\ CORNELL UNIVERSITY LIBRARY THIS BOOK IS ONE OF A COLLECTION MADE BY BENNO LOEWY 1854-1919 AND BEQUEATHED TO CORNELL UNIVERSITY The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31 9241 01 1 57661 EXPERIMENTAL CHEMISTRY. EXPERIMENTAL CHEMISTRY^ FOUNDED ON THE WOKK OF DE. JULIUS ADOLPH STOCKHARDT. HANDBOOK FOR THE STUDY OF THE SCIENCE BY SIMPLE EXPERIMENTS. By C. W. HEATON, F.C.S., PKOFESSOK OF CHEMISTRY IN THE M^ICAL SCHOOL OF CHARING CEOSS HOSFITAL. LONDON: BELL AND DALDY, YORK STREET, COYBNT GARDEN. 1872. PEEEACE. " Stockhaedt's Principles of Chemistry," in its English dress, has for many years filled a definite and useful place among elementary text books. It has appealed to the numerous class of students, both men and boys, who in spite of limited means and opportunities are anxious to acquire some experimental knowledge of the science — who intend to work at chemistry instead of merely reading about it. To such students it is useless to describe experiments which can only be performed with the aid of costly and elaborate apparatus, or with the skill derived from long practice. The great merit of Dr. Stbckhardt's book is that, while the experiments are clearly described and very numerous, they do not require for their successful performance any but the simplest and cheapest forms of apparatus. It is astonish- ing what an amount of good work may be done in chemistry with Florence flasks, tumblers, medicine bottles, basins, saucepans, tin plate, iron wire, corks and other articles, which are always at hand. If to these are added some ^lass and caoutchouc tubing, a few funnels, test tubes and beakers, a mortar and pestle, spirit lamp (if gas cannot be used), a small set of scales and weights, and a measuring glass, the student will be able to perform the great majority of the elementary experiments of chemistry. Vl PREFACE. Of course other apparatus may be added with great advantage, and apparatus is so cheap in the present day that almost every student will find it possible to make such additions to his stock as he goes on. But it is better not to begin with too much, as the beginner is almost sure to order many things which he will not really require. When the publishers put Dr. Stockhardt's work in my hands, I hoped that it might be possible to bring it into accordance with modern chemical ideas, without entirely altering its plan. This soon proved to be impracticable, and I found myself compelled to re-cast, and to a great extent to re-write the book. In doing so I have tried to preserve as far as I could the spirit of the original ; but so much has been added, so much subtracted and so much altered, that I have not thought it right to retain the original title of the work. Nearly the whole of the original work which remains consists of experimental details and technical descriptions, which, though they have required much pruning and revision, are as useful now as when first written. A great many new experiments have been added in every part of the work. The systematic classification adopted in Parts II. and III. has not been attempted in Part IV. (Organic Chemistry), because the more old-fashioned arrangement seemed better adapted for the purposes of a simple experimental study. But I have endeavoured, in two introductory chapters, to give ihe student some idea of the modern system of classifi- cation, and have, in the subsequent pages, referred constantly to these chapters. In Part I., a somewhat lengthy chapter (Chapter III.) has been devoted to the laws of chemical force. This chapter is longer than it might otherwise have been, because I have thought it right to establish the laws of constitution and chemical action, and the primary meaning of symbols and formulae, hefore taking advantage of the great assistance of PREFACE. Vll the atomic hypothesis. I trust I have succeeded in proving to the careful student that the symbols and formulas of chemistry might be used with propriety and advantage, even if the atomic hypothesis were swept away. In Parts II. and III. I was much assisted by Mr. E. Francis, F.C.S., Demonstrator of Chemistry in the Medical School of this Hospital. It is a pleasure to me to take this opportunity of thanking him for his valuable help in this and in many other things. C. W. H. Chaking Cross Hospital, Christmas, 1871. CHEMICAL APPARATUS. The following List comprises most of the apparatus required for performing the experiments described in the present work, and may be purchased by the set of Messrs. Jackson and Townson, 89, Bishopsgate Street Within, who will also forward more extended lists of apparatus and pure tests, on application, by post. FIRST SET.-16S. Packed in a Case, VJs. 1 Holder for Ketorts, Tubes, or Flasks. 2 Hard Grlasa Betorts, 4-oz. and 12. 96 Fe. 56 Mn. 55 Cr. 52 m 59 Co. 59 u. 120 Mo. 96 W. 184 Pt. 197 5 Pd. lOfi Eh. 104 Eu. 104 Ir. 198 Os. 199- EXPEEIMENTAL CHEMISTEY. PAET I. GENERAL PKINOIPLES. CHAPTEE I. MATTEB AND POEOE. Putting on one side as unsolved, and probably for ever insoluble, the great metaphysical question whether the various objects and the complex phepomena we observe in nature have any real existence, or are merely images created in our own consciousness ; and the farther and scarcely less recondite question whether, even if we admit the external existence of such objects and phenomena, we may not account for them without assuming the existence of any material substance ; let us take the ordinary, and what may be balled the common-sense view of the universe around us. In doing so, however, we must not venture to assert it dogmatically, or to stigmatise as , absurd either of the other views above referred to, startling though they may appear. Both of them have been and are held by many profound thinkers ; neither can be proved to be erroneous, neither can be said to be in direct discord with known facts. The thought- ful student will find it good to revert to them from time to time as he advances in knowledge, and as he gains a clearer conception of their meaning he will find them less and less incredible. Taking then the current view, we hold that all substances known to us, whether in the state of solid, liquid, or . gas, B 2 BXPEEIMEKTAL 0HBMI8TBT, consist of matter which has an absolute existence. Matter is subject to the operation of certain agents called forces, which determine its position in space, and confer upon it its properties. The forces can only be known to us by their operations on matter, just as motion cannot be conceived of except as of something moved. On the other hand, it is no less true that, apart from force, we can form no conception of matter. Different Forms of Force. — The following are the chief kinds of force. 1. Motion. — However motion may have been produced, it is, as long as it remains, a, true force. A stone moving through the air is exerting active force, and the planets exert a similar force in their revolution round the sun. 2. Gravity. — If a stone is suspended by a string, every one knows that the string is pulled by it. The stone and the earth attract one another, and if the string be cut, the stone will fly to the earth and come to rest. This kind of attraction is called gravitation, and it is said to be due to the force of gravity. It is found to exist in all forms of matter. Solids, liquids, and gases all tend to fly to the earth, and therefore all exhibit the force of gravity, though in very various degrees. Near its surface the great bulk of the earth causes its attraction to be so very much greater than that of any other body that the term gravity is gene- rally applied only to the tendency of bodies to fly to the earth. In other words, gravity is generally taken as identical with weight. But it is right to remember that all bodies attract one another. One stone attracts another, one drop of water another drop ; but the masses of the stones and the drops are so small that the attraction is too slight to be noticed. That the force of gravity keeps the planets in their orbits, and regulates the movements of the heavenly bodies, is known to all. It is the most important doctrine of astronomy. When the force of gravity is not resisted by some other force equal in power to itself, motion is produced. The special case of gravity that we call weight is so im portant in the study of chemistry that it will be considered separately in the next chapter. S. Cohesion. — The force which binds together the minute particles of which matter consists is called cohesion, but it MATTBK AND FORCE. 3 is probably identical in nature with, gravity. It varies very much in different substances, and even in the same substance in different states. To divide ice into smaller portions re- quires greater force than to divide water, and no force at all is required to divide steam. In solid bodies cohesion is stronger than in liquids ; in gases scarcely a trace of it can be perceived. The hardness of a solid is the measure of the force of cohesion among its particles. When cohesion is exerted between dissimilar substances it is often called adhesion. The use of glue is a good example of adhesion. Experiments. — To prove that the force of cohesidn exists in liquids, allow one pan of a pair of scales to rest on the surface of water. A number of weights must now be intro- duced into the other pan, before the first one will be removed from the water. When at last it rises, some water will still adhere to its under surface. The adhesion between the scale- pan and the water is not overcome, but only the cohesion between one portion of the water and the rest. If only half the weights required in the above experiment be introduced, and a little ether be then poured on the surface of the water, the scale-pan will rise at once. The adhesion between the ether and the scale-pan is very slight. Cohesion may also be illustrated by cutting a bullet in haK, and pressing together with the hands the two clean and recently cut surfaces. If the cut has been well made, they will unite again with great force. Two pieces of plate-glass will do the same, and the glass-makers have to be very care- ful not to allow large sheets of plate-glass to lie on one another. 4. Heat is an extremely powerful and important form of force. Its influence in chemistry is very extensive, and, like gravity, it wUl be considered in some detail in the next chapter. 5. Light is a force closely allied to heat, and is also closely concerned in many of the changes of chemistry. Almost the whole of the light and heat of our globe comes to us directly or indirectly from the sun. 6. Electricity. — Eooperiment 1. — Take a stick of sealing-wax, rub it briskly with a piece of flannel and hold it near some scraps of paper. They will be attracted by it and will fly 4 EXPERIMENTAL CHEMISTBT. upward and adhere to its surface. A tube of glass rubbed with silk wiU produce the same effect, but the substance called ebonite is more powerful than either. An ebonite comb that has been passed through dry hair will not only attract scraps of paper and small feathers, but in dry weather will emit a crackling sound and a torrent of small sparks, quite visible in a dark room. In all these cases the strange and interesting force called Electricity is set in motion. The " electrical machine " is only a plate or cylinder of glass or ebonite, which, by turning a handle, can be made to rub against a silk cushion covered with amalgam. Electricity produced in this way is called frictional electricity. Another kind of electricity is known, which is called Voltaic, or Galvanic Electricity. The following experiment will illustrate the way in which it is produced. Experiment 2. — Take a tumbler two-thirds full of water, pour into it gradually an ounce and a half by measure of sulphuric acid (oil of vitriol), and fill the tumbler up with ■water. The mixture wiU, become very hot, and must be allowed to stand until cold. Very likely a white sediment will form, but this, which is owing to the presence of lead ia the acid, will soon subside, and will do no harin. Take a strip of sheet copper, and another of zinc, not too large to go to the bottom of the tumbler, and high enough to reach to the top. Brighten one of the small ends of each with sand- paper, and solder on each bright patch a piece of copper wire about a foot long. It will improve the experiment very much if you can amalgamate the zinc plate ; that is, coat it with mercury (quicksilver.) To do this the zinc must be cleaned by immersing it for a minute in the weak sulphuric acid, and then, while covered with the acid, pouring a little mercury on it and rubbing' it over the surface with a small rag. The surface of the metal will then become as bright as a looking-glass. The two metals are now to be immersed in the acid with the wires out. They should be about half an inch apart, and must not touch one another. They can be 'kept iu their places by wedges of cork or wood. If the zinc plate has been amalgamated no action will take place until the ends of the wires are made to touch one another, when the zinc will MATTER AND FORCE. 5 immediately begin to dissolve in the acid and electricity to pass along the wires. Such an arrangement constitutes a simple and not very powerful form of voltaic or galvanic battery. It is called a " simple cell," and the ends of the wires farthest from the plates are called the " poles." If ten such cells are made, and are joined together by thick copper wires, the zinc of one cell to the copper of the next, long wires proceeding from the last zinc at one end and the last copper at the other, a tolerably powerful battery will be obtained, capable of decomposing water and doing other chemical work, but the arrangement is never a very powerful one, and it is better to buy or make one of the more powerful forms of the instrument. If the two wires from the simple cell are brought to within half an inch of one another, and are then joined with a piece of very fine platinum wire, the platinum will immediately, become red-hot. With a more powerful battery a much greater length of wire may be heated to whiteness, and even melted by the electricity. Fine iron wire may be burned in the same way, but not quite so easily. Magnetism is only a peculiar operation of electricity. 7. Chemical Force, or Chemical Affinity. — The last force that we have to consider is called chemical force, because the science of chemistry is almost entirely occupied with its nature and effects. Its operations are spoken of as chemical action. Every one knows that iron, heated to redness, changes into scales or cinders, and that exposed to moist air or earth, it is converted into rust ; that the expressed juice of the grape gradually turns to wine, and this again to vinegar ; that wood in a stove, or oil in a lamp, disappears in burning ; and that animal and vegetable substances in time putrefy, dis- integrate, dnd finally disappear. Iron cinders and rust are iron altered in constitution; iron is hard, tenacious, of a greyish-white colour and brilliant ; by heating to redness it becomes blaok, dull and brittle ; on exposure to moisture it is converted into a powder of a yellowish-brown colour. Wine is altered must, in which nothing of the sweet taste peculiar to the grape-juice can be perceived ; but it has acquired a spirituous flavour, together with a heating and intoxicating power, which was not in the 6 EXPEKIMENTAL CHEMI8TBT. must. Vinegar is altered wine ; it has an acid smell and taste, and has lost its spirituous flavour, as well as its exhilarating ■ properties, its tendency being rather cooling and sedative. Search must be made in the air for the oil and wood which have disappeared during combustion ; both these substances are converted into vapour or gas, and heat and light are thereupon evolved with the phenomenon of fire. Of a similar nature are the changes which animal and vegetable substances undergo if kept for a sufficient length of time; they are gradually converted, as they putrefy or decay, into various kinds of gas, some of which emit a very disagreeable odour. Such processes, by which the weight, form, solidity, colour, taste, sinell, and action of the substances become changed, so that new bodies with quite different properties are formed from the old, are called chemical processes, or chemical action. Wherever we look upon our earth, chemical action is seen taking place, on the land, in the air, or in the depths of the sea. The hard basalt, the glass-like lava, become gradually soft, their dark colour passes into lighter, they crumble to smaller and smaller pieces, and are finally changed to earth. A potato placed in the earth grows soft, loses its mealy taste, becomes sweet and finally decays. The bud, that sends forth a sickly pale shoot in a dark cellar, when exposed io the light and air grows up a vigorous, firm, and green plant, which, imbibing its nourishment from the moist air and soil, forms from their elements new bodies, not to be found previously in the water or the air. A delicate network of cells and tubes pervades the whole plant, imparting to it firmness ; these we call vegetable tissue, or woody fibre. We find in the sap, which passes up and down through these cells, albumin and other viscous substances ; in the leaves and in the stalks, a green colouring matter — chlorophyll ; and in the ripe tubers, a mealy substance — starch. None of these substances are injurious to health ; but if the potatoes grow in the dark and without soil, for instance, in the cellar, there is produced in their long pale shoots a very poisonous body — solanine. The potato forms one of our most important articles of food. The starch contained in it is not soluble in water but when received into the stomach, quickly undergoes such a MATTER AND FORCE. T change ttat it can be dissolved or digested, and then intro- duced as a liquid into the blood. The blood comes in con- tact in the lungs with the inhaled air ; the blood changes its colour, the air changes its constitution, and the heat which we feel in our bodies is developed. We must conclude, from these changes, that chemical action is going on in our own bodies. If a piece of iron be heated to redness, till a thick crust of scales is formed around it, and then weighed, it will be found to have increased in weight ; consequently, it must have been supplied with something ponderable from the air. This ponderable substance is a species of gas, called oxygen ; by its union with the iron it has become fixed, yet by other chemical processes it can be reconverted into its gaseous form. If this crust of iron is now exposed for a time to moist air, it will gradually become rust, and again weigh more than before ; it has attracted and united to itself water, and more oxygen from the air. Accordingly, the crust consists of iron and oxygen; the rust, of iron, oxygen, and water, which have become most closely united with each other ; — they are chemically combined. The force which produces such changes as these is called Chemical Force. In the older works on chemistry it is described as " chemical affinity," because it is assumed that the tendency of substances to combine with one another is due to a kind of liking that they have for each other. Iron is so very fond of oxygen that it cannot help combining with it whenever it gets the chance. But it is unsafe in scientific matters to use names which assert more than we really know. Now we know that iron combines with oxygen, but we do not know that there is any " affinity" between the two. We know that force is exerted, but we do not know why. The conditions under which the force is exerted will be discussed in a future chapter. Melation of the Forces to one another. — The forces we have been considering, unlike as they are in their manifestations, are very closely connected together. Almost any one of them may, under suitable circumstances, be made to produce another, and it has during the last thirty years been shown that the one is directly evolved from the other. It has long been perceived to be impossible, under the present 8 EXPERIMENTAL OHEMISTET. arrangement df the universe, for matter to be created or destroyed. It may change its form and pass ever so many times from one state of combination to another; but the total quantity remains alwayB,'as far as our means of ob- servation enable us to judge, the same. The grandest generalization of modern science, a generalization which we may be proud to remember was born within our own day, is that which has taught us that force is equally indestructible ; that it also, like matter, may undergo various and countless changes ; may appear, now as heat, now as electricity, now as chemical action, and now as visible motion, and yet its sum will always remain fixed and unalterable. There is no new creation of force within the limits of our knowledge. It may lie hid for a time— for any time — but force is force for ever, and whenever we meet with any of its operations in nature we may confidently look for its cause in the disappearance of some previously active form of energy. The birth of one form of force is always the death of some other, and the two are equivalent to one another in quantity. This grand doctrine, which is known as the doctrine of the conservation of force, requires complex apparatus, and great knowledge for its verification. The demonstration of it is indeed still incomplete, though it has gone far enough to satisfy every rational mind ; but a few simple experiments will serve to illustrate the manner in which one force may give rise to others. In other words, we may prove the correlation of various forces, though the conservation of force must be taken on trust. Experiment 1. — Eub a piece of copper wire briskly with sand-paper for a minute or two. It will become so hot that the hand cannot bear to touch it, and it will readily ignite phosphorus or the tip of a lucifer-match. Similar illustrations will occur to all. When the axle of a railway carriage gets dry, so much heat is produced that the carriage is sometimes set qn fire. A clever blacksmith can hammer a nail till it is red-hot, and so emits light as well as heat. During the boring of cannon the shavings are too hot to be touched, and, lastly, some savages are able to procure a light by rubbing two dry sticks together. In all these cases there is a direct conversion of motion into heat, and even, in some cases, into light, rriction is MATTEB AND FOBOE. » but arrested motion — motion hindered or reduced by an opposing force. If the sand-paper had not pressed on the wire, the same amount of force employed by the arms would have given rise to a much greater motion than that actually produced. The difference, though lost as motion, takes tte new form of heat. When a pound weight falls to the earth from a height of 772 feet, its motion is lost, but the weight and the earth receive heat enough to raise the temperature of one pound of water one degree Fahrenheit. We have already seen that friction may, under certain cir- cumstances, produce electricity, so that we have gained illus- trations of the conversion of motion into heat, light, and electricity. Let us now start from heat. The steam-engine affords the best possible illustration of the conversion of heat into motion. The work done by the engine is in direct proportion to the heat expended, and so ultimately to the coals burnt. When heat becomes sufficiently intense, it is always accompanied by ligM, and Tyndall has devised a direct experiment in which invisible heat becomes visible light. In fact, heat and light appear only to differ from one another as a low and high tone in music do. The conversion of heat into electricity requires for its demonstration a thermo- pile, a somewhat expensive piece of apparatus. It is doubtful whether heat is ever directly converted into chemical force, though the converse is one of the commonest of phenomena ; but the liberation of the force of cohesion during the dis- appearance of heat can be readily demonstrated, as the follow- ing experiment will show. Experiment 2. — Take a tumbler full of powdered crystals of sodium sulphate (Glauber's salt), and drench it with common hydrochloric acid (muriatic acid — spirit of salt). The salt will rapidly dissolve and become liquid, and the force of cohesion previously hidden or stored-up in the salt will become free and active. But at the same time heat will be taken so rapidly from the materials in the tumbler that the outside will become covered with hoar frost, and if a little water in a test tube be plunged into the mixture it will freeze in a minute or two. Most of the so-called freezing mixtures depend upon this principle. Experiment 3. — Now try the reverse of this experiment. Take a clean Florence oil flask, nearly fill it with hot water, 10 BXPEEIMBNTAL CHEMISTEY. dissolve as much sodium sulphate in it as the water will dissolve (filtering the solution if it appears dirty) and then, while the solution is nearly boiling, cork the flask tightly and allow it to get quite cold. There is now a great deal more of the solid in the solution than cold water could dissolve, but for some curious reason the excess does not immediately separate out. But take out the cork, and in a minute beautiful feathery crystals appear at the upper surface and pass downwards until the whole mass is solid. If the crystallization does not begin at once, drop in a small crystal of the sulphate, which will immediately produce the desired effect. As soon as the liquid has changed to solid, feel the outside of the flask with your hand. It is sensibly warm, showing that during the exertion and disappearance of the cohesive force heat has been given out. The conversion of electricity into other forms of force has already been illustrated to some extent in the battery. When the platinum becomes red-hot, it emits Tieat and light. When the poles of a powerful battery are connected with pieces of coke shaped like lead pencils, and the coke points after touching one another are separated by a short distance, a most intense light, called the "electric light," passes be- tween them. The rays given out by it are similar to those of the sun, and, like the sun's rays, they consist of three kinds : 1. Heat rays. 2. Light rays. -3. Actinic or chemical rays. The chemical rays are invisible, and are only to be recog- nised by their effect in producing chemical changes. The interesting art of photography entirely depends on the power of the rays to produce alterations of composition in certain chemical substances, and particularly the compoxmds of silver. The following experiment will illustrate this curious property. Experiment i. — In a room from which daylight is entirely excluded, but which may be lighted by a candle, dissolve sixty grains of silver nitrate (limar caustic) in an ounce of cold distilled water. Pin a sheet of smooth white paper on to a flat board, and, by means of a flat camel's hair brush, paint it all over uniformly with the colourless silver solution. MATTER AND FORCE. 11 Allow it to dry ; repeat the painting, and again allow it to dry. Paper so prepared is called "sensitive" paper. To show its properties, place upon it a piece of lace, a few fine feathers, or a sprig of fern, cover it with a sheet of window glass, and press the glass down vrith weights at the corners. The board may now be brought out of the dark room and exposed to sunlight, or to the strong diffused light of a bright day. The paper will soon begin to change colour, and after a time it will assume a rich brown tint. The whole arrangeinent must then be taken back to the dark room, -the glass, ferns, &c., removed, and the paper immersed in clean rain water and well soaked, the water being changed a good many times. A beautiful image, in white on a dark ground, of the object employed will remain on the paper, which may now be dried and exposed freely to light, for the water will have washed away all the silver salt that has not been affected, and the picture will be permanent. It has already been mentioned that the action of the sun's rays can also be produced by the rays from the electric light,, and we have therefore an instance, to which many others might be added, of the production of chemical force from electrieity. Even with the single cell described in Experi- ment 2, page 4, some striking illustrations may be obtained, as will be seen from the experiments which follow. Experiment 5. — Attach a small strip of platinum foil to the end of each wire. Cut a card so that it will stand upright in a wine-glass, and divide it in two. Then fill the glass with the card in it with a solution of the salt called potassium iodide, and bring one of the platinum poles into each of the two divisions which the card makes. The pole which is connected with the copper plate immediately pro- duces a brown colour on that side of the card. The elec- tricity breaks up, or decomposes the salt into two substances : potassium, which owing to its action on water is not seen, and iodine, the substance which gives the brovm colour in this experiment. Pour into the brown liquid on one side of the card a little of the smooth pasty liquid obtained by adding a good deal of boiling water to starch, stirring and cooling. The starch will combine with the iodine and form a- beautiful blue colour. Experiment 6.— Dissolve in some cold water as much of 12 EXPERIMENTAL OHEMISTEY. the salt called copper sulphate (blue vitriol) as the water will take up, and substitute this solution for the potassium iodide used in the last experiment. The card is unnecessary. The salt will be decomposed, and copper will be deposited on the platinum pole which proceeds from the zinc plate. If the poles are reversed the copper will soon dissolve off the one platinum plate and appear on the other. This experi- ment is a simple example of the important manufacturing process called electroplating. Other metals, such for in- stance as gold and silver, may by analogous means be deposited from their solutions. Experiment 7. — Decomposition of Water hy Electricity. — With the assistance of a more powerful battery, and the little piece Fig. 1. of apparatus shown in Fig. 1, water may be decomposed into the two gases of which it consists. Thick platinum wires pass through the sides of a glass and terminate inside in flat plates (stout platinum wires hammered flat at the ends do very well). The holes in the glass can easily be made by a bradawl filed to a square point and constantly moistened with a mixture of turpentine and camphor, and the wires may be cemented in the holes with sealing-wax. The glass is filled with water to which a drop or two of sulphuric acid has been addedj and over each of the plates a test tube filled with the same acidulated water is inverted. The two ends of the wires are now connected with the poles of the battery. In an instant bubbles of gas rise from the two plates into the test tubes. The gas which comes from the pole connected with the zinc is called hydrogen, that from the other oxygen ; and it will be observed that the volume of the former is twice as great as of the latter. When a little gas has been collected, the mouths of the tubes may be closed with the thumb, the tubes removed, and the gas examined mth a taper in the manner described under their respective names. This is the most importaAt instance of the production of chemical force at the expense of electricity that we possess. The electricity disappears during the experiment, but the hydrogen and oxygen which are produced are able, as we shall find hereafter, to exert an enormous force when they once more combine together. MATTER AND FORCE. 13 Lastly, let us study the forces which are called into existence during the exertion and consequent disappearance oi chemical force. We have, in point of fact, just been con- sidering one of the most interesting cases of this kind in the ■voltaic battery. In the battery, the electricity which is called into being proceeds directly from, and is proportionate in amount to, the chemical force which is destroyed in the cell. The zinc is constantly being dissolved by the sulphuric acid, and the force which is thereby exerted immediately takes the new form of electricity. From this electricity we can, as we have seen, produce heat, light, and finally, chemical force, so that we can ultimately recover the very same form of force that we lost in the battery. One of Faraday's greatest discoveries proved that there is no loss of forcft throughout these changes, but that, provided we can prevent the force from assuming other forms, the chemical energy produced by the decom- position of the water is exactly equal to the energy lost in the battery. One or two simple experiments will illustrate the direct production of other forces from the chemical, but it is un- necessary to multiply them, because the whole study of chemistry is full of such illustrations. Eayperiment 8. — Take a piece of phosphorus, about the size of a small pea, and about an equal quantity of iodine. Place them side by side on a slate or a piece of tin-plate, and push the phosphorus with a knife till it touches the iodine. Chemical sBction is instantly exerted, and the mass bursts into flame, producing thereby light and heat. Experiment 9. — Warm two tumblers : put into one a few- drops' of strong ammonia (spirits of hartshorn), and into the other a. few drops of hydrochloric acid (spirits of salt). Each will give out a gas, and when the mouths of the tumblers are held together these gases will combine, and a dense white smoke will be produced, which will before long settle down on the inside of the glasses in the form of a white solid powder (sal-ammoniac). The chemical action is in this case accompanied by the exertion of the force of cohesion. The lost force takes the form of heat, which, how ever, can only be perceived by the thermometer. When gunpowder or any other explosive substance is burnt, it is converted into gas; very energetic chemical 14 EXPERIMENTAL CHEMISTRY. action takes place, and a great deal of force is consumed. But the force is entirely reproduced, for the cohesion of the solid is destroyed, a great expansion, which is nothing but a motion of the particles, takes place, and heat and light are evolved. Every one knows what powerful work the expan- sion may be made to do. Heavy shot can be thrown from a gun to an enormous distance, and solid rocks torn in frag- ments by the burning even of a small weight of the powder. The result of the researches of the last quarter of a century has been to convince most scientific men that, various as are its manifestations, there is in nature but one force, namely, Motion : motion of masses, motion of particles, motion in lineSj motions of rotation and vibration, and motion in other modes. As regards heat and light this strange doctrine may be said to be already demonstrated", for these remarkable forces have been proved to be merely peculiar modes of motion in the particles of matter. And the close connection of heat with the other forms of force forbids us to doubt that its nature is essentially similar to theirs, and that they also are modes of motion. Science has still a great work before her in the investigation of force, but enough has already been accomplished to enable us to take a far wider view of the kingdom of nature than was possible to our fathers, and to reveal to us something of the unity and simplicity that underlies the marvellous complexity of the universe. objects of chemical inquiry. It has already been mentioned that the science of chemistry is concerned with the operations of chemical force. There axefowr chief points to which the attention of the chemist is mainly directed in his study of the solid, liquid, and gaseous substances which are met with in nature. 1. Their composition. — Take a piece, of bone. How is it affected when strongly heated in a furnace ? It becomes whiter, lighter, and less solid than before (bone-ashes). But how is it affected when heated in a covered vessel? It becomes lighter, and black (bone-black). If exposed to boiling water, or to steam, how is it affected ? It becomes lighter, and remains white ; but in the water is dissolved gelatine. How in hydrochloric acid? It becomes trans- OBJECTS OP OHBMICAIi INQTJIET. 15 parent ; tlie bone-earth is dissolved, and a gristly mass remains, which, when boiled with water, turns to gelatine. What is the action of fire upon the gelatine ? In a covered vessel it is converted into charcoal, in an open one it burns and disappears. These few experiments show that the bone contains gelatine which is combustible, and an earth which is not so ; they show at the same time that it is the carbonized gelatine which, in the second experiment, colours the bone- earth black, and makes it bone-blagk ; that this gelatine dis- solves in water, but not in hydrochloric acid, &c. Gelatine and bone-earth are called the proximate constituents of bone, but by continued chemical processes these can be resolved still further, that is, separated into simpler constituent^ In bone-earth are found phosphorus, a metal (calcium), and oxygen ; in the gelatine, besides carbon, three other bodies- oxygen, hydrogen, and nitrogen. These bodies can be de- composed no further by any known method of analysis, and are therefore called simple bodies, or elements. There are now about sixty known elements, and almost every year adds to their number ; but this increase is of little importance to chemical science or. its applications, for it consists of ele- ments which but very seldom occur. This separating of compound bodies into simple ones is designated by the name of decomposition, and the process of ascertaining the com- position of any substance is called analysis. "^hen a substance contains two or more elements, held together by chemical force, it is called a compound. Com- pounds are always quite different in properties from their constituents. When a substance contains two or more other substances (elements or compounds), not held together by chemical force, but present as it were accidentally together, it is called a mixture. In a mixture the properties of the separate in- gredients are still perceptible. This distinction between element, compound, and mixture is very important. The following illustrations will assist to fix it in the memory. Water is a compound of the elements hydrogen and oxygen, which are held together by chemical force. Air is a mixture of the elements oxygen and nitrogen, which are not in chemical combination with one another. Gunpowder is a mixture, containing the elements carbon and 16 EXPEBIMENTAL CHEMISTRY. sulphur and the compound saltpetre. The compound salt- petre contains the dements potassium, nitrogen, and oxygen. 2. The changes which they undergo by the acti.on of other bodies and of the various forces upon them. — Phosphorus, which is obtained from bones, is luminous in the air, and is gradually- converted into an acid liquid ; it unites with the oxygen of the air and with water, as the iron did when exposed to moist air. If the phosphorus is gently heated, this union is attended with a vivid combustion, and there is formed a body which is different from the former ; to which, if water and lime be added, a new body is formed, very similar to bone- ashes ; it is, in fact, artificial bone-ashes. The number of new bodies which may be produced by the union of the ele- ments with each other, or with compound bodies, is infinite ; and entirely different substances are often formed, according as the combination takes place under the influence of Cold or heat, in water or in air, in greater or smaller quantities. This is combination or syntliesis. 3. The causes of chemical changes and the laws according to which they take place.— li chemical experiments are performed as they should be, with the balance in the hand, it will soon be observed, that when two different bodies which can unite with each other are brought together, sometimes a part of the one, sometimes a part of the other, remains free. Further experiments will show how much of one body, in weight, can be united with the other. If all bodies are tested in the same manner, the certainty is finally attained, that all chemical combinations take place only in fixed, unchangeable "proportions, and that to every individual body is assigned a definite weight, with which it always enters into any com- bination whatever. (Chap. III.) This certainty is called a natural law. Many such laws of nature have already been ascertained, and they serve as a certain guide to the chemist in his labours, since they cannot, like human laws, be arbi- trarily evaded or changed. By them alone we attain to a scientific insight into chemical processes, and to the capability of putting direct questions to bodies by experiment, and of testing the truth of the answers received. An explanation of chemical processes based on natural laws, which presents a clear idea of the subject to the mind, is called a Theory, i. The extent to which the facts which have been discovered OBJECTS OP CHEMICAL INQUIEY. 17 may he made useful to man. — When the chemist discovers a new body, or a new property in one abeady known, or a new method of synthesis or analysis, he imparts his discovery to the apothecary, the physician, the farmer, the manufacturer, and the tradesman, that experiments may be instituted for the purpose of ascertaining whether any advantage, facility, or improvement can be derived for pharmacy, medicine, agriculture, or the arts. Phosphorus ignites spontaneously at a gentle heat ; it is used in lucifer matches. Taken into the stomach, it acts' as a violent poison ; it is at present the most common means for , the destruction of rats and mice. The constituents of bone-earth and those of gelatine have been foimd to be universally present in the seeds of different kinds of corn ; the chemist concludes from this that pul- verised bones should yield an excellent manure for corn ; the agriculturist demonstrates this by experiments on a large 5cale. In bone-black the property has been discovered of attracting many substances held in solution in liquids, and of condensing them in itself ; on account of this property it is used for making impure water potable; the sugar-refiner employs it to make brown syrup colourless ; with it the distiller purifies spirit from fusel oil. This is applied or practical chemistry. Nothing is better calculated to excite an interest in chemical knowledge than a consideration of the useful appli- cation which can be made of it in every-day life. Chemistry teaches the apothecary how to compound and prepare his medicines ; it teaches the physician how to cure maladies by means of these medicines ; it not only shows the miner the metals concealed in rocks, but aids him also in smelting and working them. Chemistry, in connection with physics, has been the principal lever by which so many arts and trades have been brought to such a degree of perfection within the last few decades, and by its means we have been supplied with numberless conveniences of life that were not enjoyed by our fathers. It cannot be doubted that the farmer must at once regard chemistry as his indispensable friend, for it is this alone which acquaints him with the constituent parts of his soil, with the proper nutriment of the plants he wishes to cultivate, and with the means whereby he can enhance the fruitfulness of his fields. 18 EXPBEIMBNTAL CHEMISTRY. The ancient so-called Elements. — The dogma of the ancient philosophers, that there are four elements, earth, air, water, and fire, has long been known to be erroneous, although the words are still repeated very often. We now know that three of them are either mixtures or compounds of the true elements, and that fire is but a peculiar operation of heat and light. ( 19 ) CHAPTEE II. GRAVITY, HEAT, PEESSURE. GRAVITY. The force of gravity is ctiefly interesting to cbemists because it confers upon all kinds of matter the property called weight. WEIGHING AND MEASURING. Weighing. — The balance is to the chemist what the compass is to the mariner. The ocean was indeed navigated before the discovery of the compass,' but not till after this could the sailor steer with confidenca to a certain place, and recover his proper course, however often lost. And so, in chemistry, no systematic method of study could be pursued before the intro- duction of the balance. The balance is the plumb-line, as well as the touchstone in chemical experiments ; it teaches us how to ascertain the true composition of bodies, and shows us whether the questions put, the answers received, or the conclusions drawn from them, are correct or false. Henoe it cannot be too strongly recommended to those commencing the study of chemistry to use the balance even in simple, experiments. For the experiments described in this book, a common apothecaries' balance is all that is requisite. Such a balance, consists of a brass or steel lever (beam), with arms of equal length, through the centre of which passes a steel wedge-shaped axis, resting on a hardened plate, so that the beam, to the extremities of which the pans are attached, may easily vibrate. It is essential that the axis should be in the right place in the beam, a little above its centi-e of gravity, as in Fig. 2, a. The centre of gravity can be found by balancing the beam on its flat side, with the 20 EXPERIMENTAL OHEMISTET. index attached to it, upon a knitting-needle, and when the beam rests horizontally, the point of the needle designates the j,j^ 2 centre of gravity. If the "■ ■ axis he placed too low 6e«ea In most cases the Latin name is the same as the English, but in a few instances it is different and the symbol must be STMB0L8 AOT) POEMULffl!. 67 remembered carefully. The following are the exceptions : Antimony is Sb., from stibium ; copper, Cu., from ciiprum ; gold, Au., from aurum ; iron, Te., from ferrum ; lead Pb., from plumbum; mercury, Hg., from hydrargyrum ; potassium, K., from kalium ; silver Ag., from argentum ; sodiimi Na., from natrium ; tin, Sn., from stannum ; and tungsten, W., from wolfram. Compounds are described by formvlcB, which consist of the symbols of the elements composing them. Thus the formula for hydrochloric acid is HCl., for mercuric oxide, HgO., and so on. Symbols then are employed to denote the elements, but they are also employed, by a very useful extension, to denote definite weights of them. What these weights are we have now to consider, confining ourselves for the present exclusively to elements in the state of gas. To begin with, let us represent the standard 2 volumes of hydrogen by the symbol H, and 2 volumes of chlorine by the symbol CL How are we in this case to represent hydro- chloric acid, which, as we have already seen, contains in 2 volumes, 1 of hydrogen and 1 of chlorine ? 2 volumes of this compound must evidently 'be represented by such a formula as this : HJ CIJ. This is inconvenient, and yet such cases will be of incessant occurrence, unless we alter our representation of the elements. Accordingly we describe the 2 volumes of hydrogen as Hg and the 2 volurqes of chlorine as Clj, and the formula for hydrochloric acid, which contains J of each, then becomes HCl. To take another instance. The symbol N might be applied to 2 volumes of nitrogen, if we did not know that 2 volumes of ammonia contain only 1 volume of nitrogen united to 3 volumes of hydrogen. If we use the symbol. N for 2 volumes of nitrogen and H for 2 volumes of hydrogen, ammonia must be described by the inconvenient formula NJ HIJ. But calling nitrogen N2, and hydrogen Hj, both of these are doubled, and the formula for ammonia becomes NH3. Again, with phosphorus : we might apply the symbol P to 2 volumes of phosphorus vapour if it were not for such com- pounds as phosphine gas, 2 volmnes of which contain only one quarter as much phosphorus as is present in 2 volumes of phosphorus vapour. But by describing phosphorus as P4 and phosphine as PH3, we get over the difficulty ; for the 68 EXPEEIMENTAL OHBMISTEY. formula show plainly, and in whole numbers, that one con- tains four times as much phosphorus in 2 volumes as the other. We thus gain more definite ideas of the signification -which may be applied to the symbols and formulae of gases. For the sake of distinctness they may as well be put in the form of definitions. : — 1. The symbol of an elementary gas is a letter or letters, used to denote the smallest fraction of the weight of the normal two volumes of it that is ever fomid in two volumes of any compownd gas. 2. The formula, whether of an elementary or compound gas, must always exhibit the composition of two volumes of it. It consists of symbols. Thus, the symbol for hydrogen is H ; the formula, Hj ; the symbol for phosphorus is P ; the formula, P,. Compounds must always be described by formula, the term " symbol " being reserved for elements. Relative Wdght of Gases. — It has already been shown (page 23) that the specific gravity of a body means its weight as compared with the weight of an equal volume of some other body which is taken as a standard. The standard for gases is hydrogen, one volume of which is said to weigh 1. We have therefore only to double the specific gravities of the gases (which have been carefully determined by experi- ment) to find the relative weights of the standard 2 volumes of each gas. If 2 volumes of hydrogen weigh 2 (2 grains, 2 pounds, or 2 hundredweight), 2 volumes of chlorine will weigh 71, 2 volumes of oxygen, 32, and so on with the rest. We must now study the relative weights of the different elements which go to make up the weight of 2 volumes of each of the more important gases, elementary and compound. It will be best to take the elementary gases first. Constitution of Elementary Gases. — It has already been seen that the formula for 2 volumes of any elementary gas is determined by the compounds which contain that gas. The fbrmula for hydrogen is Hj, because compounds are known which contain in 2 volumes only half as much hydrogen, as is contained in 2 volumes of the pure element. Now what is true of a large volume must also be true of any volume, however minute, and we are therefore led to the con- clusion that even the smallest conceivable volume of hydrogen ELEMENTARY GASES — ATOMS. 69 gas that exists in a separate state must be capable ot division into two parts, and as the weight of 2 volumes of hydrogen has already been defined to be 2 (hydrogen being the standard), each of these constituent parts must have a weight of 1. Atoms.* — The name atom is, for reasons that wiU be ex- plained hereafter, applied to the quantity of each elementary gas that is denoted by its symbol. 