ESSAYS, ON THE EFFECTS PRODUCED BY VARIOUS PROCESSES ON ATMOSPHERIC AIR; WITH A PARTICULAR VIEW TO AN INVESISigATION OF -THE CONSTITUTION OF THE ACIDS. By M. L A V O I S I E Ri Member of the Royal Academy of Sciences at Paris, See, ^ TRANSLATED FROM THE FRENCH, Bv THOMAS HENRY, F. R. S. Member of thQ Medical Society of London, and of the Literary and Philofophical Society of Manchester. WARRINGTON, printed by w. eyres, For J. John SON, N". 72, St. Paul’s jChurch-Yard, London MDCCLXXXIII. THE TRANSLATOR’S PREFACE. I N a volume of EfTays Phyfical and Chemical, written by M. Lavoifier, which I tranflated and publifhed a few years fince, a number of additional effays were announced, on various im- portant fubjeds, with which that inge- nious philofopher promifed foon to favour the public. Other avocations, it Ihould feem» have prevented the fulfilling of his engagement, and he appears to have been principally occupied in an attempt to overthrow Stalh’s dodfrine of phlogifton, and in an inveftigation of the nature and A 2 con- VI PREFACE. conftitution of the acids. The refult of his inquiries he has communicated to the royal academy of fciences in a feries of memoirs, a tranflation of which is now prefented to the public. Phlogiston had been fo much talked of, though never feen, by chemifts, being cognifable only by its elfedts, that many began even to doubt its exiftence, and to regard it rather as a creature of the imagination, than as a reab and powerful agent, concerned in fome of the mqft important operations of nature. Among others, our author had entertained thefe doubts 5 and, imagining he faw Rrong objections to Dr. Prieftley's theory of the phlogiftication of air, he thought the changes eifeCled in it, by various procelTes, might be accounted for on different prin- ciples. Dr. Priestley had fuppofed that fixed air is one of the conftituenf parts " of ; va preface. o£ common air, and that, whenever a quantity of phlogidon is thrown into the latter, it feparates the fixed air, and be- comes united to the remainder, which has a greater affinity to it than to the fixed air, and forms phlogifticated air. M. Lavoisier however contends that this is not the cafe^ that atmofpheric air confifls of about | of very pure air, and x of mephitic gas, which, when detached from its purer portion, is no longer fit I for the purpofes of air ; and he denies i that any fixed air is naturally contained I in atmofpheric air, but afferts that it proceeds from the union of coaly matter with the above pure part or Dr. Prieft- ley’s dephlogifticated air, a term which M. Lavoifier is not altogether difpofed to admit. Another objecflion of M. Lavoifier to Dr. Prieftley’s theory of the phlogifti- cation of air, was founded on the different ^ 3 views viii PREFACE. views in which thefe two philofophers beheld the phaenomena which take place during the calcination of metals, and their fubfequent redudlion to a metallic form. Dr. Prieftley had fuppofed that a fepa- ration of the fixed air being effeded by the phlogifton, this air is united to the metallic calx, and that, during the re- , dudion, the calx recovers its phlogifton, and parts with the fixed air. On this M. Lavoifier obferves, that it is probable the air abforbed is not fixed, but pure air, and that, could we reduce the calxes without addition, it would be feparated again pure. This is adually the cafe with the calx of mercury, which requires no addition for its redudion, and yields pure dephlogifticated air when it recovers its metallic form. But the other calxes requiring the addition of fome coaly mat*^ ter, this, he imagines, debafes the pure air, and changes it into fixed air. The agency of phlogifton, therefore, in this cafe alfo, he regards as gratuitous, and not fufficiently founded on fads. Th: PREFACE, IX The exiftence of phlogifton, however, has not only been proved, but Dr. Prieft- ley has clearly Ihewn that phlogifton and inflammable air are the fame thing, with this difference only, as Mr. Kirwan re- marks, that when, in a ftate of elafticity, it pofleffes fo much fire as is jequifite to give it the form of vapour, and that this air is capable of being wholly abforbed in the redudion of metals, and of re- ftoring to the calxes their priftine metallic fplendor and malleability.^ There can be little doubt, therefore, that the phlogiftication of air really takes place in many proceffes ; but perhaps it may produce its effects in a manner fome- what different to what Dr. Prieftley ori- ginally imagined. The idea of that ex- cellent philofopher feemed at firft well * I AM informed that Dr. Prieftley has delivered an account of his interefting experiments and remarks, on this fubjeft, to the Royal Society, A4 founded ; X PREFACE. founded; but recent fadts have thrown a different appearance on the fubjedt. Of thefe none are more convincing than the experiments of M. Lavoifier on the com- buftion of pyrophorus, by which almoft the whole of the dephlogifticated air em- ployed, inftead of being phlogifticated in the fenfe of Dr. Prieflley’s term, was converted into fixed air. Now as the being of phlogiflon can be no longer doubted; as Dr. Prieftley has literally given “ to airy nothing a local habitation and a name ; ” and has em- bodied and rendered vifible this Proteus which has fo long eluded the grafp and fight of the chemift; the truth may, per- haps, without much difficulty, be found, by changing M. Lavoifier’s term coaly matter, mattiere charbonneufe^ for that of phlogiflon ; and allowing that, inftead of wholly uniting with the refiduum, it partly combines with the pure or dephlo- gifticated portion of the common air, and thereby PREFACE. XI thereby forms the aerial acid or fixed air, which is, in fadt, a true phlogifticated acid. The other objedion has been anfwered by Mr. Kirwan, in his admirable paper on the fpecific gravities, &c. of faline fub- ftances.* Mercury affords inflammable air, and confequently contains phlogiflon. This phlogiflon mufl: fly off during the calcination, and form fixed air, which will be abforbed by the calx. And though the calx, when reviving, yields dephlo- gifticated air, this may depend upon the mercury’s attrading the phlogiflon from the air, and applying it to its own re- dudion. That fixed air contains phlogiflon has been proved by Mr. Kirwan, and he has even determined the amount of it to be in the proportion of 14,661 grains of * Phil. Tranf. Vol. LXXII. p. 227. phlogiflon. XU PREFACE. phlogifton, and 85,339 of pure air in 100 grams of that gas. And he computes that 100 cubic inches of dephlogifticated air are converted into ^xed air by 7,2165 grains of phlogifton, and will then be reduced to the bulk of 86,34 cubic inches; and that, reciprocally, 100 cubic inches of fixed air being decompofed, will afford 115,821 cubic inches of dephlogifticated air, and part with 7,2165 grains of phlo- gifton, fuppofing the decompofition to be complete, or, in other words, the dephlo- gifticated air to be quite pure.^ We therefore feem to be arrived at a pretty perfed: knowledge of the confti- tuent parts of one of the acids, viz. the aerial, which appears to be compounded * Phil. Tranf. Vol. LXXII. p. 236. — Mr. Kirwan alfo mentions Dr. Prieftley’s very candid approbation of his account of the conftitution of fixed air, though fo contrary to opinions which the Doftor had advanced in his laft publication. An inftance of philofophical candour highly to be admired and worthy of imitation. of Xlll PREFACE. of the pure part of atmofpheric air, united with phlogifton, and, in its elaftic ftate, alfo containing a portion of latent heat, or as M. Lavoifier, perhaps as properly calls it, fixed fire. Many of the enfuing effays llrongly tend to demonftrate that this pure air enters, alfo, as a principal component part, into the conllitution of the other acids i* but we yet remain unacquainted with the true nature of the other portion, by the variety of which, each acid feems to be diflinguiftiable from the others. M. Lavoifier has fuppofed the vitrio- lic acid to be formed by the jundtion of fulphur to pure air, and that ful- phur is formed by depriving vitriolic acid of this air. Should tiot rather fay, that when vitriolic acid is formed, the * The Abbe Fontana and Mr. Berthollet had before ftiewn, that the acid of ants and the vegetable acids confift of fixed air, or are, at leaft, refolvable into it. Vide Cavallo’s Treatife on Air, p. 607. fulphur XIV PREFACE. fulphur throws off its phlogiftoii, a part of which, joining with the pure portion of the atmofphere, is again attraded by the bafjs of the fulphur, and, thus com- bined, forms the acid ; and, on the con- trary, that when this acid is reconverted into fulphur, the bafis parts with the pure air, and recovers its phlogifton ? An experiment of Dr. Prieftley’s, which he lately communicated to Dr. Pcrcival, greatly elucidates and almoft confirms this opinion. Having mentioned his having formed fulphur by the union of inflammable air with vitriolic acid, as a proof of the identity of that air with phlogifton 5 he adds, that he had alfo proved, more unexceptionably than be- fore, that the eledric matter contains phlogifton, by making it to pafs through the air, confined by the acids, in a fyphon. “ When,” fkys he, “ I ufe the “ dephlogifticated marine acid, the air is dirninifhed by the procefs, and dephlo- “ gifticated. XV PREFACE. “ gifticated. If I ufe the pbo/p^ofic acid qv tho, phlogijlicated alkali, the air is firft “ diminifhed, and then increafed by an “ addition of inflammable air. If I ufe “ VITRIOLIC ACID Or the NITROUS ACID, there is a produBion of dephlogis- “ TIC A TED AIR, fajler than the eleBri- “ city can injure it” Now, from whence can this dephlogifticated air proceed, but from a decompofltion of the acids by the phlogiflon of the electric matter, in which the pure air is feparated, while the phlogifton, cpnabining with the remaining part or bafis of this acid, forms a fulphur ? ^ ' Whether the phlogiilon, by means of which the pure air is feparated, and which uniting therewith forms fixed air, be admitted into the compofition of the acid, or rejected when that air lofes its elafticity, is not as yet afcertained. It is probable, that the acid not only receives its acidifying principle from the pure air, but XVI PREFACE. but alfo its fire or abfolute heat. Now though Dr. Crawford has fhewn that bodies which contain much phlogifton pofTefs little abfolute fire (thefe fubftances repelling each other ; fo that the addition of phlogifton to any fubftance expels from it a part of its fire, and, on the other hand, the addition of fire feparates a part of its phlogifton) yet it appears that their coexiftence is not incompatible 5 inflammable air, as was before obferved, owing its elafticity to a portion of fire with which it is combined.* Now as a fmall portion of phlogifton, added to vitriolic acid, makes volatile vitriolic acid, and a larger dofe fixes it and forms fulphur, perhaps a very minute quantity may be necelTary to the compofition of the acid. M. La\oisier obje(5ting, and with fome reafon, to the appellation of fixed * Kirwan, Phil. Tranf. Vol. LXXII. p. 209. air. PREFACE. xvii air, has, in the fubfequent efTays, deno- minated it, the chalky aeriform fluid or acid', and the academy not fatisfied with this name, as being too confined, have preferred that of gafeous air. But, as the cuftomary term is befi; known to Englifh readers, I have thought proper to re- tain the ufe of it, till philofophers, in general, have agreed upon the adoption of a new one. THE THE through their Lungs. Page I. Essay II. On the Combuftion of Candles in Atmofpheric Air and in Dephlogijlicated Air. - - - - - 5 7- Essay III. On the Combuftion of KunckeVs Lhofphorus. - - - - 34- Essay IV. On the Exiftence of Air in the Nitrous Acid, and on the Means of de- compofing and recompofing that Acid. 52 . Essay V. On the Solution of Mercury in Vitriolic Acid. _ - - 69 . Essay XX CONTENTS. Essay VI. Experiments on the Comhuftion of Alum with Phlogijiic Subjiances, and on the Changes effected on Air in which the Pyro- phorus has burned. - - - 76. Essay VII. On the Vitriolijation of Martial Pyrites. - - - - 92. Essay VIII. General Confiderations on the Nature of the Acids, and on the Princi- ples of which they are compojed. - 96. Essay IX. On the Combination of the Matter of Fire with Evaporable Fluids-, and on the Formation of Elafiic Aeriform Fluids. 1 1 9. S S A Y essay I. experiments ON THE respiration of animals, AND ON THE CHANGES EFFECTED ON THE AIR IN PASSING THROUGH THEIR LUNGS. O F all the phenomena of the animal ceconomy, none is more ftriking, none more worthy the attention of philofo- and phyfiologifts than thofe which ac- company refpiration. Little as our acquaint- ance is with the objed of this fingular fundion, we are fatisfied that it is eflential to life, and that it cannot be fufpended for any time, with- out expofing the animal to the danger of immediate death. E It a EFFECTS OF RESPIRATION It is univerfally known that air is the agent, or rather the fubje6t of refpiration^ but at the fame time all forts of air, or more generally fpeaking, all forts of elaftic fluids, are not "proper for the purpofe, nay, there are many kinds which animals cannot breathe, without perilhing, at lead, as foon, as if they had no air to refpire. The experiments of fome philofophers, and efpecially thofe of MelTrs. Hales and Cigna, had begun to afford fome light on this im- portant objed ; and. Dr. Prieftley has lately publiihed a treatife, in which he has greatly extended the bounds of our knowledge; and has endeavoured to prove, by a number of very ingenious, delicate, and novel experiments, that the refpiration of animals has the property of phlogifticating air, in a fimilar manner to what is effeded by the calcination of metals and many other chemical proceflTes; and that the air ceafes not to be refpirable, till the inftant when it becomes furcharged, or at leafl; fatu- rated, with phlogifton. However probable the theory of this cele- brated philofopher may, at firft fight, appear; however ON AIR. 3 however numerous and well conduced may be the experiments by which he endeavours to fupport it, I muft confefs I have found it fo contradictory to a great number of phenomena, that I could not but entertain fome doubts of it. I have accordingly proceeded on a different plan, and have found myfelf led irrefiftibly, by the confequences of my experiments, to very different conclufions. It will not be neceffary, at prefent, to difcufs, particularly, each of Dr. Prieftley’s experiments, nor to fhew how they all contribute to confirm the opinion which I am proceeding to communicate in this memoir : it will be fufficient to relate my own, and to give an account of their refults. In a convenient apparatus, which it would be difficult to defcribe without the aid of en- gravings, fifty cubic inches of common air were inclofed, to which I introduced four ounces of very pure mercury, which I pro- ceeded to calcine by keeping it, during twelve days, in a degree of heat almoft equal to that which is neceffary to make it boil. Nothing remarkable occurred during the firft day : the mercury, though it did not boil, B 2 . was 4 EFFECTS OF RESPIRATION was in a continual ftate of evaporation, fmall drops of it, which were at firft very minute, lined the infide of the veflels, and gradually increafing till they acquired a certain bulk, fell again by their own gravity to the bottom. On the fecond day I could obferve fome fmall red particles fwimming on the furface of the mercury, which, in a few days, increafed both in number and bulk. On the twelfth dayy having extinguifhed the fire and fuffered the veflels to cool, I obferved that the air^ which they contained, was diminifhed to the amount of from eight to nine inches, viz. about ^ of its volume : at the fame time a confiderable por- tion of mercurius precipitatus per fe, or cal- cined mercury, was formed, which I computed to be about forty-five grains. This air, which had been thus diminifhed, did not precipitate lime-water i but it extin- guifhed candles, and animals, immerfed in it, perifhed in a Ihort time : it no longer afforded red vapours, when mixed with nitrous air, nor was diminifhed by it. In fhort, it was abfo- lutely reduced to a mephitic flate. It ON AIR. 5 It has been proved by Dr. Prieftley’s, and alfo by my own, experiments, that calcined mercury is merely a combination of that metal with about part of its weight of air, much better and more refpirable, if the exprelTion may be allowed, than common air : it fliould appear then, as proved, that, in the preceding experiment, the mercury, as it calcined, had abforbed the beft and moft refpirable part of the air, and left only the mephitic or unre- fpirable part. The following experiment con- firmed me more and more in the truth of this opinion. I CAREFULLY Collected the forty-five grains of calcined mercury which had been formed in the preceding experiment j and putting it into a very fmall glafs retort, the neck of which was turned up fo as to pafs under the edge of a bell-glafs, filled with, and inverted into, water, I proceeded to reduce it without addition. By this operation I recovered nearly the fame quan- tity of air which had been abforbed during the calcination; namely, between eight and nine cubic inches, which, when recombined with the air which had been vitiated by that procefs, re- B 3 ftored 6 EFFECTS OF RESPIRATION ftored the latter, pretty exaftly, to the fame ftate in which it had been, previous to the calcination being performed in it, viz. that of common air; for now candles were not extinguilhed in it; animals no longer perilhed in it, and it was nearly as much diminilhed as atmofpheric air, by the addition of nitrous air. We have here the moft complete proof, that chemiftry can afford, of the decompofition and recompofition of air ; from whence it evidently refults, I ft. that 4 of the air which we breathe, are mephitic, or incapable of fupporting the refpiration of animals, or the inflammation and combuftion of bodies ; adly. that the fur- plus, or only of the volume of atmofpheric air, is refpirable; 3dly. that, in the calcination of mercury, this metallic fubftance abforbs the falubrious part, leaving only the mephitic por- tion of the air : 4thly. that by reuniting thefc two portions which had been feparated, we can recompound air, fimilar to that of the atmo- fphere. These preliminary truths, relative to the cal- cination of metals, tend to lead us to plain con- fequences ON AIR. 7 fequences concerning the refpiration of animals ; and as the air, which has ferved fome time for this vital office, has much relation to that in which metals have been calcined, our know- ledge, relative to the one, leads us naturally to an application of it to the other. I PLACED a fparrow under a glafs receiver, filled with common air and {landing in mer- cury, capable of containing thirty-one cubic inches : the bird did not feem at all affefted at firft, except that it was a little ilupefied : in a quarter of an hour it began to be agitated ; its refpiration became laborious and rapid ; and, from this inflant, the fymptoms of diftrefs in- creafed, till, at the end of fifty-five minutes, it died convulfed. — -Notwithftanding the heat of the animal, which neceiTarily, at firft, rare- fied the air in the receiver, there was a fen- fible diminution of its bulk, which at the end of fifteen minutes amounted to about but inftead of increafing afterwards, the diminution became fomething lefs in about half an hour; and when the animal was dead, and the air in the receiver had recovered the tem- perature of the room where the experiment B 4 was 8 EFFECTS OF RESPIRATION was made, the diminution did not appear to be more than This air, which had been refpired by the fparrow, was become very different from that of the atmofphere : it precipitated lime-water j ex- tinguilhed candles, and fuffered no diminution by the teft of nitrous air : another bird, intro- duced into it, exifted but a few moments : it was, m Ihorr, entirely mephitic, and, in that re- fped, appeared much fimilar to that in which mercury had been calcined. But a more attentive examination difeovered to me two very remarkable differences between the two airs: iff. the diminution of that, in which the