-condensable gases are exposed to the combined action of great pressures and low temperatures. The gases when compressed were always obtained in the capillary end of thick glass tubes, so that any change they might undergo could be observed. In his earlier experiments the author employed the elastic force of the gases evolved in the electrolysis of water as the compressing agent, and in this way he actually succeeded in reducing oxygen gas to wirth of its volume at the ordinary pressure of the atmosphere. He afterwards succeeded in effect- ing the same object by mechanical means, and exhibited to the Section an apparatus by means of which he had been able to apply pressures, which were only limited by the capability of the capillary glass tubes to resist them; and while thus com- pressed the gases were exposed to the cold attained by the carbonic acid and ether bath. Atmospheric air was compressed by pressure alone to -jtt of its original volume, and by the united action of pressure and a cold of — 106° F. to ^r^th ; in which state its density was little inferior to that of water. Oxygen gas was reduced by pressure to -siirth of its volume, and by pressure and cold to Tirth; hydrogen by the united action of cold and pressure to -rsTrth; carbonic oxide by pressure to ^Ti-th, by pressure and cold to ^T^h [see footnote, p. 292]; nitric oxide by pressure to -s-ro-th? oy pressure and a cold of — 160° F. to -s-Tirth. None of the gases exhibited any appear- ance of liquefaction even in these high states of condensation. The amount of contraction was nearly proportional to the force employed, till the gases were reduced to from about -3-^th to •g-irrth of their volume; but, beyond that point, they underwent little further diminution of volume from increase of pressure. Hydrogen and carbonic oxide appear to resist the action of pressure better than oxygen or nitric oxide. 294 XXXVIL— ON THE IDENTITY OF THE BODY IN THE ATMOSPHEEE WHICH DECOMPOSES IODIDE OF POTAS- SIUM WITH OZONE. From the Proceedings of the Royal Society, 1867, vol. 16, p. 63. It was assumed for many years, chiefly on the authority of Schonbein, that the body in the atmosphere which colours iodide-of-potassium paper is identical with ozone; but this identity has of late been called in question, and as the subject is one of considerable importance, I submitted it lately to a careful investigation, the results of which I beg to lay briefly before the Society. The only property of ozone, hitherto recog- nized as belonging to the body in the atmosphere, is that of setting free the iodine in iodide of potassium; but as other sub- stances, such as nitric acid and chlorine, which may possibly exist in the atmosphere, have the same property, no certain conclusion could be drawn from this fact alone. One of the most striking properties of ozone is its power of oxidizing mercury, and few experiments are more striking than that of allowing some bubbles of electrolytic oxygen to play over the surface of one or two pounds of mercury. The metal instantly loses its lustre, its mobility, and its convexity of surface, and when moved about it adheres in thin mirror-like films to the sides of the containing glass vessel. The body in the atmosphere acts in the same way upon pure mercury; but from the very minute quantity of it which is at any time present, the experiment requires some care in order that the effect may be observed. On passing a stream of atmospheric air, which gave the usual reactions with test-paper, for some hoars over the surface of mercury in a U-tube, the metal was distinctly oxidized at the end at which the air first came into contact with it. This experiment, however, cannot be considered conclusive, as mercury will tarnish and lose its mobility under the influ- ence of many bodies besides ozone. XXXVII.] Identity of the Body in the Atmosphere, etc. 295 It is well known that all ozone reactions disappear when ozone is passed through a tube containing pellets of dry peroxide of manganese, or other body of the same class. The same thing occurs with the substance supposed to be ozone in the atmosphere. About 80 litres of atmospheric air were drawn, at a uniform rate, through a tube containing peroxide of manganese, and afterwards made to play upon very delicate test-paper. Not the slightest coloration occurred, although the same paper was distinctly affected when 10 litres of the same air, without the interposition of the manganese tube, were passed over it. But the action of heat furnishes the most unequivocal proof of the identity of the body in the atmosphere with ozone. In a former communication (Phil. Trans, for 1856, p. 12 [Ante, p. 255]), I showed that ozone, whether obtained by electrolysis or by the action of the electrical brush upon oxygen, is quickly destroyed at the temperature of 237° C. An apparatus was fitted up, by means of which a stream of atmospheric air could be heated to 260° C. in a globular glass vessel of the capacity of 5 litres. On leaving this vessel, the air was passed through a U-tube, one metre in length, whose sides were moistened internally with water, while the tube itself was cooled by being immersed in a vessel of cold water. On passing atmospheric air in a favourable state through this apparatus, at the rate of three litres per minute, the test-paper was distinctly tinged in two or three minutes, provided no heat was applied to the glass globe. But when the temperature of the air, as it passed through the globe, was maintained at 260° C, not the slightest action occurred upon the test-paper, however long the current continued to pass. Similar experiments with an artificial atmosphere of ozone, that is, with the air of a large chamber containing a small quantity of electrolytic ozone, gave precisely the same results. On the other hand, when small quantities of chlorine or nitric acid vapour, largely diluted with air, were drawn through the same apparatus, the test-paper was equally affected, whether the glass globe was heated or not. From these experiments I consider myself justified in con- cluding that the body in the atmosphere, which decomposes iodide of potassium, is identical with ozone. 296 XXXVIII.— ON THE CONTINUITY OF THE GASEOUS AND LIQUID STATES OF MATTER. The Baherian Lecture. From the Philosophical Transactions, 1869, Part II., p. 575. In 1822 M. Cagniard de la Tour observed that certain liquids, such as ether, alcohol, and water, when heated in hermetically sealed glass tubes, became apparently reduced to vapour in a space from twice to four times the original volume of the liquid. He also made a few numerical determinations of the pressures exerted in these experiments.^ In the follow- ing year Faraday succeeded in liquefying, by the aid of pressure alone, chlorine and several other bodies known before only in the gaseous form.^ A few years later Thilorier obtained solid carbonic acid, and observed that the coefficient of expansion of the liquid for heat is greater than that of any aeriform body.^ A second memoir by Faraday, published in 1826, greatly extended our knowledge of the effects of cold and pressure on gases.* Eegnault has examined with care the absolute change of volume in a few gases when exposed to a pressure of twenty atmospheres, and Pouillet has made some observations on the same subject. The experiments of Natterer have carried this inquiry to the enormous pressure of 2790 atmospheres; and although his method is not altogether free from objection, the results he obtained are valuable and deserve more attention than they have hitherto received.^ In 1861 a brief notice appeared of some of my early experiments in this direction. Oxygen, hydrogen, nitrogen, ^ Annales de Chimie, 2^™^ serie, xxi. pp. 127 and 178; also xxii. p. 410. ^ Philosophical Traiisactions for 1823, pp. 160-189. ' Annales de Chimie, 2^me s^rie, Ix. pp. 427, 432. * Philosophical Transactions for 1845, p. 155. ^ Poggendorffs Annalen, xciv. p. 436. xxxviii.] Continuity of Gaseous and Liquid States, etc. 297 carbonic oxide, and nitric oxide were submitted to greater pressures than had previously been attained in glass tubes, and while under these pressures they were exposed to the cold of the carbonic acid and ether-bath. None of the gases exhibited any appearance of liquefaction, although reduced to less than -5^ of their ordinary volume by the combined action of cold and pressure.^ In the third__eiiition of Miller's Chemical £lt^sics, published in 1863, a short account, -derived from a private letter addressed by _me-t&-Br-.~Miller,-appearedJit-S.ome new results I h.a.dJjib.tained,Junder_certairL, fixed _couditiQE§ of pressure an d temp erature, with carbonic acid. As these results "constitute the foundatioiTonEe^resent investigation and have never been published in a separate form, I may perhaps be permitted to make the following extract from my original com- munication to Dr. Miller. " On partially liquefying carbonic acid by pressure alone, and gradually raising at the same time the temperature to 88° Fahr., the surface of demarcation between the liquid and gas became fainter, lost its curvature, and at last disappeared. The space was then occupied by a homogeneous fluid, which exhibited, when the pressure was suddenly diminished or the temperature slightly lowered, a peculiar appearance of moving or flickering strife throughout its entire mass. At temperatures above 88° no apparent liquefaction of carbonic acid, or separation into two distinct forms of matter, could be effected, even when a pressure of 300 or 400 atmos- pheres was applied. Nitrous oxide gave analogous results."^ The apparatus employed in this investigation is represented ia Plate VI. It is shown in the simple form in which one gas only is exposed to pressure in figures 1 and 2. In figure 3 a section of the apparatus is given, and in figure 4 another section, with the arrangement for exposing the compressed gas to low degrees of cold in vacuo. In figures 5 and 6 a compound form of the same apparatus is represented, by means of which two gases may be simultaneously exposed to the same pressure. The gas to be compressed is introduced into a tube (fa) having a capOlary bore from ft to &, a diameter of about 2 -5 millimetres from h to c, and ^ Report, oftlie British Association for 1861. [Aiite, p. 293.] 2 Miller's ChemicaZ Physics, 3rd edition, p. 328. 298 On the Continuity of the Gaseous and [xxxvni. of 1'25 millimetre from c to /. The gas carefully dried is passed for several hours through the tube open at both ends, as represented below. The presence of a column of water of two metres in height was necessary to maintain a moderate stream of gas through the fine capillary tube. In the case of carbonic acid, the gas, after passing through the apparatus, was made to bubble by means of a connecting - tube through mercury, and a portion was collected from time to time, in order to ascertain its purity. The current was continued till the residual air, after the action of caustic potash, was reduced to a constant minimum. In re- peated trials I found that in the complicated arrangements I had to adopt, the residual air could not be reduced to less than from TOTT to rinnr of t^^ entire volume of the carbonic acid. Even after continuing the current for twenty- four hours this residue appeared ; and in discussing some of the results obtained by exposing the gas to high pressures, the presence of this small quantity of air must be carefully taken into account. The capillary end at a was then sealed, and the other end was also closed, . and afterwards in- troduced under a surface of pure mercury contained in a glass capsule. The lower end, while under the surface of the mer- i Ancbews' Papers . PlauVI. xxxviii.] Liquid States of Matter. 299 cury, was opened, and heat applied so as to expel a little of the gas. On cooling contraction occurred, and a short column of mercury entered. The capsule and lower end of the tube were then placed under the receiver of an air-pump, and a partial vacuum was formed till about one-fourth of the gas was removed. On restoring the pressure, a column of mercury entered and occupied the place of the expelled gas. By withr drawing the end of the tube from below the surface of the mercury in the capsule, and again exhausting cautiously, the column of mercury could be reduced to any required length. The tube, when thus filled, had the form shown (figure, p. 298), Two file-marks had been made, one at d, the other at e, in the narrow part of the tube, about 10 millims. distant from each other, and the capacity of the tube from a mark near a to d, and also from the same mark to e, had been determined by filling it with mercury at a known temperature and weigh- ing the mercury. The tube was now placed accurately in a horizontal position and connected by an air-tight junction with "one limb of a long U-tube filled with mercury. Each limb of the TJ-tube was 600 millims. long, and 11 millims. in diameter. By removing mercury from the outer limb of the U-tube, a partial vacuum was obtained, and the column of mercury (m n) was drawn into the narrow tube (d /). From the difference of capacity of this part of the tube, the column of mercury was now about four times longer than before. It was easy with a little care so to adjust the pressure that the inner end of the mer- curial column coincided with the mark e. When this was accomplished, the difference of level of the mercury in the two limbs of the U-tube was accurately read by means of a catheto- meter, and the height of the barometer as well as the tem- perature were carefully noted, Similar observations were made with the gas expanded to the mark d. Two independent sets of data were thus obtained for calculating the volume of the gas at 0° C. and 760 millims., and the results usually agreed to less than TTrVir part. The tube, after being disconnected with the U-tube, was cut across a little beyond e, as shown (figure, p. 298), and was now ready to be introduced into the pressure apparatus. The capillary tubes were calibrated with great care, and fa •300 On the Continuity of the Gaseous and [xxxvm. their mean capacity was determined by weighing a column of mercury whose length and position in the tube were accurately observed. One millim. of the air-tube used in these experi- ments had an average capacity of 0-00002477 cub. centim., and 1 mOlim. of the carbonic-acid-tube of 0-00003376 cub. centim. A table was constructed showing the corrected capacity of each capillary tube from the sealed end for every millimetre of its length. An allowance of 0-5 miUim. was made for the cone formed in sealing the tube. For the sake of clearness I have described these operations as if they were performed in the detached tube. In actual practice, the tube was in the brass end-piece before it was filled with gas (Plate VI. fig. 7). The construction of the apparatus employed in these experi- ments will be readily understood from figures 3 and 4, Plate VI., which exhibit a section of the simple form. Two massive brass flanges are firmly attached round the ends of a cold-drawn copper tube of great strength, and by mean's of these flanges two brass end-pieces can be securely bolted to the ends of the copper tube, and the connexions made air-tight by the insertion of leather washers. The lower end-piece (fig. 7) carries a steel screw, 180 millims. long, 4 minims, in diameter, and with an interval of 0-5 millim. between each thread. The screw is packed with care, and readily holds a pressure of 400 atmospheres or more. A similar end-piece attached to the upper flange carries the glass tube containing the gas to be compressed (fig. 7). The apparatus, before being screwed up, is filled with water, and the pressure is obtained by screwing the steel screw into the water. ^ In the compound apparatus (figs. 5 and 6) the internal arrange- ments are the same as in the simple form. A communication is established between the two sides of the apparatus through a h. It is indifferent which of the steel screws below is turned, as the pressure is immediately diffused through the interior of both copper tubes, and is applied through the moveable columns of mercury to the two gases to be compressed. Two screws ^ The first apparatus was constructed for me by Mr. J. Cumiae, of Belfast, to whose rare mechanical skill and valuable suggestions I have been greatly indebted in the whole course of this difficult investigation. xxxvin.] Liquid States of Matter. 301 are employed for the purpose of giving a greater command of pressure. In fig. 5 the apparatus is represented without any accessories. In fig, 6 the same apparatus is shown with the arrangements for maintaining the capillary tubes and the body of the apparatus itself at fixed temperatures. A rectangular brass case, closed before and behind with plate glass, surrounds each capillary tube, and allows it to be maintained at any rec[uired temperature by the flow of a stream of water. In the figure, the arrangement for obtaining a current of heated water in the case of the carbonic-acid tube is shown. The body of the apparatus itself, as is shown in the figure, is enclosed in an external vessel of copper, -which is filled with water at the temperature of the apartment. This latter arrangement is essential when accurate observations are made. The temperature of the water surrounding the air-tube was made to coincide, as closely as possible, with that of the apart- ment, while the temperature of the water surrounding the carbonic-acid tube varied in different experiments from 13° C. to 48° C. In the experiments to be described in this com- munication, the mercury did not come into view in the capillary part of the air-tube till the pressure amounted to about forty atmospheres. The volumes of the air and of the carbonic acid were carefully read by a cathetometer, and the results could be relied on with certainty to less than 0'05 millim. The tem- perature of the water around the carbonic-acid tube was ascer- tained by a thermometer carefully graduated by myself according to an arbitrary scale. This thermometer was one of a set of four, which I constructed some years ago, and which all agreed so closely in their indications, that the differences were found to be altogether insignificant when their readings were reduced to degrees. I have not attempted to deduce the actual pressure from the observed changes in the volume of the air in the air-tube. For this purpose it would be necessary to know with precision the deviations from the law of Mariotte exhibited by atmospheric air within the range of pressure employed in these experiments, and also the change of capacity in the capillary tube from internal pressure. In a future communication I hope to have 302 On the Continuity of the Gaseous and [xxxvm. an opportunity of considering this problem, which must be resolved rather by indirect than direct experiments. As regards the deviation of air from Mariotte*s la,w, it corresponds, according to the experiments of Eegnault, to an apparent error of a little more than one-fourth of an atmosphere at a pres- sure of twenty atmospheres, and according to those of Natterer, to an approximate error of one atmosphere when the pressure attains 107 atmospheres. These data are manifestly insufficient, and I have therefore not attempted to deduce the true pressure from the observed change of volume in the air-tube. It will be easy to apply hereafter the corrections for true pressure when they are ascertained, and for the purposes of this paper they are not required. The general form of the curves representing the changes of volume in carbonic acid will hardly undergo any sensible change from the irregularities in the air-tube ; nor wiU any of the general conclusions at which I have arrived be affected by them. It must, however, always be understood that, when the pressures are occasionally spoken of, as indicated by the apparent contraction of the air in the air-gauge, the approxi- mate pressures only are meant. To obtain the capacity in cubic centimetres from the weight in graimmes of the mercury which filled any part of a glass tube, the following formula was used. ^_„, 1+0-000154 .^ , . -^, . ^-^^- 13-596 -1-00012, where C is the capacity in cubic centims., W the weight of the mercury which fiUed the tube at the temperature t, 0-000154 the coefficient of apparent expansion of mercury in glass, 13-596 the density of mercury at 0°, and 1-00012 the density of water at 4°. The volume of the gas V, at 0° and 760 millims. of pres- sure, was deduced from the double observations as follows, 1 + at 760 where C is the capacity of the tube (figure, page 298) from a to d, or from a to e, t the temperature, a the coefficient of XXXVIII.] Liquid States of Matter. 303 'expansion of the gas for heat (0'00366 in the case of air, 0'0037 in that of carbonic acid), h the height of the barometer reduced to 0° and to the latitude of 45°, d the difference of the mercurial columns in the U-tube similarly reduced. Having thus ascertained the volumes of the air and of the carbonic acid before compression, at 0° and 760 millims., it was easy to calculate their volumes, under the same pressure of 760 miUims., at the temperatures at which the measurements were made when the gases were compressed, and thence to deduce the values of the fractions representing the diminution of volume. But the fractions thus obtained would not give results directly comparable for air and carbonic acid. Although the capillary glass tubes in the apparatus (fig. 6) communicated with the same reservoir, the pressure on the contained gases was not quite equal, in consequence of the mercurial columns, which confined the air and carbonic acid, being of different heights. The column always stood higher in the carbonic- acid-tube than in the air-tube, so that the pressure in the latter was a little greater than in the former. The difference in the lengths of the mercurial columns rarely exceeded 200 millims., or about one-fourth of an atmosphere. This correc- tion was always applied, as was also a trifling correction of 7 millims. for a difference of capillary depression in the two tubes. In order to show more clearly the methods of reduction, I will give the details of one experiment. Volume of air at 0° and 760 millims. calculated from the observations when the air was expanded to a e, 0'3124 cub. centim. Volume of same air calculated from the observations when the air was expanded to a d, 0'3122 cub. centim. Mean volume of air at 0° and 760 miUims., 0"3123 cub. centim. The volumes of the carbonic acid, deduced in like manner from two independent observations, were 0'3096 cub. centim and 0*3094 cub. centim. Mean 0"3095 cub. centim. The length of the column of air after compression, at l()°-76. 304 On the Continuity of the Gaseous and [xxxvm. in the capillary air-tube was 2 7 2" 9 millims., corresponding to 0'006757 cub. centim. Hence we have 0-006757 1 "0-3123 xl-0394~4S04 But as the difference in the heights of the mercurial columns in the air-tube and carbonic-acid-tube, after allowing for the difference of capillary depression, was 178 millims., this result requires a further correction (y^ of an atmosphere), in order to render it comparable with the compression in the carbonic-acid- tube. The final value for §, the fraction representing the ratio of the volume of the compressed air at the temperature of the experiment to its volume at the same temperature and under the pressure of one atmosphere, will be The corresponding length of the carbonic acid at 13°-22, in its capillary tube, was 124-6 millims., equivalent to 0-004211 cub. centim., from which we deduce for the corresponding frac- tion for the carbonic acid 0-004211 1 e 0-3095 X 1-0489 77-09 Hence it follows that the same pressure, which reduced a given volume of air at 10°-76 to -^^^ °^ ^^^ volume at the same temperature under one atmosphere, reduced carbonic acid at 13''-22 to 77^y5 of its volume at the temperature of 13°-22, and under a pressure of one atmosphere. Or assuming the compression of the air to be approximately a measure of the pressure, we may state that under a pressure of about 47-8 atmospheres carbonic acid at 13°-22 contracts to jj^g of its volume under one atmosphere. In the following Tables, ^ is the fraction representing the ratio of the volumes of the air after and before compression to one another, e the corresponding fraction for the carbonic acid, t and t' the temperatures of the air and carbonic acid respec- tively, I the number of volumes which 17,000 volumes of carbonic acid, measured at 0° and 760 millims., would occupy at the temperature at which the observation was made under thepres- XXXVIII.] Liquid States of Matter. 305 sure indicated by the air in the air- tube. The vahies of I are the ordinates of the curve lines shown in the figure, page 308.^ Table I. — Carbonic Acid at 13°-1. 5. t. e. t'. I. 1 i?50 ld'75 76lff 13-18 234-1 1 48-76 10-86 80-43 13-18 221-7 1 48-8S 10-86 8im 13-09 220-3 1 49-00 10-86 105-9 13-09 168-2 1 49-08 10-86 iffi^ 13-09 125-5 1 49-19 10-86 IMl 13-09 92-7 1 49-28 10-86 268-8 13-09 66-3 1 49-45 10-86 aifs 13-09 52-0 1 49-63 10-86 38f9 13-09 46-3 1 60-15 10-86 4^^ 13-09 38-5 1 60-38 10-86 wvi 13-09 37-8 1 64-56 10-86 Sw 13-09 37-1 1 75-61 10-86 6007 13-09 35-6 1 90-43 10-86 6107 13-09 34-9 It will be observed that at the pressure of 48-89 atmo- spheres, as measured by the contraction of the air in the air- tube, liquefaction began. This point could not be fixed by direct observation, inasmuch as the smallest visible quantity of liquid represented a column of gas at least 2 or 3 millims. in length. It was, however, determined indirectly by observing the volume of the gas 0°-2 or 0°-3 above the point of lique- 1 As Hs the entire volnme to which the carbonic acid is reduced, it does not always refer to homogeneous matter, but sometimes to a mixture of gas and liquid. Its value in the example given in the text is obtained as follows : — Z= 17000. 2^2^i?Ll = 231 -3. 0-3095 When I is homogeneous, - represents the density of the carbonic acid referred to carbonic acid gas, at the temperature t', and under a pressure of one atmosphere. U 306 On the Continuity of the Gaseous and [xxxvm. faction, and calculating the contraction the gas would sustain in cooling down to the temperature at which liquefaction began. A slight increase of pressure, it will be seen, was required even in the early stages to carry on the process. Thus the air-gauge, after all reductions were made, indicated an increase of pressure of about one-fourth of an atmosphere (from 48'89 to 49*15 atmospheres) during the condensation of the first and second thirds of the carbonic acid. According to theory no change of volume ought to have occurred. This apparent anomaly is explained by the presence of the trace of air (about xhr part) in the carbonic acid to which I before referred. It is easy to see that the increase of pressure shown in those experiments is explained by the presence of this small quantity of air. If a given volume of carbonic acid contain -j^ of air, that air wiU be diffused through a space 500 times greater than if the same quantity of air were in a separate state. Compress the mixture till 50 atmospheres of pressure have been applied, and the air wUl now occupy, or be diffused through, ten times the space it would occupy if alone and under the pressure of one atmosphere ; or it will be diffused through the space it would occupy, if alone and under the pressure of xV of an atmosphere. While the carbonic acid is liquefying, pressure must be applied in order to condense this air ; and to reduce it to one-half its volume, an increase of xu of an atmosphere is required. The actual results obtained by experiment approxi- mate to this calculation. From similar considerations, it follows that if a mixture of air and carbonic acid be taken, for example in equal volumes, the pressure, after liquefaction has begun, must be augmented by several atmospheres, in order to liquefy the whole of tl^e carbonic acid. Direct experiments have shown this conclusion to be true. The small quantity of air in the carbonic acid disturbed the liquefaction in a marked manner, when nearly the whole of the carbonic acid was liquefied, and when its volume relatively to that of the uncondensed carbonic acid was considerable. It resisted for some time absorption by the liquid, but on raising the pressure to 50 '4 atmospheres it was entirely absorbed. If the carbonic acid had been absolutely pure, the part of the curve for 1 3 °- 1 (figure, page 308) representing the fall from the gaseous XXXVIII.] Liquid States of Matter. 307 to the liquid state, would doubtless have been straight through- out its entire course, and parallel to the lines of equal pressure. Table II. — Carbonic Acid at 21°-5. s. L- f. t'. I. 1 4(i-7l) 8°63 1 67-26 21 '46 272-9 60-06 8-70 114-7 21-46 160-0 60-29 8-70 174-8 21-46 105-0 60-55 8-70 240-5 21-46 76-3 61-00 8-70 367-7 21-46 49-9 62-21 8-70 440-0 21-46 41-7 6:i-su 8-70 443-3 21-46 41-4 The curve representing the results at 21°-5 agrees in general form with that for 13°-1 as shown in the above figure. At 13°-1, under a pressure of about 49 atmospheres, the volume of carbonic acid is little more than three-fifths of that which a perfect gas would occupy under the same conditions. After liquefaction carbonic acid yields to pressure much more than ordinary liquids ; and the compressibility appears to diminish as the pressure increases. The high rate of expansion by heat of liquid carbonic acid, first noticed by Thilorier, is fully con- firmed by this investigation. The next series of experiments was made at the temperature of 31°-1, or 0°-2 above the point at which, by compression alone, carbonic acid is capable of assuming visibly the liquid , form. Since I first announced this fact in 1863, I have made careful experiments to fix precisely the temperature of this critical point in the case of carbonic acid. It was found in three trials to be 30°-92 C, or 87°-7 Fahr. Although for a few degrees above this temperature a rapid fall takes place from increase of pressure, when the gas is reduced to the volume at which it might be expected to liquefy, no" separation of the car- bonic acid into two distinct conditions of matter occurs, so far as any indication of such a separation is afforded by the action of light. By varying the pressure or temperature, but al- 308 On the Continuity of the Oaseous and [xxxviii. ways keeping the latter above 30°-92, the great changes of density which occur about this point produce the flickering moyements I formerly described, resembling in an exaggerated form the appearances exhibited during the mixture of liquids of different. XXXVIII.] Liquid States of Matter. 309 densities, or when columns of heated air ascend through colder strata. It is easy so to adjust the pressure that one-half of the tube shall be filled with uncoudensed gas and one-half with the con- densed liquid. Below the critical temperature this distinction is easily seen to have taken place, from the visible surface of demarcation between the liquid and gas, and from the shifting at the same surface of the image of any perpendicular line placed behind the tube. But above 30°-92 no such appear- ances are seen, and the most careful examination fails to dis- cover any heterogeneity in the carbonic acid, as it exists in the tube. Taelb III.— Carbonic Acid at 31°-1. 5. t. e. t'. i- I 6479 11-59 1 SO-66 31-17 235-4 1 65-96 ' 11-59 1 83-39 31-22 227-4 1 67-18 11-58 1 86-58 31-15 219-0 1 C8-46 11-55 1 90-04 31-19 210-6 1 69-77 11-41 1 93-86 31-18 202-0 61-18 11-40 1 98-07 31-20 193-3 1 62-67 11-44 1 103-1 31-19 183-9 1 6*-27 11-76 1 109-6 31-13 173-0 1 66-90 11-73 1 116-2 31-19 163-2 1 67-60 11-63 1 124-4 31-15 152-4 I 69-39 1 11-55 1 134-5 3103 140-9 1 tTW 11-40 1 147-8 31-06 128-2 1 73-26 11-45 1 169-0 31-09 112-2 7?83 13-00 1 174-4 31-08 108-7 7^40 11-62 1 311-1 31-06 60-9 7^64 2 11-65 1 31-06 51-3 79«2 1 11-16 38F0 31-10 49-4 82-44 g 11-23 396-7 31-07 47-9 86-19 11-45 1 . 406-6 31-05 46-7 310 On the Continuity of the Gaseous and [xxxvnr. The graphical representation of these experiments, as shown in the preceding page, exhibits some marked differences from the curves for lower temperatures. The dotted lines in the figure represent a portion of the curves of a perfect gas (assumed to have the same volume at 0° and under one atmo- sphere as the carbonic acid) for the temperatures of 13°'l, 31°'l, and 48°'l. The volume of the carbonic acid at 31°"1, it will be observed, diminishes with tolerable regularity, but much faster than according to the law of Mariotte, till a pressure of about 73 atmospheres is attained. The diminution of volume then goes on very rapidly, a reduction to nearly one-half taking place, when the pressure is increased from 73 to 75 atmospheres, or only by ^ of the whole pressure. The fall is not, however, abrupt as in the case of the formation of the liquid at lower temperatures, but a steady increase of pressure is required to carry it through. During this fall, as has already been stated, there is no indica- tion at any stage of the process of two conditions of matter being present in the tube. Beyond 77 atmospheres carbonic acid at 31°'l yielded much less than before to pressure, its volume hav- ing become reduced nearly to that which it ought to occupy as a liquid at the temperature at which the observations were made. Table IV. — Carbonic Acid at 32°-5. s. i. c. i'. I. 1 67-38 12°-10 1 86-90 32°-50 221-7 71-62 12-15 140-3 32-34 135-6 73-BO 12-30 15B-0 32-45 122-0 74-02 12-30 169-9 32-46 119-1 76-25 12-40 191-7 32-38 99-3 78^ 12-50 311-8 32-48 61-1 7077 12-35 361-3 32-54 54-2 SJio 12-35 387-8 32-75 49-1 XXXVIII.] Liquid States of Matter. Table V. — Carbonic Acid at 35°-5. 311 s. t. t. f. I. 1 5S'80 15°-68 1 8272 35°-49 232-5 59-34 15-70 S8-M 35-54 216-2 6215 15-66 96-41 35-52 199-5 65-23 15-66 106-0 35-51 181-4 e8'66 15-75 118-4 35-47 162-4 72-45 15-79 1351 35-48 142-3 76-S8 15-52 161-2 35-55 119-3 81-28 15-61 22S-0 35-55 84-4 86-60 15-67 351-9 35-48 54-6 89-52 15-67 3737 35-50 51-5 92-64 15-64 387-9 35-61 49-6 99-57 15-61 411-0 35-55 46-8 iore 15-47 'm^i 35-53 44-7 Table VI. — Carbonic Acid at 48°-l. 5. t. tf. f. I. 1 6-i60 15-67 1 86-45 47° -95 231-5 68-46 15-79 99-39 48-05 201-4 75-58 15-87 117-8 48-12 170-0 84-36 15-91 146-8 48-25 136-5 95-19 15-83 198-5 48-13 100-8 109-4 16-23 25f4 48-25 67-2 The curve for 32°- 5 (page 3 08) resembles closely that for 31°-1. The fall is, however, less abrupt than at the latter tem- perature. The range of pressure in the experiments at 35°- 5 extends from 57 to above 107 atmospheres. The fall is here greatly diminished, and it has nearly lost its abrupt character. 312 On the Continuity of the Gaseous and [xxxvni. It is most considerable from 76 to 87 atmospheres, where an increase of one-seventh in the pressure produces a reduction of volume to one-half. At 107 atmospheres the volume of the carbonic acid has come almost into conformity with that which it should occupy, if it were derived directly from liquid carbonic acid, according to the law of the expansion of that body for heat. The curve for 48°-l is very interesting. The fall shown in the curves for lower temperatures has almost, if not altogether, disappeared, and the curve itself approximates to that which would represent the change of volume in a perfect gas. At the same time the contraction is much greater than it would have been if the law of Mariotte had held good at this temperature. Under a pressure of 109 atmospheres, the carbonic acid is rapidly approaching to the volume it would occupy if derived from the expansion of the liquid ; and if the experiment had not been interrupted by the bursting of one of the tubes, it would doubtless have fallen into position at a pressure of 120 or 130 atmospheres. I have not made any measurements at higher temperatures than 48°'l ; but it is clear that, as the temperature rises, the curve would continue to approach to that representing the change of volume of a perfect gas. I have frequently exposed carbonic acid, without making precise measurements, to much higher pressures than any marked in the Tables, and have made it pass, without break or interruption from what is regarded by every one as the gaseous state, to what is, in like manner, universally regarded as the liquid state. Take, for example, a given volume of carbonic acid gas at 50° C, or at a higher temperature, and expose it to increasing pressure till 150 atmospheres have been reached. In this process its volume will steadily diminish as the pressure augments, and no sudden diminution of volume, without the application of external pressure, will occur at any stage of it. When the full pressure has been applied, let the temperature be[ allowed to fall till the carbonic acid has reached the ordi- nary temperature of the atmosphere. During the whole of this operation no breach of continuity has occurred. It begins with a gas, and by a series of gradual changes, presenting nowhere xxxvm.] Liquid States of Matter, 313 any abrupt alteration of volume or sudden evolution of heat, it ends with a liquid. The closest observation fails to discover anywhere indications of a change of condition in the carbonic acid, or evidence, at any period of the process, of part of it being in one physical state and part in another. That the gas has actually changed into a liquid would, indeed, never have been suspected, had it not shown itself to be so changed by entering into ebullition on the removal of the pressure. For convenience this process has been divided into two stages, the compression of the carbonic acid and its subsequent cooling ; but these opera- tions might have been performed simultaneously, if care were taken so to arrange the application of the pressure and the rate of cooling, that the pressure should not be less than 7 6 atmo- spheres when the carbonic acid had cooled to 31°. "We are now prepared for the consideration of the following important question. What is the condition of carbonic acid when it passes, at temperatures above 31°, from the gaseous state down to the volume of the liquid, without giving evidence at any part of the process of liquefaction having occurred ? Does it continue in the gaseous state, or does it liquefy, or have we to deal with a new condition of matter ? If the experiment were made at 100°, or at a higher temperature, when aU indi- cations of a fall had disappeared, the probable answer which would be given to this question is that the gas preserves its gaseous condition during the compression : and few would hesi- tate to declare this statement to be true, if the pressure, as in Natterer's experiments, were applied to such gases as hydrogen or nitrogen. On the other hand, when the experiment is made with carbonic acid at temperatures a little above 31°, the great fall which occurs at one period of the process would lead to the conjecture that liquefaction had actually taken place, although optical tests carefully applied failed at any time to discover the presence of a liquid in contact with a gas. But against this view it may be urged with great force, that the fact of addi- tional pressure being always required for a further diminution of volume, is opposed to the known laws which hold in the change of bodies from the gaseous to the liquid state. Besides, the higher the temperature at which the gas is compressed, the less the fall becomes, and at last it disappears. 314 On the Continuity of the Gaseous and [xxxvm. The answer to the foregoing question, according to what appears to me to be the true interpretation of the experiments ah-eady described, is to be found in the close and intimate rela- tions which subsist between the gaseous and liquid states of matter. The ordinary gaseous and ordinary liquid states are, in short, only widely separated forms of the same condition of matter, and may be made to pass into one another by a series of gradations so gentle that the passage shall nowhere present any interruption or breach of continuity. From carbonic acid as a perfect gas to carbonic acid as a perfect liquid, the transi- tion we have seen may be accomplished by a continuous pro- cess, and the gas and liquid are only distant stages of a long series of continuous physical changes. Under certain condi- tions of temperature and pressure, carbonic acid finds itself, it is true, in what may be described as a state of instability, and suddenly passes, with the evolution of heat, and without the application of additional pressure or change of temperature, to the volume, which by the continuous process can only be reached through a long and circuitous route. In the abrupt change which here occurs, a marked difference is exhibited, while the process is going on, in the optical and other physical properties of the carbonic acid which has collapsed into the smaller volume, and of the carbonic acid not yet altered. There is no difficulty here, therefore, in distinguishing between the liquid and the gas. But in other cases the distinction cannot be made ; and under many of the conditions I have described it would be vain to attempt to assign carbonic acid to the liquid rather than the gaseous state. Carbonic acid, at the tempera- ture of 35°'5, and under a pressure of 108 atmospheres, is reduced to -^^i; of the volume it occupied under a pressure of one atmosphere ; but if any one ask whether it is now in the gaseous or liquid state, the question does not, I believe, admit of a positive reply. Carbonic acid at 35°-5, and under 108 atmo- spheres of pressure, stands nearly midway between the gas and the liquid ; and we have no valid grounds for assigning it to the one form of matter any more than to the other. The same observation would apply with even greater force to the state in which carbonic acid exists at higher temperatures and under greater pressures than those just mentioned. In the original xxxviii.] Liquid States of Matter. 