2 volumes of hydrogen denoted by the formula Hj, weigh 2, and consist of 2 atoms, each denoted by the symbol H, and each weighing 1. In like manner, 2 volumes of phosphorus vapour are said to consist of 4 atoms ; the formula for 2 volumes being P4 and the symbol for each atom P. The atom in this case weighs 31. ia the case of mercury and a few other elements the 2 volumes of gas are said to contain but 1 atom (weighing, in the case of mercury, 200), because no gas is known which contains in 2 volumes less than 200 of mercury. We can now add the definition of an atom to those given above : 3. The atom of an elementary gas is the quantity denoted hy its symbol; that is, the smallest fraction of the weight of 2 volumes of it that is ever found in 2 volumes of any other gas. These remarks will sufficiently explain the following table (p. 70) which exhibits the composition of all the more impor- tant elementary gases. It is only necessary to point out that two of them, oxygen and sulphur, occur in two places. Two different modifications of each of these gases are known, which differ from one another in weight. The atoms are, however, the same i^ each case. Constitution of Compound Gases. — It will now be obvious that two volumes of every compound gas must contain two or more atoms of two or more kinds. The formula for a compound gas must denote the number and kind of atoms that there are in two volumes of it. Hydrochloric acid is an example 'of the simplest kind of gaseous compound, two * I use thia word in its present connection with regret. It would certainly be better to exclude it altogether from an account of gases which is independent of the truth or untruth of the atomic theory. But there is no word in use which exactly answers to the conditions, and I hold the coinage of a word to be far too serious an experiment to be undertaken in an elementary treatise, or by any but a leader in science. Might not the word " prime," originally employed by Wollas- ton, be conveniently revived for this purpose ? 70 EXPERIMENTAL OHEMISTET. ELEMENTABT GASES. Name of Gas. o o d 5«,l fg- 6:S o m g II og Mercury Zinc Cadmium .... Hydrogen .... Chlorine Bromine Iodine Oxygen Sulphur (above 1000° 0.) Nitrogen . . . . . Oxygen (as ozone) . Phosphorus .... Arsenic Sulphur (below 1000° C.) 100 200 1 Hg. 32-5 65 1 Zn. 56 112 1 Cd. 1 2 2 H. 35-5 71 2 CI. 80 160 2 Br. 127 254 2 I. 16 32 2 0. 32 64 2 S. 14 28 2 N. 21 48 3 0. 62 124 4 P. 150 300 4 As. 96 192 6 S. 200 65 112 1 H, 35-5 CL Hg. Zn. Cd. 32 80 Br; 127 L 16 0, 32 S. 14 N, 16 O3 31 P, 75 AS4 volumes of it containing, as we have already seen, one atom of hydrogen and one of chlorine. Other gases contain atoms of three and even four different elements, and there are some- times as many as twenty, thirty, or even more atoms in two volumes. In fact, we know no limit to the number of atoms which may enter into the composition of a compound gas. The following table (p. 71) shows the constitution and formulae of a few of the more important compound gases'. The rules according to which they are named will be explained hereafter. Compound Gases containing non-volatile Elements. — Many gases contain atoms of elements which have not as yet been converted into the condition of gas, or which, even if they do exist as gas, have never had their specific gravities accurately determined in that condition. In these cases the atomic weight (weight of the atom) of the non-volatile element can be found by exactly the same rule as that given before, namely, by observing the smallest weight of the element that ever enters into the composition of 2 volumes of a compound COMPOUND GASES. 71 COMPOUND GASES. Name of Gas. Specific 1 ^^f" Kind, number, and weight S'^^i^y- volumes. ""^ atoms In 2 volumes. 1 Fonnnla. Meronrio Chloride . 135-5 271 Mercury 1 = Chlorine 2 = 200 71 }|HgC], Hydrochloric Acid . 18-25 36-5 Hydrogen 1 = \Chloriue 1 = 35-5}^|HCl Hypochlorous An- 1 hydride. . . / 43-5 87 /Oxygen 1 = \Chlorine 2 = 16 71 }ci,o Water. (Steam) . 9 18 /Hydrogen 2 = \Oxygen 1 = 2 16 HjO •'l Hydrogen Sulphide. 17 34 /Hydrogen 2 = \SulphuT 1 = 2 32 }so. Sulphurous Anhy-\ dride ... J 32 64 /Oxygen 2 = \Sulphur 1 = 32 32 Ammonia . . . 8-5 17 /Hydrogen 3 = \Nitrogen 1 = 3 14 H,N Nitrous Oxide . 22 44 /Nitrogen 2 = \Oxygen 1 = 28 16 N^O Nitric Oxide 15 30 /Nitrogen 1 = \Oxygen 1 = 14 16 }no Phosphine . . . 17 34 /Hydrogen 3 = \Phospliorusl = 3 31 }H3P PhoephorousChloride 68-75 137-5 /Chlorine 3 = \Phospliorusl = 106-5\lp, p 31 1,^''^ Aisine .... 39 78 /Hydrogen 3 = \Ar6enic 1 = 3 75 1l H3A8 gas. But the definition of such an atom must be slightly modified, because as we do not know the specific gravity of the elementary gas, we cannot know the weight of 2 volumes of it, and consequently cannot know what fraction of that weight the atom is. For such atoms the following definition is accurate : 4. The, atom of a non-volatile element (or indeed of any element) is the smallegt weight of that element that is ever found in two volumes of any gas. Take the case of carbon, an element which has never been 72 EXPEEIMENTAL CHBMISTKT. converted into vapour. Many gases containing carbon are known, but not one of them contains in 2 volumes less than 12 of carbon. The atomic weight of carbon is therefore taken to be 12 and the atom is denoted by the symbol C, but not knowing the weight of 2 volumes of carbon vapour we cannot tell what fraction 12 is of that weight ; or, in other words, how many atoms of carbon there are in 2 volumes of carbon gas. It is obvious that we cannot have a/ormztZa for a non- volatile element, and that even in the case of volatile elements it is incorrect to apply the formula belonging to the gas to the liquid or solid, element. For liquid and solid elements we must be content to use the symbol which denotes the atom. The following table (p. 73) wiU show the constitution of a few important gases of the kind here specified and also the way in which the atomic weights of their non-volatile con- stituents can be determined from them. The atomic weight of iron, as deduced from the composi- tion of the vapour of ferric chloride, is 112. But ferric chloride is so similar to chromic chloride that the atomic weight of iron is held to be 56. The formula for ferric chloride is then Fej Cle ; 2 atoms of iron, each 56, united with 6 atoms of chlorine, each 35"5. This brings it into analogy with chromic chloride Cr^ Clj. The composition and properties of other iron compounds confirm this view. Calculation of the Specific Gravities of Gases from their FormulcB. — If the formula for any gas be accurate ; that is, if it truly represents 2 volumes of the gas, the specific gravity of the gas may be calculated from the formula. This may be illustrated by an example. The formula for earhonie anhydride gas is CO2. What is its Bipecific gravity ? The formida tells us that 2 volumes of the gas contain 1 atom of carbon, the weight of which we know to be 12, and 2 atoms of oxygen, each of which weighs 16, total 44. 2 volumes of carbonic anhydride therefore weigh 44, whereas 2 volumes of hydrogen weigh 2 ; which shows that carbonic anhydride is 22 times heavier than hydrogen; or, in other words, that its specific gravity is 22. To find the specific gravity of any gas, elementary or com- COMPOUND GASES. 73 pound; we have therefore only to find the weight of 2 volumes of it, by adding together the weights of the con- stituent atoms, and then to divide the number so obtained by 2. COMPOUND GASES CONTAINING NON-VOLATILE ELEMENTS. Speciflcl^^f* S^"«y- volumes. Kind, weight, and number of the atoms In 2 volumes. Formula. Symbol ani atomic welgl of the non-volatife constituent Methene Ethylene Ethene Carbonio oxide . / Oarbonie \ anhydride/ Cyanogen . Chloroform Silicon chloride Methyl silicate , Ohromyl \ chloride / Chromic \ chloride / Ferric \ chloride / 14 15 14 22 26 85' 76 159 162-5 16 28 30 28 44 52 59-75 119-5 170 152 77-75 155-5 318 325 /Hydrogen 4= 4 1 \Carbon 1= 12 J /Hydrogen 4= 4 1 \Oarbon 2= 24 J /Hydrogen 6= 6 1 \Oarbon 2= 24 J /Oxygen 1= 16 1 \Carbon 1= 12 J /Oxygen 2= 32 ) \Carbon .1= 12 J /Nitrogen 2= 28 1 \Oai-bon 2= 24 J 1 Hydrogen 1= 1 j Chlorine 8 = 106-5 Carbon 1= 12 ] /Chlorine 4=142 1 \Silicon 1= 28 J I Carbon 4= 48 ' Hydrogen 12= 12 Silicon 1= 28 Oxygen 4= 64 , Oxygen 2= 32 ' Chlorine 2= 71 Chromium 1= 52-5 CChlorine 6=213 CH, C2H4 CoH. CO C = 12 OHCI3 iCL C^Hi.SiOj CrO.Cl, Cr.CL \Ohfomium 2 = 105 /i }Fe01, . (Chlorine 6=213 \Iion 1 = 112 Si = 28 Cr= 52 Fe= 11! 74 EXPERIMENTAL CHEMISTET. COMPOSITION AS DETEEMINED BY WEIGHT. — LAWS OF COM- BINATION BY ■WEIGHT. We must now leave on one side for the present all con- siderations of volume and confine ourselves to the examina- tion of the weights of different substances which are concerned in chemical changes, and the constitution of compounds as determined by weight. This method of study is of universal application, and it is used indifferently for solids, liquids, and gases, whereas we have already seen that the study of volumes only gives satisfactory results when applied to gases. Percentage Composition. — The most obvious way of stating the composition of a compound is as parts in 100. The results of an analysis are sJways calculated in this way first of all, the figures being usually carried to ihe second decimal place. Thus, if 20 grammes of lime are analysed they are found to contaiu 14"286 grammes of calcium, and 5"714 of oxygen. By a isimple proportion sum it is then found that the percentage composition is : Calcium 71-43 Oxygen 28-57 100-00 For 20 : 14-286 : : 100 : 71-43 And 20 : 5-714 : : 100 : 28-57 The percentage composition of a few important hydrogen compounds is shown in the following table (p. 75). Simplest numerical Proportion of the Gonsliiuenls. — From the percentage composition, it is easy to calculate the propor- tion that the weight of each constituent bears to that of some one which is taken as unity. In the following table the last column shows the weights of various elements which are combined with 1 of hydrogen in a few important compounds, the proportion being of course the same as iu the percentage composition. Any other element might be taken instead of hydrogen as the standard. It was indeed common at one time to take oxygen as the standard, calling it 100, but hydrogen is more convenient and is now generally employed. When the composition of hydrogen compounds is repre- COMBINATION BY WEIGHT. 75 sented in this way, very simple numbers are for the most part obtained, and some numerical relations are observed which are hidden in the mere percentage compositions. Thus in the three carbon compounds (which are examples of a large number actually known) we observe that 1 of hydrogen unites with 3, 6, and 12 of carbon. 3 is the smallest pro- portion ever found. Name op Compound. Composition parts of 100 Composition. Hydrochloric acid . /Hydrogen \Ohlprine 2-74 97-26 1 35-5 Water .... 'Hydrogen '.Oxygen 11-1 88-8 1 8 Ammonia /Hydrogen \Nitrogen 17-65 82-35 1 4-g Methene .... /Hydrogen \Garbon 25- 75- 1 3 Ethylene . . . /Hydrogen \Carbon 14-29 85-71 1 6 Acetylene /Hydrogen \Carbon 7-69 92-31 1 12 Hydrogen sulphide. /Hydrogen \Sulphiir 5-88 94-12 1 16 By extending the above table we can easily obtain a series of numbers which represent the proportions in which a good many of the most important elements combine with one part of hydrogen. It is now necessary to extend our study to those compounds which do not contain hydrogen. And here there are two courses open to us. We may begin by choosing some other element as a standard, calling its quantity 1, and calculating the weight of other elements ■which combine with it. But this method, though it serves to exhibit some interesting relations, does not bring out the simple general law towards which we are tending. We must make the comparison in another way. Knowing the weight of any element which unites with 1 of hydrogen, let us calculate the weight of other elements which unite iidth that weight. For example : 35-5 of chlorine unite 76 EXPERIMENTAL CHEMISTRY. with 1 of hydrogen. Instead therefore of calculating how much of each other element will unite with 1 of chlorine, let us calculate how much will combine with 35'5 of chlorine. And inasmuch as 8 of oxygen combine with 1 of hydrogen, let us see what weight of each other element unites with 8 of oxygen. In examining the results so obtained, it must be remembered that two elements often unite in several different proportions. Confining ourselves to the elements mentioned on the pre- ceding table, we can obtain, from the analyses of well-known compounds, the following figures, which are merely samples of an immense number at our disposal : 35'5 parts by weight of chlorine unite with 1 of hydrogen ; with 8, 24, and 32, of oxygen ; with 3, 4, 6, and 12, of carbon, and with 32 of sulphur. 8 parts of oxygen unite with 1 and with 0'5 parts of hydrogen; with _8'875, 11-83, and 35"5 parts of chlorine; with 2-8, 3'5, 46, 7 and 14 parts of nitrogen ; with 3 and 6 parts of carbon, and with 5'5 and 8 parts of sulphui* 4-6 parts of nitrogen unite with 1 of hydrogen ; with 2-6, 5'3, 8, 10-6, and 13-3 parts of oxygen, and with 4 parts of carbon. 3 parts of carbon (the smallest quantity that unites with 1 of hydrogen) unite with 0*25, 0*5 and 1 part of hydrogen % with 8-875, 17-75, 26-625, and 35-5 of chlorine ; with 4 and 8 parts of oxygen ; with 7 of nitrogen, and 16 of sulphur. 16 parts of sulphur unite with 16 and 24 of oxygen ; with 17-75 of chlorine and with 3 of carbon. A careful study of these figures will elucidate two of the most important laws of chemistry. It will be seen : — 1. That in some cases the proportions in which two elements combine with one of hydrogen are exactly the proportions in which they unite with one another. 35-5 parts of chlorine and 8 parts of oxygen will respectively combine with 1 of hydrogeii, and a compound is known which contains in every 43-5 parts, 35-5 of chlorine and 8 of oxygen. 2. That even when two elements unite in proportions different from those in which they unite with one of hydrogen, the numbers representing the two proportipns bear a simple relation to one another. — Chlorine forms three compounds with oxygen. The one mentioned above contains 35-5 of chlorine to 8 of oxygen ; the other two, 35-5 chlorine to 24 and 32 of oxygen. ATOMIC WEIGHTS. 77 In these two latter the proportion of oxygen is exactly three and four times as great as is found combined with hydrogen in water. The five oxides of nitrogen afford a still more striking example, although some thought is required to make it apparent. We already know that 1 of hydrogen unites with 4-6 of nitrogen. In the following table the columns next to the names of the compounds show the quantities of oxygen which are combined with 4-6 of nitrogen in each of the oxides. These quantities of oxygen are repre- sented by somewhat awkward fractions. But if we multiply the d'B by 3, and note the quantities of oxygen wHch unite with 14 of nitrogen, as in the middle columns of the table, we find that the proportions of oxygen can be expressed by wholp numbers, and furthermore that these numbers are simple multiples of 8, which we already know is the proportion in which oxygen unites with 1 of hydrogen. For the sake of comparison the percentage' compositions are given in the last columns. OXIDES OF NITROGEN. Parts !n 100. Nitrous oxide ■ 4 Nitric oxide . . 4 • 6 Nitrous anhydride i'6 Nitric peroxide . 4 ■ 6 Nitric anhvdride . 4 " 6 Nitrogen. Oxygen. Nitrogen. Oxygen. Nitrogen. 2-6 ) I U : S \ { 63-6 : 36"4 5-3 14 : 16 46-7 : 53-3 8-0 = 14 : 24 } = { 36-8 : 63-2 10-6 14 : 32 30-4 : 69-6 13-5 ; l 14 : 40 J [ 25-9 : 74-1 Units of Gowhining Weight. — Combining Weights. ^Atomic Weights. — By an extension of the above methods of com- parison, it is at last made out that a number may be found for each element which js variously known as its " combining weight," " proportional number," or, for reasons which will be explained hereafter, its " atomic weight."* This number denotes the smallest quantity which is ever found united with one of hydrogen, or with an analogous quantity of any other ele- ment. For shortness it may be-spoken of as the atom of the sub- stance. When we have once fixed upon the numbers which shall stand for the atoms of the elements, it is easy to represent the composition of all compounds by stating the number and * Here, again, I think that the word " prime," used by 'WollastDii, might be conveniently applied. The expression 1, 2, or 3 primes is accurate, and involves no hypothesis ;. but to talt of 1, 2, or -3 combining weights or combining numbers, is not only inconvenient but absurd. 78 JSPEEIMENTAIi OHEMISTET. • kind of atoms whicli they contain. Thus with the oxides of nitrogen. If we agree that the atom of nitrogen is 14. and that of oxygen 8, we see by the above table that in the 5 oxides, one atom of nitrogen is united with 1, 2, 3, 4 and 5 atoms of oxygen. Use of Symbols. — The symbols which have already been used (page 68) to denote volumes of gas, may be applied with equal exactness of meaning to the atoms of elements as found by weight. Thus, H may denote 1 atom, or 1 part by weight of hydrogen. N, 1 atom, or 14 parts of nitrogen. 0, 1 atom, or 8 parts of oxygen, and so on. With 'these symbols, formulse, perfectly analogous to those already explained, may be constructed and applied to com- pounds. The formulse for the 5 oxides of nitrogen are, if the above mentioned atomic weights be adopted : NO, N0„ NOs, N0« and NO,. Modes of fixing the Atomic Weights of Elements. — The numbers found for the combining or atomic weights of the elements from the study of the percentage composition of their compounds are liable to one serious drawback. We can never be certain that the number adopted represents the weight of any real unit of the element. We cannot indeed by fair reasoning conclude that therfe is any constant unit of combining weight for each element. All that we can say is, that if there be such a unit, it must either have the weight we have assigned to it or bear some simple numerical relation to that weight. Looking at the carbon compounds, for example, in the table on page 75, we come to the con- clusion that the atomic weight of carbon is either 3, 6, or 12, for carbon unites with 1 of hydrogen in all those proportions. The atomic weight of nitrogen indicated by its hydrogen compound is 4-6, but the oxygen compounds of the same element seem to require it to be 14. In the same way the atomic weight of oxygen may be 4, 8, 16, or even some less simple number, and in all these cases analysis is powerless to tell us with any certainty which of the different numbers should be adopted. In fact, to speak accurately, analysis would appear to indicate that each element had more than one, or indeed many combining weights, but that these weights all bore a simple relation to one another. Fortunately, however, there are other facts at our disposal BQUIVAIiENTS. 79 with regard to the elements of their compounds which give clear evidence npon this point, and which not only indicate iibat there is a single unit of combination for each elemen,t,. but enable us to fix its weight with a near approach to certainty. The chief of these exterior sources of evidence may be briefly mentioned in this place. 1. The Law of Gaseous Volumes, with the extensions of it that have already been considered (page 64, et seq.). This method can of course only be applied where gases are con- cerned, but its evidence when it can be obtained is more valuable than any other. The weights of the atoms of a great many of the elements are fixed in this way, and the method has been so fuUy explained that it is unnecessary to ,do more than refer to it here. We have seen, to take a single example, that the atomic weight of oxygen is taken as 16, because 16 is the smallest weight of oxygen that occurs in 2 volumes of any gas. 2. Substitution. — Equivalents. — This is merely a modifi- cation of the method by weight which has already been des- cribed. It has been seen (page 62) that one of the commonest modes in which chemical action takes place is by the substitution of a certain weight of one substance for another. In a series of substitutions we have only to ascer- tain the weight of different substances, which will displace one another to obtain a series of numbers which are called the equivalents of those substances. Starting from hydro- chloric acid, for instance, which contains 1 of hydrogen to 35-5 of chlorine, we find we can replace the 1 of hydrogen by 23 of sodium, 39 of potassium, 20 of calcium, and so on. And in the same way the 35'5 of chlorine may be replaced (either directly or indirectly) by 8 of oxygen, 4-6 of nitrogen, 80 of bromine, 16 of sulphur, and so on. These various numbers are the equivalents of the elements, and it is found that the quantities they represent are not only equivalent to 1 of hydrogen, or 35-5 of chlorine, but also to one another. 16 of sulphur may take the place of 8 of oxygen or 80 of bromine, and 20 of calcium are always equivalent to 39 of potassium. All this is simple enough, and it would seem as if the equivalents so found might be adopted as the most convenient of " combining weights." They were ia fact adopted, and 80 EXPERIMENTAL OHEMISTET. until lately were pretty generally employed for this purpose. But certain difficulties and inconveniences attend their use and have at last occasioned their abandonment. Foi*, in the first ^lace, the equivalents of some elements do not agree with the numbers indicated by the law of volumes. The equivalent of oxygen, for instance, is 8, but its atom, as deduced from the composition of compoimd gases, is 16. A Still graver objection lies in the fact that as elements often combine in more than one proportion, it then follows that there are several equivalents for the same element. The case of the oxides of nitrogen, already cited, will make this plain. On page 76, it is stated that 8 parts of oxygen will combine witii 1 of hydrogen, and with 2-8, 3'5, 4-6, 7 and 14, of nitrogen ; it is therefore evident that these five quantities of nitrogen are all, in different compounds, equivalent to 1 of hydrogen, and that, in fact, nitrogen has five equivalents. This difficulty is indeed only another form of that which was pointed out at the beginning of this section. • But although the equivalent values of the elements are no longer thought sufficient to fix their atomic weights, this method of study is still of immense importance in chemistry, for two reasons : Firstly, because, as we have seen, the true atomic weight, when not identical with the equivalent, always bears a simple relation to it. And secondly, because it often enables to fix the exact constitution of a compound, as will be seen from the follow- ing simple illustration. The formula deduced from the analysis of acetic acid is CH2O (0 = 12, H = 1, = 16). But Mfe find by experiment that one quarter of the hydrogen of acetic acid may be replaced by a metal — by sodium, for instance, or silver. Now it is evident that, if the above formula were correct, the metal must displace half an atom of hydrogen, which, as the atom is defined to be the smallest possible quantity, is absurd. We must, therefore, double the formula and make it CjHjOa. It is then seen to consist of 2 atoms of carbon, 4 of hydrogen, and 2 of oxygen. Sodium displaces one atom of hydrogen, and the formula for the compound so obtained is CjHsNaOj. This view is com- pletely confirmed by the law of volumes. By the rule given on page 72, the specific gravity of the vapour of acetic acid SPECIFIC HEAT. 81 ought, if the formula CH2O were correct, to be 15, whereas experiment shows it to be 30. 3. Specific Heat. — Atomic Heat. — This method gives very- good results with elements in the solid state, and is of the utmost importance. Equal weights of different substances, heated to an equal extent, require very different times for cooling down to the same point. If one pound of water and one pound of mercury, at a temperature of 100° C. (boiling point) be allowed to cool down to 50°, it will be found that the water is 30 times as long in doing so as the mercury, ^nd gives out 30 times as much heat. Water at any one tempe- rature contains 30 times as much heat as an. equal weight of mercury at the same temperature, and analogous differences are observed with all other substances. The quantities of heat which equal weights of different bodies contain at the same temperature (measured by the time required for their cooliag, or in some other way) are called their specific heats. The specific heat of water is greater than that of any other known substance (except hydrogen), and it is therefore taken as the standard, and called 1. The specific heat of liquid mercury is said to be 0'033. Now if we compare together the specific heat of different elements in the solid state, we find, as the following table (page 82) will show, that no relation can be observed between them. But if we compare together the specific heats, not of equal weights, but of atomic weights, which we can easily do by multiplying the specific heats of the first column by the atomic weights, we find that the numbers are very similar to one another, and approximate to 6'3. It is therefore inferred that if. we could compare all elements in the solid state and at equal temperatures, in quantities proportionate to their atomic weights, and could avoid all errors of experiment, they would all contain the same quantity of heat. This quantity, found by multiplying the specific heat by the atomic weight, is called the aioraic heat of the element. It is easy to understand the assistance which this theory, discovered by Dulong and Petit (we must remember that it is only a theory, for its truth cannot be demonstrated), affords in fixing the atomic weights of elements. Let us take the case of zinc to illustrate it. The equivalent of zinc, as compared with hydrogen, is 32"5, and that number 6 82 EXPERIMENTAL CHBMISTEY. was formerly taten as the atomic weight of the metal. But the specific heat of zinc is ■ 0955, and this number multiplied by 32 • 5 only gives 3 • 1, so that the atomic heat of zinc must be regarded as exceptional and only half of the usual quantity. But if we take 65 as the atomic weight of zinc, the anomaly vanishes, and the atomic heat becomes 6 '2. The atomic weights of many other elements have of late years been doubled for the same reason. Some few exceptions to this rule of atomic heat are known, of which carbon and silicon are the most important. It will be seen that if we wish to find the atomic weight of an element from its specific heat, we must divide the average atomic heat 6 ■ 3 by the speci^c heat. The atomic weight so obtained will not be exact, but it will serve to indicate whether a particular number or a fraction or multiple of it is to be chosen as the true atomic weight. E.g. Atomic weight of tin is 7^^^^ = 112, which sufficiently indicates that 118, and not 59, should be taken as the atomic weight of tin. SPEOIPIO AND ATOMIC HEATS. Elemest. Specific Heat. Atom Welgl ° Atomic Heat. Bromine (solid) . . 0-0843 80 6-7440 Iodine 0-054:1 127 6-8707 Potassium . 0;1696 39 6-6144 Sodium . 0-2934 23 6-7482 Silver 0-0570 108 6-1560 Gold . . . 0-0324 196 6-8504 Phosphorus . 0-1887 31 5-8497 Aa'senic .~ . 0-0814 75 6-1050 Antimony . 0-0508 122 6-1976 Bismuth 0-0308 210 6-4680 Sulphur . 0-1776 32 5-6882 Magnesium . 0-2499 24 5-9976 Zinc . 0-0955 65 6-2075 Mercury (solid) 0-0319 200 6-8800 Copper . 0-0951 • 63 5 6-0389 Lead . 0-0314 207 6-4998 Iron . 0-1138 56 6-3728 Aluminium . 0-2143 27 5 5-8932 Tin . . . 0-0562 118 6-6316 Platinum 0-0324 197 6-3828 ISOMOEPHISM. 83 4. Isomorphism. — It was discovered by Mitsclierlicl)., that compounds which might be supposed to have a similar chemical composition, very commonly crystallized in the same form, even though quite diiferent in properties. Similar compounds of calcium, strontium, barium, and lead; similar sulphates, selenates, and chromates, and similar phosphates and arsenates, are examples of this law, and many others might be quoted. Compounds which exhibit this peculiarity are said to be isomorphous with one another (from to-os, like, and fiopfju/j, form). Mitscherlich's law, though not universal, is yet so fre- quently true that when two analogous substances yield crystals having the same angular measurement, there is a great a priori probability that their constituents are arranged in a similar manner, and this probability is sometimes of great use in fixing the atomic weight of an element. For example, the metal aluminium has only one oxide, alumina, which contains 18-3 of the metal to 16 of oxygen. As 16 is the atomic weight of oxygen, it would be natural to suppose that that of aluminium was IS'S, in which case the formula of alumina would be AlO. But alumina is isomorphbus with red oxide of iron (ferric oxide) which is known to have the formula Fe^Os, and it is therefore concluded that the formula of alumina must be Alfis, in which case the atomic weight of aluminium must be 27- 5 Of course either formula agrees equally well with the result deduced from analysis. For if:— Al = 18-3, then AlO = 18-3 Aluminium : 16 Oxygen. Al = 27-5, then Al^Os = 55 „ : 48 „ the proportion being the same in both cases. The number 27'5 is confirmed by the specific heat of aluminium, for — ^ - -* which is as near as could be expected. The atomic weights of the elements, determined by the collation of all these various facts and theories, are given in the table at the commencement of this volume. 84 EXPEKIMKNTAL CHEMISTRY. EQUIVALENT VALUE OF ATOMS. — ATOMICITY, OB QUANTIVALENOE. The above remarks will have made it evident that the quantity which is known as the atom of an element is not always the same as its equivalent. The equivalent of oxygen is 8, because 8 parts of oxygen will replace 35 "5 of chlorine, or 1 of hydrogen, but the atomic weight of oxygen is held to be 16: the equivalent of nitrogen is 4 "6, but its atomic weight is 14; and lastly, in its simplest compound, the equivalent of carbon is 3, whereas its atomic weight is 12. It follows from this, that an atom of oxygen is equivalent to two, an atom of nitrogen to three, and an atom of carbon to four atoms of hydrogen. For if 8 of oxygen be equivalent to 1 of hydrogen, 16 must evidently he equivalent to 2. The atom of each element has therefore its own equivalent value, represented by the nmnber of atoms of hydrogen to which it is equivalent. This equivalent value, as compared with that of the atom of hydrogen, is often spoken of as the atomicity, or quantivalence of the element, and its amount is described by the words monad, diad, triad, tetrad, pentad, &c., according as the atom is equivalent to one, two, three, four, or five atoms of hydrogen. Classification of Elements by their Atomicity. — All those elements of which one atom is equivalent to one atom of hydrogen, either in replacing it or combining with it, are classed together as monads. The most important monad elements are, hydrogen, chlorine, bromine, iodine, and fluorine among the non-metals, and potassium, sodium, and silver, among the metals. The chief diad elements are oxygen and sulphur among the non-metals, and barium, strontium, calcium, magnesium, zinc, copper, mercury, and lead among the metals. As examples of triads may be mentioned nitrogen, phosphorus, arsenic, and boron, and the metals bismuth and gold. Carbon, silicon, and most of the other metals are tetrads. Mode of MarMng Atomicity. — As the symbol denotes one atom, it is easy to mark the equivalent value, or atomicity, of that atom by dashes or Eoman figures placed above and to the right of the symbol, in the following maimer : — H' O" N'" ATOMICITY — BADIOALS. 85 C"" or C". Tlio monad atoms, however, are seldom marked at all. Let it be understood distinctly that a diad atom wUl take the place of or will combine with any two monad atoms. One atom, or 16 parts of oxygen, for instance, may very often, by mere substitution, be made to displace and take the place of two atoms (2 parts) of hydrogen, and we already know that 16 parts of oxygen will combine with 2 of hydrogen. The formulse for a few important compounds will illustrate the different values of the atoms more clearly than words. HCl, HjO", HgN'", H^C", KCl, K^O", Zn-'Cl^, Bi"'Cl3. Mode of Fixing Atomicity, — When an element combines with hydrogen, the hydrogen compound decides the atomicity, as with chlorine, oxygen, nitrogen, and carbon. In other cases the chlorine compound, or any other compound that the element may form with a monad, may be used instead. Thus platinum is reckoned a tetrad because it forms the chloride, Pt^Cl^, in which the atom of platinum is united with four of the monad atoms of chlorine. Perissiad and Artiad Atoms. — Those elements whose atomicity is an uneven number are called perissiads (?rept(ra-os, odd), and those in which it is even, artiads (aprios, even). There is great convenience in the use of these words, which were suggested by Dr. Odling. Variations of Atomicity: — Many elements have different atomicities in different compounds. For example, a second compound of platinum and chlorine is known, which has the formula Pf'Clj, and here the metal is clearly a diad. So carbon, which is tetrad in C'H^ and CCj (two diad atoms act, of course, like four monad ones), is diad in CO. And nitrogen, which is triad in !N'"'H3, is monad in N'jO", and pentad in N'H'^Cl'. But these variations are subject to one rule, which is of almost universal application. Perissiads are never artiads, nor a/rtiads perissiads. A pentad, for example, which of course is a perissiad, may sometimes act as a triad, or a monad, but not as a tetrad, or diad. Two of the oxides of nitrogen, NO and NOj, are almost the only certain excep- tions to this important rule, which must be borne carefully in mind in constructing formulas. Badicals. — The formula for nitric acid is HNO,. Now a 86 - EXPEEIMENTAL CHEMISTET. large number of compounds called nitrates are known, which difter from nitric acid only in containing some metal in place of hydrogen. Thus we have sodium nitrate NaNOj, and silver nitrate AgNO . In all these nitrates, however, the common quantity NO is found, and NOs is therefore called the radical of the nitrates. In the same way the formula for sulphuric acid is HjSOj, and the sulphates aU contain the radical SO4. Neither NO3 nor SO4 exist in a separate state. It is probably impossible for them to do so. We do not even know that they exist in the compounds, but we do know that their elements are present in the same proportions in a large number of compounds, and that all these compounds are linked together by a certain similarity of properties; and therefore, without troubling ourselves either to affirm or deny their existence as separate entities, it is convenient to assume their presence in certain compounds. We shall meet with many radicals as we go on, many of them very unlike one another in function ; but for the present we have to regard them only in one point of view. In the compounds which contain them, radicals play the part of elements, and, like elements, every radical has its own proper atomicity. The acids which contain radicals afford good examples of this. Nitric Acid H N O3 is like Hydrochloric Acid H CI. Sulphuric Acid HiSO, ,, Water HjO. Phosphoric Acid H3PO4 ,, Ammonia HjN. As CI is united with one of H, so NO3 is united with one of H. NO3 is therefore called a monad radical. And as SO4 is united with two of H, it may be compared to oxygen, and is called a diad radical. Their atomicity may be marked as that of elements is marked (NO,)', (SO4)", and (PO4)'", and lastly it must be remembered that in all nitrates NO3 is monad, and in aU sulphates SOi is diad. Measure of the Atomicity of iJadicaZs.— The equivalent value of a radical is measured, just as that of an element is, by the number of atoms of hydrogen or other monad element with which it combines. NO3, for instance, is a monad radical, because in HNO3 it is combined with one atom of hydrogen. A radical is in fact an incomplete compound, and it is monad, diad, or triad' according as it lacks one, two, or three monads to complete it. The following table includes some N (Cyanogen) in Cy a- 1 nides / 01 in Hypochlorites 01 Oj in Ghlorites . 01 O3 in Chlorates . 01 0^ in Perchlorates . N O2 in Nitrites . N O3 in Nitrates . P O3 in Metaphosphates RADICALS — NOMKNCLATUEE. 87 of the most important radicals of chemistry. Only a few of them have individual names. MONAD RADICALS. '^Ar^!^''^^^^.'^'^^:h'^'^'0- J^HO. Ca"(H0),.Bi"XH0)3. ^miie"^"!^"^'"^ 'i ■■ H3N. KH,N. HON. KON. Hg"(CN)2. HCfO. KCIO. H 01 Oj. K 01 Oj,. HOIO3. KCIO3. H 01 O4. K 01 0,. HN 0,. KNO2. HN 0,. KNO3. HP O3. KPO3. N H, (Ammonium) in Ammoninm Oompounds, as in N H, 01. NH, N O3. C H3 (MeSiyl) in Methyl Compounds. . . , , H3 CI. OjH, (Ethyl) in Ethyl Compounds . . ,, O2H5OI. DIADS. S O3 in Sulphites . as in H^ S O3. S O4 in Sulphates . ,, H^SO^. O3 in Carbonates . , , K^ C O3. Si O3 in MetasiUcates , , Hj Si O3. H2 (Methylene) in Methylene Compounds, as in C Hj Clj. TRIADS. P Oi in Phosphates, as in H3 P O4. K3PO,. KH^PO,. K^HPO,. As O, in Arseniates , , Hj As O4. Asj. As O4. H in such compounds as Chloroform, H CI3. TETRADS. Si 0, in Silicates . . as in H, Si O^. Mg''^ Si O4. Pj 0, in Pyrophosphates , , H4 P^ O,. Na, Pj O,. Mg''^ P2 0,. NOMENCLATURE. Names are given to chemical compounds, according to rules which, though not perfect, are better than those employed in any other science. Only a few of the simplest need be indicated in this place. 1. Compounds of two' elements only are distinguished by K2S03. Ca"S03. K2S04. KHSO4 K H O3. Oa"C03. Mg"Si03. o» EXPERIMENTAL OHBMISTET. the termination ide. Thus the compound of zinc and oxygen is called oxide of zinc, or zinc oxide ; zinc and chlorine, zinc chloride ; sodium and chlorine, sodium chloride ; and so on. This rule is invariable, though for special reasons a dif- ferent name is more often used for certain simple compounds. 2. When there are two compounds of the same two elements, the lower — that which contains the least oxygen, chlorine, &c. — is distinguished by the termination ous, and the higher by the termination ic. The lower chloride of tin SnOl2, for instance, is called stannous chloride, and the higher, SnCli, stannic chloride. The same rule is applied to acids. HNOs is called nitrous acid, and HNOb nitric acid. 3. The substances called salts which are derived froqi an acid which ends in ous have the termination ite. All the salts, for instance, which contain the radical NOj, and which therefore correspond to nitrous acid, are called nitrites. Salts which correspond to acids ending in ic, have the termina- tion ate. Nitric acid, for instance, forms nitrates, sulphuric acid, sulphates, and acetic acid, acetates. Almost the only exception to this rule is in the compounds called hydrates, which contain the radical HO, and which, instead of corre- sponding in composition to an acid, correspond to water. Other rules will be more conveniently given as instances occur. ATOMIC AND MOLECULAR HYPOTHESES. Atoms. — Atomic Weights. — Dalton, to whom we are indebted for the first clear enunciation of the laws of combination by weight, contrived a beautiful hypothesis to account for them. In its simplest form it is known as Dalton's atomic hypothesis. According to this view, matter is composed of ultimate indivisible particles called atoms (aro/nos, indivisible). Every element has its own atom, peculiar in properties and in weight. All compounds are formed by the union together of elementary atoms. The relative weights of the atoms are expressed by their combining weights, and afford a simple reason for those combining weights. Thus (taking the modern numbers), 35'5 parts of chlorine combine with 1 of hydrogen, because every atom of chlorine is attracted by and combines with one atom of hydrogen. In the same way, every one atom of oxygen, weighing 16, combines with two ATOMIC AND MOLECULAR HYPOTHESES. 89 atoms of hydrogen, weighing 2. In fact, the combining weights of the elements show the relative weights of the atoms, hydrogen being taken as unity, and this is the reason why the combining weights are generally called atomic weights. It follows from this that the ultimate particle — the smallest possible quantity — of any compound must contain at least two different elementary atoms. Compounds are groups of atoms of two or more kinds. Molecules. — Molecular Weights. — The ultimate particles of compounds, consisting, as we have seen, of groups of atoms, are called molecules (moleculus, small mass). Their weight is, of course, the sum of the weights of their constituent atoms. Thus the molecular weight of hydrochloric acid, HGl, is 36-5, and of water, 18. Eeasons have already been given for believing that the ultimate particles of most elements, at any rate in the gaseous state, consist of two or more similar atoms. The view adopted for compounds must therefore be extended to elements, and we must admit that in the gaseous state elements consist of molecules incapable of division, which molecules themselves consist of atoms of similar kind, sometimes of only one (mercury, zinc, and cadmium gases), sometimes of two (hydrogen, oxygen, &c.), and sometimes of more than two (ozone, phosphorus, arsenic, and sulphur gases). By an extension of this view, the symbols and formulte which are used to denote two volumes of any gas, elementary or compound, can also be applied with equal accuracy to denote respectively one atom and one molecule of it. The atom of hydrogen may be denoted by H, the molecule by H2 ; the atom of arsenic by As, the molecule (as gas) by As^ ; and single molecules of hydrochloric acid, steam, and ammonia may be represented by the formulae HCl, H2O, and HjN. This leads us to another important hypothesis, which of late years has been very generally adopted. It refers only to Bypoihesis of Avogadro and Ampere. — This hypothesis, suggested by Avogadro in 1811, and further developed by Ampere in 1814, may be stated in the following terms: Equal volumes of different gases, at equal pressure and tem- perature, contain equal numbers of molecules. This hypothesis explains two things. 90 EXPERIMENTAL CHEMISTRY. 1. The fact already mentioned (pages 34, 56), that all gases are equally affected in volume by variations of pressure and temperature. Physical agencies, such as heat and pressure, do not affect the nature of molecules, but only their distance from one another, and this being the same in all gases under similar conditions, the effect produced by those agencies must naturally be the same in all cases. 2. The law of gaseous volumes. If one molecule of chlorine enters into chemical action with one molecule of hydrogen, the same will be true of one thousand, or one million molecules of each. Now by the hypothesis one thousand, or one million, molecules of chlorine occupy a space equal to that occupied by one thousand, or one million molecules of hydrogen, ai)d it therefore follows that the two elements should react together in the proportion of equal volumes, which experiment proves to be the fact. In like manner, two volumes of hydrogen react with one volume of oxygen, because one volume of oxygen contaias n, and two volumes of hydrogen 2m molecules, and every molecule of oxygen reacts with two molecules of hydrogen. Structure of Gases. — Summary of Hypotheses. — The modem doctrine may be summed up in these words. 1. Equal volumes of gases, at equal pressure and temperaiute, contain equal numbers of molecules. 2. Every molecule consists of one or more atoms, either similar in kind (elementary molecules), or dissimilar in Tcind {compound molecules).* * The molecular hypothesis is sometimes referred to so loosely, that a few further remarks upon it may not be out of place. 1. The hypothesis asserts nothing of the relative bulk of molecules, or atoms. It does nut assert that one molecule of hydrogen has tlie same , bulk as one molecule of chlorine, but only that n molecules of hydrogen occupy, by their molecular movements, the same space as n molecules of cnlorine. 2. Similarly, the hypothesis does not assert that the bulk of an atom of hydrogen is equal to the bulk of an atom of chlorine, but only that two atoms of hydrogen and two atoms of chlorine occupy, respec- tively, by their atomic movements, thd space of one molecule. The atoms of matter may be almostly infinitely small, as compared with the molecules, and if the bulk of the molecules were known we should be no nearer to knowing that of the atoms. A molecule of hydrogen may, for aught we know, be comparable to an inflated bladder, with two peas rotating in it. ATOMIC AND MOLEOULAK HYPOTHESES. 91 Molecules of Solids and Liquids. — The formute applied to gases are generally extended for convenience sake, but by imperfect reasoning, to the same substances in the liquid and solid state. But it is right to point out that neither hypothesis nor experiment tell us anything of the number of atoms contained in the molecules of solids and liquids. We have good reason for believing that a molecule of iodine vapour contains only two atoms ; but, for aught we know, a molecule of solid iodine may contain a thousand. The formula for common salt, which is non-volatile, is written NaCl, on account of its analogy, not with solid, but with gaseovs HCl. The formula NaCl does indeed tell accurately, as far as our knowledge goes, the relative number of atoms of sodium and chlorine that are present in the compound, but it does not tell us the absolute number that are present in each molecule. The true formula for common salt, as compared with that of hydrochloric acid gas, HCl, would be Na„ Cl„, n standing for an unknown and probably very large number. In other words, the formula for common salt, or for any other solid or liquid, is probably only the formula for the »th part of one molecule. There is both convenience and propriety in the use of the ordinary formula for solids and liquids, inasmuch as they truly represent the relative quantities of matter which are concerned in chemical changes ; but it should not be forgotten that these formulas differ from those of gases in that the latter tell us, in addition, how much matter is present in a certain space, and also, if the molecular hypothesis be adopted, the absolute number of atoms in each molecule. Hypothesis to Account for Atomicity. — The different equiva- lent value of different elementary atoms can be accounted for by supposing that each atom has the power of fixing to itself a certain number of other atoms. It is as though a carbon atom, for example, had four arms by which it could grasp and be grasped by four hydrogen, or chlorine atoms, or two oxygen, or sulphur atoms, each of the latter having two arms of its own. It must, of course, be understood that this is a mere illustration, for no one believes that the atoms have real arms projecting from them. But the illustration gives a lively idea of the hypothesis ; and atoms are sometimes figured as circles with arms (called bonds) proceeding from them. 92 EXPERIMENTAL CHEMISTRY. The following figures represent a few of these atoms and their compounds : Q- Hydrochloric Acid ® @ -O Water ©Ho)-® Mod ad atoms Diad , , Triad , , Ammonia Tetrad ^ Methene The variations of atomicity by pairs, which have been described before (page 85), are explained by supposing that the bonds of an atom have the power, under certain circum- stances, of neutralizing one another in pairs. To carry out the simile used before, the carbon atom has four arms, and is therefore a tetrad ; but if two of those arms are clasped together, they will not so easily grasp other atoms, and the carbon atom will therefore act as a diad. The hypothesis, put in this form, appears somewhat fanciful, but it harmonizes well with known facts, and has the merit of assisting wonderfully in the comprehension of the complex compounds of organic chemistry. EQUATIONS, OE FORMULA OP CHEMICAL CHANGE. Chemical changes of all kinds can be very conveniently represented in the form of equations, the formulse for the substances concerned -being written in the first half, and the formulse for the new substances produced in the other. Thus the combination of zinc and chlorine is thus expressed : Zinc. Chlorine. Zinc Chloride. Zn" + CI2 = Zn" CI3; which may be read in the following manner. One molecule of zinc added to one molecule (two atoms) of chlorine ife equal to, or rather produces one molecule of zinc chloride. EQUATIONS, OK rORMUL« OF CHEMICAL CHANGE. 93 Such equations are often called formulce, which introduces a little confusion, since we have already seen that the term formula is also applied to the aggregate of symbols which denotes the molecule of a single element or compound. In making out an equation of this kind, it is necessary, as with algebraical equations, to take care that every atom which appears in the first half shstU duly appear and be accounted for in the second. The following equation, which expresses the oxidation of ethylene gas, illustrates this : Ethylene. Carbonic Anhydride. Water. C^H^ + 3O2 = 2 CO2 + 2 H2O. Two atoms of carbon, four of hydrogen, and six of oxygen are concerned in the change, and it will be seen that though differently arranged, they are all accounted for in the second half of the equation. The large figures in the above and in similar equations refer, it must be remembered, to the whole molecule. SOOj, for instance, means two molecules of carbonic anhydride, containing together two atoms of carbon and four of oxygen. A few more eq national formulae, one or two of them rather complex ones, may, with advantage, be studied in this place. They represent chemical changes of several kinds. Decomposition of water : 2H,0" = 2H2 + 0,. Synthesis of water : 2H2+02= 2H2O. Substitutions : Sulphuric Acid, Zinc Sulphate. H3SO4 + Zn" = Zn"SO^ + Hj. Water. Potassium Hydrate. 2 H2O" + E2 = 2 K H 0" + E2. Copper Chloride. Ferrous Chloride. Cu" CI2 + Fe" = Fe" Cl^ + Cu". Double decompositions : Mercuric Potassiui CMoride. Iodide. Hg" CI2 + 2 K I = Hg" I2 -t- 2 K CI Mercuric Potassium^'"'*" 'Mercuric Potassium Chloride. Iodide. Iodide. Chloride. 94 EXPKKIMBNTAIi OHEMISTET. Double decompositions — continued. PotasBlum Hydrochloric •arotai- Potassium Hydrate. Acid. ^°-^- Chloride. KHO" + HCl = H2O" + KCl. Copper Oxide. Nitric Acid. Water. Copper Nitrate. Cu"0" + 2H]Sr03 = H2O" + Cu"(NO,V Calcium Pbosphoric Hydrochloric Calcium Chloride. Acid. Acid, Phosphate. SCa'Cli, + 2H3PO, = 6 HCl + Ca"3(P04)"'2. The brackets in the two last examples will readily be understood. Cu"(N0s)2 expresses that one atom of the diad metal copper is united with two units of the monad radical NOs. One great advantage of these equations is that they afford us the means of calculating the respective' quantities by weight in which bodies act on one another. Take, for example, the above-described action of mercuric chloride and potassium iodide. HgCl, means one atom of mercury weighing 200 combined with two atoms of chlorine weighing 35-5 X 2 = 71, total 271. KI means one atom of potassium 39 and one atom of iodine 127, total 166 ; or, as 2KI is employed, 332. We therefore know that 271 parts (pounds, grammes, or tons) of mercuric chloride will act upon 332 parts of potassium iodide, and in a similar manner we can calculate that 454 parts of mercuric iodide (Hglj = mercury, 200 -f- iodine, 127 X 2 = 254), and 149 parts of potassium chloride will be produced during the change. Now suppose that a chemist has 100 grains of mercuric chloride, and wishes to know how much potassium iodide he must add to convert all the mercury into iodide. He knows that 271 parts of the chloride will require 332 of the iodide, and he has therefore only to perform a simple proportion sum. 271 : 332 : : 100 : a; = 122J grains. In like manner he can readily find out that he ought to obtain ad the result of the action 167 J grains of mercuric iodide and 55 grains of potassium chloride, for as 271 parts of mercuric chloride yield 454 parts of merourio iodide and 149 parts of potassium iodide, 271 : 454 : : 100 : a; = 167^ grains and 271 : 149 : : 100 : x = 55 ACIDS, BASES, SALTS. 