fparrow had died, was much lefs than that of the air which had been employed for the calcination j and, 2dly. the refpired air pre- cipitated lime-water, on which the other pro- duced no change. This difference between thefe two airs, on the one part, and, on the other, the great analogy which appeared between them, in many refpeds, led me to prefume, that two caufes are compli- cated ON AIR. 9 cated in refpiration, of which probably I was hitherto acquainted only with one; and to clear up my fufpicions on the fubjeft, the fol- lowing experiment was made. Into a jar filled with mercury, and inverted into the fame, were pafled twelve inches of air, vitiated by refpiration j and a thin ftratum of cauftic fixed alkali was introduced to the fiirface of the metal. I might have made ufe of lime- water, but the neceflary quantity of it would have been too confiderable, and would have impeded the fuccefs of the experiment. The effect of the cauftic alkali was to occa- fion a diminution in the volume of this air, of nearly ^ j while, at the fame time the alkali had, in part, loft its caufticity, and acquired the property of effervefcing with acids 5 it alfo cryftallifed within the glafs, even under a very regular rhomboidal form^ properties which we know could not be communicated to it, but by combining it with that Ipccies of air or gas, known by the name of fixed air : from whence it appears that air, vitiated by refpiration, con- tains nearly of an aeriform acid, perfe( 5 Uy fimilar to that obtained from chalk. The lo EFFECTS OF RESPIRATION The air, thus deprived of its fixable part by the cauftic alkali, was fo far from being re- eftablifhed in the ftate of common air, that, on the contrary, it approached nearer to that of the air which had been employed in the calcination of mercury, or, more properly, was exaftly the fame ; for neither candles could burn, nor ani- mals live in it ; nor could I perceive, from any experiments I made, the leaft difference be- tween the two airs. Now air which has ferved for the calcination of metals, is, as we have already feen, nothing but the mephitic refiduum of atmofpheric air, the highly refpirable part of which has com- bined with the mercury, during the calcination : and the air which has ferved the purpofes of refpi ration, when deprived of the fixed air, is exaflly the fame j and, in faft, having com- bined, with the latter refiduum, about i of its bulk of dephlogifticated air, extrafted from the calx of mercury, I re-eftablifhed' it in its former ftate, and rendered it equally fit for refpiration, combuftion, &c. as common air, by the fame method as that I purfued with air vitiated by the calcination of mercury. The ON AIR. II The refult of thefe experiments is, that to reftore air that has been vitiated by refpiration, to the ftate of common refpirable air, two effects muft be produced: ift. to deprive it of the fixed air it contains, by means of quick- lime or cauftic alkali : idly, to reftore to it a quantity of highly refpirable or dephlogifticated air, equal to that which it has loft. Refpira- tion, therefore, a6ls inverfely to thefe two effefts, and I find myfelf in this refped led to two confequences equally probable, and between which my prefent experience does not enable me to pronounce. After what we have feen, it may be con- cluded, that one of the two following cffeas is produced by refpiration : either the highly refpirable portion contained in common air, is converted into fixed air, in pafiing through the lungs, or elle an exchange is made in that vifcus ; on one part the dephlogifticated air is abforbed, and on the other, the lungs throw out a portion of fixed air, nearly equal in bulk to the other. The firft of thefe opinions is fupported by an experiment which I have already commu- nicated 12 EFFECTS OF RESPIRATION nicated to the academy. For I have fhewn in a memoir, read at our public Eafter meeting, 177 5, that dephlogifticated air may be wholly con- verted into fixed air by an addition of powdered charcoal ; and, in other memoirs, I have proved that this converfion may be effeded by feveral other methods : it is poflible, therefore, that refpi ration may poflefs the fame property, and that dephlogifticated air, when taken into the lungs, is thrown out again as fixed air. But, on the other hand, ftrong analogies feem to militate in favour of the lecond opinion, and lead us to believe that a portion of the pure air remains in the lungs, and is combined with the blood. We know that it is one pro- perty of this air to communicate a red colour to bodies, and efpecially to metallic fubftances, with which it is combined : mercury, lead, and iron furnifti examples of this fad. Thefe metals form, with highly refpirable air, beautiful red calces, the firft under the name of calcined mercury, or red precipitate of mercury; the fecond under that of minium; and the third, of colcothar. The fame efFeds, the fame phe- nomena, are obfervable, in the calcination of metals and in the relpiration of animals; all the circum- ON AIR. U circumftances arc the fame, even to the colour of the refiduums. May we not then fuppofe that the red colour of the blood depends on the combination of dephlogifticated air, or, to fpeak more accurately, of its balls with an animal fluid, in the fame manner as the colour of red precipitate of mercury and minium is owing to the combination of this bafis with a metallic fubftance ? Though this confequence has not been deduced by Mr. Cigna, Dr. Prieftley, and other moderns who are occupied on this objedl, I will venture to fay that there is none of their experiments that do not tend, in appearance, to confirm it; nay, they have proved, and more efpecially Dr. Prieflley, that the blood is red only in proportion as it is con- tinually in conta6t with atmofpheric, or with dephlogifticated air ; that it becomes black in fixed air, in nitrous, in inflammable, and in all unrefpirable airs, and alfo in the exhaufled re- ceiver of an air-pump : that on the contrary it recovers its red colour, when placed again in conta(5t with air, and efpecially if it be de- phlogiflicated, and that this refloration of colour is conftantly attended by a diminution in the volume of air. Does it not then follow, from all thefe fa5 ON AIR. mephitic part is a merely paflive medium which enters into the lungs, and departs from them nearly in the fame ftate, without change or alteration. ( I ^ 2dly. That the calcination of metals, m a given (quantity of atmofphenc air, is effe 6 ted, as I have already often declared, only in pro- portion as the dephlogifticated air, which it contains, has been drained, and combined with j the metal. ! : 3diy. That, in like manner, if an animal I be confined in a given quantity of air, it will ^ periih as foon as it has abforbed, or converted into fixed air, the major part of the refpirable i portion of air, and the remainder is reduced to j a mephitic ftate. I I 4thly. That the fpecics of mephitic air, which remains after the calcination of metals, is in no wife different, according to all the experiments I have made, from that remaining after the refpiration of animals ; provided al- ways, that the latter refiduum has been freed from its fixed air : that thefe two refiduums may be fubftituted for each other in every experi- ment. i6 EFFECTS OF RESPIRATION ment, and that they may each be reftored to the ftate of atmofpheric air, by a quantity of dephlogifticated air, equal to that of which they had been deprived. A new proof of this laft fadl is, that if the portion of this highly relpirable air, contained in a given quantity of the atmofpheric, be increafed or diminilhed, in fuch proportion will be the quantity of metal which we Ihall be capable of calcining in it, and, to a certain point, the time which animals will be capable of living in it. The limits which I have prefcribed to myfelf in this memoir, will not permit me to enter on many other experiments which tend to the fup- port of the theory I have advanced. Of this number, is a part of thofe which MelTrs. Tru- daine, de Montigny, and myfelf have lately made, in the Montigny laboratory. There is reafon to hope that thefe experiments will throw Hill additional light, not only on the refpi- ration of animals, but alfo on combuftion : operations which have a much ftronger relation- Ihip to each other, than we may, at firft fight, believe. ESSAY ON AIR. 17 ESSAY II. On the combustion of CANDLES IN ATMOSPHERIC AIR and in DEPHLOGISTICATED AIR. I T having been fufRciently proved that the air of the atmofphere is not a finnple fub- ftance or element, as the ancients believed, and has been imagined even in our own time ; but that it is compofed in part only of very pure or dephlogifticated air, and that the re- mainder, which is perhaps ftill a compound, is mephitic, and incapable of fupporting either animal life, combuftion, or flame j it will be necefTary, in order that this elTay may be in- telligible, to diftinguifli four fpecies of aeriform fluids. ift. Atmospheric air, in which we live, refpire, &c. C adly. Pure i8 EFFECTS OF COMBUSTION adly. Pure or dephlogifticated air, which forms about ^ of the compofition of atmofpheric air. 3dly. The mephitic part of atmofpheric air, which forms of its compofition ; with the nature of which we are as yet wholly unac- quainted. 4thly. Fixed air, as it is commonly called, which may exift either in a ftate of elafticity, or quiefcent and united with other bodies. Those who have been employed in making experiments on the burning of candles, have been convinced that a confiderable diminution took place, during the combuftion, in the volume of air. To prove this, a very fimple but in- conclufive experiment has been made. A lighted candle has been placed on the plate of an air- pump, and being covered with a receiver, it has been obferved that the candle was foon ex- tinguilhed, and that as foon as the veflels were become cold, the receiver adhered to the plate. But this effeft could not be produced except the volume of air, remaining in the receiver after the combuftion, were fmaller than it was previous ON AIR. 19 previous to the introduflion of the candle. But attention has not been paid to this circumftance, that a candle cannot be placed under a receiver, but the contained air muft be heated at the inftant when the candle is introduced, and before the receiver can be applied to the plate. The air included in the receiver therefore being hot, it will diminifh in bulk as it grows cool ; and this may account for the adhefion of the re- ceiver to the plate, when the candle is extin- guifhed and the veffels cooled. It is proper alfo to remark, that there are few air-pumps which do not admit of the paf- fage of fome portions of air, between the leather and the edges of the receiver j efpecially when the receiver, fo far from adhering to the plate, is rather pulhed from it, by the rarefaction of the internal air ; confequently, there is almoft always an efcape of air while the candle con- tinues to burn j and as there will not remain a fufficient quantity under the receiver to balance the preflure of the atmofphere, another caufe is formed of the receiver’s adhering to the plate. Experiments made in jars immerfed in water are equally unfatisfaCtory. ift. The air is rare- C 2 fied 20 EFFECTS OF COMBUSTION fied when the candle is introduced, and continues to dilate during the combuftion, and, therefore, a confiderable portion of it efcapes at the rim of the jar. Hence it is impolTible to afcertain the quantity of air on which we operate, nor the real amount of the diminution in its bulk, adly. The burning of candles has the property of changing a part of the atmofpheric air into fixed air ; and as the latter is capable of com- bining with water, fuppofing a diminution in the bulk of the air to have been caufed by the combuftion, and taken place during the ex- periment, it is impoflible to diftinguifh it from that which proceeds from the combination of the fixed' air with the water. These reflexions induced me to take another method, and convinced me of the neceflity of operating over mercury. I accordingly began by immerfmg a glafs jar, at the fame time in- clining it to a certain angle, into a bafin of mercury ; and then fetting it upright, I marked the place which anfwered to the furface of the quickfilver, and repeated this trial fo often, that I was aflfured that the mercury correfponded very nearly each time with the mark I had firft made on the jar. Beinc ON AIR. 21 Being thus convinced of the prafticability of always inclofing the fame quantify of air under the jar, by fufficient care and attention ; I proceeded in the fame manner, holding the jar inclined and partly plunged in quickfilver in my left hand, and, with my right, intro- ducing under it, very quickly, a fmall lighted wax candle. The introdu6lion of the candle, the immerfion and elevation of the jar, ought to be performed in an inftant, and it will be neceflary to praftife thefe evolutions, till fuch a degree of dexterity be acquired by the ex- perimenter, as to enable him to perform all thefe operations in an almoft indivifible fpace of time. In a few moments after the candle has been inclofed in the jar, it begins to give a weaker light, and, in a Ihort time, is extinguifhed. The mercury, as might be expefted, de- fcends, at firft, rapidly, owing to the heat and rarefaftion of the confined air; but when the candle is extinguiflied, and the veflels are per- feftly cooled, it returns pretty exa6lly to the mark which had been made before the intro- dudtion of the candle. I have ufed the expref- C 3 fion 22 EFFECTS OF COMBUSTION fion pretty exa^ly, as it is impoflible to anfwer for very trifling diiTerences in this experiment, becaufe that flight errors, as to the height of the mercury, may be caufed by fome little va- riation in inclining the jar more or lefs, or by fome circumftances attending its elevation. The refult of this experiment did not con- vince me that the burning of a candle occa- fioned no fenfible diminution in the volume of air j it was ftill neceflfary to determine the ftate of the air after the combuftion, and the changes that might have been effeded in it. I therefore introduced to the air in the jar, in which the candle had been extinguiflied, a fmall portion of a cauftic lixivium of fixed alkali. The volume of air was prefently diminiflied, and reduced from 26 to 23-^ inches j fo that the diminution amounted to nearly ^ of the original quantity of air. At the fame time the cauftic alkali had acquired the property of effervefcing with acids j which proved that the diminution had been oc- cafioned by the fixed air combining with the alkali : for when I added a fmall portion of vitriolic acid to the alkaline ley in the jar, a brifk efiervefcence enfued, the abforbed air was again ON A I R. 23 again feparated, and the mercury redefcended almoll exadly to the mark which I had made on the jar. Though this experiment was perfedlly con- clufive in fome refpefts, it was ftill infufficient to my views, relative to the diminution of the bulk of air by combuftion, and there remained ftill fomething incomplete on this fubjeft. For confiderable differences in the experiment might be caufed merely by inclining the jar more or lefs, and it was very poffible that the diminution of the air might have been counterbalanced by fome error in the procefs j I therefore refolved to take every precaution in my power, to obtain a refult that Ihould be more certain, and free from every kind of error; to which purpofe the following experiment appeared to me likely to be more decifive. In the middle of a glafs ftand, was placed a fmall wax candle ; and on the top of the wick, was fixed a fmall piece of Kunckel’s phofphorus, weighing about ^ grain. The ftand was then placed in a bafin of mercury and covered with a jar, and, by means pf a fyphon, I raifed the mercury, by fu6lion, to a certain C 4 elevation 24 EFFECTS OF COMBUSTION elevation which I nnarked exa6Uy with a flip of paper. Every thing being thus difpofed, I made a piece of iron wire red hot, having firfl: bent it for the purpofe, and then pafTed it through the mercury, into the jar, fo as to touch the top of the candle and fet fire to the little piece of phofphorus. Though the wire muft, neceflTarily, have been much cooled in palling through the mercury, it ftill retained fufficient heat to inflame the phofphorus, and by this means the candle was lighted, as I expedted. While the candle continued to burn, the air was rarefied; but when it was extinguifhed, the mercury remounted infenfibly, in propor- tion as the veflfels cooled, and became ftationary a little above the mark I had made before the candle was lighted. From this it was evident, that a fmall diminution in the bulk of the air was effedted, and being meafured very pre- cifely, it was found to amount exadlly to 1 of a cubic inch. But one grain of phofphorus abforbs, in combuflion, three cubic inches of air, as has been eftablifhed by feveral experi- ments.* The -pV of a grain therefore fhould * See Lavoifier’s Effays, Phyfical and Chemical, tranflated by Henry, chapter ix. abforb ON AIR. 25 abforb half an inch, which reduces the real diminution of the air, caufed by the burning of the candle, to ^ of an inch. The jar con- tained , feventy-two cubic inches. On the fup- pofition, therefore, that the diminution of i of an inch was not to be attributed to fome flight error with refpeft to the meafures, the dimi- nution occafioned by the burning of a candle in common air would not amount to above which may be regarded as a mere nullity, efpecially if it be confidered that a very trifling change in the temperature of the room, is capable of producing this difference. As the jar which 1 had ufed in this experi- ment was very long and narrow, I imagined that the candle might not have burnt fo long as it would have done, if the veflel had been lefs lofty, and the circulation of air more eafy. The experiment was therefore repeated in. a veflel which was fhorter and not capable of containing above thirty cubic inches. The circumftances, under which th<* fU ment was conduced, were exaftly t. -me as. in the former one j and when the veffels were quite 26 EFFECTS OF COMBUSTION quite cold there was a diminution of the volume of air of 4 - an inch, which precifely correfponds with the quantity which might be fuppofed to be abforbed by of a grain of phofphorus, if burnt alone under a jar. The burning of the candle, therefore, had occafioned no fenfible diminution in the bulk of air. FaoM thefe feveral experiments it may be regarded as certain, ift. that the burning of candles does not fenfibly diminilh the volume of air in which they burn. 2dly. That this combuflion has the property of converting into fixed air about of the original quantity of air. 3dly. That if the air in which a candle has burnt, be brought into contad with lime- water or cauftic alkali, in that cafe the above diminution of ^ is produced by thefe liquids abforbing the fixed air which has been formed during the combuftion. The air in which candles have thus burnt, when deprived by water, or any other means, of the portion of fixed air, formed in it, is called by Dr, Prieftley and feveral others, the phlo- gifticated part of the air. They are of opinion, that 27 ON AIR. that there arifes from candles when burning, and from metals when calcining, &c. a phlo- giftic emanation which combines with and faturates the air. My fentiments of the cafe are different, and I have already given fome proofs that the refiduum of atmofpheric air, after combuftion, &c. is its mephitic portion, which forms three fourths of its compofition, deprived in a greater or lefs degree of its pure, refpirablc part. And in faft, if we reftore to the refiduum of the original quantity of air this ^ of pure air which it has loft, we thereby reftore it to its former ftate. Now if, as Dr. Prieftley fuppofes, this air were phlogifticated, or contaminated by fome principle which rendered it unfalutary, it would not be fufficient to reftore to it the por- tion of which it had been deprived, but, in order to re-eftablifti it in the ftate of common air, it would be neceffary alfo to feparate this contaminating fubftance from it. Befides, as I am going to oppofe, by a train of experiments, Stalh’s doftrine