315 experiment of Cagniard de la Tour, that distinguished physicist inferred that the liquid had disappeared, and had changed into a gas. A slight modification of the conditions of his experi- ment would have led him to the opposite conclusion, that what had been before a gas was changed into a liquid. . These condi- tions are, in short, the intermediate states which matter assumes in passing, without sudden change of volume, or abrupt evolu- tion of heat, from the ordinary liquid to the ordinary gaseous state. In the foregoing observations I have avoided all reference to the molecular forces brought into play in these experiments. The resistance of liquids and gases to external pressure tending to produce a diminution of volume, proves the existence of an internal force of an expansive or resisting character. On the other hand, the sudden diminution of volume, without the appli- cation of additional pressure externally, which occurs when a gas is compressed, at any temperature below the critical point, to the volume at which liquefaction begins, can scarcely be explained without assuming that a molecular force of great attractive power comes here into operation, and overcomes the resistance to diminution of volume, which commonly requires the application of external force. When the passage from the gaseous to the liquid state is effected by the continuous process described in the foregoing pages, these molecular forces are so modified as to be unable at any stage of the process to overcome alone the resistance of the fluid to change of volume. The properties described in this communication, as exhibited by carbonic acid, are not peculiar to it, but are generally true of all bodies which can be obtained as gases and liquids. Mtrous oxide, hydrochloric acid, ammonia, sulphuric ether, and sulphuret of carbon, all exhibited, at fixed pressures and tem- peratures, critical points, and rapid changes of volume with flickering movements, when the temperature or pressure was changed in the neighbourhood of those points. The critical points of some of these bodies were above 100° ; and in order to make the observations, it was necessary to bend the capillary tube before the commencement of the experiment, and to heat it in a bath of paraffin or oil of vitriol. The distinction between a gas and vapour has hitherto been 316 On the Continuity of the Gaseous and [xxxvm. founded on principles which are altogether arbitrary. Ether in the state of gas is called a vapour, while sulphurous acid in the same state is called a gas ; yet they are both vapours, the one derived from a liquid boiling at 35°, the other from a liquid boiling at -10°. The distinction is thus determined by the trivial condition of the boiling-point of the liquid, under the ordinary pressure of the atmosphere, being higher or lower than the ordinary temperature of the atmosphere. Such a distinction may have some advantages for practical reference, but it has no scientific value. The critical point of tempera- ture affords a criterion for distinguishing a vapour from a gas, if it be considered important to maintain the distinction at aU. Many of the properties of vapours depend on the gas and liquid being present in contact with one another; and this, we have seen, can only occur at temperatures below the critical point. We may accordingly define a, vapour to be a gas at any temperature under its critical point. According to this defini- tion, a vapour may, by pressure alone, be changed into a liquid, and may therefore exist in presence of its own liquid ; while a gas cannot be liquefi.ed by pressure, that is, so changed by pressure as to become a visible liquid distinguished by a surface of demarcation from the gas. If this definition be accepted, carbonic acid will be a vapour below 31°, a gas above that temperature; ether, a vapour below 200°, a gas above that temperature. We have seen that the gaseous and liquid states are (inly distant stages of the same condition of matter, and are capable of passing into one another by a process of continuous change. A problem of far greater difficulty yet remains to be solved, the possible continuity of the liquid and solid states of matter. The fine discovery made some years ago by James Thomson, of the influence of pressure on the temperature at which lique- faction occurs, and verified experimentally by Sir W. Thomson, points, as it appears to me, to the direction this inquiry must take ; and in the case at least of those bodies which expand in liquefying, and whose melting-points are raised by pressure, the transition may possibly be effected. But this must be a subject for future investigation ; and for the present I will not venture to go beyond the conclusion I have already drawn XXXVIII.] Liquid States of Matter. 317 from direct experiment, that the gaseous and liquid forms of matter may be transformed into one another by a series of continuous and unbroken changes. Appendix. The following experiments, made at temperatures differing from any of the foregoing series, are added, as they may here- after be useful for reference. s. t. e. t'. 1 48-15 12-42 1 75-00 15-76 1 S3'04 11-13 1 92-53 16-45 I 47-45 11-50 1 64-14 31-91 1 7176 13-10 1 148-5 31-65 1 73-88 13-20 1 170-5 31-71 1 73-n 13-20 1 157-S 33-15 1 7377 12-74 1 152-3 33-58 1 73-89 13-14 1 144-5 35-00 1 73-89 13-21 1 140-0 36-03 1 76-05 13-27 1 153-4 36-05 1 78-35 13-38 1 171-1 36-11 1 80-74 13-40 1 197-8 36-22 1 83-31 13-45 1 261-4 36-20 1 86-01 13-50 1 323-6 36-08 1 88-92 13-53 1 368-1 36-18 1 92-06 13-55 1 377-8 36-22 318 XXXIX.— ON THE ABSOEPTION-BANDS OF BILE. From the Report of the British Association, Exeter, 1869, p. 59, A SOLUTION of bile in water or alcohol exhibits, when examined by the spectroscope, characteristic absorption-bands, which differ from those of the red colouring matter of blood or its derivatives. The most conspicuous of these bands lies nearly midway between the yellow sodium line and the green line jS calcium. Another band occurs, chiefly in the orange, extend- ing a little beyond the sodium line. A third band occurs in the green, bounded on its more refrangible side by the mag- nesium group (b, Fraunhofer). These absorption-bands are also found in solutions of biliverdin, but not in solutions of the yellow colouring-matter of bile. They are not affected by reducing agents, but are weakened, and at last effaced by the action of nitric acid. The absorption-bands furnish a ready test for bile in liquids, such as water or urine, which have no absorption-bands of their own. With a column of liquid 2| inches long, the presence of bile was in this way discovered, when diluted 100 times, and with a column 8 inches long, when the dilution was carried four times further. An estimate of its amount may also be made, and its fluctuations in disease observed from day to day. 319 XL.— ON THE HEAT DEVELOPED IN THE COMBINATION OF ACIDS AND BASES. (SECOND MEMOIE.) From the Transactions of the. Royal Society of Edinburgh, 1869-70. In a paper communicated to the Eoyal Irish Academy in 1841, I gave an account of a large number of experiments on the heat disengaged when acids and bases, taken in the state of dilute solution, enter into combination, and when bases, insoluble in water, are dissolved in dilute acids. The following general conclusions or laws were deduced from those experiments: — Law 1. — The heat developed in the union of acids and bases is determined by the base and not by the acid, the same base producing, when combined with an equivalent of different acids, nearly the same quantity of heat ; but different bases, different quantities. Law 2. — When a neutral is converted into an acid salt, by combining with one or more atoms of acid, no change of tem- perature occurs. Law 3. — When a neutral is converted into a basic salt, by combining with an additional proportion of base, the combina- tion is accompanied with the evolution of heat.-' Three years later I laid before the Eoyal Society of London the results of an experimental investigation of the heat developed when one base is substituted for another in chemical compounds. The law deduced from this inquiry is implicitly involved in the foregoing, of which it may indeed be regarded as a necessary consequence. It was enunciated in the following terms : — Zaw 4. — When one base displaces another from any of its neutral combinations, the heat evolved or abstracted is always the same, whatever the acid element may be, provided the bases are the same.^ 1 Transaction of the Eoyal Irish Academy, vol. xix. p. 228. \_Ante, p. 70.] ^Philosophical Transactions for 1844, p. 21. [Ante, p. 107. J &' 320 On the Heat Developed in the [xl. Finally, the law of metallic substitutions, first announced in the FMlosophieal Magazine for August 1844, was thus stated in a paper published in the FMlosophieal Transactions for 1848. Law 5. — ^When an equivalent of one and the same metal replaces another in a solution of any of its salts of the same order, the heat developed is always the same ; but a change in either of the metals produces a different development of heat. In 1845 a paper appeared by Graham on the heat disen- gaged in combinations, the second part of which refers to the heat produced when hydrate of potash is neutralised by different acids. ^ The results arrived at by this distinguished chemist exhibit a close agreement with those contained in my first communication to the Eoyal Irish Academy, The concluding part of the elaborate memoir of MM. Favre and Silbermann on the heat disengaged in chemical actions is chiefly devoted to the same subject. A large number of experiments are described, which are nearly a repetition of those I had previously published. Their results bear a general resemblance to those given by myself in 1841 ; but they widely differ in the details. The authors of this able memoir fully recognise the accuracy of my fourth law, which asserts the equality of thermal effect when one base is substituted for another. " M. Andrews," they observe, " avait en effet ^tabli que, quelque soit I'acide d'un sel, la quantity de chaleur ddgagfe par la substitution d'une base k une autre pour former un nouveau sel est la m^me, lorsque Ton consid^re les deux m^mes bases."^ In a preceding paragraph of the same memoir, the authors object to what they conceive to be my first law, and state that it is not in accordance with the result of their investigations. As the question is one of some importance, I may perhaps be permitted to quote the passage in the original language. " Ses conclusions, savoir : que la chaleur d^gagde par 1' Equivalent d'une m^me base combin^e aux divers acides est la mgme, ne s'accordent pas avec les r^sultats de nos recherches, et ne nous ^Memoirs of the Chemical Society, vol ii. p. 51. ^ Annales de Chimie et de Physique, 5kme serie, xxxvii. p. 497 (1853). XL.] Combination of Acids and Bases. 321 paraissent pas pouvoir etre admises." No doubt, through inadvertence, MM. Favre and Silbermann have here given an inaccurate statement of my iirst law. It did not declare that precisely the same amount of heat is disengaged by aU the acids in combining with the same base, but that the heat is determined by the base, " the same base producing, when com- bined with an equivalent of different acids, nearly the same quantity of heat." A comparison of the results of MM. Favre and Silbermann with those in my original memoir will show that I had fully recognised and described the deviations from the other acids, exhibited, on the one hand, in excess, by the sulphuric acid, and on the other, in deficiency, by the tartaric, citric, and succinic acids. " If we refer," I remarked, in the original memoir of 1841, "to the first, second, and fourth tables, as being the most extensive, from the large number of soluble compounds formed by potash, soda, and ammonia, it will be observed that the sulphuric acid developes from 0°'8 to nearly 1° more than the mean heat given by the other acids ; while the tartaric, citric, and succinic acids fall from 0°"4 to 0°"55 short of the same. A minute investigation of the influence of the disturbing sources of heat will no doubt discover the causes of these discrepancies. The high numbers for sulphuric acid are probably connected with that acid's well known property of developing much heat when combining with successive atoms of water. All the other acids develope nearly the same amount of heat in combining with the same base, the greatest divergences from the mean quantity being, in the case of potash, +0°-24, and — 0°-13; in that of soda, +0°-26, and — 0°'14; and in that of ammonia, + 0°-17 and — 0°"05. These differences are almost within the limits of the errors of experiment."^ But although there is a superficial agreement between my original results and those of MM. Favre and Silbermann, they will be found, when examined closely, to differ widely in detail, and on points of great importance. I had found that the oxalic acid disengages almost exactly the same amount of heat in combining with the soluble bases as the hydrochloric, nitric, ' Transactions of the Boyal Irish Academy, vol. xix. p. 240. [AntS, pp. 81, 82.] X 322 On the Heat Developed in the [xu and many other mineral acids, and this observation I have always regarded as one of the main foundations of Law 1. MM. Favre and Silbermann, on the contrary, have inferred from their experiments that " the following organic acids — the oxalic, formic, valeric, and citric — disengage sensibly the same quantity of heat, but it is less (plus faible) than that given by the foregoing mineral acids" — among which they enumerate the nitric and hydrochloric. According to my experiments, no distinction of this kind can be admitted between acids derived from the mineral and organic kingdom, inasmuch as the oxalic acid developes at least as much heat in combining with the bases as the hydrochloric, nitric, and several other strong mineral acids. The experiments to be described in this paper were made some years ago, but their publication has been deferred from accidental circumstances. I have, however, recently repeated a few of the more important of them, with a slightly modified form of apparatus. The solutions were taken in so dilute a state that the heat disengaged never exceeded 3°'5 C. A standard solution of sulphuric acid was prepared and carefully analysed, by precipitating a given weight with a soluble salt of barium, and weighing the sulphate of barium. The strength of the alkaline solutions was adjusted with great care by means of this standard acid. The same solution of each alkaK was employed in all the experiments, and the quantity used in each experiment was determined by careful weighing. The acid solution was of such a strength that, after being mixed with the alkali, an excess of two or three per cent, of acid was present. The alkaline solution was contained in a light glass vessel, in which a large platinum crucible holding the acid was carefully floated. By giving a rapid rotation, by means of a light stirrer, to the acid solution in the platinum crucible, a perfect equilibrium of temperature was soon established between the two liquids. , The initial temperature of the solutions was usually about 1°'5 below that of the air, and the final tempera- ture of the mixture about l°-o above it. The corrections for the heating and cooling action of the surrounding medium were determined with great care. The mechanical process of adding the acid ' to the alkaline solution produced no change of tem- XL.] Combination of Acids and Bases. 323 perature, and as the heat disengaged in the combination raised the liquid almost instantly to the maximum temperature, the whole correction required was for cooling. The first tempera- ture was read one minute after the addition of the acid to the alkaline solution, the mixture being stirred during the whole of that time. If S represents the correction, and e the excess of temperature above the air in centigrade degrees, the value of S will be given by the following expression : — ^ = ex0°-012. As a proof of the accuracy of the method of mixture adopted in this inquiry, I may mention that, being desirous to know whether the dilute acids employed in these experiments pro- duced any change of temperature when mixed with water, I made the experiment with nitric acid by the method just described, substituting water for the alkaline solution, with the unexpected result of a fall of 0°'01. On varying the conditions of the observation, so as to obtain a larger effect, it was ascer- tained not only that a diminution of temperature had actually occurred, but that the observed fall represented approximately its true amount. When hydrochloric acid of equivalent strength was diluted to the same extent, an elevation of temperature of 0°'05 was produced. The accuracy of experiments of this kind, where the whole thermal effect observed amounts only to 2° or 3°, depends greatly on the thermometer employed. Unless its indications are perfectly trustworthy in every part of the scale, the labour of the inquirer will only end in disappointment. I have there- fore taken every precaution to secure this important object. The tube of the thermometer was calibrated and divided with care, according to an arbitrary scale, by means of a dividing instrument contrived for the purpose, and provided with a short screw of great accuracy made by Troughton & Simms. The divisions, etched finely on the glass, corresponded to about 0°"05 C, and the readings could be made with certainty to less than 0°'0 1. The division of the scale, corresponding to 0°, was determined from time to time in the usual way ; and another point, about 30° C, was fixed by comparison with four other thermometers similarly constructed, whose scales extended from the freezing to the boiling point of water. The readings of 324 On the Heat Developed in the [xl. these four instruments, when reduced to degrees, rarely differed from each other within the limits to which they could be read, or 0°'02. The reservoir of the thermometer used in these ex- periments was 75 millimetres long, and, when immersed in the liquid, occupied nearly its entire depth. As some uncertainty always exists with regard to the thermal equivalent of glass vessels, I made two sets of comparative ex- periments — one with a thickly varnished copper vessel, and the other with a vessel of platinum. The mean result of these experiments coincided almost exactly with the result obtained when the glass vessel was employed. The weight of the glass vessel which contained the alkaline solution was 58 grammes, and coiTcsponded thermally to 11 '4 grammes of the solutions formed. The thermal equivalent of the reservoir of the thermometer and of the stirrer was 0*9 grammes. The alkaline solution weighed 160 grammes, and contained the equivalent of 1'738 grammes of SOg. The acid solution weighed 42-5 grammes. Hence the entire thermal value of the apparatus, in terms of the solution formed, was — Solution, - 202-5 Glass vessel, - - 11 '4 Thermometer and stirrer, 0'9 214"8 grammes. A correction (additive) of sto was made to the direct read- ings for the mercury in the stem of thermometer. The results are given to thousandths of a degree, but this apparent minuteness is due to the reduction of the indications of the arbitrary scale to degrees. In the following detailed statement of the experimental results. Inc. is the increment of temperature observed, corrected for the mercury in stem, and 8 is the correction for cooling. Potash and Sulphuric Acid. Inc. 3°-358 3°-356 3°-366 ^ -010 -024 -021 3''-368 3°'380 3°-387 Mean increment corrected, 3°-378 XL.] Combination of Acids and Bases. 325 Potash and Nitric Acid. Inc. 2°-971 2°-976 2°-977 S -018 -019 -017 2°-989 2°-995 2°-994 Mean increment corrected, 2°'993 Potash arid Hydrochloric Acid. Inc. 3°-004 3°-002 3°-005 S -017 -019 -017 3°-021 3°-021 Mean increment corrected, Potash and Oxalic Acid. Inc. 3°-036 3°-048 S -017 -017 3°-053 3°-065 Mean increment corrected, Potash and Acetic Acid. Inc. 2°-835 2°-846 S -016 -007 3°-022 3' ■•021 3''-040 •016 3°-056 3° •058 2°-851 2°^853 Mean increment corrected, 2°'852 Potash and Tartaric Acid. Inc. 2°-707 2°^717 2°^730 ^ ^014 -014 -013 2°-721 2°-731 2°^743 Mean increment corrected, 2°"732 Soda and Sulphuric Acid. Inc. 3°^322 3°^335 S -025 ^024 3°-347 3°-359 Mean increment corrected, 3°'353 326 On the Be-at Developed in the [xl. Soda and Nitric Acid. Inc. 2°-914 2'=-919 ^ -012 -012 2°-926 2°-931 Mean increment corrected, 2°*929 Soda and Hydrochloric Acid. Inc. 2°-963 ^ -019 2°-982 Increment corrected, 2°'982 Soda and Oxalic Acid. Inc. 3°-029 3°-013 8 -019 -020 3°-048 3°-033 Mean increment corrected, 3°'040 Soda and Acetic Acid. Inc. 2°-816 2°-812 8 -017 -018 2°-833 2°-830 Mean increment corrected, 2''-831 Soda and Tartaric Acid. Inc. 2''-693 2°-693 § -019 -015 2°-712 2°-708 Mean increment corrected, 2°'7lO Ammonia and Sulphuric Acid. Inc. 2°-967 2°-959 8 -017 -010 2°-984 2°-969 Mean increment corrected, 2°"976 XL.] Combination of Acids and Bases. 32'/ Ammonia and Nitric Acid. Inc. 2°-556 2°-551 h -010 -015 2°-566 2°-566 Mean increment corrected, 2°"o66 A')nmonia and Hydrochloric Acid. Inc. 2°-609 2°-607 8 -015 -015 2°-624 2°-622 Mean increment corrected, 2°'623 Ammonia and Oxalic Acid.. Inc. 8 T '•635 •015 2°-630 ■016 2°-650 2°-646 Mean increment corrected, 2°'648 Armnonia and Acetic Acid. Inc. 2°^469 2°-482 ^ -017 -016 2°-486 2°-498 Mean increment corrected, 2 "•49 2 Ammonia and Tartaric Acid. Inc. 2°-365 2°-354 ^ •Ol? -016 2°-382 2°^370 Mean increment corrected, 2°^376 In the following table I have collected the foregoing results arranging the acids in the order of their thermal action. 328 On the Heat Developed in the [xl. Acid, Sulphuric Acid, Oxalic Acid, - Potash. 3°-378 3°-058 Soda. 3°-3o3 3°040 Ammonia. 2°-976 2°-648 Hydrochloric Acid, Nitric Acid, - Acetic Acid, - 3°-021 2°-993 2°-852 2°-982 2°-929 2°-832 2°-623 2°-566 2°-492 Tartaric Acid, 2°-732 2°-710 2°-376 It is interesting to observe how closely the results in the three vertical columns agree relatively with one another. The acids follow in the same order under each base, and even the differences in the amount of heat disengaged by the several acids in combining with the different bases approximate in many cases closely to one another. Thus the heat given out when the sulphuric acid combines with potash exceeds that given out when the oxalic acid combines with the same base by 0°'320, the corresponding differences in the case of soda and ammonia being 0°'313 and 0°"328. If, in like manner, we compare the differences between the heat disengaged by the acetic and tartaric acids, we fall upon the numbers 0°"120, 0°"122, and 0°'116. Even in the case of the oxalic, hydro- chloric, and nitric acids, which disengage so nearly the same amount of heat, the same order is observed with the three bases. It must be particularly remarked that the oxalic acid disengages from 0°'022 to 0°'058 more heat in combining with these bases than the hydrochloric acid, and from 0°'065 to 0°"111 more than the nitric acid. The conclusion of MM. Favre and Silbermann, that the organic acids (oxalic, formic, acetic, &c.) disengage sensibly less heat than the mineral acids, is thus entirely disproved ; and the original results recorded in my work of 1841, according to which the oxalic acid disen- gages at least as much heat as the nitric, phosphoric, arsenic hydrochloric, hydriodic, boracic, and other mineral acids (with the exception of the sulphuric acid) are fully confirmed. The tartaric, citric, and succinic acids, it is true (as was also shown in the same work), give out about iVth less heat than the average of the other acids ; but the acetic and formic acids fall scarcely Tirth below the mean, and the oxalic acid is always above it. These results, in all their main features, are fully corroborated by the experiments recorded in this paper, which XL.] Combination of Acids and Banes. 329 were performed with a more perfect apparatus and a more exact thermometer than I had at my command in my earlier investigations. A reference to the same paper will show that, while acids, differing so widely from one another as the oxalic, phosphoric, arsenic, nitric, hydrochloric, and boracic acids, scarcely present any sensible difference in the quantities of heat which they disengage in combining with the bases ; and while of the other acids examined the sulphuric acid (and probably also the sulphurous acid) presents an extreme deviation of about ^th above the mean, and the tartaric acid group a deviation of about -^-th below it ; the bases, on the contrary (and the subsequent researches of Favre and SHbermann have confirmed this result), differ altogether in thermal power from one another. Thus equivalents of the oxides of magnesium and of silver give out 4°'l and 1°'8 of heat respectively in combining with nitric acid, the former oxide having therefore 2-3 times the thermal power of the latter. Yet, as is well known, both these bases fully saturate the acid, and the result- ing solutions are even neutral to test paper. For these reasons, I have no doubt whatever that the first law, as enunciated in 1841, is the expression of a true physical law, and that in the combination of acids and bases in presence of water the heat disengaged is determined by the base and not by the acid. It is true that in this, as in similar physical inquiries, experi- mental results cannot immediately be obtained free from complication or disturbing influences. The same remark applies to the experimental proof of the great law discovered by Dulong and Petit, which connects the specific heats and atomic weights of the elementary bodies, and also to that of the remarkable relations discovered by Kopp between the composi- tion and boiling points of many organic liquids. We have already seen an illustration of one of these disturbing influences, in the fact that dilute nitric acid, when mixed with water, gives a slight fall of temperature, hydrochloric acid, a rise ; and the differences of specific heat in the solutions formed will to a small extent modify the results. But the cause of the higher thermal power of sulphuric acid I have not been able to discover, and future researches must decide whether it depends upon some disturbing cause, or (which is less probable) upon 330 On the Heat Developed in the [xl. its possessing an exceptionally high thermal power. One con- dition is, however, essential, or Law 1 will not apply. The acid and base must be capable of combining when brought into contact, and of forming a stable compound. In the paper so often referred to, I showed that hydrocyanic acid and potash, which fail to fulfil this condition, do not disengage the normal amount of heat when mixed ; and the same observation will doubtless be found to apply to a large number of metallic oxides, which form unstable compounds with, and imperfectly neutralise, the bases. As regards the experimental proofs of the other laws, even those of the fourth law, the truth of which is admitted by MM. Favre and Silbermann, they are only approximative ; and here also we meet occasionally with peculiar and unexpected results. Thus a slight fall of temperature occurs, as Hess showed long ago, in the conversion of the neutral sulphate of potash into the acid salt ; and I found, as indeed might have been expected from their alkaline reaction, that in the conversion of the ordi- nary phosphates and arseniates into super salts, a disengage- ment of heat occurs, amounting to about one-seventh of that disengaged in the formation of the salts themselves. In other cases results, at first view startling and apparently anomalous, will be found to be strictly in accordance with the general prin- ciples already laid down. In the formation of double salts there is no disengagement of heat — a principle announced in 1841, and which ought perhaps to be enunciated as a distinct law, although it is implicitly involved in Law 2. Again, if tribasic phosphoric acid or arsenic acid is added in fractional portions to a solution of potash till the subsalts are formed, the heat disengaged on each addition of acid corresponds to the amount of acid added ; but after this point has been reached, the disengagement of heat follows a different law. The pyro- phosphoric acid, on the other hand, behaves in the same way as the nitric and most other acids, when added in successive por- tions to solutions of potash or soda ; equal increments of heat being evolved for equal additions of acid, till the pyrophosphate of potash or soda is formed.^ 1 Transactions of the Boyal Irish Academy, vol. xix. pp. 245-248. \_Ant6, pp. 86-9.] The observations of Graham confirm the statement that no heat is evolved in the formation of any double salt. Memoirs of the Chemical Society, vol. i. p. 83. XL-] Combmation of Acids and Bases. 331 APPENDIX. In the following tables I have given the results described in this communication and those of 1841 in a form which admits of comparison with one another, and with those of MM. Pavre and Silbermann. I have also added a few determinations recently made by M. Thomsen of Copenhagen.^ It will be seen that the original experiments of 1841 exhibit, on the whole, a fair agreement with those now communicated to the Society. Prom the small scale on which they were performed (the whole weight of the solutions after mixture being less than 30 grammes), the imperfect form of the apparatus, and the uncer- tainty of the thermometric indications, I have indeed been sur- prised to find them so near the truth. The results of MM. Pavre and Silbermann do not exhibit the precision which might have been expected from the high character of those experi- mentalists, and from the accuracy of other parts of their great work. The mercurial calorimeter employed by them appears to have been little adapted to its purpose ; but after making due allowance for its imperfections, I am at a loss to account for the serious errors into which they have fallen. M. Thomsen's experiments have evidently been made with care, and his results agree comparatively with my own ; but the absolute amount of heat obtained by him falls far short of what I have found. It is indeed much easier to obtain results relatively than absolutely con-ect. The numbers given in this paper will, I believe, be found rarely to differ relatively more than a-sT^th from the truth, but they may hereafter require a small correction in respect to their absolute value. That correction can, however, be scarcely more than -rs^th of the whole amount ; and I have little doubt that the number, for example, given by Thomsen to express the heat disengaged in the combination of soda with nitric acid will prove to be as far below the true number as that given by MM. Pavre and Silbermann is above it. ^ Poggendorffs Anmden, cxxxviii. p. 78. 332 On the Heat Developed in Combination. Table I.^ — Potash. [XL. Acid. Andrews, Favrb and Andrews, 1841. SlLBBRMANK". 1870. Sulphuric, 16330 16083 16701 Nitric, - 15076 15510 14800 Hydrochloric, 14634 15656 14940 Oxalic, 14771 14156 15124 Acetic, - 14257 13973 13805 Tartaric, 13612 13425 13508 Table II. — Soda. Acid. Andrews, 1841. Favre and Silbermann. Andrews, 1870. Thomsen. Sulphuric, 16483 15810 16580 15689 Nitric, - 14288 15283 14480 13617 Hydrochloric, 14926 15128 14744 13740 Oxalic, 14796 13752 15032 ■ ■ ■ Acetic, 14046 13600 14000 ... Tartaric, 1313,5 13651 13400 ... Table III. — Ammonia. Acid. Andrews, Favre and Andrews, 1841. Silbermann. 1870. Sulphuric, 14135 14690 14710 Nitric, 12440 13676 12683 Hydrochloric, 12440 13536 12964 Oxalic, 12684 • • ( 13088 Acetic, 12195 12649 12316 Tartaric, 11400 ... 11744 333 XLI.— ON THE GASEOUS AND LIQUID STATES OF MATTER Boyal Institution of Great Britain, June 2, 1871. The liquid state of matter forms a link between the solid and gaseous states. This link is, however, often suppressed, and the solid passes directly into the gaseous or vaporous form. In the intense cold of an Arctic winter hard ice will gradually change into transparent vapour without previously assuming the form of water. Carbonic acid snow passes rapidly into gas when exposed to the air, and can with difficulty be liquefied in open tubes. Its boiling point, as Faraday has shown, presents the apparent anomaly of being lower in the thermometric scale than its melting point ; a statement less paradoxical than it may at first appear, if we remember that water can exist as vapour at temperatures far lower than those at which it can exist as liquid. Whether the transition be directly from solid to gaseous, or from solid to liquid, and from liquid to gaseous, a marked change of physical properties occurs at each step or break, and heat is absorbed, as was proved long ago by Black, without producing elevation of temperature. Many solids and liquids will for this reason maintain a low temperature, even when surrounded by a white hot atmosphere, and the remarkable experiment of solidifying water, and even mercury, on a red-hot plate, finds thus an easy explanation. The term spheroidal state, when applied to water floating on a cushion of vapour over a red-hot plate, is however apt to mislead. The water is not here in any peculiar state. It is simply water evaporat- ing rapidly at a few degrees below its boiling point, and all its properties, even those of capillarity, are the properties of ordi- nary water at 96'5 C. The interesting phenomena exhibited under these conditions are due to other causes, and not to any new or peculiar state of the liquid itself The fine researches of Dalton upon vapours, and the memorable discovery by Faraday of the liquefaction of gases by pressure alone, finished 334 On the Gaseous and Liquid States of Matter. [xli. the work which Black had begun. Our knowledge of the con- ditions under which matter passes abruptly from the gaseous to the liquid, and from the liquid to the solid state, may now be regarded as almost complete. In 1822 Cagniard de la Tour made some remarkable experi- ments, which still bear his name, and may be regarded as the starting-point of the investigations which form the chief subject of this address. Cagniard de La Tour's first experiments were made in a small Papin's digester, constructed from the thick end of a gun-barrel, into which he introduced a little alcohol and also a small quartz ball, and firmly closed the whole. On heating the gun-barrel with its contents over an open fire, and observing from time to time the sound produced by the ball when the apparatus was shaken, he inferred- that after a certain tem- perature was attained the liquid had disappeared. He afterwards succeeded in repeating the experiment in glass tubes, and ob- tained the following results : — An hermetically-sealed glass tube, containing sufficient alcohol to occupy two-fifths of its capacity, was gradually heated, when the liquid was seen to dilate, and its mobility at the same time to become gradually greater. After attaining to nearly twice its original volume, the liquid completely disappeared, and was converted into a vapour so transparent that the tube appeared to be quite empty. On allowing the tube to cool, a very thick cloud was formed, after which the liquid reappeared in its former state. It is singular that in this otherwise accurate description, Cagniard de la Tour should have overlooked the most remark- able appearance of all, the moving or flickering strife, which fill the tube when, after heating it considerably, the tempera- ture is quickly lowered. This phenomenon was first described by myself in 1863, as it is seen in carbonic acid, which has been partially liquefied by pressure, and afterwards heated a little above 31°. It may be observed on a larger scale and to great advantage by heating such liquids as sulphurous acid or ether in hermetically-sealed tubes. The experiments whose results I am about to describe have occupied me for a period of fully ten years ; they involved the construction of novel forms of apparatus, in which the pro- perties of matter might be studied under varied conditions of xLi.] On the Gaseous and Liquid States of Matter. 335 temperature and pressure, such as had never been realized before. In my earlier attempts I endeavoured, as others had already done, to use the expansive force of the mixed gases which are disengaged in the electrolysis of water ; and I was able in this way to obtain pressures of 150 atmospheres and even more in glass tubes ; but the method was in many respects defective, and more than one dangerous explosion occurred, so that I eventually abandoned it. In the apparatus finally adopted, the gas to be compressed is enclosed in a long glass tube, of which the greater part of the length, or about 450 millimetres, has a capillary bore, and the remainder, about 150 millimetres, an internal diameter of 2 millimetres. The free capillary end is sealed, while the gas in a pure and dry state is passing through ; while at the other end the 'gas is confined by a movable column of mercury. The details of the method by which this is accomplished will be found in the Bakerian lecture for 1869, to which I must also refer for an account of the process by which the original volume of the gas at the freezing point of water and under one atmosphere of pressure was determined, and also the volumes of the same gas deduced from the observed measurements when it was compressed at different pressures in the capillary tube. A conical protuberance on the capillary part of the tube, a little above its junction with the wider part, corresponded as nearly as possible with a hollow cone in a stout brass fiange, the joint being rendered perfectly tight by careful packing. The body of the apparatus consisted of two cold-drawn copper tubes of great strength, to the ends of which four massive brass flanges were firmly attached. Two corresponding flanges or end pieces, each carrying a fine steel screw packed with great care, were bolted on the lower flanges. The success of the experiments depended greatly on the packing of this screw. It was effected by means of a number of leather washers, tightly pressed down and saturated in vacuo with melted lard. The apparatus was now filled with water ; the flanges with the glass tubes, one containing the gas to be examined, the other air or hydrogen to act as a manometer or measure of the pressure, were bolted down upon the upper flanges of the copper tubes. The joints 336 On the Gaseous and Liquid States of Matter. [xu. had always leather washers interposed ; and when sufficiently tightened, they resisted any pressure which could be applied, even for an indefinite time. The two copper tubes were connected by a fine horizontal tube, so that the whole of the interior of the apparatus was in free communication. The pressure was obtained by screwing one or other of the steel screws into the water. I have recently had the apparatus constructed of iron and filled with mercury. As mercury is much less compres- sible than water, the same length of screw produces a greater pressure on the interior of the apparatus, even with a larger cavity. There are other advantages in this form of the appar- atus which I hope will facilitate future research. The objec- tion to it is its extreme sensitiveness to changes of temperature, so that a variation of TOTrth of a degree alters the internal pres- sure by several atmospheres. In the actual experiments the gas under examination does not come into view till it has entered the capillary tube, and is exposed to a pressure of thirty or forty atmospheres. The limit of the pressure which can be obtained has hitherto been the capacity of resistance of the glass tubes to bursting. Fine ther- mometer glass tubes of white glass will frequently burst when exposed to a pressure of little more than 100 atmospheres ; but green glass tubes of good quality are much stronger, and will easily bear a pressure of 300 atmospheres. One of the strongest forms of glass capillary tube for resisting internal pres- sure is obtained by drawing out a thick green glass tube, heated to softening, till it becomes so fine as to be flexible. Tubes of this kind can easily be drawn out at the blowpipe table, and obtained of very uniform bore. I have compressed air in such tubes to T^th of its ordinary volume without bursting the tubes. Two rectangular brass cases, closed before and behind with plate-glass, surround, one the manometer, and the other the tube containing the gas to be examined, and allow them to be main- tained at any required temperature by the flow of a stream of water. The manometer was maintained as nearly as possible at the temperature of the apartment ; the tube containing the gas, on the contrary, was maintained at different temperatures, according to the object in view. The following observations, xLi.] On the Gaseous and Liquid States of Matter. 