95 In short, to sum up the whole reaction, 100 grains of mercuric chloride, with 122^ grains of potassium iodide, will yield 167^ grains of mercuric iodide and 55 grains of potassium chloride. It is of course equally easy to find out how much mercuric chloride and potassium iodide must be employed to yield a certain weight, say 100 grains of mercuric iodide. When the equations refer to gases they have another advantage. As every single formula for an element or com- pound denotes two volumes of gas, the volumes of different gafees concerned in a reaction can at once be inferred from the equation. In the equation given above C2H, + 3 02 = 2C02+2H2 0, Cj H4 means 2 volumes of ethylene, and SOj means 3x2 = 6 volumes of oxygen ; so that 2 volumes of ethylene require 6 volumes of oxygen for their complete oxidation. There will be produced during the action, 2OO2, that is, 4 volumes of carbonic anhydride and 2H2O, that is, 4 volumes of steam. For if CO2 represents 2 volumes, 2OO2 must evidently represent 4 volumes. It must not, however, be forgotten that these relations of volume are only correct if the pressure and temperature remain unaltered. If otherwise, a correction must be made by the methods already given (pages 34, 57). ACIDS, BASES, SALTS. Allusion has already been made (pages 49, 50) to certain substances which have long been known under the respective names of acids and bases. Acids are sour and redden litmus, and bases, when soluble, have what is called an alkaline taste, and turn the colour of reddened litmus back again to blue. They have a kind of antagonistic function, and will neutralize one another. When an acid acts on a base, a new compound called a salt is produced, which commonly has no action on either blue or red litmus. But although in well-marked cases acids, bases, and salts are so different from one another in properties, modern chemistry has taught us that the compounds usually known by those names bear so much resemblance to one another and to other compounds in structure, that it is impossible to 96 EXPERIMENTAL CHEMISTRY. frame accurate definitions for them. If possible it would perhaps be 'as well to banish the terms altogether ; but as that would produce great inconvenience, it is better to take such imperfect definitions as we can get. 1. Acids. — An acid is composed of hydrogen with one of those radicals, elementary or compound (page 86), which are called acid radicals. The hydrogen can be replaced iy metals, in which case one of the compounds called satis is formed. Acids redden litmus, and are commonly sour. The following are important examples : — Hydrochloric Acid, HCl; Nitric Acid, UNO,; Sulphuric Acid, H^SO^; Phosphoric Acid, H3PO4. In the first of these hydrogen is united with the elementary acid radical CI, in the others, with the compound radicals NOj, SO4, and PO4. The imperfection of the definition will be apparent if we remember that we can only define an acid radical as a radical which, united with hydrogen, forms an acid. • Basity of acids. — Acids are said to be monobasic, dibasic, or tribasic, according as they contain one, two, or three atoms of hydrogen which can be replaced by acids. In the previous examples HGl and HNOs are monobasic, H2SO4 is dibasic, and HsPOi is tribasic. Of course this is equi- valent to saying that the radicals of those acids are monad, diad, or triad. PO4 is a triad radical, and its acid may be written in this way, Ha(PO,)"'. Acids which contain more than one atom of replacable hydrogen are said to he polybasic. Oxygen Acids, or Oxy-acids.— Most acids contain oxygen as a part of their radical, and these are related in a very simple manner to a particular series of oxides, which, for that reason, are called acid oxides or anhydrides. When one of these anhydrides combines with water, an acid is formed, and when, on the other hand, water is removed from an acid, the corresponding anhydride is obtained. ' Nitric Acid. Nitric Anliydride. N2O5 + H2O = 2HNO3. Sulpburic Sulpbui ic Anhydride. Acid. SO3 4- H^O = H2SO4. iosphoric Phosphoric nhydride. Acid. P2O5 + 3H2O = 2H3PO4. ACIDS, BASEB, SALTS. 97 One molecule of nitric anhydride, uniting with one of water, forms two molecules of nitric acid. In a similar manner, if from one molecule of sulphuric acid one molecule of water be taken, one molecule of sulphuric anhydride will remain. It must not, however, be supposed the acids are always, or even generally, prepared in practice from the anhydrides. One anhydride, indeed, silicic anhydride, SiOa, will not combine directly with water, although its acid can be obtained by indirect means. The anhydrides of many acids have not yet been obtained, and one anhydride (carbonic anydride, COj) is known to which no corresponding acid can be proved to exist. The formula for the acid should be H,CO,. 2. Salts. — A salt is a compound containing a metal and am, elementary or compound acid radical. A salt only differs from an acid by containing a metal in place of hydrogen. Taking, for example, the salts of sodium, those corresponding to the acids already mentioned are— Na CI Sodium chloride ; corresponding to H CI. NaNOs ,, nitrate ,, HNO3. Na^SOi ,, sulphate ,, H2SO4. Nag P O4 , , phosphate , , Hg P 0^. The proportion which the metal and radical bear to one another depends of course on the atomicity of each. Thus the chloride, nitrate, sulphate, and phosphate of the diad metal calcium, and of the triad metal bismuth, are formulated in this way : Ca" C\ Ca" (N 03)2 Ca" (S O4)" Ca", (P O^)'^. Bi"'Cl3 Bi"'(N03)3 Bi"',(SO,)"a Bi"'(P04)"'- In many salts of polybasic acids the hydrogen is only partially replaced by metals. Thus we have Phosphoric Sodium-dlhydrogen Disodium-hydrogen Sodium Phosphate, or Acid. Phosphate. Phosphate. Trisodium Phosphate H3PO4. NaHjPOi. Na^HPO^. NagPO^. It will be seen from the above remarks that acids are really hydrogen salts. Some chemists indeed name them accordingly, and call H^SOi "hydrogen sulphate," instead 98 EXPERIMENTAL CHEMISTKT. of sulphuric acid. The term acid is applied by them to the anhydrides, so that the formula for svdphuric acid becomes SOj. Many salts are known which are more or less ir- regular in their composition, but modern chemical theory enables us to give a tolerably satisfactory account of all of them. 3. Bases. — A base is a metallic hydrate (that is, a compound of a metal with the radical HO) which is capable of reacting with acids to form salts. As HO is a monad radical, the constitution of hydrates is closely analogous to that of chlorides, nitrates, &c. For example : Sodium Hydrate. NaHO is like NaOl and NaNO,. Calcium Hydrate. Ca"(HO), is like Ca"Cl2 and Ca"(N03),. Bismuth Hydrate. Bi"'(H0)3 isHke Bi"'Cl3 and BiCNO,),. Bases, like acids, are related to a particular series of oxides called basic oxides. These oxides are sometimes called bases. They differ from the true bases by the elements of water. Sodium Oxide. Sodium Hydrate. Na,0 + H2O = 2NaH0. Calcium Oxide. Calcium Hydrate. Ca"0 + H,0 = Ca"(H0)2. Bismuth Oxide. Bismuth Hydrate. Bi"'aO"s + 3H2O = 2Bi"'(H0)s. Some basic oxides, however (bismuth oxide, for instance), will not combine directly with water ; and, on the other hand, some basic hydrates (sodium hydrate, for instance) cannot be dehydrated by heat. Calcium oxide and hydrate are examples of compounds which experience both changes with ease. The oxide (quick lime) combines eagerly with water, great heat is produced, and calcium hydrate (slacked lime) is formed. When slacked lime is heated, water is expelled, and quick lime once more obtained. Ca"0 + Hsj0 = Ca"(H0),; and Ca" (H 0)j - H^ = Ca" O. A0ID8, BASES, SALTS. 99 Formation of Salts, — Salts can be formed by a variety of processes, only a few of which can be specified here, with one or two examples of each. It must not be supposed that every process is practicable in all cases. , 1. By the action of metals on acids : Ha S 0, + Zn" = Zn" S 0, + H^. 2. By the action of metallic oxides on acids : Ca" + 2 H CI = Ca" 01^ + H^ O. 3. By the action of bases on acids : NaHO + HCl = NaCl + HaO; Ca" (H 0)2 + 2 H CI = Ca" Clj + 2 H^ 0. This is the case before referred to. 4. By the action of anhydrides on metallic oxides: SOs+NajO = Na^SO^. 5. By the action of anhydrides on bases : CO^+ajSTaHO = Na,003+H«0. It will be seen that ia most of these reactions water is formed simultaneously with the salt. ( 100 ) PAET II. NON-METALUC ELEMENTS. INTRODUCTION. The old distinction between organic and inorganic chemistry- is fast fading away. It was formerly believed that vegetables and animals had the power of producing in their organisms chemical compounds which could not be formed artificially ia the laboratory. Vast numbers of compounds were known which owed their origin directly or indirectly to the animal or vegetable kingdom, and which could not be obtained from any other source. To the department of chemistry which dealt with such compounds, the name " Organic Chemistry " was very properly applied. But the progress of scientific research has taught us to manufacture a great number of these compounds from inorganic materials, and there is therefore no longer any reason why they should be separated from other compounds in a general system of classification. The so-called organic compounds have, however, one feature in common. They all contain carbon, and it is therefore convenient for purposes of study to retain them in a separate department of chemistry. Moreover, although some few carbon compounds enter into the composition of important minerals, a very large number of them bear some direct or indirect relation to the processes of life, and the term " organic " may therefore, in this limited sense, stiU be applied to them. It is only necessary to bear in mind that what is stm genei^ally called organic chemistry is but the chemistry of carbon compounds. In the present division of the book we shall say as little 'about it as possible. INTRODUCTION. 101 A less important distinction is that which is commonly made between metallic and non-metallic elements. No exact definition can be attached to the word metal, no one property can be connected exclusively with it, and there is no line of demarcation that can be drawn between the two classes. We shall trouble ourselves very little with the precise meaning of the word metal, but shall use it in its current sense, and shall introduce the elements in the order which appears most simple and convenient, grouping them according to their atomicities (page 84). The present part contains an accoimt of the elements generally classed as non-metallic. Part III. is devoted to the metals, and Part IV. to organic chemistry. ( 102 ) CHAPTEE I. NON-METALLIO MONABS. (Hydrogen, Chlorine, Bromine, Iodine, Fluorine.) HYDEOGEN. Symbol, H = 1. Formula, H^. This element in its cliemical relations resembles the monad metals. It stands alone among the non-metals, and it must, for convenience, be studied first. PBBPABATION. Hydrogen occurs in nature almost exclusively in a state of combination, but various means are known by which it can be set free and obtained in a state of purity. AVe have already seen that when a current of electricity from a tolerably powerful battery is transmitted through water, slightly acidulated with sulphuric acid, the water is decom- posed, oxygen goes to one pole of the battery and hydrogen to the other ; and both gases can easily be collected (p. 12). Many other compounds containing hyi^ogen will yield it up under similar treatment. The ordinary processes for preparing hydrogen almost all involve the use of some metal. A certain number of the metals have the power of displacing hydrogen from its combinations, either easily or with difficulty. For common purposes zinc or iron is used. Mcperiment 1. — Boil some water for fifteen minutes, that all the air contained in it may be expelled ; let it cool, and fill a bowl and a test-tube with it; close the latter with the finger, and invert the mouth of it under the water in the HYDROGEN. 103 bowl. Now fasten to a wire a piece of sodium, of the size of a small pea, and thrust it quickly under the mouth of the test-tube ; the metal frees itself from the wire, and as it is lighter than water, it ascends into the tube, floating there with a rotatory motion ; a gas is evolved from the water, and collects in .the upper part of the tube. This gas is hydrogen. The metal sodium displaces one half of the hydrogen from water, in the manner shown in the following formula : 2 HjO + Na, = 2 NaHO + H,. The compound NaHO is called sodium hydrate. It remains dissolved in the Water, and may be obtained in a pure state if the water is evaporated off. Close the tube again with the finger, remove it from the bowl, and apply a light to the mouth, the gas will burn with a flash of light. This experiment proves hydrogen to be a combustible gas. Pour into the bowl some solution of litmus, which has been reddened with a drop of vinegar or other acid, the litmus will be immediately changed to blue, showing that sodium hydrate is one of the substances called bases (pp. 50, 98). Experiment 2. — Lay a piece of blotting-paper on the surface of some water contained in a saucer, and throw upon it a small piece of sodium, an energetic decomposition of the water will take place, and in a few moments the sodium will apparently burst into flame, and bum for some time with an intense yellow colour. This apparent combustion of the sodium is really due to the burning of the hydrogen, set free by that metal, which is inflamed by the intense heat which accompanies its evolution. This experiment differs only from the preceding one inasmuch as in the former case the hydrogen is collected, while in the latter it is burnt as it is liberated. The sodium hydrate may be rendered evident as before by the addition of red litmus solution to the water. Experiment 3. — Throw a piece of potassium on some water (the blotting-paper may be dispensed with in this case), the same effect as in the preceding experiment will occur, the water will be more violently decomposed, and the hydrogen — but apparently the potassium — will burn instantaneously with a beautiful violet flame. Potassium hydrate, KHO, 104 EXPERIMENTAL CHEMISTRY. remains in solution in the water. It is a base like sodium hydrate. Experiment 4. — What sodium and potassium accomplish at ordinary temperatures, iron can do if it be heated to redness. Pass water in the form of steam, obtained by boiling the water in a flask, or a retort, through a red-hot iron pipe, as a gun or gas barrel, containing small iron nails or wire. At this high temperature the iron in the pipe unites with the oxygen in the water, forming a black oxide of iron, and the hydrogen is set free and may be collected in the manner described below. The reaction is as follows : 4 H2O + 3 Fe = Fe^Oi + 4 Hj. The best means, however, for obtaining hydrogen is by the decomposition of an acid by iron or some other metal, zinc being generally chosen for the purpose. Collection of Gases. — For collecting considerable quantities of gases the following contrivance, called a pneumatic trough, may be used. Make a shelf out of slate or a piece of lead, from three to four inches broad, and so long that it will rest about half way up the sloping sides of a pan or wash-hand basin ; cut a hole about half an inch in diameter through the centre of the shelf, and having placed the latter in position, •n,. „g pour into the pan sufficient water to cover it an inch deep. The shelf ig for the purpose of supporting the vessel intended for the reception of the gas, which, filled with water, is placed with its mouth exactly over the hole. The gas to be collected is then delivered from a tube, the extremity of which is placed directly under the mouth of the inverted vessel. The accompanying figure conveys an idea of the kind of apparatus required. Experiment 5. — Put half an ounce of granulated zinc * in a bottle or flask, and pour over it a little water. No action takes place, but if a small quantity of sulphuric acid be gradusdly added, efiervescence, and heating of the mixture will ensue. The effervescence is caused by the escape of * Zinc is granulated by being melted, in an iron ladle or spoon, and poured from the height of a few feet into cold water. HTDEOGEN. 105 hydrogen gas. Insert into the mouth of the bottle a cork, which has previously been perforated and fitted with a tube bent BO that the mouth of it may be conveniently placed beneath the hole in the shelf of the pneumatic trough.* Allow time for the hydrogen to displace the air contained in the flask and bent tube (two or three minutes is sufficient if the effervescence is tolerably brisk). While the air is being expelled, preparation may be made for collecting the gas by filling several bottles quite full of water. One of the bottles is then closed with a smooth card or glass plate, and rapidly inverted in the pneumatic trough with its mouth directly over the hole in the shelf. The tube being then placed beneath, the gas will ascend and displace the water in the bottle. When the entire displacement is effected the bottle is corked or stoppered while still in the trough, removed and replaced by another bottle, inverted in the same manner, and so on until the evolution of gas ceases. There is one indispensable caution to be observed in experimenting with hydrogen, which is, not to begin to collect the gas until all the atmospheric air existing in the flash has been expelled, as otherwise an explosion might take place. To be quite safe, it is as well to reject the first bottleful of hydrogen collected. PEOPEETIES. Experiment &. — Inflame hydrogen contained in a bottle, and immediately pour in some water. The water -p. gg does not extinguish the flame, but rather in- ' creases it, since it rapidly forces the gas out of ^F^ the flask. The gas does not bum in the interior of the vessel, but only on the outside, where it is surrounded by atmospheric air. Experiment 7. — Open a bottle of hydrogen under an inverted tumbler, and, after a minute I or two, apply a lighted taper to the mouth of the tumbler. A flame will burst forth from the tumbler * Instead of a rigid glass tube, it is more convenient for this and similar purposes to carry the gas to the pneumatic trough by means of a piece of india-rubber tubing, of about one-eigljth of an inch internal diameter. It may be slipped over a short piece of glass tubing which passes through the cork. 106 EXPBEIMENTAL CHBMISTET. with a slight report. The gas has ascended from the bottle into the tumbler, and is consequently lighter than common air. In this experiment the lower vessel must not be immediately exposed to the lighted taper, because, if all the hydrogen is not displaced, an explosion might ensue that might break the bottle ; but if the taper be applied after ten minutes have elapsed, the bottle will be found no longer to contain any combustible gas, the gas having entirely escaped. Hydrogen is the lightest of all gases. Its specific gravity is 1, and 14J measures of it weigh only as much as one measure of atmospheric air. On account of this lightness, it may be used for filling balloons. Experiment 8. — If, instead of the glass tube, a piece of J.J ^Q tobacco-pipe be adapted to the cork of the flask from which hydrogen was evolved, and the gas then lighted, it will burn like a taper. To kindle the gas, instead of a match or a taper, very finely divided platinum may be employed. This can be prepared in a few minutes by dropping a solution of platinum chloride on blotting-paper, attaching it to a wire, and igniting it over a spirit-lamp, till nothing but a grey coherent ash remains. I^The platinum is thus reduced to an extremely I minute state of subdivision, and in this state it exhibits the remarkable property of igniting in hydrogen and inflaming it. It is called spongy platinum, and is employed as tinder in the well-known JDohbereiner's The apparatus here represented consists of a flask, having the bottom broken off, and to the neck of which the cover of the glass vessel, c, with the cock, e, is fastened air- tight. A piece of zinc is suspended in the flask by means of a wire. If diluted sulphuric acid is now poured into the vessel, c, upon which the cover with the flask, attached is placed, then, the cook being opened, that the air contained in the flask may be displaced by the acid from beneath, hydrogen is immediately evolved by the contact of the zinc with the acid, which hydrogen must be collected in the flask by closing the cock, e, the acid being thereby forced into the exterior vessel, until it no longer touches the zinc. Upon opening the stop-coik, e, the gas issues from the fine HYDEOGEN. 107 jet, and is directed against the spongy platinum, /. As the gas escapes, the sulphuric acid passes again into the interior vessel, and gene- rates fresh hydrogen upon reaching the zinc. Spongy platinum possesses, in a high degree, the power of absorbin oxygen and condensing it within ii pores ; if hydrogen be then presented i it, these two gases will be brought int such intimate contact, by the powerfi I force of attraction, that they will chem cally combine to form water, and th heat thus liberated is sufficient to ignii ^ ^^£f the' platiniun tinder, and to inflame the ~ gas, which subsequently issues from the jet. Many aeriform bodies, which do not freely unite with each other, can be forced to combine by means of spongy platinum. Experiment 9. — To observe the remarkable lightness of hydrogen, a small balloon of gold-beater's skin may be filled with hydrogen by means of the apparatus used in Ex- periment 5. The balloon is squeezed flat to expel the air, and the tube delivering the gas is passed a short way into its orifice, and secufed there with a piece of thread. When the inflation is complete, the tube is withdrawn, and the twine tightened simultaneously, thus preventing any escape of gas. The balloon, if unimpeded, will then ascend to a great' height. It may be made captive with a piece of thread. Experiment 10. — Pour the contents of the flask in which the hydrogen was generated (Experiment 5) into a porce- lain dish, boil until they are reduced in bulk to one-half or thereabouts, and filter them (page 49). A black residue will remain on the filter, which consists of the impurities contained in the zinc; the zinc itself has been dissolved^ and has been converted into a salt (page 97), called zinc sulphate, which, on the cooling of the solution, is deposited in colourless crystals. The reaction which takes place between zinc and sulphuric acid is represented by the following equation : Sulphuric Acid. Zinc. Zinc Sulphate. Hydrogen. H^CSO^) + Zn = Zn(804) + H^. 108 EXPBEIMBNTAL CHEMISTET. CHLOBINE. Symbol, CI = 35-5. Formula, Cla. Chlorine is one of a group, the members of which are characterized by a remarkable similarity of chemical properties. It consists of the elements cUorine, bromine, iodine, and fluorine, the three first of which are often termed hdogens (from aA.s, sea-salt), in allusion to their marine origin. Chlorine is a greenish-yellow gas, 2J times heavier than air, suffocating and irrespirable unless very much diluted with air. Its odour, when very dilute, is somewhat like that of sea-weed, a peculiarity wMch it shares with the ' other halogens. Chlorine occurs only in combination ; chiefly with sodium as common salt (sodium chloride, NaCl), which forms immense deposits in England and else- where, and is the chief ingredient of sea-water. PEEPABATION. Experiment 1. — Pour one ounce and a half of hydrochloric acid upon a quarter of an ounce of finely-powdered black oxide of manganese, and heat it gradually in a flask, to which p- ^2 is adapted a bent glass tube ; a yellowish-green gas is dis- engaged, which is collected by the process already described. The pneumatic trough is, how- ever, filled with warm water instead of cold. This gas is chlorine (from j^Xmpds, green). Fill with it several six-ounce bottles of white glass, and cork them up. FiU, likewise, a bottle with two-thirds of chlorine and one-third of water, and shake it up; suction is exerted upon a finger which closes the mouth of it, — a proof that a vacuum has been produced. If the finger be removed, the air immediately rushes in. This vacuum was caused by the chlorine having dissolved in the water, which might be inferred also from the disappearance of the yellow colour CHLOKINE. 109 from the upper part of the bottle. One measure of cold water dissolves two measures of chlorine. This solution is called chlorine water. The mode in which chlorine is formed in this experiment is shown in the following formula : > Manganese ' Manganese Peroxide. Chloride. MnOa + 4 HCl = Mn 01^+ 2B.J0 + Cl^. When the evolution of gas has quite ceased the liquid in the flask may be filtered and evaporated, when it will yield on cooling pink crystals of MnClg. Exiperiment 2. — Chlorine may also be prepared from common salt by mixing three quarters of an otmce of it with half an ounce of black oxide of manganese, two ounces of sulphuric acid, and one ounce of water, and heating the mixture : Sodium Manganese Sulphuric Sodium Manganese Gbloride. Peroxide. Acid. Sulphate. Sulphate. 2 NaCl+MnOi,+ 2 H^SOi = NajS04+MnSO,+2 H, O + Cl^ Chlorine acts as a poison on being inhaled; hence, care must he taken not to inhale it while preparing it. For greater security, pour some drops of alcohol and ammonia upon a cloth and wave it frequently in the air ; the chlorine contained in the air will then be so altered that it will lose its injurious properties. PROPBBTIBS. Experiment 3. — In order to recognise the odour of chlorine, spiell chlorine water (but not the gas) cautiously ; the chlorine water may be tasted also without danger. Experiment 4. — If a flask containing chlorine gas be ex- posed to the air for a short time, no diminution of the chlorine will be perceptible ; but if the flask be inverted it will soon contain only atmospheric air. Chlorine is two and a half times heavier than common air, and may be easily poured from one vessel to another like water without material waste; its specific gravity is 35'5 (H = l). Experiment 5. — -Introduce a piece of litmus-paper into chlorine gas, and it becomes white; pour chlorine water upon red wine, or ink, and both the liquids will lose their colour. Chlorine bleaShes and destroys most colours derived 110 EXPERIMENTAL OHEMISTEY. from, the animal or vegetable hingdom. In coneequence of this property, chlorine has become a most important agent in bleaching ; and linen, cotton, paper, and other materials, may be rendered perfectly white by it in a few hours ; while, by the old method of laying them on the grass in the sun, weeks, and even months, were required for effecting it. Substances called antichlors are sometimes used to remove the last traces of chlorine. Sodium hyposulphite is the most powerful. The modern method of bleaching is very excellent, and does not in the least injure the strength of the fabric, provided aU the chlorine be completely removed after the bleaching is finished, which is not so easily done as might be supposed. If this precaution is not observed, or if the chlorine water is too strong or in excess, then, indeed, after the colour is destroyed, the fibres of the yarn or fabric itseK will be attacked. The substance commonly called chloride of lime is now used instead of chlorine. It is a salt from which chlorine is easily disengaged, even by mere exposure to the air. Experiment 6. — Apply chlorine water to decaying and nauseous substances (water in which flowers have been kept, manure, rotten eggs, &c.) ; the bad odour will at once entirely vanish. Thus it not only decomposes colours, but also the volatile comhinations formed during putrefaction, and which occasion disagreeable odours. It acts in a similar manner also upon morbific matter (matters of contagion, miasmata), which, being diffused in the air or attached to clothes and beds," may communicate disease. Chlorine is, therefore, a powerful disinfecting agent, and is used for purifying all putrefying matter and infected atmospheres, and for arresting the decay of organic substances. Musty casks may also be purified by wasfing them first with chlorine water, and then with some milk of lime. Mouldy cellars, in which milk or beer cannot be kept without turning sour, are again rendered serviceable for a long time by fumigating them with chlorine gas, or by washing them with chlorine water, or a solution of. chloride of lime. Experiment 7. — Fill a small bottle with chlorine water, and invert it in a vessel filled with water ; if this is put away in a dark place, it remains unchanged ; but if it is exposed to the sun, a colourless gas will collect in the upper part of the OHLOEINB. Ill in which a glowing taper will inflame ; this gas is oxygen. After some days the water will entirely lose its odour of chlorine, and will have acquired a sour taste, and instead of bleaching blue litmus-paper, it will redden it. Three elements only were present, the constituents of water and chlorine ; thus it is obvious that the chlorine must have united with the hydrogen of the water to form hydrochloric acid, the oxygen being set free : HsO + Cl2 = 2 HCl + 0. Bottles in which chlorine-water is kept should, therefore, be protected from the light, and this can be most conveniently done by pasting black paper round them. The bleaching and disinfecting power of chlorine is now easily explained by its strong affinity for .hydrogen. All animal and vegetable substances contain hydrogen, which is taken from them by chlorine. But if a single chemical pillar falls, the whole chemical structure tumbles with it. By the abstraction of the hydrogen, the colouring matter becomes colourless, the odorous principles scentless, the morbific matter innoxious, insoluble substances are very frequently rendered soluble, &c. Experiment 8. — Provide two bottles of chlorine, and place in one of them some dry calcium chloride. This salt eagerly absorbs water, and wUl thoroughly dry any gas in contact with it. In a few hours introduce a piece of blue litmus- paper into the dry chlorine ; no change in the litmus will be apparent, or, at most, it will be but slightly reddened. Perform the same operation in the pther bottle, and the litmus-paper will be rapidly bleached ; proving that the presence of water is necessary to enable chlorine to exert its power in this respect. Experiment 9. — Put into chlorine water some gold-leaf; it will soon disappear, as the element chlorine combines with the element gold. The combination is called auric chloride ; it is soluble in water. Chlorine has a very great tendency to combine mih the metals. These combinations com- port themselves as salts ; they are called metallic chlorides, and most of them are soluble in water. Experiment 10. — Pour into a vessel filled with chlorine gas a little metallic antimony, in fine powder ; it wiU fall in a 112 EXPERIMENTAL CHEMISTRY. red-hot state to the bottom, as though it were a shower of fire. The red heat is caused by the violent combination of the chlorine with the antimony. The white smoke which fills the Bask is the new combination formed, viz., antimonic chloride. If a fine brass wire, on which a piece of tinsel has been fastened, be introduced into chlorine gas, both will burn with vivid combustion, and with the emission of fumes. Here combustion is another name for combination with chlorine. Brass consists of zinc and copper ; accord- ingly, chlorides of zinc and copper are formed. Both dissolve in water, and the copper chloride imparts to the solution a green tinge. Experiment 11. — If a piece of sodium of the size of a pea is thrown into a cup c6ntaining chlorine water, it um. Hold the end of the tube from which the gas is ssuing in a flame. You will perceive that the gas burns rith a greenish flame as long as the jet is heated, but that it foes out when the lamp is removed. Ammwnia will ham jhen strongly heated. During its combustion its hydrogen is xidized to water, and its nitrogen escapes ffee. 156 EXPERIMENTAL CHEMISTRY. Experiment i. — Remove the stopper downwards from a bottle of ammonia, and afterwards immerse the mouth of the bottle in water. The water wiU rise rapidly, and if the bottle was quite full of gas, will fill it. If a piece of '•-red litmus-paper is dipped in the water of the bottle its bhie colour will return. Ammonia is soliible in water, and its soiaijmi is a base. On\yolume of water at freezing point will dissolve 1149, and at Srdinary temperatures about 700 volumes of the gas, so that ifii is even more soluble than hydrochloric acid. A concentrated, solution of it may be prepared like that of hydrochloric Acid (page 113). It is sold under the name of solution of ammonia, or " liquor ammonise," and has a specific gravity of 0-88. Weaker solutions are sometimes called " hartshorn,"* or " spirits of hartshorn," because they were formerly obtained by the distillation of horn. Experiment 5. — Ammonia gas, like hydrochloric acid, can easily be prepared by gently heating its concentrated solution.- By prolonged boiling all trace of ammonia may be removed from water. Experiment 6. — The direct combination of ammonia and hydrochloric acid gases has already been noticed (page 13). The. experiment may be repeated with equal volumes of the pure gases. Sal-ammoniac or ammonium chloride is formed : NH3 + HGI = NH,C1. Experiment 7. — Carefully neutralize a dilute solution of ammonia with nitric acid, so that it has no effect on either blue or red litmus. The solution will contain a salt called ammonium nitrate, which may be obtained in the dry state by evaporation : NHa-t-HNOs = NH^NOs. Ammonium compoimds. — The compounds of ammonia are so similar in many of their properties to those of potassium and sodium, that they are generally supposed to be analogous in structure, and to contain a sort of compound metal called ammonium, NH^, which has recently been isolated. When the gas dissolves in water it is assumed that the hydrate of this quad metal is formed : NH3 -)- H2O = NH^HO. The theory cannot be proved, but it is probable and useful. The AMMtfNIUM COMPOUNDS. 157 following table shows tie analogy which on this view exists' between potassium and ammonium salts :— K HO Potassium Hydrate. NH< HO Ammonium Hydrate (?). K 01 „ Chloride. NH, CI „ Chloride. K NO3 „ Nitrate. NH4 NO3 „ Niti-ate. K^SO, „ Sulphate. (NHJj SO4 „ Sulphate. It wiU be seen that to represent the composition of any ammonium salt we need only take the formula of the corresponding potassium or sodium compound and write NH4 instead of K or Na. It must be remarked that although solution of ammonia may contain the hydrate NH^HO, no proof that such is the case has been obtained. Experiment 8. — Put about an ounce of mercury into a mortar and press into it with the pestle a few fragments of clean dry sodium. The two metals will combine with a flash of light, and a semi-fluid mass called sodium amalgam will be obtained. When cold, throw this into a tumbler about one-third full of a cold saturated solution of sal-ammoniac. The amalgam, will immediately begin to swell, and will soon assume such an enormous volume as to float in the liquid as a metallic mass, which feels like butter. From the moment of its formation, however, this curious substance begins to change into ammonia, hydrogen and mercury. It is called ammonium amalgam, and it is believed to be formed by the temporary combination of the ammonium, which has lost its chlorine, with mercury. The following formula, in which n denotes an unknown mmiber of atoms, explains its for- mation : NH,C1 -f NaHg„ = NH,Hg„-f NaOl. By washing with water the mercury is afterwards recovered without loss. The specific gravity of ammonia gas is 8 '5, a little more than half that of air (14-47). By a pressure seven times that of the atmosphere the gas can be condensed into a liquid, and if cooled to -75° 0. (-103° F.) it freezes to a transparent, ice-like solid. It must be borne in mind that the name ammonia is often given to the solution, which should be called ammonium hydrate. 158 EXPEEIMBNTAL CHEMISTBY. COMPOUNDS OF NITROGEN AND OXYGEN. Oxides. Corresponding Acids. N2O Nitrous oxide. NjOa or NO Nitric oxide. N2O3 Nitrous anhydride. HNO2 Nitrous acid. N2O4 or NO2 Nitric peroxide. NjOj Nitric anhydride. HNO3 Nitric acid. Of these compounds nitric acid is undoubtedly the most important, and as, moreover, it is the source from whence the other oxides are obtained, it claims our first attention. The oxide N2O5, nitric anhydride, corresponding to nitric acid, is prepared with difficulty. It is a white, crystalline solid, wHch combines eagerly with water : N20e + H2O = 2HNO3. Nitric Acid or Aquafortis, HNO3. Experiment 1. — Introduce into a small retort half an ounce of powdered saltpetre and half an ounce of common sulphuric acid, and let the retort stand erect for some time, in order that as much as possible of the sulphuric acid re- mainiag in the neck may flow down into the retort Then surround the latter with sand contained in an iron basin, adapt to the ■^ beak of it a receiver, wrap I round the joint some strips ■ of moistened blotting- paper, and heat gently. In a short time a yellowish fuming, fluid passes over into the receiver, which is placed in a vessel filled with water, and must "frequently be sprinkled with cold water ; this fluid is heavier than water, and is called nitric acid. Saltpetre is potassium nitrate, KNO3. When it is acted upon by sulphuric acid the metal and part of the hydrogen change places ; we get nitric acid and a salt, called hydrogen potassium sulphate, HKSO,, in which half the hydrogen of the acid is replaced by potassium : KNOs + BSOt = HNOs + HKSO4. NITEIO ACID. 159 At a higher temperature the hydrogen potassium sulphate will decompose another molecule of potassium nitrate : ■ KNO3 + HKSOi = HNO3 + K^SO^ ; but on the small scale it is better not to push the action so far or the retort will be apt to break. Ki^SOj is called neutral, or di-potassium sulphate. By using perfectly dry potassium nitrate and concentrated sulphuric acid, true nitric acid, HNOj, can be obtained as a yellowish liquid, which fumes strongly when exposed to the air. It is hence called fuming nitric acid, and is the strongest that can be prepared. It is one and a half times heavier than water, its specific gravity being 1-52. A weaker kind is commonly met with in commerce as ordinary nitric acid, or aquafortis. It consists of 60 parts of true nitric acid and iO of water, and has a specific gravity of 1"42. This acid is colourless when pure, but usually possesses a yel- lowish tint. When very strong or very weak nitric acid is heated, acid of this strength is obtained. It can be distilled unchanged. Experiment 2. — A drop of nitric acid is sufficient to acidify several spoonfuls of water, and even at a greater dilution it will redden blue litmus-paper ; nitric acid is accordingly dis- tinctly characterised as an acid. Eo^eriment 3. — If lead be heated for a long time in the air it abstracts oxygen from it, and becomes converted into a reddish-yellow powder^ called lead oxide, or litharge. Take up a small portion of this litharge on the point of a knife, put it into a test-tube, and add some dilute nitric acid. The greater part will be dissolved by gentle heating. Filter the solution while warm, and put it in a cold place ; a salt wUl be deposited from it in white brilliant crystals ; this is lead nitrate. This shows that lead oxide is a basic oxide, as it combines with acids forming salts. ■ Nitric acid dissolves most of the metallic oxides, and forms with them salts, all of which are soluble in water. For this reason, nitric acid is often used for cleaning metals, for in- stance, copper and brass instruments, which, during the pro- cess of annealing, soldering, &c., have become covered with a coating of oxide. Experiment 4. — Pour over some shot, common nitric acid. 160 BXPEEIMBNTAL CHEMISTET. slightly diluted with water ; a solution is also effected in this instance, but it is accompanied by the evolution of a yellow- ish-red vapour of a suffocating smell. This vapour is nitric peroxide. Part of the nitric acid is decomposed, while another part of it combines with the lead, and forms the same salt, as in the former experiment. This likewise crystallises from its solution, if it is evaporated until a film forms on its surface. In this case the lead is apparently dissolved, but it is ob- vious that this is quite a different kind of solution from that of common salt or sugar in water. The salt and sugar are unchanged in the solution, while the lead is not contained in the liquid as a metal, but as a salt, a nitrate. The same thing occurs with all other metals which are soluble in nitric acid ; as, for example, with sUver, mercury, copper, iron, &c. Gold is not dissolved by it ; hence gold may be separated from silver by means of nitric acid. Nitric acid readily parts with a portion of its oxygen. It is therefore a powerful oxidizing agent. Experiment 5. — Place a few fragments of tin in a wine- glass, and pour over them a little nitric acid. A violent action is set up, and red suffocating fumes are copiously evolved. The tin is not dissolved and converted into nitrate as the lead was, but becomes a white insoluble powder, an oxide of tin called meta-stannic acid. Experiment 6. — Some of the non-metallic elements, as well as of the metals, are oxidized by nitric acid ; charcoal, on being boiled in it, becomes carbonic anhydride ; sulphur, sulphuric acid ; phosphorus, phosphoric acid, &c. In all these cases yellowish-red fumes are evolved. Experiment 7. — Organic substances also, as wool, feathers, wood, indigo, &c., are oxidized and decomposed by heating them with nitric acid. This sort of decomposition may be regarded as combustion in the moist way. If substances of animal origin are allowed to remain for a short time only in contact with this acid, they will assume a yellow colour. In this manner wood may be stained, and silk may be dyed yellow ; the hands and clothes are also stained yellow by nitric acid. Cotton undergoes a most remarkable change if soaked for a short time in the strongest nitric acid ; it will then detonate and explode, like giinpowder, only far more NITEOUS OXIDE. 161 violently (gun-cotton). Strong nitric acid is partially decompoBed, and coloured yellow, by the rays of the sun. If you colour some water blue in a test-tube with one drop of solution of sulphate of indigo, and add to it oi} boiling one drop of nitric acid, the blue colour will disappear. This reaction often serves for the detection of nitric acid. Experiment 8. — The nitrates are easily decomposed. Having powdered some of the nitrate of lead, obtained in Experiment 3 or 4, throw it upon a red-hot coal ; active combustion of the coal will ensue, at the expense of the nitrate, and globules of metallic lead will remain beyond. Nitric acid is monobasic ; that is, it contains but one atom of hydrogen which can be replaced by metals. Its salts are called nitrates, and it must be remembered that they all con- tain the monad radical, NOj. HKTOs Nitric acid. KNOg Potassium nitrate. NH^NOg Ammonium nitrate. Cu"(N03)2 Copper nitrate. Bi"'(N03)3 Bismuth nitrate. The nitrates are less easily decomposed than the chlorates, , but they resemble the latter salts in the readiness with which they part with their oxygen to combustibles. In consequence of this property, potassium nitrate is a constituent of some inflammable and explosive mixtures, such as gunpowder, fuses, coloured fires, &c. Nitrous Oxide, N 0. Experiment 1. — Cautiously heat the ammonium nitrate, made by Experiment 7 (page 156), in a Elorence flask to which a gas delivery tube is connected. The salt will gradually melt and soon effervesce briskly, as a gas — nitrous oxide — is evolved. When the air has been expelled from the flask the issuing gas may be collected at the pneumatic trough, which must be filled with warm water instead of cold, as the gas is soluble in the latter. The change which occurs is simple. Heat decomposes ammonium nitrate NH4NO3 entirely into water and nitrous oxide : NH4N08 = 2HaO-|-N20. 162 ' BXPEKIMENTAL CHEMISTET. Nitrous oxide is seen to be a colourless gas. It can, however^ be condensed to the liquid state by great pressure. It is respirable in moderate quantity, and its effects when inhaled are peculiar. At first it produces a pleasurable kind of intoxication — whence its name of hmghing gas; but after a time it causes complete insensibility to pain. It is now much used as a substitute for chloroform in minor surgical operations. Nitrous oxide is a good supporter of combustion, its power in this respect being little inferior to that of oxygen. The experiments which were performed with the latter gas may be repeated with nitrous oxide, with little difference in their results. Nitric Oxide, NO, m- N2O2. Tkeperiment 1. — Pour over a few scraps of copper, placed in a wide-mouthed bottle, a little water, and then add by degrees some nitric acid, until a brisk effervescence ensues. This effervescence is caused by the evolution of nitric oxide, which must be collected in a jar of white glass over the pneumatic trough. Close the mouth of the jar under water ; it seems to be empty, for the nitric oxide is colourless ; but if the jar be opened, and air be carefully blown in, then the jar becomes fiUed from above downwards with yellowish-red vapours. The nitric oxide takes thereby from the air one atom of oxygen, and is converted into nitric peroxide. NO becomes NO2. On account of this property, it has an im- portant application in the preparation of common sulphuric acid (page 148). The following is the somewhat complicated formula which describes the formation of nitric oxide : Nitric Acid. Copper Nitrate. 8HN0a + 3Cu = 3Cu"(NOs)2 + ffl^O + 2N0. The copper nitrate remains as a blue solution in the bottle, and it may be obtained in crystals by evaporation. Nitric oxide supports combustion, although not with the readiness of PHOSPHORUS. l63 flitrous oxide. If a piece of phosphorus be ignited and plunged into nitric oxide while feebly burning, it will be extinguished, but if the phosphorus burns briskly when immersed in the gas the combustion proceeds with energy. Nitrous anhydride, N2O3, is a red gas, easily condepsed to a blue liquid by cold. With water it forms the very unstable nitrous acid, HNO2. Nitric peroxide, NO2, or N2O4, is the red gas formed when nitric oxide comes in contact with excess of oxygen. It is absorbed by water and converted into a mixture of nitrous and nitric acids : aiSrOa + H2O = HNO2 + HNO3. PHOSPHORUS. Symbol, P = 31. Formula for vapour, P^. Great care is required in experimenting with phosphorus that it does not take fire at an unseasonable moment, as it continues burning with the greatest violence, and might occasion dangerous wounds. It may catch fire even when lying upon blotting-paper, particularly in summer-time, or by the heat of the finger. Hence it must be kept, and also cut, under water. On being taken from the water, it should be held by a pair of forceps, or be stuck on the point of a knife. Prudence also would dictate to experiment with small quantities only at a time, and to have a vessel of water in readiness, in which it may be quenched in case it should catch fire. Phosphorus, like sulphur, melts, boils, evaporates, and bums, but far more easily and rapidly. In winter it is brittle, in summer flexible as wax. When pure d,nd freshly prepared it is colourless, transparent, and amorphous (non- crystalline), but after a time it becomes yellow, and coated over with a white crusti Phosphorus is insoluble in water, but soluble in ether, carbon disulphide, and oils. Phosphorus is an exceedingly violent jjoiaon, and is, for this reason, frequently employed for the extirpation of rats and mice. The rat paste, as it is called (phosphorus dough), is composed of one drachm of phosphorus, 8 ounces of hot water, and 8 ounces of flour. 164 EXPEBIMENTAL OHEMISTET. Prffparation of Phosphorus. — Phosphorus was formerly obtained from urine, but is now prepared from bone-ash. Bones consist chiefly of gelatin (or rather ossein)^ and calcium phosphate, Ca"3(P04)2. When the bones are cal- cined the gelatin burns away and the phosphate remains. The ash is treated with sulphuric acid, which converts the greater part of the calcium into the insoluble calcium sulphate, CaSOi, while impure phosphoric acid remains in solution. This is dried with charcoal powder and intensely heated in a clay retort. The carbon takes oxygen from the acid, forming carbonic oxide gas, CO, which escapes with the hydrogen 6f the acid. The phosphorus also comes over as gas, but is condensed by passing through cold water. The changes which occur in the above processes are somewhat more complicated than the description, which is only intended as an approximation, would imply. Experiments with Phosphorus. Ea^eriment 1. — Put into a smaU flask first a quarter of an ounce of ether, then a piece of phosphorus, of the size of a pea. Cork the flask and let it stand some days, frequently ' shaking it. Decant the liquid ; it contains in solution about one grain of phosphorus, and will serve for the following experiments. Eayperiment 2. — Pour some drops of this solution upon the hand, and rub them quickly together ; the ether will evaporate in a few moments, but the phosphorus will remain upon the hands in a state of minutest division. The more finely it is divided, so much the more easily does it combine with the oxygen of the air. During this combination it diflfuses a white smoke and a f»iut light (it phosphoresces), causing the hands to shine in the dark ; hence its name, phosphorus, from ^Ss, light, and ^ipai, to carry. It under- goes slow combustion and is converted into phosphorous anhydride, P2O3, which rapidly takes up water from the air and becomes phosphorous acid : PA + SHjO = 2H3P03. Experiment 3. — Moisten a lump of sugar with the solution of phosphorus in ether and throw it into hot water. The surface of the water will glow prettily in a dark room. PHOSPHOEUB. 165 I^eriment 4. — Instead of ether use a few drops of carbon disulphide to dissolve the phosphorus. This liquid takes up more phosphorus than ether does, and the solution is highly- dangerous. It is the basis of the modern " Greek fire." Its inflammability may be observed in the following way : Eayperiment 5. — Pour some of the solution upon fine blotting-paper ; the latter ignites spontaneously after the liquid has evaporated. The more minutely the phosphorus is divided, so much the more readily it begins to burn. Es^eriment 6. — Put a piece of phosphorus of the size of a pea on blotting-paper, and sprinkle over it some soot or pul- verised charcoal ; it melts after a while, and spontaneously inflames. The finely pulverised charcoal ca,uses this com- bustion, owing to its porosity. It eagerly absorbs oxygen from the air, imparts it again to the phosphorus, and, being a bad conductor of heat, the cooling of the latter is pre- vented. Phosphorus is also easily ignited by friction, and is, for this reason, employed in the manufacture of lucifer-matches. The combustible mass is prepared from hot mucilage, at 158° P. (70° C), to which small pieces of phospjiorus are added, being thoroughly incorporated with it by constant rubbing till cold. But as the mass, by becoming hard on drying, prevents the access of air to the phosphorus, there must be added some substance rich in oxygen, as black oxide of manganese, nitre, or red-lead, from which the phosphorus can abstract the Pig. 61. oxygen necessary for its ignition. If part of phosphorus, 4 of gum Arabic, i of water, 2 of nitre, and 2 of red-lead, form a good inflammable mass. A temperature of 149° F. (65° 0.)