of phlogifton,* the objedions which I ftiall adduce on that occafion will militate equally againft the fuppofed phlogifti- cation of air. * See the preface. From 28 EFFECTS OF COMBUSTION From my account, atmofpheric air confifts of about of its bulk of pure rcfpirable air. The combuftion of candles converts only of it into fixed air ; fuppofing, then, the volume of air to have been loo before the combuftion, there fhould remain, after the operation, feventy- five parts of mephitic, and fifteen of pure air : and we accordingly find that animals will live, or phofphorus burn, in this refiduum, after a candle has been extinguifhed by it j and even after this proof, there will ftill remain five parts of pure air. This laft portion is fo firmly united to the mephitic part, that I know of no other means of feparating it than by the combuftion of pyrophorus j which will appear in a fucceed- jng effay. There remains nothing to complete what I have to fay on the fubjedl, except an account of the phenomena which attend the burning of candles in very pure air. Thefe experiments will furnifh me with frefti weapons againft the gratuitous dodrine of the phlogiftication of air. Into a glafs jar, filled with very pure air, obtained from calcined mercury, a candle was introduced. ON AIR. 29 introduced. This jar was fixed in a bafin of quickfilver. The candle burnt with a vivid light, an enlarged flame, and all the circum- llances defcribed by Dr. Prieftley. The heat, during the combuftion, was fo great, that a portion of air paflfed by the rim of the jar, and efcaped, but the quantity was not very con- fiderable. When the candle was extinguiflied and the veflels cooled, I introduced fome cauftic fixed alkali, over the furface of the quickfilver in the jar. Immediately the fixed air was ab- forbed, and I found by this trial that two thirds of the pure air had been converted into fixed air by the combuftion. But, what was ftill more interefting, the remaining third, after the ab- forption of the fixed air, was ftill almoft pure : for having transferred it into a fmaller jar, a candle was again lighted in it j it afforded an enlarged flame, and about one half of it was converted into fixed air. The remainder, after the abforption by cauftic alkali, was nearly of the fame goodnefs as common air. When, therefore, a candle is made to burn in ajar containing one hundred parts of pure or dephlogifticated air, fixty-fix parts are changed into 30 EFFECTS OF COMBUSTION into fixed air, ^nd of* the thirty-four remaining parts, twenty-one and ^ are ftill pure air, capable of being changed into fixed air. Out of 100 parts, only 12^, or about remain of air capable of extinguifhing a candle without producing any precipitation in lime-water, and this appears to have been a portion of mephitic air contained in the dephlogifticated air. Un- doubtedly this portion would have been ftill fmaller, if the air had been more pure. Now if, as is fuppofed by the celebrated philofopher. Dr. Prieftley, combuftion were pof- fefled of the property of phlogifticating air, the quantity of phlogifticated air, formed during the procefs, fhould be greater in proportion to the quantity of combuftible matter confumed. For the combuftion is almoft four times as much in dephlogifticated, as in an equal bulk of com- mon, air } and therefore four times as much phlogifticated air ftiould be formed ; whereas on the contrary we obtain nine times lefs. The difproportion, then, of what we really have, to that which we ought to expedt, according to Dr. Prieftley’s opinion, is as i to 36. Lastly, ON AIR. 31 Lastly, the refiduum after the combuftion of phofphorus, and cfpecially of pyrophorus, in dephlogifticated air, is ftill lefs than that after the burning of candles, and may be confidered as a mere nothing ; whereas, according to Dr. Prieftley’s theory, it ought to be more con- fiderable. It cannot therefore be to the addition of phlogifton that the formation of the mephitic refiduum of atmofpheric air after combuftion is to be attributed, and it therefore muft have exifted, as I have advanced, previous to the combuftion. The preceding experiments feem therefore to have proved the following fafts : I ft. That the mephitic portion which forms of the compofition of atmofpheric air, con- tributes nothing to the phenomena of com- buftion. 2 dly. That the adion of combuftion is con- fined to the portion of pure or dephlogifticated air, which forms the other ^ of atmolpheric air. 3dly. That 32 EFFECTS OF COMBUSTION 3dly. That only 4. of this pure air cart be converted into fixed air, by the burning of candles, and that the other | remain united to the mephitic portion, without combuftion having the power to feparate them. 4thly, That phofphorus has a greater power than candles, as it is capable of feparating ^ of the pure air contained in atmofpheric air. 5thly. That pyrophorus a6ls yet more for- cibly, and feems to Convert almoft the whole portion of pure, into fixed air. These confequences might be carried much further, and it might be fhewn, that fixed air, which is formed during the combuftion of i candles, is nothing but the inflammable air feparated from the candle, united with a greater proportion of the pure part of the air in which the combuftion is carried on, and a fmaller, though confiderable, portion of the matter of fire which enters into the compofition of both kinds of air. But the proofs which might be adduced of thefe aflertions are fuch as my readers are riot yet prepared to receive, and I muft ON AIR. 33 muft defer the elucidation of this theory, till, on one part, I have demonftrated the exiftence of the matter of fire in aeriform fluids, and have fhewn in a future effay, that fixed air may be formed, by combining inflammable, with the balls of dephlogifticated, air. D ESSAY 34 ON THE COMBUSTION ESSAY III. On the combustion of KUNCKEL’s PHOSPHORUS, AND ON THE NATURE OF THE ACID RESULTING FROM THE PROCESS. SECTION I. On the Combujiion of PhoJphoruSy and the Formation of its Acid. I HAVE already related, in chap. IX. part II. of my Effays Phyfical and Chemical, fome of the principal phenomena attending the com- bullion of phofphorus, and the formation of its acid; but the intelligence I have acquired, fince the publication of that work, enabling me to give a more accurate account of the refults, and to be more certain in my explanations, I fhall refume the fubjed in a fummary way, and lhall firft fpeak of the formation of the phof- phoric acid, before I proceed to the relation of the OF PHOSPHORUS. 35 the refults of its combination with different mineral and vegetable fubftances. Ir Kunckel’s phofphorus be lighted, by means of a burning glafs, under a jar inverted into a bafm of mercury, we obferve, ift. that only a given quantity of phofphorus can be burnt in a determined quantity of air, and that thefe proportions are about one grain of the former to from fixteen to eighteen cubic inches of air. 2dly. That as foon as this quantity is burnt, the phofphorus is extinguifhed, without any poffibility of kindling it again, except by bring- ing it into contact with frefh air, which has not hitherto been employed for combuflion. 3dly. That frefh phofphorus, introduced under the fame receiver, does not burn better than the former. 4thly. That during the combuftion, a large quantity of white flowers or flakes are formed, which refemble very fine fnow, and attach themfelves every where to the infide of the receiver. Thefe conftitute the concrete phof- phoric acid. D - 5thly, That ON THE COMBUSTION 36 5thly. That at the beginning of the com- bullion, the air in the receiver is confiderably dilated, on account of the heat which is pro- duced; but, in a very fhort time, its bulk be- comes fo much diminilhed, that, when the veffels are cooled, it occupies no more than about i or 4 - the fpace it filled previous to the combuftion. If the flowers are colle 6 led and carefully weighed, before they come in contadl with frefli air, or have attrafted any moifture from it, they will be found to be 24 times the weight of the phofphorus em- ployed for their formation ; or in other words, with one grain of phofphorus there will have been formed 2I grains of concrete phof- phoric acid. This very extraordinary increafe of weight is pretty exadly proportioned to the quantity of air abforbed ; for the abforption is aftually about three cubic inches of air for each grain of phofphorus that has been burnt ; and as three cubic inches of air weigh about one grain and half, this weight, added to one grain of phofphorus, gives 24. grains, the weight which the flowers have been obferved to poflTefs. The OF PHOSPHORUS. 37 The air thus reduced, as much as it can be, by the combuftion of phofphorus, is fo far from being more denfe than atmofpheric air, that its fpecific gravity is even rather diminifhed than augmented. It is no longer capable of ferving for the refpiration of animals, of fupporting the combuftion or inflammation of bodies, and, in fiiort, is abfolutely in a mephitic ftate, and therefore to avoid confounding it with any other fpecies of air, I fhall diftinguifli it, in this memoir, by the name of atmofpheric gas : but if to this air, thus decompofed, and which no longer pofTeATes the principal charafleriftics of common air, be added a quantity of dephlo- gifticated or highly refpirable air, obtained from the calx of mercury or of lead, equal to the bulk of air which was abforbed during the combuftion, it is again rendered capable of fupporting the refpiration of animals, the com- buftion of bodies, &c. and in a word re-aflTumes all the properties it polf :ired before the ope- ration. If after the above defcribed re-eftablifliment of the air, the phofphorus be kindled again, exadly the fame effefts are obferved as in the D 3 former 3^ ON THE COMBUSTION former combuftion ; and the air may be re- peatedly reduced to a mephitic ftate, and reftored to that of common air, by the fame methods. It is however proper to obferve, that if we wifli to carry this experiment to fome length, it will be neceflary to add, each time, a fome- what larger proportion of dephlogifticated air, than has been abforbed in the preceding com- buftion; becaufe this air is never perfectly pure, but always contains a fmall portion of atmo- fpheric gas, fo that the quantity of the latter will be fomething increafed, though very in- confiderably, during each combuftion ; and this increafe will be lefs perceptible in propor- tion to the purity of the highly refpirable air employed in the procefs ; nay, we may arrive at fuch precifion, in making the experiment, as to be able previoully to determine the quan- tity of this pure air which will be required, according as its degree of purity has been afcer- tained by the teft of nitrous air. We know, from experiments, of which I have already given an account, that atmofpheric air contains « OF PHOSPHORUS. 39 contains about ^ of dephlogifticated or highly relpirable air. The abforption, however, which takes place, during the combuftion of the phof- phorus, never exceeds, and is generally lefs than, ■i, from whence it is evident, that the whole of this pure air, contained in the atmofpheric air, is not feparated by the combuftion : fre- quently the remainder which is left mixed with the atmofpheric gas, is fometimes more; fo that this air, which has been drained and rendered noxious by the above procefs, when it has been well walked, is capable of becoming again refpirable, of ftipporting flame, &c. The following relation contains what has been done on this fubje6t. Though the mephitic portion of atmofpheric air does not eafily combine with water, yet this combination in fome degree, effecTted, if it be agitated for a confiderable length of time in a large quantity of water. The highly refpirable air is ftill lefs difpofed to unite with that fluid. If therefore we agitate in the above manner the air in which phofphorus has been burnt, and which is compofed, as has been feen, of xV of highly refpirable air, and 41 of atmo- D 4 fpheric 40 ON THE COMBUSTION fpheric gas ; the highly refpirable air, which at firft formed only will be found to amount to a larger portion, and this will increafe in proportion as the atmofpheric gas is abforbed by the water. The air then which has ferved for the combuftion of phofphorus, being walhed and well agitated in a large quantity of water, mull pafs through all the intermediate ftates from that to which it Vv’as reduced by com- buftion, to that of dephlogifticated air. But the change cannot be effefted, without a dimi- nution of its volume, which is, for the moft part, made at the expence of the noxious part. The whole of this theory, relative to the combuftion of phofphorus, and the formation of its acid, is equally applicable to the combuftion of fulphur, and the formation of the vitriolic acid ; with this difference only, that the com- buftion of fulphur, not being fo eafily fupported, and this fubftance extinguifhing more readily than phofphorus, it is rhore difficult to deprive a given quantity of air of its highly refpirable part, by the one than by the other i accordingly, as foon as or t of the air is confumed, the fulphur ceafes to burn ; whereas bodies fuch as phofphorus, 41 OF PHOSPHORUS. phofphorus, which are more combuftible, and more fufceptible of being kept in a ftate of ignition, will burn in it longer. By this diffi- culty I have been prevented from obtaining fuch exa£b refults from the combuftion of fulphur as from that of phofphorus, and I have there- fore omitted, at prefenr, to give the detail of them. But thus far I can affert, that if fulphur be burned in a glafs jar, inverted into mercury, the diminution in the volume of air will be proportionable to the confumption of fulphur, and that a very concentrated vitriolic acid will be produced, which will be two or three times the weight of the fulphur employed to form it. This is a fubjed which I lhall in future refume, and fhall beftow upon it all poffible accuracy. I FLATTER myfelf that I am fufficiently au- thorifed by the event of the preceding experi- ments, both on phofphorus and fulphur, to de- clare, I ft. that atrnofpheric air is compofed of about ^ of highly refpirable or dephlogifticated air, and of mephitic, noxious air. idly. That phofphorus, during its combuftion, ads only on the highly refpirable part, leaving the mephitic, which may be confidered as a mere paffive me- dium. 42 ON THE COMBUSTION dium, unaltered. 3dly. That the phofphoric and Vitriolic acids are compofed, of above one half of their weight, of highly refpirable air. I iliall hereafter Ihew how thefe two acids may be decompoled, and in what manner we may recover, by means of combinations, this pure air which forms one of their component parts. The phofphoric acid, which is obtained by the above procefs, diflblves almoft immediately on coming into contaft with the airj and, by thus running ad deliquium, becomes a highly concentrated, heavy acid, polTefling no more fmeil than concentrated vitriolic acid, refem- bling it in its oily appearance, and in every other point. This is the acid which has been employed in all the experiments to be related in this memoir ; but I have obtained it by a method fomewhat more expeditious and convenient, which confifts in burning the phofphorus under large glafs jars, on the infide of which a little diftilled water has been thrown. As foon as the vapours formed by the firft combuftion are difperfed, a frefh quantity of phofphorus is to be 43 OF PHOSPHORUS. be introduced and burnt in the lame manner, and thus the procefs is to be carried on for feveral days, till a fufficient quantity of acid be obtained. It may be fuppofed that the acid procured by this means will be lefs concen- trated than the former, as being diluted with water ; but it is in other refpefts exadly of the fame nature, and may be ufed in every experi- ment, where a highly concentrated acid is not requifite. Having Ihewn in what manner this acid is produced, it remains to purfue it through the different unions which it is capable of con- trafting. To avoid confufion, and to facilitate the making of references to the experiments contained in the following part of this memoir, I lhall divide it into different articles. article I. Phojphoric Salt with a Calcareous Bafts. ON adding phofphoric acid, drop by drop, to lime-water, the water became turbid, and a white precipitate fublided, which at firft fight appeared 44 ON THE COMBUSTION appeared to be fimilar to that produced by throvv'ing fixed air into it j but on more clofe examination, the fediment was found to be of a cryftalline form, a true neutral fait, not effer- vefcing with acids, diflblving entirely in water, but requiring a much larger portion to keep it diflblved, than is requifite for felenite, or even lime. The water on evaporation afforded more of thefe cryffals, the figure of which was not eafy to be defcribed. A SIMILAR fait was obtained by adding the acid to quicklime and to chalk. The mixture with the latter was attended with effervefcence j and in both cafes the fait fell to the bottom of the veffel as faff as it was formed, owing to its difficult folubility. This fait poffeffed feveral remarkable fingu- larities : firfl, in whatever manner it was made, ' it always retained an excefs of acid. So far from being able to give it a fuperabundancy of ^ calcareous earth, the attempt was vain to render it exaftly neutral; and, by wafhing, the fait, with its fuperabun'dant acid, is diffolved in the water, whereas the excefs of -calcareous earth remains unchanged on the filter. It OF PHOSPHORUS. 45 It diflblved more readily in water to which fome phofphoric acid had been added, than in fimple water j but, on evaporation, it did not retain this additional acid, which was drained from it by means of brown paper, or wafhed away by water. Its affinity to calcareous earths was weaker than to alkaline falts, on the addition of which the fame appearances enfued, as when they are I added to folutions of calcareous falts, formed ! with the other acids. On adding, drop by drop, a folution of filver I in nitrous acid to a folution of this phofphoric ■ fait, a greyiffi faline precipitate was immediately formed, which gradually became red, approach- ing the colour of leys of wine ; but if added to i a folution of quickfilver in the fame acid, the I precipitate was white and powdery. Neither this fait, nor the phofphoric acid, communicates any particular colour to the flame i of fpirit of wine : whereas phofphorus itfelf i gives fpirit of wine a light green colour. But : it is remarkable that the phofphorus does not take 46 ON THE COMBUSTION take fire, as long as it is covered b)r the fpirit of wine, and thereby defended from contadt with the air, but immediately inflames as foon as fo much of the fpirit is evaporated, as to leave any part of the phofphorus uncovered. ARTICLE II. Phofphoric Salt with Bafts of Magnefia Alba. ON throwing, gradually, fome magnefia alba into wea.: phofphoric acid, it was diffolved with effervefcence j but as the fait which was formed, pofTefTed but a fmall degree of folu- bility, it precipitated, as fall as it was formed, to the bottom of the velTel. On adding dif- tilled water, the precipitate was diffolved ; and the folution being left to fland, all night, in a cold place, a great number of very fmall regular cryftals of a flattifli needle-like form, were found in the morning: they were many lines in length, cut off obliquely at each end, and refembled very exaflly, in figure, the cryftals which are obtained by a very flow and infenfible evaporation of a folution of that kind of gypfum called lapis fpecularis : but on at- tempting OF PHOSPHORUS. 