337 published in 1863, contain the results of my earliest experi- ments on this subject : — " On partially hquefying carbonic acid by pressure alone, and gradually raising the temperature at the same time to 88° Fahr., the surface of demarcation between the liquid and gas becomes fainter, loses its curvature, and at last disappears. The space is then occupied by a homogeneous fluid, which exhibits when the pressure is suddenly diminished or the temperature slightly lowered, a peculiar appearance of moving or flickering strise throughout its entire mass. At temperatures above 88° no apparent liquefaction, or separation into two distinct forms of matter, could be effected, even when a pressure of 300 or 400 atmospheres was applied. Nitrous oxide gave analogous results." [Miller's Chemical Physics, 1863, p. 329.] Fig. 1. Cloud below critical point. Fig. 2. Strise above critical point. The flickering strise referred to can be admirably shown, as I mentioned before, in hermetically-sealed tubes of strong glass, partially filled with such liquids as sulphurous acid or ether. T 338 On the Gaseous and Liquid States of Matter. [xli. The liquid must in the first instance be heated a few degrees above what I have designated the " critical " point. The appearances exhibited by the ascending and descending sheets of matter of unequal density are most remarkable, but must be seen in order to be understood. They only occur in this strik- ing form in fluids heated a little above the critical point, and are produced by the great changes of density which slight vari- ations of pressure or temperature produce in this case. They are always a clear proof that the matter in the tube is homo- geneous, and that we have not liquid and gas in presence of one another. These striae are in short only an extraordinary development of the movements seen in ordinary liquids and gases when they are heated from below. The experi- ments to be immediately described will explain their grea,t intensity above the critical point. When the temperature falls below the critical point, the formation of a cloud indicates that we have now heterogeneous matter in the tube, fine drops of liquid in presence of a gas. We must take care, however, not to suppose that a cloud neces- sarily precedes the formation of true liquid. If the pressure be sufficiently great no cloud of any kind will form. I now proceed to describe the general results of the experi- ments upon carbonic acid. If a certain volume of carbonic acid at the temperature of 13°"1 and under a pressure of one atmos- phere be exposed to a gradually-increasing pressure, its volume will steadily diminish, but at a faster rate than according to Boyle's law, till at the pressure of 48 "9 atmospheres its volume is reduced to about bV of the original volume at one atmosphere. Liquefaction now begins and continues with very slight aug- mentation oi pressure, the necessity for which I traced to the presence of a minute quantity of air (about -j^th part) in the carbonic acid. On augmenting the pressure after lique- faction, the volume slowly diminished, but at a much faster rate than in the case of ordinary liquids. Later experiments carried to much higher pressures have fully confirmed this result. At 21°' 5 similar results were obtained, but a pressure of nearly 60 atmospheres was required before liquefaction began. At 30°"9 C, or 87°"7 Fahr., the critical point of temperature xLi.] On the Gaseous and Liquid States of Matter. 339 is reached. It is the temperature at which liquid ceases to be formed under any pressure. At a temperature a little below this point the surface of separation between liquid and gas becomes very faint and loses its curvature, the density and other physical properties of the liquid and gas being now identical and the tube filled with homogeneous matter. If the temperature and pressure be kept steady, no evidence of heter- ogeneity will be obtained by optical tests under the most varied conditions of volume. If we now follow the course of a given volume of carbonic acid gas at 31°-1, or 0°'2 above the critical point, we shall find that its course resembles that of the gas at lower tempera- tures till the volume is reached at which liquefaction might be expected to begin. A rapid but not (as in the case of the formation of liquid) abrupt fall then supervenes, after which the carbonic acid undergoes a slow diminution of volume as the pressure augments. The curves, which are here exhibited as they were represented in the Bakerian lecture [p. 308, above], illustrate very clearly these statements. We have thus carbonic acid at 0°'2 above the critical point, and at a pressure of 73 atmospheres behaving very nearly as if it liquefied. At this pressure an augmentation of only ^th of the entire pressure ■diminishes the volume of the carbonic acid to about one half. Yet during the whole of this fall, no evidence of heterogeneity, or of two states of matter present together in the tube, could at any period be obtained. Carbonic acid at this tem- perature of 31°'l, and under a pressure of 75 atmospheres, behaves much more as a liquid than as a gas when the pressure is either augmented or diminished ; yet it never exhibits under any conditions the characteristic properties of the liquid state ; that is to say, no surface of separation is formed by change of pressure, nor will it collect into drops and form a cloud. At 32°'5 the fall, when liquefaction might be expected, is less abrupt than at 31°"1 ; and at 35°"5, although still manifest, it is further reduced. At 48°'l the fall shown at lower temperatures can no longer be distinctly observed, and the curve representing the change of volume approximates to that of a perfect gas. There can be little, if any, doubt that 340 On the Gaseous and Liquid States of Matter, [xli. at a higher temperature carbonic acid would behave under augmenting pressures nearly as nitrogen or hydrogen.^ I have frequently exposed carbonic acid, without making precise measurements, to much higher pressures than any of the foregoing, and have made it pass without break or inter- ruption from what is regarded by every one as the gaseous state, to what is, in like manner, universally regarded as the liquid state. Take, for example, a given volume of carbonic acid gas at 50° C, or at a higher temperature, and expose it to increasing pressure till 150 atmospheres have been reached. In this process its volume will steadily diminish as the pressure augments, and no sudden diminution of volume, without the application of external pressure will occur at any stage of it. ' These different modes of passing from the gaseous to the liquid state are admirably illustrated by a solid model constructed by Prof. J. Thomson, which was exhibited at the lecture. I have been favoured by Prof. Thomson with the following description of this model : — " The model combines Dr. Andrews' experimental results in a manner tend- ing to show clearly their mutual correlation. It consists of a curved surface referred to three axes of rectangular co-ordinates, and formed so that the three co-ordinates of each point in the curved surface represent, for any given mass of carbonic acid, a pressure, a temperature, and a volume, which can co-exist in that mass. " In Dr. Andrews' diagram of curves, published in his paper in the Trans- actions of the Royal Society for 1869, p. 583, the experimental results, for each of several temperatures experimented on, are combined in the form of a plane curved line referred to two axes of rectangular co-ordinates. The curved surface in the model is obtained by placing these curved lines with their planes parallel to one another, and separated by intervals proportional to the differences of the temperatures to which the curves severally belong, and with the origins of co-ordinates of the curves situated in a straight line perpendicular to their planes, and with the axes of co-ordinates of all of them parallel in pairs to one another, and by cutting the curved surface out so as to pass through those curved lines smoothly or evenly. " The curved surface so obtained exhibits in a very obvious way the remark- able phenomena of the voluminal conditions at and near the critical point of temperature and pressure in comparison with the voluminal conditions through- out other parts of the indefinite range of gradually varying temperatures and pressures. This curved surface also helps to afford a clear view of the nature and meaning of the continuity of the liquid and gaseous states of matter. It does so by its own obvious continuity throughout the expanse to which it might be extended round the outside of the critical point in receding from the range of the points of pressure and temperature where an abrupt change of volume can occur by gasification or condensation. On the curved surface in the model, Dr. Andrews' curves for the temperatures 13°'l, 21°*5, 31°'l, 3o°'5, and 48° '1 centigrade, from which it was constructed, are shown drawn in their proper places. The model admits of easily exhibiting in due relation to one another a second set of curves in which each curve would be for a constant pressure, and in which the co-ordinates would represent temperatures and corresponding volumes. It serves generally as an aid towards bringing the whole subject clearly before the mind." xLi.] Oifi the Gaseous and Liquid States of Matter. 341 When the full pressure has been applied, let the temperature be allowed to fall till the carbonic acid has reached the ordinary temperature of the atmosphere. During the whole of this operation no breach of continuity has occurred. It begins with a gas, and by a series of gradual changes, present- ing nowhere any abrupt alteration of volume or sudden evolu- tion of heat, it ends with a liquid. The closest observation fails to discover anywhere indications of a change of condition in the carbonic acid, or evidence, at any period of the process, of part of it being in one physical state and part in another. That the gas has actually changed into a liquid would, indeed, never have been suspected, had it not shown itself to be so changed by entering into ebullition on the removal of the pressure. For convenience, this process has been divided into two stages, the compression of the carbonic acid and its subsequent cooling ; but these operations might have been performed simultaneously, if care were taken so to arrange the application of the pressure and the rate of cooling, that the pressure should not be less than 76 atmospheres when the carbonic acid had cooled to 31°. We are now prepared for the consideration of the following important question. What is the condition of carbonic acid when it passes, at temperatures above 31°, from the gaseous state down to the volume of the liquid, without giving evidence at any part of the process of liquefaction having occurred ? Does it continue in the gaseous state, or does it liquefy, or have we to deal with a new condition of matter ? If the experiment were made at 100°, or at a higher temperature, when all indications of a fall had disappeared, the probable answer which would be given to this question is that the gas preserves its gaseous condition during the compression ; and few would hesitate to declare this statement to be true, if the pressure were applied to such gases as hydrogen or nitrogen. On the other hand, when the experiment is made with carbonic acid at temperatures a little above 31°, the great fall which occurs at one period of the process would lead to the con- jecture that liquefaction had actually taken place, although optical tests carefully applied failed at any time to discover the presence of a liquid in contact with a gas. But against this 342 On the Gaseous and Liquid States of Matter. [xli. view it may be urged with great force, that the fact of addi- tional pressure being always required for a further diminution of volume, is opposed to the known laws which hold in the change of bodies from the gaseous to the liquid state. Besides, the higher the temperature at which the gas is compressed, the less the fall becomes, and at last it disappears. The answer to the foregoing question, according to what appears to me to be the true interpretation of the experiments already described, is to be found in the close and intimate relations which subsist between the gaseous and liquid states of matter. The ordinary gaseous and ordinary liquid states are, in short, only widely separated forms of the same condition of matter, and may be made to pass into one another by a series of gradations so gentle that the passage shall nowhere present any interruption or breach of continuity. From carbonic acid as a perfect gas to carbonic acid as a perfect liquid, the transition we have seen may be accomplished by a continuous process, and the gas and liquid are only distant stages of a long series of continuous physical changes. Under certain conditions, of temperature and pressure, carbonic acid finds itself, it is true, in what may be described as a state of instability, and suddenly passes, with evolution of heat, and without application of additional pressure or change of temperature, to the volume, which by the continuous process can only be reached through a long and circuitous route. In the abrupt change which here occurs, a marked difference is exhibited, while the process is going on, in the optical and other physical properties of the carbonic acid which has collapsed into the smaller volume, and of the carbonic acid not yet altered. There is no difficulty here, therefore, in distinguishing between the liquid and the gas. But in other cases the distinction cannot be made ; and under many of the conditions I have described it would be vain to attempt to assign carbonic acid to the liquid rather than the gaseous state. Carbonic acid, at the temperature of 35°-5, and under a pressure of 108 atmospheres, is reduced to xirr of the volume it occupied under a pressure of one atmos- phere ; but if anyone ask whether it is now in the gaseous or liquid state, the question does not, I believe, admit of a positive reply. Carbonic acid at 35°'5, and under 108 atmospheres of xLi.] On the Gaseous and Liquid States of Matter. 343 pressure, stands nearly midway between the gas and the liquid ; and we have no valid grounds for assigning it to the one form of matter any more than to the other. The same observation would apply with even greater force to the state in which carbonic acid exists at higher temperatures and under greater pressures than those just mentioned. In short, the passage under great pressures from the liquid to the gaseous state may be effected by the application of heat without break or breach of continuity. That a marked change in the physical properties of the substance occurs during this process is no objection to its being continuous. If mercury as a liquid is opaque and as a gas is transparent, the red and translucent bromine, on the other hand, when heated above the critical point, becomes so opaque as almost to resemble a mass of resin. Frankland has shown that the flame of hydrogen becomes continuous when the gas is burned under a pressure of 20 atmospheres, and these experiments have been since extended by the same able chemist and Lockyer. "We must not, however, suppose that one inter- mediate state exists between liquid and gas ; on the contrary, an infinite succession of intermediate states may truly be said to connect the liquid proper and the gas proper ; in other words, the passage is continuous. When the critical point is attained, the density of the liquid and gas becomes the same, and the tube is filled with homogeneous matter. As regards the question of the continuity of the solid and liquid states, it would be necessary, in order to establish this continuity, to obtain, by the combiued action of heat and pressure, the solid and liquid, of the same density and of like physical properties. To accomplish this result will probably require pressures far beyond any which can be reached in transparent tubes ; but it may be possible to show by experi- ment that the solid and liquid can be made to approach to the required conditions. 344 XLII.— ADDEESS TO THE CHEMICAL SECTION OF THE BRITISH ASSOCIATION. Edinburgh, August 3rd, 1871. (Amidst the vicissitudes to which scientific theories are liable, it was scarcely to be expected that the discarded theory of Phlogiston should be resuscitated in our day and connected with one of the most important generalizations of modern science* The phlogistic theory, elaborated nearly two hundred years ago by Beecher and Stahl, was not, it now appears, wholly founded in error ; on the contrary, it was an imperfect anticipa- tion of the great principle of energy, which plays so important a part in physical and chemical changes. The disciple of Phlogiston, ignorant of the whole history of chemical combina- tion, connected, it is true, his phlogiston with one only of the combining bodies, instead of recognizing that it is eliminated by the union of all. " There can be no doubt," says Dr. Crum Brown, who first suggested this view, " that potential energy is what the chemists of the 17th century meant when they spoke of phlogiston." " Phlogiston and latent heat," playfully remarks Volhard, " which formerly opposed each other in so hot a combat, have entered into a peaceful compact; and to banish all recollection of their former strife, have assumed in common the new name of energy." But, as Dr. Odling well remarks, " in interpreting the phlogistic writings by the light of modern doctrine, we are not to attribute to their authors the precise notion of energy which now prevails. It is only con- tended that the phlogistians had in their time possession of a real truth in nature, which, altogether lost sight of in the inter- mediate period, has since crystallized out in a definite form." But whatever may be the true value of the Stahlian views, there can be no doubt that the discoveries which have shed so bright a lustre round the name of Black mark an epoch in the history of science, and gave a mighty impulse to human pro- xLii.] Address to Chemical Section of British Association. 345 gress. A recent attempt to ignore the labours of Black and his great contemporaries, and to attribute the foundation of modern chemistry to Lavoisier alone, has already been amply refuted in an able inaugural address delivered a short time ago from the Chair formerly occupied by Black. The statements of Dr. Crum Brown may, indeed, be confirmed on the authority of Lavoisier himself Through the kindness of Dr. Black's representatives, I have been permitted to examine his corre- spondence, which has been carefully preserved, and I have been so fortunate as to find in it three original letters from Lavoisier to Dr. Black. They were written in 1789 and 1790, and they appear to comprise the whole of the correspondence on the part of Lavoisier which passed between those distinguished men. Some extracts from these letters were published soon after Dr. Black's death by his friends. Dr. Adam Ferguson and Dr. Eobison; but the letters themselves, as far as I know, have never appeared in an entire form. I will crave permission to have them printed as an appendix to this address.^ Lavoisier, it will be seen, addresses Black as one whom he was accustomed to regard as his master, and whose discoveries had produced important revolutions in science. It may, indeed, be said with truth that Lavoisier completed the foundation on which the grand structure of modern chemistry has since arisen ; but Black, Priestley, Scheele, and Cavendish were before Lavoisier, and their claims to a share in the great work are not inferior to those of the illustrious French chemist. Among the questions of general chemistry, few are more interesting, or have of late attracted more attention, than the relations which subsist between the chemical composition and refractive power of bodies for light. Newton, it will be re- membered, pointed out the distinction between the refractive power of a medium and its refractive index, and gave for the former the expression , where /j. is the refractive index, d and d the density of the refracting medium. Sir J. Herschel, anticipating later observations, remarked, in 1830, that Newton's function only expresses the intrinsic refractive power ' [It has not been judged necessary to reproduce these letters here. — P.G.T.] 346 Address to the Chemical Section of the [xlii. on the supposition of matter being infinitely divisible ; but that if material bodies consist of a finite number of atoms, differing in weight for different substances, the intrinsic refractive power of the atoms of any given medium will be the product of the above function by the atomic weight. The same remark has since been made by Berthelot. Later observations have led to an important modification in the form of Newton's function. Beer showed that the experiments of Biot and Arago, as well as those of Dulong, on the refractive power of gases, agree quite as well with a simpler expression as with that given by Newton ; and Gladstone and Dale proposed in 1863 the formula , as expressing more accurately than any other d the results of their experiments on the refractive power of liquids. The researches of Landolt and Wtillner have fully con- firmed the general accuracy of the new formula. An important observation made, about twenty years ago, by Delffs has been the starting-point for all subsequent investigations on this sub- ject. Delffs remarked that the refractive indices of the com- pound ethers increase with the atomic weight, and that isomeric ethers have the same refractive indices. The later researches of Gladstone and of Landolt have, on the whole, confirmed these observations, and have shown that the specific refractive power depends chiefly on the atomic composition of the body, and is little influenced by the mode of grouping of the atoms. These inquiries have gone further, and have led to the dis- covery of the refraction-equivalents of the elements. By com- paring the refractive power of compound bodies differing from one another by one or more atoms of the same element, Landolt succeeded in obtaining numbers which express the refraction-equivalents of carbon, hydrogen, and oxygen ; and corresponding numbers have been obtained for other elements by Gladstone and Haagen. The whole subject has been re- cently discussed and enriched with many new observations in an able memoir by Gladstone. As might be expected in so novel and recondite a subject, some anomalies occur which are difficult to explain. Thus hydrogen appears in different classes of compounds with at least two refraction-equivalents, one three times as great as the other ; and the refraction-equivalents ^"i-] British Association. 347 of the aromatic compounds and their derivatives, as given by observation, are in general higher than the calculated numbers. A happy modification of the ice-calorimeter has been made by Bunsen. The principle of the method (to use as a measure of heat the change of volume which ice undergoes in melting) had already occurred to Herschel, and, as it now appears, stiU earlier to Hermann ; but their observations had been entirely overlooked by physicists, and had led to no practical result. Bunsen has, indeed, clearly pointed out that the success of the method depends upon an important condition, which is entirely his own. The ice to be melted must be prepared with water free from air, and must surround the source of heat in the form of a solid cyclinder frozen artificially in situ. Those who have worked on the subject of heat know how difficult it is to measure absolute quantities with certainty, even where relative results of great accuracy may be attained. The ice-calori- meter of Bunsen will therefore be welcomed as an important addition to our means of research. Bunsen has applied his method to determine the specific heats of ruthenium, calcium, and indium, and finds that the atomic weight of indium must be increased by one half in order to bring it into conformity with the law of Dulong and Petit. He has also made a new determination of the density of ice, which he finds to be 0-9167. In a report on the Heat of Combination, which was made to this Association in 1849, the existence of a group of isothermal bases was pointed out. " As some of the bases " (potash, soda, baryta, strontia), it was remarked, " form what we may perhaps designate an isothermal group, such bases will develop the same or nearly the same heat in combining with an acid, and no heat will be disengaged during their mutual displacements." The latest experiments of Thomsen have given a remarkable extension to this group of isothermal bases. He finds that the hydrates of lithium, thallium, calcium, and magnesium produce, when all corrections are made, the same amount of heat, on being neutralized by sulphuric acid, as the four bases before mentioned. The hydrate of tetramethylammonium belongs to the same class of bases. Ethylamin, on the other hand, agrees with ammonia, which, as has been long known, gives out less 348 Address to the Chemical Section of the [xlii. heat in combining with the acids than potash or soda. An elaborate investigation of the amount of heat evolved in the combustion of coal of different kinds has been made by Scheurer- Kestner and Meusnier, accompanied by analyses of the coal. Coal rich in carbon and hydrogen disengages more heat in burning than coal in which those elements are partially replaced by oxygen. After deducting the cinders, the heat produced by the combustion of 1 gramme of coal varied from 8215 to 9622 units. Tyndall has given an extended account of his experiments on the action of a beam of strong light on certain vapours. He finds that there is a marked difference in the absorbing power of different vapours for the actinic rays. Thus nitrite of amyl in the state of vapour absorbs rapidly the rays of light com- petent to decompose it, while iodide of allyl in the same state allows them freely to pass. Morren has continued these ex- periments in the south of France, and among other results he finds that sulphurous acid is decomposed by the solar beam. Eoscoe has prosecuted the photo-chemical investigations which Bunsen and, he began some years ago. For altitudes above 10 degrees, the relation between the sun's altitude and the chemical intensity of light is represented by a straight line. Till the sun has reached an altitude of about 20 degrees, the chemical action produced by diffused daylight exceeds that of the direct sunlight ; the two actions are then balanced ; and at higher elevations the direct sunlight is superior to the diffused light. The supposed inferiority of the chemical action of light under a tropical sun to its action in higher latitudes proves to be a mistake. According to Eoscoe and Thorpe, the chemical intensity of light at Para under the equator in the month of April is more than three times greater than at Kew in the month of August. Hunter has given a great extension to the earlier experi- ments of Saussure on the absorptive power of charcoal for gases. Cocoanut- charcoal, according to Hunter's experiments, exceeds all other varieties of wood-charcoal in absorptive power, taking up at ordinary pressures 170 volumes of ammonia and 69 of carbonic acid. Methylic alcohol is more largely absorbed than any other vapour at temperatures from 90° to 127°; but at xLii.] British Association. 349 159° the absorption of ordinary alcohol exceeds it. Cocoanut- charcoal absorbs forty-four times its volume of the vapour of water at 127°. The absorptive power is increased by pressure. Last year two new processes for improving the manufacture of chlorine attracted the attention of the Section : one of these has already proved to be a success ; and I am glad to be able to state that Mr. Deacon has recently overcome certain diffi- culties in his method, and has obtained a complete absorption of the chlorine. May we hope to see oxygen prepared by a cheap and continuous process from atmospheric air ? With baryta the problem can be solved very perfectly, if not economi- cally. Another process is that of Tessier de Mothay, in which the manganate of potassium is decomposed by a current of superheated steam, and afterwards revived by being heated in a current of air. A company has lately been formed in New York to apply this process to the production of a brilliant house-light. A compound Argand burner is used, having a double row of apertures ; the inner row is supplied with oxygen, the outer with coal-gas or other combustible. The applications of pure oxygen, if it could be prepared cheaply, would be very numerous ; and few discoveries would more amply reward the iuventor. Among other uses it might be applied to the pro- duction of ozone free from nitric acid by the action of the elec- trical discharge, and to the introduction of that singular body, in an efi&cient form, into the arts as a bleaching and oxidizing agent. Tessier de Mothay has also proposed to prepare hydro- gen gas on the large scale by heating hydrate of lime with anthracite. "We learn from the history of metallurgy that the valuable alloy which copper forms with zinc was known and applied long before zinc itself was discovered. Nearly the same remark may be made at present with regard to manganese and its alloys. The metal is difficult to obtain, and has not in the pure state been applied to any useful purpose ; but its alloys with copper and other metals have been prepared, and some of them are likely to be of great value. The alloy with zinc and copper is used as a substitute for german silver, and possesses some advantages over it. Not less important is the alloy of iron and manganese prepared according to the process of Henderson, by 350 Address to the Chemical Section of the [xlii. reducing in a Siemens's furnace a mixture of carbonate of man- ganese and oxide of iron. It contains from 20 to 30 per cent, of manganese, and will doubtless replace to a large extent the spiegeleisen now used in the manufacture of Bessemer steel. The classical researches of Eoscoe have made us acquainted for the first time with metallic vanadium. Berzelius obtained brilliant scales, which he supposed to be the metal, by heating an oxychloride in ammonia ; but they have proved to be a nitride. Eoscoe prepared the metal, by reducing its chloride in a current of hydrogen, as a light grey powder, with a metallic lustre under the microscope. It has a remarkable affinity both for nitrogen and silicon. Like phosphorus, it is a pentad, and the vanadates correspond in composition to the phosphates, but differ in the order of stability at ordinary temperatures, the soluble tribasic salts being less stable than the tetrabasic com- pounds. Sainte-Claire DevUle, in continuation of his researches on dissociation, has examined the conditions under which the vapour of water is decomposed by metallic iron. The iron, maintained at a constant temperature, but varying in different experiments from 150° C. to 1600° C, was exposed to the action of vapour of water of known tension. It was found that for a given temperature the iron continued to oxidize, till the tension of the hydrogen formed reached an invariable value. In these experiments, as Deville remarks, iron behaves as if it emitted a vapour (hydrogen), obeying the laws of hygrometry. An interesting set of experiments has been made by Lothian Bell on the power possessed by spongy metallic iron of splitting up carbonic oxide into carbon and carbonic acid, the former being deposited in the iron. A minute quantity of oxide of iron is always formed in this reaction. The fine researches of Graham on the colloidal state have received an interesting extension by Eeynolds's discovery of a new group of coUoid bodies. A solution of mercuric chloride is added to a mixture of acetone and a dilute solution of potas- sium hydrate till the precipitate which at first appears is redis- solved, and the clear liquid poured upon a dialyzer which floated upon water. The composition of the coUoid body thus obtained in the anhydrous state was found to be ((CHj) 260)2 Hg^ O3. xLii.] British Association. 351 The hydrate is regarded by Reynolds as a feeble acid, even more readily decomposed than alkaline silicates. A solu- tion containing only five per cent, forms a firm jelly when heated to 50° C. Analogous compounds were formed with the higher members of the fatty ketone series. In the same direc- tion are the researches of Marcet on blood, which he finds to be a strictly colloid fluid containing a small proportion of diffus- ible salts. In organic chemistry the labours of chemists have been of late largely directed to a group of hydrocarbons which were first discovered among the products of the destructive distillation of coal or oil. The central body round which these researches have chiefly turned is benzol, whose discovery will always be associated with the name of Faraday. With this body naph- thalin and anthracene form a series, whose members differ by C4 Hg, and their boiling-points by about 140°. The recent researches of Liebermann have proved, as was before suspected, that chrysene is a fourth member of the same series. I may add that ethylene, which boils at about — 70°, corresponds in composition and boiling-point to a lower member of the same series. KekuM propounded some time ago with great clearness the question as to whether the six atoms of hydrogen in benzol are equivalent, or, on the contrary, play dissimilar parts. According to the first hypothesis, there can be only one modi- fication of the mono- and penta-derivatives of benzol ; while three modifications of the bi-, tri-, and tetra-derivatives are possible. On the second hypothesis, two modifications of the mono-derivatives are possible, and in general a much larger number of isomeric compounds than on the first hypothesis. Such is the problem which has of late occupied the attention of some of the ablest chemists of Germany, and has led to a large number of new and important investigations. The aromatic hydrocarbons, toluol, xylol, &c., which differ from one another by CHj, have been shown by Fittig to be methyl derivatives of benzol. According to the first of the two hypotheses to which I have referred, only one benzol and one methyl benzol (toluol) are possible, and accordingly no isomeric modifications of these bodies have been discovered. But the three following member of the series ought each to be capable of .existing in three 352 Address to the Chemical Section of the [xui. distinct isomeric forms. The researches of Fittig had already established the existence of two isomeric compounds having the formula Cg H,„, — methyl-toluol (obtained synthetically from toluol) and isoxylol (prepared by the removal of an atom of methyl from the mesytelene of Kane). The same chemist has since obtained the third modification, orthoxylol, by the decom- position of the paraxylylic acid. These three isomeric hydro- carbons may be readily distinguished from one another by the marked difference in the properties of their trinitro-compounds, and also by their different behaviour with oxidizing agents. Other facts have been adduced in support of the equality or homogeneity of position of the hydrogen atoms in benzol. Thus Hiibner and Alsberg have prepared aniline, a mono-derivative, from different bi-derivatives, and have always obtained the same body. The latest researches on this subject are those of Eichter. Baeyer has prepared artificially picoline, a base isomeric with aniline, and discovered by Anderson in his very able researches on the pyridine series. Of the two methods described by Baeyer, one is founded on an experiment of Simpson, in which a new base was obtained by heating' tribromallyl with an alcoholic solution of ammonia. By pushing further the action of the heat, Baeyer succeeded in expelling the whole of the bromine from Simpson's base in the form of hydrobromic acid, and in obtaining picoline. The same chemist has also prepared artificially coUidine, another base of the pyridine series. To this Hst of remarkable synthetical discoveries, another of the highest interest has lately been added by Schiff — the prepara- tion of artificial coniine. He obtained it by the action of ammonia on butyric aldehyde (C^HgO). The artificial base has the same composition as coniine prepared from hemlock. It is a liquid of an amber-yellow colour, having the characteristic odour and nearly all the usual reactions of ordinary coniine. Its physiological properties, so far as they have been examined, agree with those of coniine from hemlock ; but the artificial base has not yet been obtained in large quantity, nor perfectly pure. Valuable papers on alizarine have been published by Perkin and Schunck. The latter has described a new acid, the anthra- xLii.] British Association. 353 flavic, which is formed in the artificial preparation of alizarine. Madder contains another colouring principle, purpurine, which, like alizarine, yields anthracene when acted on by reducing agents, and has also been prepared artificially. These colouring principles may be distinguished from one another, as Stokes has shown, by their absorption bands,; and Perkin has lately con- firmed by this optical test the interesting observation of Schunck, that finished madder prints contain nothing but pure alizarine in combination with the mordant employed. Hofmann has achieved another triumph in a department of chemistry which he has made peculiarly his own. In 1857 he showed that alcohol bases, analogous to those derived from ammonia, could be obtained by replacement from phosphuretted hydrogen ; but he failed in his attempts to prepare the two lower derivatives. These missing links he has now supplied, and has thus established a complete parallelism between the deriva- tives of ammonia and of phosphuretted hydrogen. The same able chemist has lately described the aromatic cyanates, of which one only, the phenylic cyanate (CO, CgHj, IST), was previously known, having been discovered about twenty years ago by Hofmann himself. He now prepares this compound by the action of phosphoric anhydride on phenylurethane, and by a similar method he has obtained the tolylic, xylylic, and naph- thylic cyanates. Stenhouse had observed many years ago that when aniline is added to furfurol the mixture becomes rose-red, and communi- cates a fugitive red stain to the skin, and also to linen and silk. He has lately resumed the investigation of this subject, and has obtained two new bases, furfuraniline and furfurtoluidine, which, like rosaniline, form beautifully coloured salts, although the bases themselves are nearly colourless, or of a pale brown colour. The furfuraniline hydrochlorate (C^yH^gOgN^Cl) is prepared by adding furfurol to an alcoholic solution of aniUne hydrochlorate containing an excess of anihne. We have also from Stenhouse a new contribution to the history of orcin, in contimiation of his former masterly researches on that body. He has prepared the trinitroorcin (CyHg(E'02)g02), a powerful acid, having many points of resemblance to picric acid. In connexion with another research of Stenhouse made many years z 354 Address to the Chemical Section of the [xui, ago, it is interesting to find his formula foi* euxanthon, which was also that of Erdmann, confirmed by the recent experiments of Baeyer. The interesting work of Dewar on the oxidation of picoline must not be passed over without notice. By the action of the permanganate of potassium on that body, he has obtained a new acid which bears the same relation to pyridine that phthalic acid does to benzol. Thorpe and Young have pub- lished a preliminary notice of some results of great promise which they have obtained by exposing paraffin to a high temperature in closed vessels. By this treatment it is almost completely resolved into liquid hydrocarbons, whose boiling- points range from 18° C. to 300° C. Those boiling under 100° have been examined, and consist chiefly of defines. In con- nexion with this subject, it may be interesting to recall the experiments of Pelouze and Cahours on the Pennsylvanian oils, which proved to be a mixture of carbohydrogens Tjelonging to the marsh-gas series. An elaborate exposition of Berthelot's method of transforming an organic compound into a hydrocarbon containing a maximum of hydrogen has appeared in a connected form. The organic body is heated in a sealed tube, with a large excess of a strong solution of hydriodic acid, to the temperature of 275°. The pressure in these experiments Berthelot estimates at 100 atmospheres, but apparently without having made any direct measurements. He has thus prepared ethyl hydride (OjHg) from alcohol, aldehyde, etc., hexyl hydride (CgH^^) from benzol. Berthelot has submitted both wood-charcoal and coal to the reducing action of hydriodic acid, and among other interesting results he claims to have obtained in this way oil of petroleum. By the action of chloride of zinc upon codeia, Matthiessen and Burnside Have obtained apocodeia, which stands to codeia in the same relation as apomorphia to morphia, an atom of water being abstracted in its formation. Apocodeia is more stable than apomorphia, but the action of reagents upon the two bases is very similar. As regards their physiological action, the hydrochlorate of apocodeia is a mild emetic, while that of apomorphia is an emetic of great activity. Other bases have XLii.] British Aasociafiork 355 been obtained by Wright by the action of hydrobromic acid on eodeia. In two of these bases, bromotetracodeia and chloro- tetracodeia, four molecules of the eodeia are welded together, so that they contain no less than seventy-two atoms of carbon. They have a bitter taste, but little physiological action. The authors of these valuable researches were indebted to Messrs. Macfarlane for the precious material upon which they operated. "We are indebted to Crum Brown and Eraser for an important Work on a subject of great practical as well as theoretical interest,— ^the relation between chemical constitution and physiological action. It has long been known that the ferro- cyanide of potassium does not act as a poison on the animal system, and Bunsen has shown that the kakodylic acid, an arsenical compound, is also inert. Crum Brown and Fraser find that the methyl compounds of strychnia, brucia, and thebaia are much less active poisons than the alkaloids themselves, and the character of their physiological action is also different. The hypnotic action of the sulphate of methyl- morphium is less than that of morphia ; but a reverse result occurs in the case of atropia, whose methyl and ethyl de^ rivafcives are much more poisonous than the salts of atropia itself. Before proceeding to the subject of fermentation, I may refer to Apjohn's chemico-optical method of separating cane-sugar, inverted sugar, and grape-sugar from one another when present in the same solution, by observing the rotative power of the syrup before and after inversion, and combining the indications of the saccharometer with the results of an analysis of the same syrup after inversion. Heisch's test for sewage in ordinary water is also deserving of notice. It consists in adding a few grains of pure sugar to the water, and exposing it freely to light for some hours, when the liquid will become turbid from the formation of a well-marked fungus if sewage to the smallest amount be present. Frankland has made the important observation that the development of this fungus depends upon the presence of the phosphate, and that if this condition be secured, the fungus will appear even in the purest water. 