— 158° F. (70° C.) is re- quisite for kindling such matches ; in this case the temperature is caused by friction. The coating of the match is thus broken and kindled, and the continued burning is now maintained by the oxygen of the air. i BxpertTaent 7. — Put a piece of phos- j^ phorus, of the size of a pea, into a wine- glass, and pour hot water upon it until the glass is half filled ; the phosphorus melts, but doefi not 166 EXPEEDBENTAL OHBMISTET. ignite, as access of air is prevented by the water. But if air ba carefully blown by the mouth through a long glass tube upon the bottom of the wine-glass, combiiation will ensue, which is visible, especially in the dark. Experiment 8. — Heat gently a piece of phosphorus of the size of a pea, placed in the middle of a glass tube, about twelve inches long. When igni- tion commences, remove the lamp. While the tube is held horizon- tally, the combustion is feeble and imperfect, because the heavy smoke, consisting of phosphoric and phosphorous anhydrides, passing off slowly, allows the admission of only a small quantity of air. But the com- bustion immediately becomes more vivid on inclining the tube, and when the tube is held perpendicularly it is com- plete, as then the draught of' air is most powerful. In this way phosphorus may be oxidized to either degree required ; it may be slowly burnt to form phosphorous anhydride, or completely, to form phosphoric anhydride. Phosphorus, like sulphur, is capable of existing in several different states {aUotropic states). Besides the ordinary kind the most interesting is that called red, or amorphous phos- phorus. This is prepared by heating ordinary phosphorus to a temperature of about 240° C. (464° P.) for some time, in a vessel filled with carbonic anhydride to prevent it fiom burning. Eed phosphorus is curiously different in properties from the ordinary kind, being insoluble in carbon disulphide^ not poisonous, and only inflammable at a high temperature. It is now used extensively in the manufacture of "safety matches." The tips of these matches do not contsdn phosphorus, but when rubbed on the outside of the box they take up a little of the red phosphorus with which the side is covered, and combustion ensues. PHOSPHINE, PH,. Experiment 1. — Put into an ounce flask a quarter of an ounce of slaked lime, and a piece of phosphorus the size of a pea, fill it up to the neck with water, and place it in a small vessel containing a strong solution of salt, prepared by adding PHOSPHINE. 1G7 half an ounce of common salt to an ounce and a half of water. Fit to the flask a bent glass tube, one end of which is made to dip into a basin of water ; heat the salt water to boiling, and a gas will be evolved, which, as it issues from the tube Fig. 63. and comes in contact with the air, taltes fire spontaneously. This gas consists chiefly of phosphine, or phosphuretted hydrogen, but contains several combinations of phosphorus and hydrogen. If you collect it in a small jar filled with water, it immediately takes fire upon the admission of air. Both the phosphorus and the hydi-ogen combine with the oxygen of, the air, and there results phosphoric anhydride, P2O5, and water, H2O. The first appears as a white smoke, which, when it issues in separate bubbles from the water, rises in rings. Phosphuretted hydrogen, when unburnt, emits the smell of garlic. In this experiment, the flask is placed in salt water, in order to guard against the ignition of the phosphorus, in case the flask should accidentally break. Salt water, at the strength specified, will not boil under 228° F. (109° C.) ; consequently, the boiling in the flask is more active than if it had been placed in pure water, the temperature of which, under ordinary pressure, can only be raised to 212° F. (100° C). The apparatus for heating substances by means of hot water or saline solutions is called a water or saline hath. By such contrivances extracts are evaporated, and substances dried, which, at a stronger heat, would easily bum, or other- wise be decomposed. Phosphine, when pure, is inflammable, but not spontaneously inflammable. When prepared as above it contains a little of the vapour of another compound of phosphorus and hydrogen 168 EXPERIMENTAL OHEMISTEY. — a liquid — which has the formula P2H4. It is the latter compound which is spontaneously inflammable. COMPOUNDS OF PHOSPHOBUS AND OXYGEN. P2O3, Phosphorous anhydride. P2O5, Phosphoric anhydride. It has been already stated that these oxides can be formed by the direct union of oxygen and phosphorus. The lower oxide and its corresponding acid are unimportant. Both oxides are white, snow-like powders, and they greedily com- bine with water to form acids. PJmsphoric Anhydride. Experiment 1. — Ignite a small piece of phosphorus on a plate and cover it with a dry bottle or bell-jar. Phosphoric anhydride will be abundantly formed, as a white cloud, which settles on thfr sides of the bottle and on the plate. Shake the powder into a saucer, and pour a little water on it. A sharp hissing noise will be heard, testifying to the energy with which combination ensues. A solution of phos- phoric acid is produced. Phosphoric Acid, H3PO4. Experiment 2. — Place a piece of phosphorus and a little water in a flask, and carefully heat them until the water boils ; then add half an ounce of nitric acid and continue the heat. The phosphorus slowly dissolves, and is oxidized into phosphoric acid. Phosphoric acid prepared in this way is of course contaminated with the excess of nitric acid left undecomposed. This can be removed by evaporating to dryness and boiling the residue with water. Phosphoric acid is tribasic, containing three replaceable atoms of hydrogen ; and inasmuch as one, two, or all three of these atoms may be replaced by metals, its salts are very numerous. With sodium, for instance, the three following salts may be obtained : NaHgPO^ Sodium di-hydrogen phosphate. NajHPOi, Di-sodium hydrogen phosphate. NasPOj, Tri-sodimn phosphate. PHOSPHORIC ACID. 169 A very great variety of compoimd salts may be formed by substituting part of the hydrogen with one metal, and part with another. As, for instance, in ammonium magne- sium phosphate, NH^Mg'TOi, in which one atom of hydro- gen i^ replaced by the monad group of atoms, or compound radical, NH4, and the remaining two atoms by the diad metal magnesium, Mg". Hxperiment 3. — Add ammonia to a solution of sodium phosphate, and then a little solution of magnesium sulphate, Mg"S04 (Epsom salts). A white precipitate will be pro- duced, consisting of the above-mentioned ammonium magne- simn phosphate : MgSOi + Na^HPOi + NH.HO = ^8280,4- NH^Mg'TOi + H2O. Phosphoric acid or any other soluble phosphate would pro- duce the same effect. Ammonium hydrate and magnesium sul- phate therefore serve as a test for phosphoric acid and its salts. The body of an adult man contains from 9 to 12 pounds of bones, containing „ 6 „ 8 pounds of bone ashes, containing „ 5 „ 7 pounds of calcium phosphate, containing „ 1 „ If pounds of phosphorus. Phosphates are also contained in the blood, flesh, and other "portions of the body. Whence does it obtain this phos- phorus ? The answer is, from the meat and vegetables which it consumes. The phosphates occur in bread, in all kinds of grain, in leguminous and many other plants, particularly in their seeds. But how do the plants obtain these salts ? By means of the soil. If arable land contained no such salts, no seeds could be produced. If we increase their quantity by mixing ground bones with the soil, we place the latter in a situation to produce a larger quantity of grain ; consequently, bones furnish us with a powerful manure. Besides ordinary phosphoric acid, two other compounds of phosphoric anhydride are known, differing in constitution from ordinary phosphoric acid by the relative quantities of water combined with the anhydride. These compounds are distinguished by the prefixes " pyro " and " meta " from ordinary or or CoJce, or carbonised coal, has a grey colour, is more or less porous, is very hard, and has a metallic lustre ; it burns with- out forming soot, and gives out an intense heat ; hence it is an excellent fuel, and especially adapted for the smelting of iron, and for the heating of locomotive boilers. Coke is obtained as a secondary product in the preparation of illumi- nating gas from coal. Bone-black, or animal charcoal, is obtained by heating bones in close vessels. The carbon contained in it amounts i only to about one-tenth part of the whole, the other nine-tenths being bone-ashes ; but, notwithstanding this, its decolorising power is so strong, that it is preferred to all other kinds of charcoal as a means of abstracting colour from the syrup of brown sugar, or from other dark liquids. Two sorts of carbon found in the mineral kingdom, viz., graphite and the diamond, possess very remarkable, yet different, properties. GrojpMte, or plumbago, a grey substance, having a metallic 176 EXPEEIMBNTAL OHEMISTBT. lustre, imparts its colour so readily to other bodies, that it is used for makmg pencils, and for giving a black polish to iroji articles, such as stoves, &c. ; it is so soft and lubrica- ting, that it is added to grease for the purpose of preventing friction in wheels and machinery ; it is also so nearly incom- bustible, that crucibles are made of it, which stand the strongest heat without burning (blue-pots). Diamond is the hardest of all bodies. In external appear- ance it has not, indeed, the slightest resemblance to charcoal, yet it can be entirely burnt up in oxygen, and carbonic anhy- dride is the only product obtained from it ; and exactly so much is obtained as would have resulted from the combustion of an equally heavy piece of wood-charcoal or coke. In order to crystallise a substance, it must first be rendered fluid, which is done either by melting or diasolving it. Charcc$>l can neither be melted by the strongest heat, nor dissolved in any known liquid. Should a method ever be discovered for rendering it liquid, it is probable that diamonds could be prepared artificially. Carbon shows very clearly how one and the same body can have quite different forms and different properties. In wood- charcoal, soot, coke, and animal charcoal, it is black, without any determinate shape (amorphous), and very combustible; ' in graphite it is black, with a crystallised foliated structure, and is nearly incombustible ; in the diamond it is co1out1«ss, and is crystallised as a double four-sided pyramid (octahedron), and is likewise almosfinoombustible. Hence carbon is said to be dimor'phous, having two different crystalline forms. If a body can assume more than two crystalline forms it is said to be polymM-phous (having many forms). Charcoal undergoes no change on exposure to the air, or when imbedded in the ground. It is not decomposed at com- mon temperatures, that is, it does not enter into combiuation with the oxygen of the air or of water. But this, as is well known, takes place very readily, when heated to redness. It then burns and disappears, with the exception of a small quantity of ashes. The heat thus developed is the result of its chemical combination with the oxygen of the air. The gas generated is called carbonic anhydride, which forms, with lime-water, a white precipitate (calcium carbonate), as has been stated previously. CAEBON AND OXYGEN. 177 COMPOUNDS OF OAKBON AKD OXYGEN. Carbonic anhydride, CO2. Carbonic acid, H^COa (?). Carbonic oxide, 00. Carbonic anhydride, COj. — It has already been shown (page 126) that all ordinary kinds of fuel contain carbon, and therefore yield, during their combustion, carbonic anhydride, and that this gas may^be detected by lime-water, which is thereby rendered turbid, owing to the formation of calcium carbonate. Calcium carbonate occurs in nature in immense quantities as chalk, marble, limestone, &o. By treating calcium carbonate with almost any acid it is decomposed, and carbonic anhydride is liberated, which is thus procured more conveniently than by burning carbon. Em^eriment 1. — Place some fragments of white marble with a little water in the apparatus used for preparing hydrogen, and then add small quantities of hydrochloric acid until a brisk effervescence is produced. Carbonic anhydride is rapidly evolved, and as it is a heavy gas it may be collected in dry bottles by downward displacement (page 114). The reaction is as follows : Ca(C03) + 2HC1 = CaCla + H^O + CO^. Solution of calcium chloride remains in the bottle when all the marble has disappeared, and it may be yig. 67. obtained solid by evaporation. Experiment 2. — A burning taper is extinguished when held in carbonic acid, and it is fatal to men and animals if they inhale it. Carbonic acid gas can neither support combustion nor life. Experiment 3. — Invert a jar filled with carbonic anhydride over one containing only atmospheric air ; if after some moments you introduce into each of these jars a burning taper, that in tli~ upper vessel will continue to burn, while that i the lower one will be extinguished. Carboni acid is heavier than common air ; it has sunk inl the lower jar, while the atmospheric air has ascended into the upper one. If a bottle, filled with carbonic anhydride, be held with its mouth obliquely over N 178 EXPEEDTEirrAL CHEMISTKY. the flame of a lamp, so that the gas can flow ont, the light will be extinguished. Experiment 4. — Eepeat the experiment with the two jars, filling, instead of the upper one, ■the lower one with carbonic anhydride. If, after some hours, you add lime-water to both of the jars, and shake them, you will obtain in both of them a precipitate of calcium carbonate — a proof that the carbonic anhydride has partly ascended into the upper jar. Both gases have become intimately mixed, or the carbonic anhy- dride, though heavier, has ascended, and the common air, though lighter, has diffiised itself downwards. This voluntary mixing of the different kinds of gases together is called diffusion of gases. This diffasion of gaseous bodies, since it maintains a constant equality and balance of the constituents of the atmosphere, is of great importance in the economy of nature, and accounts for the fact that the constitution of the air is everywhere nearly uniform, although in one place free oxygen is withdrawn from it, and in another place carbonic acid is added to it. Experiment 5. — Fill a bottle containing carbonic anhydride half full of pure water, close it with the finger, and shake it ; the water takes up the carbonic anhydride, and, as a vacuum is formed, the finger is pressed into the mouth of the bottle by the external air. Carbonic anhydride is solvble in water ; and the solution is supposed to be one of carbonic acid : One measure of water will absorb about one measure of carbonic anhydride at the ordinary temperature of the air. If the gas be condensed by pressure, water will still absorb the same volume, but of course a much greater weight. The water thereby acquires an acid taste, and the property of effervescing. Experiment 6. — Throw a piece of chalk into vinegar ; vinegar is one of the weakest of common acids, yet it is able to expel carbonic anhydride. Formerly carbonic anhydride was only known in its gaseous state; but in recent times it has been converted into a liquid by strong compression at a low temperature. This liquid evaporates with such greait rapidity, that a cold of nearly —212° F. (^100° C.) is produced. By this means OAEBON AND OXYGEN. 179 chemists have succeeded in rendering carbonic anhydride a solid. It then has. the appearance of snow. Experiment 7. — To prove that carbon is contained in the colourless carbonic anhydride, take a test-tube, break the bottom of ^ig- ^8. it, and adapt to it, by means of rr=^IPiimuiiT i ri i^^ a perforated cork, a glass tube, 11 1 and connect it with a bottle 8 ^^^& in which carbonic anhydride is Ft ^Hf evolved. Introduce into the test- M \ ^-"Si^ Bi tube a piece of potassium of the »-;n3| ^ I H| size of a pea, previously dried l^^^" j ■ ^ r between blotting paper, and heat the place where it lies with a lamp. The potassium will remove the oxygen from the COj and black carbon will re- main in the tube. Garbonates. — Although we must regard carbonic acid, Hj COa, as hypothetical, its salts are well-known and stable com- pounds. They contain the diad radical 00s. The following are examples of important carbonates : NaHCOs, Sodium hydrogen carbonate. NagCOg, Sodium carbonate. Ca"C03, Calcium carbonate. Carbonic oxide, CO. — When charcoal during combustion has a sufficient supply of oxygen, carbonic anhydride, CO2, is formed ; but if there is a deficiency of oxygen, the lower oxide, CO, is produced. This gas is generally formed when charcoal bums slowly, for example, in a chafing-dish, because the ashes, accumu- lating round the pieces of charcoal, obstruct the access of air ; and it is also formed when the damper of a stove is closed, before the coal is burnt out, since in this case the draught of air, and consequently the supply of sufficient oxygen, is prevented. Carbonic oxide burns when kindled, with a blue flame ; it takes up the deficiency of oxygen not supplied to it by the air while forming, and is converted into carbonic anhydride ; that is, it takes up as much oxygen again, and CO becomes CO2. The blue flame which is often perceived in large masses of glowing coals is burning carbonic oxide gas. 180 KXPERIMENTAL CHEMISTET. Carbonic oxide can be prepared by passing carbonic anhydride through a red-hot tube containing fragments of charcoal : one molecule of carbonic anhydride combines with one atom of carbon, and forms two molecules of carbonic oxide : 00^ + 0= 2C0. The gas can be collected at the pneumatic trough. Car- bonic oxide is extremely poisonous when inhaled. COMPOUNDS OF GABBON AND HYDBOGEN. A great number of compounds of carbon and hydrogen are known, but most of them belong to the department of organic chemistry. A classification of them will be found in Part III., Chap. I. It will, however, be convenient to study two or three of them in this place. Methene, or Marsh Gas, CH^. — If the mud at the bottom of a pond is stirred up with a stick, bubbles of gas rise which consist chiefly of marsh gas, mixed with carbonic anhydride. Experiment 1. — FUl a wide-mouthed bottle with water, invert it in a pond and collect the bubbles which rise on stirring. The bottle can then be removed with a saucer. If a piece of moist potash is then passed up into the bottle, the carbonic anhydride will soon be absorbed. The remaining gas will burn when a flame is applied to its moutL This experiment proves, 1, that methene is formed during vegetable decay, and, 2, that it is an inflammable gas. Experiment 2. — Dry some sodium acetate thoroughly at a gentle heat, and weight out half an ounce of it. Then add half an ounce of dry caustic soda and three-quarters of an ounce of quick lime. Grind them together quickly in a mortar, and introduce the mixture into a dry Florence flask fitted with a somewhat wide delivery tube. On the application of heat methene is given ofij and can be collected at the pneumatic trough : Sodium Acetate. Sodiom Carbonate. NaOjHsOj + NaHO = NajCOs + CH^. The lime is only used to prevent the action of the alkali on the glass. Experiment 3. — Next to hydrogen, methene is the lightest CARBON AND HTDEOGEN. 181 of all known gases. Its specific gravity is only 8 (eigtt times heavier than hydrogen). Balloons may be filled with it as with hydrogen, and the gas be transferred from one vessel to another by the method of inverted pouring used in the case of hydrogen. Experiment 4. — We have already seen that methene is inflammable. In burning it is converted into carbonic anhy- dride and water : CH4 + 2O2 = CO2 + 2H2O. rill a soda-water bottle one-third with methene, and two- thirds with oxygen. On the application of a light a loud explosion will be produced. We see therefore that, like hydrogen, methene will burn either quietly or with explosion, according to circumstances. The dangerous fire-damp, as the miners call it, which is given out from the beds of coal in coal-mines, is almost pure methene. The disastrous explosions we so often hear of are caused by the accidental contact of a light with a mixture of fire-damp and air. Methene is not poisonous. Miners can work in an atmo- sphere largely charged with it, but its combustion produces the deadly poison carbonic anhydride. This hangs about the passages of a mine after an explosion, and often suffocates the poor creatures who have escaped from the explosion. The miners call it choke-damp, or after-damp. Methene is sometimes called " light carburetted hydrogen." Mhylene, or Olefiant gas, C2H4. — Sometimes called " heavy carburetted hydrogen." Experiment 1. — Mix one volume (half an ounce hy measure) of strong alcohol, or methylated spirit, with four volumes of strong sulphuric acid. Heat the mixture in a flask and collect over warm water the gas that is given off. It is ethylene. The sulphuric acid acts by removing the elements of water from the alcohol : Alcohol. C AO - H2O = C,H,. Experiment 2. — Ethylene may be burned at a jet, or at the mouth of a bottle, like methene. To explode it, it must be mixed with three volumes of oxygen : 182 EXPBRIMEHTAL CHBMISTBY. CA + 30^ = 2CO2 + 2B.fi. (2 vols.) (6 vols.) (4 vols.) (4 vols.) This will be apparent from the above equation, since the formula for every gas denotes two volumes of it (page 68). Experiment 3. — ^Mix equal volumes of ethylene and chlorine in a bottle over water. Allow the bottle to remain for a short time with its mouth under water. The two gases will combine, and an oily liquid, called ethylene chloride, or Dutch liquid, will be produced, and will float on the water : CaH^ -f- OI2 = C2H4CI2. Eayperiment 4. — Mix one volume of ethylene with two volumes of chlorine in a tall bottle or jar, and apply a light. A very curious combustion, attended with the formation of thick black smoke, -wiil take place. The chlorine com- bines with hydrogen, and carbon is separated : CJS.t+2Cl^ = 4HC1+20. Acetylene, C2H2. — This interesting gas is formed by the direct union of its elements when the electric light passes between two charcoal points in an atmosphere of hydrogen. All the processes for preparing it are difficult. OAKBON DISULPHIDB, OSj. Just as charcoal at a red heat will combine with oxygen, so it wiU with sulphur. The compound so produced is called carbon disulphide, or " bisulphide of carbon." It is a heavy liquid (specific gravity 1-27), which boils at 43° C. (110° F.), has a disgusting odour, and is extremely inflammable. Experiment 1. — Boil a little oil in a test tube, and bring the end of the tube in contact with a few drops of carbon disulphide in an egg-cup. The liquid will ignite and bum with a blue flame. It is therefore evident that carbon disulphide ignites at a very low temperature. Experiment 2. — Shake a few drops of the disulphide in a wide-mouthed bottle, and apply a light. The vapour will burn with a blue flame, or if the quantity of liquid was very small, a slight explosion will be produced. A portion of the sulphur escapes oxidation and remains on the sides of the bottle. When, however, the liquid or vapour bums in an OTANOQEIf. 183 open vessel or at a jet, both the sulphur and carbon are oxidized, carbonic and sulphurous anhydride being formed : CS2+3O2 = CO2+2SO,. Experiment 3. — Eepeat the last experiment with a half-pint wide-mouthed bottle of oxygen. A very loud explosion will be produced. Hxjp&rim&nt 4. — Very fine iron wires may be burned in the flame of" carbon disulphide, the iron combining with the sulphur to iaiva. ferrous sulphide, FeS. In consequence of its remarkable volatility and inflam- mability, carbon disulphide is a very dangerous liquid to work with. All the above experiments must be made with very small quantities, and with the greatest caution. Carbon disulphide is a very useful solvent. Iodine, sulphur, phosphorus, and fixed oils are among the sub- stances which can be dissolved in it. CYANOGEN, CaNj. Carbon and nitrogen do not unite directly with one another, but by various indirect processes a series of im- portant salts called cyanides can be prepared. When, for instance, a mixture of potassium carbonate and charcoal is heated in a tube, and nitrogen gas is passed through it, the following change takes place : Potassium Potassium Carbonate. Cyanide. K^C03 + 4C4-N2 = 2KON+3CO. Potassium cyanide is in practice prepared from the salt called potassium ferrocyanide, or yellow prussiate of potash. The last-named salt, which is a very important article of commerce, is prepared by heating strongly a mixture of potassium carbonate, iron filings, and refuse animal matters, such as cuttings of horn and leather, woollen rags, dried blood, and the like. From potassium cyanide other cyanides can readily be prepared. The cyanides all contain the monad radical CN, which is often denoted by the symbol Cy, just as if it were an ele- mentary atom. The cyanides are, in fact, closely analogous to the chlorides. Cyanogen itself, and most of the cyanides, are deadly 184 EXPERIMENTAL OHEMISTKT. poisons. For this reason it would not be wise for a beginner to make many experiments with them. Experiment 1. — Heat a small quantity of mercuric cyanide in a hard glass test-tube fitted with a short jet. The white crystals decompose into mercury, which condenses on the upper part of the tube, and cyanogen gas, which escapes, and can be burned at the jet. It burns with a beautiful peach- coloured flame : Hg(ON), = Hg-f C,N,. A brown substance, called paracyanogen, is formed at the same time. It will be seen that cyanogen gas is the radical ON dcnMed. Its formula is therefore often written as (CN)2, or Cya. The resemblance of cyanogen and the cyanides to chlorine and the chlorides is then perfect : Cyanogen . (CN)a orCy, Kke CI,. Hydrocyanic Acid. HON „HCy „ HCl. Potassium Cyanide KCN „KCy „ KCl. Mercuric Cyanide Hg(ON), „ HgOy, „ HgCI,. Cyanogen is soluble in water. To obtain it pure it must be .collected over mercury, for it would not be safe to collect it by displacement. Hydrocyanic Add, HCN, or HCy. — Often called prussic add. This deadly poison is obtained by the action of sulphuric acid on cyanides. It is am exceedingly volatile liquid, soluble in water in all proportions. Experiment 2. — Put a few grains of potassium cyanide into a small beaker, and moisten the salt with dilute sulphuric- acid. Hydrocyanic acid will be set free with effervescence, and its peculiar odour — that of bitter almonds — will be recognised. It must, however, be remembered that the acid is most deadly as vapour. Experiment 3. — ^Repeat the last experiment, covering the beaker with a piece of glass moistened with a drop of silver nitrate. The hydrocyanic acid vapour will decompose the silver salt, and the white insoluble silver cyanide, AgCy, will be formed. This substance is very like silver chloride, except that it does not turn purple on exposure to light, and is soluble in hot nitric acid. Like the chloride, it dissolves in ammonia. DESTEUOTIVE DISTILLATION. — FLAME. 185 Experiment 4. — Moisten the glass plate with a drop of solution of potassium hydrate (potash) and expose it for some minutes to the vapour. No change will be perceived, but the potash will be partly converted to potassium cyanide. Add a drop of ferrous sulphate (green viteiol) to the liquid on the plate, and then, after standing for ten minutes, a few drops of hydrochloric acid. A beautiful blue precipitate (Prussian blue) will be formed. This is a most delicate test for cyanogen. Experiment 5. — The salt called potassium ferrocyanide has the formula KiCyePe. It is regarded as containing a tetrad radical (CysFe)", the iron being a part of the radical. Many other ferrocyanides can be formed from this one by double decomposition. Add solution of potassium ferro- cyanide to solutions of the following salts. 'In each case a feu'ocyanide of the metal will be precipitated : Copper Sulphate. — Purple brown. Lead Acetate. — White. Ferrous Sulphate. — ^White, or pale blue, soon changing to dark blue. Ferric Sulphate, or Chloride. — Dark blue (Prussian blue). If the ferrous salt be absolutely free from ferric salt, a white precipitate is obtained, but this is rarely the case. DESTEUOTIVE DISTILLATION.— FLAME. When wood, coal, and many other substances are heated in close vessels, an entire rearrangement of their con- stituent elements takes place. A portion of the carbon remains behind as charcoal, or coke (page 171), the rest distils over in combination with the other constituents, in the form of a number of volatUe compounds, some of which readily condense into liquids or solids, while others are permanent gases. The nature of these volatile products cannot be fully discussed in this place. Many of them are combustible — these are for the most part compounds of carbon and hydrogen. Most can be applied to some useful purpose. Processes of this kind, in which substances are destroyed in the retort, and volatile compounds formed and distilled from them, are called processes of destructive distillation. The preparation of gas from coal is the most important example. 186 EXPBEIMENTAL OHEMISTRT. Distillation of Goal. — Experiment 1. — Take a piece of hard tube about half an inch in external diameter, and a foot in length. Convert it into along test-tube by drawing off a short piece from one end, and then bend it twice at right angles thus; /v. Fit the open end with a small cork and short jet. This is a very useful piece of apparatus for experiments of this kind, acting at once as retort and receiver. Introduce some fragments of dry coal into the closed end and apply a strong heat (a Bunsen's burner does very well). Water and tar will distil over and condense in the bend, while coal gas will pass over and may be ignited at the jet. When no more gas is evolved, cohe will remain in the retort. Gas Manufacture. — On the large scale, the coal is distilled in iron retorts. The vapours pass first into the ' hydraulic main, a broad iron pipe placed horizontally in front of the retorts. Prom this it passes up and down through a series of vertical pipes called the condensers. In the hydraulic main and condensers the gas is cooled, and the greater part of the tar and water, which are the chief liquid products, are con- densed and separated. It then passes through a box filled with perforated trays containing slaked lime. This is called the lime purifier. It removes the chief remaining impurities of the gas. The gas is then carried to immense reservoirs called gas Jiolders, from which it is distributed for use. The products of the distillation of coal may be roughly classified as follows. The list is not complete : 1. Ooke (carbon). Eemains in the retort. 2. Tar and water. Mostly removed when 3. Gases and va- pours injuriam to the gas. 4. Diluents. 5. Useful. Ammonia. Carbonic anhydride. Sulphurous „ Sulphuretted hydro- gen. Cyanogen. Carbon disulphide. Hydrogen Methene. Acetylene. Ethylene. Vapours of liquid hydro-carbons. the gas is cooled. Chiefly remains in the water in combination with the following : Partly remain in the water as ammonium salts. Partly absorbed by the lime. Very difSoult to separate. I Do not contribute to lumi- I nosity. I Contribute luminosity. \ Ditto. Also cause the / smell of the gas. DESTRUCTIVE DISTILLATION. FLAME. 187 Flame. — What we ordinarily call a flame is the space in which gases are combining with oxygen. Flame is only produced by the union of gases. This at first sight appears BtartUng. It is natural to ask whether the burning of a coal or a candle is not the burning of a solid, and the burning of spirit or oil, of a liquid. But, in reality, we do not bum these substances, but the gases or vapours which they give off when heated. Charcoal burns without flame, because it gives out no vapour. In burning phosphorus, sulphur, or spirits of wine, we really burn the vapours of these sub- stances, and in burning coal, wax, wood, oil, or paper, we burn the gases which are produced by a destructive (fistUla- tion of those substances. A candle is a miniature gas factory. In it wax or tallow is distilled, and the gas so obtained is burned. Blow out a candle and apply a light to the white smoke which ascends from the wick. It will ignite, and the flame will run down and settle on the wick. It has been previously stated that hydrogen bums very easily, and with a flame, while carbon burns more difficultly, and without flame ; this explains why fuel burns with a flame at the commencement of the combustion, but finally only glows; it is the gases which first burn with a flame, and afterwards the carboil, with a mere glow, without flame. AU combustible substances that contain hydrogen and carbon burn in a similar manner. Burning wood presents a simple illustration of this fact. The flame of alcohol consists of two parts; the dark central part is alcohol vapour, and the bright yig. 69. envelope around this is alcohol vapour uniting chemically with the oxygen of the air. The tapering form of the flame is owing to the ascent of. the hot gases, and the rushing in of cold air from below. The alcohol is drawn up from the i lamp by the capillarity of the wick ; it burns with little light, but if a twisted wire or some other solid body be introduced into it, it will then bum vividly. If a thin wire is placed across the flame, it will be heated to redness near the margins of the flame, while in the interior it will remain dark ; consequently, the external part is much hotter than the central part of the flame. The point of 188 EXPEEIMENTAL CHEMISTET. greatest heat is indicated by the mark in the figure, and vessels to be heated over the spirit-lamp should never be placed below this point. This may be rendered very evident by applying a lucifer-match to this part of the flame, when it will take fire at once ; but not so quickly if thrust into the centre of the flame. The flame of hydrogen is similar to that of alcohol. In the fiame of a candle or lam/p, three parts can be dis- •p. „Q tinguished; in the middle (a. Pig. 7G), the dark ' centre, consisting of illuminatuig gas (decomposed Ji tallow) ; around this (6), the luminous conej> con- sisting of burning hydrogen, intimately mixed' with carbon at a white heat ; and on the very outside (c), a thin, scarcely perceptible veil, in which carbon is burning. If we imagine the flame to be cut hori- zontally through the centre, it would present neaaiy the same appearance as in Fig. 71. The middfe circle is illuminating gas ; the hydrogen of which burns first, and the great heat thus evolved brings the carbon to a white heat (this is indicated by the second circle) ; and finally, in the exterior circle, the carbon is burnt. The heated carbon in the second ring imparts to the flame its il- luminating pbwer, just as the glowing wire rendered the alcohol flame luminous. If a cold knife be introduced into the flame^ia portion of the carbon will be so much cooled that it cannot bum, and wUl be deposited upon the knife in the form of soot. If a wire be held through the flame, the glowing part at the hot margins will remain clear, while soot will be deposited upon that part of it which is in the interior of the flame. The brightness of a flame depends, as the foregoing' ex- periments show, upon the presence of a solid body, usually soot, which glows in the flame ; if it be only heated to redness, the flame will give out a smoky red light, but, on the contrary, a brilliant light when heated to a white heat. The hlowpipe. — In its simplest form, this valuable little instrument consists of a tapering metal tube bent at a right angle near its end, and terminating in a fine jet. With it a current of air can be forced through a small flame, sending Pig 71. HHI 1 Rii^^Mi H DKSTKTTOTIVK DISTILLATION. — FLAME. 189 it down horizontally, increasing its temperature very much and altering its character. The blowpipe flame is not hollow, like the candle flame. It consists of two cones ; an inner one, which is blue, and has the power of removing oxygen from many metallic oxides, and an outer one, which is pale yellow, and has the opposite power of promoting oxidation. The inner cone, which is much hotter than the other, is called the reducing flame ; the outer, the oxidizing flame. The flame of the oxyhydrogen blowpipe (page 131) is similar to the ordinary blowpipe flame in structure. ■Temperature necessary for flame. — A certain definite tem- perature is necessary for the combustion of each combustible substance, and if the temperature is reduced below that point the combustion ceases. A piece of cold metal will extinguish a candle flame, because the metal, being a good conductor, reduces the temperature of the flame. When we " blow out " a flame, the sudden current of cold air exerts a similar cooling action. It is impossible to blow out the flame of phosphorus or carbon disulphide, because those substances enter into combustion at a very low temperature. Sir Himiphry Davy made the important discovery that the flre-damp (methene) of coal-mines requires a very high temperature for its combustion. From this knowledge he was led to invent the " safety lamp," which has done so much to mitigate the horrors of coal-mining. It is simply an oil ^mp in which the flame is entirely surrounded by fine wire gauze. If this lamp is burned in an atmosphere containing fire-damp, or even ordinary coal gas, the gas will enter and burn inside the lamp, often extinguishing the oil flame, but the flame cannot pass through the wire gauze, and an explosion is therefore impossible, unless the lamp is out of order, or improperly used. The wire gauze acts by cooling the flame below the point required for combustion. Its effect rig. 72. can be shown by pressing a piece down on an ordinary gas or candle flame. The flame is, as it were, crushed down by the gauze, though , the gas passes freely through, and can be burned on the other side. ' flames. — When the supply 190 EXPEBIMENTAl CHEMISTRY. of air to a flame is insufScient, it smolees ; that is, a part of the carbon escapes oxidation. A chimney often obviates this ; the heat produces an upward current in it, whereby more air is drawn in. In the argand burner the flame is ring-shaped, and air enters through the centre, as well as outside the flame. SILICON. Si = 28. Formula unknown. Silicon is the most abundant solid element. It is always found in combination, and is, only isolated with great diffi- culty. It enters into the composition of so many minerals that the greater part of the science of mineralogy is occupied with the history of the silicon compounds. Silicon, like carbon and boron, may be obtained in three conditions : amorphous, graphitoid and adamantine (sometimes called " diamond silicon "). In the free state the element is too expensive to be of any practical importance. Like carbon and boron, it is insoluble in all agents that do not change it, and non-volatile. Silicic anhydride, Si"0"2, also called silica and silex, is the only known oxide of silicon. It occurs native and tole- rably pure, as quartz, sand, flint, and almost perfectly pure as rock-crystal, which is found beautifully crystallized in trans- parent six-sided prisms. Camelian, agate, jasper, opal, calce- dony, and some other well-known precious stones, consist, likewise, of silica ; their colours are chiefly owing to the presence of minute quantities of metallic sUicates. Three varieties of silicic acid analogous to the three phosphoric acids are recognised. They must be prepared by indirect means, for silicic anhydride will not combine directly with water. The normal, or orf^sUicic acid, HjSiOt, has not been obtained free from water. All silicates are insoluble in water except certain alkaline silicates. Soluble Glass. — Eoaperimeat 1. — Heat a common flint stone in a fire, and when it is red-hot quench it in cold water. The sudden cooling so influences and diminishes the internal cohesion, that now the flint can easily be reduced to a fine white powder. Boil in a clean iron ladle two drachms of the powder with four drachms of caustic potash (potassium hydrate) and two ounces of water, for some hours, supplying SILICON. 191 fresh water occasionally as the other evaporates ; then let the mixture stand in a corked bottle to settle. The silica dissolves in the potash solution and forms with it a thick fluid, potassium dlicate. Or one part of the powdered flint may be fused with four parts of dry sodium carbonate (com- mon washing soda), in a crucible over the fire. The soda soon commences to effervesce, from the escape of carbonic anhydride, which is replaced by the silicic anhydride. The mass on being boiled with water and filtered furnishes a solution of sodium silicate. These soluble silicates are often called soluble glass, and their solutions, liquor silicum. Liquor silicum has of late years been largely employed for the hardening of soft building stone, and the artificial preparation of hard stone from sand. ] Experiment 2. — Add some hydrochloric acid to a strong solution of sodium or potassium silicate. A white gelatinous mass of silicic acid (probably H^SiO,) is thrown down. If this jelly is collected on a filter, washed well with water and dried, a white powder, consisting of pure silica in the amor- phous state, is obtained. JExperiment 3. — If, on the contrary, the silicate solution be diluted with ten or twelve times its bulk of water, and then the alkali be removed with hydrochloric acid, no precipitate is produced, the silicic acid remaining in solution. This solubility is but a temporary state, as after the lapse of a, certain time, depending on the proportion of silica present, the solution suddenly undergoes a remarkable conversion into a transparent jelly-like mass, the siHcio acid passing into the insoluble modification. By the addition of more alkali it may be again redissolved and the experiment repeated. Almost all our springs, as well as our plants, contain small quantities of soluble silicates. If we evaporate spring-water, we find silica in the insoluble residue ; and if we burn a plant, we obtain it in the ashes. Grasses, and the different kinds of grain, are particularly rich in siHca, and for this reason they have been called silicious plants. Silica is to these plants what bones are to men, — the substance to which the stalk owes its firmness and stif&iess. If the soil is deficient in soluble silica (or if there is not enough potassa, which renders the siUca soluble), these properties will be wanting 192 EXFEEIMGNTAL OHEMISTBY. in the stalk, and it will bend. The horse-tail plant (Equisetum) contains so much silica that it may be used for polishing wood. Silica is found even in the animal kingdom, particularly in the class of Infusoria, which are only visible under the microscope ; the shells of many Infusoria are composed of silicic anhydride. In its natural state, silica is so hard as to produce sparks with steel, and is quite insoluble in water and acids, except hydrofluoric acid. Silicates. — The silicates are the most numerous and com- plicated of all sorts. Their study, however, belongs to the science of mineralogy. Among important sUicates may be mentioned felspar, mica, horneblende, serpentine, and meer- schaum. The different varieties of clay are silicates of aluminium. Glass is a mixture of various silieates, with excess of silica. Silicon Fluoride, SiPj. — This interesting gas is obtained by the action of hydrofluoric acid on silica, or any silicate. To its formation the power which hydrofluoric acid possesses of etching glass (p. 120) is due : SiOa + 4HF = SiF. + 2H,0. It is immediately decomposed by water, with formation of silica and an acid called hydrofluosilicic acid, 2HP, SiPi. Experiment 4. — Heat powdered glass, fluor-spar and sul-^ phuric acid in a flask, and carry the gas produced to the bottom of a glass of water, in which some mercury has been placed. As the gas rises from the mercury it is decomposed by the water, and beautiful tubes of silica are built up. If it were not for the mercury, the mouth of the tube would soon be choked up by the silica, and the flask would then be apt to burst. ( 193 ) PAET III. METALS. CHAPTEE I. METALLIC MONADS. (Potassium, Sodium (Ammonium), Silver.) POTASSIUM. K = 39-1. This interesting metal was discovered by Davy, who obtained it by decomposing caustic potash (potassium hydrate) by means of a powerful galvanic battery. Potassium is now prepared by putting potassium carbonate and charcoal into an iron bottle, provided with an iron exit- tube, and exposing them to the strongest white heat. At this extremely high temperature the charcoal combines with the oxygen of the carbonate, forming carbonic oxide gas, which escapes. The liberated potassium is also converted into vapour, which is conducted into naphtha, where it con- denses into a solid mass, resembling silver : K^COa-f 20 = SCO + Kj,. It has been shown, under carbonic acid, that potassium, at a moderate heat, can withdraw the oxygen from the carbon ; while here, at a higher temperature, the contrary takes place. Similar incongruities in chemical actions are not unfrequent ; they show that the affinities of bodies for each other are greatly altered by the temperature. Experiment. — If a piece of potassiimi is cut with a knife, it presents a glistening surface like silver ; but it immediately tarnishes on exposure to air, and soon becomes converted into solid potassium oxide. This experiment shows the softness of the metal, and also its great affinity for oxygen. Consequently, to preserve potassium flrom oxidation, it is necessary to keep it in mineral naphtha, or some other liquid 194 EXPERIMENTAL CHEMISTKT. which contains no oxygen. Its symbol, K, is derived from the Latin name Kalimn. Potassium oxide, KjO. — A. small piece of potassium, if heated on the point of a knife, burns to a white mass of potassium oxide. This substance combines eagerly with water, and forms potassium hydrate : Kfi + HjO = 2KH0. Potassium hydrate, KHO. — Caustic potash — Potassa. — This important substance is obtained when potassiam acts on water (p. 103), but is more economically prepared as follows : — Esaperiment 1. — ^Place half an ounce of quick lime in a plate, sprinkle it with warm water, and let it stand until it is slaked, that is, until it becomes a fine Fig. 73. dusty powder. Then put half an ounce of potassium carbonate into an iron basin with six ounces of water, and boil it, and, during the boiling, gradually add half of the slaked lime by tea- spoonfuls, stirring it at the same time. After the mixture has boiled for some time, put a tea-spoonful of it upon a paper filter, and pour the filtrate into vinegar. If it effer- vesces, still more lime must be added ; but if no effervescence ensues, pour the whole into a bottle, close it up, and let it remain quiet for some hours, that the sediment may subside. Decant the clear liquor, and preserve it in a well-stoppered bottle. , It is a solution ot potassium hydrate. Slaked Ume is calcium hydrate : when it is boiled with potassium carbonate, calcium carbonate and potassium hydrate are formed by double decomposition, and the former, being insoluble, is precipitated : Calcium Potassinm Calcium Potassium hydrate. carbonate. carlJODate. hydrate. Ca"(H0)2 + K.COs = Ca"CO, -f 2KH0. Experiment 2. — Evaporate a portion of the potash solution in a clean iron vessel (glass and porcelain are attacked by it) ; all the water is expelled and a white mass finally remains behind, dry potassium hydrate. This may be melted at a stronger heat, and cast into sticks or plates. POTASSIUM. 195 Experiment 3. — Expose some dry potash to the air ; it will soon become moist ; it will deliquesce, and on longer exposure will effervesce upon the addition of an acid. Potash absorbs both water and carbonic anhydride from the air, and is then converted into potassium carbonate. Experiment 4. — Heat in one test-tube some white, and in another some brown blotting-paper, with some solution of potassium hydrate ; both papers will be decomposed and dissolved, the vegetable fibres of the white paper (linen or cotton) more slowly than the animal fibres of the brown paper (wool). Potash exerts a very corrosive action, especially on animal substances. The slippery feeling caused by rub- bing lye between the fingers is owing to a gradual solution of the skin. Experiment 5. — Boil in a test-tube a little tallow or fat with a solution of potassium hydrate ; a union gradually takes place; soap is formed. The soap prepared from potash remains soft, and is called soft-soap. Experiment 6. — Dissolve a piece of blue vitriol (copper sulphate) in water, and add to it some solution of potash. The copper is precipitated as a hydrate, and potassium .sulphate remains in solution : Cu"S04 + 2KH0 = K,SO, + Cu"(HO),. Potassium hydrate being a strong base precipitates many other metals from their salts as hydrates, by an interchange of the respective radicals. Potassium Carbonate, KjCO.. Experiment 1. — Fit into a funnel a filter of blotting-paper, and , place upon it a handful of wood ashes, and gradually pour hot water over them. The liquid Fig. 74. filtered through has an alkaline taste, and turns red test-paper blue. If you evaporate it to dry- ness in a porcelain dish, a grey mass finally re- mains behind, which becomes white after being heated to redness in a porcelain crucible ; it is pearlash, or impure potassium carbonate. In those countries where wood is abundant — in America, Russia, &o. — it is prepared in a similar manner on a large scale, and is an article of great demaiud in commerce. 