47 tempting to feparate and dry them in a ftove, they fell into powder. Nor was I able, by fub- fequent evaporations, to procure fuch regular cryftals as thefe which were obtained fponta- neoufly with a large portion of water. This fait was immediately decompofed by vitriolic acid, which, uniting with the magnefia, formed the bitter purging fait, commonly called Epfom fait. ARTICLE III. Phojphoric Sak with Bafis of Fixed Alkali. MINERAL fixed alkali .r^'as difiblved with efiervefcence in dilute phofphoric acid. The folution was not bitter, but rather agreeable to the tafte, fomething like that of a folution of fea fait. The fait obtained by this union had not the lead: excefs of acid, as is the cafe with almoft all the other phofphoric falts. It re- fufed to form into cryftals, whatever degree of evaporation was ufed, and whether the folution were made fuperabundantly acid or alkaline. The refult was, always, a tenacious gummy refiduum, which roped like thick turpentine, attradled moifture from the air, and deliquefced in it. The 48 ON THE COMBUSTION The vegetable fixed alkali diflblved alfo, in the phorphoric acid, with efrervefcence. When the combination was formed, it was fet to evaporate, and, when grown cold, cryftals were obtained of a columnar fiiape, perfedly fquare, terminated by a pyramid, having alfo four fides, commonly equal to each other, and correfponding exaftly to the four fides of the cryftalline column. Hot water diflfolved nearly double the quantity of this fait that was capable of folution in cold water. The fait had a fmall degree of acidity. Thrown on burning coals it puffed up, but melted with difficulty j but as foon as it flowed, it lofl all its faline tafte. I have not yet purfued the inveftigation of this extraordinary circumflance, which affords a key to fome interefting phenomena. This fait gives a very flight red tinge to the flame of fpirit of wine j whereas that with the mineral alkali affords no fuch appearance. They both precipitate filver from nitrous acid in form of a white powder, which is diftinguifb- able from the precipitate produced by marine falts in being very much divided, and not col- ledted in flakes or curds. They alfo feparate mercury OF PHOSPHORUS. 49 mercury from that acid in form of a yellowifh white, and lead in that of a white precipitate, the latter being rather faline. ARTICLE IV. Phofphoric Ammoniacal Salt. THE concrete volatile alkali effervefces with phofphoric acid, and forms with it a neutral ammoniacal fait, more foluble in hot than in cold water, the cryflals of which have fome fimilitude to alum ; but as they are very com- plicated, it would not be eafy to defcribe them without figures. ARTICLE V. Phofphoric Metallic Salts. DILUTE phofphoric acid has no aftion on mercury in the cold. Globules of mercury have been kept feveral months in it without the leaft appearance of folution : perhaps if it ; had been very concentrated and ftrongly heated, its aftion might have been ftronger j but I have not had an opportunity of making the trial. E Poured 50 ON THE COMBUSTION Poured on a foliition of filver in nitrous acid, it produced no precipitate. When cold, it had little efFeft on iron, but when hot, a brifk effervefcence enfued. A taper being plunged into the vacant part of the jar in which the combination had been efFeCled, continued to burn as in common air, but with a lightifh green flame. The folution being evaporated, yielded no regular cryftals, but a faline mafs, of a green colour, and very foluble in water. M. Sage has aflTerted in many of his works that the phlogifticated alkali, which is ufed for the preparation of PrufTian blue, is only an alkali faturated with phofphoric acid, and has given his theory an air of probability which may tend to miflead. If the aflertion were true, the phofphoric falts with alkaline bafes Ihould form PrufTian blue when combined with martial vi- triol. — But the contrary is the cafe. The pre- cipitate is whitilh, dilTolves, though with difli- culty, in acids, and leaves only a fmall infoluble portion, which has only a blueifh tinge, fcarcely perceptible. Such OF PHOSPHORUS. 51 Such are the experiments which the provifion of phofphoric acid I had made, has enabled me to make. I wifhed to have gone further, and to have repeated the whole of them j but cir- cumftances having led me to another kind of experiments, and the difficulty of procuring, fo.r a long time, a fufficient quantity of pure acid, having deterred me from waiting, I have de- termined to give them to the fociety as they are; and. hope, that, though incomplete, they may be of fome ufe to chemiftry, either by eftabliffiing new fads, or by deftroying falfe theories. I can anfwer for the accuracy of my experiments. E 2 ESSAY ON THE AIR 52 ESSAY IV. On the existence of AIR in the NITROUS ACID, and on the means of decomposing and recomposing That ACID. /It I N the firfl: volume of my Phyfical and Che- mical ElTays, it was Ihewn, that when Kunckel’s phofphorus was burnt under a glafs jar inverted into water, about | of the air con- tained under the jar was abforbedi and that this diminution of air was proportioned to the increafe of weight in the phofphoric acid re- fulting from the combuftion,* I therefore concluded that this acid was, in part, compofed of air, or, at lead, of an elaftic fubftance con- tained in the air. As exaflly the fame phe- * See alfo the third EiTay in this colleftion. nomena IN NITROUS ACID, &c. 53 nomena take place in the combuftion 6 \ ful- phur, and the formation of the vitriolic I'cid, I had equal reafon to conclude that air alfo enters into the compofition of the latter. These firft Heps led me to refledt on the nature of the acids in general, and on examining the circumftances of their formation, and de- ftrudlion, I thought that I began to difcover that they were all compofed, in great meafure, of air; that this fubilance was common to them di, and that they wc e varied from each other by the addition of different principles peculiar to each acid. What was at firft only probable conjedlure, was converted to fufficient certainty when ex- periment was applied to theory ; and I am at prefent enabled to declare pofitively, not only that air, but the moft pure part of the air, enters into the compofition of all the acids without exception ; and that on this fubftance their acidity depends, in fo much that we may, at pleafure, deprive them of that quality or reftore it to them again, according as we take away, or give to them, the portion of air effential to their compofition. E 3 Before 54 OTvJ THE AIR Before I proceed further on this fubjefi:, it fcems neceflary to inform the public, that one part of the experiments contained in this me- moir are not properly mine ; perhaps, ftridUy fpeaking, there is not one of which Dr. Prieftley may not claim the original idea. But as fimilar fafts have led us to fomewhat different con- fequences, I truft, that if I fhould be accufed of having borrowed my experiments from the works of that celebrated philofopher, I fhall, at lead, be allowed the merit of the conclufions. It is a generally known fadl that elaftic va- pours are feparated from almoft all folutions of metals in acids, which form fpecies of air, the properties of which vary according to the nature of the acids, by the afliftance of which we are enabled to form them. These different kinds of air by no means proceed from the metal, as I fhall have frequent occafions to fhew ; they are to be attributed to the decompofition of the acid itfelf; and I imagined that from hence we might be fupplied with a fimple method of analyfing the acids. It Teemed probable, for inflance, that by dif- folving 55 IN NITROUS ACID, &c. folving mercury in nitrous acid, colleamg the different elaftic principles which efcape from this combination, and attentively obferving the phenomena which appear from the firft mftant of the folution, to the point, when the mercury, after having fucceffively palTed through the ftate of mercurial fait and red precipitate, re- appears finally in its metallic form, 1 ibould infallibly acquire information concerning the nature of the principles which enter into the compofition of nitrous acid. The experiments which I am going to relate n.ight have fucceeded equally with any other metal ; but I gave the preference to mercury, becaufe this metal poffeffes the property of being reduced without addition; and I there- fore "concluded that I fhould meet with iefs complication in the courfe of my experiments, and fhould be led, in a more fimple manner, to the conclufions at which I wifhed to arrive. 1 therefore took a fmall matras, with a long narrow neck, which I bent in the flame of a lamp, fo that the extremity might pafs under a glafs iar, filled with water, and plunged into a veffel E, 4 containing 5^ ONTHEAIR containing the fame fluid. Into this matras I introduced two ounces of nitrous acid, which fmoked moderately, the fpecific gravity of which was to that of diftilled water in the pro- portion of 131607 to 100000 ; and I added two ounces one drachm of mercury, heating the mixture gently in order to accelerate the folutlon. As the acid was ftrongly concentrated, the ef- fervefcence was brifk and the reparation of air very rapid. I received the difengagcd air in dif- erent jars, that I might examine the varieties which might poffibly occur between the par- cels feparated at the beginning, and thofe at the end of the effervefcence. When the effervef- cence was finilhed, and the whole of the mercury dilTolved, I continu'-u to make the folution hot in the fame veffel. In a Hiort time the effervef- cence was fucceeded by an ebullition, during which, the produflion of air continued almoft as great as at firff The procefs was carried on, till, the whole of the fluid having been converted into air or watery vapours, I had nothing left in the matras but a white mercurial fait, of a pally form, rather dry than moill, and beginning IN NITROUS ACID, &c. 57 beginning to turn yellow on the furface. The quantity of air, which had been already ob- tained, amounted to about 162 cubic inches. All this air was of the fame nature, and in no re- fped differing from that to which Dr. Prieftley I has given the name of nitrous air. I The operation being continued, I perceived red vapours to arife from the mercurial fait, fimilar to thofe of the nitrous acid ; but this circumftance was not of long duration, and ' prefently the air, contained in the upper part of the matras,* recovered its tranfparency. Having fet apart the air, amounting to ten or twelve inches, which had paffed during the continuance of the red vapours, it was found to be very different from that which had been hitherto , collefted, and not to differ from common air, I except that candles burnt fomething better in it. I At the fame time the mercurial fait was changed ! * These vapours owe their origin to a portion of I nitrous air, and of highly pure air, which are dif- I engaged at the fame time from the mercurial fait, and j combining together, form nitrous acid. This explana- j tion will not be well underftood till the whole of this i Eflay has been read. into ON THE AIR 58 into a beautiful red precipitate, and continuing to urge it with a moderate degree of fire, 1 ob- tained, in the fpace of feven hours, 2.34 cubic inches of air, much purer than common air, in which candles burned with a very enlarged flame, and which, by all its chara6ters, con- vinced me that it was the fame I had extrafted from the calx of mercury, commonly called mercury precipitated per fe, and which Dr. Prieftley has obtained from a great variety of lubflances, by mixing them with fpirit of nitre. In proportion as this air was difengaged, the' mercury was reduced, and I recovered, within a few grains, the two ounces one drachm which had been employed in the foiution. This trifling lofs proceeded from a fmall portion of a yellow and red fublimate which adhered to the dome of the retort. The mercury having been recovered from this experiment, in its former ftate, without change either in its quality or weight, it is evident that the 426 cubic inches of air, which had been obtained, could not have been pro- duced but by the decompofition of the nitrous acid, I had therefore reafon to conclude that two IN NITROUS ACID, &c. 59 wo ounces of nitrous acid are compofed, ift. 190 inches of nitrous air; 2dly. of 12 inches ►f common air; 3dly. of 224 inches of air fetter than common air; 4thly. of phlegm, ^ut, as it has been proved, by Dr. Prieftley’s fcxperiments, that the fmall portion of common air 1 had obtained could be nothing but air better than common air, the fuperior quality Df which had been altered by a mixture of litrous air, in the tranfition from one to the pther, I may re-eftablilh the quantity of thefe two airs, as previous to their mixture, and fuppofe that the 12 inches of common air, which I obtained, proceeded from a mixture of 24 inches of nitrous air, and a like quantity of air fuperior to that of the atmofphere. In thus re-eftablilhing the quantities, we lhall have, as the produd of two ounces of nitrous acid. Inches. Of nitrous air - 196. Very pure air - 246. Total 442. iAnd for the produft of one pound of the fame acid. Nitrous 6o ON THE AIR Inches. Nitrous air - 1568. Very pure air - 1968. Total 3536. If It were poflible to know the abfolut< weight, as well as the bulk, of thefe quantitiei of air, it would be eafy to determine the weigh of phlegm, and we fhould then poflefs a com< plete analyfis of the nitrous acid. The experh ments of Dr. Prieftley to this purpofe are fai from being fatisfadory, and I confefs that I hav« not been able to arrive at any certain conn clufions. I lhall, however, fuppofe here, as j have every reafon to prefume, that the pure air^ obtained from mercury, is fcmething heavier than common air, and chat it weighs 3 grain to the cubic inch. I fliall alfo fuppofe, that nitrous air is fomething lighter than atmo- fpheric air, and that its weight is of a grain to the cubic inch ; on this fuppofition we fhall find that a pound of nitrous acid, fuch as that employed, will be compofed as follows, viz. Oz. 2 • Grs. Nitrous air - i Very pure air -17 2t- Phlegm, or Water 13 18. Total Ibj. Here, IN NITROUS ACID, &c. 6i Here, then, we are prefented with a method If decompofing the nitrous acid, and demon- bating the exiftence of air, or rather of more ^ure and perfedt air than that of the atmo- phere ; but a complete proof of this fad was obtained, when, after having decompofed the litrous acid, I was able to recompofe it by igain combining the fame materials. This is \ power which I have adually attained; but )revious to the relation of that experiment, it vill be necelTary to give Tome account of the lature of nitrous air. Those who have not read the experiments elated in Dr. Prieftley’s firft volume on difFer- ;nt kinds of air, and efpecially thofe of Mr, iA/'illiam Bewley, which are inferred at the end )f that volume, may perhaps imagine nitrous ur to be merely nitrous acid in the form of /apour. It will be fufEcient, in order to over- hrow this opinion, to make it appear that it is ‘ven doubtful whether nitrous air be in a ftate of acidity, and this the refult of the following ex- periments tends to prove. I ft. Nitrous Air is capable of pafling through very confiderable quantities of water, and 62 ON THE AIR and even of remaining, for many months, ii contadt with it, m glais jars, without forming any combination with it, without condenfinj into the form of a fluid, or fuffering the leal change either in bulk or quality. The vapour of fpirit of nitre, on the contrary, combin with water with the utmoft facility, and thj common method of condenfing them is U bring them into contaft with that fluid. idly. It is not without great difliculty anc long courfe of time that a fmall portion q nitrous air can be combined with either fixe^ or volatile alkalies : and it is only by particula operations, which are always tedious and dif ficult, that we are, even then, able to accomplifl their uni?n. Even when this is done, the re, fult is neither falt-petre, nor ammoniacal nitre, except a quantity of common air be combinec with the other ingredients. i It was therefore evident that the nitrous acid, by its combination with mercury, hac been feparated into two different airs, whichj when difunited, were not acid. Nothing then remained but to mix thefe together again, and to IN NITROUS ACID, &c. 63 to fee whether an acid would refult from the mixture, and if that acid would prove to be the nitrous. I accordingly filled a tube, which was clofed at one end, with water, the length of the tube having been previoufly divided into equal portions, and the divifions marked by a file. The tube was then inverted into another velfel filled with water, and I introduced feven parts and a third of nitrous air, into the upper part, and then fuddenly mixed with it four parts of air purer than that of the at- mofphere, which had been previoufly meafured in another tube. At the very inftant, when the two airs met, the eleven parts and ^ occupied the fpace of from twelve to thirteen meafures j but as foon as ever they had penetrated each other, they immediately combined. Red va- pours, like thofe of fmoking fpirit of nitre, were formed, which were immediately condenfed by the water, and in a few feconds the whole was reduced to about -1 of a meafure, or to about part of the original bulk. The water contained in the tub was become fenfibly acid after this operation, and was in- deed a mere weak nitrous acid for by fatu- rating 64 ON THE AIR rating it with alkali, and evaporating the water, a true nitre was obtained. With a view of obtaining the acid in a more concentrated ftate, I endeavoured to fub- ftitute mercury in the place of water, by form- ing the fame mixture in a tube filled with, and inverted into, mercury, taking care to leave a fmall ftratum of water over the furface of the metal. The penetration of the two airs was nearly as rapid in this as in the preceding ex- periment j the vapours of nitrous acid were con- denfed by the fmall portion of water contained in the tube, and by proportioning properly the quantity of water, I was capable of forming either a very fmoking fpirit of nitre, as ftrong as can pofTibly be made, or one that was more weak, and fimilar to that originally employed in the operation. This experiment Ihould be made with all poffible expedition, becaufe the fmoking fpirit of nitre, which is formed and comes into contad with the mercury, ads upon the metal, diffblves it, and again forms frefli nitrous air. This laft circumftance furniflies an additional proof of the recompofition of the nitrous acid. It IN NITROUS ACID, &c. 65 It may perhaps appear furprifing, that feven parts and f of nitrous air, and only four parts of .very pure air, are necelTary to compofe the nitrous acid; wher as in the decompofition of it, a fomewhat larger quantity of pure than of nitrous air was obtained. I am uninformed of the caufe of this circumftance, but the fa6l is certain, that the above proportions of nitrous and pure air exactly faturate each other: and confequently that by employing the very ma- terials, which have been afforded by the nitrous acid in its decompofition, it is impoffible to form again the quantity of acid which exifted before the folution, and that a defedt appears of nearly one half of the pure air. Having fhewn that the principles of the nitrous acid are capable of difunion and re- combination, it remains for me to demonftrate that we may produce the fame effedt with ma- terials which are not all derived from the nitrous acid. Inftead of very pure air, procured from the red precipitate of mercury, atmofpheric air I may be employed. But a greater proportion of it will be neceffary, and inftead of four, nearly fixteen parts will be wanting to faturate feven parts and ^ of nitrous air. The whole ; F of 66 ON THE AIR of this laft is deftroyed or condenfed in this, as in the preceding experiment j but that is not the cafe with the common air, of which not above -i or ^ is abforbed, and the remaining part is no longer in a ftate fit for the fupport of flame, or the refpiration of animals. It fliould appear to be proved, therefore, that the air which we breathe contains only ~ of real aij; and that this true air is mixed, in our atmo- fphere, with I of noxious mephitic air, which would be fatal to moft animals, were its quan- tity a little more confiderable. The deleterious effedls of the vapour of charcoal, and of feveral other exhalations, are further proofs how nearly this fluid approaches the boundaries beyond which it would become mortal to animals. I hope foon to be able to difcufs this idea, and to give ocular demonftration to the academy of the experiments on which it is founded. From the experiments, contained in this memoir, it appears, that when mercury is dif- folved in nitrous acid, the metal attracts the portion