356 Address to the Chemical Section of the [xwi. The nature of fermentation, and in particular of the alcoholic fermentation, has been lately discussed by Liebig with consummate ability, and his elaborate memoir will well repay a careful perusal. Dr. Williamson has also given a most instructive account of the subject, particularly with reference to the researches of Pasteur, in liis recent Cantor lectures. A brief statement of the present position of the question will therefore not be out of place here. It is now thirty-four years since Cagniard de La Tour and Schwann proved by inde- pendent observations that yeast-globules are organized bodies capable of reproduction by gemmation ; and also inferred as highly probable that the phenomena of fermentation are induced by the development or living action of these globules. These views, after having fallen into abeyance, were revived and extended a few years ago by Pasteur, whose able researches are familiar to every chemist. Pasteur, while acknowledging that he was ignorant of the nature of the chemical act, or of the intimate cause of the splitting up of sugar in the alcoholic fermentation, maintained that all fer- mentations properly so called are correlative with physio- logical phenomena. According to Liebig, the development and multiplication of the yeast-plant or fungus is dependent upon the presence and absorption of nutriment, which be- comes part of the living organism, while in the process of fermentation an external action takes place upon the substance, and causes it to split up into products which cannot be made- use of by the plant. The vital process and the chemical action, he asserts, are two phenomena which in the explanation must be kept separate from one another. The action of a ferment upon a fermentable body he compares to the action of heat upon organic molecules, both of which cause a movement in the internal arrangement of the atoms. The phenomena of fermentation Liebig refers now, as formerly, to a chemico- physical cause, — the action, namely, which a substance in a. state of molecular movement exercises upon another of highly complex constitution, whose elements are held together by a feeble affinity, and are to some extent in a state of tension or strain. Baeyer, who considers that in the alcoholic and lactic fermentations one part of the compound is re- xLii.] British Association. 357 duced and another oxidized, adopts the view of Liehig, that the molecules of sugar which undergo fermentation do not serve for the nourishment of the yeast-plant, but receive an impulse from it. All are, however, agreed that fermen- tation is arrested by the death of the plant; and even a tendency to the acetous fermentation in wine may be checked, as Pasteur has shown, by heating the wine to a temperature a little below the boiling-point in the vessel in which it is afterwards to be kept. I regret that the limits of an address like the present forbid me to pursue further this analysis of chemical work. Had they admitted of abridgment, I should gladly have described the elaborate experiments of Gore on hydrofluoric acid and the fluoride of silver. The important researches of Abel on ex- plosive compounds will be explained by himself in a lecture with which he has kindly undertaken to favour the Association. Mr. Tomlinson will also communicate to the Section some observations on catharism and nuclei, a difficult subject, to which he has of late devoted much attention. And I am also informed that we shall have important papers on recent improvements in chemical manufacture. No one can be more painfully alive than myself to the serious omissions in the historical review I have now read, more particularly in organic chemistry, where it was wholly impossible to grapple with the large number of valuable works which even a few months produce. I cannot, however, refrain from bearing an humble tribute to the great ability and in- domitable perseverance which characterize the labourers in the great field of organic chemistry. It would scarcely be possible to conceive any work more intelligently undertaken or more conscientiously performed than theirs, yet much of it, from its abstruse character, receiving Uttle sympathy or encouragement except from the band of devoted men who have made this subject the chief pursuit of their lives. They will, however, find their reward in the consciousness that they have not lived in vain, but have been engaged, and successfully engaged, in the noble enterprise of extending for the benefit of the human family the boundaries of scientific knowledge. Nor is there any real ground for discouragement. Faraday, Graham, 358 Address to Chemical Section of British Association, [xur. Magnus, and Herschel, who have left their impress on this age, were all distinguished chemical as well as physical discoverers ; and the relations of the sciences are becoming every day so intimate that the most special research leads often to results of wide and general interest. No one felt this truth more clearly or illustrated it better in his writings than our lamented and distinguished friend, Dr. Miller, whose presence used to cheer our meetings, and whose loss we all most sincerely deplore. S59 XLIIL— ON THE DICHRQISM OF THE VAPOUR OF IODINE. Prom the Jteport o/theBritUh Association, Edinburgh, 1871. The fine purple colour of the vapour of iodine arises from its transmitting freely the red and blue rays of the spectrum, while it absorbs nearly the whole of the green rays. The transmitted light passes freely through a red copper or a blue cobalt glass. But if the iodine vapour be sufficiently dense, the whole of the red rays are absorbed, and the transmitted rays are of a pure blue colour ; they are now freely transmitted, as before, by the cobalt glass, but wiU not pass through the red glass. A solu- tion of iodine in sulphide of carbon exhibits a similar dichroism, and according to its density appears either purple or blue when white light is transmitted through it. The alcoholic solution, on the contrary, is of a red colour, and does not exhibit any dichroism. 360 XLIV.— ON THE ACTION OP HEAT ON BROMINE. From the Report of the British Association, Edinburgh, 1871. If a fine tube is filled one half with liquid bromine and one half with the vapour of bromine, and after being hermetically sealed is gradually heated till the temperature is above the critical point, the whole of the bromine becomes quite opaque, and the tube has the aspect of being filled with a dark red and opaque resin. A measure of the change of power of trans- mitting light in this case may be obtained by varying the pro- portion of liquid and vapour in the tube. Even liquid bromine transmits much less light when heated strongly in an hermeti- cally sealed tube than in its ordinary state. 361 XLV.— ADDRESS ON OZONE. Delivered before the Royal Society of Edinburgh, 22nd December, 1873. From the Journal of the Scottish Meteorological Society. Towards the end of the last century, Van Mamm, while experimenting with his powerful electrical machine, observed that oxygen gas through which electrical sparks had been passed acquired a peculiar odour and the property of attacking mercury. This subject attracted no further attention for upwards of half a century after the publication of Van Marum's observations. The discovery of ozone was announced by Schonbein in a memoir which he presented in 1840 to the Academy of Munich. In this important communication he states that, in the electrolysis of water, an odorous substance accompanies the oxygen evolved at the positive pole ; that this substance may be preserved for a long time in well-closed vessels ; and that its production is influenced by the nature of the metal which serves as the pole, by the chemical properties of the electrolytic fluid, and by the temperature of that fluid as well as of the electrode. The same body he found to be produced by holding a strip of platinum or gold near the knob of the prime conductor of an electrical machine in good order. With great sagacity he recognised the identity of the peculiar odour which accompanies a flash of lightning with that of the new substance. In this memoir; Schonbein supposes the odorous body, for which in a note at the end he proposes the name of ozoTie, to be a new electro-negative element, belonging to the same class as chlorine and bromine ; and in a paper published a little later, he throws out the hint that ozone may be one of the constituents of nitrogen. Schonbein soon afterwards discovered that ozone is formed when phosphorus oxidizes slowly in moist air or oxygen. 362 Addres$ on Ozone. [xlv. In the following year he returned to the consideration of the subject, and, partly from his own observations, partly frbm experiments communicated to him by De la Eive and Marignac, he abandons his former view of the elementary nature of ozone, and concludes that it is an oxide of hydrogen, different from the peroxide of hydrogen of Thdnard. Many of the properties of ozone described by Schonbein were soon afterwards verified by Marignac, who found, as Schonbein had already stated, that it is only in the presence of moisture that air or oxygen, when passed over phosphorus, produces ozone, and that no ozone can be formed from air, even if moist, which has been deprived of its oxygen. He also confirmed the observations of Schonbein, that the peculiar properties of ozone disappear when it is heated to a temperature between ^^00° CJ. and 400° C, and that it is not absorbed by water or sulphuric acid. In a subsequent investigation (1845) which Marignac con- ducted with De la Eive, the important fact was established that ozone is formed by the passage of electrical sparks through pure and dry oxygen gas. Fr^my and Becquerel also showed that pure oxygen, contained in a tube inverted over a solution of iodide of potassium, is entirely absorbed by that liquid if electrical sparks are passed for a sufficiently long time through the gas. The last hypothesis of Schonbein, according to which ozone is an oxide of hydrogen, was manifestly inconsistent with the production of that body by the passage of electrical sparks through pure and dry oxygen. On the other hand, it received support from some experimental inquiries which appeared about this time, and particularly from an elaborate investigation which was conducted by Baumert in the laboratory of the University of Heidelberg, and published in PoggendoriFs Annalen for 1853. Baumert maintained that water is always formed when dry ozone prepared by electrolysis is destroyed or decomposed by heat ; and further endeavoured to establish its composition by determining the increase in weight of a solution of iodide of potassium when it is decomposed by ozone. He inferred, as the result of his researches, that two distinct bodies had been confounded under the name of ozone, — (1) allotropic XLV.] Address on Ozone. 363 oxygen, formed by the passage of the electrical spark through oxygen; and (2) a teroxide of hydrogen, produced in the electrolysis of water. The experiments and conclusions of Baumert attracted a great deal of attention at the time they were published, and received very general assent. Having repeated, soon after it was announced, the experiment of Baumert, in which ozone prepared by electrolysis was de- stroyed by heat, and having failed to obtain the slightest trace of water in numerous trials, I deemed it important to undertake a careful investigation of the subject, the results of which were communicated in 1853 to the Eoyal Society of London. By employing an acidulated solution of iodide of potassium, I found that its increase in weight, when decomposed by ozone, exactly agreed with the weight of the ozone calculated, as allotropic oxygen, from the iodine set free. The numbers, deduced from five careful experiments, were 0'1179 gramme for the increase in weight of the solution, and O'llVS gramme for the calculated weight of the oxygen. As regards the supposed formation of water in the destruction of ozone by heat, it may be sufficient to mention the results of two experiments, per- formed with great care, in one of which 6 '8 litres of electrolytic oxygen, containing 27 milligrammes of ozone, and in the other 9'6 litres of the same gas, containing 38 milligrammes, were exposed to the action of heat, so as to destroy all ozone reactions, when not a trace of water was obtained; the increase in weight of the desiccating apparatus being in the first case only one-third, and in the second case one-half, of a milli- gramme. If Baumert's experiments had been correct, 24 milligrammes of water should have been formed in these experiments. The general conclusions at which I arrived were : ' That no gaseous compound having the composition of a peroxide of hydrogen is formed during the electrolysis of water; and that ozone, from whatever source derived, is one and the same iody, having identical properties and the same constitution, and is not a compound body, hit oxygen in an altered or allotropic condition' {Phil. Trans, for 1856, p. 13). The next step in the investigation of this singular body was the discovery that oxygen gas, in changing into ozone, diminishes in volume, or becomes condensed, recovering its original volume 364 Address on Ozone. [XLV when the ozone is changed back into oxygen by the action of heat or otherwise. This relation between ordinary oxygen and ozone was first announced in 1860 by Professor Tait and myself, in a communication to the Eoyal Society of London. Oxygen gas in a dry and pure state was introduced into a tube sealed at one end, and terminating at the other in a fine tube, bent as shown in the figure, which contained a short column of sulphuric acid. Two platinum wires were hermetically sealed into the sides of the wide tube, the distance of the ends within the tube beinsr about 20 millimetres. When an electrical discharge, without \dsible sparks, was passed between the extremities of the platinum wires, the sulphuric acid rose in the adjacent leg of the U tube ; and from the change of level, the amount of the condensation, or diminution of volume, which the oxygen had undergone was easily calculated. The apparatus was then hermeti- cally sealed, and the reservoir heated to 270° C, so as to destroy the ozone. After allowing the reservoir to cool, the sealed end of the TJ tube was opened, when the original volume of the gas was found to be restored. Strong electrical sparks were found to give scarcely one-fourth of the contraction which occurred with the silent discharge ; and if sparks were passed through the gas when fuUy contracted by the silent discharge, the contraction was reduced to that which the spark would have produced in the original gas. In the same paper it was shown that no further diminution of volume occurred when the contracted gas was agitated with a solution of iodide of potassium, so as to absorb the ozone. A similar result was obtained on agitating the contracted gas with iodine. The ozone reaction in all these cases disappeared, but without any change in the volume of \ xLv.] Address on Ozone. 365 the gas. With mercury and silver not only was there no con- traction, but expansion actually occurred, which was explained on the assumption that the oxide at first formed exercised a catalytic action on a part of the ozone, and restored it to the state of ordinary oxygen. Similar results were obtained with electrolytic ozone. Three years later, these experiments on the condensation of oxygen in changing into ozone, and on the action of ozone upon a solution of iodide of potassium, were repeated and confirmed by Von Babo, and by Von Babo and Glaus. We did not attempt to give any absolute explanation of these singular facts, but discussed them under different aspects. We showed that, on the allotropic view of the constitution of ozone, its density must be enormously great ; unless it was assumed that, ' when ozone comes into contact with such sub- stances as iodine, or a solution of iodide of potassium, one portion of it, retaining the gaseous form, is changed back into common oxygen, while the remainder enters into combination, and that these are so related to one another that the expansion due to the former is exactly equal to the contraction arising from the latter,' On this assumption, which, however, we did not consider probable, we remarked that ' our experiments may be reconciled with the allotropic view and an ordinary density, but still one greater than that of oxygen.' A similar explana- tion of our experiments, but connected with a peculiar view of the molecular constitution of oxygen, was proposed in 1861 by Dr. Odling. ' If we consider,' he remarks, ' ozone to be a compound of oxygen with oxygen, and the contraction to be consequent upon their combination, then, if one portion of this combined or contracted oxygen were absorbed by the re-agent, the other portion would be set free, and by its liberation might expand to the volume of the whole. Thus, if we suppose three volumes of oxygen to be condensed by their mutual combination into two volumes, then, on absorbing one-third of this combined oxygen by mercury, the remaining two-thirds would be set free, and consequently expand to their normal bulk, or two volumes : — - + - + + - + - O + Hg2 = Hg2 0-HO 0.' 366 Address on Ozone. [xlv. Soret, experimenting in 1866 upon the mixture of oxygen and ozone obtained by electrolysis, made the important dis- covery, that if this mixture is brought into contact with oil of turpentine or oil of cinnamon, a diminution of volume takes place equal in amount to twice the augmentation of volume which the same mixture would sustain if the ozone were con- verted by heat into ordinary oxygen. In other words, the volume of ozone, measured by its absorption by the essential oil, is twice as great as the difference between the volume of the same ozone and oxygen. Hence, Soret concluded that the density of ozone is one and a half times that of oxygen gas. The latest investigations on this subject are due to Meissner and Brodie. The former has fully confirmed my early experi- ments, according to which the increase in weight of an acid solution of iodide of potassium, when electrolytic ozone is passed through it, corresponds exactly to the weight of oxygen absorbed, as calculated from the liberated iodine. Meissner has also found, as I had long before stated, that when a neutral solution of iodide of potassium is employed, the results are variable and untrustworthy. Brodie has examined the action of ozone on a variety of liquids, and has confirmed the results of Professor Tait and myself, — that no diminution of volume occurs when ozone is removed from a mixture of ozone and oxygen by a solution of iodide of potassium. With other liquids he has obtained volu- metric results which he considers to be .definite, and which differ from any previously observed. I am inclined to think that they are rather complex cases, involving the volumetric changes already known in variable proportions. His experi- mental results, moreover^ when examined in detail, do not appear to be sufficiently concordant to justify the sharp con- clusions he has deduced from them. Brodie has obtained for ozone prepared by the electrical discharge the same density (one and a half times that of oxygen) which Soret had previously obtained for ozone pre- pared by electrolysis. He considers a suggestion of Professor Tait and myself, that oxygen may possibly be decomposed by the electrical discharge, not to be supported by the facts he has observed. xLv.] Address on Ozone. 367 I will now give a brief statement of the methods of preparing ozone, and of its leading properties. Ozone may be obtained by the action of the electrical spark, or the glow or silent discharge, on pure oxygen. With the silent discharge, as has been before stated, a much larger proportion of the oxygen is converted into ozone than with the spark ; and if sparks are passed through oxygen containing its maximum amount of ozone, the greater part of the ozone will be rapidly destroyed, or rather changed back into ordinary oxygen. Thus, in an experiment performed by Professor Tait and myself, a contraction of 20 millimetres in the volume of the oxygen from the passage of the silent discharge was reduced to a contraction of only 4 millimetres by the spark discharge. As regards the actual amount of oxygen which, under the most favourable conditions, can be converted into ozone, the highest recorded result is an experiment by Professor Tait and myself, in which a contraction of one-twelfth of the original volume of the oxygen, or 8 '3 per cent., occurred; but we were unable in other trials to obtain again so great a diminution of volume. The largest contraction attained in the experiments of Von Babo and Glaus amounted to 5"74, and in those of Brodie to 6'52 per cent. The doubt which existed as to the accuracy of our solitary experiment I have lately been able to remove, and, by the aid of the excellent induction tube of Siemens, I have succeeded in attaining greater contractions than any hitherto recorded. In one of the first trials the diminution of volume amounted to more than 10 per cent. ; and there can be little doubt that with care even greater contractions than this may be attained. As the method referred to enables the contraction of oxygen in changing into ozone to be exhibited as a class experiment, I will describe it in some detail. The induction tube of Siemens, in which the electrical discharge from an induction coil acts upon air or oxygen as it flows between two thin plates of glass, whose surfaces are at a distance of a few millimetres from one another, has hitherto been employed to obtain a continuous stream of ozone in a more or less concentrated state. But this apparatus can easily be modified, so as to show the contraction which takes place when oxygen is converted into ozone. Fig. 1 368 Address on Ozone. [XLV. exhibits the modification I have given for this purpose to the ordinary form of Siemens' tube. At C it terminates in a capillary tube, the end, of which is hermetically sealed after a stream of pure and dry oxygen gas has been passed through Piff-l the apparatus for a sufiicient time to displace the air. In exact experiments the end b is also sealed, and afterwards opened under sulphuric acid. For class purposes it will be found sufficient to immerse it quickly under the acid contained xLv.] Address on Ozone. 369 in the beaker a, as shown in Fig. 2, where the induction tube is seen surrounded to within 12 millimetres of its upper surface with water contained in an insulated ' cylindrical vessel (A A'). The inner cavity of the induction tube is also filled with water to about the same level. By means of wires covered with caoutchouc except at the lower ends (p p'), the discharge from an induction coil, capable of giving 1 niillimeti-e sparks in air, can be passed through the apparatus. The water in A A' is maintained as steadily as possible at the temperature of the apartment, and any slight changes of temperature in the course of the experiment are noted by means of a delicate thermometer. The variations of the barometer are also carefully observed. In very exact experiments the surfaces of the induction tube should be covered with tinfoil, and the cylindrical vessel filled with ice. Before commencing the observation, it will be found convenient, if the temperature has not already effected the adjustment, to expel a little oxygen from the induction tube, so that the level of the acid may stand somewhere about V. On passing the electrical discharge, the acid will at first be depressed a few millimetres, from the repulsive action of the particles of the electrified gas, but will afterwards steadily rise, and for some time with such rapidity that the ascent of the column can be easily followed by the eye. When the current is interrupted, a sudden rise of the acid column will occur, equal to the depression which took place on first making connection with the induction coil, after which the new level of the acid may be read. Another method of obtaining ozone is by the electrolysis of water, and of certain acid and sahne solutions. The most convenient liquid for this purpose is a mixture of 1 part of sulphuric acid and 6 or 8 parts of water ; and the lower the temperature at which the electrolyte is maintained during the process, the greater is the amount of ozone. The simplest and most efficacious arrangement for obtaining ozone by this method is one I have used for many years, and exhibited in my lectures. It consists of a glass bell jar (a), open below, and contracted to a neck above, into which a bent connecting tube is fused. This bell jar is suspended in a round cell (h ¥) of porous earthenware, leaving a clear space of two inches between its 2a 370 Address on Ozone. [XLV. lower edge and the bottom of the j)orous cell. The whole is placed in a glass jar (c e') of somewhat larger dimensions than the cell ; a bundle of platinum wires (p) suspended below the beU jar acts as the positive pole, and a broad ribbon of platinum (n n'), placed between the outer glass jar and the porous cell, as the negative pole of a voltaic arrangement of three or four couples. Prom the bell jar the mixture of oxygen and ozone disengaged at the positive pole passes to a sulphuric acid drying tube (d), and thence through the connecting tube (e) to other tubes, for the purpose of illustrating the properties of 1^==* ozone. Thus, in the figure it is represented as traversing a tube of hard glass (//') covered with fine wire gauze, and terminating near the surface of mercury contained in the flask (h). So long as the gas is heated strongly as it passes through the tube (ff) by the spirit lamps (g g'), not the slightest change is produced upon the mercury ; but when the lamps are removed, and the tube allowed to cool, the mercury is rapidly attacked. I ought, perhaps, to mention that all the junctions are made with dry and tightly fitting corks, care being taken that the ends of the connecting tubes project a little beyond the corks. With these precautions, the loss of ozone from its action on the corks is altogether insignificant. Ozone can also be obtained by the slow oxidation of phos- phorus and of certain ethers and essential oils in presence of moisture. xLv.] Address on Ozone. 371 Several of the properties of ozone have already been referred to. At the common temperature of the atmosphere it may be preserved, if dry, for a very long time in sealed tubes, but by slow degrees it becomes changed again into ordinary oxygen. This conversion goes on more rapidly as the temperature is raised, and at 237° C. it is almost instantaneous (PMl. Trans. 1856, p. 12). The alteration of volume which occurs at the same time has been already sufficiently described. A similar ■effect to that of heat is produced by several oxides, such as the ■oxide of silver or the peroxide of manganese, which by contact, or, as it is termed, catalytically, instantly change ozone into ■■Drdinary oxygen. Ozone is also destroyed by agitation with water, provided the ozone is in a highly diluted state. But the most singular fact of this kind is one which I have recently observed, and which I hope to be able to exhibit to the Society. Dry ozone, even if present in such quantities as freely to redden iodide of potassium paper, is readily de- stroyed by agitating it strongly with glass in fine fragments, although, as we have seen, it may be preserved for almost an indefinite period in sealed glass tubes. This experiment, as it appears to me, forms a new and closer link than any hitherto observed between a purely mechanical action and a chemical ■change. Ozone is a powerful oxidizing agent. It attacks metallic mercury and silver with great energy, and converts them into •oxides. The experiment with mercury is very striking, and is a delicate test for ozone, either in the dry or moist state. A few bubbles of oxygen, containing not more than -gwth part of •ozone, will alter wholly the physical characters of several pounds <:>{ mercury, taking away the lustre and convexity of the metallic surface, and causing the mercury to form an adhering mirror to the surface of the glass vessel in which it is contained. If •ozone in a diluted state is slowly passed through a tube filled with .silver leaf, the metal will be oxidized to the distance of 2 •or 3 millimetres, but the oxidation will not proceed further although the ozone reactions are wholly destroyed. This strik- ing result is due to the catalytic action of the portions of oxide which are at first formed. So small is the amount of oxide produced in this case, that in a glass tube through which many 372 Address on Ozone. [xlv. litres of electrolytic ozone had been passed, the increase in weight from the formation of oxide scarcely amounted to an appreciable fraction of a milligramme. The action of water on ozone, when the latter is present in small quantities, is probably also of a catalytic character. If a bottle containing a little water, and filled with air or oxygen, mixed with a sufficient amount of ozone to redden instantly iodide of potassium paper, is shaken violently for a few minutes, all the ozone reactions will disappear. Ozone is insoluble in water, which cannot therefore acquire its odour or any of its. other properties. Ozone is absorbed by oil of turpentine, oil of lemon, and other essential oils. These oils have also, like phosphorus, the power of changing oxygen into ozone while they are slowly oxidizing ; so that, if oil of turpentine is shaken for some time in a flask filled with air or oxygen, the oil will acquire ozone properties. Ozone decomposes a solution of iodide of potassium, liberat- ing the iodine, which may be discovered by its red colour, or its blue compound with starch. If the action is continued sufficiently long, the free iodine disappears from the formation of iodate of potassium, and the solution becomes colourless. Eeddened litmus paper moistened with a solution of iodide of potassium is turned blue when exposed to the action of ozone, in consequence of the caustic alkali formed by the decomposi- tion of the salt. In employing this test it will be found advantageous to remove the free iodine by washing the paper with strong alcohol. This form of the iodide of potassium test has been proposed by Houzeau for the discovery of ozone in the atmosphere. Ozone produces other reactions of a similar character, which it will be sufficient here barely to mention. Paper moistened with sulphate of manganese becomes brown when exposed to this agent, from the formation of the hydrated peroxide. Solutions of thallous oxide are in Yika manner converted into the brown peroxide, the black sulphide of lead into the white sulphate, and the yellow ferrocyanide of potassium into the red salt. The action of ozone on tincture of guaiacum, which it turns blue, was made a subject of special study by Schonbein. xLv.] Address on Ozone. 373 The bleaching properties of ozone are highly characteristic, and have attracted a great .deal of attention. It deprives indigo of its blue colour, converting it into isatin, and bleaches readily litmus and other vegetable colouring matters. Attempts have been made to apply this property of ozone in the arts, and particularly to the refining of sugar and the bleaching of linen. It has been stated that these and other applications of ozone, as a decolorizing or bleaching agent, have been success- ful ; but the results of my inquiries on this point have, I regret to say, been unfavourable, and it remains yet to be seen whether this singular body can be made subservient to the useful purposes of life. For the preparation of ozone on the large scale from ordinary air, a modification of the excellent tube generator of Siemens has been proposed by Beanes, and is an efScient and powerful instrument. I will not detain the Society by an account of the history or properties of the problematical body to which Schonbein gave the name of antozone. He considered this body to be oxygen possessing permanently positive properties, while ozone itself he regarded as negative oxygen. Ordinary or inactive oxygen, according to him, is formed by the union of ozone and antozone. These views have not been supported by recent investigations, which leave little doubt that the antozone of Schonbein is identical with the peroxide of hydrogen of Th(5nard. Soon after the discovery of ozone, Schonbein, having observed that the air of the country frequently coloured a delicate ozone test-paper in the same manner as ozone itself, inferred that ozone is a normal constituent of our atmosphere. He concluded that the amount of this body present in air is different in different localities, and in the same locality at different times ; and with great boldness he attempted to con- nect its presence or absence with the prevalence or rarity of certain catarrhal affections. A new field for investigation was thus opened up, which has been assiduously cultivated by a large and zealous band of observers. Before referring, however, to their labours, it will be necessary briefly to allude to the present state of our knowledge regarding the existence of ozone in the atmosphere. 374 Address on Ozone. [xlv- Schonbeiu always maintained that ozone is a constituent of atmospheric air, and his various , papers on this subject alone would, if collected, fill a large volume. In his last memoir he observes, that the active substance in the air acts in a parallel manner on iodide of potassium and suboxide of thallium papers, although more slowly on the latter ; and that the thallium paper which has been coloured brown by the air behaves towards re-agents in the same manner as that which has been exposed to artificial ozone. From these facts he infers that the active substance in the air is neither peroxide of nitrogen nor sulphuretted hydrogen. He further states that the atmos- phere never contains free nitric acid, although nitrate of ammonium in small quantities is often present ; and that neither chlorine nor bromine can be present in the free state in air on account of their affinity for hydrogen. Houzeau also maintained that the existence of ozone in the air was proved by the alkaline reaction of iodide of potassium paper which had been decomposed by exposure to the atmosphere. Altliough experiments and arguments of this kind were sufficient to give probability to the view that the active substance in the atmos- phere which produces these reactions is ozone, they were at the same time far from conclusive ; and some of the ablest chemists, accordingly, considered the question doubtful, while others attributed the effects observed to the presence of oxidiz- ing agents altogether different from ozone. I will only cite on this point the opinion of M. Fremy, whose researches, in con- junction with M. Becquerel, on ozone have already been referred to. ' Without denying,' he remarked at a meeting of the Academy of Sciences in 1865, 'the importance of the indications given by the paper of M. Schonbein or by that of M. Houzeau, I do not find that these reactions demonstrate with sufficient certainty the existence of atmospheric ozone. 1 am of opinion that the presence of ozone in the air m\ist be established anew by incontestable experiments.' In 1867 I made a set of experiments which I had contem- plated some years before, for the purpose, if possible, of finally settling this important question. The method I proposed was to ascertain whether, in addition to the power of decomposing solutions of iodide of potassium and of certain other salts, the XLV.] Address on Ozone. 375 active body in the atmosphere possessed the other properties of ozone, some of which are highly distinctive. The inquiry was a delicate one, in consequence of the very minute quantity of the active body which is present, even under the most favourable conditions, in atmospheric air. The results of this investigation are given in a short note which was published in the Proceedings of the Royal Society for 1867 [p. 294, above]. (1) By passing a stream of atmospheric air, which gave the usual reaction with iodide of potassium paper, for some hours over the surface of mercury in a U tube, the metal was distinctly oxidized. (2) The ozone i-eactions disappeared TO ASPIRATOR- A, glass globe covered with wire gauze. B, burner to raise A to 260 C. C 0, U tube moistened internally with water, p, iodide of potassium paper. C C was immersed in a vessel of cold water, which is not represented. ,^-V -™, when the air was passed through a tube containing pellets of dry oxide of manganese. The experiment was continued till 80 litres of air had traversed the manganese tube without producing the slightest discoloration of a delicate test-paper. (3) But the crucial experiment was to ascertain whether the active body in the air loses its characteristic properties, or is destroyed, at about the same temperature (237° C.) as ozone. 376 Address on Ozone. [xlv. To determine this point, a steady stream of atmospheric air which gave strong ozone reactions was passed through a glass globe, covered with wire gauze, of 5 litres capacity, and after- wards through a U tube, one metre in length, whose sides were moistened internally with water, while the tube itself was kept cool by being immersed in a vessel of cold water. After traversing the glass globe and the moistened U tube, the air flowed- over a slip of delicate test-paper, in order to ascertain the presence or absence of ozone. When the atmospheric air was drawn through this apjDaratus at a uniform rate by means of an aspirator raised by clock-work, the iodide of potassium paper was distinctly reddened in two or three minutes, pro- vided no heat was applied to the globe. But on heating the air, as it passed through the globe, to a temperature of about 2.60° C, not the slightest action was produced on the paper, however long the current of air continued to pass. On the other hand, when air free from ozone, but containing traces of chlorine, or of the higher oxides of nitrogen, was drawn through the apparatus, the test-papers were equally affected whether the globe was heated or not. These experiments have since been successfully repeated by Dr. C. Fox. The identity of the active body in the atmosphere with ozone we may now assume to be established beyond dispute, and the accuracy of Schonbein's views on this subject to be fully con- firmed. To determine, however, the actual amount of ozone in the atmosphere is a problem of surpassing difficulty, on account of the extremely small proportion in which it exists, even when at a maximum. Its presence can be easily discovered by any of the ordinary iodized starch papers, or even more readily by white bibulous paper which has been moistened with a dilute solution of iodide of potassium and allowed to dry spontaneously in a dark room. If a slip of this paper is exposed for five minutes to a current of air, which will often be supplied by the wind, or may be produced by walking briskly, it will be found to have acquired a delicate red tint if ozone be present even in the smallest quantities. The tint will be best ob- served by comparing the slip after exposure with another slip of the same paper which has not been exposed. The action of the diffused light of day on the paper is rarely XL v.] Address on Ozone. 