196 KXPKEIMBINTAI, CHBMISTET. It can be purified by recrystallization. Experiment 2. — Put one portion of potassium carbonate in a vessel, and let it stand in a dry apartment, and put anotber portion in a cellar. Tbe former becomes moist ; the latter deliquesces. Both attract water from the air, but that in the dry atmosphere of the room less than that in the damp air of the cellar. Potassium carbonate is a very deliquescent salt. Experiment 3. — Boil for some time, in a vessel containing a quarter of an ounce of potassium carbonate and two ounces of water, a piece of grey linen, and some dirty or greasy linen or cotton rags ; the liquid will become of a dark colour, while the rags are made white and clean. Dirt, as it is com- monly called, is dust, which adheres to the skin, garments, &c., particularly after they have become moistened by perspiration, or have come in contact with greasy or other adhesive sub- stances. These last-mentioned substances may be dissolved and removed by pearlash ; on this depends the various appli- cation of this substance in cleaning and washing. Hydrogen potassium carbonate, HKOOs. — This salt, which is commonly termed bicarbonate of potash, differs from the preceding compound in having but one atom of the hydrogen in carbonic acid replaced by potassium. It consequently belongs to the class called acid salts, and is prepared by passing a current of carbonic anhydride through a solution of ordinary potassium carbonate until no more is absorbed : KjCOa + HaO + CO, = 2KHCO3 Potassium sulphate, K2SO4. — Dissolve half-an-ounce of potassium carbonate in two ounces of warm water, and then add diluted sulphuric acid in very small quantities until no more effervescence is produced on stirring. -p; „g Filter and evaporate the liquid until a film of crystals appears on the surface, then set it aside. The hard crystals obtained (six-sided double pyramids) are potassium sulphate ; they are sparingly soluble ia water, and have a somewhat bitter taste. Hydrogen potassium sulphate, HKSO4, some- times called potassium bi-sulphate, is obtained as a secondary product in the preparation of nitric acid from Fig. 76. H POTASSIUM. 197 saltpetre (p. 158). It is an extremely acid salt, and much more soluble than tte neutral sulphate. Potassium Nitrate, iSOs- Experiment 1. — Dissolve half an ounce of potassium car- bonate in one ounce of hot water, and neutralise Fig. 76. with nitric acid ; afterwards boil and filter the liquid, and set it aside to cool ; prismatic crystals of potassium nitrate will be deposited from it, which have a cooling taste, and undergo no altera- tion in the air. This salt is known as nitre and saltpetre ; after fusion,' it solidifies to a crystalline mass, sometimes called salprunella. Experiment 2. — Throw a little nitre on a red-hot coal, it will cause a brisk sparkling ; it deflagrates. The nitre is decomposed and gives up its oxygen to the coal, and thus causes it to bum more energetically. The hard saline mass, congealed from its melted state, remaining on the coal, has a basic reaction, and effervesces with acids; it is potassium carbonate. In order to render substances more inflammable, they are often soaked in a solution of nitre ; as, for example, tinder, touch-paper, &c. Experiment 3. — Mix thoroughly in a mortar fifteen drachms of powdered nitre, three drachms of charcoal-powder, and two drachms of sulphur ; this mixture contains the con- stituents of gunpowder. Take a little on the point of a knife, put it on a stone, and ignite it with a match ; a brisk defla- gration will ensue. Knead the rest of the powder, with some drops of water, into a paste, and squeeze it through a tin colander. The thread-like mass thus obtained is, when partly dry, divided into small grains by gently rubbing with the fingers ; this is gunpowder. Experiment 4. — Place some gunpowder upon an iron plate, and ignite it; the deflagration takes place more rapidly, because the materials are more intimately mixed. In this deflagration there are eVolved from the charcoal and the nitre carbonic anhydride and nitrogen, two gases which in- stantly occupy a space several thousand times greater than before. Sulphur not only causes an easier ignition of the gunpowder, but it causes also a stronger evolution of gas ; since it combines with the potassium of the nitre, forming 198 EXPERIMENTAL CHEMISTRY. potassium sulphide, and liberates three molecules of carbonic anhydride, while without sulphur but half the quantity of gas' could be set free. The change which occurs when gunpowder is burnt may be represented by the equation 2KNO3 + S + 30 = K,S + Ns + 300^. If the deflagration of the gunpowder takes place in a con- fined space, as in a gun-barrel, the' explosive violence with which the two gases are suddenly expanded is strong enough either to project the ball or to burst the gun. The potassium sulphide remaining soon becomes moist in the air, and then emits the odour of sulphuretted hydrogen ; at the same time, the iron is blackened by the formation of sulphide of iron upon the surface. If nitre be heated with sulphuric acid, nitric acid escapes (p. 158). Animal substances are preserved from putrefying by nitre ; it is therefore used in salting meat. The manufacture of nitre is conducted in a very peculiar manner. Animal substances, for instance, pieces of flesh, hides, hair, &c., are mixed with wood-ashes and earth, and then moistened with water or urine, and suffered to putrefy slowly. Animal substances are rich in nitrogen, which, during putrefaction, is set free in the form of ammonia (NH3) ; this, after a time, unites with the oxygen of the a,ir, forming nitric acid, which acid is immediately neutralised by the potassium of the wood-ashes. If animal substances decay without the presence of potash, or some other strong base, no nitric acid, but only ammonia, will be produced. After the completion of the putrefaction, water is added to extract the nitre, and the solution being evaporated it is deposited in crystals. Nitre beds, so called, are prepared in this way. We also obtain nitre from the East Indies, wLpre it is found as an incrustation on the surface of the soil. Potassium chlorate, KClOj. — This salt is very similar to nitre, but it is more easily decomposed. By mere heat it is resolved into oxygen and potassium chloride ; therefore it is used for the preparation of oxygen (p. 122). Its preparation has already been described (p. 136). Experiment 1. — When thrown on glowing coals, it defla- grates still more briskly than- nitre; the oxygen, as it is POTASSIUM. 199 liberated, occasions a very energetic combustion of the coal. This salt cannot be employed in tbe preparation of gunpowder, as the rapidity with which it explodes would be too much for the guns ; yet, on this very account, it is extremely serviceable in fireworks, especially for producing variegated fires. The greatest caution must be observed in pulverising and mixing it with combustible materials, as it may explode by merely rubbing or pounding it. The -mixing of it with other substances must always be done with the fingers. Experiment 2. — Introduce some crystals of potassium chlorate into a beaker-glass, and add a small quantity of alcohol, and afterwards a few drops of sulphuric acid ; the siilphuric acid expels chloric acid, which is immediately decomposed, and there is so great an evolution of heat as to set fire to the alcohol. JExperiment 3. — Mix some potassium chlorate between the fingers with about half as much flowers of sulphur, and throw the mixture into sulphuric acid, contained in a beaker-glass; a brisk crackling ensues, and the sulphur takes fire. Potassium Chloride, KCl. Dissolve half an ounce of potassium carbonate in water, and neutralise with hydrochloric acid ; upon con- Fig. 77. /, centfating the solution, cubic crystals will be obtained, having a taste similar to that of com- | mon salt. Potassium Iodide, KI. This salt likewise crystallises in cubes, is easily soluble in water, and is employed in medicine as a valuable remedy. Experiment 1. — To prove that iodine is really contained in ihis white salt, heat a small portion of it in a test-tube with a little black oxide of manganese and some drops of sul- phuric acid, when violet fumes will be evolved. If common salt is treated in the same manner, chlorine, as is known, will be given off. The chemical action is the same in both cases. Potassium Tersulphide, K283. Sulphur combines with potassium in five different propor- tions, forming Hi-defined compounds. One of the most impor- tant of them is prepared as follows : QOO EXPERIMENTAL CHEMISTET. Experiment 1. — Put a mixture of one draclim of sulphur and two drachms of dry potasBium carbonate into an iron ladle, cover it with a strip of sheet iron, and heat it until the effervescence has ceased and the mass flows quietly. The fused mass has the colour of liver, and on this account has received the name liver of sulphur : pour it upon a stone, and if it should inflame, cover it with a vessel to extinguish it. On exposure for some time to the air it becomes greenish and moist, and evolves an odour like that of rotten eggs. It consists of a mixture of potassium tersulphide with potassium sulphate. A similar preparation has already been described (p. 139). Experiment 2. — ^Pour water into a test-tube containing some liver of sulphur ; you obtain a yellowish-green solu- tion. If to this you add diluted sulphuric acid, a strong evolution of sulphuretted hydrogen takes place, and the liquid becomes milky from the precipitation of two-thirds of the sulphur (milk of sulphur) : KjSs + HjSO, = K2SO4 + HsS + 2S. The same thing is effected, though far more slowly, by the carbonic anhydride of the air, and thus is explained why the liver of sulphur (as well as the residue left on the com- bustion of gunpowder) emits a smell like that of rotten eggs when it is left exposed to the air. The other sulphides of potassium can be formed by varying the proportions of the potassium carbonate and sulphur. SODIUM. ]Sra = 23. Sodium was discovered by Davy soon after the isolation of potassium. Like potassium, it is obtained by reducing its carbonate with charcoal. It is much easier to prepare than potassium. Sodium is a soft, white, and easily fusible metal, lighter than water, and very similar to potassium in chemical characters. Eaperiment 1. — The action of sodium on water has already been described (p. 103). It is closely analogous to that of potassium. Sodium oxide, NajO, and Sodium hydrate, NaHO, are ob- SODIUM. 201 tained in the same way as the potassium compounds, and are so analogous to them that the descriptions given of the latter are applicable, with few exceptions, to either. Sodium, chloride, or common salt, NaCl.- — Salt has twice previously been artificially prepared ; namely, once from sodium and chlorine (page 112), and again from soda and hydrochloric acid (page 115) ; its constituents are accord- ingly already known. It has the formula NaCl. The earth and sea abound in common salt ; it may there- fore be easily procured in large quantities. In many places it is found in the interior of the earth, in immense beds, from which it is broken up and dug out. This salt looks like a transparent stone, and is, therefore, called rook-salt. In those places where the rock-salt is mixed with stones and earth, a hole is bored in the middle of the bed, and water is let into it. The water is pumped out again as soon as it has become saturated with the salt, and is again expelled by evaporation. In some places springs are found containing salt in solution — the so-called natural hrine springs. These are always occasioned by the water permeating the earth over a bed of rock-salt, and appearing as a spring at some lower level. In hot countries, salt is also prepared from sea-water, which is evaporated in shallow tanks by the heat of the sun. It is called hay-salt, and has a bitterish taste, owing to the presence of salts of magnesium. A pound of sea-water con- tains from one-half to five-eighths of an ounce of common salt. Salt is indispensable to the life of animals, and is there- fore a constant and necessary ingredient of food. It is also used for preserving animal and vegetable substances, because it has the power of preventing putrefaction or decay. Meat and fish are salted down, and wood for the purpose of building is rendered more durable by being impregnated with salt. Such substances are called antiseptics. Experiment 1.— Dissolve one ounce of salt in two oimces and three-fourths of cold water ; the water will dissolve no more, even if added. Eepeat the experiment, using hot instead of cold water ; the result is almost exactly the same. Common salt has the remarkable property of being nearly as soluble in cold as it is in hot water. A larger quantity of 202 EXPERIMENTAL CHBMISTET. almost all other salts is dissolved by hot than by cold water. Put one of these solutions in a warm place ; by the gradual Fig 78 evaporation, regular transparent cubical crystals of common salt are formed. Boil down the other solution, quickly stirring it all the while ; it I yields a granular, opaque, saline powder. Salt is prepared as last described on a large scale, and hence the granular state of common salt, i . Experiment 2. — If you expose a solution of salt in an open place during the extreme cold of winter ( — 10° C. or -)- 14;° F.), transparent prismatic crystals will be formed, which contain more than one-third of water of crystallization, NaGl,2HsO. When placed on the hand they quickly become opaque and deliquesce into a syrupy mass, in which numerous small cubic crystals may be perceived. Experiment 3. — Heat some common salt on platinum foil ; it will crackle briskly, and part of it will be thrown off the foil ; that which remains melts when the foil becomes red-hot. The crackling (decrepitation) proceeds from a trace of water, which has remained in the interstices of the crystals; on being heated it expands and bursts the crystals asunder. Sodium sulphate, NajSOj. — As most of the potassium salts and potassium are prepared from potassium carbonate, so most of the sodium salts are prepared &om common salt. In the latter case, however, an indirect process must often be resorted to, since chlorine is not so easily removed from ■pj 79 sodium as carbonic acid is ffom potassium. The J-_ ' sodium chloride must first be converted into ^]j— [1 sodium sulphate. We are already acquainted with this salt, it having remained in the retort after the preparation of hydrochloric acid, where common salt was heated with sulphuric acid. It was formerly taken as a popular medicine, under the name of Glauber's salts, so called from its discoverer, the physician Glauber. We find it also in many mineral waters; for instance, in the Cheltenham and Carlsbad waters. It is readily soluble, crystallizes in four or six sided prisms, and has a saline, bitter taste. Experim:ent 1. — Place half an ounce of crystals of sodium sulphate in a warm place ; they soon become covered with SODItTM. 203 an opaque white coating ; they effloresce. The powder ob- tained weighs hardly a quarter of an ounce. That which was lost was water. Crystals of sodium sulphate contain more than half their weight of water of crystallization. Their composition is expressed by the formula NajSOijlOHaO. The' transparency of the salt is lost when this chemically combined water is separated, but reappears when the anhydrous salt is dissolved in water and recrystallized. Salts which effloresce must be kept well-corked up. ' Experiment 2. — If a crystal of sodium sulphate is heated on charcoal before the blowpipe, it soon melts, because it dis- s6lves in its water of crystallization (watery fusion) ; it be- comes dry as soon as the water is expelled ; but finally it melts for the second time when heated to redness (igneous fusion). Those salts which contain no water of crystallization can undergo only the latter kind of fusion. ' Experiment 3 . — Heat in a small flask half an ounce of water to 91° F. (38° C), and keep it at this pjg. go. t&mperature, gradually adding crystal- lized sodium sulphate, as long as they are dissolved, amounting to about an ounce and a half. If a stronger heat be now applied to the saturated solu- tion, a salt will separate (anhydrous crystals, NasSO^) ; if you let it cool, a salt will likewise separate (hydrated crystals, Na^SO^, lOHjO) ; — furnishing another example of the great influence exerted by temperature on the affinity of water for other substances. Sodium sulphate has the peculiar property of '^ being most soluble in water, not at the boiling point, but at a lower temperature. The curious manner in which a hot saturated solution of the salt can be cooled without immediate crystallization taking place, has already been noticed (page 9, Exp. 3). Experiment 4. — If you dissolve crystallized sodium sul- phate in water, cold is produced ; but if, on the contrary, you dissolve the anhydrous salt in water, then Jieat is produced. Tou will observe exactly the same phenomena if you perform this experiment with sodium carbonate, taking first the crys- 204 EXPERIMENTAL CHEMISTRY. tallized and then the calcined salt. Whence the source of this heat ? It is due to a part of the water combining with the anhydrous Glauber salts, or the anhydrous sodium carbonate, as water of crystallization. Sodium sulphide, Na^S. — Experiment 1. — Mix a small „. o- portion of anhydrous sodium sulphate with a little charcoal powder, and heat the mixture on charcoal before the blow- pipe ; they will melt with ' brisk effervescence into a brown ,_ mass, which dissolves in water, i forming a yellowish liquid. The 'i charcoal, when heated to redness," abstracts the oxygen, and forms with it carbonic oxide gas, which escapes with efferves- cence ; sodium and sulphur remain behind, combined with each other. That is, the charcoal deoxidizes the sodium sulphate, or reduces it to sodium sulphide. If you drop hydrochloric or diluted sulphuric acid into the solution, the disagreeable smell of sulphuretted hydro- gen will be given off. Sodium Carbonate, or Carbonate of Soda, NaaCOg. Experiment 1. — Prepare some more sodium sulphide in the manner just described, rub it in a mortar with the adher- ing particles of charcoal and with about its own weight of chalk, and ignite it again before the blow-pipe. Boil the baked saline mass in water, and then filter the liquid. A grey powder remains behind, which, when drenched with hydrochloric acid, evolves sulphuretted hydrogen ; it is calcium sulphide. The liquid, after being evaporated on a shallow glass dish, leaves behind a white powder, which has an alkaline reaction and effervesces with hydrochloric acid, but yet without emitting any disagreeable odour ; it is sodium carbonate. The sulphur has thus passed to the calcium of the chalk, while the carbonic acid radicle of the chalk has passed to the sodium. As sodium carbonate possesses almost exactly the same SODITTM. 205 properties as potassium carbonate, and can be advantageously employed instead of the latter in washing and bleaching, and also in the manufacture of glass and soap, it is now manu- factured on an enormously large scale in chemical works. The process pursued is essentially the same as that already described, except that the two operations, described sepa- '^' ' rately above, are united into one ; the chalk or limestone is added, in the first place, to the Glauber salts and char- coal, and the whole mass is heated. This is done in ^ a 1 1 \ large oven-shaped furnaces, ► "~ ~ ^ 1 represented in the figure, a is f I / the grate, 6 the ash-pit,^ the chimney, d d the hearth for receiving the mixture, i the aperture for throwing in the ■ i ||||| .' mixture, and g an opening for ' ij "^ IHII. 1 stirring it and scooping it out. | 1 ^ '^77' I They are called reverberatory- -'Z. . _ 't— '■ furnaces, because the heating is effected, not by the fuel itself, but by the flame, which is reverberated after passing over the bridge c ; they possess this important advantage, that the ashes of the coal or peat d.0 not become mixed with the siibstance to be heated. In many countries sodium carbonate is also obtained from the ashes of marine plants (kelp). Sodium carbonate occurs in commerce, either crystallized— it then contains more than half its weight of water of crys- tallization, .]Sia„CO3,10B[2O, and effloresces very readily— or calcined, consequently anhydrous. The latter, accordingly, when it occurs pure, is of more than twice the strength of the crystallized. Sodium carbonate is easily soluble in water. Many mineral waters— for example, the Carlsbad springs- contain great quantities of it in solution; Carlsbad salt, obtained by evaporating the waters of the spring, is a mixture of carbonate and sulphate of sodium. Hydrogen sodium carbonate, HNaCOs, is chiefly used for preparing effervescing powders. It is prepared like the 206 EXPEEIMENTAIi CHEMISTRY. similar potassium salt (p. 195), and is commonly called bicarbonate of soda. Sodium nitrate, NaNOa- — Dissolve some sodium carbonate ■p- go in water, neutralize with nitric acid, evaporate the solution, when crystals will separate, having the form of an obliqne rhombic prism ; they are nitrate of soda. They deflagrate on charcoal like potassium nitrate, and have the greatest similarity to it in other respects. Large districts of this salt ai'e found in America, whence whole ship-loads of it are exported, under the name of Chili saltpetre ; and it is substi- tuted for the more costly nitre in the manufacture of nitric acid and some of its salts. But it does not answer for making gunpowder, as the powder thus prepared becomes moist. Sodium Phosphate, NajHPOi. Experiment. — Neutralise sodium carbonate, dissolved in water, with phosphoric acid ; filter the liquid, and evaporate the filtrate until a film forms on the surface ; on cooling, tramsparent crystals will be deposited, which contain more than half their weight of water of crystallization : NagHPOi, 12HjO. They easily effloresce, and yield a yellow precipi- tate with a solution of silver nitrate. Other phosphates of sodium of less importance are known. Sodium di-horate, or Borax, 'NsLiBfij. — The hard colourless crystals' commonly called borax are an irregular sodium salt of boric acid (p. 172). Tincal is p. native borax found in China and Thibet. Borax contain ten molecules of water of crystallization : NajBiO^lOHjO. Experiment 1. — Heat some powdered borax upon a small loop of platinum wire before the blow-pipe ; it will puff up and swell in its water of crystallization, and be converted into a porous spongy mass ; on being further heated, it fuses to a transparent lead. Moisten this bead with the tongue, apply it to litharge so that some of the latter may adhere to it, and again hold it in the outer flame of the blow-pipe ; the litharge is dissolved ; the bead remains colourless and trans- parent. If you now substitute for the litharge other metallic oxides, you will likewise observe that the oxides will dissolve, but that at the same time the bead mil be coloured by them ; namely, yellowish-red, by sesquioxide of ii'on and oxide of SODIUM. 207 antimony ; green, by the oxide of chromium ; hlue, by oxides of copper and cobalt ; violet, by a small portion of oxide of manganese ; and hrownish-blach, by an excess of manganese. On account of this property which borax has of dissolving metallic oxides, it is used in chemistry as a blow-pipe test for the detection of metallic oxides, and in the trades for soldering, or joining one metal with another. Sodium Silicates (Glass, dc). 'Experiment. — Melt some potassium or sodium carbonate upon a platinum wire before the blow-pipe, and then add a little finely pulverised sand ; upon placing it again in the blow- pipe flame, effervescence will ensue, and afterwards a clear bead will be formed. If the proportion of sand used be small, the glass formed will dissolve in water on long-continued boiling ; it is then called soluble glass (p. 190). If more sand is taken, a glass is obtained which is very difficult to dissolve in water. To make a glass which shall be entirely insoluble, not only in water but also in acids, beside alkalies, some other earth or metallic base — for instance, lime or litharge — must be added. Common glass is thus manufactured in glass-houses : The materials which are chiefly employed in the manu- facture of glass are, — a) quartz, flint, or sand ; 6) potassium carbonate or wood-ashes; c) sodium carbonate; d) lime or chalk ; e) litharge or lead oxide. These substances, after being pulverised, are mixed together, thrown into earthen pots, and heated in a furnace until the mass forms a uniform fluid. In this state it may be moulded like wax, cut and bent, pressed into moulds, and blown, and may accordingly be manufactured into all possible shapes and forms : on cooling, it becomes hard and brittle. In order, to diminish in a measure the brittleness, the glass must be cooled very slowly (annealed). Glass vessels that are rapidly cooled often crack when they are carried from a warm into a cold room ; this defect may, to a certain degree, be corrected, by gradually heating the vessels in water till it boils, and then allowing it to cool very slowly. For colouring and painting glass various metallic oxides are employed. The milk-white colour which we observe in the opaque glass of the lamp-screens, and in the enamel of 208 ESPKKIMENTAL CHEMISTEY. the dial-plate of watches, is produced by finely-ground bone- earth or meta-stannic acid — -neither of which substances is dis- solved by the vitreous mass, but only mixes with it mecha- nically, and renders it opaque, as chalk does water. Glass is ground by sand and emery, polished by ferric oxide and tripoli, etched by hydrofluoric acid, and very easily perforated by the point of a three-cornered file, which should be frequently moistened with oil of turpentine. The two pripcipal kinds of glass are — Grown or Bohemian glass, consisting of sodium and calcium silicates. Flint or crystal glass, consisting of potassium and lead silicates. Common hottle-glags contains the same ingredients as crown glass, with the addition of ferric oxide, which imparts to it a brownish-yellow colour ; of ferrous oxide, which gives it a green tinge ; of alumina, &c. The iron is contained in the impure materials (yellow sand and wood-ashes) used in the preparation of the ordinary sorts of glass. AMMONIUM. NH, = 18. Although ammonium is a compound radical and not an element, its compounds, which are often called ammonia salts, are so similar to those of potassium ajid sodium, that they are generally placed among the metals. Their constitution has already been explained (p. 156). Ammonium hydrate, NH4HO. — The solution of ammonia gas in water is assumed to contain this compound. The solution is strongly alkaline and caustic, like that of potassium, or sodium hydrate. Ammonium chloride, NH4CI. Sal-ammoniac. — Formed by the direct union of ammonia and hydrochloric acid (p. 156). It is generally prepared from the " ammoniacal liquor " of gas- works (p. 186). It is a tough, fibrous solid, which may be purified either by crystallization from water or by svhlimation. Experiment 1. — Heat some impure sal-ammoniac in a dry test-tube. It will volatilize, and the colourless vapour will condense on the sides of the tube as a white mass, which, however, is still apt to contain iron. AMMONIUM. 209 Experiment 2. — Dissolve some crude sal-ammoniac in water, and add a few drops of ammonium sulphide. If iron be present, a black precipitate will appear, and will subside after a time. Tbe filtered liquid may then be evaporated to dryness, the mass dissolved in water, the solution filtered and evaporated until it crystallizes. The crystals will consist of pure ammonium chloride. Ammmium sulphide, (NH4)2S, and SulpJiydrate, NH4H8. — These compounds correspond to the hypothetical oxide and hydrate of ammonium, (NH4)20, and NH^HO. Experiment 1. — Pass sulphuretted hydrogen gas, prepared as described on page 141, first through a bottle containing a little water to remove impurities, and then into some dilute ammonia. The gas will be absorbed in large quantity. When the ammonia is saturated, there will remain a solution of ammonium sulphydrate : NH4HO + H^S = NH^HS + HA If this solution is mixed with a quantity of ammonia equal to that first employed, the sulphydrate becomes sulphide : NH4HS + NH^HO = Q^n^)S + H2O. This sulphide precipitates many metals, and is therefore a valuable test. When freshly prepared it is colourless, but soon turns yellow from the formation of a higher sulphide. The change 'does not hinder its usefulness as a test. Ammonium carbonate. — Experiment. — Mix an ounce of chalk (calcium carbonate) and half an ounce of ammonium chloride in powder. Heat the mixture in a dry Florence flask with the neck broken off, over which is inverted a small beaker. Double decomposition takes place ; calcium chloride remains in the flask, and the volatile ammonium carhonate sublimes and condenses in the beaker. This is the well-known smelling salts. It has, as its com- mon name implies, a strongly ammoniacal odour. In reality the salt has a very complex constitution, but the student may safely regard it as ammonium carbonate (^H^^GO^. Ammonium nitrate, NH4NO3, has already been described (p. 156). All ammonium salts, when warmed with solution of potash, p 210 EXPEEIMBNTAL CHEMISTET. or milk of lime, give off ammonia gas. They may readily be identified by this means : Ammonium Potassium Nitrate. Nitrate. NH,N03 + KHO = KNO3 + NHs + HA SILVER. Ag=108. Silver, though a monad, has but little analogy v?ith the other metals of this group. It sometimes occurs native (uncombined), but more frequently as sulphide, either pure or associated with the sulphide of lead or copper. It is also found as chloride (horn-silver), and in small (j^uantities in sea-water. Several processes are adopted for its extrac- tion. From galena (lead sulphide) it is obtained by reducing both metals to the metallic state, by roasting and smelting the ore with charcoal. The silver is then separated by a process called eupellation. The alloy is placed on a hearth or cupel, made of bone ash, and strongly heated in a current of air. The lead is rapidly converted into oxide, which, fusing, is partly volatilized, and partly absorbed by the porous hearth, leaving the silver in the metallic state. If the lead be poor in silver, ^the alloy is melted, and allowed to cool slowly in iron pots. The portions which, solidify first consist chiefly of lead, and, being removed with ^a- perforated lad]^, the re- maining lead becomes gradually much richer in silver. Com- plete separation is finally effected by eupellation. This method, known as Pattison's process, can be used economically, even when the lead contains less than ^-j^j-j- its weight of silver. SUver is obtained from the copper ores by reducing them to the metallic ctindition. The copper containing the silver is fused with lead, and the alloy, after solidifying, is gradually heated. The lead and silver melt first, and run off, leaving the copper. The silver is finally isolated by eupellation. Silver is often extracted by means of mercury from the ores containing pure sUver or silver sulphide, but no lead. But in the case of silver-glance (sUver sulphide) the metallic silver must first be separated from the sulphur. This is done by twp operations. In the first. SILVER. 211 the stamped ore is roaeted with common salt, by which process silver chloride and sodium sulphate are formed ; in the second, the roasted ore is mixed with water, iron, and mercury, and kept in constant agitation for some time in closed casks. Chloride of iron and metallic silver are there- by formed, the latter of which is dissolved in the mercury. The excess of mercury is then filtered off, and a solid silver amalgam is obtained by subjecting it to pressure, and the mercury is at last completely removed from the amalgam by difitiUation. As pure silver is very soft, and would quickly wear out in using, it is generally alloyed with copper, whereby it is rendered harder, without losing its ductility. If the pro- portion of copper is only one-fourth, the silver still retains its beautiful white colour ; but if more copper is added, the alloy becomes yellow, and finally red, by use. The standard silver, used in England for coinage, consists of 9t parts of pure silver and f of copper. Silver nitrate, AgNOa. — Experiment 1. — Heat a sixpence in some dilute nitric acid until it is dissolved. Silver nitrate is formed, but is contaminated with copper, as the blue colour of the solution betokens. Experiment 2. — Place a bright sheet of copper in the silver solution, and let it stand for a few hours. The copper immediately becomes covered with a black powder, which soon increases to a mass of brilliant metallic crystals of silver. The copper decomposes the silver nitrate, forming copper nitrate and free silver : 2AgN03+ Cu" =Cu"(N03)2 + 2Ag. By washing the crystals well with water in a filter, and drying them, pure silver is obtained, which, by being again dissolved in nitric acid, and evaporated to dryness at a gentle heat, furnish a white mass of pure silver nitrate. This may be dissolved in water, and crystallized, or fused and formed into sticks, when it constitutes lunar caustic. The crystals are anhydrous. Experiment 3. — Place a small piece of silver nitrate upon charcoal, and heat it before the blow-pipe ; it deflagrates and yields metallic silver, which may be easily fused at ai stronger heat. • 212 EXPEEIMEajTAL CHEMISTET. Experiment 4. — Add some ammonia to a solution of silver nitrate ; the dark-grey precipitate is silver hydrate, AgHO. If more ammonia is added, it is redissolved.- It would be dangerous to continue this experiment any further, as the silver combines with ammonia, and forms fulminating silver, which explodes violently on percussion or friction. Silver chloride, AgCl. — Experiment 5. — To a solution of silver nitrate add hydrochloric acid or a solution of common salt ; you obtain a white curdy precipitate of silver chloride. This precipitate is so insoluble in water that it will impart a cloudiness to a solution of silver diluted a millionfold ; it is, however, easily dissolved by ammonia. This reaction is made use of by assayers for testing silver alloyed with copper, as the quantity of pure silver in the alloy may be estimated from the amount of the solution of salt required for its complete precipitation (humid assay of silver). Silver chloride is also called horn-silver, having formerly received this name from the horn-like, appearance it assumes on meltiiig. Experiment 6. — After having decanted the supernatant liquid, rub the si,lver chloride with a cork upon a sheet of paper, and let it dry in a dark place — in a drawer, for instance ; it remains white. Now place the sheet partly in a book, so that one-half may be exposed to the light ; this part soon acquires a violet, and finally a black colour, while that protected from the light remains white. Thus light is capable of decomposing this salt. On this action of the solar light on certain substances is founded the art of photography, in which light acting upon the salts of silver (especially the chloride, bromide, and iodide) may be made to yield faithful representations of any objects. Silver sulphide, AgjS. — If you add sulphuretted hydi'ogen to a solution of silver you obtain a black precipitate of silver sulphide. This compound occurs in nature as the most important silver ore ; it is called silver-glance. , ( 213 ) CHAPTEE II. METALLIC BIADS. Group i. — Calcium, Strontium, Barium, Magnesium, Zinc. CALCIUM. Oa = 40. This metal never occurs pure, but many of its compounds, such as chalk, marble, limestone, and gypsum, are found in enormous quantities. Calcium is a yellow metal of no practical value. It can only be separated in small quantities, and with the greatest difBculty. It is very light. (Sp. Gr. 1"8), and decomposes water at ordinary temperatures, though with less energy than potassium and sodium exhibit. Calcium oxide (Lime), CaO. — Experiment 1. — Heat a small piece of chalk on charcoal before the blow-pipe for several minutes. It will be converted into calcium oxide, or quick- lime, by losing carbonic anhydride : CaC03=CaO + C02. Lime is obtained by burning a mixture of coal and chalk, or limestone, in chambers called lime hilns. Galcium hydrate (Slaked lime), Ca"(H0)2. — Experiment 2. — Lime combines eagerly vnth water to form the hydrate. Put some lime in a saucer, and sprinkle it with water. In a few minutes, it cracks in various places, and becomes very hot ; steam is copiously evolved, while the lime crumbles to a white powder, called slaked lime. This is calcium hydrate. It is alkaline and caustic, and slightly soluble in water. Put a little in a bottleful of water, and shake for a few minutes. A portion will dissolve. Allow the remainder to subside, and pour the clear solution into a fresh bottle, and 214 EXPEEIMENTAL CHEMISTRY. label it lime-water. It becomes milky on exposure to the air, from the formation of calcium carbonate by the absorp- tion of carbonic anhydride, hence it is often used as a test for that gas (p. 124). Calcium carbonate, Ca"COs, exists in nature as chalk, marble, and limestone, and as the beautiful, transparent crystals of Iceland spar. Calcium carbonate is insoluble in pure water, but soluble, to a small extent, in water impregnated with carbonic acid. It is therefore found in most natural waters, and is a frequent cause of what is termed the hardness of water. Experiment 3. — Pass a current of carbonic anhydride gas through a little lime-water in a wine-glass. The lime-water at first becomes milky, from the formation of carbonate ; but, after a time, the precipitate dissolves in the dissolved gas, and the liquid becomes clear. The carbonates of mag- nesium, and some other metals, behave in the same way. Experiment i. — Boil a little of the above solution in a test-tube. The CO2 which held the carbonate in solution is expelled, and the calcium carbonate is once more precipi- tated. This explains why water which owes its hardness to carbonates is softened by boiling. The fur which collects inside tea-kettles and boilers is generally formed in this way. For this reason hardness due to carbonates is called temporary hardness. Experiment 5. — Temporary hardness may be removed from water 'without boiling. Take a little of the solution prepared in Experiment 3, and add lime-water to it. The lime-water will neutralize the carbonic acid which held the carbonate in solution, and the whole of the calcium will then be precipitated as carbonate. This process for softening water is called " Clark's process." It has been found very useful on the large scale. Experiment 6. — Sodium carbonate may be used instead of lime-water in the preceding experiment. The sodium car- bonate combines with the carbonic acid, forming hydrogen sodium carbonate, NajCOs -|- H2CO3 = 2HNaCOs. We have already seen that carbonic anhydride can be expelled from calcium carbonate by strong heat, and also (p. 175) by the action of acids. Calcium sulphate, Ca"S04, is found native as gypsum. STKONTIUM. 215 alabaster, &c. It then contains two molecules of water. By heating gypsum to about 250° C. (482° F.) the water is driven off, and a white powder, the so-called plaster of Paris. is left. This, on being mixed to a paste with water, again unites with it, and the mass becomes solid and compact. Calcium sulphate is slightly soluble in water, and is a frequent cause of hardness in spring water. Hardness due -to sulphates is not removed by boiling, and is therefore called permanent hardness. Calcium chloride, Ca"Cl2. — This salt is formed when marble is dissolved in hydrochloric acid, as in the prepara- tion of carbonic anhydride. The solution, if very much concentrated by evaporation, deposits colourless crystals (CaClaBHaO) ; or, if evaporated to dryness, furnishes a spongy mass of the anhydrous chloride, which, in this state, is much used for drying gases, as it absorbs water with great avidity. Calcium fluoride, Ca'Tj, commonly known as fluor-spar, occurs crystallized in Derbyshire and Cumberland, and is interesting as the source of fluorine. The remaining compounds of calcium are of little im- portance, with the exception of calcium chloro-hypochlorite, Ca"Cl(C10), or bleachmg-powder, which has already been described under chlorine, and calcium jAosphate, 0a"3(PO4)2,' or bone-earth, which was discussed under phosphorus. Calcium phosphate occurs native as apatite and phosphorite. STEONTIUM. Sr=87-5. The compounds of this metal are similar to those of cal- cium ; but they exist only in small quantities. Their chief sources are the carbonate called strontianite, and the sulphate known as celestine by mineralogists. The metal resembles calcium, both in appearance and the difficulty which attends its extraction. It is of no importance. Strontium oxide, SrO, or strontia, like Hme, combines with water to form a hydrate. It is most easily prepared by heating the nitrate. By dissolving the carbonate in different acids, the other salts of strontium can be prepared. The most remarkable characteristic of the strontium salts is that of communi- 216 BXPEKIMBNTAL CHEMISTRY. eating a crimson colour to the flame of burning substances. Strontium nitrate, like the other nitrates, deflagrates upon burning charcoal, and is used for producing a crimson flame -in fireworks. Strontium chloride is soluble in alcohol, and imparts a crimson tint to its flame. BAEIUM. Ba = 137. Barium compounds are more extensively distributed than those of strontium. It chiefly occurs as heavy-spar (sulphate) and wiiherite (carbonate). The metal can only be obtained with difficulty in powder. Barium oxide, BaO, or baryta, is best obtained by heating the nitrate : it forms a hydrate with water which is much more soluble than the hydrates of calcium and strofatium. By passing air or oxygen over the heated oxide the curious compound, barium peroxide, BaOa, is obtained. This substance is used for preparing hydrogear peroxide (p. 133). Barium carbonate is insoluble in water. Barium sulphate is insoluble in everything, and is obtained whenever a soluble barium salt is added to sulphuric acid or a sulphate. Tor this reason barivm chloride, Ba"Cl2, and barium nitrate, Ba"(N03)2, which are soluble salts, are much employed as tests for the presence of sulphuric acid and sulphates (p. 148). Barium salts communicate a green colour to flame : unlike the strontium compounds, they are very poisonous. MAGNESIUM. Mg = 24=. The chief source of magnesium is dolomite, or magnesian limestone, which is a carbonate of calcium and magnesium. The element occurs also in sea- and spring-water as sulphate and chloride. The metal is now prepared in somewhat large- quantities, by decomposing heated magnesium chloride with sodium : MgCI^ + Naa = 2Na01 + Mg. Magnesium is a silver-white metal, which does not easily tarnish in dry air. It is malleable, and may be rolled into ribbon or drawn into wire. The most notable property of magnesium is the dazzling brilliancy with which it burns when held in a flame. This fact has led to its adoption as ZINC. 217 an illuminating agent in certain cases where a strong light is required. For this purpose it is used in the form of ribbon or powder, and burnt in specially contrived lamps. The light of burning magnesium forms a valuable substitute for sun-light in photography, owing to its extreme richness in rays of chemical power. Magnesium rapidly dissolves in most acids, with the evolution of hydrogen. Magnesium oxide {Magnesia), Mg"0. — Experiment. — Set fire to a piece of magnesium wir« with the flame of a spirit-lardp, or Bunsen's burner. It will burn rapidly, and be converted into a pure white powder. This is magnesium oxide, or magnesia (sometimes sold as calcined magnesia), formed by the direct union of its constituents. It is prepared in quantity by strongly heating the carbonate, which, like chalk, loses carbonic anhydride and yields the oxide. When treated with water, the oxide , yields a hydrate analogous to that of calcium, but much less soluble in water. Magnesium carbonate, Mg"C03, occurs crystallized as magnesite, and is the chief constituent of the magnesia alba of the shops. It is soluble, with effervescence, in acids. Magnesium sulphate (Epsom salts), 'M.g"SOi,7'SjO, is the chief salt of magnesium, owing to its extensive use in medicine as a purgative. It is largely prepared by dissolving dolomite in sulphuric acid, and from its superior solubility is easily separated from the very sparingly soluble calcium sulphate which is formed simultaneously with it. To the chemist magnesium sulphate is valuable as a test for phosphates (p. 169). ... Magnesium chloride, Mg"01z, is a very soluble salt, prepared by neutralizing hydrochloric acid with magnesium carbonate or oxide. It can only be obtained in the solid state by indirect means, as the solution decomposes on evaporation into magnesia and hydrochloric acid. znsro. Zn = 65. Zinc resembles magnesium closely, but is more easily extracted from its ores, the chief of which are zinc-blende (sulphide) and calamine (carbonate). Zinc is obtained by con- verting the ore into oxide by roasting in a current of air. 218 EXPEBEHBNTAL C3HBMISTKT. The oxide being mixed with charcoal is then heated in a cru- cible, through the bottom of which a tube passes high into the interior. The carbon removes the oxygen as carbonic oxide, while the liberated zinc being converted into vapour, descends through the tube and is condensed below. Zinc readily dissolves in acids, with evolution of hydrogen ; hence it is much employed for the preparation of that gas. Not very long ago, zinc was hardly used except for making brass and pinchbeck ; but since the art of rolling it out into sheets, of forging it, and of drawing it out into wire, has been acquired, it is used also for the manufacture of many, articles which were formerly made of lead, copper, and iron ; for instance, for making nails, gasometers, gas-pipes, gutters, and for roofs of houses, for Hning refrigerators, &c., as it is harder, and yet lighter than lead, cheaper than copper, and less liable than iron to be, destroyed by air and water. It usually occurs in commerce in the form of plates, which are so brittle that they may be broken by the hammer into small pieces; the fresh fracture exhibits a crystalline structure, and a bluish-white colour. Experiment 1. — If a piece of polished sheet zinc be alternately exposed to the action of water and of air, it will become gradually covered with a white film ; it rusts like iron, but the rust of zinc has a white colour. In iron the oxidation proceeds rapidly towards the interior, but not in zinc, or only very slowly ; therefore articles made of zinc, when exposed to the wind and weather, last much better than those made of iron, and for this reason, also, iron articles are frequently coated with zinc (galvanised iron). Zinc attracts not only oxygen, but also some carbonic acid, from the air, and this may be recognised by the effervescence which follows when some acid is dropped upon the tarnished metal.' Experiment 2. — Hold a rod of zinc by means of a pair of tongs or pincers in the alcohol-flame, until it hisses if you touch it with a piece of moist wood ; if you now quickly hammer it upon a stone or anvil previously heated, it does not break, but spreads out like lead into a thin, coherent sheet. Zinc has the singular property of being ductile between 212° F. (100° C.) cmd 302° F. (150° C), but belme or above this temperature it is brittle. Ever since it has been known that zinc is thus affected by heat, it has been found easy to ZINC. 219 overcome the difficulties which formerly opposed the con- version of this metal (which is unpliant when cold) into sheets and wire. Experiment 3.— Zinc, when heated to 774° F. (412° C.) melts, as may easUy be seen by holding a small pi,ece of it in an iron spoon over an alcohol flame. In this case a grey 'film of suboxide is formed ; but this after a time assumes a yellow colour, and is converted into oxide (ZnO). On cool- ing, the yellow colour passes to white ; the oxide of zinc belongs to those substances which present a colour in the heat different from the colour at the ordinary temperature. Experiment 4.— At a still stronger heat (1100°C. = 2012?^.), zinc evaporates and burns at the same time with a blue flame, as may be seen by heating a thin strip in the blow-pipe flame. The product of the combustion is zinc oxide, ZnO, portions of which are carried up, and being very Hght, float in the air in curious flocks. Zinc oxide, Zn"0, is a white light powder prepared by heating the metal strongly in air. It is insoluble in water, but dissolves in acids, forming the zinc salts. Zinc hydrate, Zn"(IIO)j. — Experiment 5. — Add potassium or sodium hydrate to a soluble zinc salt, such as the sulphate. A white precipitate of zinc hydrate will be produced : ZnSOi + 2KH0 = K^SO, -j- Zn(H0)2. Zinc hydrate is soluble in the alkaline hydrates, therefore care must be taken not to add too great an excess, or the precipitate will disappear. By heating the hydrate, water is driven off and the oxide is obtained. Zinc sulphate ( White vitriol), Zn"S04,7H20, is one of the most important salts of zinc. It is easily soluble and crystallizes in colourless prisms, containing nearly half their weight of water. It may easily be obtained by eva- porating the waste liquors left after generating hydrogen from zinc and sulphuric acid (p. 107). In commerce the sulphate is prepared by roasting the native sulphide (zinc- blende) in a current of air. The sulphide takes up oxygen and is converted into sulphate. The other salts of zinc are of little interest. The carbonate may be prepared by adding sodium carbonate to zinc sulphate ; the sulphide, by adding ammonium sillphide. They are both white, insoluble substances. The native sulphide 220 EXPEEIMENTAI. OHEMISTET. possesses a reddist colour, owing to impnrities. The chloride is used as a disinfectant under the name of " Burnett's dis- infecting fluid." Cadmium is a somewhat scarce metal, often found in zinc ores. It is very similar to zinc, but yields a beautiful yellow sulphide when its nitrate is treated with ammonium sulphide. Artists call the sulphide cadmium yellow. Geoup ii. — Copper, Mercury, Lead. COPPER. Cu = 63-5. Copper is often met with in the free state (native copper), but seldom in any quantity. The following are some of the more important ores of the metal : — 1. Eed oxide, GnjO. \ 2. Black oxide, CuO. I at x i, j t o ri T n a } Not very abundant. 6. (Jopper glance, Vxija. I ■' 4. Indigo Copper, GuS. J 5. Malachite, CuGOs, Cu(H0)2. The chief Australiaji ore. 6. Azurite, aCuCOs, Cu(H0)2. 8. S5:SS?ctSts3.1 The chief EngHsh ores. The processes by which the metal is smelted from these ores differ very much. The ores which do not contain sulphur are sometimes reduced by fusion (after previous roasting) with coke and lime. The roasting converts the metal to oxide ; this when heated with carbon loses its oxygen, while the silica, which would otherwise combine with some of the copper, is removed by the lime. The ores which contain sulphur, and especially the English ores, reqiuire an extremely complex series of processes for their reduction. These processes may be roughly summed up as follows : — 1. Processes of roasting, fusion and calcination, by which nearly the whole of the other constituents are removed, and the copper left as the red cuprous sulphide, Cu^S, called « fine metal." 2. Partial oxidation of the fine meftil in a " roasting furnace," by which a portion of the sulphide is converted to oxide : Cu,S + 20^ = 2CuO + SOs,. COPPER. 221 3. The draught is stopped and the heat increased, when the sulphide and oxide reduce one another, as the similar lead compounds do : CU2S + 2CUO = 4Cu+802. The copper so obtained is called " blistered copper." 