of air contained in the acid which con- llitutes its acidity : on one part the metal, combined with the air, is reduced to a calx ; and, on the other, the acid, deprived of its air. IS IN NITROUS ACID, &c. 67 h expanded and forms nitrous air. That thefe things really happen, during the operation, is proved by the mixture of the two airs, which originally entered into the compofition of the nitrous acid, again forming pure nitrous acid fimilar to what it was previous to the feparation of its principles. Nitrous acid then confifts of nitrous air combined with -rV of its bulk of the pureft part of common air, and a confiderable portion of water. It will, doubtlefs, be alked, whether the phlogifton of the metal may not contribute fomething in the operation ? Without pre- fuming to decide on a queftion of fuch great confequence, I (hall only anfwer, that as the mercury is left, after the procefs, precifely the fame as before, it does not appear that it has either loft or recovered its phlogifton j except it can be fuppofed that the phlogifton neceflary to the redudtion of the metal had pafled through the veflels : but this is to admit of a fpecies of phlogifton different from that of Stalh and his difciples, and to return to the principle , of fires to fite combined in bodies j a fyftem of greater antiquity than that of Stalh, and very different from it. F 2 I SHALL 68 ON THE AIR, &c. I SHALL conclude this memoir, as I began it, by acknowledging my obligations to Dr. Prieft- ley for the greateft part of what interefting matter it may contain. But the love of truth, and the promotion of fcience, to which all our efforts ought to be direded, oblige me at the fame time to take notice of one error into which he has fallen, and to which it might be dangerous to accord. This juftly celebrated philofopher having obferved that, by combining nitrous acid with any kind of earth, he con- ftantly obtained common air, or air of even a purer nature than common air, believed that it might therefore be concluded that atmofpheric air is compounded of nitrous acid and earth. This theory will be fufficiently confuted by the experiments contained in this memoir. It is evident that it is not the air that is compofed of nitrous acid, as the Dodor has imagined j but, on the contrary, the nitrous acid which is compofed ofair j and this remark alone fupplies a key to a great number of experiments con- tained in Dr. Prieftley’s fecond, third, fourth, and fifth volumes on air. ESSAY SOLUTION OF MERCURY, &c. 69 essay V. On the solution of MERCURY in VITRIOLIC ACID. H aving fhewn in former effays that nitrous acid is the refult of a combination of a certain proportion of dephlogifticated, with nitrous, air j that fulphur and phofphorus are incapable of acquiring acidity but in propor- tion as they are combined with a very confider- able portion of dephlogifticated airj and having declared that it is poflible to difcover, in the vitriolic acid, by chemical experiments, the dephlogifticated air which entered into its com- pofition in the combuftion of the fulphur : I fliall proceed in the prefent eflay to prove, by means of analylis, what I have hitherto only accompliftied by means of compofition. F3 Four 70 SOLUTION OF MERCURY Four ounces of mercury, and fix ounces of vitriolic acid, were put into a fmall glafs retort, and gradually heated by an open fire in a reverberatory furnace. The extremity of the retort, the neck of which was very long, was immerfed in a bafin of mercury, and the air, in proportion as it arofe, was received into tall narrow jars filled with, and inverted into, mercury. The folution was effefted with con- fiderable effervefcence, during ftrhich, a very confiderable quantity of volatile vitriolic* air was feparated, which, as long as it is confined in mercury, and does not come into contadl; with water, preferves its elafticity, and is in- capable of either rarefadlion or condenfation, except by various degrees of compreffion or heat. This air, when expofed to water, is but flowly abforbed, and the combination is at- tended with fenfible heat. The water which has been thus impregnated is clear and limpid, and forms what we call volatile, fulphureous, or vitriolic, acid. But the quantity of this air, abforbable by water, varies confiderably, ac- cording to the different temperature, and is greateft when the water is coldefti whereas, on the IN VITRIOLIC ACID. 71 the contrary, when the water is nearly boiling, it is incapable of abforbing a particle of it. I could not poflibly determine with accuracy how I much of this air would be neceffary to faturate 1 a given quantity of water in different degrees of temperature. But thus far is certain, that the water is capable of abforbing a greater portion of this, than of fixed, air, but much lels than of marine acid air. •> If it be defired to colled the whole of this vitriolic air, it will be only neceffary to adapt, to the retort, a tubulated receiver, fimilar to that defcribed by Mr. Woulfe and improved by Mr. Bucquet j by which means we catch in the receiver, the fulphureous acid, in the higheft ftate of concentration, and that, which cannot be condenfed, is found united to the water in the bottles conneded with the receiver. The firft portions of volatile vitriolic air are very pure, but, as the procefs advances, it becomes mixed with common air, and even with fome portions of dephlogifticated air. Thefe may be feparated by placing the whole in con- tad with cauftic alkali, for the vitriolic air will F 4 he 72 SOLUTION OF MERCURY be inftantly abforbed, and the conamon or the dephlogifticated air left behind. If when the mercury is almofl: reduced to drynefs, the fire be urged rather more brifkly, a fmall portion of volatile vitriolic air ftill con- tinues to pafs; but the quantity of dephlo- gifticated air which comes over, at the fame time increales continually ; and when the re- fiduum is quite dry, it is neceflary to change the apparatus, becaufe the fire neceflary to the fuccefs of the operation would melt the retort if it were not placed in fand. An aperture was therefore made in a Paris crucible, which might admit the neck of the retort to pafs through it. The crucible was ufed as a fand bath, in which the retort was placed, having its upper part thinly coated with moift refradory clay, to prevent the glafs being affefted by the cold air, as it ought to be equally heated in every part, and alfo that the retort might be lefs expofed to be broken. Into an apparatus, fuch as is now defcribed, I put two ounces of mercurial vitriol, dry and deprived IN VITRIOLIC ACID. 73 deprived of the greater part of its water of cryflallization, and the produdt of the preceding operation. A briflc fire was applied. The pro- cefs continued above an hour and half, and during the whole courfe of it, there were col- lefted, I ft. a fmall portion of volatile vitriolic air, which was abforbed in the water of the tub into which the neck of the retort was immerfed : 2 dly. eighty inches of dephlogifticated air, which was of fuch a degree of purity, that four parts of it required for its faturation feven parts or meafures of nitrous air, and the whole eleven meafures were reduced to i 4-. So that the de- phlogifticated air obtained from mercurial vi- triol approaches much nearer to abfolute purity than any we have hitherto poflefled. In proportion to the feparation of the volatile vitriolic, and dephlogifticated air,, the mercury, which had been combined with them in the mercurial vitriol, was revived, recovered its form, and pafled over in diftillation as running mercury. This however was not wholly the cafe, for two fpecies of calx of mercury fublimed into the neck of the retort. The one was white and had a faline appearance; the other was grey. 74 SOLUTION OF MERCURY grey. I fhall take an opportunity of examining thefe calxes, which are fuch as M. Beaume has declared to be incapable of being reduced with- out addition. When the operation was finilhed, nothing remained in the retort. On calculating the products of this laft ope- ration, and comparing them with thofe I had obtained from an equal quantity of mercurial vitriol, in a common apparatus for diftillation, I found that two ounces of this metallic com- pound yield, 3. Grs. I ft. Of water or phlegm 1 ad. Running mercury 6 12 3d. White calx of mercury, fublimed 3 18 4th. Grey calx of mercury 40 Total I 2 70 The quantity of mercurial vitriol was 2 The lofs therefore amounted to o 5 2 This lofs may doubtlefs be accounted for, by the eighty cubic inches of dephlogifticated air which were collefted, and by the volatile vitriolic air which was abforbed by the water. It IN VITRIOLIC ACID. 75 It is apparent that as no other fubftance was employed in this operation but vitriolic acid and mercury, and as the latter is recovered in its original metallic form, the dephlogifticated air could only proceed from the vitriolic acid j and, according to the opinion I had advanced, the dephlogifticated air, which had been ab- forbed during the combuftion of the fulphur, is found by analyfis in the vitriolic acid. Another fad, which it is impoflible to deny, after the experiments that have been related, is, that volatile vitriolic acid is common vi- triolic acid, deprived of a part of its dephlo- gifticated air. ESSAY 76 ON PYROPHORUS AND ESSAY VI. EXPERIMENTS on the COMBUSTION OF ALUM WITH PHLOGISTIC SUBST ANCES, AND ON THE CHANGES EFFECTED ON AIR IN WHICH THE PYROPHORUS HAS BURNED, S it will be needlefs to repeat every thing that has been written on the fubjed: of Homberg’s pyrophorus, and to difcufs the va- rious opinions which have, fuccefliveiy, pre- vailed concerning the caufe of its fpontaneous inflammation, I fhall confine myfelf to recurring to a memoir of Mr. Homberg, which is printed among thofe of the Academy of Sciences for the year 1718, page 238, and efpecially to that of M. de Suvigny, publifhed in the third volume of Memoirs of Mathematics and Phyfics, prefented to the academy by learned foreigners. It will be proper on this occafion to re- coiled, that it has been proved by the experi- ments 77 ITS EFFECTS ON AIR. merits of M. de Suvigny, ift. that not only alum, but alfo all the vitriolic falts with a I bafis of fixed alkali, fuch as Glauber’s fait, ! vitriolated tartar, &c. mixed with a proper proportion of any light porous matter contain* ing phlogifton, and urged by a degree of fire fufficient to bring the mixture to a red heat, leave a refiduum of a blackifh hue, which has the property of taking fire fpontaneoufiy in the air. adly. That in all thefe operations the vi- triolic acid is converted into fulphur, fo that it may be faid that Homberg’s pyrophorus, and all thofe formed by M. de Suvigny on fimilar principles, are merely phlogiftic hepars of fulphur with either a fixed alkali or aluminous earth for their bafis. 3dly. That it is a proof of the converfion of vitriolic acid into fulphur in the formation of the pyrophorus, that in whatever manner this fubftance be analyfed, not an atom of vitriolic acid, nor of the vitriolic falts which had been employed in the operation, is to be found, but only liver of fulphur and fulphur. 4thly. 78 ON PYROPHORUS AND 4thly. That very good pyrophorus may be formed without making ufe of any vitriolic fait, by a combination of fulphur, alkali, and pow- dered charcoal ; a fa< 5 t which proves molt in- conteftably that pyrophorus is a true hepar fulphuris.— Having ftated thefe preliminaries, I lhall proceed to give an account of my own experiments. Two parts of alum and one part of fugar were mixed together, and the mixture calcined in an iron ladle, without making it red hot, till the fugar was entirely converted into char- coal, and neither fmoke nor vapour continued to rife. I TOOK two ounces of this calcined mixture, and placing it in a glafs retort, in a fand heat of a reverberating furnace, the fire was raifed, and the air which feparated was received into jars filled with water. About 120 inches of fixed air firfl pafTed, then about 160 inches of air compofed of equal parts of fixed, and of inflammable air j and the lafl produdl obtained confifted of 180 inches of air, three fourths of which were inflammable, and one fourth only fixed ITS EFFECTS ON AIR. 79 fixed air ; and the laft portions were only pure inflammable air. The fixed air may be feparated from the in- flammable, either by fufFering them to remain for fome days together in the jars, flanding in water, when the fixed gas will be abforbed, leaving the inflammable, which does not readily unite with water j or the abforption may be accelerated by placing them in contafb with a lixivium of cauftic alkali, or over lime-water. This liquor entirely and rapidly abforbs the fixed air, and the inflammable air which remains will be quite pure. By thefe methods I have difeovered that of 460 cubic inches of elaflic fluid which were obtained in this operation, 215 were inflammable, and 245 fixed air. But this calculation of the produfl mufl; not be re- garded as quite exad, with refpedt to the fixed air, becaufe this acid being obliged to pafs through a confiderable quantity of water in its way to the upper part of the jar, a part of it was neceflfarily abforbed by that liquid during the courfe of the operation, and before its bulk could be determined. This circumftance may be fuppofed to have occafioned a lofs of at leaft a fourth 8o ON PYROPHORUS AND a fourth or a fixth of the quantity of fixed air, fo that the whole that was feparated in the procefs mud have amounted to, at lead, 300 inches. I During almod the whole courfe of the ex- periment, a confiderable quantity of fulphur was feparated, part of which was fiiblimed and condenfed in the neck of the retort, and part, pafiing in vapours through the water, was de- pofited on its furface in form of. a fine powder. The operation continued about an hour and half. The refiduum in the retort was Homberg’s pyrophorus, was very good and drong, and flamed as foon as it came into contad with the air. Thf quantities and qualities of the air dif- charged in the operation being fufficiently de- termined, I proceeded to the following experi- ments. Two drachms of this pyrophorus were placed on the fcale ol a very fenfible balance, and I obferved, that it began to increafe in weight the ITS EFFECTS ON AIR. 8i the moment *the combuftion commenced, and that this augmentation continued to take place for feveral minutes : in order to difcover the caufe on which it depended, it was thought proper to obferve all the circumftances of the combuftion with the utmoft attention. I ACCORDINGLY began by introducing fuc- ceflively two drams of pyrophorus into different jars filled with fixed air, and with nitrous air. It did not give any light, nor afford any re- markable phenomenon. But the cafe was different when I placed the pyrophorus under jars filled with common, or with dephlogifticated air ; and as the cir- cumftances of thefe experiments are very re- markable, I ftiall give a full relation of them. About half an ounce of pyrophorus was put into a fmall glafs bottle, which was covered with a little glafs cover, and the jundlures being luted fo that the whole apparatus might be paffed through water without any of the water getting into the bottle, it was conveyed under a jar filled with common air, and I accurately G marked 82 ON PYROPHORUS AND marked the height at which the water Rood in the jar. Then introducing my hand under the jar, I removed the cover that was affixed to the bottle, and made a free communication between the pyrophorus and the air of the jar. A con- fiderable degree of heat was immediately pro- duced without combuftion, and, at the fame time, a diminution of the quantity of air took place, which was, at firft, pretty rapid, but abated in about five minutes ; yet did not en- tirely ceafe till after the fpace of between forty- five minutes and an hour had elapfed. This diminution of the volume of air was greater than any I had hitherto obferved, and bore the proportion of loo to 724-, or to more than ^ i whereas, in almoft all operations of this kind, it fcarcely amounts to a fifth. When the experiment was made over lime- water, inftead of common water, the diminution was the fame j and, as it advanced, I obferved a precipitation of the lime to be formed, which evinced that one of the caufes of this diminu- tion was owing to the converfion of a part of the air in the jar, into fixed air, which was ab- forbed by the lime-water. This ITS EFFECTS ON AIR. 83 This experiment induced me to repeat the experiment in dephlogifticated or highly refpi- rable air j but I perceived the neceffity of making ufe of a much larger jar, that the phe- nomena might be more diftinguifliable j in other refpedts I conduced the operation much in the fame manner as before. As foon as the little cover was detached from the bottle, and the pyrophorus came into con- tad with the pure air, it took fire, and burned with a fparkling and decrepitation, and particu- larly with a very fplendid light and extreme ra- pidity. In a fhort time, the violence of the combuftion abated, and the light began in- fenfibly to diminifh, till, in fome minutes, it was entirely extinguifhed. The pyrophorus, in this experiment, muft not be put into a glafs bottle, but into a fmall vefTel made of tin, and without folder, on ac- count of the great degree of heat which is pro- duced, and would break the glafs, or melt the folder. At the firfl inftant, the great heat produced a fmall increafe in the volume of air contained G 2 m 84 ON PYROPHORUS AND in the jar, but it was prefently fucceeded by a rapid diminution which alfo abated in about a quarter of an hour, but did not wholly ceafe till the air was reduced to a feventh of the fpace it occupied previous to the combuftion of the pyrophorus j nor was it diminilhed fo far as it was capable of being, for, when lime-water was admitted, it was again reduced, nearly one half, fo that the remainder did not amount to above a twelfth or thirteenth part of the original volume of air. The remaining parcel of air was ftill almoft pure or dephlogifticated, and by continuing to burn frelh phofphorus in it, I at length fuc- ceeded in rendering of the original quantity of air abforbable by water. This experiment was frequently repeated, and particularly in prefence of Dr. Franklin and feveral members of the academy ; the circum- ftances having been varied by fometimes em- ploying common water, and fometimes lime- water i and I am convinced that in the com- buftion of pyrophorus, very pure or dephlogifti- cated air is changed into fixed air, except the portion which is abforbed by the pyrophorus itfelf. ITS EFFECTS ON AIR. 85 kfelf, as I fhall prefently fhew, and that this fixed air conribines with the water. These effe< 5 ls of the connbuftion of pyro- phorus in dephlogifticated air, throw great light oa the phenomena attending the combuftion of that fubflance in common air. The effedls are nearly the fame, but with this difference, that atmofpheric air not containing above i of pure, genuine air, no more than that quantity of fixed air is formed and abforbed. The remaining |- are the mephitic part of the air, the nature of which is not as yet at all underftood, and which, as I have demonflrated on another occafion, is utterly incapable of fupporting either animal or vegetable life. What has been hitherto faid, relates only to that portion of pure air which' is converted into fixed air, during the combuftion of the pyro- phorus. It remains that I ftiould give an ac- count of fome circumftances which, to me, ap- pear to prove, that a confiderable portion of this air is abforbed by the pyrophorus, while burning, and combines with it j and that it is the furplus only that is changed into fixed air. G 3 And, 86 ON PYROPHORUS AND And, ift. the diminution of the volume of de- phlogifticated air, at the beginning of the com- buftion of the pyrophorus, is much greater than could proceed from the mere combination of fixed air with water. It is well known that this combination is not, in general, efFefted very readily, without agitation, whereby the points of contaft between the fixed air and the water are multiplied. Thefe circumftances do not take place under the jar where the combuftion of the phofphorus is carried on, and, on the contrary, the great degree of heat which is ex- cited is an almoft infurmountable obftacle to the union of the air and water. 