377 perceptible after so short an exposure, but this source of error ■can be easily avoided by enclosing the paper in a hollow •cylinder of wood. Although, with the experimental resources now at our ■command, we can scarcely venture even to estimate the actual amount of ozone at any time present in the atmosphere, yet it may be possible, as Schonbein long ago proposed, by applying a chromatic scale to the indications of the test-papers, to ascertain approximately its relative amount in different localities and its variations in the same locality. Such estimates must, however, be most uncertain, since the shades of colour produced •on test-papers hardly admit of being defined by numbers ; and in this particular case they are liable to a special source of ■error, as there can be little doubt that a large but unknown part of the ozone in the air which comes into contact with the paper is catalytically destroyed, and produces no chemical •effect whatever. At the same time the ozonometer, especially when used with an aspirator, does unquestionably give indica- tions of value regarding the ozone states of the atmosphere ; and, till more accurate methods are devised, these observations ought certainly to be continued. Ozone is rarely found in the air of large towns, unless in a suburb when the wind is blowing from the country ; and it is only under the rarest and most exceptional conditions that it is found in the air of the largest and best ventilated apartments. It is, in fact, rapidly destroyed by smoke and other impurities which are present in the air of localities where large bodies of men have fixed their habitations, and I have often observed this destructive action extending to a •distance of one or two miles from a manufacturing town, even in fine and bright weather. Ozone is rarely, if ever, absent in fine weather from the air of the country; and it is more abundant, on the whole, in the air of the mountain than of the plain. It is also said to occur in larger quantity near the sea than in inland districts. It has been found to an unusual amount after thunderstorms, — a fact which is favourable to the view that the presence of ozone in the atmosphere is due to the action of the free electricity of the latter on the oxygen of the air. The amount 378 Address on Ozone. [xlv. of ozone in the air is greater, according to some observers, in winter than in summer, in spring than in autumn ; according to others, it is greater in spring and summer than in autumn and winter. As regards the influence of day and night, the observations do not all tell the same tale. Ozone has usually been found more abundantly in the air at night than by day,, but some careful observers have found the reverse of this statement to be true. Schonbein was the first who attempted to connect the fluc- tuations of atmospheric ozone with the prevalence or absence of epidemic disease ; and since this suggestion was first pub- lished, numerous observations have been made in different countries, with the view of ascertaining whether there is really any connection between the indications of the ozonometer and the health of a district. It has been asserted, for example, as the result of observation, that an outbreak of cholera is accom- panied by a marked diminution of atmospheric ozone ; but this- statement has been disproved by later and more trustworthy observations. On the whole, I think it may he safely asserted that no connection has yet been proved to exist between the amount of ozone in the atmosphere and the occurrence of epidemic and other forms of disease. The permanent absence of" ozone from the air of a locality may, however, be regarded as a proof that we are breathing, if I may venture to use the phrase, adulterated air. Its absence from the air of towns and of large- rooms, even in the country, is probably the chief cause of the difference which every one feels when he breathes the air of a town or of an apartment, however spacious, and afterwards inhales the fresh or ozone-containing air of the open country. It is, indeed, highly probable that many of the most important actions by which the products of vegetable and animal waste are removed by oxidation from the air are due to the action of ozone, and could not be effected by ordinary or inactive oxygen. If the amount of ozone in the atmosphere appear too small tO' produce such large results, we must remember that, from its powerful affinities, ozone is being continually used up, and must therefore be constantly renewed. The physiological action of ozone on the animal system is a subject of interest, and I am able to state the general results of ^Lv.] Address on Ozone. 37f> two independent inquiries, — one conducted, a few years ago, by Dr. Eedfern, in Queen's College, Belfast, the other recently communicated to this Society by Mr. Dewar and Dr. M'Ken- drick. Dr. Kedfern's experiments have not been published, but he has kindly supplied me with the following note on the subject: — 'The general results,' he says, 'I obtained from about forty experiments, conducted from May to September 1857, to find the effects of oxygen and ozone on different animals were as follows: — The respiration for a very short time of oxygen containing about l-240th part of ozone is certainly fatal to all animals. The same gas, when passed over peroxide of manganese and freed from ozone, is comparatively harmless, even when respired for long periods. Eespiration of such a mixture of ozone for 30 seconds kills small animals, some dying after respiring it only 1 5 seconds ; whilst similar animals will live in good health for months after respiring oxygen alone for 37 hours, the carbonic acid being removed during the experiment. Death is not due to the closure of the glottis, for it occurs when a large opening has been made in the trachea. Ozone causes death by producing intense con- gestion of the lungs, with emphysema, and distension of the right side of the heart with fluid or coagiilated blood, frequently attended by convulsions. If ozone be respired iii a dilute form, the animals become drowsy, and die quietly from coma, the condition of the lungs and heart being the same, except that the emphysema is less marked. Animals which have respired oxygen for more than twelve hours will now and then die suddenly from the formation of coagula in the heart, even after they have appeared in good health for some days.' The following are the conclusions which Mr. Dewar and Dr. M'Kendrick have deduced from their researches; — Inhala- tion of an atmosphere highly charged with ozone diminishes the number of respirations per minute, and reduces the cardiac pulsations in strength, the temperature of the animal being at the same time lowered from 3° to 5° C. After death the blood is found to be in a venous condition. Neither the capillary circulation nor the reflex activity of the spinal chord is appre- ciably affected. The same remark applies to the contractility 380 Add^'ess on Ozone. [xlv. and work-power of the muscles. Ozone acts on the coloured and colourless corpuscles of human and frog blood like a weak acid, and in the case of the coloured corpuscles of the frog like carbonic acid. Ciliary action is not affected by ozonized air or oxygen ; but if the layer of liquid be very thin, the cilia are readily destroyed. The thermal changes which accompany many of the re- actions of ozone are well marked, and their investigation, which has been undertaken by Mr. Dewar, promises to yield a valu- able addition to our thermo-chemical knowledge. 381 XLVI.— ON THE COMPOSITION OF AN INFLAMMABLE GAS ISSUING FEOM BELOW THE SILT-BED IN BELFAST. From the Report of the British Association, Belfast, 1874. In sinking for a well upon the premises of Messrs. Cantrell and Cochrane, in George's Lane, Police Square, Belfast, after having passed through a deposit of silt to the depth of 3 3 feet, a layer of gravel was reached, seven feet in thickness, and containing a quantity of organic debris. It rested upon a thick deposit of very tenacious clay. On entering the gravel-bed, a large flow of water occurred, which rose to within four feet of the surface of the ground, and interrupted the operation of boriag, till a pump, worked by a small steam-engine, was erected, which, so long as it was in action, kept the boring free from water as far as the surface of the gravel-bed. A workman, having lowered a light to examine the bottom of the well, was surprised to see a lambent flame playing over the surface. On examination, this was found to arise from a disengagement of inflammable gas, which had accumulated between the lower surface of the bed of silt and the layer of gravel. An iron pipe, terminating in a funnel-shaped mouth, about one foot in diameter, was now sunk tUl it reached the gas stratum, and the water in the well was kept by pumping at such a level that an extra pressure of about one inch of water was maintained upon the gas below. The gas now flowed freely, at the rate of about 40 cubic inches per minute, through the upper end of the iron pipe, and when ignited, burned with a yellow flame, which could scarcely be distinguished from that of ordinary coal gas. Two portions of the gas were carefullj' collected by displace- ment, the stream of gas being allowed to pass till the whole of the atmospheric air in the vessels was completely swept away. The connecting tubes were then carefully sealed, and the gas was afterwards analysed in the laboratory of Queen's College. A measured volume of the gas, standing over mercury, was 382 On the Composition of an Inflammahle Gas. [xlvi. exposed to the action, first, of caustic potash, and afterwards of pyrogallic acid, and the residual gas was afterwards analysed, with the following results : — ' V. T. B. a Atmospheric air. 78-7 12-2 770-6 30 8-8 After addition of residual gas, 120-5 12-4 771-5 272-2 After addition of oyxgen. 190-0 12-8 771-8 221-8 After explosion, 126-5 13-0 771-7 271-6 After action of potash, , 90-0 11-8 772-0 299-7 In this table V is the volume of the gas ; T its temperature in centigrade degrees ; B the height of the barometer in milli- metres ; and G the height of the mercury in the tube in whicli the observations were made. From these data and the results of the previous action of the caustic potash and pyrogallic acid, it follows that the composition of the gas was : — Marsh gas (CHJ, 83-75 Carbonic acid, 2-44 Oxygen, 1-06 Nitrogen, 12-75 The density of the gas (air=l) was found to be 0-661, which corresponds nearly to the foregoing composition. The gas was inodorous and contained no compound of carbon and hydrogen except marsh gas. From this analysis, it is evident that the gas formed in this subterranean sheet of water is in all respects the same as that which is produced in stagnant pools containing leaves and other vegetable matters. 383 XLVII.— PEELIMINARY NOTICE OF FURTHER RESEARCHES ON THE PHYSICAL PROPERTIES OF MATTER IN THE LIQUID AND GASEOUS STATES UNDER VARIED CONDI- TIONS OF PRESSURE AND TEMPERATURE. From the Procevdiwjs of the Roijal Society, vol. 23, No. 163, 1875, p. 514. The iavestigation to which tl)is note refers has occupied me, with little intermission, since my former communication in 1869 to the Society, " On the Continuity of the Liquid and Gaseous States of Matter." It was undertaken chiefly to ascertain the modifications which the three gxeat laws dis- covered respectively by Boyle, Gay-Lussac, and Dalton undergo when matter in the gaseous state is placed under physical conditions differing greatly from any hitherto within the reach of observation. It embraces a large number of experiments of precision, performed at different temperatures and at pressures Tanging from twalve to nearly three hundred atmospheres. The apparatus employed is, in all its essential parts, similar to that described in the paper referred to ; and so perfectly did it act that the readings of the cathetometer, at the liighest pressures and temperatures employed, were made with the same ease and accuracy as if the object of the experiment had been merely to determine the tension of aqueous vapour in a barometer-tube. In using it the chief improvement I have made is in the method of ascertaining the original volumes of the gases before compression, which can now be known with much less labour and greater accuracy than by the method I formerly described. The lower ends of the glass tubes contain- ing the gases dip into small mercurial reservoirs formed of thin glass tubes, which rest on ledges within the apparatus. This arrangement has prevented many failures in screwing up the apparatus, and has given more precision to the measure- ments. A great improvement has also been made in the method of preparing the leather- washers used in the packing 384 Further Researches on Physical Properties of [xlvh. for the fine screws, by means of which the pressure is obtained. It consists in saturating the leather with grease by heating it in vacuo under melted lard. In this way the air enclosed within the pores of the leather is removed without the use of water, and a packing is obtained so perfect that it appears, as- far as my experience goes, never to fail, provided it is used in a vessel filled with water. It is remarkable, however, that the same packing, when an apparatus specially constructed for the purpose of forged iron was filled with mercury, always yielded, even at a pressure of 40 atmospheres, in the course of a few days. It is with regret that I am still obliged to give the pressures in atmospheres as indicated by an air- or hydrogen-manometer, without attempting for the present to apply the corrections required to reduce them to true pressures. The only satis- factory method of obtaining these corrections would be to compare the indications of the manometer with those of a column of mercury of the requisite length ; and this method, as is known, was employed by Arago and Dulong, and after- wards in his classical researches by Eegnault, for pressures reaching nearly to 30 atmospheres. For this moderate pres- sure a column of mercury about 23 metres, or 75 feet, in length had to be employed. For pressures corresponding to 500 atmospheres, at which I have no difficulty in working with my apparatus, a mercurial column of the enormous height of 380 metres, or 1250 feet, would be required. Although the mechanical difficulties in the construction of a long tube for this purpose are perhaps not insuperable, it could only be mounted in front of some rare mountain escarpment, where it would be practically impossible to conduct a long series of delicate experiments. About three years ago I had the honour of submitting to the Council of the Society a proposal for con- structing an apparatus which would have enabled any pressure to be measured by the successive additions of the pressure of a column of mercury of a fixed length ; and working drawings of the apparatus were prepared by Mr. J. Cumine, whose services I am glad to have again this opportunity of acknow- ledging. An unexpected difficulty, however, arose in conse- quence of the packing of the screws (as I have already stated) xLviT.] Matter in the Liquid and Gaseous States. 385 not holding when the leather was in contact with mercury instead of water, and the apparatus was not constructed. For two years the problem appeared, if not theoretically, to be practically impossible of solution ; but I am glad now to be able to announce to the Society that another method, simpler in principle and free from the objections to which I have referred, has lately suggested itself to me, by means of which it will, I fully expect, be possible to determine the rate of compressibility of hydrogen or other gas by direct reference to the weight of a liquid column, or rather of a number of liquid columns, up to pressures of 500 or even 1000 atmospheres. For the present it must be understood that, in stating the following results, the pressures in atmospheres are deduced from the apparent compressibility, in some cases of air, in others of hydrogen gas, contained in capillary glass tubes. In this notice I will only refer to the results of experiments upon carbonic acid gas when alone or when mixed with nitrogen. It is with carbonic acid, indeed, that I have hitherto chiefly worked, as it is singularly well adapted for experiment ; and the properties it exhibits wiU doubtless, in their main features, be found to represent those of other gaseous bodies at corresponding temperatures below and above their critical points. Liquefaction of Carbonic Acid Gas. — The following results have been obtained from a number of very careful experiments, and give, it is believed, the pressures, as measured by an air- manometer, at which carbonic acid liquefies for the tempera- tures stated : — Pressure in atmospheres. 35-04 40-44 47-04 53-77 61-13 65-78 70-39 I have been gratified to find that the two results (for 13°- 09 and 21°-46) recorded in my former paper are in close agree- 2b Temperatures in Centigrade degrees. 5-45 11-45 16-92 22-22 25-39 28-30 386 Further Researches on Physical Properties of [xlvii. ment with these later experiments. On the other hand, the pressures I have found are lower than those given by Eegnault as the result of his elaborate investigation (Memoires de r Academic des Sciences, vol. xxvi. p. 618). The method employed by that distinguished physicist was not, however, fitted to give accurately the pressures at which carbonic acid gas liquefies. It gave, indeed, the pressures exercised by the liquid when contained in large quantity in a Thilorier's reservoir ; but these pressures are always considerably in excess of the true pressures in consequence of the unavoidable pres- ence of a small quantity of compressed air, although the greatest precautions may have been taken in filling the apparatus. Even -5-517 part of air will exercise a serious dis- turbing influence when the reservoir contains a notable quantity of liquid. Zaw of Boyle. — The large deviations in the case of carbonic acid at high pressures from this law appeared distinctly from several of the results given in my former paper. I have now finished a long series of experiments on its compressibility at the respective temperatures of 6°-7, 63°-7, and 100° Centigrade. The two latter temperatures were obtained by passing the vapours of pyroxylic spirit (methyl alcohol) and of water into the rectangular case with plate-glass sides in which the tube containing the carbonic acid is placed. The temperature of the vapour of the pyroxylic spirit was observed by an accurate thermometer, whose indications were corrected for the unequal expansion of the mercury ; while that of the vapour of water was deduced from the pressure as given by the height of the barometer and a water-gauge attached to the apparatus. At the lower temperature (6°'7) the range of pressure which could be applied was limited by the occurrence of liquefaction ; but at the higher temperatures, which were considerably above the critical point of carbonic acid, there was no limit of this kind, and the pressures were carried as far as 223 atmospheres. I have only given a few of the results ; but they will be sufficient to show the general effects of the pressure. In the following Tables p designates the pressure in atmospheres as given by the air-manometer, f the temperature of the carbonic acid, e the ratio of the volume of the carbonic acid under one xLvii.] Matter in the Liquid and Gaseous States. 387 atmosphere and at the temperature f to its volume under the pressure p' and at the same temperature, and d the volume to which one volume of carbonic acid gas measured at 0° and 760 millimetres is reduced at the pressure p and temperature f. Carbonic Acid at 6°"7. p- t'. c. e. at. 13-22 6-90 1 14-36 0-07143 20-10 6-79 1 23-01 0-04456 24-81 6-73 1 29-60 0-03462 31-06 6-62 1 89-67 0-02589 40-11 6-59 1 5S--10 0-01754 Carbonic Acid at 63°-7. p- i'. e. e. at. 16-96 63-97 1 17-85" 0-06931 54-33 63-57 1 66-06 0-01871 106-88 63-75 185-9 0-00665 145-54 63-70 1 327-3 0-00378 222-92 63-82 1 446-9 0-00277 Carbonic Acid at 100°. 1^- t'. e. e. at. 16-80 100-38 1 17-33 0-07914 53-81 100-33 1 60-22 0-02278 105-69 100-37 1 137-1 0-01001 145-44 99-46 1 218-9 0-00625 223-57 99-44 1 380-9 0-00359 388 Further Researches on Physical Properties of [xlvii. These results fully confirm the conclusions which T formerly deduced from the behaviour of carbonic acid at 48°, viz. that while the curve representing its volume under different pressures approximates more nearly to that of a perfect gas as the temperature is higher, the contraction is nevertheless greater than it would be if the law of Boyle held good, at least for any temperature at which experiments have yet been made. From the foregoing experiments it appears that at 63°*7 carbonic acid gas, under a pressure of 223 atmospheres, is reduced to zxt of its volume under one atmosphere, or to less than one half the volume it ought to occupy if it were a perfect gas and contracted in conformity with Boyle's law. Even at 100° the contraction under the same pressure amounts to ^T part of the whole. Prom these observations we may infer by analogy that the critical points of the greater number of the gases not hitherto liquefied are probably far below the lowest temperatures hitherto attained, and that they are not likely to be seen, either as liquids or solids, till much lower temperatures even than those produced by liquid nitrous oxide are reached. Law of Gay-Lussctc. — That the law of Gay-Lussac in the case of the so-called permanent gases, or in general terms of gases greatly above their critical points, holds good at least at ordinary pressures, within the limits of experimental error, is highly probable from the experiments of Eegnault ; but the results I have obtained with carbonic acid will show that this law, like that of Boyle, is true only in certain limiting condi- tions of gaseous matter, and that it wholly fails in others. It will be shown that not only does the coefficient of expansion change rapidly with the pressure, but that, the pressure or volume remaining constant, the coefficient changes with the tem- perature. The latter result was first obtained from a set of preliminary experiments, in which the expansion of carbonic acid under a pressure of 17 atmospheres was observed at 4°, 20°, and 54°; and it has since been fully confirmed by a large number of experiments made at different pressures and well- defined temperatures. These experiments were conducted by the two methods commonly known as the method of constant pressure and the method of constant volume. The two xLvn.] Mattel' in the Liquid and Gaseous States. 389 methods, except in the limiting conditions, do not give the same values for the coefJicient of expansion ; but they agree in this respect, that at high pressures the value of that coefficient changes with the temperature. While I have confined this statement to, the actual results of experiment, I have no doubt that future observations will discover, in the case, at least, of such gases as carbonic acid, a similar but smaller change in the value of the coefficient for heat at low pressures. The numerous experiments I have made on this subject will shortly be communicated in detail to the Society; and for the present I will only give the following results: — Expansion of Heat of Carbonic Acid Gas under high pressures. Pressure. Vol. CO2 at 0° and 760milliins. =1. Vol. COo at 6° -05 and 22-26 at. = 1. 1 Temperature. at. 22-26 22-26 22-26 0-03934 0-05183 0-05909 1-0000 1-3175 1-5020 6°•05^ 63-79^ (A) 100-loJ Pressure. Vol. CO2 at 0° and 760 millims. = 1. Vol. CO2 at 6°-62 and 31-06 at. = 1. Temperature. at. 31-06 31-06 31-06 0-02589 0-03600 0-04160 1-0000 1-3905 1-6068 6-62. 63-83 - (B) 100-64J Pressure. Vol. CO2 at 0° and 760 millims. = 1. Vol. CO2 at 6°-01 and 40-06 at. = 1. Temperature. at. 40-06 40-06 40-06 001744 0-02697 0-03161 1-0000 1-5464 1-8123 6•01^ 63-641 (C) 100-60J 390 Further Researches on Physical Properties of [xlvii. Taking as unit 1 vol. of carbonic acid at 6°-05 and 22'26 atmospheres, we obtain from series A the following values for the coefficient of heat for different ranges of temperature: — «=0-005499 from 6°-05 to 63°-79. a=0-0Cr5081 from 63°-79 to 100°-1. From series B, with the corresponding unit volume at 6'-62 and 31'06 atmospheres, we find:^ — ■ a=0-006826 from 6°-62 to 63°-83. a=0-005876 from 63°-83 to 100°-64. And in like manner from series C with the unit volume at 6°-01 and 40*06 atmospheres: — a=0-009481 from 6°-01 to 63°-64. a=0-007l94 from 63°-64 to 100°-60. The coefficient of carbonic acid under one atmosphere re- ferred to a unit volume at 6° is a=0-003629. From these experiments it appears that the coefficient of ex- pansion increases rapidly with the pressure. Between the temperatures of 6° and 64° it is once and a half as great under 22 atmospheres, and more than two and a half times as great under 40 atmospheres, as at the pressure of 1 atmosphere. Still more important is the change in the value of the co- efficient at different parts of the thermometric scale, the pressure remaining the same. An inspection of the figures will also show that this change of value at different tempera- tures increases with the pressure. Another interesting question, and one of great importance in reference to the laws of molecular action, is the relation between the elastic forces of a gas at different temperatures while the volume remains constant. The experiments which I have made in this part of the inquiry are only preliminary, and were performed not with pure carbonic acid, but with a mixture of about 11 volumes of carbonic acid and 1 volume of air. It will be convenient, for the sake of comparison, to calculate, as is usually done, the values of a from these experi- ments ; but it must be remembered that a here represents no J[onger a coefficient of volume, but a coefficient of elastic force. Temperature. 13-70 Elastic Force, at. 22-901 40-63 25-741 ( 99-73 31-65J 13-70 31-181 35-44'- ( 44-29. 40-66 99-75 xLvii.] Matter in the Liquid and Gaseous States. 391 Elastic force of a mixture of 1 1 vol. CO^ and 1 vol. air heated under a constant volume to different temperatures. Vol. COg. 8661 366-2 40-63 25-74}- (A) 366-2 256-8 256-8 40-66 35-44 [- (B) 256-8 From series A we deduce for a unit at 13°-70 and 22-90 atmospheres: — a=0-004604 from 13°-70 to 40°-63. a=0-004367 from 40°-63 to 99°-73. And from series B: — «=0-005067 from 13°-70 to 40°-66. a=0-004804 from 40°-66 to 99°-75. The coefficient at 13°-70 and 1 atmosphere is a=0-003513. It is clear that the changes in the values of a, calculated from the elastic forces under a constant volume, are in the same direction as those already deduced from the expansion of the gas under a constant pressure. The value of a increases with the pressure, and it is greater at lower than at higher temperatures. But a remarkable relation exists between the coefficients in the present case which does not exist between the coefficients obtained from the expansion of the gas. The values of a, deduced for the same range of temperature from the elastic forces at different pressures, are directly propor- tional to one another. We have, in short, Q-QQ^^^^ = 0-9485, ^:^=0-9481. 0-004604 0-05067 How far this relation will be found to exist under other conditions of temperature and pressure will appear when ex- periments now in progress are brought to a conclusion. Zaw of Dalton. — This law, as originally enunciated by its author, is, that the particles of one gas possess no repulsive or attractive power with regard to the particles of another. 392 Physical ProTperties of Matter. [xlvii. " Oxygen gas," he states, " azotic gas, hydrogenous gas, carbonic acid gas, aqueous vapour, and probably several other elastic fluids may exist in company under any pressure and at any temperature without any regard to their specific gravities, and without any pressure upon one another." The experiments which I have made on mixtures of carbonic acid and nitrogen have occupied a larger portion of time than all I have yet referred to. They have been carried to the great pressure of 283-9 atmospheres, as measured in glass tubes by a hydrogen manometer, at which pressure a mixture of 3 volumes carbonic acid and 4 volumes nitrogen was reduced at 7°' 6 to -^ts of its volume without liquefaction of the carbonic acid. As this note has already extended to an imusual length, I will not now attempt to give an analysis of these experiments, but shall briefly state their general results. The most important of these results is the lowering of the critical point ly admixture vjith a non-condensable gas. Thus in the mixture mentioned above of carbonic acid and nitrogen, no liquid was formed at any pressure till the temperature was reduced below — 20°C. Even the addition of only -ru of its volume of air or nitrogen to carbonic acid gas will lower the critical point several degrees. Finally, these experiments leave no doubt that the law of Dalton entirely fails under high pressures, where one of the gases is at a temperature not greatly above its critical point. The anomalies observed in the tension of the vapour of water when alone and when mixed with air find their real explana- tion in the fact that the law of Dalton is only approximately true in the case of mixtures of air and aqueous vapour at the ordinary pressure and temperature of the atmosphere, and do not depend, as has been alleged, on any disturbing influence produced by a hygroscopic action of the sides of the containing vessel. The law of Dalton, in short, like the laws of Boyle and Gay-Lussac, only holds good in the case of gaseous bodies which are at feeble pressures and at temperatures greatly above their critical points. Under other conditions these laws are interfered with; and in certain conditions (such as some of those described in this note) the interfering causes become so power- ful as practically to efface them. 393 XL VIII.— PRESIDENTIAL ADDEESS. Delivered at the Glasgow Meeting of the British Association for the Advancement of Science, September 6, 1876. Six and thirty years have passed over since the British Association for the Advancement of Science held its tenth meetiag in this ancient city, and twenty-one years have elapsed since it last assembled here. The representatives of two great •Scottish families presided on these occasions ; and those who had the advantage of hearing the address of the Duke ■of Argyll in 1855 will recall the gratification they enjoyed while listening to the thoughtful sentiments which reflected a mind of rare cultivation and varied acquirements. On the present occasion I have undertaken, not without anxiety, the duty of filling an office at first accepted by one whom Scot- land and the Association would alike have rejoiced to see in this Chair, not only as a tribute to his own scientific services, but also as recognizing in him the worthy representative of that long line of able men who have upheld the preeminent position .attained by the Scottish schools of medicine in the middle of the last century, when the mantle of Boerhaave fell upon Monro and CuUen. The task of addressing this Association, always a difficult •one, is not rendered easier when the meeting is held in a place which presents the rare combination of being at once an ancient •seat of learning and a great centre of modern industry. Time will not permit me to refer to the distinguished men who in early days have left here their mark foeliind then) ; and I regret it the more, as there is a growing tendency to exaggerate the value of later discoveries, and to underrate the achievements of those who have lived before us. Confining our attention to a period reaching back to little more than a centuryj it appears that during that time three new sciences arose, at least as far as any science can be said to have a distinct origin, in this city 394 Presidential Address. [xlvih. of Glasgow — Experimental Chemistry, Political Economy, and Mechanical Engineering. It is now conceded that Black laid the foundation of modern chemistry ; and no one has ever dis- puted the claims of Adam Smith and of Watt to having not only founded, but largely built up, the two great branches of knowledge with which their names will always be inseparably connected. It was here that Dr. Thomas Thomson established the lirst school of Practical Chemistry in Great Britain, and that Sir W. Hooker gave to the chair of Botany a European celebrity ; it was here that Graham discovered the law of gaseous diffusion and the properties of polybasic acids ; it was here that Stenhouse and Anderson, Eankine and J. Thomson made some of their finest discoveries : and it was here that Sir William Thomson conducted his physico-mathematical investigations, and invented those exquisite instruments, valuable alike for ocean telegraphy and for scientific use, which are among the finest trophies of recent science. Nor must the names of Tennant, Mackintosh, Neilson, Walter Crum, Young, and E^apier be omitted, who, with many others in this place, have made large and valuable additions to practical science. The safe return of the ' Challenger,' after an absence of three and a half years, is a subject of general congratulation. Our knowledge of the varied forms of animal life, and of the remains of animal life, which occur, it is now known, over large tracts of the bed of the ocean, is chiefly derived from the observations made in the ' Challenger ' and in the previous deep-sea expedi- tions which were organized by Sir Wyville Thomson and Dr. Carpenter. The physical observations, and especially those on the temperature of the ocean, which were systematically con- ducted throughout the whole voyage of the ' Challenger,' have already supplied valuable data for the resolution of the great question of ocean-currents. Upon this question, which has- been discussed with singular ability, but under different aspects, by Dr. Carpenter and Mr. CroU, I cannot attempt here to enter ; nor will I venture to forestall, by any crude analysis of my own, the narrative which Sir W. Thomson has kindly under- taken to give of his own achievements and of those of his staff during their long scientific cruise. Another expedition, which has more than fulfilled the ex- xLviii.] Presidential Address. 395 pectations of the public, is Lieutenant Cameron's remarkable journey across the continent of Africa. It is by such enter- prises, happily conceived and ably executed, that we may hope at no distant day to see the Arab slave-dealer replaced by the legitimate trader, and the depressed populations of Africa gradu- ally brought within the pale of civilized life. From the North Polar Expedition no intelligence has been received ; nor can we expect for some time to hear whether it has succeeded in the crowning object of Arctic enterprise. In the opinion of many, the results, scientific or other, to be gained by a full survey of the Arctic regions can never be of such value as to justify the risk and cost which must be incurred. But it is not by cold calculations of this kind that great dis- coveries are made or great enterprises achieved. There is an inward and irrepressible impulse — in individuals called a spirit of adventure, in nations a spirit of enterprise — which impels mankind forward to explore every part of the world we inhabit, however inhospitable or difficult of access ; and if the country claiming the foremost place among maritime nations shrink from an undertaking because it is perilous, other countries will not be slow to seize the post of honour. If it be possible for man to reach the poles of the earth, whether north or south, the feat must sooner or later be accomplished ; and the country of the successful adventurers will be thereby raised in the scale of nations. The passage of Venus over the sun's disk is an event which cannot be passed over without notice, although many of the circumstances connected with it have already become historical. It was to observe this rare astronomical phenomenon, on the occasion of its former occurrence in 1769, that Captain Cook's memorable voyage to the Pacific was undertaken, in the course of which he explored the coast of New South Wales, and added that great country to the possessions of the British Crown. As the transit of Venus gives the most exact method of calculating the distance of the earth from the sun, extensive preparations were made on the last occasion for observing it at selected stations — from Siberia in northern, to Kerguelen's Land in southern latitudes. The great maritime powers vied with each other to turn the opportunity to the best account ; 396 Presidential Address. [xlviii, and Lord Lindsay had the spirit to equip, at his own expense, the most complete expedition which left the shores of this country. Some of the most valuable stations in southern lati- tudes were desert islands, rarely free from mist or tempest, and without harbours or shelter of any kind. The landing of the instruments was in many cases attended witli great difficulty and even personal risk. Photography lent its aid to record automatically the progress of the transit ; and M. JanSsen con- trived a revolving plate, by means of which from fifty to sixty images of the edge of the sun could be taken at short intervals during the critical periods of the phenomenon. The observations of M. Janssen at Nagasaki, in Japan, were of special interest. Looking through a violet-blue glass he saw Venus, two or three minutes before the transit began, having the appearance of a pale round spot near the edge of the sun. Immediately after contact the segment of the planet's dislc, as seen on the face of the sun, formed with what remained of this spot a complete circle. The pale spot when first seen was, in short, a partial eclipse of the solar corona, which was thus proved beyond dispute to be a luminous atmosphere surrounding the sun. Indications were at the same time obtained of the existence of an atmosphere around Venus. The mean distance of the earth from the sun was long sup- posed to have been fixed within a very small limit of error at about 95,000,000 miles. The accuracy of this number had already been called in question on theoretical grounds by Hansen and Leverrier, when Foucault, in 1862, decided the question by an experiment of extraordinary delicacy. Talcing advantage of the revolving-mirror, with which Wheatstone had some time before enriched the physical sciences, Foucault suc- ceeded in measuring the absolute velocity of light in space by experiments on a beam of light, reflected backwards and for- wards, within a tube little more than thirteen feet in length. Combining the result thus obtained with what is called by astronomers the constant of aberration, Foucault calculated the distance of the earth from the sun, and found it to be one thirtieth part, or about .3,000,000 miles, less than the com- monly received number. This conclusion has lately been con- firmed by M. Cornu, from a new determination he has made of xLviii.] Presidential Address. 397 the velocity of light according to the method of Fizeau ; and in complete accordance with these results are the investigations of Leverrier, founded on a comparison with theory of the observed motions of the sun and of the planets Venus and Mars. It remains to be seen whether the recent observations of the transit of Ventis, when reduced, will be sufficiently concordant to fix with even greater precision the true distance of the earth from the sun. In this brief reference to one of the finest results of modern science, I have mentioned a great name whose loss England has recently had to deplore, and in connexion with it the name of an illustrious physicist whose premature death deprived France, a few years ago, of one of her brightest ornaments — ^Wheat- stone and Foucault, ever to be remembered for their marvellous power of eliciting, like Galileo and N"ewton, from famUiar phenomena the highest truths of nature ! The discovery of Huggins that some of the fixed stars are moving towards and others receding from our system, has been fully confirmed by a careful series of observations lately made by Mr. Christie, in the Observatory of Greenwich. Mr. Huggins has not been able to discover any indications of a proper motion in the nebulae ; but this may arise from the motion of transla- tion being less than the method would discover. Few achieve- ments in the history of science are more wonderful than the measurement of the proper motions of the fixed stars, from observing the relative position of two delicate lines of light in the field of the telescope. The observation of the American astronomer Young, that bright lines, corresponding to the ordinary lines of Fraunhofer reversed, may be seen in the lower strata of the solar atmos- phere for a few moments during a total eclipse, has been con- firmed by Mr. Stone, on the occasion of the total eclipse of the sun which occurred some time ago in South Africa. In the outer corona, or higher regions of the sun's atmosphere, a single green line only was seen, the same which had been already described by Young. I can here refer only in general terms to the observations of Eoscoe and Schuster on the absorption-bands of potassium and sodium, and to the investigations of Lockyer on the ab- 398 Presidential Address. [xlviii. sorptive powers of metallic and metalloidal vapours at different temperatures. From the vapour of calcium the latter has obtained two wholly distinct specti'a, one belonging to a low, and the other to a high temperature. Mr. Lockyer is also engaged on a new and greatly extended map of the solar spectrum. Spectrum analysis has. lately led to the discovery of a new metal — gallium — the fifth whose presence has been first indi- cated by that powerful agent. This discovery is due to M. Lecoq de Boisbaudran, already favourably known by a work on the application of the spectroscope to chemical analysis. Our knowledge of aerolites has of late years been greatly increased ; and I cannot occupy a few moments of your time more usefully than by briefly referring to the subject. So recently as 1860 the most remarkable meteoric fall on record, not even excepting that of L'Aigle, occurred near the village of New Concord in Ohio. On a day when no thunder-clouds were visible, loud sounds were heard resembling claps of thunder, followed by a large fall of meteoric stones, some of which were distinctly seen to strike the earth. One stone, above 5 pounds in weight, buried itself to the depth of two feet in the ground, and when dug out was found to be still warm. In 1872 another remarkable meteorite, at first seen as a brilliant star with a luminous train, burst near Orvinio in Italy, and six fragments of it were afterwards collected. Isolated masses of metallic iron, or rather of an alloy of iron and nickel, similar in composition and properties to the iron usually diffused in meteoric stones, have been found here and there on the surface of the earth, some of large size, as one described by Pallas, which weighed about two thirds of a ton. Of the meteoric origin of these masses of iron there is little room for doubt, although no record exists of their fall. Sir Edward Sabine, whose life has been devoted with rare fidelity to the pursuit of science, and to whose untiring efforts this Association largely owes the position it now occupies, was the pioneer of the newer discoveries in meteoric science. Eight and fifty years ago he visited with Captain Eoss the northern shores of Baffin's Bay, and made the interesting discovery that the knife-blades used by the Esquimaux in the vicinity of the xLviii.] Presidential Address. 