4. Blistered copper partly oxidized in "refining furnace.'' Nearly all the remaining impurities are now removed in the slag. 5. " Poling." The melted metal is stirred up with the trunks of young trees. The gases given off from the wood remove almost every trace of oxygen, and the copper is obtained very pure. In ancient times copper was chiefly obtained from the island of Cyprus, whence its Latin name cuprum. The red colour and other physical characters of the metal are well known. Its specific gravity is 8'9 ; rather higher than that of iron (7-8). It is very tough and ductile, that is, it can be drawn into fine wire. It melts at a bright red heat. Copper is not easily altered by exposure to air. In pure air or water it undergoes no change. In moist air it takes up CO2, and acquires a green film of basic carbonate. At a red heat it takes up oxygen, and yields black scales of oxide, CuO. It combines easily with chlorine, bromine and iodine, and at a red heat, with sulphur and phosphorus. It is not acted on by dilute hydrochloric or sulphuric acid. Boiled with strong sulphuric acid, it yields copper sulphate and sulphurous anhydride (p. 144). Dilute nitric acid dissolves it easily, with liberation of nitric oxide (p. 162). Alloys of Copper. — Copper forms very important alloys with several other metals. Gold and copper form the common gold, silver and copper the' common silver, from which gold and silver articles and coins are made. The well-known brass, and other metallic compounds having the appearance of gold, such as tombac, similor, prince's metal, red brass, &c., are composed of zinc and copper. Spurious gold-leaf is made by hammering out tombac into exceedingly thin leaves, which, when finely pulverised, constitutes the so-called gold bronze: Yellow metal contains 2 of zinc to 3 of copper. It is used for sheathing 22'2 EXPERIMENTAL CHEMISTET. ships' bottoms. Purple or copjper bronze is prepared by gently heating the gold-coloured bronze till it turns to a purple-red colour. Zinc, nickel, and popper constitute the ingredients o£ German silver (paekfong, white copper). Tin and copper form a very hard grey alloy, from which statues, cannons, bells, mirrors, &c., are cast (bronze, gun- metal, bell-metal, speculum-metal). Copper, like mercury, forms two distinct classes of salts, one denominated cuprous, the other cupric. Thus we have cuprous oxide, iUujO, and cupric oxide, CuO; cuprous chloride, CujCls, and cupric chloride, CUCI2. In the cuprous compounds, two atoms of metal behave as a single diad atom (Cu^)". The cuprous compounds are, for the most part, unimportant. Cuprous oxide, Cu"20. — Etsperimemi, 1. — ^On heating a piece of bright copper in a smokeless flame, it passes through various shades of colour — crimson, violet, blue, and finally to grey. On speedily quenching the metal in water it becomes brownish-red ; this red coating is cuprous oxide. Cuprous oxide, when thrown into melting glass, colours it blood-red ; in this manner a beautiful red colour is flashed on glass in the glass factories. This accounts, also, for the red colour of the slag which forms during ihe calcination and fusion of copper. Experiment 2. — Cuprous oxide may easily be prepared by boiling a solution of copper sulphate and grape or starch sugar, to which an excess of an alkaline hydrate has been added. This will be further noticed under sugar. Cupric oxide, Cu"0. — If the copper be heated for a longer time it becomes coated with a black substance. This is cupric oxide; it contains a larger proportion of oxygen. By long continued ignition, the whole mass of the copper may be converted first into cuprous and ultimately into cupric oxide. The glowing cinders which fall off in the workshops of the copper-smiths (copper-scales)consist of a mixture of the two oxides. • Cupric oxide is extensively used as an agent for effecting the combustion of organic substances, with a view to their ultimate analysis. Por this purpose it is usually prepared by heating cupric nitrate. i COPPER. 223 Fig. 84. Experiment 3. — Introduce some eupric oxide into a test- tube, the bottom of which is broken, heat it, and then pass over it a stream of hydrogen, which is evolved by zinc and diluted sul- phuric acid ; in the heat, the hydro- gen abstracts from the oxide of copper its oxygen, and forms with it water, which escapes. A process by which this reaction has been utilized as a means of determining | the composition of water has already been described (p. 132). Cupric hydrate, Cu"(H0)2. — Experiment i. — Most of the metaUio hydrates are usually formed by adding an alkaline hydrate to a salt of the metal. Thus, on adding potassium hydrate to cupric sulphate there are obtained potassium sulphate and cupric hydrate. The latter substance is pre- cipitated as a light-blue powder. Boil the liquid in which it is contained, and it will become black, for it is resolved into black cupric oxide and water : Cu(H0)2 = CuO-j-H^O. This furnishes another example of chemical decomposition effected by mere elevation of temperature. Experiment 5. — Eepeat the former experiment, but instead of potash take ammonia; here also the copper hydrate is first precipitated, but this is redissolved by adding more ammonia, forming a splendid blue liquid. Ammonia is there- fore a test for salts of copper. Pour upon the blue liquid an equal quantity of strong alcohol, and direct the stream against the side of the glass, so that the alcohol may float on the surface ; after the lapse of twenty-four hours, a mass of dark-blue acicular crystals is perceptible, which consist of a compound of copper sulphate with ammonia, and are called cupric ammonio-sulphate. By dissolving them in water, the Hue liquid of the apothecaries' show-bottles is prepared. Cuprous chloride, Cu"2Cl2, is an unimportant compound, ob- tained by digesting cupric chloride with copper, out of con- tact with air. It is colourless, but. rapidly changes to green cupric chloride when, its acid solution is exposed to the air. Cupric chloride, Ou"01a. — By boiling hydrochloric acid with copper oxide, a green solution is obtained, and, by evaporation, a green salt — cupric chloride. It is soluble in 224 EXPERIMENTAL CHEMISTRY. spirit, and the solution, if ignited, burns with a beautiful green flame. Cupric nitrate, Cu"(N03)2,3HsO.-^Beautiful blue deliques- cent crystals, prepared, as already described, by dissolving copper in dilute nitric acid. Cupric sulphate (Blue vitriol), Cu"S04,5H^O. — This im- portant salt is prepared in large quantities by roasting native or artificial sulphide : CuS + 202 = CnS04. It is also formed by boiling copper with sulphuric acid, sulphurous anhydride being evolved (p. 144:). Experiment 1. — If half an ounce of copper sulphate is heated to boiling with an ounce and a half of water in a porcelain basin, and then boiled a few minutes with some granulated zinc, metallic copper separates as a powder, and zinc sulphate is formed. The powder obtained is washed, and then boiled with water and a few drops of sulphuric acid, in order to remove all the zinc. It must be dried quickly, but not at a high heat, for ■copper in this state of minute subdivision attracts oxygen with more avidity than when it is in a compact mass. Experiment 2. — Push an iron rod into a good-sized, large- Fig. 85. mouthed phial, forcibly enough to break out the bottom, file off the sharp edges of the fractured part, and bind some moistened bladder over the mouth of the phial. Then twist a wire firmly round the phial, in such a manner as to form two or three supports, by means of which it may be suspended in a tumbler. Let a strip of strong sheet zinc, of the width of Fig. 86. the finger, and five inches long, be soldered to a strip of thin copper plate, ten inches long, and bend the strip of copper as represented in the annexed figure. Put a coin upon the lower horizontal part of the copper strip, — for instance, a bright half- crown,;— or some other metallic object, the impres- sion of which you wish to take. Now fill the phial three-quarters full with very diluted sulphuric acid (one drachm of sulphuric acid to two ounces of water), intro- duce the zinc, and suspend the apparatus in a tumbler, in MERCURY. 225 which a saturated solution of copper sulphate, and also a few whole crystals of copper sulphate, have been put. In the course of a few minutes the coin will he covered with a thin film of metallic copper, and after several days, with a layer several lines in thickness, which may be removed as a coherent mass. Tallow or wax must be smeared over those parts of the coin and plate on which the copper is not to be deposited. The sunk impression thus obtained may be used in the same way again, instead of the coin, as a mould for obtaining a raised impression. When the evolutiqp of the gas in the phial has ceased, a few drops of strong sulphuric acid may be stirred in, or the liquid, which contains zinc sulphate in solution, may be replaced by a fresh supply of diluted sulphuric acid. Salt water may also be used instead of sulphuric acid, but then the separation of the copper takes place more slowly. The decomposition of the salt has, in this case, been effected by the galvanic current, which is always generated when, different kinds of metals, in contact, are introduced into liquids capable of being decomposed. The bladder is a porous substance, which allows the galvanic current to pass, but prevents the liquids from mixing. This experiment is a modification of Experiment 6, page 11. It affords an illustration of the art of electrotyping. Solutions of gold, silver, &c., may be decomposed in the same maimer (eZecfro-plating and gilding). MERCUKY. Hg = 200. This metal exists at ordinary temperatures as a liquid. From its appearance it is commonly called quicksilver, and in pharmacy hydrargyrum. It often occurs native ; but the chief supply is obtained from the native sulphide (cinnabar). The most celebrated mine is that of Almaden in Spain. From cinnabar it is easily obtained by heating the ore in a free current of air ; the sulphur burns to sulphurous anhy- dride and escapes, while the merciuy volatilizes and can readily be condensed. In the northern regions of the 226 EXPEKIMENTAL CHEMISTEY. earth mercury becomes Bolid in winter, whenever the cold reaches — 40° F. ( — 40° C.) ; but in our climate it can only be solidified by artificial frigorific mixtures. Mercury boils at 360° C. (680° F.), and yields a colourless vapour, the specific gravity of which is 100. Hence it is easy to purify the metal by distillation. Experiment 1. — Fasten to the cork of a phial containing mercury a piece of wood, affixing to the bottom of the latter some genuine gold-leaf; the gold, after some days, will have assumed a white colour, and be converted into an alloy of gold and mercury. It is obvious from this, that fumes of mercury must be contained in the air of the phial, and that mercm'y, like water, evaporates slowly even at ordinary tem- peratures. The vapour of mercury, and the preparations of mercury, are very iajurious ; they first produce involuntary salivation, and afterwards lingering, dangerous maladies ; therefore, in experimenting with mercury, not only the inhalation of the fumes should be avoided, but it must be weighed and decantered over a bowl, so that, if any portion of it should happen to be spilt, it may not fall upon the floor. As, in comparison with water, mercury bolls at a very high, and freezes at a very low temperature, and as it has a great specific gravity (13-6), it is excellently adapted to the construction of thermometers, barometers, areo- meters, &c. Mercury, if quite pure, retains its metallic lustre in the air and water, and it is therefore ranked among the rwhle metals ; but if it is mixed or adulterated with other metals, as lead, tin, or bismuth, a grey film will gradually form upon its surface. When mercury is kept for a month or so in contact with air, at a temperature near its boiling point, it absorbs oxygen, and is converted into the scarlet mercuric oxide, HgO, from which oxygen gas was first prepared by Priestley (p. 61). Mercury is not acted on by hydrochloric acid, nor by cold sulphuric acid. When it is boiled with strong sul- phuric acid, mercuric sulphate, HgSOi, is formed, and sul- phurous anhydride expelled. Nitric acid, even when cold, dissolves it easily. Heated in chlorine it takes fire, and mercuric chloride, HgOlj, is formed. Mercury, like copper, forms two series of compounds, the . OXIDES. 227 mercurous and mercuric. In the former two diad atoms of the metal play the part of a single diad atom, as the follow- ing comparison of a few important compounds will show. Mercurous. Mercuric. Chloride . . . (Sg^)"Cl^. Hg"CU. Oxide .... (Hg,)"0. Hg"0. Nitrate .... {Hg,)"(N03),. Hg-'CNO,),. Mercurous Oxide — Mercury Suboxide — HggO. Experiment 1. — Dissolve a globule of mercury in a slight excess of cold nitric acid. Mercurous nitrate is formed, and nitric oxide set free. To the solution add caustic potash. A black precipitate of mercurous oxide is formed. It is very unstable. Mercuric oxide. — Mercury peroxide. — Hg"0. — Dissolve a globule of mercury in excess of boiling nitric acid. Mercuric nitrate is thus obtained. On adding potash solution a yellow precipitate will be produced : it is mercuric oxide. Wash and dry it. This substance may also be obtained by heating solid mercuric nitrate, and by the direct union of its con- stituents with the aid of heat. Mercurous nitrate, or mercury sub-nitrate, Hg"2(N'03)2. — This salt, it has already been stated, is formed by acting on mercury with cold nitric acid. It may be obtained crystal- lized by pouring half an ounce of nitric acid and a few drops of water on an ounce of mercury in a porcelain basin. In a few days the mercury will be covered with white crystals of thff salt in question. They may be preserved and dissolved in water, with the aid of a drop of nitric acid as required. .Experiment 1. — If a drop of the solution of mercurous nitrate is rubbed upon a copper coin, the mercury separates as metal, and effects a false silvering of the copper. Experiment 2. — Make a stroke across a thin brass plate with a wooden stick that has been dipped in the solution of mercury ; if the plate is afterwards bent at this place it will break, as though it had been cut ; because the reduced mercury penetrates the brass with great quickness, and renders it brittle. Thus the brazier can make use of this solution instead of shears. 228 BXPEEraENTAL CHEMISTKT. Mercuric nitrate, Hg"(N0s)2. — Formed in the manner already described : when heated, red fames escape, and mercuric oxide is formed. CHLORIDES. Mercurous Chloride, or Mercury Svh-chloride {GalomeC), Hg",Cl,. Experiment 1. — Add some hydrochloric acid, or a splution of common salt, to a diluted solution of mercurous nitrate ; a heavy white precipitate of mercurous chloride is produced, which is insolMe in water. When well washed and dried, this salt of mercury forms the highly important medicine known as calomel (precipitated). If some of it is moistened with an alkaline hydrate it becomes black, from the formation of mercurous oxide; thus is explained the Greek name calomel (koAo's, beautiful, /ieXas, black). Calomel is now almost exclusively obtained by a process which will be described presently. Mercuric Chloride (^Corrosive SiMimate'), Hg"Gl2. Eaperiment 1. — Heat some mercuric oxide with hydro- chloric acid, and continue adding the latter till a complete solution is obtained; the white prismatic crystals which separate on cooling are mercuric chloride, or mercury hi- or perchloride — one of the most violent poisons. The same com- pound is obtained on a large sca£e, in white, transparent, heavy masses, by the following process : Experiment 2. — Grind sixty grains of mercuric sulphate- in a mortar, with an equal quantity of common salt. Heat half the mixture thus obtained in a test-tube. A white crystal- line crust will condense on the upper and cooler part of the tube, and may be removed and dissolved in boiling water. It consists of mercuric chloride : HgSOi + 2NaCl = NajSOi -f HgClj. Eaperiment 3. — Add twenty grains of mercury to the other half of the mixture, and grind them together until ■ the mercury loses its fluidity and becomes incorporated with the other materials to a grey powder. Heat this mixture in OHLOEIDES. 229 a tube as before. A similar white crust is produced ; but it cannot be dissolved. It is mercurous chloride, or calomel : 2NaCl + HgSO< + Hg = 2^82804 + Hg^Clj. The same result would be produced by heating the proper proportion of mercury directly with mercuric chloride instead of the materials for preparing it. Experiment i. — Add ammonia to a solution of mercuric chloride; a white and not a yellow precipitate is formed. It is a complex compound, known in medicine as white precipitate. Mercuric iodide, Hg"Ii. — This deadly poison is chiefly interesting from its brilliant red colour, and the change which the latter undergoes under the influence of heat. It is very volatile, and its vapour is remarkable as being more than fifteen times heavier than air (Sp. Gr. 227, H = 1). It lA^y be prepared by the direct union of its constituents. 'Eayperiment 1. — Triturate a few grains of iodine in a mortar with a small globule of mercury and a drop of alcohol. The formation of the iodide will become apparent by its red colour. Experiment 2. — By far the best method of forming this body is by the addition of an iodide to a soluble mercuric salt. Add potassium iodide slowly to mercuric chloride. Each drop of the iodide as it falls and mixes with the other solution presents the most beautiful appearance. Testoons of a canary-yellow precipitate are formed, and gradually change their colour to a brilliant red. The colour disappears on stirring if the mercuric chloride be in excess, but is repro- duced by the addition of more iodide. The red precipitate is also soluble in excess of potassium iodide. Experiment 3. — Collect some of the red precipitate, wash and diy it. Smear a little on a sheet of wjiite paper, and warm the latter over a lamp. TEe red colour will be changed to yellow. Eub the changed colour with a hard body as a stirring-rod ; wherever the rod touches the red colour will reappear. The original colour also returns spontaneously in a few days. The difference in colour is not owing to altered composition, but to a change in molecular arrange- ment. Mercuric sulphate, Hg"SOt. — This salt is obtained by 230 EXPEEIMKNTAL CHEMISTRY. boiling mercury with sulphuric acid in a Plorence flask until a white mass is left. It is chiefly used for preparing calomel and corrosive sublimate. It is decomposed by water. Mercuric Sulphide, Hg"S. Experiment. — If a solution of mercuric chloride is agitated with a little sulphuretted hydrogen water, or ammonium sulphide, a white precipitate is formed, which, on adding more of the precipitating body, becomes yellow, brown, and finally black ; the black substance is mercuric sulphide. This compound is also obtained by mixing mercury with melted sulphur, or indeed by rubbing it for a day with flowers of sulphur (Ethiops mineral). If this black sulphide is sublimed in a glass tube, then a blackish-red crystalline mass is obtained, the colour of which, by friction, passes into the most magnificent scarlet red. The sulphide in this state is called vermilion, or cinnabar. The red and the black sulphide have precisely the same composition, and yet a very great difierence in appearance. Vermilion is also frequently prepared in factories in the moist way, by triturating together for a day mercury, sulphur, and a solution of potassa. When vermilion is pure, it volatilises completely on a glowing coal, emitting, at the same time, a blue sulphurous flame ; but if adulterated with red lead, beads of metallic lead remain behind. On account of its insolubility, it is less prejudicial to health than many of the, other compounds of mercury. Cinnabar also occurs in nature, and we have in it the most important ore, from which we obtain mercury on a large scale. Small globules of pure mercury are also found in many porous stones. AMALGAMS. Experiment. — ^Introduce a globule of mercury into a porcelain dish, put upon it a piece of lead, and let them remain for some time in contact ; both metals will in- timately combine together. If the proportion of mercury is small, a friable mass is produced ; but by increasing the quantity, a paste, and, if still more is added, a liquid solution, is obtained. Mercury will combine in a similar manner with most of the metals, forming what are called amalgams. The amalgam of tin is especially important for silvering glass. LEAD. 231 LEAD. Pb = 207. Lead does not occur free in nature, but chiefly as sulphide, PbS, called by mineralogists galena. In smelting galena, the ore is first roasted in a current of air, with the addition of lime. The object of the lime is to remove impurities as slag. During the process part of the sulphide combines with oxygen, and there are formed lead oxide and sulphurous anhydride, which last escapes as gas. The air being then excluded and the heat raised, the sulphide which remains, reacting with the oxide, forms sulphurous anhydride and metallic lead : 2PbO + PbS = S0,+ 3Pb. Galena generally contains silver in varying quantities. The silver is economically extracted by the process already de- scribed (page 210). The physical properties of lead, its blue lustre, its easy fusibility, - softness and pliability, its high specific gravity (11-3), &c., are well known. It contracts during solidification, and it is therefore impossible to obtain sharp casts with it. Lead-shot. — Lead may be granulated, like zinc, by being melted and poured into water. In the manufacture of shot, the drops of lead are let fall from such a height that they solidify before reaching the water. For making the largest- sized shot, a tower of at least 150 feet high is required. A small quantity of arsenic is usually added to the lead, to render the drops perfectly globular. As lead and arsenic are both poisonous, shot should be used with caution in washing out bottles. Lead is not changed by exposure to air which is perfectly free from water, or water perfectly free from dissolved air. But in ordinary air it tarnishes rapidly, and in ordinary water its surface is soon converted into lead hydrate, Pb(H0)2, which dissolves in the water, and communicates to it poisonous properties. This corrosion is, however, almost immediately arrested in many cases by the action of the carbonates and sulphates so often found in drinking water. Carbonates convert the soluble lead hydrate into an insoluble double salt (Pb(H0)j,PbC03), and sulphates into an equally in- 232 EXPEEIMENTAL CHEMI8TKT. soluble lead sulphate (PbSO,), either of which soon covers the metal with a coating which prevents the further action of the water, ^ew lead pipes and cisterns are, therefore, more dangerous than old ones. Neither should in any case be used for water which does not contain notable quantities of carbonates, sulphates (or phosphates, which have a similar effect). Chlorides and nitrates have a contrary effect, and increase the corrosive action of the water. Eayperiment 1. — To detect the presence of minute traces of lead in water, evaporate half a pint of the water to dryness, add a little nitric acid, evaporate again, very gently, till the residue is pasty, add half an ounce of distilled water, warm and filter. Through the cold filtered liquid pass sulphuretted hydrogen gas for some minutes. A very minute trace of lead would in this case yield a brown colouration ; a larger quantity of the metal would cause a black precipitate (PbS). Experiment 2. — The action of water on lead may be tried by placing bright slips of lead in two glasses, one filled with rain, the other with hard spring water, and allowing them to remain for some days. The water in each glass may then be carefully filtered and tested in the manner above described. It will generally be found that the spring water does not hold any lead, or only a very small trace, in solution, while the rain water has dissolved a good deal. COMPOUNDS. Lead oxide, Pb"0. — Experiment 1 . — If lead is heated before the blow-pipe in the exterior flame, it melts at 617° F. (325° C), and is thereby coated with a grey film ; indeed, it is finally entirely converted into a grey powder. This may be regarded as a mixture of oxide of lead with metallic lead. By continued blowing, this grey colour is changed to yellow ; the yellow body is lead oxide (PbO). At a stronger heat the oxide melts, and solidifies on cooling into a reddisVyellow mass, composed of brilliant scales, the well-known litharge. By directing upon it the inner blow-pipe flame, metallic lead will again be obtained. This easy reducibleness, which is peculiar to almost all salts of lead, together with the incrmtor tion of yellow oxide, deposited upon the charcoal, is a certain test for the presence of lead. Litharge has many applications in the arts and trades. LEAD. 233 Lead-glass (flint-glass), lead-glaze, and sugar of lead are prepared from it ; the manufacturing chemist likewise pre- pares from it red lead, white lead, and other lead colours, and lead salts; the apothecary compounds insoluble soap (lead plaster), by boiling it with olive-oil ; the cabinet-maker makes a varnish that dries rapidly, by boiling it with linseed oil, &c. Lead di-oxide, PVOj. — Experiment 2. — If you heat some red lead gently in nitric acid for a few minutes, it is con- verted partly into nitrate, which dissolves, and partly into di-oxide, which remains undissolved as a dark-brown powder. Med oxide of lead. — Experiment 3. — Heat in a ladle one drachm of litharge and a quarter of a drachm of potassium chlorate ; the yellowish mixture smoulders to a red powder, which must be well washed with water. The same thing happens on heating the litharge for a day, but not to the melting point ; and at the same time frequently stirring it. By both methods the litharge receives one-third more of oxygen ; in the former case from the chlorate, in the second case from the air ; and is thereby converted into PbsOi ; this compound is called red- lead, or minium, and is much used as a scarlet pigment. It may be regarded as a compound of 2PbO, and PbOj. Lead hydrate, Pb"(H0)2. — This substance is obtained as a white precipitate when potassium or sodium hydrate is added to a soluble lead salt, as the nitrate. It is soluble in excess of the alkali, and in most acids. Lead nitrate, Pb"(N03)2. — The best solvent of lead is warm nitric acid, diluted with water ; the product is lead nitrate. It may be obtained in crystals, by evaporating and cooling the solution. Litharge may be used instead of metallic lead. When dry lead nitrate is heated in a test tube, nitric peroxide, NOa, escapes. Lead chloride, Pb"Cls. — Experiment 4. — Heat to boiling one drachm of litharge, with half an ounce of hydrochloric acid and half an ounce of water, and decant the clear liquid from the sediment into a glass vessel ; you obtain, on cooling, lustrous white acicular crystals of lead chloride (horn-lead). This salt is but very sparingly soluble in water. Experiment 5. — If two grains of litharge and fifteen grains of sal ammoniac are fused together in an iron spoon, there is 234 BXPEEIMENTAL CHEMISTBT. obtained a combination of a small quantity of lead chloride, with, a large proportion of lead oxide, in the form of a brilliant, yellow, laminated mass, which when triturated yields a beautiful yellow powder. This powder is used by painters under the name of Cassel or mineral yellow. Lead acetate, Pb"(Ci,H30j)2,H20, which contains one- Fig. 88. seventh of its weight of water of crystallization, ?4 forms the most important soluble salt of lead, sugar of lead, which commonly crystallizes in four-sided prisms. On exposure to the air, some of its acetic acid is driven off by the carbonic acid of the air, and the salt then yields with water a turbid soln- tion, but which may be rendered transparent by adding to it a few drops of acetic acid. Basic lead acetate is prepared by digesting a solution of sugar of lead with oxide of lead, whereby part of the oxide of lead is dissolved. This combination is kept in the apothecaries' shops in a liquid form, under the name of solw- tion of svhacetaie af lead, or Goulard's extras. When mixed with water it forms the so-called Goulard water, which has often a milky appearance, because some lead carbonate is formed and separated by the carbonic acid of the water. Lead sulphate, Pb"SO<. — This salt is easily formed when sulphuric acid or a soluble sulphate is added to a solution of lead. Even in a solution of lead more than a thousand times diluted, a white turbidness is produced, since the lead sulphate is an entirely insoluble salt ; we have, accordingly, in sulphuric acid, a very delicate test for salts of lead. Lead carhonaie, Pb"COs. — Experiment 6. — Add to a solution of sugar of lead a solution of sodium carbonate as long as a precipitate is formed ; the precipitate is lead carbonate. The pigment known under the name of white lead is likewise carbonate of lead, but mixed with variable quantities of lead hydrate. This is prepared on a large scale in different ways. a. According to the English method, litharge is mixed with vinegar to form a paste ; this is then spread upon a stone slab, and exposed to the fumes of burning coke, the carbonic anhydride from which combines with the oxide of lead. The acetic acid acts in this case the part of a mediator. It dis- solves the oxide of lead and forms acetate, which is decom- posed by the carbonic anhydride, acetic acid being reformed. LEAD. 235 It is obvious that in this way a small quantity of acetic acid (or else of sugar of lead) is sufficient to aid in converting gradually a large quantity of litharge into white lead. 6. By the oldest, the Butch method, a large number of jars, in which some vinegar has been poured, are arranged in a building upon a layer of stable-manure or tan, and rolls of sheet-lead are then suspended in the jars above the vinegar, and the whole covered with another layer of stable-manure. After the lapse of several months, the rolls of lead are found to be mostly, if not entirely, converted into white lead. The manure is decaying straw, tan is decaying wood ; decay is a slow combustion, or, what is the- same thing, a slow conver- sion of organic substances into carbonic anhydride and water. In every combustion or decay, heat is liberated ; this in the present case is sufficient to evaporate gradually the vinegar. Accordingly, oxygen, aqueous vapour, fumes of vinegar, and carbonic anhydride, are present in the air of the white-lead chambers. If you suppose that these substances combine with the lead in the succession just mentioned, the following order of changes will take place : 1, lead oxide ; 2, lead hydrate ; 3, lead acetate, 4, lead carbonate. Thus there is formed first lead oxide, which, just as in the former process, is converted into lead carbonate through the mediation of acetic acid. The finest kind of white lead is that of Krems, called on the continent of Europe white of Kremnitz. Lead carbonate is extensively used as a white paint, and for this purpose it is very valuable, but from its poisonous nature is often productive of serious disease to those who work with it. Many less dangerous substitutes have conse- quently been proposed, but none have been found to equal it in the opacity, or " body " it possesses. Powdered barium sulphate (heavy spar) is commonly used to adulterate inferior kinds. This impurity may be detected by dissolving the white lead in dilute nitric acid, when the barium sulphate, being quite insoluble, remains behind. On heating white lead, carbonic anhydride is evolved and lead oxide remains. Lead-Tree. — Experiment 7. — Dissolve half an ounce of sugar of lead in six ounces of water, filter the liquid, pour it into a phial, and then suspend in the latter a zinc 236 EXPEEIMENTAL CHEMISTET. j,od, by attaching it to the cork; the zinc is soon covered „ „. with a grey coating, from which brilliant metaUic ^' ' spangles will gradually shoot forth, finally filling up the interior of the phial. They consist of pure lead (the lead-tree). After twenty-four hours, no trace of lead can be found in the solution ; it has been replaced by zinc ; the stronger zinc has forced the weaker lead from its combination. This experiment might be made to illustrate not only the relative combining powers of the two metals, but also their equivalents. It would only be necessary to weigh the lead formed, and the zinc before and after the experiment, to ascertain that the weight of the precipitated lead is to ttie loss of zinc as 207 is to 65. An atom of lead is therefore replaced by an atom of zinc. A similar experi- ment, in which silver is precipitated by means of copper, forming the silver-tree, was described in page 211. Lead tartrate, Pb"C4H406. — Experimient 8. — Make a strong solution of lead acetate, and add to it a sqlution of tartaric acid. The white precipitate of lead tartrate formed is . collected on a filter, washed well with water and dried. It is interesting from the fact, that on being heated strongly in a close vessel it is decomposed, and furnishes a mixture of finely-divided metallic lead and carbon which, on exposure to air, spontaneously ignites. Such a substance is termed a pyrophorus. Lead pyrophorus is prepared as follows. Select a glass tube, as thick as a lead pencil, and seal one end with the blow-pipe. Inti oduce siifficient dry lead tartrate to fill it for about an inch and a half; then at three inches from the closed end soften a part of the tube in the blow-pipe fiame, and draw it out so as to constrict the tube to a narrow channel. When the tube is cold, hold it horizontally and shake -the tartrate, so that it occupies the whole space to the constriction, and leaves a clear channel above the substance. The tube must then be heated, gradually and progressively, from the sealed end to the constriction, with a spirit-lamp. As soon as the tartrate is heated it begins to decompose and blacken, coloured drops of moisture are formed and driven along the tube, and a thick smoke is evolved which smells like burning sugar. When the evolution of fumes ceases, the heating is discontinued and the tube allowed to cool ; the black sub- LEAD. 237 stance obtained is the pyrophorus, and wlien shaken out into the air it takes fire, and burns with a great glow and much yellow smoke. By applying the blow-pipe flame, the tube may be sealed at the constriction, and the contents will then retain their pyrophoric powers for an indefinite time. The yellow powder produced by the ignition is lead oxide. Lead sulphide, Pb"S. — This is a black powder, obtained whenever a lead salt is precipitated with sulphuretted hydrogen. It occurs native as galena, and is easily recog- nised by its greyish-black colour, its shining metallic lustre, and its high specific gravity. 238 EXPKEIMENTAL CHEMISTET. CHAPTEK III. METALLIC DIADS, OE TETEADS. Gsonp i. — Iron, Chromium, Manganese, Aluminium, Cobalt, Nickel. The three first metals of this group yield two well-defined series of compounds, analogous to those of copper and mercury.- In one series the metal is a simple diad. Such compounds are sometimes called proto-compcmnds, but are more frequently designated by the termination ous. Ferrous chloride, or iron protochloride, re"Cl2, is an example. In the other series two atoms of the metal play together the part of a single hexad atom, e.g., (Fe^)". This is perfectly consistent with the tetratomicity of the metal, as will be fully explained in the introduction to organic chemistry (Part III., Chap. I.^. Compounds of this kind have the termination ic, but are also known as per, or sesqui compounds. Ferric chloride (iron perchloride, or iron sesquichloride), (Fe2)"Glj, illustrates their composition. The following table of a few important iron compounds will explain the constitution of the two series more clearly than words : Ferrous. Ferric FeCla Fe,Cle Chloride. FeO Fe,Os Oxide. Fe(H0)2 Fe,(HO), Fe,(NO,)e Hydrate. Fe(N03), FeSO^ Nitrate. Fe,(S0,)3 Sulphate. Besides these compounds, in which the metal is basic, several of the metals of this group (notably chromium, and man- ganese) yield interesting and important acid radicals. With the exception of aluminium, neutral oxides of all of them are IRON. 239 known. No aluminious and no nidkelic compounds (except nickelic oxide, NisOj) are known. IRON. Fe = 56. This most important metal is rarely found native. The meteorites which sometimes fall from the sky often contain more than 90 per cent, of iron, together with nickel, cobalt, and other elements. The following are the most important ores of iron : Fe304, Magnetic ore (Loadstone). — Found in Norway, Sweden, the United States, &c. The most valuable ore of iron. FojOs, B,ed haematite. — Found in England and elsewhere. The same oxide occurs in combination with water, as hrovm hcematife, 2FeaOs3H:,0. FeCOs (Ferrous carbonate). — Nearly pure as spathic ore, found in Styria, &o. Clay-iron ore, the great English ore, is ferrous carbonate, with clay and other impurities. It occurs in Staffordshire, &c., in grey nodules. Blach band, the chief Scotch ore, is clay-iron, with from 10 to 30 per cent, of bituminous matter. FeSa, Iron pyrites. — Very abundant. It yields bad iron, but is valuable as a source of sulphur. It is often used as a substitute for sulphur in making sulphuric acid (p. 148). MBTALLUEGY OF IBON. CAST IKON — SMELTING. The methods adopted for the separation of iron from its ores vary a good deal, according to the nature of the ores. The most important is that used in England for clay iron. 1. The ore is roasted at a dull red heat. This is effected by pUing it in heaps, with alternate layers of coal, and burning the coal with free access of air. The ferrous car- bonate loses COi, just as chalk does in a lime kiln, and at the same time takes up oxygen : 2FeCOs + = Fe^Os + CO^. The water, sulphur, &c., of the ores are expelled at the same time. 2. The smelting is effected in a hlast-furnace (Fig. 90), which is often 50 feet or more in height. The furnace is 240 EXFE&IMENTAL CHEMISTBY. charged with alternate layers of coal, roasted ore, and lime- stone (CaCOs), or lime, and fresh charges of each are added every few hours, as the mass sinks in the furnace. In this, way the action of the furnace is rendered continuous, and it can be worked for years without cessation. As the ore sinks down, the ferric oxide is reduced to metallic iron, which, in the lower and hotter part of the furnace, is melted. Melted iron accumulates on the hearth of the furnace, and is drawn off from time to time into rough moulds printed in sand. When the iron is cold it is broken up into bars, which are Fig. 90. Mouth. Redncing. Melting. Hearth called jpigrs. The combustion of the fuel is msdntained by air forced in through conical apertures, called tuyeres, just above the hearth. To avoid waste of heat this air is now generally heated to about 300° C. (572° F.) before it is blown in. (Hot blast.) Chemistry of the blast-furnace. — The accompanjring wood- cut represents one form of the blast-fnmace, and the technical names of the different parts of it. In the lower part of the furnace, where the air comes in contact with the fuel, the heat is most intense. Combining with the oxygen of the air, lEON. 241 the carbon of the fuel is here converted to carbonic anhydride, which passes upward through the hot mass above. But we have already seen (p. 180) that when carbonic anhydride passes over red-hot carbon it is reduced to carbonic . oxide : CO2 -)- C = 2C0. The latter gas is, therefore, formed in large quantity. In the upper and cooler part of the furnace this carbonic oxide comes in contact with the heated ferric oxide, and at once reduces it to a porous mass of metallic iron : PeA + 3C0 = 2Fe + SCO^. As this porous iron descends into the intensely hot portion of the furnace (the boshes) it combines with carbon, and melts, and the liquid compound accumulates on the hearth, whence from time to time it is drawn off into the moulds. (Cast iron.) The use of the lime in this operation is very interesting. It combines with the silica and the other foreign matters of the ore and fuel, forming with them a kind of rough glass (the sl(ig), which melts at a much lower temperature than iron. The melted metal is always covered with a layer of this liquid slag, which is constantly flowing off through apertures arranged for the purpose. . The slag from the blast-furnaces has generally a green or blue colour, owing to the protoxides of iron and of manganese diesolved'in it. It is sometimes formed into square blocks, and used for building-stones. Cast or Grvde Iron.- — The metal obtained by the above process is by no means pure iron, but a compound of iron and carbon. A hundredweight of iron takes up, at the hottest white heat, from about four to five pounds of carbon, and likewise some silicon from the silicic acid, some aluminimi from the clay, and also traces of sulphur, phos- phorus, arsenic, &c., when these were contained in the iron ore. Cast-iron, thus obtained, is characterised by the following properties : a.) It is fusible at a much lower temperature than pure iron ; therefore it is especially adapted for those iron articles which are made by casting. For remelting iron on a small scale, graphite crucibles are made use of; but on a large scale shaft-furnaces, or the so-called cupola-furnaces. 242 EXPERIMENTAL CHEMISTBT. 6.) Cast-iron is hritUe, and can neither be forged Tior welded (bar-iron and steel may be bent, forged, and welded). 5'he application of cast-iron must, therefore, be limited to the manufacture of sucb articles as are not exposed to being bent, or to strong concussions. There are two kinds of cast-iron in commerce, known as grey and white iron. The grey iron is almost black, has a granular texture, and admits of being filed, bored, &c. ; the vihite iron, on the contrary, is of a silvery whiteness, possesses a lamellar-crystalline texture, and is so hard as not to be acted upon by steel instruments. Crude white iron, by remelting and very slow cooling, is changed to grey ; on the other hand, the grey is changed to white iron by being heated and suddenly cooled. Grey iron is best adapted for cast- ings ; white iron is the most suitable for the manu&cture of bar iron and steel. When grey iron is dissolved in dilute acids a mass of graphitic carbon remains. Mottled iron is inter- mediate between white and grey. Malleahle, Wrought, or Bar Iron. — Cast-iron, by being deprived of its carbon, is converted into malleable iron, and acquires the following very important properties : a.) Bar-iron possesses great ductility and tenacity, and may be hammered or rolled into sheets, and drawn out into fine wire, which is not the case with cast-iron. 6.) At a less degree of heat than that of fusion it becomes soft, like wax or glass, so that two glowing pieces may be welded into one. Upon this property depends its capacity of being welded. c.) Wrought-iron is sufficiently soft to be worked by steel instruments, and it does not become harder ii, when heated to redness, it is suddenly quenched in water (steel is thereby rendered brittle). d.) Wrought-iron is distuiguished, moreover, from cast- iron by its fibrous texture, composed, as it were, of threads incorporated together ; while cast-iron has the appearance of being a baked granular mass. But it is a very striking fact that fibrous wrought-iron, by repeated jolts or blows, be- comes gradually granular and brittle, as, for example, in the axletrees of carriages. By thoroughly heating and rework- ing, the former strength and flexibility, as well as the fibrous texture, is restored to the ii-on. IRON. 243 Wrought-iron is not entirely free from carbon ; it contains, however, only O'l to 0'5 per cent, of it. Iron entirely free from carbon is softer and more tenacious than bar-iron. Thus we see that it is the chemical combination of the carbon with the iron, as in cast-iron, which destroys these two properties of softness and tenacity. Refinery of Iron. — The method which is employed for separating carbon from the cast-iron is very simple. The carbon is hwmt out by heating the iron to fusion, and constantly stirring it (puddling) while exposed to a current of air (or, as in the famous Bessemer process, by forcing air through the melted metal), the oxygen of which combines with the carbon, forming carbonic oxide gas. During the operation, a considerable portion of the iron is converted by oxidation into oxide, which fuses with the sand, that is purposely strewed upon the hearth, and forms with it a heavy black slag of iron silicate. The iron mass becomes gradually more tenacious, since the iron melts with more dif&culty the less carbon it contains ; and finally, in the form of a loosely coherent mass (the hloom), is placed under a steam hammer, by a few blows of which the remaining slag is pressed out, and the iron particles are formed into a compact mass. The latter is afterwards usually hammered or rolled into- bars or bands. This method of converting brittle cast-iron into ductile and malleable iron is called puddling. It is some- times preceded by a separate process called refining. Steel. — Steel holds a middle place between cast and wrought iron, both as to the quantity of carbon it contains, and other properties. a.) If quenched when heated to redness, it is rendered hard and brittle (like cast-iron) ; if cooled somewhat more slowly, it is rendered elastic ; and if cooled very slowly, it is soft, ductile, and malleable (like bar-iron). 6.) It is less fusible than cast-iron, and more so than bar- iron. c.) It contains about 1'5 per cent, of carbon. To these properties steel owes its importance as a material for thousands of articles, especially for cutting instruments, since it may be made soft or hard, elastic or brittle, at pleasure. The article manufactured is usually first heated to redness, then suddenly cooled by quenching it in water, 244 , EXPERIMENTAL OHEMISTET. and afterwards tempered, in order to diminish its hardness and brittleness. Experiment. — Hold a steel knitting-needle in the flame of a spirit-lamp till it is red-hot, and then quickly plunge it in cold water ; it thereby becomes so brittle as to break on any attempt to bend it. Again hold the needle in the fire, and observe the changes of colour which it passes through ; it will first become yellow, then orange, crimson, violet, blue, and finally dark-grey. The change of colour is owing to the formation of a film of oxide, which at first is thin, and has a yellow appearance, but gradually it becomes thicker and also darker, as the heat increases. A definite degree of hardness and elasticity of the steel corresponds to each of these tints, the needle when covered with the yellow film being the hardest and most brittle, and when presenting a blue aspect being in its softest and most elastic condition. The workmen in steel impart to their articles various degrees of hardness and elasticity by tempering ; files and razors are made very hard and brittle, — saws, watchsprings, &e.,, soft and elastic. Steel may be prepared in various ways : — 1. By partly refining cast-iron, so that only one half of the carbon is burnt out (crude steel) ; or 2. By the process of cementation, which consists in filling an iron box with bar-iron and powdered charcoal, and then maintaining the whole for several days at a red heat. The carbon gradually penetrates into the iron, thus converting it into steel (blistered steel). Both these kinds of steel must be rendered uniform, either by repeated hammering (tilting) of it when heated to redness (tiUed steel), or by remelting (cast steel). Steel may be orna- mented by corroding its polished surface with acids, whereby a variety of light and dark coloured shades and impressions will be produced. From the constituents of bar and cast iron it may be inferred that steel can be made by an intimate combination in equal proportions of those two substances. In this manner, indeed, the outer surface of wrought-iron articles — as, for instance, of agricultural implements, chains, &o. — can easily be converted into steel, by being heated in melted cast-iron (case-'hardening). This object may be attained COMPOUNDS OF IRON. 245 more easily by strewing ferrooyanide of potassium over the red-hot iron. Iron, nickel, and cobalt, are the only metals which are attracted by the magnet in a sensible degree. Magnetism immediately vanishes from bar-iron when it is removed from the magnet; while steel, on the contrary, retains the magnetic power, but loses it on being heated to redness. Absolutely pure iron can only be prepared with great difficulty. Its specific gravity is 7-8. When treated with acids,' pure hydrogen m evolved, whereas ordinary iron yields impure hydrogen, as is sufficiently proved by its disagreeable smell. COMPOUNDS OF lEON. Ferrous oxide. — Protoxide of iron, Fe"0, is almost unknown, so readily does it take up oxygen and pass to a higher oxide. Black, or magnetic oxide, FejOi. — Experiment 1. — Place a few grains of iron filings upon p. g^ a piece of charcoal, and heat it ^ for some minutes in the flame ^i of the blow-pipe, directed upon ^ one spot ; it becomes red-hot, ^ and the heat spreads throughout \t^ ^^^^^B the whole mass, as is apparent ^ <^^^^^B from the iridescent tints which ^^^^^f^'^j^^^^tf precede the red heat. The iron ^^m^^^^S!