2 dly. It is a known fadt that pyrophorus increafes in weight while burning; that this augmentation is very rapid, and nearly equal to the portion of air which we may reafonably imagine to be abforbed in this procefs. It is true that thofe who have obferved that pyro- phorus thus increafes in weight, have attributed the increafe to the moifture of the air which they fuppofed it to attradt, and indeed it muft be allowed, that this is likely to happen at firft; but when once the pyrophorus is ftrongly heated, when ITS EFFECTS ON AIR. 87 when it is become red and burns with violence, we cannot then fuppofe that it attrafls moifture from the air, for it is evident that this great heat muft, on the contrary, difpel and reduce it into vapour, if it exifted in the pyrophorus. It feems certain, therefore, from both thefe confiderations, that the pyrophorus abforbs and fixes a confiderable portion of pure air during its combuftion. — ^It may perhaps be alked what becomes of this air, and what alteration does it produce in the nature of the pyrophorus? This I intend to explain in the remaining part of this effay, and hereby to prove, in a more con- vincing manner, that there is really an abforp- tion and combination of air in the combuftion of this fubftance. If pyrophorus be tafted previous to its com- buftion, we perceive nothing of the ftypticity of alum, but a very difagreeable tafte of hepar fulphuris: when, on the contrary, it has burned in pure air, all the coaly part is confumed, it is perfeftly white, it has a part of the ftyp- ticity of alum, and on diflblving and evapo- rating it, we obtain an alum, fuperfaturated with G 4 earth, 88 ON PYROPHORUS AND earth, fuch as Mr. Beaume has defcribed iti his Chemiftry. This laft oblervatlon difcovers to us every thing which happens in the formation and com- buftion of pyrophorus. We clearly perceive that the vitriolic acid of the alum pafles into the ftate of fulphur while the pyrophorus is forming ; whereas it changes again to the ftate of vitriolic acid when the pyrophorus is burning. Now we have been informed by the experiments related in former eflays, that fulphur is vitriolic acid deprived of its dephlogifticated air, or, what is much the fame, that the vitriolic acid is a combination of fulphur v/ich that air, or, what will perhaps approach more nearly to accuracy, with the bafts of this pure air. Vitri- olic acid therefore cannot be changed from a ftate of acidity to that of fulphur, without a feparation of dephlogifticated air being pro- duced, and, on the other hand, fulphur cannot pafs from its own form to the ftate of vitriolic acid, without a fixation of this air being effedted ; and this has been adtually obferved in the ex- periments related in this elTay. For we have feen that from a mixture of burnt alum and charcoal, ITS EFFECTS ON AI*R. 89 charcoal, amotinting to the weight of two ounces, about 400 cubic inches of air were feparated, a part of which was fixed, and the other part inflammable air. But the pyrophorus, on the contrary, when in combuftion, abforbed a very large quantity of pure air; which fafts fully confirm the theory I have advanced. It will undoubtedly be alked, if the vitriolic acid of the alum contains pure air, why do we principally obtain fixed air during the cal- cination of the alum and charcoal, and alfo from whence proceeds the inflammable air which pafles with it? To the firft queftion it is an- fwered, that the pure air, or its bafis, is con- verted into fixed air, by uniting with the coaly fubftances. Of this we have a proof in the redudtion of the calx of mercury : if it be reduced without addition, it yields only de- phlogifticated air ; but if charcoal or any phlo- giftic fubftance be added, we obtain fixed air. As to the inflammable air, the quantity feparated in this operation is not conftantly the fame, but is proportionable to the quantity of charcoal employed. Nor is this air of the fame nature as that we obtain from the folution of certain ON PYROPHORUS AND 90 certain metallic fubftances in the vitriolic and marine acids j it is lefs inflammable, burns with much more difficulty, and makes very little expiofion when mixed with two thirds of com- mon air. This inflammable air pofTelTes one remark- able property, viz. that of being changed into fixed air by combuftion. The other inflam- mable airs which are obtained by the folution of metals, either in the vitriolic or marine acids, differ in this refpe6t, and inftead of being con- verted into fixed air, at the time they are in- flamed, appear to yield acids fimilar to thofe by which they have been extradled. Thefe confiderations, and fome others which it would be improper to introduce in this effay, lead me to fufpeft that there may be three fpecies of inflammable air, viz. vitriolic, marine, and fixed inflammable. That which is feparated during the combuftion of the pyrophorus is of this laft fpecies. And as this inflammable air produces exadlly the fame effefts, in burning, on the pure part of atmofpheric air, as charcoal does, I am ftrongly inclined to believe that it is the fubftance of the charcoal itfelf reduced to 9t ITS EFFECTS ON AIR. to vapour, and in the form of air. For the fame reafon the two other inflammable airs ap- pear to me to be, the one, a Ipecies of vitriolic fulphur, the other of marine fulphur in an aeriform ftate. But as my experiments are not quite complete, I muft content myfelf with this tranfient view of the fubjeft. ESSAY 92 VITRIOLISATION OF E S S A Y VII, On THt viTRiOLisAnoM OF MARTIAL PYRITES. HE pyrites which are the fubjeft of this memoir, are the common vitriolic mar- tial pyrites, of the moft common Ipecies, which are frequently found in chalk, and in almoft all clays, &c. with the nature of which we are well acquainted. But with relpedt to my pre- fent views, it will be only neceffary to confider them as compounded of iron and fulphur. If pyrites be diftilled in an earthen retort, with a red heat, a confiderable quantity of ful- phur is fublimed, and colle6ted in the neck of the retort. If, on the contrary, thefe pyrites remain in a warm moift air, they crack on their furface, fplit, fall in pieces, and become covered with vitriolic efflorefcences. And, when they have been expofed for a fufficient time to the air. if MARTIAL PYRITES. 93 if they be lixiviated, they yield a great quan- tity of martial vitriol ; but if diftilled in this ftate, not a particle of fulphur will be obtained. I The intervention of air is indifpenfibly necef- fary to the vitriolifation of pyrites, which may be preferved in their original ftate as long as they can be proteded from the adion of that fluid. A flight covering of oil is fufficient for this purpofe i and we find by experience, that they may be kept unchanged under water. Since pyrites, therefore, are compofed of fulphur and iron before their efflorefcence, and, after it, of vitriolic acid and iron, it is evident that the fulphur is converted into that acid, by the effed of the vitriolifation. Now as I have declared, and, I truft, proved, in the eflays on the combuftion of fulphur, and phofphorus, vitriolic acid is compounded merely of fulphur faturated with very pure or dephlo- gifticated air; or in other words, that fulphur is vitriolic acid deprived of part of its dephlo- giilicated air, and vitriolic acid is fulphuf with an over-proportion of the fame air : the ful- phur of pyrites, therefore, cannot be changed mto vitriolic acid without abforbing pure air. The 94 VITRIOLISATION OF | I The neceffity of expofure to the air for] vitriolifing pyrites, was a ftrong prefumption in favour of the theory ; but as it was poflible to confirm it by experiments, and as, in che- miftry, we fhould never be content with reafoning, when we may prove by fads, I proceeded in the following manner. I KEPT fome martial pyrites in a moderately warm place, till they began to efflorefce, when they were immediately removed and placed under a glafs receiver, plunged in water. The progrefs of the vitriolifation went on at firft as rapidly as in the open airj it afterwards abated, and at the end of eighteen or twenty days, was entirely fufpended. During all this time the water continued to rife in the jar, in proportion to the rapidity of the vitriolifation, and on the eighteenth day began to remain ftationary. The air, in which the pyrites had been con- fined, extinguiflied candles, but it neither pre- cipitated lime-water, nor united with alkalies. It was reduced to that ftate which I have denominated the mephitic portion of the atmo- fphere, which had loft about of dephlo- gifticated air ; fo that the pyrites in acquiring a vitriolic MARTIAL PYRITES. 95 a vitriolic property, had abforbed a portion of pure air, from the atmofpheric air under the receiver, and the tranfition of the fulphu- reous part of the pyrites to vitriolic acid is fubjeft to the fame law, and cannot take place, but by the union of dephlogifticated air with the fulphur. The progrefs of the vitriolifation of pyrites is much more rapid, if the operation be carried on in dephlogifticated air. But as I have not purfued this experiment with fufficient attention, I lhall poftpone giving a particular account of it. The vitriolifation of pyrites therefore depends on the addition of dephlogifticated air or its bafis to the fulphur of the pyrites, whereby the vitriolic acid is formed, which meeting with iron in a ftate of very minute divifion, muft neceflarily attack and diflblve it as faft as it is formed j and from this union proceeds martial vitriol. ESSAY 96 NATURE AND COMPOSITION ESSAY VIII. General considerations on the NATURE OF THE ACIDS, AND ON THE PRINCIPLES OF WHICH THEY ARE COMPOSED. W HEN the ancient chemifts had arrived at the power of reducing a body into oil, fait, earth and water, they believed that they had attained the utmoft bounds of che- mical analyfis, and they accordingly beftowed, on fait and oil, the appellation of chemical principles. But as the art was continually improving in its progrefs, fucceeding chemifts perceived that the fubftances which they had been taught to conftder as principles, were ftill capable of decompofition i and they foon difcovered that all the neutral falts, for example, were formed by 97 OF THE ACIDS. by the union of two fubftnncesj viz. of loiTie acid, with a faline bafis of either an earthy or metallic nature. Hence the whole theory of neutral falts, which engaged the attention of chemifts for above an age, is at prefent brought to fuch a degree of perfe6tion, that it may be regarded as the moft certain and complete part of chemiftry. In this (late, in which the fcience of chemiftry has been delivered to us by our predeceflbrs, it remains for us to perform, on the conjiituent -parts of neutral falts, what preceding chemifts have effefted on thofe falts themfelvesj — to examine the acids and the bafes of which they are compofed, and to advance this kind of chemical analyfis fomewhat farther beyond its prefent limits. In the foregoing eflays I have endeavoured to prove as clearly as is poflible by phyfics and chemiftry, that the very pure air which Dr. Prieftley has denominated dephlogifticated air, enters, as a conftituent part, into the com- pofition of feveral acids, and efpecially into that of the phofphoric, vitriolic, and nitrous acids. H Many 98 NATURE AND COMPOSITION Many additional experiments enable me to generalife this doftrine, and to declare that this pure and highly refpirable air, is the conftitutive principle of acidity ; that this principle is com- mon to all the acids, j and that the difference by which they are diftinguifhed from each other is produced by the union of one or more prin- ciples befides this air, fo as to conftitute the particular form under which each acid appears. These fa6ls being, in my opinion, firmly eftablifhed, I Iball in future diftinguifh dephlo- gifticated or highly refpirable air, in a ftate of combination or fixity, by the name of the acidifying principle, or, if any perfon prefer to exprefs the fame fignification by a Greek word, the oxyginous principle. This name will prevent circumlocution, give more exadlitude to my mode of expreffion, and enable me to avoid thofe errors, which might be continually occa- fioned by ufing the word air. For this name, fince the modern difcoveries, is become a generic term, and is moreover applicable to fubftances in an elaftic flate j whereas at prefent we are to confider them as combined, and either in a liquid or concrete form. Without OF THE ACIDS. 99 Without repeating the particular details which I have before related, I fhall only in a few words, and in the new terms I have adopted, call back the recolledion of the academy to the following pofitions : ift. That the acidifying or oxyginous prin- ciple, combined with the matter of fire, of heat, and of light, forms pure or dephlogifticated air. It mull be allowed, that this firft propofition is not ftriftly proved, and perhaps is not capable of abfolute demonftration. I have therefore advanced it merely as an idea which I appre- hend. is very probable j and it muft not be con- founded with the following, which arefupported by experiment and pofitive proofs. 2dly. That the fame acidifying principle, combined with phlogiftic fubftances or charcoal, forms fixed air. 3dly. That with fulphur it forms vitriolic acid. 4thly. That with nitrous air it forms nitrous acid. 5thly. That with Kunckel’s phofphorus it forms phofphoric acid. H 2 6 thly. loo NATURE AND COMPOSITION 6thly. That with iTietallic fiibftances in general it forms metallic calces, faving the exceptions which I fhall mention in this or fome future elTay. Thus far then does our prefen t knowledge, of the combination of the acidifying principle with the various fubftances in nature, extend^' and it is not difficult to perceive that there is^ ilill a vaft field left to be traverfed ; that there' remains a part of chemiftry which is quite new- and hitherto entirely unknown, and which can- not be complete, till we are able to determine the degree of affinity which this principle bears to all the fubftances with which it is capable of conf^bining, and to know the different fpecies or compounds, which refult from thofe com- binations. Every chemift is fenfible that the more fimple the bodies are on which we operate, and the nearer approaches we make in the reduftion of fubftances to their elementary atoms, the more difficult become the means of their decompofition, and recompofition. We know, therefore, that to decompofe and recompofe lOI OF THE ACIDS. recompofe the acids, muft be attended with much greater difficulties than the analyfis of the neutral falts, into the combination of which they enter. I hope, however, to be able to ffiew, in future, that there is no acid, that of fea fait perhaps excepted, which may not be decompounded and recompounded, and which we cannot deprive of the principle of acidity, and reftore it again whenever we pleafe. This kind of experiment requires great variety of method j and the proceffes neceffary to perform the combination vary according to the different fubftances on which we are to operate. In fome cales we are obliged to have recourfe to combuftion, either in atmofpheric or very pure air, as when fulphur, phofphorus or charcoal are the objedts. Thefe lubftances, during the combuftion, abforb the acidifying principle, and by its acceffion are converted into vitriolic, phofphoric, and aerial acid or fixed air. With refpeft to other fubftances, the mere expofure to the air, aided by a moderate degree of heat, is fufficient to pro- duce the combination j and this happens to all vegetable fubftances, that- are capable of H 3 paffing loa NATURE AND COMPOSITION pafling to the acid fermentation. In every operation of this kind,, there is an abforption of the pure part of the atmofpheric air, and the acidifying principle forms as many particular acids as there are fubftances capable of paffing to the acid fermentation. After all, we are obliged, in moft cales, to have recourfe to the fcience of affinities, and to employ the acidify- ing principle which is previoufly engaged in another combination. The example of this nature, which I defign to adduce, is one taken from an experiment which has been very well known for fome years, and related in Mr. Bergman’s memoirs, viz. the formation of the acid of fugar. This acid, according to the experiments which I am going to relate, appears to me to confift only of the fugar itjelf combined with the acidifying or oxyginous principle: and I intend to demonftrate, in feveral fucceffive memoirs, that we may, by proceffes analogous to this, unite this principle with the horn of animals, with filk, with animal lymph, with wax, effiential oils, exprefled oils, manna, ftarch, arfenic, iron, and, probably, with many other fubftances of the 103 OF THE ACIDS. the three kingdoms, which are thereby con- verted into true acids. Before we proceed farther, it may be necef- fary to recolleft that the nitrous acid, as appears from the experiments I have formerly related, is the refult of the combination of nitrous air with the acidifying principle j that the proportion of thefe two principles varies in different parcels of nitrous acid ; that, for example, the fmoking acid is fuperfaturated with nitrous airs fo that we rnay confider the fmoking fpirit of nitre as a nitrous acid impregnated and overcharged with nitrous airj whereas, on. the other hand, that which yields white vapours is fuperfatu- rated with dephlogifticated air. To thefe opinions I lhall add that from a number of experiments I have made fince the publication of my former memoir on this fubjeft, I am convinced that the nitrous acid, which I have employed on thefe occafions, and which was con- ftantly the fame, contains about 240 cubic inches of aeriform fluid in every ounce, viz. 120 inches of nitrous, and about an equal quantity of dephlogifticated air, which is nearly equal in weight to 48 grains of nitrous air, and 60 H 4 gtains 104 NATURE AND COMPOSITION grains of the acidifying principle to each ^ ounce.- The whole of the remainder confifts j of phlegm or water. ' From thele premifes it may be always con- cluded, that whenever I have introduced, into a combination, one ounce of nitrous acid, and have obtained, in the courfe of the operation, 120 inches of nitrous air, there will remain in the combination 120 inches of very pure air, or 60 grains of the acidifying principle. Let us then apply thefe fa6ts to the combination of nitrous acid with fugar. Into a fmall glafs retort were put four drachms of fugar, to which were added two ounces of water, and cv/o oun''es of the nitrous acid, I have above defcribed. The retort was placed over an open fire in a fmall reverberatory furnace, and to its neck, which was very long, a bottle, with two necks, was adapted, into which were introduced eight ounces, feven drachms, and twenty-four grains of diftilled water. To the fecond neck of the bottle a glafs tube was luted, and communicated with a common chemico-pneumatic apparatus ftand- jng in water. It OF THE ACIDS. 105 It is plain that by thefe difpofitions I had a double advantage; on the one hand that of retaining, in the intermediate bottle, whatever might pafs in diflillation, and be capable of being condenfed: and, on the other, that of receiving in the jars, the different kinds of air which might be feparated ; fo that there could be no defed: in afcertaining the whole amount of the produds of the operation. All the jundures were carefully luted with fat lute, which was covered with flips of cloth fpread over v/ith a mixture of white of egg and fallen lime; and as foon as this exterior cover- ing had become fo dry as to be fufiicient to fecure the fat lute, in cafe of its growing moifl, fome lighted coals were put under the retort. At firfl: the fugar diffolved quietly; but as foon as the liquor had acquired forty or forty- five degrees of heat, by Reaumur’s thermometer, a very briflc ebullition, or rather effervefcence enfued, which proceeded from a very rapid feparation of nitrous air, the pureft and flrongefl I had ever obtained. It is necelfary to proceed very io6 NATURE AND COMPOSITION very gradually in this operation, otherwife the acid of fugar itfelf would be decompofed, and, inftead of obtaining pure nitrous air, we fhould have a confiderable mixture of inflammable and fixed air. It will be neceflary therefore to withdraw all the fire, the moment the ebullition commences, and to replace it only in fuch portions as may be neceflTary to keep up the boiling. When the operation is advanced one half or two thirds, the nitrous air no longer pafTes fo pure; it at firft becomes mixed with a fmall portion of fixed air, which keeps con- tinually increafing, and a little inflammable air; and, when nothing pafles but thefe two fpecies of air, the operation may be confidered as finilhed. Having divided, into a great number of portions, the aeriform fluids which had been feparated during the procefs, I proceeded to examine their nature, by the different methods with which we are fupplied by modern che- miftry, and I found that the two ounces of nitrous acid, and the four drachms of fugar, which had been employed, had yielded Of OF THE ACIDS. 