399 Arctic highlands were formed of meteoric iron. This observation was afterwards fully confirmed ; and scattered blocks of meteoric iron have been found from time to time around Baffin's Bay. But it was not till 1870 that the meteoric treasures of Baffin's Bay were truly discovered. In that year Nordenskiold found, at a part of the shore difficult of approach even in moderate weather, enormous blocks of meteoric iron, the largest weighing nearly twenty tons, imbedded in a ridge of basaltic rock. The interest of this observation is greatly enhanced by the circum- stance that these masses of meteoric iron, like the basalt with which they are associated, do not belong to the present geologi- cal epoch, but must have fallen long before the actual arrange- ment of land and sea existed, — during, in short, the middle Tertiary, or Miocene period of Lyell. The meteoric origin of these iron masses from Ovifak has been called in question by Lawrence Smith ; and it is no doubt possible that they may have been raised by upheaval from the interior of the earth. I have indeed myself shown by a magneto-chemical process that metallic iron, in particles so fine that they have never yet been actually seen, is everywhere diffused through the Miocene basalt of Slieve Mish in Antrim, and may likewise be dis- covered by careful search in almost all igneous and in many metamorphic rocks. These observations have since been verified by Eeuss in the case of the Bohemian basalts. But, as regards the native iron of Ovifak, the weight of evidence appears to be in favour of the conclusion, at which M. Daubr^e, after a careful discussion of the subject, has arrived — that it is really of meteoric origin. This Ovifak iron is also remarkable from containing a considerable amount of carbon, partly com- bined with the iron, partly diffused through the metallic mass in a form resembling coke. In connexion with this subject, I must refer to the able and exhaustive memoirs of Maskelyne on the Busti and other aerolites, to the discovery of vanadium by E. Apjohn in a meteoric iron, to the interesting observa- tions of Sorby, and to the researches of Daubr^e, Wohler, Lawrence Smith, Tschermak, and others. The important services which the Kew Observatory has rendered to meteorology and to solar physics have been fully recognized; and Mr. Gassiot has had the gratification of witnessing thefinal success 400 Presidential Address. [xlviii. of his long and noble efforts to place this observatory upon a permanent footing. A physical observatory for somewhat similar objects, but on a larger scale, is in course of erection, under the guidance of M. Janssen, at Fontenay in France, and others are springing up or already exist in Germany and Italy. It is earnestly to be hoped that this country will not lag behind in providing physical observatories on a scale worthy of the nation and commensurate with the importance of the object. On this question I cannot do better than refer to the high authority of Dr. Balfour Stewart, and to the views he expressed in his able address last year to the Physical Section. Weather telegraphy, or the reporting by telegraph the state of the weather at selected stations to a central office, so that notice of the probable approach of storms may be given to the seaports, has become in this country an organized system ; and considering the little progress meteorology has made as a science, the results may be considered to be on the whole satis- factory. Of the warnings issued of late years, four out of five were justified by the occurrence of gales or strong winds. Few storms occurred for which no warnings had been given ; but unfortunately among these were some of the heaviest gales of the period. The stations from which daily reports are sent to the meteorological office in London embrace the whole coast of Western Europe, including the Shetland Isles. It appears that atmospheric disturbances seldom cross the Atlantic without being greatly altered in character, and that the origin of most of our storms lies eastward of the longitude of Newfoundland. As regards the velocity of the wind, the cup-anemometer of Dr. Eobinson has fully realized the expectations of its dis- coverer ; and the venerable astronomer of Armagh has been engaged during the past summer, with all the ardour of youth, in a course of laborious experiments to determine the constants of his instrument. From seven years' observations at the Observatory of Armagh, he has found that the mean velocity of the wind is greatest in the S.S.W. octant and least iii the opposite one, and that the amount of wind attains a maximum in January, after which it steadily decreases, with one slight exception, till July, augumenting again till the end of the year. Passing to the subject of electricity, it is with pleasure that xLviii.] Presidential Address. 401 I have to annoiince the failure of a recent attempt to deprive Oerstedt of his great discovery. It is gratifying thus to find high reputations vindicated, and names which all men love to honour transmitted with undiminished lustre to posterity. At a former meeting of this Association, remarkable for an un- usual attendance of distinguished foreigners, the central figure was Oerstedt. On that occasion Sir John Herschel in glowing language compared Oerstedt's discovery to the blessed dew of heaven which only the master-mind could draw down, but which it was for others to turn to account and use for the fertilization of the earth. To Franklin, Volta, Coulomb, Oerstedt, Ampfere, Faraday, Seebeck, and Ohm are due the fundamental dis- coveries of modern electricity — a science whose applications in Davy's hands led to grander results than alchemist ever dreamed of, and in the hands of others (among whom Wheat- stone, Morse, and Thomson occupy the foremost place) to the marvels of the electric telegraph. When we proceed from the actual phenomena of electricity to the molecular conditions upon which those phenomena depend, we are confronted with questions as recondite as any with which the physicist has had to deal, but towards the solution of which the researches of Faraday have contributed the most precious materials. The theory of electrical and magnetic action occupied formerly the powerful minds of Poisson, Green, and Gauss ; and among the living it will surely not be invidious to cite the names of Weber, Helmholtz, Thomson, and Clerk Maxwell. The work of the latter on electricity is an original essay worthy in every way of the great reputation and of the clear and far-seeing- intellect of its author. Among recent investigations I must refer to Professor Tait's discovery of consecutive neutral points in certain thermo- electric junctions, for which he was lately awarded the Keith prize. This discovery has been the result of an elaborate in- vestigation of the properties of thermo-electric currents, and is specially interesting in reference to the theory of dynamical electricity. Nor can I omit to mention the very interesting and original experiments of Dr. Kerr on the dielectric state, from which it appears that when electricity of high tension is passed through dielectrics, a change of molecular arrange- 2c 402 Presidential Address, [xlviii. ment occurs, slowly in the case of solids, quickly in the case of liquids, and that the lines of electric force are in some cases lines of compression, in other cases lines of extension. Of the many discoveries in physical science due to Sir "William Grove, the earliest and not the least important is the hattery which bears his name, and is to this day the most powerful of all voltaic arrangements ; but with a Grove's battery of 50 or even 100 cells in vigorous action, the spark will not pass through an appreciable distance of cold air. By using a very large number of cells, carefully insulated and charged with water, Mr. Gassiot succeeded in obtaining a short spark through air ; and lately De La Eue and MiiUer have constructed a large chloride-of-silver battery giving freely sparks through cold air, which, when a column of pure water is interposed in the circuit, accurately resemble those of the common electrical machine. The length of the spark increasing nearly as the square of the number of cells, it has been calcu- lated that with 100,000 elements of this battery the dis- charge should take place through a distance of no less than eight feet in air. In the solar beam we have an agent of surpassing power, the investigation of whose properties by Newton forms an epoch in the history of experimental science scarcely less im- portant than the discovery of the law of gravitation in the history of physical astronomy. Three actions characterize the solar beam, or, indeed, more or less that of any luminous body — the heating, the physiological, and the chemical. In the ordi- nary solar beam we can modify the relative amount of these actions by passing it through different media, and we can thus have luminous rays with little heating or little chemical action. In the case of the moon's rays it required the highest skill on the part of Lord Eosse, even with all the resources of the obser- vatory of Parsonstown, to investigate their heating properties, and to show that the surface of our satellite facing the earth passes, during every lunation, through a greater range of tem- perature than the difference between the freezing- and boiling- points of water. But if, instead of taking an ordinary ray of light, we analyze it as Newton did by the prism, and isolate a very fine line of xLviii.] Presidential Address. 403 the spectrum (theoretically a line of infinite tenuity), that is to say, if we take a ray of definite refrangibility, it will be found impossible by screens or otherwise to alter its properties. It was his clear perception of the truth of this principle that led Stokes to his great discovery of the cause of epipolic disper- sion, in which he showed that many bodies had the power of absorbing dark rays of high refrangibility and of emitting them as luminous rays of lower refrangibihty — -of absorbing, in short, darkness and of emitting it as light. It is not, indeed, an easy matter in all cases to say whether a given effect is due to the action of heat or light ; and the question which of these forces is the efficient agent in causing the motion of the tiny disks in Crookes's radiometer has given rise to a good deal of discussion. The answer to this question involves the same principles as those by which the image traced on the daguerreo- type plate, or the decomposition of carbonic acid by the leaves of plants, is referred to the action of light and not of heat ; and applying these principles to the experiments made with the radiometer, the weight of evidence appears to be in favour of the view that the repulsion of the blackened surfaces of the disks is due to a thermal reaction occurring in a highly rarefied medium. I have myself had the pleasure of witnessing many of Mr. Crookes's experiments, and I cannot sufficiently express my admiration of the care and skill with which he has pursued this investigation. The remarkable repulsions he has observed in the most perfect vacua hitherto attained are interesting, not only as having led to the construction of a beautiful instru- ment, but as being likely, when the subject is fully investigated, to give valuable data for the theory of molecular actions. A singular property of light, discovered a short time ago by Mr. WiUoughby Smith, is its power of diminishing the electri- cal resistance of the element selenium. This property has been ascertained to belong chiefly to the luminous rays on the red side of the spectnim, being nearly absent in the violet or more refrangible rays and also in heat-rays of low refrangi- bility. The recent experiments of Prof. W. G. Adams have fully established the accuracy of the remarkable observation, first made by Lord Eosse, that the action appeared to vary inversely as the simple distance of the illuminating source. 404 Presidential Address. [xlviii. Switzerland sent, some years ago, as its representative to this country the celebrated De la Eive, whose scientific life formed lately the subject of an eloquent doge from the pen of M. Dumas. On this occasion we have to welcome, in General Menabrea, a distinguished representative both of the kingdom of Italy and of Italian science. His great work on the deter- mination of the pressures and tensions in an elastic system is of too abstruse a character to be discussed in this address ; but the principle it contains may be briefly stated in the following words : — " When any elastic system places itself in equilibrium under the action of external forces, the work developed by the internal forces is a minimum." General Menabrea has, bow- ever, other and special claims upon us here, as the friend to whom Babbage entrusted the task of making known to the world the principles of his analytical machine — a gigantic con- ception, the effort to realize which it is known was one of the chief objects of Babbage's later life. The latest development of this conception is to be found in the mechanical integrator of Prof. J. Thomson, in which motion is transmitted, according to a new kinematic principle, from a disk or cone to a cylinder through the intervention of a loose ball, and in Sir W. Thom- son's machine for the mechanical integration of differential equations of the second order. In the exquisite tidal machine of the latter we have an instrument by means of which the height of the tide at a given port can be accurately predicted for all times of the day and night. The attraction-meter of Siemens is an instrument of great delicacy for measuring horizontal attractions, which it is pro- posed to use for recording the attractive influences of the sun and moon, upon which the tides depend. The bathometer of the same able physicist is another remarkable instrument, in which the constant force of a spring is opposed to the variable pressure of a column of mercury. By an easy observation of the bathometer on shipboard, the depth of the sea may be approxi- mately ascertained without the use of a sounding-line. The Loan Exhibition of Apparatus at Kensington has been a complete success, and cannot fail to be useful, both in ex- tending a knowledge of scientific subjects and in promoting scientific research throughout the country. Unique in charac- xLviii.] Presidential Address. 405 ter, but most interesting and instructive, this exhibition will, it is to be hoped, be the precursor of a permanent museum of scientific objects, which, like the present exhibition, shall be a record of old, as well as a representation of new inventions. It is often difficult to draw a distinct line of separation between the physical and chemical sciences ; and it is perhaps doubtful whether the division is not really an artificial one. The chemist cannot, indeed, make any large advance without having to deal with physical principles ; and it is to Boyle, Dalton, Gay-Lussac, and Graham that we owe the discovery of the mechanical laws which govern the properties of gases and vapours. Some of these laws have of late been made the subject of searching inquiry, which has fully confirmed their accuracy, when the body under examination approaches to what has not inaptly been designated the ideal gaseous state. But when gases are examined under varied conditions of pressure and temperature, it is found that these laws are only particular cases of more general laws, and that the laws of the gaseous state, as it exists in nature, although they may be enunciated in a precise and definite form, are very different from the simple expressions which apply to the ideal condition. The new laws become in their turn inapplicable when from the gaseous state proper we pass to those intermediate conditions which, it has been shown, link with unbroken continuity the gaseous and liquid states. As we approach the liquid state, or even when we reach it, the problem becomes more complicated ; but its solution even in these eases will, it may confidently be expected, yield to the powerful means of investigation we now possess. /^ Among the more important researches made of late in /physical chemistry, I may mention those of F. "Weber on the '-specific heat of carbon and the allied elements, of Berthelot on thermo-chemistry, of Bunsen on spectrum analysis, of Wiillner on the band- and line-spectra of the gases, and of Guthrie on the cryohydrates. Cosmical chemistry is a science of yesterday ; and yet it already abounds in facts of the highest interest. Hydrogen, which, if the absolute zero of the physicist does not bar the way, we may hope yet to see in the metallic form, appears to 406 Presidential Address. [xlvui. be everywhere present in the universe. It exists in enormous quantity in the solar atmosphere, and it has been discovered in the atmospheres of the fixed stars. It is present, and is the only known element of whose presence we are certain, in those vast sheets of ignited gas of which the nebulas proper are com- posed. Nitrogen is also widely diffused among the stellar bodies, and carbon has been discovered in more than one of the comets. On the other hand, a prominent line in the spectrum of the Aurora BoreaHs has not been identified with that of any known element ; and the question may be asked : — Does a new element, in a highly rarefied state, exist in the upper regions of our atmosphere ? or are we with Angstrom to attribute this line to a fluorescent or phosphorescent light produced by the electrical discharge to which the aurora is due ? This question awaits further observations before it can be definitely settled, as does also that of the source of the remarkable green line which is everywhere conspicuous in the solar corona. I must here pause for a moment to pay a passing tribute to the memory of Angstrom, whose great work on the solar spectrum will always remain as one of the finest monuments of the science of our period. The influence, indeed, which the o labours of Angstrom and of Kirchhoff have exerted on the most interesting portion of later physics can scarcely be ex- aggerated ; and it may be truly said that there are few men whose loss will be longer felt or more deeply deplored than that of the illustrious astronomer of Upsala. I cannot pursue this subject further, nor refer to the other terrestrial elements which are present in the solar and stellar atmospheres. Among the many elements that make up the ordinary aerolite, not one has been discovered which does not occur upon this earth. On the whole we arrive at the grand conclusion that this mighty universe is chiefly built up of the same materials as the globe we inhabit. In the application of science to the useful purposes of life, chemistry and mechanics have run an honourable race. It was in the valley of the Clyde that the chief industry of this country received, within the memory of many here present, an extraordinary impulse from the application by Neilson of the XL VIII.] Presidential Address. 407 hot blast to the smelting of iron. The Bessemer steel process and the regenerative furnace of Siemens are later applications of high scientific principles to the same industry. But there is ample work yet to be done. The fuel consumed in the manufacture of iron, as, indeed, in every furnace where coal is used, is greatly in excess of what theory indicates ; and the clouds of smoke which darken the atmosphere of our manufac- turing towns, and even of whole districts of country, are a clear indication of the waste, but only of a small portion of the waste, arising from imperfect combustion. The depressing effect of this atmosphere upon the working population can scarcely be overrated. Their pale, I had almost said etiolated, faces are a sure indication of the absence of the vivifying in- fluence of the solar rays, so essential to the maintenance of vigorous health. The chemist can furnish a simple test of this state of the atmosphere in the absence of ozone, the active form of oxygen, from the air of our large towns. At some future day the efforts of science to isolate, by a cheap and available process, the oxygen of the air for industrial purposes may be rewarded with success. The effect of such a discovery would be to reduce the consumption of fuel to a fractional part of its present amount ; and although the carbonic acid would remain, the smoke and carbonic oxide would disappear. But an abundant supply of pure oxygen is not now within our reach ; and in the mean time may I venture to suggest that in many localities the waste products of the furnace might be carried off to a distance from the busy human hive by a few horizontal flues of large dimensions, terminating in lofty chim- neys on a hillside or distant plain ? A system of this kind has long been employed at the mercurial mines of Idria, and in other smelting-works where noxious vapours are disengaged. With a little care in the arrangements, the smoke would be wholly deposited, as flue-dust or soot, in the horizontal galleries, and would be available for the use of the agriculturist. The future historian of organic chemistry will have to record a succession of beneficent triumphs, in which the efforts of science have led to results of the highest value to the well- being of man. The discovery of quinine has probably saved more human life, with the exception of that of vaccination. 408 Presidential Address. [xlviii. than any discovery of any age ; and he who succeeds in devising an artificial method of preparing it will be truly a benefactor of the race. Not the least valuable, as it has been one of the most successful, of the works of our Government in India, has been the planting of the cinchona-tree on the slopes of the Himalaya. As artificial methods are discovered, one by one, of preparing the proximate principles of the useful dyes, a temporary derangement of industry occurs, but in the end the waste materials of our manufactures set free large portions of the soil for the production of human food. The ravages of insects have ever been the terror of the agriculturist, and the injury they inflict is often incalculable. An enemy of this class, carried over from America, threatened lately with ruin some of the finest vine districts in the south of Prance. The occasion has called forth a chemist of high renown ; and in a classical memoir recently published, M. Dumas appears to have resolved the difficult problem. His method, although immediately applied to the Phylloxera of the vine, is a general one, and will no doubt be found serviceable in other cases. In the apterous state the Phylloxera attacks the roots of the plant ; and the most efficacious method hitherto known of destroying it has been to inundate the vineyard. After a long and patient investigation, M. Dumas has dis- covered that the sulphocarbonate of potassium, in dilute solution, fulfils every condition required from an insecticide, destroying the insect without injuring the plant. The process requires time and patience ; but the trials in the vineyard have fully confirmed the experiments of the laboratory. The application of artificial cold to practical purposes is rapidly extending ; and, with the improvement of the ice- machine, the influence of this agent upon our supply of animal food from distant countries will undoubtedly be immense. The ice-machine is already employed in paraffin-works and in large breweries ; and the curing or salting of meat is now largely conducted in vast chambers, maintained throughout the summer at a constant temperature by a thick covering of ice. I have now completed this brief review, rendered difficult by the abundance, not by the lack of materials. Even con- fining our attention to the few branches of science upon which xLviii.] Presidential Address. 409 I have ventured to touch, and omitting altogether the whole range of ^ure chemistry, it is with regret that I find myself con- strained to make only a simple reference to the important work of Cayley on the Mathematical Theory of Isomers, and to elaborate memoirs which have recently appeared in Germany on the reflection of heat- and light-rays, and on the specific heat and conducting power of gases for heat, by Knoblauch, E. Wiedemann, Winkelmann, and Buff. The decline of science in England formed the theme, fifty years ago, of an elaborate essay by Eabbage ; but the brilliant •discoveries of Faraday soon after wiped off the reproach. I will not venture to say that the alarm which has lately arisen, here and elsewhere, on the same subject will prove to be equally groundless. The duration of every great outburst of human activity, whether in art, in literature, or in science, has always been short, and experimental science has made gigantic -advances during the last three centuries. The evidence of any great failure is not, however, very manifest, at least in the physical sciences. The journal of Poggendorff, which has long- been a faithful record of the progress of phj^sical research throughout the world, shows no signs of flagging ; and the Jubelband by which Germany celebrated the fiftieth year of Poggendorff's invaluable services was at the same time an ovation to a scientific veteran, who has perhaps done more than any man living to encourage the highest forms of research, and a proof that in N"orthern Europe the physical sciences con- tinue to be ably, and actively cultivated. If in chemistry the ■case is somewhat weaker, the explanation, at least in this country, is chiefly to be found in the demand on the part of the public for professional aid from many of our ablest •chemists. But whatever view be taken of the actual condition of scientific research there can be no doubt that it is both the •duty and the interest of the country to encourage a pursuit so ennobling in itself, and fraught with such important conse- ■quences to the wellbeing of the community. ISTor is there any ■question in which this Association, whose special aim is the advancement of science, can take a deeper interest. The public mind has also been awakened to its importance, and is prepared 410 Presidential Address. [xlviu. to aid in carrying out any proposal which offers a reasonable prospect of advantage. In its recent phase the question of scientific research has been mixed up with contemplated changes in the great univer- sities of England, and particularly in the University of Oxford. The national interests involved on all sides are immense, and a false step once taken may be irretrievable. It is with difiS- dence that I now refer to the subject, even after having given to it the most anxious and careful consideration. As regards the higher mathematics, their cultivation has hitherto been chiefly confined to the Universities of Cambridge and Dublin, and two great mathematical schools will probably be sufScient for the kingdom. The case of the physical and natural sciences is different, and they ought to be cultivated in the largest and widest sense at every complete university- Nor, in applying this remark to the English universities, must we forget that if Cambridge was the alma mater of Newton and Cavendish, Oxford gave birth to the Eoyal Society. The ancient renown of Oxford will surely not suffer, while her material position cannot fail to be strengthened, by the expan- sion of scientific studies and the encouragement of scientifie research within her walls. Nor ought such a proposal to be regarded as in any way hostile to the literary studies, and especially to the ancient classical studies, which have always- been so carefully cherished at Oxford. If, indeed, there were any such risk, few would hesitate to exclaim — let science shift- elsewhere for herself, and let literature and philosophy find shelter in Oxford ! But there is no ground for any such anxiety. Literature and science, philosophy and art, when properly cultivated, far from opposing, wiU. mutually aid one another. There will be ample room for all, and, by judicious arrange- ments, all may receive the attention they deserve. A University, or Studium Generale, ought to embrace in its- arrangements the whole circle of studies which involve the material interests of society, as well as those which cultivate- intellectual refinement. The industries of the country should look to the universities for the development of the principles of applied as well as of abstract science ; and in this respect no institutions have ever had so grand a possession within. xLvni.] Presidential Address. 411 easy reach as have the universities of England at this conjuncture, if only they have the courage to seize it. With their historic reputation, their collegiate endowments, their commanding in- fluence, Oxford and Cambridge should continue to be all that they now are ; but they should, moreover, attract to their lecture-halls and working cabinets students in large numbers preparing for the higher industrial pursuits of the country. The great physical laboratory in Cambridge, founded and equipped by the noble representative of the House of Cavendish, has in this respect a peculiar signiiicance, and is an important step in the direction I have indicated. 'But a small number only of those for whom this temple of science is designed are now to be found in Cambridge. It remains for the University to perform its part, and to widen its portals so that the nation at large may reap the advantage of this well-timed foundation. If the Universities, in accordance with the spirit of their statutes, or at least of ancient usage, would demand from the candidates for some of the higher degrees proof of original powers of investigation, they would give an important stimulus to the cultivation of science. The example of many continental universities, and among others of the venerable University of Leyden, may here be mentioned. Two proof essays recently written for the degree of Doctor of Science in Leyden, one by Van der Waals, the other by Lorenz, are works of unusual merit ; and another pupil of Professor Rijke is now engaged in an elaborate experimental research as a qualification for the same degree. The endowment of a body of scientific men devoted exclu- sively to original research, without the duty of teaching or other occupation, has of late been strongly advocated in this country ; and M. Fremy has given the weight of his high authority to a somewhat similar proposal for the encouragement of research in France. I will not attempt to discuss the subject as a national question, the more so as after having given the proposal the most careful consideration in my power, and turned it round on every side, I have failed to discover how it could be worked so as to secure the end in view. But whatever may be said in favour of the endowment of 412 Presidential Address. [xlviii. pure research as a national question, the Universities ought surely never to be asked to give their aid to a measure which would separate the higher intellects of the country from the flower of its youth. It is only through the influence of original minds that any great or enduring impression can be produced on the hopeful student. Without original power, and the habit of exercising it, you may have an able instructor, but you cannot have a great teacher. No man can be expected to train others in habits of observation and thought he has never acquired himself. In every age of the world the great schools of learning have, as in Athens of old, gathered around great and original minds, and never more conspicuously than in the modern schools of chemistry, which reflected the genius of Liebig, Wohler, Bunsen, and Hofmann. These schools have been nurseries of original research as well as models of scientific teaching; and students attracted to them from all countries became enthusiastically devoted to science, while they learned its methods from example even more than from precept. Will any one have the courage to assert that organic chemistry, with its many applications to the uses of mankind, would have made in a few short years the marvellous strides it has done, if Science, now as in medifeval times, had pursued her work in strict seclusion, Semota ab iiostris rebus, seiuuctaque longe, Ipsa suis pollens opibus, nil indiga nostri ? But while the Universities ought not to apply their resources in support of a measure which would render their teaching in- effective, and would at the same time dry up the springs of intellectual growth, they ought to admit freely to university positions men of high repute from other universities, and even without academic qualifications. An honorary degree does not necessarily imply a university education ; but if it have any meaning at all, it implies that he who has obtained it is at least on a level with the ordinary graduate, and should be eligible to university positions of the highest trust. Not less important would it be for the encouragement of learning throughout the country that the English Universities, remembering that they were founded for the same objects, and xLviii.] Presidential Address. 413 derive their authority from a common source, should be pre- pared to recognize the ancient universities of Scotland as freely as they have always recognized the Elizabethan University of Dublin. Such a measure would invigorate the whole university system of the country more than any other I can think of It would lead to the strengthening of the literary element in the northern, and of the practical element in the southern univer- sities, and it would bring the highest teaching of the country everywhere more fully into harmony with the requirements of the times in which we live. As an indirect result, it could not fail to give a powerful impulse to literary pursuits as well as to scientific investigations. Professors would be promoted from smaller positions in one university to higher positions in another, after they had given proofs of industry and ability ; and stagnation, hurtful alike to professorial and professional life, would be effectually prevented. If this union were estab- lished among the old universities, and if at the same time a new university (as I myself ten years ago earnestly proposed) were founded on sound principles amidst the great populations of Lancashire and Yorkshire, the university system of the country would gradually receive a large and useful exten.sion, and, without losing any of its present valuable characteristics, would become more intimately related than hitherto with those great industries upon which mainly depend the strength and wealth of the nation. It may perhaps appear to many a paradoxical assertion to maintain that the industries of the country should look to the calm and serene regions of Oxford and Cambridge for help in the troublous times of which we have now a sharp and severe note of warning. But I have not spoken on light grounds, nor without due consideration. If Great Britain is to retain the commanding position she has so long occupied in skilled manufacture, the easy ways which (owing partly to the high qualities of her people, partly to the advantages of her insular position and mineral wealth) have sufficed for the past, will not be found to suffice for the future. The highest training which can be brought to bear on practical science will be imperatively required ; and it will be a fatal policy if that training is to be sought for in foreign lands, because it cannot 414 Presidential Address. [xlviii. be obtained at home. The country which depends unduly on the stranger for the education of its skilled men, or neglects in its highest places this primary duty, may expect to find the demand for such skill gradually to pass away, and along with it the industry for which it was wanted. I do not claim for scientific education more than it will accomplish, nor can it ever replace the after-training of the workshop or factory. Eare and powerful minds have, it is true, often been indepen- dent of it; but high education always gives an enormous advantage to the country where it prevails. Let no one suppose I am now referring to elementary instruction, and much less to the active work which is going on everywhere around us, in preparing for examinations of all kinds. These things are all very useful in their way; but it is not by them alone that the practical arts are to be sustained in the country. It is by education in its highest sense, based on a broad scien- tific foundation, and leading to the application of science to practical purposes — in itself one of the noblest pursuits of the human mind — that this result is to be reached. That educa- tion of this kind can be most effectively given in a university, or in an institution like the Polytechnic School of Zurich, which differs from the scientific side of a university only in name, and to a large extent supplements the teaching of an actual university, I am firmly convinced ; and for this reason, among others, I have always deemed the establishment in this country of Examining Boards with the power of granting degrees, but with none of the higher and more important functions of a university, to have been a measure of questionable utility. It is to Oxford and Cambridge, widely extended as they can readily be, that the country should chiefly look for the development of practical science ; they have abundant resources for the task ; and if they wish to secure and strengthen their lofty position, they can do it in no way so effectually as by showing that in a green old age they preserve the vigour and elasticity of youth. If any are disposed to think that I have been carrying this meeting into dream-land, let them pause and listen to the result of similar efforts to those I have been advocating, under- taken by a neighbouring country when on the verge of ruin, xLviii.] Presidential Address. 415 and steadily pursued by the same country in the climax of its prosperity. " The University of Berlin," to use the words of Hofmann, " like her sister of Bonn, is a creation of our century. It was founded in the year 1810, at a period when the pressure of foreign domination weighed almost insupportably on Prussia; and it will ever remain signiiicant of the direction of the German mind that the great men of that time should have hoped to develop, by high intellectual training, the forces necessary for the regeneration of their country." It is not for me, especially in tlois place, to dwell upon the great strides which E"orthern Germany has made of late years in some of the largest branches of industry, and particularly in those which give a free scope for the application of scientific skill. " Let us not suppose," says M. Wurtz in his recent report on the Artificial Dyes, " that the distance is so great between theory and its industrial applications. This report would have been written in vain, if it had not brought clearly into view the immense influence of pure science upon the progress of industry. If unfortunately the sacred flame of science should burn dimly or be extinguished, the practical arts would soon fall into rapid decay. The outlay which is incurred by any country for the promotion of science and of high instruction will yield a certain return; and Germany has not had long to wait for the ingathering of the fruits of her far-sighted policy. Thirty or forty years ago, industry could scarcely be said to exist there ; it is now widely spread and successful." As an illus- tration of the truth of these remarks, I may refer to the newest of European industries, but one which in a short, space of time has attained considerable magnitude. It appears (and I make the statement on the authority of M. Wurtz) that the artificial dyes produced last year in Germany exceeded in value those of all the rest of Europe, including England and France. Yet Germany has no special advantage for this manufacture except the training of her practical chemists. We are not, it is true, to attach undue importance to a single case ; but the rapid growth of other and larger industries points in the same direction, and will, I trust, secure some consideration for the suggestions I have ventured to make. The intimate relations which exist between abstract science 416 Presidential Address. [xlvih. and its applications to the uses of life have always been kept steadily in view by this Association, and the valuable Eeports, which are a monument to the industry and zeal of its members, embrace every part of the domain of science. It is with the greater confidence, therefore, that I have ventured to suggest from this Chair that no partition wall should anywhere be raised up between pure and applied science. The same senti- ment animates our vigorous ally, the Prench Association for the Advancement of Science, which rivalling, as it already does, this Association in the high scientific character of its proceedings, bids fair in a few years to call forth the same interest in science and its results, throughout the great provincial towns of France, which the British Association may justly claim to have already effected in this country. No better proof can be given of the wide base upon which the French Association rests, than the fact that it was presided over last year by an able representative of commerce and industry, and this year by one who has long held an exalted position in the world of science, and has now the rare distinction of representing in her historic Academies the literature as well as the science of France. Whatever be the result of our efforts to advance science and industry, it requires no gift of prophecy to declare that the boundless resources which the supreme Author and Up- holder of the Universe has provided for the use of man will, as time rolls on, be more and more fully applied to the improvement of the physical and, through the improvement of the physical, to the elevation of the moral condition of the human family. Unless, however, the history of the future of our race be wholly at variance with the history of the past, the progress of mankind will be marked by alternate periods of activity and repose ; nor will it be the work of any one nation or of any one race. To the erection of the edifice of civilized life, as it now exists, all the higher races of the world have contributed ; and if the balance were accurately struck, the claims of Asia for her portion of the work would be immense, and those of Northern Africa not insignificant. Steam-power has of late years produced greater changes than probably ever occurred before in so short a time. But the resources of Nature are not confined to steam, nor to the com- xLviii.] Presidential Address. 