^^^^ on cooling acquires a darker, ^^^^w ^^'-- almost a black colour, and bakes ^^^m^^^ into a coherent mass of this ^s^^^f^ intermediate oxide. It is the same compound as is formed when iron burns in oxygen or air (p. 125). Ferric oxide. — Peroxide of iron, Fe^jO^. — Experiment 2. — Iron cinders (Fefii), when exposed for a long time to the outer or oxidising blow-pipe flame, become covered with a red pulverulent coating ; they take yet more oxygen from the air, and become peroxide of iron. It may be prepared more easily in the following manner : Place a crystal of green vitriol upon charcoal, and heat it until it has become of a brownish-red colour. The salt is decomposed and the peroxide remains. The red colour of the latter is more clearly brought out by rubbing it on paper 246 EXPERIMENTAL 0HBMI8TET. with the nail. In the same manner, peroxide of iron remains behind when green vitriol is heated in the preparation of Nordhausen sulphuric acid (p. 147) ; this forms an article of commerce under the name of eotcothar, or rouge, and is a favourite and cheap pigment for varnish, and is also used in the polishing of glass and metals. Ferrous hydrate, re"(H0)2. — Experiment 3. — Add potassium hydrate to a freshly-prepared solution of green vitriol (ferrous sulphate). A green precipitate of impure ferrous hydrate will be produced by double decomposition : re"(S04) + 2KHO = K2(S0^ + Fe"(H0)2. If it ■ were pure ferrous hydrate the precipitate would be white, but it is never obtained so except when oxygen is completely excluded. The green precipitate, on exposure to air, becomes brown by conversion into ferric hydrate. Ferric hydrate, Fe"2(H0)e. — Ferrous salts, when kept for any length of time in contact with air and water, take up oxygen, and become ferric salts. The former are green, the latter brownish-red. Experiment 4. — Make a solution of ferrous sulphate, filter, and set it aside. The solution will gradually become turbid, and a brown precipitate will settle on the sides of the vessel, while in a few days the bright green colour of the solution will give place to a decided brown. The change of colour indicates the conversion of the proto- into the per-salt. Ea^eriment 5. — To a fresh and dilute solution of ferrous sulphate in a test-tube add a few drops of sulphuric and nitric acids, and heat. The mixture will become of a dark brown, almost black colour, which, as the heat approaches boiling-point, suddenly vanishes and leaves the reddish colour of .the per-salt. The conversion of the proto-sulphate into per-sulphate, which in the former experiment requires an inconvenient length of time, is in this way completed almost instantaneously by the oxygen supplied by the nitric acid : 6FeS04 + 3H2SO4 + 2HNO3 = 3Fe2(S04)3 + 4:B.J0 + 2N0. The dark substance first formed is a compound of ferrous sulphate with nitric oxide, 2Fe^04.NO. Ea^erivient 6. — Add ammonia or potash to the solution of per-sulphate obtained in the last experiment. Instead of a green, a red precipitate will be obtained, indicating the COMPOUNDS OF IKON. 247 change which has taken place. The red precipitate is ferric hydrate, Fe2(H0)fi. The precipitate may be washed on a filter. Any ferric salt may readily be prepared by dissolv- ing the moist hydrate in the acid. When the hydrate is heated ferric oxide is obtained. Ferrous chloride, re"Gl2, is a green salt obtained in crystals by dissolving iron in hydrochloric acid and evaporat- ing the solution. Ferric chloride, Fe^'aClj. — This is one of the most important of the per-salts of iron. It may be obtained by dissolving iron per-hydrate or per-oiide in hydrochloric acid, or by converting the proto-chloride by boiling with nitric and hydrochloric acids. The salt cannot be obtained crystallized, but only as a brown mass by evaporation to dryness. Ferrous sulphate. — Green vitriol. — Copperas, Fe"S04. — This most important salt may be obtained in a variety of ways. (1) By dissolving iron in sulphuric acid. (2) It remains in solution in the bottle in which sulphuretted hydrogen is generated by the action of sulphuric acid on ferrous sulphide (p. 141). It is manufactured on the large so lie by the gradual oxidation of iron pyrites by the action of moist air, and subsequent solution and crystallization. This salt is largely nsed in dyeing for the production of black colours, and also in the manufacture of writing-ink. The crystals of ferrous sulphate have the formula FeSO^ifHaO. Ferric sulphate, Fe''2(S04)3. — The preparation of this salt, by boiling the proto-sulphate with nitric acid, has already been described. It may also be formed by dissolving ferric oxide, or hydrate, in sulphuric acid. Ferric nitrate, Fe''2(N03)e, is obtained by adding iron filings to warm dilute nitric acid as long as they continue to dissolve in it. This solution is of a brown colour, and is used in dyeing. If some aquafortis is dropped upon cast- iron, steel, or bar-iron, black spots are produced, because the iron, but not the carbon, is dissolved. These spots are darker in cast-iron and lighter in bar-iron. Ferric acetate, Fe''^2(C2H302)6, may be prepared directly, by dissolving freshly-precipitated and still moist ferric hydrate in acetic acid. When the shoemaker pours beer upon iron nails to prepare the iron-black with which he blackens his 248 EXFEBIMENIAL CHEMIS'^BY. leather, he obtains this salt, for, on exposure to the air, the beer is changed into vinegar. Ferrous sulphide, re"S. — On adding some sulphuretted hydrogen water to a slightly acidified solution of green vitriol, no precipitate is produced; but if ammonium sul- phide is added to the neutral solution, a deep black pre- cipitate is formed ; this precipitate is ferrous sulphide. Ferrous sulphide is largely used by the chemist for the preparation of sulphuretted hydrogen (p. 141). It is best prepared in the following manner : Experiment 7. — Heat a clay crucible to redness in a clear fire and throw in, in small portions at a time, a mixture of 4 parts of iron filings and 2J parts of flowers of sulphur. The moment the mixture is thrown in, the cover should be placed on the crucible, to prevent, as far as possible, the access of air. The black mass so obtained is very like cast- iron. It may be broken from the crucible, when cold, with a chisel. A compound of ferrous and ferric sulphides occurs native, and is called magnetic pyrites, FeaSipFeS.FcaSs. If you moisten ferrous sulphide with water, and let it remain exposed to the air for some weeks, small green crystals will be found disseminated throughout the mass, the sulphur having gradually attracted oxygen from the air, FeS thus becomes FeSO^. Iron disidphide. — Iron pyrites, Fe^'Sj. — ^Iron combined with twice as much sulphur as in the proto-sulphide, occurs native in many ores, and frequently in common coal, and is called iron pyrites. It has the appearance of brass, and usually occurs in cubic crystals. If heated in a retort, a •p. go portion of the sulphur distils over, and is collected, and magnetic pyrites remains behind. Green vitriol is prepared from the residue, by piling it in heaps, and leaving it for several months exposed to the air. The green vitriol thus formed is freed from earthy impurities by lixiviation and evaporation. When iron pyrites is heated in the air, both its elements are oxidized : 2FeS2 + 110 = FeA -f 4SO2. The mineral is therefore often used instead of sulphur in the manufacture of sulphuric acid. CHKOMIUM. 249 Tests for iron. — The best test for iron is potassium ferro- cyanide (p. 185), whicL gives, with ferrous salts, a white or pale blue, and with ferric salts, a dark blue precipitate. CHEOMIUM. Cr = 52-5. Chromium has only been known within a few decades, and already several of its combinations have become common and valued articles of commerce. The cause of this rapid exten- sion is owing to the beautiful colour of many of the prepara- tions of chromium, on account of which they are excellently adapted for pigments. This also has given rise to the name chromium (colour). 'Chromium itself is little known; from the dificulty at- tending its isolation it can only be obtained in the smallest quantities. It is remarkable for its infusibility, which even exceeds that of platinum. The chief ore of chron^ium contains chromic oxide and ferrous oxide (FeOjCrjOs), and is called chrome-iron-stone, or dhrome-iron-ore. Chromium likewise occurs in a mineral called crocoisite, which is a lead salt of chromic acid, PVCrO,,, and in small quantities in many other minerals, but its distribution is by no means abundant. Experiment 1. — Procure a piece of chrome-iron-ore from any dealer in minerals, grind a few grains to fine powder and mix them with equal quantities of j>ig. 93. powdered nitre and potassium carbonate. Place the mixture in a small iron spoon /.>■ -vQ and heat strongly with the bloW-pipe or // // in a fire for several minutes. When the f^ {/ ignited mass is cold, detach it from the ^ spoon and boil with a little water in- a test-tube, and filter the solution. It will be of a bright yellow colour from the presence of a salt called potassium ehromate, EjCrOi ; a compound which will be described further on. Add dilute sulphuric acid in minute quantities to the yellow solution. Effervescence will be produced by the unaltered potassium carbonate. The addition of acid is stopped the instant the colour of the liquid changes to orange-red. The acid removes half the potassium, and a new salt, called potassium dichromate, 250 EXPKEIMENTAL CHEMISTET. KjCrjOT, is formed. This salt may be obtained by the evaporation of its solution in beautiful tubular or prismatic orange-red crystals. Immense quantities of potassium di- chromate are prepared from chrome-iron-ore by a method very similar to the one just described. From this salt, directly or indirectly, all other chromium compounds are formed. The constitution of the chromium compounds has already been indicated. The chromous compounds are difficult to prepare, and are of no interest. Of the chromic compounds the following are the most important : Chromic oxide, Cr'^aOj. — Experiment 2. — Mix a few grains of powdered potassium dichromate with a quarter of its weight of starch, and ignite the mixture in the iron spoon. After the ignition, boil the mass with some water. This will dissolve out the pofassium carbonate formed during the reaction, and will leave chromic oxide as a green powder.' Wash the powder once or twice, and dry it. This substance- is employed as a pigment, y Starch, in the seeds and other parts of plants. Glycogen, in the tissues of animals. Dextrin, formed by the alteration of starch, &c. Arabin, in gum arabic. EasBorin, in gum tragacanth. J Glucose, or grape-sugar, found in honey, fruits, &c., also in the animal body. Can also be formed from cellulin, starch, dextrin, &c. Lactose, or milk-sugar, in the milk of animals. All of which have the formula ) CeHijOs- 306 EXPERIMENTAL 0HEMI8TBY. Sucrose, or cane-sugar, found in the I sugar-cane, maple, beet-root, and > GyiH^On. otter plants. J Mannite, in manna. OeHi^Os. Pectin, or vegetable jelly, in fruits. CsaH^sOsa ? The true formulsB of many or all of these compounds are probably multiples of those here given. CBLLULIN. All the cells and vessels of plants are composed of cellulin. This substance is to plants what bones, flesh, and skin are to the animal body ; it forms the solid mass of all vegetable organs, and consequently imparts to plants their shape and firmness ; it forms the ducts or veins of the plants, through which the sap circulates. We find it very finely ramified, tender, soft, and easily digestible in the young leaves, flowers, and stems, ayd in the -so-called pulp of fruit and roots, as apples, plums, carrots, &o. ; hard and indigestible in straw, wood (woody tissue), and in the husks of grain (bran) ; hardened like stone in the stones of plums, cherries, and peaches, and in the shells of nuts ; light, porous, and elastic in the pith of the elder, and in cork ; lengthened and pliant in hemp, flax, and cotton. The transverse section of the stem of a tree illustrates the influence which age exerts upon the Fig. 100. vegetable tissue, and how this tissue varies in one and the same tree. In- side the hark (a) lies the inner fibrous bark (6), which consists of lengthened tubes, and is peculiarly adapted to supply the place of veins in the tree. Here the sap principally circulates, and therefore a tree will die when the inner bark is girdled, whilst (as seen in many hollow trees) the tree will live on if only the inner and outer bark remain, though the wood itself is entirely rotten and gone. From the inner bark towards the exterior is deposited every year a new layer of bark, and towards the centre a new OELLULIN. 307 layer of wood (annual circles). The light and whiter wood, lying next the inner bark, is called sap-wood (c); but this, by the annually increasing compressure, „ ^ becomes denser and more solid, and ^' then it is called heart-wood (d). The latter is usually darker, and is fre- quently impregnated with colouring matter (red-wood). The annexed figure will give an idea of the internal struc- ture, which is manifest even in appa- rently simple dense wood, when viewed j [ under a strong magnifying glass. It represents the transverse section of a pine bough, the portion marked a repre- senting young ligneous cells, those marked b the matured cells. Most plants contain in the inner and outer bark a sub- stance which- has an astringent taste, is soluble in water, and which is known by the name of tannin, or tannic acid. lAnen is the inner bark of the flax-plant. During the process of retting, the outer bark, by the long-continued influence of moisture and air, passes into decay, and then, after rapid drying, may be rubbed off by bending it backwards and forwards (breaking') ; but the filaments of the inner bark, which do not so readily decay, remain behind, and after being parted into their finest fibrils, and arranged parallel by the so-called heckling, form the well-known flax. The tow, which falls off during this process, consists of tangled fibres of the inner bark. Flax has a grey colour, because it contains a grey colouring matter, which is not soluble in water and lye, though it becomes soluble in lye by exposing the flax, the thread spun, or the linen woven from it, during a long time, to the action of light, water, and air. This is done in the bleaching-yard by spreading it on the grass (grass bleaching). The colouring matter, hereby altered and rendered soluble, is removed from time to time by boiling with lye. Bleaching may be accom- plished more rapidly by the application of chlorine, which, on account of its very strong af&nity for hydrogen, attracts hydrogen from all organic substances, whereby they become colourless and soluble {chlorine bleaching). The colouring, 308 EXPEKIMENTAL CHBMISTKT. matters of flax, &c., are more easily destroyed by chlorine than the fibres. If, when the linen has become white, the bleaching were still continued by either of these methods, the vegetable tissue would be decomposed and become rotten ; a case which often occurs when linen, cotton, or paper is treated too long, or with too strong a solution of chlorine. Bast. — Soak the bark of the lime-tree in water till the outer baik is decomposed, and has become brittle ; when it is dry, the inner fibrous part of the bark can be peeled from it, and it then forms the lime hast, used for tying up plants. The outer covering of the trees, which is commonly, but erroneously, called bark, consists by no means of the proper bark only, but of two essentially different parts, which have grown very closely together ; the external layer is the proper bark (epidermis), the inner is the bast (liber). Cotton consists of delicate hollow hairs, which form in the cotton-plant in considerable quantities around the seeds. As it exists in nature it is beautifully white (except the Nankin cotton, which is yellow), and consequently requires no bleaching. It is nearly pure cellulin, whereas most kinds of vegetable tissue contain other compounds in considerable quantity. When cotton thread or cotton fabrics are bleached, it is merely in order to remove the oily, sweaty, and mealy substances (weaver's glue, &c.) which have become attached to them during spinning and weaving. This is now usually effected by boiling with soda-lye or milk of lime, or im- mersing them in a weak solution of chloride of lime. The lime which remains adhering is then removed by exceedingly dilute acids (acid hath), and the acid, in its turn, by rinsing in water. Paper, which is made by beating vegetable fibres, such as those of linen and cotton, with water, and straining the pulp with wire sieves, is of course nearly pure cellulin. Vegetable Tissue and Water. — Experiment 1. — Pour some lukewarm water over sawdust, and let it stand for a day; then squeeze out the liquid through a cloth and boil it ; a slight turbidity will appear, and on longer standing a loose sediment will be deposited. Water does not dissolve the woody fibre, though it does the sap contained in it ; in this sap, as in that of all other plants, there is always found a substance in solution, which is very analogous to the white OELLULIN. 309 of eggs, and which, like it, coagulates in hoiling ; it is called vegetable albumin (see next chapter). There are also con- tained in the liquid, separated from the albumiji, various other substances in solution (mucus, gum, tannin, &c.), which are not precipitated by boiling. If the sawdust, after it has been dried, is treated with alcohol, this will also dissolve some substances f resin, &c.) ; and so also will ether, lye, and other licLuids. Therefore, in the preparation of perfectly pure woody tissue, it must be treated with various solvents in order to remove all the constituents of the sap. Properties of Cellulin. — Cellulin is insoluble in all ordinary solvents, except those which alter it, but is dissolved by ammonio-sulphate or hydrate of copper, from which it can be reprecipitated by the addition of hydrochloric acid. Strong sulphuric and nitric acids act upon it in a very remarkable manner. Vegetable Parchment. — Experiment 2. — If a sheet of white blotting-paper is immersed in a cold mixture of two measures of sulphuric acid with one measure of water, and is then washed very thoroughly (for the last time with very dilute ammonia) and dried, it is changed into a tough substance very like parchment, which does not appear to differ from the original paper in composition. It is now much used for tying over pots of jam and for other purposes. Experiment 3. — If cellulin is beaten at intervals for some hours in a mortar with strong sulphuric acid, it becomes liquid, and is converted into .dextrin, arid ultimately, after adding water and boiling, into glucose. The excess of acid may be removed by chalk, and the filtered liquid on evapo- ration will yield glucose. Gun-coUon, pyroxylin, or trinitro-cellulin. — Experiment i. — Mix half an ounce of the strongest nitric acid (sp. gr. = 1-5) with one ounce of strong sulphuric acid ; pour the mixture into a porcelain mortar, or a cup, and press into it with the pestle as much cotton (cotton-wool, calico, printing-paper, &c.) as can be moistened by the acid. When the cotton has soaked for some hours, it is to be taken out with a glass rod, put into a vessel containing water, and washed repeatedly with fresh quantities of water, until it no longer reddens blue test-paper. The cotton is then squeezed out with the hand, spread upon a sheet of paper, and dried in an airy 310 BXPBEIMENTAL CHEMISTBY. place. It is dangerous to dry it upon a stove, as it easily takes fire. If the gun-cotton thus prepared is struck smartly with a hammer upon an iron anvil, it detonates violently ; when touched with a hot wire or a lighted match, it burns instan- taneously, without leaving any residue ; when fire-arms are loaded with it, it acts like gunpowder, but its explosive power is much greater than that of the latter. Gun-cotton being, therefore, an exceedingly dangerous substance, the greatest caution is indispensable in conducting experiments with it, and only very small quantities should be used at once. Another kind of gun-cotton dissolves in a mixture of alcohol and ether into a syrupy liquid, which on spontaneous evapo- ration leaves the cotton behind in the form of a transparent film. This solution is called collodion. It is used instead of court-plaster, and for making small air-balloons, &c. The chemical change which takes place in the manufacture of gun-cotton has already been described (page 304). It is described by the formula : CelluUn. Tiinitr<)-ceUulin. CeHioOs -f 3N0JE0 = CeH,(N02)305 + 3H,0. The use of the sulphuric acid is to absorb the water which is formed in the reaction, and thus keep the nitric acid at its maximum strength. The explosive force of gun-cotton is due to the large quantity of oxygen which it contains, and to the fact that when burnt it is entirely converted into gases, which occupy an enormously larger volume than the substance itself. Experiment 5. — Scraps of well-prepared gun-cotton may be ignited on the palm of the hand without danger, in con- sequence of the suddenness with which the change to gas is effected. Spread a little gunpowder on a plate, and rest a few grains of gun-cotton on it. The gun-cotton can be inflamed without igniting the gunpowder. A mealy substance, which is known under the name of starch, or fecula, is deposited in most vegetables, particularly at the period of ripening, from tl^e juices with which the cells of the plants are filled. STARCH. 311 It appears to the naked eye like particles of meal, but under a powerful microscope it is found to consist of small, generally regular grains or globules. Their position in the plant is shown in the annexed figure, which jijg io2. represents a section of some of the cells of a potato. If a fresh plant is bruised and macerated in water, and the liquid then squeezed out, a large portion of the starch will pass with the juice from the vegetable tissue, and will settle, after standing quietly a while, as a mealy mass. Potatoes, grain,' and leguminous plants are very rich in starch. ■Potatoes. — Experiment 1. — Easp sortie potatoes on a grater, knead the pulp thus obtained with water, and squeeze it in a linen cloth; the fibrous particles of the cells remain behind, but the juice, together with a large portion of the starch, runs through. If you let the turbid liquid remain quiet for some hours, it becomes clear, because the heavier starch settles at the bottom. Now decant the liquid, wash the starch several times with fresh water, allowing it to settle each time, and then dry it in a moderately warm place. Experiment 2. — Heat in a flask the clear liquid decanted from the starch ; it becomes turbid when the heat approaches the boiling point, and, after boiling for a few moments, deposits a flaky, greyish-white substance, which is to be col- lected on a filter. It is the same substance already referred to (page 309), vegetable albumin, characterised by its property of dissolving in cold and warm water, but of coagulating in boiling water. It contains nitrogen, which the starch does not. Experiment 3. — jPut some of the coagulated albumin upon a piece of platinum foil, and heat it over a lamp ; it will burn and emit a very disagreeable empyreumatic odour. When starch is treated in the same manner, it also gives off an empyreumatic, but far less unpleasant smell. Many nitro- genous substances comport themselves in this respect like albumin ; many non-nitrogenous substances, like starch ; there- fore, when a piece of woollen cloth is singed, it diffuses a far more disagreeable odour than a piece of cotton or liiien, because nitrogen is contained in the wool, but not in the cotton or linen. 312 EXPERIMENTAL CHEMISTRY. A freshly-cut potato has a white colour, which, however, on longer exposure to the air, passes to brown ; a similar change takes place in the liquid pressed out from the grated potatoes ; at first it is colourless, but gradually be- comes darker. The substance, not yet accurately studied, which effects this change of colour, is designated by the general term colouring maiter ; it is soluble in water, as is evident from the last-mentioned property. Experiment 4. — Mix twenty drops of sulphuric acid with three ounces of water, and pour this acid water upon a potato cut in thin slices ; after standing twenty-four hours the slices are- to be taken out, and washed with water till they have no longer an acid taste, and then dried. During this process the potatoes lose their juices, and also their albumin and colouring matter, and, after drying, form a solid, mealy, white, and tasteless substance, which swells up and becomes soft when boiling water is poured upon it. Potatoes dried without this treatment become grey and horn- like, and acquire an unpleasant smell. Peas. — Experiment 5. — Pour a handful of peas into a capacious vessel containing water, and let it stand for some days in a warm room ; a great part of the water is absorbed by the peas, causing them to swell up, and finally to become so soft that they can easily be mashed between the fingers. When in this state, bruise them in a mortar, and add suffi- cient water to form with them a thin paste, which may be squeezed out by means of a linen cloth. Here, also, we ob- tain, as from potatoes -^1, a fibrous substance, which remains on the cloth ; 2, starch, which is deposited, after standing, from the turbid liquid ; 3, vegetable ciOmmin, when the de- canted liquid is heated to boiling. Experiment 6. — ^When you have separated the vegetable albumin, by boiling and filtering, fyom the above-mentioned liquid, add to the latter a few drops of any acid ; a flaky white body will again be deposited ; this is called legumin, or vegetable casein (cheesy matter), on account of its great simi- larity to the cheese contained in milk (animal casein) in its constitution and also in its properties. Vegetable casein, like vegetable albumin, contains nitrogen ; but it is distinguished from the latter by this, namely, that it is not coagulated by boiling, though it is by acids. It occurs in the juice of BTAEOH. 313 I many plants, but it is most abundant in the seeds of legu- minous plants; potatoes, likewise, contain small quantities of it. Wheat-flour. — Experiment 7. — Moisten a handful of wheat- flour with sufficient water to form a stiff paste when triturated in a mortar ; inclose it in a piece of thick linen, and knead it frequently, adding water as long as the liquid, which runs through continues to have a milky appearance. After standing some time, a white powder wiU settle from the turbid water ; this is wheat starch. Starch is one of the principal constituents of flour, as, indeed, of all sorts of meal ; the second constituent remains behind in the cloth, mixed with vegetable fibre, and is a viscous, tough, grey substance, which has received the name gluHn (vegetable fibrin). The glutin only swells up in water, without being coyipletely dissolved; in its constitu- tion it corresponds exactly with albumin, and, like this, contains nitrogen. When the water decanted from the starch is boiled, it becomes turbid, and, when partially evaporated, yields a flocculent precipitate; thus, wheat-flour contains also some vegetable albumin. If the results of these experiments are grouped together, we shall find that there are always present in potatoes and peas, and also in wheat-flour, the two non-nitrogenous sub- stances, vegetable tissue and starch, and also one or several of the nitrogenous compounds, vegetable albumin, casein, and gluten. Non-Nitrogenous Substances. In potatoes : cellulin, starch. In peas : cellulin, starch. In wheat : cellulin, starch. Nitrogenous Substances. In potatoes: vegetable albumin, casein (little). In peas : vegetable albumin, casein (much). In wheat : vegetable albumin, glutin (much). The three substances above named, containing nitrogen and sulphur, have the general name of albuminoid compounds. Small quantities of one or more of them occur in the sap of 314 EXPERIMENTAL CHEMIBTET. every plant. We shall learn more of them in the next chapter Fig. 103. Potato starch exhibits, under the microscope, the form of egg-shaped grains, consisting of many scales overlapping each other ; it glistens in the sun, is hard to the touch, and has always more of a pulverulent than of a concrete cha- racter. Fig. 104 ^ In the starch of peas many of the grains are concave longitudinally, while others seem to be ^ '^ formed by the growing together of several glo- bules. Fig. 105. Wheat starch consists of dull, flattened, lenti- go ^^ cular grains, which, when moist, readily adhere o° ■ It is a distinguishing peculiarity of the colouring matter of the blood, that it always contains iron. Experiment 2. — If the blood freshly drawn from the veins is beaten up during cooling, it does not coagulute; the fibrin certainly becomes insoluble, but it separates as a thread-like coherent mass, which, when kneaded for some time with water, becomes finally white, and, after drying, resembles the muscular fibre. Indeed, it may be regarded as half-formed flesh, since it has the same composition, and the flesh of the animal body is formed from it. The blood ALBUMINOID 6K0UP. 327 remaining behind (whipped blood) retains, after the separation of the fibrin, its red colour, and coagulates on boiling to a jelly of a dark-red colour, as may be perceived in the so- called hlack-puddings. The metamorphosis of the blood just treated of is, accordingly, as follows : Water, Albumin, Blood Corpuscles Mbrin remain liquid. becomes solid. Casein. — This substance, which constitutes the curd of milk, is thought by some chemists to be identical with coagulated albumin. It has already been mentioned that it agrees in composition and properties with the legumin which is obtained from peas and beans. The following short account of milk includes a sufficient study of casein. Milk. — Milk consists of a solution of casein and sugar of milk, in which solution small globules of oil are held sus- pended. The latter render the milk opaque, and give it the appearance of an emulsion. The casein appears to exist in the milk in the form of a soluble sodium compound, and is therefore thrown down when the sodium is removed by means of an acid. Experiment 1. — The oil globules cannot be separated from the milk by filtration alone, as they are so small that they pass with it through the pores of the finest paper ; but it may be accomplished in the following manner : Dissolve an ounce of sodium sulphate and a couple of grains of sodium carbonate in half an ounce of lukewarm water, and agitate the solution with half an ounce of fresh milk. If you now transfer this mixture to a filter, the fatty portions (cream) remain behind, while a liquid, only slightly opalescent, passes through. The saline solution added does not act chemically upon the constituents of the milk, but it only acts mechanically, causing the globules to form a more compact mass, and to be more readily separated from the watery liquid. Experiment 2. — If you add to the filtered liquor a few drops of hydrochloric acid, the casein separates from it as a white flaky mass ; accordingly, the animal casein is coagu- lated and rendered insoluble by acid, in the same manner as vegetable casein. Pure casein is insoluble in water, but it dissolves in it when alkalies are present. 328 'EXPEEIMENTAL CHEMISTRY. .Experiment 3. — If you filter the casein from the Kquid, and then boil the latter, it again becomes turbid, although less so than before. It is the cHhumiu which separates, small quantities of it being present in all milk. Experiment 4. — Let a small piece of the dried membrane of the stomach of a calf (rennet) remain standing one night in a spoonful of water, and afterwards pour this water upon a quart of new milk ; the milk, after having stood for some hours in a warm place, will coagulate into a gelatinous- mass, which is to be put upon a filter. What remains behind consists of an intimate mixture of the curdled casein with globules of fat. By pressing and drying, we obtain from it the so-called cream- or new-milk cheese (Swiss, Dutch, Cheshire, &c., cheese). Experiment 5. — Separate the filtered liquid (sweet whey) from its alhumin by boiling, and, having again filtered it, evaporate until only a few ounces of it remain. If left in a warm place, hard, prismatic white crystals of sugar of milk will be deposited (page 323). By this method sugar of milk is procured on a large scale. Consequently the sweet whey is to be regarded principally as a solution of sugar of milt (together with some albumin and some salts) in water. Experiment 6. — Dissolve again in water the sugar of milk obtained, and put a piece of rennet in the solution ; the liquid will soon become sour in a warm place, because the sugar of milk is converted into lactic acid. Experiment 7. — The coagulation of the milk, which was produced by the rennet in a few hours, is effected instanta- neously by the addition of acids, as is rendered obvious by adding a few drops of some acid to heated milk. In this curdled mass are contained all the casein and fatty particles of the mUk (cheese and butter). Experiment 8. — Fill a bottle with fresh milk, close it, and keep it, inverted, from twenty-four to thirty-six hours in a cool place; then loosen the stopper a little, so that the lower, thinner portion of the milk (blue or skim milk) may run off, but the upper, thicker part (cream) remain behind. On standing, the lighter oil-globules of the milk ascend, and form on the surface the well-known fatty, thick cream. If this is shaken for some time, the membranes of the oil- globules are torn, and the latter then unite together, forming ALBUMINOID 6B0UP. 329 masses o£ butter. The thin milk which passes off from beneath may be separated, in the way abeady described, into casein, albumin, and sugar of milk. Experiment 9. — If you let milk stand for some time in open vessels, its sugar of milk is gradually converted into lactic acid, and this, like every other acid, causes a curdling of the milk, and, at the same time, its well-known sour taste. But the curdling first commences after most of the oil- globules have collected on the surface (sour cream). Prom this cream, butter is often prepared, and therefore the buttermilk remaining (a mixture of curdled casein, lactic acid, and water, with some particles of butter remaining behind) has an acid taste. The so-called curd beneath the cream now contains only traces of fat, and consists accord- ingly of water, lactic acid, and coagulated casein. By pressing we obtain from it the sour whey, and, as a residuum, the coagulated casein, from which common shim-milk cheese is made. When kept damp this undergoes a decomposition (putrefaction), and a soft saponaceous mass is produced. If the putrefaction advances still farther, there will be finally generated also volatile compounds of a very offensive odour. Gelatin. — The organic matter (about one-third) of bones consists of a compound called ossein, or hone cartilage, which is insoluble in water, but which, after prolonged .boiling, changes into the well-known substance gelatin, which, though scarcely soluble in cold water, dissolves easily in hot. The skin and some other parts of the animal body experience the same change when long boiled with water. If the water is made to boil at a higher temperature (about 220° F., or 105° C), by enclosing it in a strong iron vessel, the conversion is effected mtich more rapidly, as it is also by superheated steam. Isinglass, which is prepared from the air-bladder of the sturgeon, is nearly pure gelatin. Glue, prepared from the hides, cartilages, &c., of animals, is impure gelatin. Experiment 10. — Immerse a bone in a large jar of hydro- chloric acid diluted with nine parts of water, and allow it to remain for a day or two. The acid will dissolve out the mineral portion of the bone, consisting chiefly of tricalcium phosphate, CagPjOj, and a tough, cartilaginous and semi-transparent mass of ossein, having the form of the 330 EXPBBIMENTAL CHEMISTRY. bone, ■will remain. The calcium phosphate can be pre- cipitated from the acid solution by the addition of ammonia. The ossein can, after thorough washing, be converted to gelatin by boiling it for some hours. The average composition of bone may be stated roughly as follows : Ossein .... Tricalcium phosphate Calcium carbonate . Calcium fluoride Magnesium phosphate 33 57 8 1 1 100 ( 331 ) CHAPTEE V. FEKMENTATION. ETHYL-COMPOUNDS. The compounds described in the last chapter, when exposed to the air in a moist state and between certain limits of temperature, experience a peculiar change, which is called putrefaetion. They decompose and are converted into simpler compounds, some of which are gaseous, and possess a foetid odour. This change, which is an example of many similar ones which are known, is due to the absorption from the air of minute germs — seeds, or eggs — of low forms of vegetal, or (more probably) animal life. If air be entirely excluded the change cannot take place, because the germs cannot enter ; but when once commenced it will continue without any assistance from the air. The organisms develope and reproduce themselves; they feed on the compounds with which they are in contact, and throw out as excretions the compounds which we know as products of putrefaction. It appears probable that very minute organised germs of many kinds float constantly in the atmosphere, ready to develope and increase whenever they meet with suitable food and suitable conditions of temperature, moisture, &c. Some have been detected, and their developments studied with great care, but even the existence of many of them can only be inferred from their effects. FEKMENTATION. The albuminoid substances, when in a state of incipient putrefaction, have a remarkable power of causing decom- positions in solutions of sugar. These changes, which are akin to putrefaction in their nature, are effected by peculiar 332 EXPBEIMENTAL OHBMISTET. organisms, the germs of whicli are derived from the air. The organisms feed on the albuminoid substances and sugar jointly, and thereby convert them into new and simpler compounds, which are distinguished from the products of putrefaction by being, for the most part, destitute of offensive odour. Changes of this kind are called fermentations, and the substances which produce them ferments. There are several kinds of fermentation, but the most important is that known as vinous, or alcoholic fermentation. Experiment 1. — Half an ounce of honey is dissolved in four ounces of water, and some glutin or flour, which haS' been kept in a warm room for about a week till it has begun to putrefy, is added to it ; the liquid is then put in a moderately warm place, from 64° F. (18° C.) to 75° P. (24°C.), when it soon enters into fermentation, with the evolution of a large quantity of gas. If you perform the experiment in a bottle furnished with a bent glass tube, one end of which is passed under a second bottle, filled with water, which is in- verted over the pneumatic trough, the gas may easily be collected ; it consists of carbonic anhydride. If the liquid still retains a sweet taste after the evolution of the gas has ceased, add another portion of the glutin to it, whereby the fermenta- tion is again renewed. Finally, all the saccharine taste will have disappeared, and the liquid will have acquired a spirituous flavour. The fermented liquor is called mead ; instead of grape-sugar it contains alcohol, and this is the cause of its intoxicating effect. A portion of the gluten is found at the bottom of the vessel, converted into a brownish residue. Teast. — ^While the foregoing process is going on, the liquid contains a multitude of minute egg-shaped bodies called yeast cells, because yeast is mainly composed of them,, which are the agents by which the sugar is converted into alcohol and carbonic anhydride. The scientific name for the yeast cell is Torvula cerevisice. Yeast is, of course, the most powerful of ferments. WINE. 333 The change which grape-sugar undergoes in fermentation is represented in the following formula : Glucose. Alcohol. Carb. Anhydride. CaH,A = 20,HeO + 200^. But some other compounds are also formed in small quantity during the fermentation. Of these the higher alcohols (page 297), glycerin (page 297), and succinic acid (page 300), may be mentioned. Experiment 2. — Repeat the former experiment, adding, instead of the glutin, a tea-spoonful of yeast, or a few fragments of the German dried yeast ; the fermentation will now proceed more rapidly and regxilarly. Experiment 3. — Instead of honey, take a solution of cane- sugar and add some yeast to it. In this case the fer- mentation will not begin so soon, for the cane-sugar has first to take up the elements of water and change to grape- sugar : C12H2A1 + H,0 = 2CeHiA. All sweet vegetable juices pass spontaneously into fer- mentation without the necessity of adding to them a fer- ment, because they always contain sugar and one of the albuminous substances, as albumin, casein, or glutin, in which yeast cells will soon develope. Experiment 1. — Submit freshly expressed beet-juice to a temperature of from 20° to 25° C. (68° to 77° F.) ; the juice will soon effervesce, deposit a sediment, and be con- verted into a spirituous liquid (beet- wine). In the same manner currant and gooseberry wines are prepared from currants and gooseberries, cider from apples, the so-called cherry-water by fermenting and afterwards distilling cherry juice, rum by fermenting and afterwards distilling the juice of the sugar-cane, &c. The most common of all the fermentations of this kind is the fermentation of grape-juice, wine being the result. In order to prepare white wine, the grapes are pressed, the juice (must) is poured into vats and allowed to remain in them in the cellar, where, as the temperature is tolerably low, the fermentation proceeds so slowly that it is not com- 334 EXPEEIMENTAL CHEMISTEY. pleted until after some months. The new wine is racked off from the lees, and poured into fresh vats ; it stUl contains a small quantity of sugar and albuminous matter, which are both gradually converted, the former into alcohol and carbonic anhydride, the latter into lees (secondary fer- mentation). In the manufacture of red wine, the purple grapes are bruised, and then fermented, together with their skins and stalks ; by which means a red colouring matter is extracted from the skins, and tannin from the stalks and seeds, the tannin imparting to this kind of wine its astringent taste. SparJding wine (Champagne) is made by allowing the secondary fermentation to take place in corked- up bottles, whereby the carbonic anhydride formed is retained in the wine. The acidity of most wines is due to tartar (acid potassium tartrate, KHCiH^Os), which is contained in grapes. A good deal of this subsides when the wine is kept. Minute crystals of it are often seen on the corks of claret bottles. Many wines, champagne for instance, are sweetened by the addition of sugar, and some (port and sherry), are fortified, or rendered stronger by the addition of spirit. Experiment 2. — If some wine is put into a retort, and ■p.^ .-„ subjected to distLLLation at "■ ' a moderate heat, at first the more volatile alcohol, together with certain fra- grant ethers, will pass over. A very agreeably smelling spirit is thus obtained, known in commerce under the name of Cognac, or French hrandy. In the wine countries, the lees remaining after the wine is racked off are generally used for this purpose, since,, in the swollen, pap-like state in which they settle in the vats, they retain mechanically a large quantity of wine. Next to wine, heer and spirits are the most important fermented liquors. The manufacture of them differs essen- BEEB. 335 tially from that of wine in this respect ; that materials are employed which contain no sugar already formed, but instead of it starch, such as barley, wheat, rye, potatoes, &c. Starch cannot, like sugar, be resolved directly into alcohol and carbonic acid ; and, when employed in the manufacture of alcohol, it must previously be converted into sugar. This conversion is effected by the diastase of the barley-malt in the so-called mashing process of the brewers and distillers (page 317.) Experiment 1. — Pour a mixture of an ounce and a half of cold water and two ounces of boiling water upon half an ounce of bruised malt, and set it aside for some hours in a warm place, where it will reach a temperature of from 65° to 75° C. (149° to 167° F. ) ; a sweet liquid is thus obtaiaed, composed not only of dextrin and sugar, but con- taining also the altered glutin, thereby rendered soluble, which was present in the malt. The brewer calls this liquid the wort. Strain it with pressure through a cloth, and boil the liquid for some time, until it becomes clear and trans- parent ; then let it cool to 86° P. (30° C), and add to it a teaspoonful of yeast ; it will soon begin to ferment, and after some days will clarify again ; the clear, fermented liquor is heer. This is the mode of making the Berlin white or pale beer, which is not bitter. If during the boiling, some hops (female flowers of the hop-plant) are added to the wort, an aromatic bitter substance is dissolved from them, which not only imparts to the beer a pleasant and bitter taste, but also makes it keep better. What is particularly remarkable in the above fermentation (surface fermentation^ is the great quantity of yeast that is formed. It is called surface yeast, it being raised to the surface in consequence of the great evolution of carbonic anhydride, and if the casks are full, it is forced out of the bimghole ; it is the best yeast, and the quantity obtained in the last experiment is sufficient to bring to complete fermentation the wort of a whole pound of malt. ^^' Its power of exciting fermentation is destroyed when it is rendered quite dry, or when it is boiled, or very finely triturated ; and likewise by mixing antiseptic substances with it, as, for instance, alcohol, carbolic acid, sulphurous acid, volatile oUs, &c. 336 EXPERIMENTAL CHEMISTRY. This yeast, when examined through the microscope, has the form of simple cells (a) ; and their increase in the wort takes place in the same manner as in the most simple plants, new cells or buds developing themselves on each globule of the old yeast. New beer contains, also, some sugar and glutin in solu- tion ; therefore, like wine, it undergoes, when kept, a second slight fermentation (secondary fermentation). If; this is allowed to take place in well-stopped bottles, so that the carbonic anhydride cannot escape, a foaming beer (hotded beer) is obtained, in the same way as in the manuflEicture of sparkling Champagne. But all the glutin is not separated, even by the second fermentation, and hence the beer undergoes a still farther change on being exposed to the air; it is the alcohol, however, which is now altered by the albuminous matter undergoing decomposition ; it passes into vinegar, and the beer becomes acid (acetous fermentation). Experiment 2. — Eepeat the former experiment, but cool the wort below 50° F. (10° C.) before adding the yeast, and then let the liquid remain in a cool place ; ^ very slow fermentation takes place, which will not be completed for several weeks, perhaps even months. During this process, the carbonic acid is evolved in very small bubbles, and the yeast settles at the bottom of the vessel (bottom fermentation, bottom yeast). The beer thus prepared contains scarcely a trace of glutin or yeast, and therefore can be kept for years without becoming sour. Bavarian beer is made in this way. SPIRITS. The preparation of spirit is similar to that of beer; inasmuch as substances containing starch are employed in the preparation of it, and as the starch must first be con- verted into sugar before the fermentation can proceed. This is done, as in the case of beer, by the mashing process — that is, by the operation of the diastase of the malt upon the starch. To this end either boiled and mashed potatoes or rye are mixed with bruised barley-malt and hdt water, so as to form a paste, which is to be kept at a temperature of 158° F. (70° C.) until a complete formation of sugar is effected ; then brewers' yeast (surface yeast) is added to the SPIKITS. 337 sweet masli or wort previously cooled, whereby fermentation is induced. When this fermentation is concluded, the mass is put into a copper still, and the Volatile alcohol distilled from the non-volatUe parts (husks, glutin, fibrous matter, &c.). The residue is used as a nourishing food for the fattening of cattle. Formerly simple retorts were used for this distillation, and a weak spirit was obtained, which con- sisted of about one-third of alqohol and two-thirds of water ; but now a more complicated apparatus is universally em- ployed, by means of which a spirit of double the strengtii is obtained (rectified spirW). The principle upon which this apparatus depends will be explained in the following experiments. Bectification or strengthening of Spirit. — Experiment 1. — Pour three ounces of common spirit of wine into a capacious flask, and carefully distil half of it into a vessel, which is cooled by means of very cold water, or what is still better. Fig. 112. by ice. If the spirit contained thirty per cent, of alcohol, then the ounce and a half of alcohol first parsing over will contain at least fifty per cent. Alcohol is more volatile than water ; therefore it passes over first,, in company with a smaller quantity of the latter, while the greater part of the water, together with the fusel oil (amyl alcohol, &c.), which might have been contained in the spirit, remains behind in the flask (pMegm). 338 EXPEEIMBNTAL CHEMISTKT. Experiment 2. — If you connect with the flask and the receiver an intermediate vessel, a wide-mouthed bottle, for instance, which is easily done by means of two glass tubes Fig. 113. *T\ bent at right angles, and a cork perforated with two holes, and then repeat the above experiment of distillation, the alcoholic vapours passing over will first condense in the - middle vessel. But, as this vessel is not cooled down the liquid condensed in it will finally also boil, and the vapours thua formed will pass over into the receiver surrounded with cold water, and will there be condensed for the second time. In this manner a double distillation (rectification) is effected. The flask contains boUing spirit at (30° Tralles*) ; the intermediate vessel, boiling rectified alcohol (at about 50° Tralles). After the termination of the experiment, the first vessel will contain phlegm ; the second, weak spirif ; and the third, very strong, highly-rectified spirit (of 70°Jl:o 80° Tralles). If you adapt to the corks of the first two vessels a couple of thermometers, which shall dip into the liquid, you will find that the liquid in the flask boiled at the commencement of the experiment at 185° P. (85° C), and at the end of the experiment at from 203° P. (95° C.) to 212° F. (100° C), while that contained in the second vessel commenced boiling at 176° P. (80° C), and ended with boUing at from 185° F. (85° C.) to 194° F. (90° C). It is obvious from this that * The alcoholometer of Tralles floats to a figure on the stem, which indicates the percentage of alcohol, by volume, at 60° F. (1 5-5° C), in the liquor in which it is placed. ' BBBAD. 339 strong spirit boils at a much lower temperature than that at which weaker spirits boil. The strongest alcohol Cabsolute) boils at 173° F. (78° C). Experiment 3. — Connect with a flask a tolerably large glass tube, which is so bent that its middle part has a slight inclination upwards, as is shown in the annexed figure : Pig. 114. from h, this tube is wound round with moistened wick-yarn, the end of which hangs down at a. At a, bind a strip of cloth (several times folded together and smeared with a few drops of oliye-oil) round the tube, so that the water from the wick may not run down upon the flask. Now distil as' before three ounces of spirit, but during the distillation con- tinually drop cold water upon the wick-yarn, at h, in order to cool the vapour of the spirit as it passes over. Catch the water running down the outside of the tube in a vessel placed below the end of the wick-yarn. If the distillation is arrested when about one ounce of the spirit has passed over, we shall have a stronger spirit in the receiver than was obtained in Experiment 1, because, by the partial cooling of the vapour of the spirit, the principal part of the steam was condensed,' and, therefore, .a vapour richer in alcohol passed into the receiver, while the water condensed in the tube flowed back into the flask. BEEAD. Experiment 1, — Mix some flour with lukewarm water to 340 EXPERIMENTAL 0HEMI8TBT. a thick paste, cover it with a board, and let it remain for eight or ten days in a warm place. The paste is gradually altered, and two distinct periods may be observed during the change. In the first place, on the third or fourth day bubbles of air are evolved from it, having a sour, unpleasant smell, and the dough now possesses the capacity of con- verting sugar into lactic acid, as may be readily perceived by adding a little of it to some sugared water, and letting it stand in a warm place. After six or eight days the dough acquires a pleasant smell, and it now acts, when added to a solution of sugar, like yeaSt ; that is, it effects a decomposi- tion of the sugar into alcohol and carbonic anhydride. If the dough is allowed to stand still longer, it again acquii-es an apid taste," but which now proceeds from the acetic add into which the alcohol previously generated is gradually con- verted (leaven). In this state also it excites a spirituous fermentation in sugared water ; but this spirituous fermen- tation is immediately changed into the acid — into the for- Tnation of vinegar. It is obvious, from what has previously been stated, that the different actions of the flour, when in a state of decomposition, upon the sugar, depend upon the albuminous matter, the glutin, contained in the flour ; con- sequently, we might call the slightly altered glutin a lactic acid ferment, that which is more altered an alcohol ferment, and that which is still further altered a linear ferment. Bread. — What thus takes place slowly, proceeds rapidly in the making of bread, since a ferment is purposely added to the flour, which has been stirred up vrith water. In the making of white bread, the surface-yeast of beer is used as a ferment. The sugar contained ia the flour is thereby resolved into alcohol and carbonic anhydride, which struggle to escape, whereby the tough mass of dough is disintegrated, and rendered light and porous {rising of the dough). These substances, together with about half the water employed, volatilise by the rapid heating in an oven, having a temperature of from 320° F. (160° C.) to 356° P. (180° C), and the cellular partitions of the baked bread acquire such solidity, that they retain their form and place even after cooling. But if the heat of the oven is not sufBcient, or the dough is too watery, then the partitions harden too slowly, and, on the escape of the carbonic acid, BEBAD. 