107 Of nitrous air. Fixed air. Inflammable air Inches. 190. 90. JOS- When I had feparated the veflels, there were found in the retort, two ounces, fix drachms, and eighteen grains of a tranfparent colourlefs acid, fimilar to that defcribed by Bergman, except that it was liquid ; and the water in the intermediate bottle was increafed in weight one ounce, two drachms and twelve grains, was moderately acid, and had a flight nitrous odour. It will readily be underflood, that in order to be accurate in the account of the products of this experiment, it was neceffary that the quality and quantity of the acid, which had been diftilled and condenled in the intermediate bottle, fhould be clearly afeertained, as no exaft calculation could be made without deduding this from the whole quantity of acid employed. For this purpofe I gradually dropped, into the acid liquor of the intermediate bottle, an alka- line lixivium, compofed of five parts of water. and io8 NATURE AND COMPOSITION and four of very pure fixed vegetable alkali. The quantity neceflary to produce an exaft fatu- ration amounted to fix drachms twelve grains. I then determined by another experiment, how much of the original acid would be required to faturate an equal portion of the alkaline liquor, and found the quantity to be three drachms fifty-fix grains and And therefore, of the two ounces of nitrous acid employed, three drachms, fifty-fix grains had paflfed unchanged into the receiver, and confequently not above one ounce, four drachms, fifteen grains i- had really contributed to the other produdls of the experimen Now one ounce of nitrous acid is compofed, as has juft been obferved, of 240 cubic inches of aeriform fluids, viz. of lao cubic inches of nitrous air, and 120 inches of very pure or de- phlogifticated air, fo that in the above experi; ment I had adually combined with the fugar 183 cubic inches of nitrous air, and the fame quantity of very pure air, which amount in weight to fomewhat more than one drachm of, nitrous air, and nearly one drachm and half of the acidifying principle. It has been feen OF THE ACIDS. 109 that during the combination there were fepa- rated 190 inches of nitrous air, vvhich amounts to the whole quantity employed ; there remained therefore combined 183 inches of pure air j and in the compofition of two ounces, fix drachms, eighteen grains of faccharine acid remaining in the retort, were contained four drachms of fugar and 183 inches, or one drachm thirty grains of very pure air, or the acidifying principle j ex- clufive of the portion of fixed air, which was feparated towards the conclufion of the procefs, and proceeded, as will be prefently Ihewn, from the decompofition of the faccharine acid itfelf, Mr. Bergman, and all fubfequent writers on this fubjeft, have therefore been millaken in confidering the faccharine acid as the refult of the decompofition of the fugar j for it appears certain, on the contrary, that this acid is formed by the combination of the fugar with nearly 4 of its weight of the acidifying principle.* Not wiftiing to depend on this firft experi- ment, I was defirous of knowing the difference * It is, notwithftanding, probable that the phlogifton of the fugar, at leall, in part, unites with a portion of the nitrous acid, to form the nitrous air. T. H. in no NATURE AND COMPOSITION in the refults, when different portions of fugar and nitrous acid might be ufed ; and I there- fore repeated the experiment with the fame circumftances, and the fame quantities of nitrous acid and water, but with only three, inftead of four, drachms of fugar, and I obtained Of nitrous air. Inches 176, Fixed air. 127. Inflammable air. 17. 320. I impute the greater portion of fixed air obtained in this procefs to the fire having been raifed rather more towards the conciufion, and having been continued for rather a longer time, than in the former experiment. The operation being finiflied, and the veffels unluted, the retort was found to contain one ounce, fevefi drachms, forty-eight grains of liquid faccharine acid, and proceeding in the fame manner as before, there appeared to have paffed by diftillation, into the intermediate bottle, four drachms, nine grains and half of the nitrous acid originally employed j fo that the quantity of OF THE ACIDS. Ill of nitrous acid, which had adually entered into the experiment, amounted to no more than one ounce, three drachms, fixty-two grains and half; which, according to the above de- termined proportions, fhould contain 178 inches of nitrous air, and as much pure air; from whence it appears, ift. that the whole of the nitrous air had been thrown off*, the pure air or acidifying principle only remaining. 2dly. That the three drachms of fugar em- ployed had attradled, during the efFervefcence, eighty-nine grains of the acidifying principle, and that thefe two fubftances, when united, and combined with phlegm, formed together the quantity of one ounce, feven drachms, forty-eight grains of faccharine acid. Independent of the information, which experiments of this kind afford, upon the nature of acids, they furnifh us with a new method of analyfing animal and vegetable fub- ff ances ; and though I have nothing quite complete to prefent on this fubjedf, I fhall proceed to give an account of the firfl effay which I have made upon fugar. In Ill NATURE AND COMPOSITION In the fame apparatus that was ufed in the preceding experiments, I mixed two ounces of nitrous acid, with an equal quantity of water and fix drachms of fugar, and proceeded in the fame manner, receiving, in an inter- mediate bottle, the nitrous acid, which came over in diftillation. When no more nitrous air was feparated, and nothing remained in the retort, but the faccharirie acid, the veffels were unluted, the intermediate bottle was re- moved, and I continued to keep up a gentle fire under the faccharine acid, receiving the air, which was feparated, diredly into jars, till at laft, having raifed the fire a little higher, towards the end, there was left only a fmall coaly refiduum in the retort. I divided, into ten parts, the elaftic fluid which had been difengaged during the operation, and very attentively and accurately feparated the dif- ferent kinds which I had obtained. The fol- lowing table prefents the whole refults of the experiment. An OF THE ACIDS. “3 An Account, in Cubic Inches, of the Kinds and Quantities of the different Aeriform Fluids obtained in the Combination of Two Ounces of Nitrous Acid, and Six Drachms of Sugar, the Operation being carried on to Drynefs. I’ortions. Nitrous Air Fixed Air. Inflammable Air. Total. Firft 56 f -- -- 56 1 ‘Second 49 TO 6 -- 55 t % Third 23t 22i 4-4 504 Fourth 2l/o 30 1 44 56t^o Fifth 14to 454 2t% 63 Sixth IS 394 74 61 -1 Seventh -- 284- 84 364 Eighth -- 48 ii^ 59 T^ Ninth -- 32/0 8 40to Tenth -- 25t% 17 42/0 Totals 27744-0- 74t4 52244 I, AT this time, put no water in the inter- mediate bottle; and when the operation was finilhed, there were found in it two ounces and half of weak nitrous acid, which, from the quantity of alkaline liquor faturated by it, an- fwered to four drachms, feventeen grains of I the 1 14 NATURE AND COMPOSITION the original acid ufed in the experiment. From hence it appears, that only one ounce, three drachms, fifty-five grains of nitrous acid had been decompounded : and this quantity is compofed, according to the foregoing propor- tions, of about 177 inches of nitrous air, and an equal portion of pure or highly refpirablc air. It is apparent from a view of the above table, that the nitrous air which had entered into the combination as one of the conflituent parts of the nitrous acid, was thrown off in the form of gas, or in an aeriform ftate ; but it may be afked what is become of the pure air or acidifying principle, which conftituted the other principle of the nitrous acid ? We have feen, from the preceding experiments, that it, at firft, entered into combination with the fugar, in order to form with it a particular acid; and from the prefent experiment, we learn, that if, after the faccharine acid has been formed, the fire be moderately raifed, the acid is almoft wholly refolved into fixed and inflam- mable air. For what is fixed air ? 1 have de- monftrated, in another place, that it is the re- fill t OF THE ACIDS. 115 ult of a combination of phlogiftic matter with he acidifying principle j from whence it fhould cem that fugar is compofed of a fmall portion >f inflammable air and much coaly matter, rhe latter uniting with the acidifying principle 3f the nitrous acid, forms with it the large quantity of fixed air which is obtained towards :he end of the operation. I intend, by further jxperiments, to illuftrate any obfcurity which nay attend this mode of analyfis. Every thing 1 have related as to fugar, may, IS I have already remarked, be applied to a Treat number of animal and vegetable fub- lances j from almofl; all of which, by com- Dining them with nitrous acid, or, more pro- perly, with the acidifying principle contained in hat acid, we obtain particular acids, many of vhich have, indeed, fome properties in common, put afford diftindt charadters in the refult of Jreir combinations. Here, therefore, we have I new road opened in chemiftry and that part )f this fcience which treats of falts, to which bme German chemifts have given the name of 'oalotechnic, inflead of employing five or fix icids, is now pofTeffed of more than double I 2 that ii6 NATURE AND COMPOSITION that number, reckoning only thofe of which^ I have already acquired a knowledge; and it; is not to be doubted, but the number will be^ in future, confiderably increafed. ( From all thefe refledtions, and from the ex-| periments contained both in this effay anc fome of the preceding ones, it refults, ill. That when the acidifying principle ii combined with any body without decompofing it (excepting, however, moll: metallic fubftances,] it converts fuch fubftance into a particular acid which, exclufive of the general properties whicl are common to all the acids, has others whicl are peculiar to itfelf. 2dly. That, with refpedl to metallic bodies it forms, with moll of them, compounds knowr by the name of metallic calces. It mull how* ever be added here, that, even in this clafs a fubllances, there are fome, as ari'enic, iron, anc perhaps feveral others, which, when combinec with the acidifying principle, to a certain degrel of fuperfaturation, not only alTume a faline cha* racier, but even acquire properties common t^ the acids, and, like them, become true folvents. 3dly. Tha*: OF THE ACIDS. 117 jdly. That the acidifying principle, like all the others, has its different degrees of affinity i and poffeffies, for inftance, a much ftronger [ affinity to fugar and moft animal and vegetable ! fubftances, than to nitrous air ; and that it is 1 in confequence of this preference that it quits the latter to form, with different fubftances, various kinds of acids. qthly. That the number of acids, which may be formed, is as yet wholly indeterminate, as we are unacquainted with the whole of the fub- ftances which are fufceptible of combining with the acidifying principle ; and we are ftill lefs informed of the means which may be ufed to effect this combination. 5thly. That the nature of the nitrous acid appearing to be better known, at prefent, than it was formerly; and two diftindt principles, viz. nitrous air, and pure air, or the acidifying prin- ciple, being proved, almoft to demonftration, to exift in that acid ; it affords to chemifts a valuable means of analyfis, and is capable of throwing confiderable light on that of vegetable fubftances. I3 f 6 thly. That 1 1 8 NATURE AND COMPOSITION, &c. 6thly. That it feems not altogether im- poflible, efpecially from the laft experiment re- lated in this eflay, that the phlogiftic matter is wholly formed in vegetables, and is not, as chemifts have hitherto imagined, the effed of fire. All thele conclufions will be illuftrated and more firmly ellablifhed by examples, which I defign to adduce in a fubfequent train of me- moirs on this fubjed. essay COMBINATION OF FIRE, &c. 119 On the combination of the MATTER of jrjRE WITH EVAPORABLE FLUIDS, AND ON THE FORMATION OF ELASTIC AERIFORM FLUIDS. I SHALL fuppofe in this effay, that every part of the planet we inhabit is fur- rounded with a very fubtile fluid, which penetrates, without any apparent exception, all the bodies which compofe this globe i that this fluid, which I Ihall call the igneous fluids the matter of fire, of heat and of light, has a tendency to place itfelf in equilibrium in all bodies, but is not capable of penetrating all, with equal facility ; and that it exifts, fometimes in a Rate of liberty, and fometimes in a fixed form and combined with other fubftances. 120 COMBINATION OF FIRE This opinion, of the exiftence of an igneous fluid, is fo far from being new_, that it was embraced by many philofophers among the ancients ^ and it will therefore be unnecelTary that I Ihould relate the fafts on which it is founded : efpecially as the future memoirs which I have to prefent on the fubjedl, will ferve as proofs of its reality. Indeed if I Ihew that this theory is univerfally agreeable to all the phenomena, and explains all the circumftanccs attending experiments in phyfics and chemif- try, it will almofl; amount to demonflration. Whenever we form certain combinations in water j when, for example, we unite a fluid acid, that is, an acid dilTolved in water, with a fixed alkali, alfo, in a fliate of folution, a neutral fait is formed, and, if the quantity of water be fufficient, the fait is kept diflblved. In every experiment of this kind, the water a6ts in two diftinft ways. One part is ab* forbed by the faline combination, and is called, by chemifts, the water of compofition ; ano-^ ther part takes the name of the water of fo, lution, and keeps the particles of the fait fo equally WITH ELASTIC FLUIDS. 121 equally feparated from each other, that every portion of the liquor is equally impregnated with them. The fame phenomena prevail relative to the igneous fluid. As all the bodies in nature are immerfed in this fluid, and have imbibed fome of it, there is fcarcely any combination whatever but contains a greater or fmaller quantity of the matter of fire. We fhould therefore diftinguifh, in bodies, between the fire of folution, and the fire of combination ; between fire in a ftate of freedom, and fire when combined j in the fame manner as was above obferved, with refpeft to water, in the folution of falts. After this explanation, it will not be difficult to give a prccife idea of what we underftand by heat. Its intenfity is meafured by the quantity of free and uncombined igneous fluid contained in bodies. Though we have no exadl fcale to determine the proportion of igneous matter, we are at leafl poflelTed of methods of ejiimating it. Thefe means are fupplied by the dilatation of bodies, which is effedled merely by introducing into them a greater quantity of the matter of fire. 122 COMBINATION OF FIRE fire. Thus, when a thermometer is heated, and made to rife, we only mix a greater quantity of that matter with the liquor in the tube j for it is not at all furprifing, that in mixing two fluids together, the mixt fhould occupy a greater Ipace than was held by one of the ingredients only. With regard to the impreflion which the igneous fluid makes on our organs — an im- prelTion pleafant and reviving when moderate, but painful and deflrudlive when it exceeds certain limits — it proceeds entirely from the tendency in that fluid to combination. We fhall prefently fee that befides the power of pene- trating into bodies, and feparating their par- ticles, it pofiTeffes the property of converting fluids into vapour, when combined with them in certain proportions 5 and this converfion into vapour neceflTarily implying a deftru6tion of organifation, muft confequently occafion a pain- ful fenfation. . Having thus fufliciently defined what I mean by the matter of fire, or rather by free fire, and by fire in a ftate of combination, it remains for WITH ELASTIC FLUIDS. 123 for me to add fome general reflexions upon what mufl neceflfarily happen in the different combinations. We know that every mixt, every compound, has its own proper portion of igneous fluid ; a kind of exaX point of faturation : for the law of faturation feems to be general in every phyfical and chemical combination. From whence it follows, that whenever mixts and compounds are brought together, fo that de- compofitions and new compofitions are the re- fult, one or other of the three following cafes takes place ; either the quantity of fire, which enters into the combination, will be the fame as before, or there will be a decreafe, or laftly, an increafe of it. It is evident, that in the firfl cafe neither a feparation or abforption of the matter of fire is effeXed j or, in other words, that there is neither any portion of free fire which paffes into a flate of combination, nor any fire that has efcaped from a combined, to a free, flate. But the fecond cafe will be different j for a fmaller quantity of the matter of fire enters into 124 COMBINATION OF FIRE into the new combination, than exifted in the former one j fo that a part of the igneous fluid, which was combined, previous to the decompofition, will become free fire after the recompofition, will recover its properties, and produce the effeds which we call heat, and be diffipated by dividing itfelf infenfibly among all the furrounding bodies, till an equilibrium be formed. In the third cafe, in which a greater quan- tity of the matter of fire enters the new, than exifted in the former, combination ; the igne- ous fluid of the furrounding bodies will be abforbed, and be changed from the ftate of free, to that of combined, fire. The confe- quence of which will be a diminution of free fire in thofe bodies, which will be perceptible by the degree of cold which takes place j which cold will continue till all the furrounding bodies have feverally fupplied the deficient portion of free fire, fo as to reftore an equi- librium. Thus we are furniflied with a very fenfiblc and plain criterion, by which we may deter- mine WITH ELASTIC FLUIDS. 125 mine whether an abforption or reparation of the matter of fire has taken place in any com- bination. In the firlt cafe, cold will be pro- duced in the furrounding bodies ; in the fecond, there will be an augmentation of heat. We know how impoflible it is, from the property of free fire to penetrate all fubftances, and from its tendency to preferve an equili- brium, to attain to any great accuracy in this kind of experiments. We can eafily meafure, in a jar, the air which is feparated during the forming of any combination; but as we hav.