417 bustion of coal. The steady water-wheel aud the rapid turbine are more perfect machines than the stationary steam-engine ; and glacier-fed rivers with natural reservoirs, if fully turned to account, would supply an unlimited and nearly constant source of power depending solely for its continuance upon solar heat. But no immediate dislocation of industry is to be feared, although the turbine is already at work on the Ehine and the Ehone. In the struggle to maintain their high position in science and its applications, the countrymen of Newton and Watt will have no ground for alarm so long as they hold fast to their old traditions, and remember that the greatest nations have fallen when they relaxed in those habits of intelligent and steady industry upon which all permanent success depends. D 'H.s XLIX.— ON THE GASEOUS STATE OF MATTEE. The Bakerian Lecture. From the Philosophical Transactions, 1876, pt. 2, p. 421. Since the investigation " On the Continuity of the Gaseous and Liquid States of Matter," which formed the subject of the Bakerian Lecture for 1869, was communicated to the Society, I have continued to pursue the inquiry in a more extended form, with the view of discovering the general laws which determine the physical conditions of matter in the gaseous and liquid states. The subject in its whole extent and under all its aspects is so vast in itself, and its investigation in many cases has been surrounded by experimental difficulties of so high an order, that I must crave the indulgence of the Society if the amount of work actually accomplished appear small for the time devoted to it. I will give in the first place a few details regarding the method of mounting the apparatus, which will aid greatly any one who may hereafter desire to pursue the inquiry. The apparatus employed is, in all the essential parts, the same as that which I formerly described. The packing of the steel screw, by which the pressure is produced, is an important part of the operation. It is effected by means of a number of circular disks of leather, pierced centrally with a fine hole, and rendered impervious to water by being saturated in vacuo with melted lard. These disks are introduced, one by one, into a cylindrical cavity above the female screw in the lower end- piece, care being taken to press down each disk separately by a few gentle blows of a wooden mallet. After the introduction of the leather packing, the brass end-piece is placed with the face downwards on a small wooden block, and the whole is firmly clamped to a steady bench or table. The steel screw is xLix.] On the Gaseous State of Matter. 419 then inserted, and screwed through the leather packing till it enters into the wooden block. The connexion between the metal and glass tube in the upper end-piece is estabhshed by forming a protuberance on the glass tube accurately corre- sponding to a conical surface in the passage through the end-piece. The conical surface of the glass tube and the adjoining cylindrical surface for an inch and a half below the cone were covered with several layers of fine thread coated with ordinary shoemaker's wax. The brass end-piece was gently heated before the introduction of the glass tube, and the latter was firmly fixed in its place by steady pressure. So perfectly have these arrangements fulfilled their purpose, that the apparatus, when successfully mounted, will remain in perfect order and without a trace of leakage for an indefinite period of time. The greatest pressure to which I have exposed the apparatus is 500 atmospheres, but it would be easy with very fine glass tubes to make accurate observations even at much higher pressures. As the metallic tubes, whether made of cold-drawn copper or of forged iron, which form the body of the apparatus, are, as at present constructed, f of an inch in internal diameter, I have been able to make an important improvement in the arrangements. The glass tubes containing the gases now dip into small mercurial reservoirs formed of thin test-tubes, which rest on ledges within the metal tubes. This arrangement has prevented many failures in screwing up the apparatus, and has given greater precision to the measurements. In the following experiments the glass tube was filled witli the gas in a pure and dry state by passing a stream for a long time through it while in an upright position ; and when the air was entirely expelled, the upper end was hermetically sealed. The stream of gas being still maintained across the lower end of the tube, which was enclosed in a test-tube partly filled with mercury, the whole apparatus was left for half an hour in an apartment at a steady temperature, after which the gas was imprisoned at a known temperature and pressure, by bringing the lower or open end of the tube into contact with the surface of the mercury in the test-tube. By this process the original volumes of air in the manometer, and of carbonic 420 On the Gaseous State of Matter. [xlix. acid in the carbonic acid tube, could be fixed with great accuracy. The -capacities of the entire tubes and of their capillary parts were ascertained by a set of careful determinations of the weight of mercury which filled them at a known temperature. Before the introduction of the mercury, the interior of each tube was carefully cleansed by boiling nitric acid in it, and afterwards washing it with distilled water and absolute alcohol. No attempt was made to I'emove by boiling the thin film of air which, even in the most carefully cleansed tube, is always interposed between the surface of the glass and the mercury drawn into the tube. Under the conditions of these experi- ments this correction must be very small ; and its estimation would be a matter o£ extreme difficulty, as in screwing up the apparatus air of different densities would be imprisoned between the glass and mercury. On a future occasion I hope to lay before the Society the results of a special investigation of this subject. The average capacity of the capillary part of the tube of the air-manometer used in the greater number of the following experiments was for 1 millimetre 0'00018121 cubic centimetre, and this tube bore a pressure of upwards of 200 atmospheres without bursting. I have completed a series of experiments at higher pressures, which I hope soon to com- municate to the Society, with a hydrogen manometer, whose capacity for each millimetre was only 0"000016861 cubic centimetre, or xt of the preceding. Such a tube would bear a pressure many times greater than the former, and no serious difficulty would arise in operating with even finer tubes. There is therefore scarcely any limit to the pressures which may be measured in glass tubes. The glass of which these tubes were made was of excellent quality, and was specially prepared for me by J. Powell & Sons. No pains were spared in calibrating the capillary portions of the tubes. For this purpose a dividing and calibrating engine was employed, which was devised some years ago by myself. It was provided with a short steel screw of remarkable accuracy, specially constructed for this dividing engine by Troughton & Simms. The results of the calibration were plotted on a large scale, and the small errors arising from the xLix.] On the Gaseous Statu of Matter. 421 abrupt passage between the calibrated lengths of the tube were estimated by a simple method, for which I am indebted to my friend Professor James Thomson. The thermometers employed were the same to which I formerly referred. They were all calibrated and divided by myself, and their agreement through- out the whole range between 0° and 100° was almost perfect. The shifting of the zero-points has not been considerable, but it was carefully observed from time to time. The capacity c^ of the glass tube at 0° C. in cubic centi- metres was calculated by the following equation, in which w is the weight of the mercury, t . the temperature at which the observation was made, and / (0-000158) the apparent dilata- tion for 1° C. of mercury in glass: — 13-596 «0='^-' • -TTTTFTT^- (1) The value of Cq, as given by this expression, may be used without notable error for temperatures differing only by a few degrees from 0° C, but at high temperatures a correction is required for the expansion of the glass vessel. If the readings had been made by means of fine divisions etched on the tube, this correction would correspond to the cubic expansion of the glass ; but when, as in my method of working, cathetometric readings are made from the extreme end of the internal cone above to the bounding surface of the mercury below, the correction will be the difference between the cubic and linear expansion of glass, or for small differences of this order it will be two thirds of the cubic expansion. If c^ be the capacity at the temperature t, k the cubic dilatation of glass for 1° C. (0'0000272), we shall have, under the conditions stated above, ,;=Co(l+U-0- (2) Combining equations (1) and (2), we obtain a general ex- pression for Cp 1o'59d 422 On the Gaseous State of Matter. [xlix. The original volume of gas at 0" and 760 millimetres was calculated by the usual formula, .-.. ^ .V (4) " '■ 1+at 760' where v^ is the capacity of the tube in cubic centimetres, a the coefiicient of expansion at the ordinary pressure of the atmos- phere (0'00367 for air and 0'0037l for carbonic acid), t the temperature of the observation, and p the height of the barome- ter reduced to 0° C. and the latitude of 45°. The pressure in atmospheres, as indicated by the air- manometer, on the gas in the carbonic acid tube was given by the equation ^- V, ■" 760' ^^ in which 'N ^ is the volume of the air at 0° and 760 milli- metres, Vj the observed volume at the temperature t, and q the difference of level (corrected when necessary for difference of capillary depression) of the surface of the mercury in the manometer and carbonic acid tubes, the negative sign applying to the case in which the mercury stands higher in the carbonic acid tube than in the manometer. The value of e, which is the ratio of the volume of the carbonic acid at the pressure p (as indicated by the air- manometer) and temperature t! to its volume at the same temperature t' under one atmosphere, is given by the equation V e= 1 . - (6) If we represent by the volume to which one volume of carbonic acid measured at 0° and 760 millimetres is reduced at the pressure p and temperature t', we shall have V 1 0) It was manifestly impossible, at the great pressures em- ployed, to surround the manometer and carbonic acid tubes xux.] On the Gaseous State of Matter. 423 with outer tubes of glass subjected internally to the same pressure, so as to equalize the pressure on both sides of the glass. Nor would any useful purpose have been attained if such an arrangement had been possible, as the thickness of the glass walls of the capillary tubes was never less than eight times the diameter of the bore, and any change in the capacity would be too small to affect sensibly the results. From a long series of experiments undertaken for the purpose of making a new determination of the compressibility of mercury, but not yet completed, I will give only the following result, as being sufficient for our present purpose: — A column of mercury 445 millimetres in length was exposed in a tube with a fine capillary bore to a pressure ranging from 5 to 110 atmos- pheres, at the temperature of 17°"60, the temperature scarcely varying 0°'01 during the experiments. The apparent change of volume for one atmosphere was found to be 0-0000070. In a repetition of the same experiment at 18°'55, the result was 0-0000072. From a series of experiments between 3-3 and 9-5 atmos- pheres of pressure, Eegnault has calculated the absolute compressibility of mercury by the aid of a set of equations which were furnished to him by M. Lamd, and found it to be 0-0000035. Although this latter result can only be regarded as an approximation to the truth, from the limited range of pressure employed, as well as from the uncertainty of some of the prin- ciples upon which the mathematical expressions depend, it may be taken to be sufficiently accurate for our present purpose. Combining it with the mean of the two foregoing numbers, we obtain for the change of internal capacity of the glass tube for one atmosphere of pressure K=0-0000036. From other experiments it would appear that the value of K diminishes as the pressure increases, a result which might 424 On the Gaseous State of Matter. [xlix. be expected from the change of volume being chiefly due to the yielding of the inner layers of the glass of which the tube was composed. For 100 atmospheres the eiitire correction would, according to these experiments, amount only to ao' oo part. I have not thought it necessary to apply this correc- tion, as it falls in most cases within the limits of the errors of observation ; but the data I have given are sufficient to allow this omission to be readUy supplied. I have deemed it important to attempt the solution of a problem of the highest interest in itself and of the greatest importance to the accuracy of many fundamental determina- tions in physics and chemistry, but which, so far as I know, has never been made the subject of direct investigation. It is to ascertain whether mercury has to any extent the property of absorbing gases in the same manner as water and alcohol. The i'act that gases like ammonia, which are largely absorbed by water, may be readily collected and preserved over mercury, and the absence of any diminution of volume in gaseous mixtures standing for long periods of time over mercury, rendered it highly improbable that any such absorption would take place. It was, however, important to ascertain whether under great pressures any indications of absorption could be found. The following is the way in which I have attempted to resolve this question. Having reduced the pressure to 10 atmospheres in the apparatus, mounted with an air-manometer and carbonic acid tube, I allowed it to remain undisturbed at this low pressure for ten days. At the end of this time, on a sunless day, which favoured accurate observations, water was made to circulate from a large cistern, at a steady temperature of 8°'39, through the rectangular vessels which enclosed the tubes ; and the pressure was then quickly raised from 10 atmospheres till half a millimetre of liquid was formed in the carbonic acid tube. The air-manometer was then read, and the apparatus left at the new pressure for five days. It was again adjusted care- fully, so that half a millimetre of liquid carbonic acid was formed as before. The temperature at this reading was 8°"45. The calculated pressures, from the indications of the air-gauge, were on the first occasion 43-94 and on the last 44'00 xLix.] On the Gaseous State of Matter. 425 atmospheres. A difference of pressure of 0'06 atmosphere corresponded therefore to a difference of temperature of 0°'06. From experiments to be described in a future communication, it will appear that at this pressure a change of 0'06 atmos- phere corresponds to 0°'055. The agreement is complete, and the air in the manometer had therefore undergone no diminu- tion of volume or absorption, after an interval of five days, from a change of pressure from 1 to 44 atmospheres. Having thus shown that air is not absorbed by mercury, it remained to extend the inquiry to the case of carbonic acid gas. For this purpose the apparatus was again left at a pressure of 10 atmospheres for some days, and the pressure was then quickly raised at 4°'99 to 35'89 atmospheres, at which pressure the carbonic acid was still wholly in the gaseous state. After reading the volumes of air and carbonic acid gas in the two tubes, the apparatus was left at the new pressure for two days, when the observation was repeated at the same temperature, the pressure having been adjusted as at the first observation. The readings of the two tubes were precisely the same as before. Now as the former experiments had proved that the air in the manometer under increased pressure under- goes no absorption, the last experiment evidently extends this conclusion to carbonic acid gas. In confirmation of this result, I may mention that after allowing the apparatus to stand for many hours at a pressure of above 100 atmospheres, and then suddenly reducing the pressure to 10 atmospheres, not the slightest evidence of the escape of gas from the surface of the mercury could be detected even with the aid of a strong magnifier. In filling a barometer-tube the air which is expelled by ebullition has not been dissolved in the mercury, but comes from the thin shell of air interposed between the mercury and the surface of the glass. Two questions still remain to be considered. 1. Do the glass tubes undergo a permanent increase of capacity when exposed for a long time to these high pressures ? 2. Is there any absorption of oxygen in the air-manometer from its slow combination with the mercury ? To both questions I am able to give a satisfactory answer. The apparatus was mounted on October 30, and three days after the pressure at which carbonic 42C On the Gaseous State of Matter. [xlix. acid liquefies when the temperature is 8°-41 was found in two experiments to be 43-90 and 43-94 atmospheres, the mean being 43-92 atmospheres. During the following two months the apparatus was in daily use for a long course of experiments, in which the pressures varied from 12 to 120 atmospheres, and the latter pressure was often maintained for the space of 24 hours. On the 1st of January the pressure required for liquefaction was again determined at the same temperature of 8°-41. In three experiments it was found to be 43"96, 43-96, and 43-94 atmospheres — the mean, or 43-95 atmospheres, differing only by 0-03 atmosphere from the former result. This is quite within the limits of error of observation, as it corresponded to a difference of less than O'l millimetre in the actual readings. It follows therefore that there has been no appreciable enlargement of the internal capacity of the tube, or reduction of the volume of the air from chemical combina- tion or absorption, during a period of two months of active work. That no oxidation of the mercury had occurred was further shown by the bright metallic surface of the fine mercurial column, and the absence of any tendency to drag when the mercury rose or fell from change of pressure.^ It is with regret that I am still unable to give the true pressures which correspond to the indications of the air- manometer. Since my former communication in 1869, I have given the most careful consideration to this subject, and I hope soon to submit to the Society a detailed statement of the only method by which, as far as I can discover, this highly im- portant question can be resolved for high pressures. Even for pressures under 3 atmospheres the discordant results at which such distinguished physicists as Oersted and Swendsen, Arago and Dulong, and Eegnault have arrived, afford ample proof of the extraordinary difficulties of the investigation.^ I shall ^ While writing the above I have carefully examined the apparatus, and find it to be now in as perfect order as when it was mounted five months ago, the mercury in the air-manometer moving through its extreme range as readily and with as much precision as in a thermometer of the best construction. — [March 22.] ^ Arago and Dulong inferred from their experiments, extending from 1 to 27 atmospheres, that the law of Boyle is strictly true in the case of air ; and the same conclusion was also drawn by Oersted and Swendsen from their own ex- xLix.] On the Gaseous State of Matter. 427 have occasion presently to recur to this subject, and to refer to the attempts which have since been made by other methods to ascertain the compressibility of air and of the permanent gases at high pressures. In the absence of precise data, I have not attempted in this paper to correct the indications of the air-manometer so as to reduce them to true pressures. "We shall see hereafter that up to 250 atmospheres there is good reason for believing that the deviations of the air-manometer from true pressures are not considerable, or such as to interfere v?ith any general conclusions. In the present investigation on the properties of the gaseous state of matter I have, as in my former researches, selected carbonic acid gas (CO,) for experiment, partly from the facility with which it can be prepared in a state of parity, but chiefly from its critical temperature being only 81° above the freezing- point of water. It may fairly be taken as a typical representative of the gaseous state, and, as we shall see, it is in a condition peculiarly favourable for the discovery of the laws which govern the action of the internal or molecular forces in that state. The experiments of Oersted and Swendsen, of Despretz and of Pouillet, have shown that when exposed to increasing pressure it deviates sensibly from the law of Boyle ; and Eegnault has measured with precision its compressibility at 3° for pressures reaching to 27 atmospheres, and has like- wise confirmed the observation of Von Wrede, that even at pressures below one atmosphere it deviates sensibly from Boyle's law. The carbonic acid gas was prepared by the action of pure and dilute sulphuric acid, deprived of its air by boiling, upon marble. It was carefully desiccated by passing through a U-tube filled with fragments of pumice freed from chlorides, and moistened with pure sulphuric acid. In Tables I., II., and III. will be found the results of a large number of experi- ments on the compressibility of carbonic acid at temperatures differing little respectively from 6°'5, 64°, and 100°. For the periments. From a careful analysis of their results, as given in the original memoir of Arago and Dulong (Mimoires de I'Acadimie des Sciences, x. p. 207), it appears to me that their experiments rather indicate a deviation from the law of Boyle, but to not more than one third of the amount given by the subsequent researches of Regnault (Mim. de I'Acad. des Sciences, xxi. p. 421). 428 071 the Gaseous State of Matter. [xlix. lower temperature a stream of cold water from a large cistern was made to flow at a uniform rate around the carbonic acid tube. The manometer-tube was kept at a steady temperature by a similar arrangement. The temperature of 64° was obtained by passing the vapour of pure and anhydrous methyl-alcohol through the apparatus.^ About two thirds of a litre of the alcohol was distilled over in each observation, the temperature being observed by one of the thermometers before referred to. The temperature obtained in this way, after every precaution has been taken, is far from being so steady as that given by the vapour of water ; but with a little care very accurate deter- minations can be made. A deduction of 0°-14 was made from the direct reading as a correction for the error of the thermo- meter due to irregular expansion of the mercury. For temperatures about 100°, vapour of water from a boiler in an adjoining apartment was passed around the carbonic acid tube and conveyed away by an exit-pipe through an outer wall of the apartment. Its pressure when in the vessel around the carbonic acid tube was usually about 50 millimetres of water above that of the atmosphere, as ascertained by a U-shaped water-gauge connected with the apparatus. By adding the pressure indicated by the water-gauge to the height of the barometer, the elastic force of the steam, and conse- ({uently its temperature, was known. In the following tables I have recorded the results of direct experiments, all made by myself, and reduced by the equations already given. In every case two experiments at least, and often more than two, were made, the apparatus being thrown out of adjustment and readjusted between each observation. The mean numbers given in the tables- scarcely differed by an appreciable amount from the results of the individual experi- ments. In Tables I., II., and III., p is the pressure in the carbonic ^ Both the air-tnbe and carbonic acid tube were enclosed in rectangular brass vessels, having plate-glass sides inserted before and behind, by which means accurate readings, not attainable in ordinary glass cylinders, were secured. Through these rectangular vessels the water or vapour circulated, by means of which the tubes were maintained at fixed temperatures. A detailed description, with a figure of the apparatus, will be found in my former communication, Phllo.iophkal Transactions iov 1869, p. 578. [jIb^p, pp. 300,301.] XLIX.] On the Gaseous State of Matter. 429 acid tube calculated from the indications of the air-manometer, t the temperature of the manometer, e the ratio of the observed volume of the carbonic acid at the pressure p and temperature t' to its volume at the same temperature t' under a pressure of one atmosphere, t' the temperature of the carbonic acid, and the volume to which one volume of carbonic acid, measured at 0° and under one atmosphere, is reduced at the pressure p and temperature t'. By one atmosphere of pressure is meant the pressure of a column of mercury 760 millimetres in length measured at 0° and under the latitude of 45°. Table I. — Compressibility of Carbonic Acid Gas. — 6°'0-6°'9, p- t. - i'. e. 12-01 6-91 1 6-89 0-07921 13-22 6-90 1 14-38 6-90 0-07143 14-68 6-90 1 Iti-lli 6-90 0-06364 17-09 6-45 1 19-12 6-44 0-05371 20-10 6-79 1 23-01 6-79 0-04456 22-26 6-07 1 25-91) 6-05 0-03934 24-81 6-72 1 29-00 6-73 0-03462 27-69 6-07 34 -uy 6-05 0-02999 31-06 6-65 89-57 6-62 0-02589 34-49 6-03 45-96 6-02 0-02224 Table II. — Compressibility of Carbonic Acid Gas.- 63°-6-64°-0. P' t. - t'. e. 17-60 9°-30 1 18-57 63°-86 0-06671 20-36 9-19 1 21-66 63-76 005710 22-56 8-82 1 24-iy 63-79 005113 25-06 8-82 1 27-09 63-77 0-04564 28-07 8-85 1 30-63 63-85 004035 31-39 8-85 1 34-68 63-83 0-03560 430 On the Gaseous State of Matter: Table II. — Continued. [XLIX. p- t. - t'. 0. 34-92 8-85 1 39-10 63°-65 0-03162 40-54 8-75 1 4B-37 63-64 0-02665 46-56 8-97 ■1 5J-6i 63-68 0-02264 54-33 8-99 1 6S-00 63-57 0-01871 64-96 9-05 1 83-63 63-74 001480 81-11 9-13 1 114-2 63-75 0-01083 106-88 9-20 1 181i-0 63-75 0-00665 145-54 9-25 1 32?-6 63-70 0-00377 222-92 9-22 1 447-0 63-82 0-00277 Table III. — Compressibility of Carbonic Acid Gas.- 99°-5--100°-7. p- t. fc. t'. 0. 17-42 5-83 1 18-01 106-39 0-07628 20-17 6-04 1 20-97 100-37 0-06543 22-37 6-01 1 23-34 100-41 0-05880 24-85 6-00 1 20-07 100-72 0-05269 27-76 5-83 1 29-30 100-65 0-04687 31-06 5-88 1 33-03 100-64 004158 34-57 5-92 1 37-00 100-62 0-03705 40-09 5-94 1 43-50 100-60 0-03156 45-99 6-31 1 60-60 100-37 002712 53-81 6-34 1 60-20 100-33 0-02277 64-27 6-34 1 73-89 100-37 0-01857 80-25 6-35 1 36-52 100-37 0-01422 105-69 6-36 1 137-3 100-37 0-01000 145-44 8-73 1 219-0 99-46 0-00625 223-57 8-72 1 380-3 99-44 0-00359 xLix.] On the Gaseous State of Matter. 431 Before discussing these results on the compressibility of carbonic acid, it will be convenient to have accurate data for reducing the experiments in each table to the same tem- perature. These data will be supplied when the coefficients of expansion of carbonic acid under vaaied pressures and at different parts of the thermonietric scale are known. The determination of these coefficients will form the subject of the next section. §11. In the limiting case of the so-called perfect gas, which is closely approximated to but probably never actually realized in nature, the change of volume under a constant pressure would for the same range of temperature correspond exactly to the change of elastic force under a constant volume.^ In the case of carbonic acid, Eegnault has shown that, even at low pressures, there is a marked difference in the value of a as given by the two methods ; and from the experiments I am about to describe, it will appear that at high pressures the results diverge so widely that they must not in any way be confounded with one another. For the sake of precision, I propose to designate by a the coefficient of expansion for change of temperature under a constant pressure, and by a the coefficient of elastic force for change of temperature under a constant volume. We shall confine our attention in this section to the determination of the values of a under varied pressures and at different parts of the thermal scale. In the next table the results are given of a set of experi- ments I have made to determine the average coefficient of expansion for heat of carbonic acid from 0° to about 7°'5 under pressures varying from 12 to 34"5 atmospheres. For this range of temperature the pressures could not be carried higher, on account of the liquefaction of the gas. In this table p is the pressure as indicated by the air-manometer, t the temperature of the manometer, and v' the volume in ' Accordin!^ to Rudberg the coefficient of expansion of air between 0° and 100°, deduced from the two methods, is precisely the same ; according to Regnault there is an actual difference of ^J^- part of the wliole coefficient {Poggendorffs Annaleu, vol. xliv. p. 122 ; M4m. tie I'Acad. des Sciences, vol. xxi. p. 119). 432 On the Gaseous State of Matter. [XLTX. cubic centimetres of the carbonic acid at the pressure 2> and temperature t'. Table IV. — -Values of a from 0° to 7°-5. — Constant Pressure. p- t. v'. t'. a. 12-02 12-00 7-53 6-73 0-07298 0-07065 7-54 0-00 0-00462 16-22 16-25 7-65 6-65 0-05243 0-05031 7-64 0-00 0-00520 20-10 20-09 7-61 6-64 0-041.08 0-03928 7-63 0-00 0-00607 24-81 7-63 0-03192 7-64 0-00700 24-80 6-64 0-03031 0-00 27-70 7-44 0-02775 7-45 0-00782 27-66 6-47 002627 0-00 31-07 31-06 7-65 6-64 002386 002234 7-65 0-00 0-00895 34-49 7-45 002058 7-46 001097 34-48 6-64 0-01903 000 In calculating the values of a in the foregoing table, the observed volume {v') of the carbonic acid at the higher temperature (7°-54 etc.) was in each case corrected for the small differences of pressure which occurred in the observa- tions at that temperature and at 0°. In many cases it would have been suflScient to make this correction by Boyle's law ; but the exact data for the purpose being supplied by Tables I., II., and III., I have in these and other similar cases always employed the direct results given by experiment of the com- pressibility of carbonic acid at the pressures and temperatures indicated. In the two following tables the values of a are calculated from the results in Tables I., II., and III., the value of 6 in Table I. having been first reduced to 0° by means of the coefficients at the respective pressures given in Table IV. xLix.] On the Gaseous State of Matter. 433 Table V. — Values of a from 0° to 64°. — Constant Pressure. p- t'. 0. u. 17-09 20-10 22-26 24-81 27-69 31-06 34-49 0-00 63-86 0-00 63-76 0-00 63-79 0-00 63-77 0-00 63-85 0-00 63-83 00 63-65 0-05190 0-06892 0-04280 0-05790 0-03785 0-05188 0-03306 0-04614 0-02864 0-04096 0-02444 0-03603 0-02086 0-03208 0-005136 0-005533 0-005811 0-006204 0-006737 0-007429 0-008450 Table VI. — Values of a from 0° to 100°. — Constant Pressure. p- t'. 0. a. 17-09 20-10 22-26 24-81 27-69 31-06 34-49 6-00 100-39 0-00 100-37 0-00 100-11 000 100-72 0-00 100-65 000 100-64 000 100-62 0-05190 0-07792 0-04280 0-06567 0-03785 0-05906 0-03306 0-05278 0-02864 0-04700 0-02444 0-04158 0-02086 0-03715 0-004994 0-005324 0005597 . 0-005922 0-006369 0-006968 0-007762 1 ' By an entirely diflferent method Regnault has examined the expansion by heat of carbonic acid gas between 0° and 100° for pressures varying from 1 to 15-6 atmospheres. As his results form a consecutive series with those of Table VI. I subjoin them. It must be remembered that p represents here true pressures in atmospheres. p. a. p. a. 1-00 0-003710 917 0-004227 3-32 00.3845 11-27 0-004408 5-64 0-004006 15-61 0-004858 (Mim. de I'Acad. des Sciences, vol. xxi. p. 117, and vol. xxvi. p. 575.) 2 E 434 On the Gaseous State of Matter. [XLIX. From Tables V. and VI. it is easy to calculate the values of a from 64° to 100° referred to the unit volume at 0°. These values will be found in the fourth column of the next table, and for comparison the values of a at the corresponding pressures from 0° to 7°-5 and from 0° to 64°, have been taken directly from the same tables. Table VII. — Values of a at different temperatures.- Pressure. -Constant p- u. 0°-7°-5. 0°-64°. 64°-I00°. 17-09 0-005136 0-004747 20-10 0-00607 0-005533 0-004958 22-26 0-005811 0-005223 24-81 0-00700 0-006204 0-005435 27-69 0-00782 0-006737 0-005730 31-06 0-00895 0-007429 0-006169 34-49 001097 0-008450 0-006574 It has hitherto been assumed, but without direct experi- mental proof, that matter in the gaseous state will expand for every degree through which it is heated by the same fraction of its volume at 0°, provided the pressure remains constant. This important law, which is due to Gay-Lussac, is un- questionably true in the case of the perfect (ideal) gas ; and in the case of air a:nd other gases which have not been liquefied, it may be employed for all practical purposes without sensible error. But, as far as I have been able to discover, no experiments have hitherto been published to determine under what limitations it applies to the gaseous state as that state is presented to us in nature.^ It will be evident from a cursory ^ Biot states, indeed, somewhat vaguely, that Gay-Luasac verified this law experimentally for air and other gase3 and found it to be strictly true ; but the experiments themselves have never been published, and the methods of xLix.] On the Gaseous State of Matter. 435 inspection of Table VII. that this law does not hold good in the ease of carbonic acid gas even at moderate pressures, and that the divergence from the law becomes greater as the pressure is increased. Thus under a pressure of 20"1 atmos- pheres the coefficients of expansion, referred to the same unit, between 0° and 7°-5, 0° and 64°, and 64° and 100° respectively, are in the ratio of the numbers 1-000, ' 0-911, 0-817; and under a pressure of 34-49 atmospheres the corresponding ratios for the same ranges of temperature are 1-000, 0-770, 0-599. It is scarcely necessary to add that if the law of Gay-Lussac held good, the coefficients in all these cases would have been the same, and their ratios expressed by 1-000. I have not made any comparative experiments at pressures lower than 1 7 atmospheres ; but there can be no doubt that, even at the ordinary pressure of the atmosphere, carbonic acid gas will diverge sensibly from Gay-Lussac's law, and that its coefficient of expansion under constant pressure will change with the temperature, being less at high than at low temperatures. It follows from these observations that the coefficients of expansion in the foregoing tables are the average coefficients for the ranges of temperature to which they apply. It would not be difficult from the experimental results to obtain an empirical formula which would give approximately the coefficient or rate of expansion, at any temperature and under any pressure, within the range of the experiments, so as to construct tables showing the expansion by heat of carbonic acid under different pressures. But I have refrained from doing so, as such a table would seldom be required in practice ; and for scientific purposes, as I have had occasion in the course of this inquiry investigation employed by Gay-Lussao are now known to have been imperfect, so that they failed even to show the differences in the dilatation by heat of different gases (Biot, Traiti de Physique, vol. i. p. 188). The experiments of Kegnault on the comparative march of the air and carbonic acid thermo- meter, to which I shall have occasion hereafter to refer, were made by observing the change of elastic force under a constant volume. Regnault states expressly that he made no corresponding experiments under constant pressure (Mim. de V Acad, des Sciences, vol. xxi. pp. 168-171). 436 On the Gaseous State of Matter, [XLIX. more than once to observe, the results of empirical formulse are apt to mislead the investigator and rarely aid research. For the same temperature, the coefficient of expansion increases as the pressure augments, and more rapidly at low than at high temperatures. In the preceding tables, the pressures, being always referred to the unit volume at 0°, could not be carried beyond 34-5 atmospheres. In the next table the coefficient of expansion for heat of carbonic acid gas, referred to the unit volume at 64°, is given at pressures ranging from 17 to 223 atmospheres. Table VIII. — Values of a from 64° to 100°. — Constant Pressure. Volume at 64°=!. p- t'. e. u. 17-09 20-10 22-26 24-81 27-69 31-06 34-49 40-54 46-54 63-86 100-39 63-76 100-37 63-79 100-11 63-77 100-72 63-85 100-65 63-83 100-64 63-65 100-62 63-64 100-60 63-68 100-37 0-06892 0-07792 0-05790 0-06567 0-05188 0-05906 0-04614 0-05278 0-04096 0-04700 0-03603 0-04158 0-03208 0-03715 0-02665 0-03118 0-02264 0-02676 0-003572 0-003657 0-003808 0-003892 0-004008 0-004187 0-004266 0-004596 0-004946 XLIX.] On the Gaseous State of Matter. Table VIII. — Continued. 437 p- t. e. u. 54-33 63-57 100-33 0-01871 0-02252 0-005535 64-96 63-74 100-37 0-01480 0-01833 0-006512 81-11 63-75 100-37 0-01083 0-01402 0-008033 63-75 0-00665 106-9 100-37 0-00986 0-013150 145-5 63-70 99-62 0-00377 0-00625 0-018222 2230 63-82 99-44 0-00277 0-00360 0-008402 The coefficient of expansion, it will be observed, steadily increases with the pressure, till at 145-5 atmospheres it has reached the large value of 0-01822. But as the pressure is further augmented, the coefficient, instead of continuing to increase, begins to diminish; and at 223 atmospheres it has actually fallen to 0-008402, or to less than one-half its value at 145 atmospheres. This change of direction in the value of the coefficient is easily explained, if we observe that carbonic acid at 64° has entered, under these high pressures, into those intermediate conditions which form the link between the gaseous and liquid states of matter. It has, in short, at 223 atmospheres, approached the liquid volume without liquefying, and its coefficient begins to change to that which belongs to the liquid state. We shall find in the course of this inquiry abundant proofs of the accuracy of this statement. §111. We now proceed to consider the change in the elastic force of a gas when, the volume being maintained constant, the 438 On the Gaseous State of Matter. [XLIX. temperature is altered. As in the expansion of a gas under constant pressure, we have here two distinct questions to con- sider, both of which are highly important in reference to the laws of molecular action. The first question is the effect of increase of pressure on the value of the coefficient ; the second, the change, if any, of the coefficient for different parts of the thermal scale. The apparatus required no modification what- ever for these experiments ; but in making the adjustments for constant volume, the change of volume of the glass tube must be carefully allowed for, as the same reading by the catheto- meter wiU not correspond to the same volume at different temperatures. The correction was always made by the equation given before, Ct, = e^{\ +W)- As I have already mentioned, the coefficient of elastic force under constant volume will be designated by a', to distinguish it from a the coefficient of expansion under constant pressure. In the following tables the letters p, t, and t' have the same signification as before, but instead of Q, the actual volumes, in fractions of a cubic centimetre, of the carbonic acid are given in the column designated COg. In calculating the coefficients, a slight correction had to be applied to the observed pressures when the volume of the carbonic acid was not precisely the same at the corresponding observations. Table IX.— Values of a' from 0° to 6°-5. — Constant Volume. p- t. CO^. t'. a'. 21-48 7°-27 0-03623 d-QO 0-00537 22-18 6-08 0-03623 6-07 25-87 26-86 7-17 6-51 0-02867 0-02867 0-00 6-51 0-00588 33-53 7-27 0-01983 0-00 35-13 6-51 0-01983 6-50 000734 XLTX.] On the Gaseous State of Matter. 439 Table X. — Values of a from 0° to 64°. — Constant Volume. p- t. CO2. t'. b-00 64-00 a'. 16-42 21-42 7-29 3-68 0-04969 0-04968 0-004754 21-48 28-65 7-27 3-69 0-03623 0-03624 0-00 63-80 0-0052.37 25-87 35-29 7-17 3-70 0-02867 0-0-2869 o-od 63-74 0-005728 30-37 42-74 6-75 3-27 0-02304 0-02303 0-00 63-98 0-006357 33-53 48-40 7-27 3-36 0-01983 0-01986 6-60 63-94 0-006973 Table XI. — Values of a' from 0° to 100°. — Constant Volume. p- t. CO2. t'. a'. 