*4io velfels which can contain, without lofs, the matter of free fire ; as jars, and, in general, all veflels, are fo porous as to admit of a free accefs of it ; all we can do is to judge, whether, in a fiiort given time, there be any, or no efflux of the matter of fire; for, if it were poffible to eftimate its quantity, it could only be effected by means of a very complicated ap- proximation. I do not, however, defpair of making fome ufe, even of thefe methods. These principles, once eftablilhed, it will not be difficult to apply them to the formation of 126 COMBINATION OF FIRE of vapours, and of aeriform, or daftic fluids, in general. We have juft feen that whenever there is an abforption of the matter of fire in any com- bination, a certain degree of cold is produced in the neighbouring bodies. Therefore, reciprocally, whenever cold is produced, we may equally conclude, that a portion of free fire has paffed into a ftate of combination, or in other words, that the com- pound has abforbed a portion of the matter of fire or igneous fluid. If, therefore, I prove that whenever there is a formation of vapours, cold is produced, I fhall alfo have proved that there is an abforp- tion of the matter of fire in the formation of vapours, or, what amounts to the fame thing, that vapours are the refult of a combination of the matter of fire, with the fluid, in a highly rarefied ftate. I FIND my only embarralTment to proceed from the great choice of proofs of this pofition, and WITH ELASTIC FLUIDS. 127 and I might tranfcribe every thing that has been written on the fubjeft of cold, arifing from evaporation, by Meflrs. Richman de Mairan, Cullen, and Beaume. It will be unnecelTary to give a particular account of the experiments of thefe philofo- phers. They merit to be read and attentively :confidered in the original works. It will be fufficient to remark that they have Ihewn, I ft. that if a thermometer be immerfed into any evaporable fluid, and then fuddenly with- drawn, the thermometer will defcend, feveral degrees, during the time the ball of it is dry- ing, and that it afcends again infenfibly as foon as all the fluid is evaporated, till it has recovered the exad temperature of the air and of the furrounding bodies in general. 2dly. That ’ as the degree of cold produced is in proportion : to the evaporability of the fluid, fo the defcent of the thermometer is lefs rapid, and does not ! proceed fo far '^len the bulb is moiftened with water, as when fpirit of wine, volatile alkali, I or efpecially asther, is employed, ^dly. That if the evaporation be accelerated by any other i means than of heat, the increafe of cold will be pro- 128 COMBINATION OF FIRE proportionable 5 fo that not only all evapora- tion is attended with cold, but even the cold produced is governed by a certain law pro- portioned to the rapidity of the evaporation. 4thly. That by continuing to moiften the bulb of the thermometer, as fall as it becomes dry, with evaporable fluids, the cold is increafed more and more, becaufe the efficient caufe is hereby continued. If the temperature of all bodies depends, as we have endeavoured to prove, merely on the quantity of the matter of fire, or free igneous fluid which they contain, it will follow that when the bulb of a thermometer is moiftened with an evaporable fluid, the defcent of the mercury which enfues is occafioned by no other caufe, but becaufe the fluid at the time it is reduced into vapour, carries off from the mer- cury a part of the matter of free fire which kept it elevated to the degree at which it before flood. Fluids, therefore, when they evaporate, deprive the furrounding bodies of a part of their matter of fire ; and confequently vapours, and, in general, all aeriform bodies, are compofed of fome fluid, difTolved and combined with the matter of fire. All WITH ELASTIC FLUIDS. 129 All the phenomena relative to cold may be rendered more evident, by placing the evapo- rable fluids in fuch circumftances as may be favourable to, and accelerate the formation of vapours ; as, for inftance, in the vacuum of an air-pump. What I am going to relate on this fubjed, is extrafted from a very confiderable work, undertaken jointly by M. de la Place and myfelf, of which the academy has been already informed, and from a memoir which was read at the public meeting, laft Eafler. One experiment alone, which I lhall relate, goes to prove three points : ift. that the re- fiftance of the atmofphere is a refiftance to be overcome, a force in oppofition to the evapo- ration of fluids ; 2dly. that as foon as this com- preflTing power is removed, the evaporable fluids expand and are changed into elaftic aeriform fluids, or fpecies of air ; and jdly. that the tranfition of common fluids to a ftate of elaf- ticity, is accompanied by an abforption of the matter of fire, which is taken from all the fur- rounding bodies. Let a fmall bottle, or merely a glafs tube of three or four lines in diVmeter, be filled with K jether. IJO COMBINATION OF FIRE SEthcij 3nd covered with e wet bladder, which is to be faftened clolely by pafling feveral rounds of thread about it, and for greater fecurity a fecond covering may be faftened in the fame manner. The bottle, or tube, is to be fo filled with $ther, as to admit of no portion of air between the liquor and the bladder. Let it then be placed upon a good air-pump, the receiver of which muft be furniftied at top with a leathern covercle, penetrated by a fhank, to which an awl or fome other fliarp-poinred in- ftrument is to be firmly attached, for thepurpofe of pricking the bladder which covers the bottle at the inftant it appears proper. Every thing being thus difpofed, let the receiver be exhaufted, till the mercury in the barometer of the pump defeend to two or three lines of its fcale, and then let the bladder, which covers the bottle, be pundured. Immediately the asther will begin to boil, to evaporate with furprifing rapidity, and to be converted into an elaftic fluid, which, in the winter, will keep the barometer up to eight or ten inches, and, in very hot fummer weather, to twenty or twenty-five inches. If WITH ELASTIC FLUIDS. 131 If a fmall thermometer be introduced into the bottle containing the $ther, the fluid in it defcends confiderably during the evaporation, on account of the great quantity of free fire which paflTes, in this experiment, into a flate of combination, in order to reduce the asther into vapour. If the air be permitted to re-enter, the thermometer recovers its ordinary height, viz. about 28 inches. But it is very remarkable that the aether, thus mixed with atmofpheric air, is not thereby condenfed, but remains as a permanently elaftic fluid, and forms a particular kind of inflammable air, which I have not hitherto had an opportunity of examining. This experiment fucceeds with all evaporable fluids, with fpirit of wine, and even with water j but, with this difference, that the atmofphere of fpirit of wine, which is formed in the re- ceiver of the air-pump, can only elevate the mercury one inch in winter, and four or five in fummer, and the quantity of vapour is lefs than when aether is employed : confequently, the abforption of igneous fluid, and the degree K 2 of IJ2 COMBINATION OF FIRE of cold produced will be fmaller. But it is not from hence lefs certain that, in all thefe ex- periments, the cold which is obferved, with different fluids, is always nearly proptytioned to the quantity of fluid evaporated. The above phenomena are lefs flriking when, inflead of putting the fluid into a bottle clofely covered with a bladder, an open veffel is ufed ; but as this manner of conducing the experi- ment, gives rife to particular obfervations, which may afford great light to the fubjefl in queftion, it feems neceffary to give fomc account of it. Let us fuppofe fpirit of wine to be the fluid, the quantity of it, employed in the experiment, to be but fmall, and the temperature to be fifteen degrees. As foon as the barometer of the pump has defcended to nineteen lines of its fcale, the fpirit of wine will begin to boil, but the ebullition will not continue, as in the former experiment: it will ceafe, on the con- trary, for two reafons, as foon as we difcontinue the pumping: ift. becaufe the fpirit of wine, as it evaporates, is tranfmuted into an elaflic fluid ; WITH ELASTIC FLUIDS. 133 fluid; which, forming a kind of atmofphere that preflTcs on the furface of the fpirit, refifts the progrefs of the evaporation ; and 2dly. be- caufe at the inftant of ebullition a portion of free fire paflfes into the ftate of combined fire, ' in order to conftitute the elaftic fluid which is formed, and this circumftance neceffarily occafions a cooling of the whole quantity of fpirit of wine, the neceffary efFeft of which mufl: be to retard its ebullition : fo that fup- pofing, as we have, that the fluid has, at firft, begun to boil, the barometer being at nineteen lines, it fhould not boil, after it has been, cooled by the firfl: ebullition, till the barometer has defcended to eighteen lines. If, after the firfl: ebullition of the fpirit of wine, which has been produced under the receiver, the working of the pump be continued, the fpirit will not again boil fo rapidly as at firft, becaufe no greater quantity of fpirit will evapo- rate at each ftroke of the piflon, than will be neceffary to replace what has been carried off through the capacity of the piflon ; fo that this ebullition will always be ftronger in proportion as the body of the pump is larger. K 3 These 134 COMBINATION OF FIRE These phenomena refpefting the evaporation of volatile fluids in vacuo, are fimilar with the volatile alkali, aether, and feveral others : but one very important circumftance is worthy of obfervation, viz. that all thefe fluids evaporate, principally, from the bottom of the veflfel, or in other words, that it is from thence the bubbles are feparated. Thefe bubbles mount up, and burfl upon the furface, like thofe of water when boiling in a kettle. The caufe of this phenomenon appeared to me, at firfl:, to be an immediate confequence of the enfuing faffs, and I reafoned as follows : in proportion as any fluid evaporates, it is cooled, as has been already fhewn, and does not recover the tem- perature of the place in which the operation is performed, till the furrounding bodies have re- fupplied the quantity of free fire, of which the fluid has been deprived. It neceffarily follows therefore, that the fluid confined under the receiver of an air-pump muff be colder than the vefiel which contains it. But the hottefl: parts fhould be the firfl which evaporate, and thofe will be the hottefl which are in contafl with the fides and bottom of the veffel, as re- ceiving heat from it. In a word, it is at the furface WITH ELASTIC FLUIDS. 135 fiirface that the fluid is cooled, and, on the contrary, it is at its bottom, and by its contaft with the containing veflel, that it recovers the igneous fluid from the furrounding bodies : it is confequently from the bottom that the ebullition muft proceed. But however plaufible this ex- planation may appear, I confefs that fome ex- periments have rendered it doubtful, and it is not without great hefitation that I have now related it. But to refume, in few words, the whole theory of evaporation in vacuo ; it appears cer- tain that the tranlimutation of liquids into elaftic aeriform fluids is fubjcdl to two laws, the effedls of which are oppofite to each other. On the one part, the degree of heat, to which they are expofed, tends to evaporate them j on the other, the prefliire of the atmofphere refills their evaporation j infomuch that they are either in an elaftic or liquid ftate, according as one or other of thefe powers becomes prevalent. But this theory will be greatly elucidated by the experiments which I am now employed in making, in concert with M. de la Place, an account of which I hope foon to be able to lay before the academy. K 4 Before 136 COMBINATION OF FIRE Before I conclude this elTay, it may be proper to obviate one objedlion which the favourers of a different opinion will certainly deem unanfwerable. If, as has been declared, elaftic or aeriform vapours confift of the matter of fire combined with an evaporable fluid ; and if no air or aeriform fluid can be formed with- out a portion of free fire palfing to a ftate of combination ; it ought to follow that, in every formation of air, cold fhould be produced ; and it will not fail to be remarked that, when calcareous earth and alkalies are combined with acids, fo far from cold, a fenfible degree of heat is often obfervable during the Jeparatioriy or rather during the formation of the air. An examination of what happens, on this occafion, inftead of weakening, is the ftrongeft proof of the truth of, this theory. It muft be allowed, that in the combination of acids with alkalies or calcareous earths, we fometimes obferve heat. But this circumflance only proves that a greater portion of the matter of fire is difengaged in thefe combinations, than is neceffary to the formation of the fixed air, which then recovers its elaftticity. This aflertion WITH ELASTIC FLUIDS. 137 affertion wilj be proved, by fliewing that we can, at pleafure, increafe or diminifh the heat, in proportion to the increafe or diminu- tion of the quantity of fixed air contained in the alkaline bafis. The following experi- ments are, in my opinion, indilputable proofs of the faft. In five feparate bottles were placed as many mixtures, each confifting of four drachms of concrete volatile alkali diflblved in two ounces of diftilled water. This alkali was nearly faturated with fixed air. To the firft of thefe bottles was added one drachm, to the fecond, two, to the third, three, and, to the fourth, four drachms of quicklime ; the fifth was left without any adc ition. As foon as the lime was mixed with the alkaline folu- tion, it attraded, from its fuperior affinity, the fixed air of the volatile alkali, and was precipitated to the bottom of the vefiel, in the ftate of chalk or effervefcent calcareous earth. All thefe liquors being decanted, were placed in as many glafs bottles, and when they had recovered the fame degree of tempe- rature, they were faturated with nitrous acid, moderately IJS COMBINATION OF FIRE moderately diluted, and the change of tem- perature occalioned by the effervefcence, was obferved by means of one of M. de Luc’s mercurial thermometers. The following is an exaft relation of the refults. The volatile alkali, to which no addition had been made, and which had been deprived of no part of its air, fo far from producing any heat, during its faturation with the acid, on the contrary, lowered the thermometer two Complete degrees. The alkaline folution which had been de- prived of a portion of its fixed air, by the addition of one drachm of lime, afforded two degrees of heat ; that to which two drachms of lime had been added gave three degrees ; that with three drachms, four degrees ; and, laftly, by that with four drachms of lime, four degrees and half of heat were produced. This laft alkaline folution, though depri- ved of more of its fixed air than the others, ftill contained fufficient to form a brilk effervefcence with the nitrous acid, though not WITH ELASTIC FLUIDS. 139 not nearly fo much as the folution to which no lime had been added. These augmentations of cold or heat would have been more fenfible, if the alkaline folu- tions had contained a greater quantity of fait, but the concrete volatile alkali not being foluble, in cold water, in. greater pro- portion than that of one part of fait in four of water, it was not poffible for me to pro- cure a folution more ftrongly faturated. In order to complete my experiment therefore, I was obliged to have recourfe to volatile alkali obtained by diftillation with quick- lime ; and though this alkali was not fo far concentrated as it might have been, its com- bination with diluted fpirit of nitre produced 27 degrees of heat. For the thermometer, which before flood at 16, fuddenly rofe to 43 degrees, at the inftant of the combination. The phenomena are fimilar, if fixed alkali be employed. A folution of this fait, entirely divefted of fixed air, or in a ftate of caullicity, produces, with weak nitrous acid, a degree of heat, nearly equal to that of boiling water, whereas 140 COMBINATION OF FIRE whereas a folution .of the fame alkali, fatu- rated with fixed air, produces 6 degrees of cold. It is proved, then, that pure alkaline falts, whether fixed or volatile, generally produce heat when combining with nitrous acid j but that the heat diminifhes in proportion to the greater quantity of fixed air they contain i infomuch that when they are faturated with air, fome degrees of cold are produced. Fixed air, therefore, in paffing from a concrete ftate to that of vapour or elaftic fluid, carries olF with it a part of the matter of fire or igneous fluid, which is naturally difengaged whenever an alkali is united with an acid ; and we may conclude that this igneous fluid enters into the compofition of the fixed air, as into that of all vapours and elaftic fluids, of every kind. Of this aflfertion, give me leave to add a yet ftronger demonftration. A very weak Iblution of fixed alkaline fait, nearly faturated with fixed air, was put into a bottle of ftrong flint-glafs, into which a fmall thermometer was WITH ELASTIC FLUIDS. 141 W3.S introduced ; 3- cjuantity of fpirit of nitre was added, and the bottle immediately Hop- ped. The preffure, effeded by the want of communication with the atmofphere, foon abated the effervefcence, and confequentiy heat was produced, and the mercury in the thermometer mounted feveral degrees j where- as it would have defcended if the experiment had been made in the open air. Having un- ftopped the bottle, after fome minutes, and agitated the liquor, the effervefcence which had been before prevented, and, as it were, fuffocated, recommenced. In fome time, the heat, which had been acquired while the bottle was clofed, was diffipated, and the mercury of the thermometer fettled fomewhat below the degree of temperature of the external air. From all thefe fads, I conclude, as has been already declared, that all vapour, air, and in general, every elaftic aeriform fluid, is a combination of the matter of fire with a fluid, or even with any volatile folid body ; and that volatility is nothing elfe, but the property, which bodies poffefs, of being, in fome manner, diffolved, of combining with 142 COMBINATION OF FIRE, &c. with the igneous fluid, and, with it, form- ing aeriform fluids. Experiments, which I defign, in future, to publifli, on this fubjed, will feive to elucidate my theory in a more clear and perfed manner. the end. La*ely fuhUJhedy : Printed for J. Johnson, N®. 72, St. Paul’s Church -Yard, London, Price TWO shillings and six-pence, EXPERIMENTS AND OBSERVATIONS ON THE FOLLOWING SUBJECTS; I. Preparation, Calcination and Medicinal V-/ Ufes of Magnesia Alba. 2. On the Solvent Qualities of Calcined Magnesia. 3. On the Variety of the Solvent Powers of Quick-Lime, when ufed in different Quantities. 4. On various Abforbents, as promoting or retarding Putrefaction. 5. On the comparative antifeptic Powers of Vegetable Infusions, prepared with Lime, &c. 6. On the Sweetening Properties of Fixed Air. By Thomas Henry, Apothecary, F. R. S. Alfo, by the fame Author, 1. A Letter to Dr. Glass, containing a Reply to his Examination of Mr. Henry’s Strictures on the Magnesia fold under the Name of the late Mr. Glass. To which are added, fome further Tellimonies jf the Truth of thofe Stridures. 2. An Books printed for J. Johnson. 2. An Account of the Medicinal Virtues of Magnesia Alba, more particularly of Calcined Mag\esia,|1 with plain Direftions for the Ufe of them. Towhichl is prefixed, a concife Detail of the Invention andi gradual Improvement of thefe Medicines. | (4 3. An Account of a Method of PRESERVING V/ATERj] at Sea from Putrefaction, and of reftoring to theji Water its original Pleasantness and Purity, by] a cheap and eafy Procefs. To which is added, a Mode! of impregnating- Water, in large Quantities, with'- Fixed Air, for Medicinal Ufes, on board Ships and in Hofpitah ; and likewife a Procefs for the Preparation of Artificial Yeast, Price 2s. Likewife, Price six shillings in Boards, ESSAYS PHYSICAL and chemical, by M/i Lavoisier, Member of the Royal Academy of Sciences at Paris, Volume the Firft, tranflated from the French with Notes. and an Appendix. By Thomas Henry, F. R. S. &c. And alfo. Price two shillings and six-pence, MEMOIRS of Albert de Haller, M. DJ Member of the Sovereign Council of Berne ; Prelidentj of the Univerfity, and of the Royal Society o'* Gottingen ; Fellow of the Royal Society of London, &c Compiled, chiefly, from the Elogium fpokeri befdn the Royal Academy of Sciences at Paris, and froir the Tributes paid to his Memory by other foreigr Societies. By Thomas Henry, F. R. S. &c.