16-42 24-19 7°-29 3-70 0-04969 0-04969 6-00 100-67 0-004700 21-48 7-27 0-03623 0-00 0-005138 32-60 3-70 0-03622 100-67 25-87 7-17 0-02867 0-00 0-005610 40-44 3-73 0-02870 100-67 30-37 49-25 6-75 3-65 0-02304 0-02303 0-00 100-54 0-006177 33-53 56-16 7-27 3-64 0-01983 0-01986 0-00 100-48 0-006741 440 On the Gaseous State of Matter. [XLIX. From Tables X. and XL the values of a from 64° to 100° referred to the unit pressure at 0° are easily calculated. In the next table the values of a at the different parts of the thermal scale are given, ^ being the initial pressure in each case. Table XII. — Values of a at different temperatures. — Constant Volume. p- a\ 0°-6°-5. 0°-64°. 64°-100°. 16-4:2 0-004754 0-004607 21-48 0-00537 0-005237 0-004966 25-87 0-00588 0-005728 0-005406 30-37 ■ • ■ • * < 0-006357 0-005861 33-53 0-00734 0-006973 0-006334 It follows from this investigation that the value of a is greater at high than at low pressures ; it changes also with the temperature, the pressure remaining constant, being less at high than at low temperatures. The values are, for this reason, average values for each range of temperature. The law of Gay- Lussac, therefore, fails both in the case of a and of a ; that is to say, the dilatation hy heat of a tody in the ordinary gaseous state, whether measured hy its expansion under constant pressure or by the increase of elastic force under constant volume, is not a simple function of the initial volume or initial elastic force, hut a complex function changing with the temperature} In the next Table will be found the change in the value of a' between 64° and 100° under a large range of pressure and referred to the pressure at 64° as unit. ^The statement of Kegnault that the air and carbonic acid thermometei'S march sensibly together appears to be at variance with this conclusion. But Eegnault's own experiments, which were made at pressures differing little from that of the atmosphere, indicate an unequivocal although small difference, and in the right direction, between the two thermometers. With a sulphurous acid thermometer the difference was considerable, and in conformity with the result stated in the text (Mim. de I'Acad. des Hciencet, vol. xxi. pp. 187-88). XLIX.] On the Gaseous State of Matter. 441 Table XIII. — Values of a from 64° to 100".— Constant Volume. Pressure at 64°= 1. p- t'. C0„. a'. 21-42 24-19 64-00 100-67 0-04968 0-04969 0-003526 28-65 32-60 63-80 100-67 0-03624 0-03622 0-003718 35-29 40-44 63-74 100-67 0-02869 0-02870 0-003956 42-74 49-25 63-98 100-54 0-02303 0-02303 0-004166 48-40 56-16 63-94 100-48 0-01986 0-01986 0-004387 67-65 80-99 63-80 100-50 0-01288 0-01289 0-005392 94-27 118-60 63-78 100-50 0-00778 0-00778 0-007018 §IV. We are now prepared for the discussion of the general results of this investigation. For this purpose it will be convenient to reduce the values of e as given in Tables I., II., and III. to the exact temperatures of 6°-5, 64°, and 100° respectively. The differences between the temperatures (f) at which the observa- tions were made and these numbers are so small that the reductions presented no difficulty with the data furnished in § II. In the last column of the three following tables will be found the values of p as given by the equation p = ep. 442 On the Gaseous State of Matter. Table XIV. — Values of jo at 6°-5. [XLIX. p- t'. c. P- 12-01 6-5 1 12-95 0-9274 13-22 6-5 1 14-37 0-9200 14-68 6-5 1 16-13 0-9101 17-09 6-5 1 19-12 0-8938 20-10 6-5 1 23-U3 0-8728 22-26 6-5 1 26-96 0-8575 24-81 6-5 1 29-62 0-8376 27-69 6-5 34-03 0-8137 31-06 6-5 1 J1J-S9 0-7845 34-49 6-5 1 45-81) 0-7530 Table XV. — Values of p at 64°. p- t'. «. P- 17-60 64 1 i8-5r 0-9478 20-36 64 1 21-65 0-9404 22-56 64 1 24 18 0-9330 25-06 64 1 27-08 0-9254 28-07 64 1 30-64 0-9161 31-39 64 1 34-67 0-9054 34-92 64 1 39-08 0-8935 40-54 64 1 46-34 0-8748 46-56 64 1 64-57 0-8532 54-33 64 1 66-97 0-8235 64-96 64 1 83-44 0-7785 81-11 64 1 114-0 0-7115 106-88 64 1 186-6 0-5762 145-54 64 1 325-9 0-4466 222-92 64 1 446-4 0-4994 XIJX.] On the Gaseous State of Matter. Table XVI. — Values of p at 100°. 443 p- t'. P- 20-17 100 aras 0-9614 22-37 100 23-35 0-9580 24-85 100 26 OS 0-9525 27-76 100 2a -32 0-9468 31-06 100 3305 0-9398 34-57 100 37T)9 0-9320 40-09 100 SU 0-9208 45-99 100 5^63 0-9083 53-81 100 6M0" 0-8924 64-27 100 ra-97 0-8689 80-25 100 S6-65 0-8303 105-69 100 137^ 0-7681 145-44 100 818-0 0-6671 223-57 100 1 379-3 0-5894 Trom the results given in the last three tables, it is mani- fest that the values of p, which in the case of a perfect (ideal) gas would always be unit, steadily diminish for the same tem- perature as the pressure increases. An important exception to this remark occurs in the last recorded result in Table XV., from which it appears that at the temperature of 64° the value of jo, which had diminished from 0-9478 to 0-4466 as the pressure was raised from 17"6 to 145-5 atmospheres, instead of continuing to diminish with a further increase of pressure, actually changes its direction, and at 223 atmospheres has increased to 0-4994. No change of this kind occurs at 100°, although the experiments were carried to 224 atmospheres. The explanation of this change in the value of p, after a certain pressure has been reached, I have already anticipated when referring to a similar change in the coefficient of expansion by heat at high pressures, as shown in Table VIII. At the temperature of 64°, and under a pressure of 223 atmospheres, carbonic acid has in fact approached the liquid volume, while 444 On the Gaseous State of Matter. {xlix. passing through those intermediate conditions of matter which, in a former Bakerian Lecture, I have described as establishing an unbroken continuity between the ordinary gaseous and ordinary liquid states. At 100° carbonic acid under the same external pressure has not reached this stage of the process ; but if the experiment had been carried to higher pressures, a like change in the value of p would no doubt have occurred. These remarks will be fully confirmed when I give the values of p for the gaseous and liquid states at the same temperature, as calculated from my former experiments.^ The true import of the values of |0 at a constant temperature will be considered hereafter. From Tables XIV., XV., and XVI. it further appears that the values of p approach more nearly to unit the higher the temperature, in accordance with the principle I deduced from my former experiments, that as the temperature becomes higher the curves representing the change of volume of carbonic acid at different pressures approach more nearly to the curve of a perfect gas. But to find the actual relation which exists between these curves it will be necessary to make a prelimi- nary calculation. In the curves representing the changes of volume of a gas by pressure at different temperatures, I propose to designate those points where the values of p are equal, homologues, or homologous points, and the lines passing through corresponding homologues, homologous lines. Let ju. be the ratio between the external pressures p and p' at homologous points on the curves of any two temperatures, or P In Tables XVII. and XVIII. the values of /jl are calcu- lated for the respective temperatures of 6°'5 and 64°, and of 64° and 100°, from the values of jo in the preceding tables. The necessary reductions to obtain the homologous points at each temperature were carefully made. 1 Philosophical Trmiaactionn for 1809, p. 581. [Ante, p. 305.] xLix.] On the Gaseous State of Matter. Table XVII. — Values of m for 6 "-5 and 64° 445 p- P (6°-5). P' (64°). /J.. 0-9254 12-31 25-06 0-491 0-9161 13-79 28-07 0-491 0-9054 15-39 31-39 0-490 0-8935 17-13 34-92 0-491 0-8748 19-81 40-54 0489 0-8532 22-83 46-56 0-490 0-8235 26-51 54-33 0-488 0-7785 31-73 64-96 0-489 Prom the foregoing table it appears that the values of fi within the limits of pressure employed are always equal — that is to say, the ratio of the external pressures is always the same for homologous points of the curves of 6°-5 and 64°. The experi- ments could not be carried to higher pressures on account of the liquefaction of the gas at 6°-5. In the next table the values of /x for the homologues of 64° and 100° are given. Table XVIII. —Values of /x for 64° and 100°. p- P (64°). p' (100°). /t. 0-9404 20-36 30-79 0-661 0-9330 22-56 34-10 0-662 0-9254 25-06 37-88 0-662 0-9161 28-07 42-37 0-662 0-9054 31-39 47-39 0-662 0-8935 34-92 53-29 0-655 0-8748 40-54 61-76 0-656 0-8532 46-56 70-95 0-656 0-8235 54-33 83-04 0-654 0-7785 64-96 101-53 0-640 0-7115 81-11 127-96 0-634 0-5762 106-80 236-84 0-451 The values of /x are again equal till very high pressures are reached. Thus from 20-4 to 31-4 atmospheres, and from 30-8 to 47"4 atmospheres, the agreement is absolute ; after which 446 On the Gaseous State of Matter. [XLIX. a slight diminutioii in the value of /j. occurs, but only to the amount of ^ of the whole, till the respective pressures of r)4"3 and 83-0 atmospheres are attained. Even at 81'1 and 128-0 atmospheres the value of /x has only fallen from 0'661 to 0"634. But at still higher pressures we reach a new phase, and at the respective pressures of 107 and 237 atmospheres the value of M- has fallen to 0'451. I have calculated the values of p and /m from the experiments at lower temperatures in my former communication.^ As these experiments were chiefly made at temperatures not much above the critical point of carbonic acid, when the intermediate con- ditions of matter corresponding to the fall from the gaseous to the liquid state, and those corresponding to the liquid state itself, are easily recognized, they form a valuable complement to the foregoing. Table XIX.— Values of f at 31°-1, 35°-5, and 48°-l. 31 °-i. 35 °-5. 48 --1. p- P- P- p- P- p- 54-79 0-6802 56-80 0-6866 62-60 0-7241 55-96 0-6710 59-34 0-6672 6846 0-6888 57-18 0-6604 62-15 0-6446 75-58 0-6416 58-46 0-6493 65-23 0-6154 84-35 0-5746 59-77 0-6368 68-66 0-5799 95-19 0-4795 61-18 0-6238 72-45 0-5363 109-40 0-3666 62-67 0-6078 76-58 0-4751 64-27 0-5864 81-28 0-3565 65-90 0-5671 86-60 0-2461 67-60 0-5434 89-52 0-2395 69-39 0-5159 92-64 0-2388 71-25 0-4821 99-57 0-2423 73-26 04335 107-60 0-2501 73-83 0-4233 75-40 0-2424 77-64 0-2103 79-92 0-2087 82-44 0-2083 85-19 0-2101 'Philosophical Transaetiom for 1869, pp. 584-86. [Ante, pp. 309-11.] xLix.] On the Oaseoua State of Matter. Table XX. — Values of /j. for 31°-1 and 48°-l. 447 />• p (sr-i). P' (48°-l). /*• 0-6802 54-79 69-81 0-785 0-6710 5596 71-26 0-785 0-6604 57-18 72-93 0-784 0-6493 58-46 74-51 0-785 0-6368 59-77 76-25 0-784 0-6238 61-18 78-06 0-784 0-6078 62-68 80-00 0-784 0-5864 64-27 82-81 0-777 0-5671 65-90 85-20 0-773 0-5434 67-60 87-91 0-769 0-5159 69-39 91-04 0-762 0-4821 71-25 94-90 0-751 0-4335 73-26 100-98 0-726 0-4233 73-83 102-26 0-722 0-2424 75-40 125-00 0-603 Table XXI. — Values of m for 3o°-5 and 48°-l. p- p (35° -5). P' (48°-l). M- 0-6866 56-80 68-81 0-826 0-6672 59-34 71-86 0-826 0-6446 62-15 75-16 0-827 0-6154 65-23 79-22 0-824 0-5799 68-66 83-71 0-820 0-5363 72-45 88-98 0-814 0-4751 76-58 95-72 0-800 These results, calculated from experiments published seven years ago, are in complete accordance with the conclusions 1 have deduced from the present investigation. On comparing the pressures with the graphic representation given in the UH On the Gaseous State of Matter. [XLIX. paper referred to, it will be seen that, so long as the values of fi are equal, the carbonic acid is in the gaseous state proper at the lower as well as at the higher temperature ; but^ when they undergo a marked diminution, the carbonic acid has k entered into the intermediate conditions corresponding at lower temperatures to the fall to the liquid state. Finally, when the liquid volume has been attained, the value of p itself changes its direction, as may be seen in the results of the final experi- xLix.] On the Gaseous State of Matter. 449 ments at 64°, 31°-1, and 3o°-5 (Tables XV. and XIX.). In the annexed sketch the portions of the curves above a, a, a" are in the gaseous state ; from a to 6 we have in the curve for 21°- 5 the fall from the gaseous to the liquid state; and from a' to b' and a" to h", in the curves for 31°-1 and 35°-5, the intermediate conditions between the gaseous state and liquid volume corresponding to the fall to the liquid state at lower temperatures. As in a gas below the critical tempera- ture we have, (1) the gaseous state, (2) the fall to the liquid, and (3) the liquid state, so in a gas above the critical tem- perature we have, (1) the gaseous state, (2) the intermediate conditions corresponding to the fall, and (3) the conditions corresponding to the hquid volume. The first or gaseous state is characterized by the external pressures for homologous points at any two given temperatures being always in the same ratio to one another ; in the second state, or state of change corresponding to the fall to the liquid, this ratio changes rapidly ; while in the third, or, as we may designate it, the liquid-volume state, new molecular conditions supervene, as shown by the increase in the value of p. As the result of the foregoing investigation, the relations between pressure and volume in the ordinary gaseous state at different temperatures may be stated in the following terms :— - On any two isothermal curves which show the volume of carbonic acid gas under change of pressure at definite tem- peratures, the values of p at the homologous points being always equal, or pv=p'v' ... ... (A) (where, it must be carefully observed, v and v' are the volumes of the gas on different isothermals), it has been shown that for all such homologous points on any two isothermals 4 = M (B) jp where /x is a constant. The full import of homologous points will be further under- stood from the following considerations : — Let the line a h represent a volume of carbonic acid gas at the temperature t and pressure p, and let the pressure be increased to p, the 2f 450 On the Gaseous State of Matter. [XLIX. new volume a' V of the gas will be less than aS— • Let the gas be now heated at the pressure / till its volume a'c is equal to a6^, and let the temperature be now t' ; the point c on the isothermal t' will be the homologue of the point I on the isothermal t. If the gas from p to p' had diminished in volume as a perfect gas, c would have been a point on the XLIX.] On the Gaseous State of Matter. 4-51 isothermal t. In short, the homologue c, of the point b on the isothermal t, is a point on the isothermal t' at which the action of the internal forces, in reducing the volume of the gas when the external pressure is increased from p to p', is exactly counterbalanced by the action of the expansive forces in heating the gas from t to t'. By means of equations (A) and (B), if we know the relations of pressure and volume for a gas at any one temperature, we can, by the observation of a homologue at any other tempera- ture, calculate the volume corresponding to all pressures at the second temperature. Thus the whole relations of volume and pressure in the case of a gas can be discovered from a set of primary observations at one fixed temperature, and the determination of a single homologue at each of the other temperatures. We have now to inquire into the relations between the pressure and volume in the case of a gas at a constant temperature ; in other words, to discover, if possible, the character of the primary curve from which, as we have seen, by means of the homologues, the curves of other temperatures may be traced. For this purpose we must find the values of 1—p from Tables XIV., XV., and XVI., and thence calculate the values of e(l — p) as given in the fourth column of the following tables. Table XXII. — ^Values of e(l—p) at 6°-5. p- e. t'. 1-p. e(l-p). 12-01 1 12-96 6°-5 0-0726 0-00561 13-22 14-37 6-5 0-0800 0-00557 14-68 le-13 6-5 0-0899 0-00557 17-09 19-12 6-5 0-10G2 0-00555 20-10 23-03 6-5 0-1272 0-00552 22-26 25-96 6-5 0-1425 0-00549 24-81 29-02 6-5 0-1624 0-00549 27-69 I Mm 6-5 0-1863 0-00547 31-06 1 39-69 6-5 0-2155 0-00544 452 On the Gaseous State of Matter. Table XXIII. — Values of e(l—p) at 64°. [XLIX. p- c. t'. 1-p. e(l-p). 17-60 1 is-sr o 64 0-0522 0-00281 20-36 1 21-05 64 0-0596 0-00275 22-56 1 M-18 64 0-0670 0-00277 25-06 1 2(-08 64 0-0746 0-00275 28-07 1 30-64 64 0-0839 0-00274 31-39 1 34-67 64 0-0946 0-00273 34-93 1 39-08 64 0-1065 0-00273 40-54 1 46-34 64 0-1252 0-00270 46-56 1 54-57 64 0-1468 0-00269 54-33 1 65-07 64 0-1765 0-00268 64-96 1 83-44 64 0-2215 0-00266 81-11 1 114-0 64 0-2885 0-00253 106-88 1 185-6 64 0-4238 0-00228 145-54 1 325-9 64 0-5534 0-00170 222-92 "1 4J(i-4 64 0-5006 0-00112 Table XXIV.— Values of e(l—p) at 100° p- e. t'. 1-p. e(l-p). 20-17 1 20-98 100 0-0386 0-00184 23-37 23-35 100 0-0420 0-00180 24-88 26-09 100 0-0475 0-00182 27-76 29-32 100 0-0532 0-00181 31-06 33-05 100 0-0602 0-00182 34-57- 37-09 100 0-0680 0-00183 40-09 43-54 100 0-0792 0-00182 45-99 80-68 100 0-0917 0-00181 53-81 1 60-30 100 0-1076 0-00178 64-27 1 73-97 100 0-1311 0-00177 80-25 1 96-65 100 0-1697 0-00176 105-69 1 137-6 100 0-2319 0-00169 145-44 1 218-0 100 0-3329 0-00152 223-57 1 379-3 100 0-4106 0-00108 XLIX.] On the Gaseous State of Matter. 453 From these tables it is evident that the value of e(l—p) is constant so long as the carbonic acid is in the gaseous state, but that it rapidly diminishes when the gas passes into the inter- mediate conditions, till at high pressures it falls nearly as low as if the liquid had actually been formed. This will at once appear from the following short table, calculated from my former experiments at 13°-1, showing the values of e{l—p) in the gaseous and liquid states : — Table XXV. — Values of e(l—p) at 13°-1. p- e. t'. l-p. e(l-p). 47-50 1 76-16 13-1 0-3763 0-00494 48-76 1 80-43 13-1 0-3938 00490 48-89 1 80 'W 13-1 0-3957 0-00489 54-56 1 480-4 13-1 0-8864 0-00184 75-61 1 600-r 13-1 0-8490 000169 90-43 1 6iU-7 13-1 0-8229 0-00161 From this investigation it follows that the relations of pres- sure and volume at a constant temperature for a body in the gaseous state is given by the equation v(l-2>v)^c (C) where p is the external pressure, v the volume of the gas, and c a constant. Prom this equation the properties of homologous points already given in equations (A) and (B) follow as a direct consequence. For if and v'(l—p'v') = c' be the equations of any two isothermals ; then, since at homologous points pv = p'v', we shall have v' c' and p c p c 454 On the Gaseous State of Matter. [xlix. If the values of FeO, 21-59 4-681 MgO, - 6-45 2-58/ 1-00 99-45 2. Massive specimen from Greenland. Oxygen. Fefia, 69-22 20-76 3-05 FeO, 29-30 6-5l"i MgO, 0-71 0-29/ 99-23 1-00 506 Co7)iposition of Magnetic Oxide of Iron. [uv. A trace of oxide of manganese was discovered in both these minerals. 3. Small octahedral crystals from Penzance in Cornwall. FeA. - - 66-91 20-07 2-85 FeO, 31-49) 7-00] [ 1-00 [ I'OO MgO, 0-091 O-lsJ 98-49 In a specimen from the Isle of Muck, off the coast of Antrim, where the mineral occurs in basalt in large octahedrons, I found 2-00 per cent, of magnesia and 0-23 oxide of manganese. Magnetic oxide of iron is perhaps the most widely diffused of all minerals. It may easUy be detected by a simple mechanical process, which also furnishes us with the means of removing it from any specimen of rock before subjecting it to chemical analysis. The rock is reduced to a moderately fine powder in a porcelain mortar, and the pole of a steel magnet, which for convenience should terminate in a fine point, is gently moved to and fro through the powder. After this operation, a small quantity of magnetic powder will generally be found adhering round the pole, which by gentle friction or blowing can easily be separated from any non-magnetic particles with which it may be mixed. The magnetic portions are now carefully removed from the magnet and placed in the field of a good microscope, which is furnished with an object glass of low power (1-inch focus), so that they may be examined by reflected light. Their true nature is easily recognized by their perfect opacity, black colour, metallic lustre, and also often by the occurrence of striated and triangular facets. They also gene- rally exhibit distinct evidence of polarity. It is surprising how closely the external characters of the mineral when thus separated agTee, whatever the rock may be from which it has been extracted. By this mode of analysis, I have ascertained that the magnetic oxide of iron is a constituent of the following rocks : — 1. In massive hornblende rock from Areudal in Korway, and Ln-.] Composition of Magnetic Oxide of Iron. 507" in a basaltic dyke which traverses the clay slate of the County of Down in Ireland. Very abundant. 2. In all the varieties of basalt which occur in the N.E. of Ireland, including the fine-grained columnar basalt of the Giant's Causeway, the coarse-grained basalt of Fairhead — the green basalt of Slievemish and the amygdaloidal variety which so often abounds in zeolites. Also in the granite of Mourne and KiUiney, in primitive limestone from Tor Point, in trachyte from Auvergne — in porphyry, and in the metamorphic lias slate of Portrush. Less abundant, but easily discovered. 3. In the hardened chalk of the Antrim Coast, in grey wacke slate, in black band iron stone, in the matrix of the tin stone of Cornwall, and in magnesian limestone. Can be discovered, but in microscopic quantities. 4. In the following rocks its presence is doubtful : — Hema- tite — serpentine — ^marble (Italy) — and the matrix of native mercury and cinnabar (Idria). Kative Irmi. — It is weU known that native iron of terrestrial origin is one of the rarest minerals, having hitherto only been observed in a very few isolated instances. I have recently made the unexpected observation that it is a common con- stituent of many igneous, and even of some metamorphic rocks, being difiused through their mass in exceedingly minute quan- tity, but not difficult to recognize by the employment of chemical tests in the field of the microscope. The rock broken into small fragments without the application of a metallic hammer is reduced to powder in a porcelain mortar, and the magnetic portions extracted and placed under the microscope as in the process for detecting the magnetic oxide. While in the field of the microscope, they are moistened with a solution of sulphate of copper, acidulated slightly with sulphuric acid, when metallic iron, if present, is immediately indicated by the formation of a deposit of metallic copper, which is easily recog- nized by its colour, its lustre, its crystalline texture and solubihty, with the disengagement of gas in moderately dilute nitric acid. The rock from which I have obtained by this method the largest indications of metallic iron is a glassy basalt of a greenish hue — considered by some geologists to be a true greenstone, which forms the remarkable eminence of Slievemish 508 Composition, of Magnetic Oxide- of Iron. [liv. in Antrim, and occurs also at the Maiden Eocks and in other localities. Even in this rock, however, the quantity is exceed- ingly small; the deposits of metallic copper from 100 grains of the pulverized rock rarely exceeding three or four in number, and varying in linear dimensions from x^jth to xinrTjth of an inch. Metallic iron occurs also difPused through the other basaltic rocks of the North of Ireland, and in the indurated clay slate (lias) of Portrush. I have also detected it in a specimen of trachyte from Auvergne. 509 INDEX. Acids, combinations of, with bases, see Heat. Address to British Association, 393 ; to chemical section do., 344 ; on ozone, 361 ; on edacation, xxx. Aerolites, 398. Air, action of silent discharge on, 2S7. Alcohol, latent heat of vapour of, 170, 177 ; latent heat of vapour of methylic, 175. Alcoholic beverages, suggestions for checking the hurtful use of, xliv. Amagat, measurement of very high pressures, IviL Ammonia, heat evolved by combina- tion with acids, 79, 84, 327, 332, 493 ; heat evolved; when sails of, are decomposed by potash, 113. Angstrom, spectrum researches, 406. Apjohn, Dr., method of separating Afferent sugars from the same solution, 355, letters from Br. Andrews to, 492, xxv. Apjohn, R., discovery of vanadium in a meteoric iron, 399. Apparatus for determining heat of combination, 71, 94, 109, 130, 181, 322, 495 ; for experiments on latent heat of vapours, 164, 165 ; a new aspirator, 235 ; for experiments on ozone, 242, 262, 269, 291, S&ietseq.; pressure, for researches on the properties of gases and liquids, 297, 300, 335, 383, 419, 460 ; projected, for measuring true pressures, 384, 3S5, 426, Ivii. et seq. Arago and Dulong, method of obtain- ing true pressures, 384. Armature, horse-shoe, 473; cylindrical, 474 ; ring, 476, 480, 483. Aspirator, '221, 235. Babium atomic weight of, 229. Baryta, on the detection of, when in union with lime, 3 ; application of bicarbonate of, to quantitative an- alyses, 234, xlvi. Baiytes, heat evolved in combination with acids, 79, 83, 84 ; salts of, heat evolved when decomposed by potash, 112 ; SEilts of, heat evolved in precipitation by sulphates and dilute acids, 210 ei seq. Bases, combinations of with acids, see Heat; isothermal group of, 206, 347. Basic substitutions, thermal changes accompanying, see Heat ; law of, 108. Baumert, his researches on ozone, 241, 242, 362. BUe, absorption-bands of, 318. Bismuth, action of nitric acid on, 45, 49. Black, doctrine of latent heat, 163, importance of his discoveries, 345. Blood, chemical researches on the, of cholera patients, 7; changes pro- duced in the, by repeated bleedings, 21. Boisbaudran, Lecoq de, discovery of gallium by, 398. Boyle, law of, 405, 464 ; deviations from law of, 338, 386, 427. Brodie, action of ozone on liquids, 366 ; density of ozone, ib. Bromine, heat evolved during com- bination with zinc, 97, 105 ; with 510 Index. iron 92, 100, 105 ; specific heat of, 161 ; action of heat on, 360 ; latent heat of vapour of, 171. Brown, Dr. Cram, his view of Phlo- giston, 344; his researches with Fraser on the relation between chemical constitution and physiolo- gical action, 355. •Cagniaed de la Tour, experiments on liquids, 296, 334. Capillary tubes, calibration of, 299, 420. Carbon, sulphuret of, latent heat of vapour of, 172. ■Carbonic acid gas, compressibility of, at different temperatures, 305 et seq., 317, 387, 429 et seq.; liquefac- tion of, 305, 338, 385 ; compres- sibility of, after liquefaction greater than that of 'ordinary liquids, 307 ; co-e£Eicients of expansion for change of temperature under a constant pressure, 390, 432 et seq.; co- efficients of elastic force, under a constant volume, 438 etseq.; critical temperature of, (see Critical point). Carbonic acid gas and air, elastic force of a mixture of, 391. Carbonic acid gas and nitrogen, ex- periments on, 392, 461 ; compressi- bility of a, mixture of, at different temperatures, 462 et seq.; tempera- ture and pressure for critical state, (see Critical point). Chlorine, heat evolved in combination with zinc, 97, 105, 155; with iron, 92, 99, 105 ; with potassium, 152, 498 ; with tin, 153, 498 ; with antimony ib.; with arsenic, 154, 498 ; with mercury, 154 ; with phosphorus, 155, 499 ; with copper, 156. Continuity of the Gaseous and Liquid States of Matter, 296-317, 337 et seq,, 448, li. el seq.; curves showing the, 308, 448; transition of carbonic acid from a gas to a liquid without breach of, 312, 314 ; modification of molecular forces involved in the, 315 ; change of direction at high pressures and temperatures in the coefficient of expansion of COj and in the product of pressure and vol- ume explained by, 437, 443, 444; diminution in the values of fi and of e (1-p) the result of the, 448, 453. Copper, peculiar state of, 50, 54; heat evolved during solution of, in nitric acid, 215; heat evolved in salts of, when decomposed by potash, 117 ; in precipitation of by zinc, 180 et seq., by iron, 186 et seq. , by lead, 188. Crassamentum in blood of cholera patients, 8 et seq. Critical point, of carbonic acid, 307, 338, 465, liii. ; lowering of, by admix- ture with a permanent gas, 392, 465, 471 ; inferred by analogy of tases not hitherto liquefied, 388 ; ickering striaa above, produced by changes of density, 297, 308, 337 ; great compressibility of carbonic acid near to, 307, 310 ; a criterion for distinguishiug a vapour from a gas, 316, 461 ; cloud oelow, pre- cedes formation of liquid at certain pressures, 334, 337, 338, 467; at temperatures a little below, change in surface of demarcation between liquid and gas, 339, 466 ; of a mixture of CO2 and nitrogen, 467, 468. Crookes' radiometer, 403. Dalton, law of, 391, 405, 457; deviations from, 392, 464, 471. Delffs, refractive Ludices of ethers, 346. DevUle, Sainte-Claire, vapour of water decomposed by iron, 350. Dewar and M 'Kendrick, physiological action of ozone, 379. Dilatation by heat of a body in the gaseous state, 440. Dividing engine for graduating glass tubes, 239, 420. Dulong, heat of combination, 134 et seq. (see Arago and). Dumas, xii. et seq.; letters from, xxiii., xxxii. ; phylloxera, 408. Elbctbical discharge, action of, on oxygen, 267 et seq.; on hydrogen, 284 ; nitrogen, carbonic acid, cyano- gen, protoxideof nitrogen, deutoxide of nitrogen, 285 ; carbonic oxide, 286, 290 ; atmospheric air, 240, 287, (see Oxygen). Electro-Magnetic machines, 472. Electrolysis of water (see Ozone), gases evolved by, used as a com- pressing agent, 293, 335, xxviii. Ethers, latent heat of, 172 et seq., 177. Index. 511 Esqnimanx, their knife-blades made of meteoric iron, 39S. Expansion of gases (see Carbonic acid). Fakadat, xix.; letter from, xxi. ; on electricity, 25, 258, 472 ; liquefac- tion of gases by pressure, 296, 333. Pavre and Silbermanu, heat of com- bination, 141 «., 204, 209, 218, 320 et seq., 331, 493. Flames, action on, by flame of blow- pipe, 1, X.; conducting power of certain, and of heated air, 25. Fittig, on hydrocarbons, 351. Foucault, determination of distance of earth from sun, 3P6. Frankland, flame of hydrogen, 343, on a test for sewage, 355. Ft^my and Becqnerel, on ozone, 241, 256, 362. Galyajsic combinations, their effect upon chemical action, 55, 65. Galvanometer, constructed by Gour- jon, 36, xix. Gas, from below a silt-bed, composi- tion of, 381. Graseous state of matter, 418 ; proper- ties of, 4o4. and liquid states of matter, 296, 333, 383, 457 (see Continuity of). Gases, cooling power of, 66; com- pressibility of (see Carbonic acid); deviatious from law of Boyle, 310, 338, 386, 427 et seq.; of Gay-Lussac, 388, 435, 440; of Dalton, 392, 464, 471 ; mixed, experimente on, 392, 461 ; difiusion of, at high pressures, 470. Gay-Lussac, on mixed vapours, 458 ; deviations from law of, 388, 435, 440. Glass, heated, electrical currents through, 43. Graham, xviiL ; letters from, xliii.; heat of combination, 88 ei seq., 121 etseq., 203 et seq., 320, 493, 500, 501. Heat of combination, 70, 90, 107, ISO, 179, 319, 492 ; fundamental experi- ment, 71. 73 ; laws of, 77, 108, 180. 205, 319, 503 ; report on, 196 ; xlvi etseq. Heat developed during the combina- tion of acids and b^es, 70 et seq.. 204, 319, 492 ; during the forma- tion of the metallic compounds of chlorine, bromine, and iodine, 90 (see Chlorine, Bromine,Iodine, Iron); during basic substitntions, 107 et seq.; during combinations of oxygen, 130 ei seq., 217, 498 (see Oxygen) ; during combinations of chlorine, 150, 219,498 (see Chlorine) ; during metallic substitutions, 179, 216, 499; during precipitation of neutral solu- tions, 210 ; during precipitation of a, neutral solution n-ith a dilute acid, 213; during solutions of metals in nitric acid, 215. Heat, specific, of bromine, 161; latent, of vapours, 163. Hess, researches on heat of combina- tion, 89 !i,, 202 etseq. Homologue, or homologous point, definition of a, 444, 450 ; properties of a, 449, 451, 453 ; the whole rela- tions of volume and pressure of a gas at a particular temperature ascertained from one, and a primary curve, 451. Homologous lines, designation of, 444. Hygrometric moisture in the air, apparatus for determining the quan- tity of, 221. Ice-Calokimetes, Hermann, Her- schel, Bnnsen, 347. Iodide of potassium, te^t of electrical current, 26 et seq. Iodine, heat evolved, during formation of metaUic compounds of, 90; in combination with zinc, 98, 99, 105 ; with iron, 92, 100, 102, 105; action of ozone upon, 266, 276 ; dichroism of vapour of, 359. Iron, peculiar state of, 51 ; heat evolved in combination (see Bromine, Chlo- rine, Iodine) with oxygen, 145 ; in conversion of sesqnicompounds into protocompounds of, 92, 100, 497; salts of, heat evolved when decom- posed by potash, 114, 118. Janssen, observation of transit of Venus, 396 ; Physical Observatory at Fontenay, 400. KKKUii, on benzo and its deriva- tives, 351. Lavoisieb, 141, 345. 512 Index. Lead, oxide of, heat evolved in com- bination with acids, 81 ; salts of, heat evolved when decomposed by potash, 116; in precipitation by sulphates and dilute acids, 212 et seq.; by zinc, 192, Liebermann, researches on chrysene, 351. Liebig, xxvi. ; letter from, xxii. Lime, heat evolved in combination with acids, SO ; when salts of, are decomposed by potash. 111. Liquefaction of carbonic acid, tem- peratures and pressures for, 385 ; when mixed with nitrogen, 468 ; diminution of volume after, 307, 338. Liquid and gas, disappearance of surface of separation between, 297, 466. volume state, 307, 437, 443, 449. Magnesia, heat evolved in combina- tion with acids, 80 ; salts of, heat evolved when decomposed by potash, 112. Magnetic iron ore, new variety of, 234. Magnetic oxide of iron, 231, 505. Magneto-electric machine, used to determine conducting power of tiame, 30 ; of Pixii, 473 ; Paxton, 474; Siemens, 474; WUde, 474; Pacinotti, 475 ; Gramme, 479. Magnus, tension of mixed vapours, 458. Manganese, salts of, heat evolved when decomposed by potash, 114. Marignac and De la Kive, researches on ozone, 241, 362. Marum Van, peculiar properties of oxygen after passage of electrical spark, 361. Matthiessen and Burnside, researches on apocodeia, 354. Maxwell, Clerk-, letters on mixed gases, liv., Iv. Menabrea, General, 404. Mercury, compressibility of, 423 ; gases not absorbed by, 424 ; action of ozone upon, 265, 274 et seq.; peroxide of, heat evolved in com- bination with acids, 83; salts of, heat evolved when decomposed by potash, 116 ; in precipitation by zinc, 192. Metallic iron, meteoric masses of, 398; minute particles of, in basaltic and ■ metamorphio rocks discovered by a magneto-chemical process, 231, 399, 507. Methyl, latent heat of vapour of ace- tate of, 175; iodide of, 175; formiate of, 176. Molecular forces in gases under ' pressure, 315, 455, Moon, heating properties of rays of, 402. Nattbrbb, experiments at high pressures, 296. Nitric acid, modification of the ordi- nary action of, 45 ; action of, on bismuth, 49 et seq. ; copper, 50, 54 ; iron, 51 et seq. ; tin, 54 ; zinc, 54 ; heat evolved in combination with potash, 73 et seq., 493 ; solution of metals in, 214, 503. Nitrogen and carbonic acid, experi- ments on mixture of, 392, 461 et seq. Oersted, 401, 427, 472. Odling, constitution of ozone, 365. Oxygen, effect of electrical discharge on, 267, 273 et seq., 364; differ- ence of action of silent and spark discharge on, 273, 364, 367; amount of contraction, when con- verted into ozone, 367 ; heat evolved during combination with permanent gases, 130, 157, 217 ; with solid and fluid bodies, 137, 157, 217 ; with metals, 144, 498, 503. Ozone, xlix., constitution and proper- ties of, 240 ; discovery by Schbnbein, 240, 361 ; obtained by electrolysis of water, 240, 369, by action of electri- cal discharge on oxygen, 254, 256, 260, 268, 273, 362, 364, 367, by slow oxidation of phosphorus and other bodies, 240, 370 ; action on iodine, 266, 276, on mercury, 265, 274, on silver, 265, 276 ; destruction or conversion into ordinary oxygen by heat, 253, 273, 295, 371, by agita- tion with glass in small fragments, 371 ; action of water on, 255, 371, 372, density of, 262, 264, 276 et seq., 365, volumetric relations of, 267, existence in atmosphere, proved by experiment, 294, 374 et seq. ; bleaching properties of, 373 ; an oxidizing agent, 371, absorption of, by some essential oils, 372. Index. 513 Pkrkin and Sohunk, researches on alizarine, 352. Phlogiston, theory of, 344. Phosphorus (see Ozone) ; latent heat of protoohloride of, 171, 177. Platinum, salts of, heat evolved in pre- cipitation by zinc, 193 ; atomic weight of, 229. Poggendorff, 409, Iv. Poles exposing unequal surfaces, in- fluence of, ou chemical decomposi- tion, 37. Potash, heat evolved in combination with nitric acid, 71, 73 ef seq., with different acids, 78 etseq., 109 et seq., 324: et seq., 332,493, 501. Pressures, effect of great, combined with cold on non-condensable gases, 293 ; experiments on carbonic acid under high, 297 et seq., 338 et seq., 429 et seq.; ou mixed gases under high, 392, 461 et seq.; reference to a new method of determining true, 384, 385, 426, Ivii. et seq. Rathlin, caves of, 20. Reactions, on the heat developed in chemical, 495. Redfern, Dr., physiological action of ozone, 379. Refraction-equivalents, 346. Regnault, method employed by, of obtaining a vacuum, 224 ; of obtain- ing true pressures, 384 ; his ex- periments on gases, 296, 427 et seq. , tension of mixed gases and vapours, 458 et seq. Research, scientific, 410 et seq,, xxxix. Robinson, Dr., cup-anemometer, 400. Salts, conducting power of fused, 36. Saxifrages, note on, 129. Schonbein, bismuth, 50 ; discovery of ozone, 240, 267, 361 ; letter from, 1. Screws, mode of packing, 335, 418, 460 n. Serum, in blood of cholera patients, 8 et seq. Siemens, attraction metre of, 404 ; armature of, 474. Silbermann on heat of combination, see Favre. Silver, salts of, heat evolved, in pre- cipitation by zinc, 188 et seq., by copper, 191, by potash, 118. 2k Soda, heat evolved in combination of, with acids, 79, 84, 325, 326, 493; when salts of, are decomposed by potash, 112; discovery of minute quantities of, by polarized light, 228. Solutions, use of dilute, in determin- ing heat of combination, 70, 73, 81, 89 n. Specific heats of fluids, determination of, 124. Stenhouse, researches of, 353. Stokes, Prof. , epipolic dispersion, 403. Strontia, detection of, when in union with lime, 3. Studium Generale, xxxvi. et seq. Tables of experiments on blood of cholera patients, 8 et seq.; ratios of zinc dissolved at different tempera- tures in concentrated sulphuric acid when alone, and when voltaic- ally connected with platina, 59 et seq.; of cooling powers of gases, 67 ; of heat evolved in combination of acids and bases, 78 et seq., 324 et seq., 332, 501 ; in formation of metallic compounds, 97 et seq.; in basic substitutions. 111 et seq.; in combustions in oxygen, 133 et seq.; in combustions in chlorine, 152 et seq.; in metallic precipitations, 183 et seq.; in precipitation of neutral solutions, 210 et seq.; in precipita- tion of a neutral solution by a dilute acid, 213 et seq., during solu- tion of metals in nitric acid, 215 et seq.; of experiments on specific heat of bromine, 161 ; of latent heat of vapours, 169 et seq.; of specific heats of fluids, 127, 128, 199 et seq.; of experiment on ozone, 260, 278, 282 ; of compressibility of carbonic acid at 13°-1, 305 ; at 2r-5, 307 ; at 3r-l, 309 ; at 32°-5, 310 ; at 35°-5, 48°'l, 311 ; at various temperatures, 317; at 6° 7, 63° 7, 100°, 387; at 6°-0-6°-9, 63°-6-64°, 429; 99°-5- 100° 7, 430 ; expansion of heat of carbonic acid, under high pressures, 389 ; liquefaction of carbonic acid gas, 385 ; coefficients of expansion for heat under constant pressure from 0° to 7° -5, 432 ; from 0° to 64°, 0° to 100°, 433 ; at different tem- peratures, 434; from 64° to 100°, 436 ; coefficientsof elastic force under constant volume, from 0° to 6°'5, 438 ; from 0° to 64°, 0° to 100°, 439 ; at different temperatures, 440; 514 Index. from 64° to 100°, 441 ; of elastic force of 11 V. COg and 1 v. air at different temperatures, under constant volume, 391 ; of the general results of the investigation of the gaseous state of matter 442- 447, 451-453 ; of compressibility of 3 V. COj and 4 v. N, at 2° -2, 462 ; at 7°-5, 463; at 31°-3, ib.; at 48°-4, 464. Tait, Prof., quaternions, xxviii.; dis- covery of consecutive neutral points in thermo-electric junctions, 401 ; on ozone, in conjunction with Dr. Andrews, 262, 264, 267, 364, 367. Thermo-electric currents between metals and fused salts, 36. Thermometer, large, for determining the specific heats of fluids, 125 ; precautions to insure accuracy in a, 165 ; method of determining errors of calibre after sealing, 497 n. Thomsen, heat of combination, 332, 347. Thomson, Prof. J., influence of pres- sure on ; melting-points of bodies, 316; model to illustrate Dr. Andrews' experimental results with carbonic acid, 340 n.; mechanical integrator of, 404. Thomson, SirW.,maohinefor mechani- cal integration of differential equa- tions, tidal machine, 404. Tin, bichloride of, latent heat of vapour, 171, 172. Tin, peculiar state of, 54. Uni VEESITT, functions of a, 410 et seq. , xxxvi. et seq. Vacuum, method of obtaining a perfect, 223. Vapour, definition of a, 316. Vapours, latent heat of, 163. Venus, transit of, 395. Voltaic circles, properties of, in which concentrated sulphuric acid is the liquid conductor, 57. combination, influence of, in chemical action, 47. Water, latent heat of vapour of, 169; polar decomposition of, by common and atmospheric electricity, 258. Water-power, value of, 417. Wurtz, M., on artificial dyes, 415; letter from, xxix. Young, bright lines of solar atmos- phere, 397. 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