341 collapse, or run into each other (slack hahing). This happens most frequently with dark bread, since, in consequence of its greater amount of glutin, it retains the water more ob- stinately, and accordingly dries and hardens more slowly than white bread, in which the starch is more abundant. Leaven is commonly used as a ferment in the preparation of black bread. There is formed, during the process, be- sides alcohol and carbonic anhydride, a little acetic and lactic acids (perhaps also some butyric acid), which com- municate to the bread an acid taste. From three pounds of flour we obtain about four pounds of bread ; consequently, a quarter of the bread consists of fixed water. The light, porous bread dissolves easily in the stomach ; we say that it is easily digestible, and that the compact heavy bread is difficultly digestible. It is known (p. 315) that starch is converted, by roasting, into gum (dextrin) ; a part of the starch undergoes, also, this change in the oven, particularly on the surface of the baked bread, which receives the strongest heat from the roof of the oven. If the crust of the hot bread is rubbed over with water, and the bread is then replaced for a few minutes in the oven, some of the dextrin is dissolved, and forms, after the evaporation of the water, the shining coating which we see on loaves of bread and rolls. Carbonic anhydride, as applied to the rising of bread, may be more or less advantageously generated in other ways than by the fermentation of sugar ; indeed, entirely different substances, which become aeriform on the application of heat, may be used for the purpose. Experiment 2. — Mix intimately together two grains of finely pulverised hydrogen sodium carbonate (bicarbonate of soda), and a drachm and a half of flour, and knead the mixture into a dough with one drachm of water, to which four drops of hydrochloric acid have previously been added. Let the dough remain for some time in a warm place, and then bake it on the hot flue of a stove, or in a spoon over an alcohol lamp. A porous mass of bread is obtained, because the carbonic anhydride of the sodium salt is expelled by the hydrochloric acid, and raises the dough while it is still soft. The common salt which is formed remains behind in the bread, and imparts to it a saline taste. This method has been 342 EXPERIMENTAL CHEMISTRY. introduced in many places for making bread, cakeS, &c., on a large scale. Experiment 3. — Eub a drachm and a half of flour with a few grains of ammonium carbonate, and then knead it with a drachm of lukewarm water into a dough, and treat it as in the last experiment. In this case, also, the mass will become light and porous after the rising and baking, because the salt is rendered aeriform by the heat, and during its escape the particles of the dough are forced asunder. In this way the bakers usually prepare their light and spon^ cakes, as, for instance, gingerbread, &c. Aerated bread is prepared by forcing carbonic anhydride into the dough by powerful pumps. When the pressure is removed, the gas escapes and the dough rises. ALCOHOL. — ETHTL HYDRATE. CAO = CH^O. Although alcohol can be prepared by other processes, it is always in practice obtained by the fermentation of sugar. In the preceding pages we have shown how alcohol is formed, how it is rendered stronger, and how it is purified. This is done by partial distillation, or by partial condensa- tion, since the alcohol is more difficult to volatilise than water, whilst its vapour is more difficult to condense than steam. But all the water cannot be separated in this way from the alcohol, as the alcohol retains one-tenth part of the water so firmly that it can neither be withdrawn from it by distillation nor by cooling. In order to procures it ab- solutely anhydrous, a body must be presented to it which has a greater affinity for water, and fixes it so firmly, that it cannot evaporate with the alcohol at the boiling point of the latter. Such a body is quicklime. Experiment. — Put into a flask one ounce of quicklime that has been broken into small pieces, and pour upon it one ounce of very strong alcohol ; connect a receiver with the flask, as in Experiment 1 (p. 337), and let the mixture remain in repose for one day. The lime gradually combines with the water of the alcohol (it slakes), and the latter is procured anhydrous by distilling it off at- a moderate heat. The best method of distilling in this case is' over the water-bath. ETHBE. — HTDEATE OXIDE. 343 Anhydrous alcohol is also called absolute alcohol. In this experiment, the vessels used must be previously rinsed out, not with water, but with strong alcohol, because the moisture adhering to the vessel would again impart water to the anhydrous alcohol. Properties of Alcohol. — Alcohol is the hydrate of the monad radical ethyl, C2H5, and has accordingly the formula C2H5HO (p. 295). It has a burning taste, and a pene- trating, agreeable odour. Strong alcohol, especially ab- solute alcohol, acts as a poison when swallowed; but when diluted, it is, as is well known, stimulating and intoxicating. Absolute alcohol has never yet been frozen ; it is there- fore well adapted for use in thermometers which are to measure low temperatures. Its specific gravity is 0*8. When exposed to the air it evaporates, and at the same time absorbs water, and so becomes weaker. It may be mixed with water in all proportions. If 50 measures of alcohol are mixed with 50 of water, the diluted alcohol has only a volume of about 97, a condensation taking place during the mixture. Alcohol is a very valuable solvent, for it dissolves many substances, resins, for instance, which are insoluble in water. On the other hand, some substances which are soluble in water are insoluble in alcohol. Alcohol, from the small proportion of carbon it contains, burns with a smokeless flame. In burning it is converted into water and carbonic anhydride. Methylated Spirit. — The Excise permits the sale, duty free, of strong alcohol mixed with ten per cent, of the wood spirit (methyl alcohol, see p. 297) which is obtained in the destructive distillation of wood. This mixed spirit is equal to pure alcohol as a solvent, and it cannot be used for .drinking purposes on account of the burning taste of the wood spirit. Moreover, the latter cannot be separated by any economical process. Methylated spirit is a treasure to the chemist. Other Alcohols. — The term alcohol is applied in chemistry to all hydrates of hydrocarbon radicals (page 297). The other alcohols are for the most part of no great practical importance. 344 EXPERIMENTAL OHEMISTET. ETHEK. — ETHYL OXIDE. CHioO = (CA),0. It has already been shown (page 292), that the term ether is applied to the oxides of hydrocarbon radicals. Common ether, sometimes called sulphuric ethevy because sulphuric acid is used in its preparation, is the most important member of the class, and the only one that needs description here. It differs from alcohol just as potassium oxide differs from potassium hydrate : KHO Potassium hydrate C^HsHO Ethyl hydrate (Alcohol). KjO Potassium oxide (G^)jD Ethyl oxide i Ether). Like the other ethers, it is obtained by removing the elements of water from alcohol. This is generally effected by sulphuric acid. Preparation of Ether. — Experiment 1. — Put two fluid ounces of strong alcohol (or methylated spirit) into a good-sized flask, and add slowly one fluid ounce of sb:ong sulphuric acid. Connect the flask with a receiver by means of a glass tube, close the opening remaining between the neck of the receiver and the glass tube by binding round it a piece of moistened bladder, in which some fine holes are pierced, and heat the flask carefully in a sand-bath till the contents of it assume a bubbling motion. M^aintain the boiliug of the liquid tiU about one ounce of the liquid is distilled over. In this ex- periment the liquor, as it is distilled, must be subjected to a powerful refrigeration, because it is extremely volatile ; it is therefore advisable, if possible, to •perform the experiment jj^ winter, and to surround the receiver with snow or ice. Cai-e must also be taken not to bring any burning substance too near the vapours of the liquid which pass over, as they are exceedingly inflammable. The distilled, colourless liquid possesses a penetrating, pleasant smell; it is called crude ether. In order to purify it, shake it up in a small vessel with half an ounce of water, and one drachm of strong solution of potash ; close the phial, and let it remain standing for an hour with the bottom upwards. Crude ether contains a mixture of water, alcohol, and frequently also, when the distillation is ETHER. BTHYl OXIBE. 345 continued too long, some sulphurous aoid ; these substances combine with the water and the potassa added, and form with them the heaviet liquid layer, which settles at the bottom of the phial. The very thin and mobile liquid floating above is ether, which separates, because it comports itself towards water in the same manner as oil does, and is dissolved by it only in very small quantity. If you now loosen the stopper of the inverted phial, the aqueous liquid will run out, while the ether remains behind. If the latter is required entirely pure it must be again distilled or rectified. The most profitable way of preparing ether on a large scale is the following : Nine pounds of sulphuric acid and five pounds of alcohol are mixed together, and heated to the boil- ing point. While the mixture is still boiling, just so much alcohol is allowed gradually to drop in as there is ether dis- tilled over. One single pound of sulphuric acid is then sufficient gradually to convert into ether thirty pounds of alcohol, at ninety per cent., or an unlimited quantity of absolute alcohol. This is called the continuous process for the manufacture of ether. It will be seen that the materials used for the preparation - of ether are the same as for ethylene gas (page 181). But the proportion of sulphuric acid is smaller, and the dehydration of the alcohol is therefore not carried so far : CjHsHO - HjO = C2H4, Ethylene. 2C2H5HO - H2O = (C2H5)20, Ether. The curious fact that sulphuric acid will convert an in- definite quantity of alcohol into ether and water is explained by supposing that hydrogen ethyl sulphate, HC2HJSO4, a salt of ethyl analogous to hydrogen-potassium sulphate, HKSO4, is first formed and then decomposed by another molecule of alcohol: C2H5HO + H2SO1 = B.JO + HC2H5SO4, and HC2H5SO4 + CjHgHO = (Cj,H5)20 + H^SO^. The water distils over with the ether, while the sulphuric acid remains to act on a fresh quantity of alcohol. Ex'periment 2.— Pour some drops of ether upon the hand; it will evaporate in a few moments, imparting to the hand a perceptible feeling of coldness. Ether is so very volatile that it 346 EXPERIMENTAL OHEMISTBT. boils at 95° P. (35° C.) ; therefore it must always be kept in' tightly-closed bottles, and in a cool place. Experiment 3. — Dip one piece of wood into ether, another into alcohol, and hold both to the flame of a candle ; the ether hams with far greater briskness, and also with a much more luminous and a somewhat fuliginous flame. Its stronger illuminating power is simply explained by its containing a larger amount of carbon. The process in burning is the same as with alcohol ; the ether being also converted into carbonic anhydride and water. Experiment 4.— -If you pour some drops of ether into a tumbler, and after some minutes, when the ether is converted into vapour, apply to it a burning taper, a sudden ignition ensues, accompanied by a small explosion. The vapour of ether forms, like hydrogen or marsh gas, when mixed with atmospheric air, a kind of explosive gas, and several violent explosions have been occasioned by carrying lighted candles or lamps into those places where, owing to the breaking of a bottle filled with ether, its vapour has become diffased in the air. Put a piece of tallow, or a few drops of oUve oil, into a test-tube with some ether ; both will entirely dissolve in it. But they are not soluble in alcohol or water. Therefore ether may be advantageously employed for dissolving and separating such substances as will dissolve in it, but not in other liquids. Besides the fixed oils and fats, ether dissolves many resins, caoutchouc (india-rubber), gutta-percha, &c. Ether is sparingly soluble in water, but may be mixed with alcohol in any proportion. It is very light (Sp. Gr. 0-736). Other Ethers. — Ethers corresponding to many of the other alcohols are known, but few have any importance. SALTS OF ETHYL. It has been shown (page 298) that salts, sometimes called compound ethers, of the alcohol radicals can be prepared which are in all respects comparable to metallic salts. Thbse of ethyl, which is the most important of alcohol radicals, are very numerous and interesting, but, as they do not possess much practical importance, we may pass them by in the simple practical study which we have in hand. ( 347 ) CHAPTER VI. ORGANIC ACIDS. The constitution of the simpler organic acids and their re- lation to the alcohols have already been explained (page 299). The student will find it well to read that section again before commencing the practical work of this chapter. MONOBASIC ACIDS. ACBTIO ACID. CjHA = HC2H3O2 or CAOHO. This acid, which is contained in -vinegar, is by far the most important member of the series called the " fatty acids " (page 299). It is often obtained by the oxidation of alcohol, two atoms of hydrogen being replaced by one atom of oxygen : C,HeO + O2 = C^H A + HA but it is also formed during the destructive distillation of wood,' and by other means. Acetous fermentation, — Vinegar. — When weak wine or beer is exposed to the air, a peculiar organised ferment (page 332) soon appears in it, which has the remarkable power of effect- ing the oxidation of the alcohol into acetic acid. These " vinegar cells " differ from yeast cells in that they cannot develope except in the presence of oxygen, but that they are organised cells, capable of transplantation and increase, there is no doubt. Like yeast cells, they can only develope in presence of their appropriate food, and at a suitable temper- ature. Experiment 1. — Mix in a glass vessel haK an ounce of brandy with three ounces of water, and put in the liquid a 348 EXPERIMENTAL CHEMISTET. slice of leavened bread, which has been previously soaked in strong vinegar, or instead of it a little leaven (page 340) ; covei: the vessel with a piece of perforated pasteboard, and put it in a place where the temperature is between 86° F. (30° C. ( and 104° F. (40° C.) ; the spirituous liquor will, after some weeks, be converted into vinegar. This conversion does not take place in a closed vessel, as the oxygen of the air is in- dispensable to the process. Neither is any vinegar formed if you do not add the bread or the leaven. As a solution of sugar does not of itself pass into alcohol, neither does the alcohol of itself pass over into vinegar. In the same manner as with pure diluted alcohol, all other alcoholic liquids, as beer, wine, cider, &c., may, by receiving oxygen, be converted into vinegar, and it is well known that vinegar is frequently prepared from them. If, as is ordi- narily the case, they contain glutin or lees in solution, theti these substances afford food for the vinegar ferment, and the acidification ensues spontaneously, when the liquid is exposed in loosely covered vessels to a temperature of from 86° P. (30° C._) to 104° (40° C). This acidification most readily occurs immediately after a spirituous fermentation, which has taken place at too high a temperature \ for this reason, in the hot months of summer,, the brewers and distillers find diffi- culty in keeping their fermenting wort and mash from turn- ing sour, which can only be prevented by rapid cooling. Experiment 2. — Fill two tumblers loosely with the stalks of grapes, and fill one entirely and the other only half full with wine, beer, or a mixture consisting of one part of brandy, one part of beer, and six parts of water. • Put both vessels in a warm place, and once or twice every day pour the mixture from one vessel into the other, so that each may be alternately full and only half full of the liquid. The alcohol contained in the brandy will, in this manner, be much more rapidly oxidised into vinegar, because the liquid adhering to the grape-stalk is, in this state of fine division, surrounded by air, and thus has a far better opportunity of attracting oxygen from the latter. The effervescence taking place at the com- mencement is owing to the sugar contained in the beer and the grape-stalks, and which was first converted into alcohol and carbonic anhydride. The alcohol thus formed is likewise afterwards changed into vinegar, and this is the reason why AOKTIO ACID. 349 Fig. 115. T t]ie vinegar thus produced is more acid, that is, richer in ^cetfc acid, than that obtained by the former experiment. Quick Method of maMng Vinegar. — The transition of alcohol into acetic acid takes place still more rapidly by subdividing the alcohol still further, or by exposing a still greater surface of the liquid to the air than in the way just described. This is effected in the following manner : A tub four or five yards high is filled with shavings of beech wood, and is furnished with a perforated shelf, which is placed somewhat below the upper opening. Through each of the small holes a straw or a piece of packthread is passed, prevented from falling through by a knot at the upper end. By this means an extreme divi- sion of the alcohol is effected, as when it is poured in at the top, it only trickles slowly down tlirough the holes by means of the straw or packthread, and then diffuses itself over the shav- ings, forming a very thin liquid layer, which presents to the air a surface many thousand times more extensive than was pro- duced by any former method. Several large holes are bored round the lower part of the tub, and likewise in the perforated ,sb.elf ; glass tubes are 'fitted into ] the holes made in the latter, in ^ such a manner that the liquid, - when poured into the top, may not run off through them. A free circulation of air is hereby produced, the cooler air enters by the openings in the tub, gives up its oxygen to the alcohol diffused over the shavings, and, in consequence of this oxidation, or slow combustion, so much heat is evolved in the interior of the tub that the temperature rises to 104° F. (40° C). The air hereby becoming warmer, and consequently lighter, passes out of the tub through the glass tubes in the shelf, from an eighth to a fourth poorer in oxygen than when it entered. Strong vinegar is used to assist the fermentation in this process, the tub pxid shavings having previously been 350 EXPERIMENTAL CHBMISTET. moistened with it, and a certaan quantity being also added to the mixture of spirit which is to be converted into \dnegar. In such a tub (vinegar-generator'), warmed spirit, beer, wine, &o., may be converted into vinegar in a few hours, by beipg passed through the cask three or four times ; hence this is called tTie guich method of making vinegar. Aldehyde. — During this oxidation of alcohol, an intermediate compound called aldehyde is first formed, and then oxidised to acetic acid. It is regarded as hydride of acetyl, (C2H3OH, acetic acid being the hydrate (page 299) : Alcohol, CAO. Aldehyde. CAO. Acetic acid. Its peculiar and suffocating odour can often be perceived in vinegar chambers. Wood Vinegar. — When wood is distilled in close vessels (page 185), besides charcoal, tar and gas, a certain quantity of acetic acids is always formed. This impure acid is sometimes called pyroligneous acid. When neutralised by sodium carbonate, sodium acetate, NaCgHsOa, is formed, and can be purified by crystallization. From this salt it is easy to obtain pure acetic acid. Experiment 3. — Mix some dry sodium acetate with strong sulphuric acid in a flask connected with a cool re- ceiver, and apply a gentle heat. Acetic acid will distil over, and may be collected in a state of purity : NaCjHsOj + H2SO4 = HG2HA + NaHSO^. Fig. 116. LACTIC ACID. 351 Pure acetic acid is an ice-like solid below 63° F. (17° C), and is therefore sometimes called glacial acetic acid. It boils at 244° F. (118° C). Tte strongest English vinegar contains about 5 per cent, of the true acid. Acetio anhydride, or Acetyl oxide, (C2H30)20, can only be prepared with difficulty. In constitution it is analogous to nitric anhydride : (C^HsO^O, is like (N02)20 or NA- Acetates. — Those of lead (sugar of lead) and sodium are amcmg the most important. Acetates can be recognised by warming them with sulphuric acid, when the odour of vinegar will be apparent. LACTIC ACID. CsHeOs = HOsHA or G,Bj:)(JB.O),. Lactic fermentation. — When milk is kept for some hours in a warm place, the milk-sugar undergoes a fermentation analogous to those already described. It is converted entirely into lactic acid, which renders the milk sour, and precipitates the casein as curd (page 829). The simple nature of the change, is shown by the following formula : Milk Sugar. Lactic Acid. CsHijOs = 2C3H5O3. Lactic acid can only be purified with difficulty. It is a colourless, oily liquid, which is decomposed by heat. A variety of lactic acid known as sarcolactic acid is found in the juice of flesh. Butyric fermentation. — If the fermentation of milk is pushed past the stage in which lactic acid is formed, butyric acid is produced by a distinct organised ferment. The odour and taste of rancid butter and putrid cheese are partly due to this acid. It is one of the fatty acids. BENZOIC ACID. C,HA = HC,HA or CHjOHO. Experiment 1. — Put some powdered gum benzoin into a saucer, cover it with a sheet of white filtering-paper on which rests a cone of writing-paper. Apply a very gentle 352 EXPEEIMBNTAL CHEMISTRY. heat to the saucer by means of a sand bath, and after an hour or so the inside of the cone will be found to be covered with beautiful white crystals of benzoic acid. The gum contains about 14 per cent, of the acid, and the acid being volatile passes in vapour through the porous paper, and condenses on the cone. The filter paper absorbs some volatile oil which is given off with the acid. Experiment 2. — Add benzoic acid to a solution of sodium carbonate until it no longer dissolves. Effervescence will take place from the escape of CO^, and sodium benzoaie, Na C7H1JO2, will remain in solution, and may be obtained in the solid state by crystallization. From this salt other benzoates may be prepared by double decomposition. Experiment 3. — Add solution of ferric chloride (rendered neutral by ammonia) to solution of sodium benzoate. A buff-coloured precipitate oi ferric henzoate will be produced. Experiment 4. — To a tolerably strong solution of sodium benzoate add hydrochloric acid. Pearly crystals of benzoic acid will be thrown down. Benzoates can be decomposed in this manner by almost all acids. The precipitation of the acid is due to its sparing solubility. It recLuires 200 times its weight of cold water for solution. DIBASIC ACIDS. OXALIC ACID. C2HA = H2CA or CA(HO),. This important acid corresponds to an oxide of carbon. Fig. 117. CjOa, intermediate between carbonic oxide and carbonic anhydride. This oxide is however un- known. The relation of oxalic acid to ethylene alcohol has already been shown (page 299). Experimemt 1. — Heat with free access of air, in a porcelain dish, one-fourth of an ounce of sugar, mixed with one and a half ounce of concentrated nitric acid, and one ounce of water. In a short time a strong evolution of yellowish-red fumes (NaOj) will com- mence. Continue boiling until these vapours cease, and then put the liciuid in a cool place ; colourless crystals (oblique rhombic prisms) of oxalic acid will OXALIC ACID. 353 separate, wliicli must ^be purified by recrystallization. They have a strong acid reaction, and are poisonous. Starch, or even saw-dust (impure cellulin), may be substituted for sugar in this experiment. The crystals contain H2CA.2H2O. Bxp&riment 2. — Pour into a test-tube twenty grains of oxalic acid, and one drachm of strong sulphuric acid, and carefully heat the mixture ; a gas will be evolved. Let this pass through solution of potash contained in anotheiN test- tube. One half of the escaping gas is absorbed by the potash ; this is carbonic anhydride (CO2). The other half escapes through the open tube, and burns, when kindled, with a bluish flame ; this is carbonic oxide (CO). When the evolution of gas ceases, there will be found in the first test-tube common sulphuric acid ; consequently, the sul- phuric acid has removed water from the oxalic acid. The oxalic acid, when it loses its water, is resolved into the two gases just mentioned, in the following manner : H,C A = H,0 4- CO -f CO2. Hxperiment 3. — Place some crystals of oxalic acid upon a piece of platinum foil, and hold them in the flame of a spii^it-lamp. They melt, take fire, and burn without becoming hlaeh or leaving any residue. The product of the combus- tion is carbonic acid ; HjCA and (from the air) are con- verted into 2CO2 + H2O. Experiment 4. — Neutralise a hot concentrated solution of oxalic acid with a hot concentrated solution of potassium carbonate; neutral potassium oxalate (KaOA), an easily soluble salt, is formed. If you now add as much more oxalic acid, hard crystals will be deposited on cooling, which have an acid reaction ; they are called acid oxalate of potassium, or hydrogen potassium oxalate, HKC2O4. The acid oxalate is likewise formed by the vital process in many plants, and it is found abundantly in the leaves of the wood- sorrel (Oxalis), from which it may be obtained. The acid salt is lar less soluble than the neutral, Experiment 5. — Heat some potassium oxalate upon platinum foil ; it will be converted into potassium carbonate. The oxalate loses carbonic oxide : K2C2O4 = K2CO3 + CO. Many 2 A 354: EXPERIMENTAL CHEMI8TBT. other oxalates are converted into carbonates when treated in this way. Experiment 6. — Agitate a little calcium sulphate with water and let the liquid settle ; the decanted water contains a small quantity (^^) of the sulphate in solution. If a solution of oxalic acid is poured upon this solution, you will soon obtaiii a precipitate of calcium oxalate. The decomposition takes place more rapidly and perfectly when the oxalic acid has been previously neutralised by ammonia. Oxalic acid, or ammonium oxalate, is the best test for calcium gaits. Experiment 7. —Add some spoonfuls of water to a piece of green vitriol of the size of a pea, and moisten with the solu- tion a piece of white blotting-paper ; when this has imbibed the liquid, spread it over some ammonia. The ammonia pre- cipitates green ferrous hydrate 09 the paper, which soon , absorbs oxygen, and is converted to the yellow ferric hydrate. In a similar manner, cotton, and other fabrics, are often dyed brown or yellow. When it is dry, mix some oxalic acid with water into a thin paste, and dot the yellow paper with it in several places ; the colour will soon disappear from these spots, and you obtain a white pattern on a yello"w ground. Oxalic acid dissolves ferric oxide, and both are removed by washing. Upon this is founded an important use of this acid in calico-printing, as likewise its application for the re- moval of ink spots from linen or paper. One of the principal constituents of ink is an iron salt, which being dissolved by the oxalic acid, the black colour of the ink disappears also. This explains why, on removing ink-spots by oxalic acid or salt of sorrel (which acts in the same manner as the free acid) from yellow and brown articles of dress, the colour of which often depends upon iron, the colour of the stuff also disappears. TARTARIC ACID. CAOe = H2C4HA or CiHACHO)^. Tartaric acid is generally prepared from tartar or argol, which is obtained in large quantities from the wine countries, where it is deposited from wines in the casks, as a white or reddish crust. It is impure hydrogen potassium tartrate. Tartaric acid might be very easily obtained from this salt by TAETABIO ACID. 355 meaus of sulphuric acid; but then two soluble substances would be obtained, which could not well be separated from each other. Fox this reason, the potassium is first replaced by another metal, namely, by calcium, which forms with sulphuric acid an insoluble, or at least very difficultly solu- ble compound. By boiling tartar with water, and adding chali to it, then calcium tartrate is obtained, as a white inso- luble, powder ; if this, after being sufficiently washed, is put hj for some time with water and sulphuric acid in a warm place (digested), calcium sulphate is formed, whilst the tar- taric acid dissolves in the water, and crystallizes from the solution after evaporation. Tartaric acid has very much the appearance of a salt ; it crystallizes in colourless oblique prisms, which are permanent in the air, and have a very acid taste. Experiment 1. — Place a small crystal of tartaric acid upon a piece of platinum foil, and heat it over the flame of a lamp ; it will first melt, then become brown, and finally black, and emit at the same time a peculiar j,. -,,g empyreumatic odour. If, during the process of charring, you hold over the acid a dry, cold glass vessel, it will be- come lined with globules of water ; con- sequently the acid contains oxygen and hydrogen. The dark residue resembles charcoal, but it is more certainly recog- nised as such by its burning completely at a higher heat. Accordingly tartaric acid, when heated, behaves like wood. JEa^eriment 2. — Pour a little warm water over some tai'taric acid ; it will dissolve therein, for it is readily soluble in water. If you dilute the solution with more water, and put it aside in a moderately warm place, slimy flakes will be deposited, and the acid taste will gradually be lost — -it decomposes. Many other organic acids, when they are diluted with water, decompose after a time. Experiment 3. — Neutralise a solution of potassium carbon- ate with a solution of tartaric acid; carbonic anhydride escapes; the liquid, however, remains clear, because the neutral potassium tartrate (KiC^fii) formed is an easily solu- ble salt. But by adding yet more tartaric acid, the liquid becomes turbid, and deposits a quantity of small transparent 356 BXPEEIMBNTAL CHBMISTBY. crystals, which are difficultly soluble in water, have an aciil taste, and contain only half as much metal as the neutral salt. These crystals are called acid tartrate of potassium, or hydrogen potassium tartrate, HKC4H4O6 ; commonly, tartar, or when they are pulverised, cream of tartar. The salts of potassium may accordingly be used as tests for tartaric acid. Experiment 4. — If you heat the crystalline powder of tartar, obtained in the last experiment, on platinum foil, it will, like the tartaric acid, become black, and bums with an empyreinnatic odour ; but there will, however, finally remain a white powder, which has an alkaline taste, a basic reaction, and which, on the addition of an acid, will effervesce. It is potassium carbonate. TEIBASIC ACIDS. CITRIC ACID. CaHsO, = HsCeHA or CeH50,(HO)3. This is the characteristic acid of lemons, but it is also found in many other fruits. Experiment 1. — Add chalk in small portions to some lemon juice, until no further effervescence occurs. The white sedi- ment consists of impure calcium citrate. It may be carefully decomposed by sulphuric acid (avoiding excess), the free citric acid filtered from the insoluble calcium sulphate, and crystal- lized. It is however somewhat difficult to obtain it pure by this process. Experiment 2. — Citric acid resembles tartaric acid in its appearance and many of its properties. The effect of lieai on the crystals may be tried. Experiment 3. Add some lime water to a solution of citric acid. No precipitate, or only a very slight one, is formed. Boil the liquid and an abundant precipitate will appear, but will again disappear as the liquid cools. Calcium citrate is more solvhle in cold water than in hot; a remarkable exception to the general rule. ( 357 ) GALLIC ACID. — TANNIN. Gallic Acid, CjSJ^n. Tannin, G^Hj^^On- Tannin, Tannic Acid, GaUotannic Acid. Ea/periment 1.— Take a large test-tube with a small hole in its end, plug the hole with cotton wool, and fill the tube half full of the best Aleppo gall nuts in fine powder. The gall nuts found on English oaks are very inferior. Support the tube upright, and pour in some common ether. Com- mercial ether always contains some water and alcohol, both of which in small quantity are necessary for the success of the operation. The ether soon percolates through the gall nuts, and may be received in a small bottle. Eepeat the addition of ether several times, and then cork up the bottle and allow it to remain at rest for some time. The liquid will separate into two layers, the upper one of which consists mainly of ether, which may be drawn oflf with a pipette,* and the ether purified by distillation. The lower layeB consists chiefly of an aqueous solution of tannin, or tannic add, a peculiar astringent substance which is contained in gall nuts, and in less quantity in a great many vegetable products. Oak-bark contains from 6 to 10 per cent, of it. The aqueous solution may be evaporated to dryness at a gentle heat, when the tannin is obtained as an amorphous mass of strong astringent taste. It is very soluble in water and alcohol, but insoluble in pure ether. The chief importance of tannin arises from its power of combining with gelatin and gelatigenous substances, and formiag with them a substance, leather, which does not putrefy. The process of tanning may be illustrated in the following manner : Experiment 2. — Add a solution of gelatin to a dilute solution of tannin, or to a decoction of oak bark or gall nuts ; a white flocculent precipitate will be formed. Eayperiment 3. — Take a clean, dry piece of skin, weigh it, and suspend it for some days in a solution of tannin, or a decoction of bark. It will gradually remove the whole of * Pipettes are tubes drawn out to a fine jet at one end. They are very useful for sucking up small quantities of liquid. They are often made with a bulb in the middle. 358 EXPEBIMENTAL CHEMISTRY. the tannin, and be converted to an imperfect leather. When dried and weighed it will be found to have gained in weight, the increase affording a rough measure of the amount of tannin that the solution contained. For the tanning of thick hides many months are often required. Experiment 4. — A solution of tannin gives with ferric sajts a blue-black precipitate, which is the colouring matter of ordinary ink. Pure ferrous salts give a white precipitate with tannin, which absorbs oxygen from the air and turns black. The reason why so many inks become darker when the writing is exposed to air is that a ferrous salt has been used in their manufacture. Experiment 5. — Writing ink. — Take one pound of bruised Aleppo gall nuts, six ounces of green vitriol (ferrous sul- phate), six ounces of gum arabic, a few drops of carbolic acid ( or creosote), and one gallon of cold water. Mix them in a stone jar, and stir at intervals for three weeks ; then let the ink settle and decant it for use. The gum gives thickness to the ink, the carbolic acid keeps it from turning mouldy. Experiment 6. — Tea contains a good deal of tannin. Ex- periments 2, 3, and 4 may be repeated with a decoction of tea. Tea made with waters which contain iron has an inky appearance. Experiment T.^When a solution of tannin is boiled with very dilute sulphuric acid, it is converted into glucose and an acid called gallic acid : C^UAi + 4H2O = SCHeOfi + CeH,A- A similar change can be effected by merely exposing it in a moist state to the air for some weeks. The sugar is, however, lost in the latter case. Substances which readily split up into glucose and another body are called glucoside^. Gallic Add. Esffperiment 8. — To prepare gallic acid, moisten some powdered gall nuts with water, and keep them for a month in a warm place (about 20° C, or 68° F.), replacing the water as it evaporates, and removing the mould which forms. Press the mass in a calico bag, and afterwards boil GALLIC ACID. — TANNIN. 359 it with water and filter while hot. As the solution cools, silky crystals of gallic acid will deposit. Gallic acid is distinguished front taimin by its power of crystallizing and by the fact that it does not precipitate gelatin. It is useless in tanning. Eayperiment 9. — GaUic acid gives with ferric salts an even more intense blue-black colour than tannin does. Its solution affords a most delicate test for those compounds. Pyrogallic Acid, OsHsOa. Experiment 10. — Heat some gallic acid, very gently, in the apparatus used for preparing benzoic acid (page 351). After some time beautiful silky crystals of pyrogallic acid are found in the paper cone : C,H A = CeHeO, + CO2. Pyrogallic acid is used in photography. Its alkaline solution absorbs oxygen rapidly and turns brown ; it is therefore much used in gas analysis. 360 EXPERIMENTAL CHEMI8TET. CHAPTER VII. PATS AND FIXED OlliS, SOAP, &C. Group i. — Non-drying Fats and Oils (Glyceridee). Group ii. — Drying Oils (also Glycerides). Group iii. — Wax, Spermaceti, &c. (not Glycerides). Group i. — Non-drying Fats and Oils. Throughout the vegetable and animal kingdoms a class of substances is distributed which is of 'very great interest and importance. The members of this class are generally called fats when solid, and oils when liquid at ordinary tempera- tures. They are almost invariably mixtures in various proportions of two or more definite compounds. They possess in common certain well-marked peculiarities, which may be shortly enumerated. 1. They are all compounds of carbon, hydrogen and oxygen only. 2. They are lighter than water. 3. They aro non volatile, being destroyed and converted into gases when heated above a certain point, 4. They are insolvhle in water, scarcely soliMe in alcohol, very soluble in ether, benzol and carbon disulphidoi 5. They are fusible at a temperature much below that of boiling water. 6. When boiled with caustic alkali they all yield glycerin, and peculiar salts of the alkaline metal (soaps : the change is called saponification'). Proximate constituents of the members of this group. — The most important of these are : stearin, CgTHjirjOe, a white solid, the chief constituent of suet, tallow, and lard, con- tained also in some vegetal oils ; palmitin, CsiHagOg, solid, ANIMAL FATS AND OILS. 361 not SO hard as stearin, found in palm oil, and in all animal and vegetal fats; and olein, C57H104O6, liquid, the chief constituent of olive and many other oils, and also present in most fats. These three substances are called glycerides, because they are salts of the triad radical glyceryl, CsHb (page 297), of which glycerin is the hydrate, CsH6(H0)s. Each of them contains the monad radical of a distinct acid ; stearin, of stearic acid, HGisHseOs; palmitin, of ^aZinJiic acid, HCisHsiOa ; and olein, of oleic acid, HCigHaaOj. Their constitution may be repre- sented in the following manner : stearin. CffiHnoOs = C3H5(Ci3H3502)s, oT GlycBTyl tristearate. Palmitin. CsiHgaOe = C3Hg(0]6H3iO2)s, or Glyceryl tripalmitrate. Olein. CstHimOs = C3H5(0i8H3sO3)3, or Glyceryl trioleate. Palmitic and stearic acids are members of the formic, or "fatty acid " series ; oleic acid, of the acrylic series (page 300), ANIMAL FATS AND OILS. Experiment 1. — Boil some fat pork, cut up into small pieces, for soiiie time in a little water, and while the soft mass is still hot, press it in a linen cloth ; a fat oil will float on the surface, but it is fluid only at a temperature of about 86° ¥. (30° C.) ; below this temperature it congeals into a solid, yet soft, white substance. This is lubricating to the touch, and produces greasy spots on paper. Those kinds of fat, which, at the common temperature, have a soft unctuous consistency, are called lard; and the cellular membrane and skin remaining in the cloth, and saturated with fat, are called scraps. The suet of mutton, when treated in the same way, yields a fat which, when hot, is also fluid, like oil, but which, when cooled only to about 97° F. (36° C), congeals, and then forms tallow, a harder substance than lard. By boiling and roasting, we can melt out fat from all animal substances, especially from those of the domestic animals, in which we are able to produce a great quantity of fat by keeping them confined, and giving them a plentiful supply of food. The fats obtained by boiling with water are white, as 362 EXPEKIMENTAL OHEMISTET. thereby they do not become heated above 242° F. (100° C.) ; while those obtained by roasting have a yellow or brown colour (brown butter, gravy of roast meat, &c.), because in this case a portion of the fat" becomes burnt by being sub- jected to a stronger heat — to a heat, perhaps, even above 572° F. (300° C). These substances consist mainly of stearin, palmitin and olein, the first predominating. When lard is strongly pressed, olein is obtained from it (lard oil). Train, or whale oil, is obtained from the blubber of the whale. Sperm oil, from cavities in the skull of the sperm whale. God liver oil, obtained from the liver of the cod, contains minute quantities of bromine, iodine, sulphur, phosphorusiu and free acids, in addition to stearin, palmitin, and olein;^ . To the bromine and iodine the value of the oil in medicine is often ascribed Grearrii — Butter. — That singularly complex and important liquid milk owes its opacity to myriads of minute globules of oil which float in it. Under the microscope these are seen to be perfectly transparent, for milk is opaque, just as powdered or ground glass is opaque, only, because the rays of light which faU on it are scattered by the irregtilarity of the globules or fragments. When milk is kept for a time, most of the oil globules rise to the surface and constitute cream. They do not run together, because each is enclosed liui a delicate membrane ; but when the cream is violently agitated (churned), the membranes are broken and a solid mass— butter — is obtained. SJcitn-milh is milk from which the greater part of the cream has been skinmied. Butter-milk is the liquid residue left after butter has been made from cream. Both consist chiefly of milk-sugar and casein (page 827) and mineral salts, with much water. Fresh butter consists chiefly of olein, palmitin and stearin, with small quantities of other glycerides, and of albuminoid bodies (casein, &c.). When kept, the albuminoids begin to putrefy, and a kind of fermentation takes place, which appears to consist in the partial separation of the fatty acids from the glycerin. To some of these fatty acids (butyric, capryliCj capric, &c.) the disagreeable taste and smell of rancid butter is due. The change can be to a great extent prevented by VEGETAL FATS AND OILS. 363 salt, which acts as an antiseptic, or by purifying the butter by melting it in hot water, and removing the solid mass when cold. The latter process however injures the delicate flavour of the butter. VEGETAL FATS AND OILS. Almond oih — Experiment 1. — Break open an almond, and squeeze the white meat together by means of the finger-nail ; small drops of fluid will be expressed, which are slippery to the touch, and render blotting-paper greasy and transparent. This liquid is called oil of almonds. If the almonds are first pounded, and then subjected in a cloth to strong pressure we shall^ obtain more than one-fourth of their weight of oil of almonds. A great many plants contain a similar oily juice, especially in their seeds, and from many of the latter oils are obtained by pounding and expressing. They occur, in small quantity in almost all plants, even in those where we should not expect to find any ; for instance, in different kinds of corn, grasses, &c. Palm oil is obtained from the fruit of certain kinds of palm. It is yellow and has the consistence of butter. It consists chiefly of palmitin, with olein, &c. It is largely used in the manufacture of soap and candles, and also, with tallow and a little soda, for greasing the wheels of railway (Arriages. For the two former purposes it is bleached by exposure to air in a melted state for ten or fifteen hours. Cocoa-nut oil is a soft white solid, somewhat like palm oil. Olice ml, expressed from the fruit of the olive tree, 4s too well known to require description. A simple experiment shows that it is a mixture. Experiment 2. — Expose some olive oil to the cold of a wiater's night, or surround it for some time with ice. It will become semi-solid, and will be full of granules. These granules consist of stearin and palmitin. Subject the mass to gentle pressure in calico without allowing the temperature to rise ; a clear oil will be expressed, which does not solidify at 32° F. (0° C). This consists almost entirely of olein. Colza oil and Bape oil are obtained from the seeds of several species of brassiea, to which genus the cabbage, turnip and rape belong. They are said to contain the glyceride of a peculiar acid, hrassic acid. 364 EXPERIMENTAL CHEMISTKY. The following experiment illustrates the mode in which rape oil is refined or purified. Experiment 3. — Mix one ounce of crude rape oil with eight drops of common sulphuric acid, and shake it frequently; in half an hour add half an ounce of water; again shake the mixture briskly, and set it aside for some days, when the oil floating on the surface will be freed from mucilage (purified). The slimy parts, charred by the sulphuric acid, and rendered insoluble, are found settled in the water at the bottom of the vessel. The sulphuric acid still adhering to the oil is re- moved by repeated washing with water. Sulphuric acid chars, as is known, all organic substances, some (for instance, muci- lage) easily, others (for instance, oil) with difficulty ; if just enough sulphuric acid, therefore, is added to the oil to char the mucilage, then the mucilage only is destroyed, and the oil remains undecomposed. A larger quantity of sulphuric acid would also attack the oil. Castor oil, from the seeds of Bicinus communis,, consists chiefly of the glyceride of a peculiar acid, ricinoleic acid. It also contains small quantities of a peculiar alkaloid, ricinine. The oil is remarkable for being easily soluble in alcohol. SAPONIPICATION.^SOAP. When any one of the preceding fats and oils — in fact, any glyceride, or mixture of glyoerides — is exposed at a suitable temperature, different with different oils, to the action of a strong solution of caustic soda or potash (alkaline lye), a double decomposition takes place, glycerin is formed, and with it a sodium or potassium salt of the acid, or acids of the oil. These salts are called soaps, and the change is called saponification. The following formulae will show how similar the action is to some of the changes of mineral chemistry : stearin, or Glycerin, or Stearin Soap, or Glyceryl Stearate. Glyceryl Hydrate. Sodium Stparate. CsH/OisHssOs+SNaHO = C3H,(H0), + SNaCigHsA- Bismuth Nitrate. Biemuth Hydrate. Sodium Nitrate, Bi"'(N03)3 + 3NaH0 = Bi"'(H0)3 + SNaNOs. Soaps are in fact salts of the higher fatty acids. The ordinary hard soaps are sodium salts. Soft soaps s.ve potassium salts. These soaps are soluble in water, alcohol, &c., but others, such as lead soap (lead plaster), calcium soap, &c., can SAPONIFICATION. — SOAP. 365 be prepared which are insoluble in water. It will readily be understood that ordinary washing soaps are mixtures of stearate, palmitate and oleate of sodium. Hard soap. — Experiment 1. — Make first a strong lye with one drachm of the caustic soda of com- j^jg ii9_ merce and one ounce of water, and next, a weak lye, with one drachm of caustic soda and two ounces of water. Boil the latter gently with an ounce and a half of beef-suet, for half an hour, in a vessel only half- filled with the mixture, and then add the strong lye gradually while ' the boiling continues. The fat and lye gradually unite and form a uniform mass, of a gluey con- sistency, which after a time becomes thick and frothy. If a drop of this, when pressed between the fingers, presents firm white flakes, then add half an ounce of common salt, boil for some minutes, and let the whole mass cool quietly. We obtain a firm mass {soap) and a watery liquid, in which the common salt and some free soda remain dissolved {under- lye). If the soap, when boiled with distilled water, forms a turbid solution, it still contains some unsaponified tallow, in which case add to it some weak lye, and continue boiling until the sample gives a clear solution in water ; add again some common salt, and let it cool. The soap prepared in this manner has the same composition as common house- soap. Palm oil or cocoa-nut oil is often used partly or entirely to supply the place of tallow ; the palm oil because it is cheaper than tallow, and the cocoa-nut oil because it communicates to the soap the property of forming a very strong lather. Experiment 2. — Kepeat the former experiment, using olive oil instead of tallow ; hard soap is likewise obtained (oil- or Marseilles soap). Soft soap. — Experiment 3. — Prepare again some oil-soap, as above described, but instead of soda, use potash-lye, which is prepared from caustic potash and water, and omit the addition of common salt ; the glutinous mass does not then pass by boiling into a hard soap, but, after sufficient evaporation of the water, yields a soft mass. This kind of soap is frequently employed in print-works for the cleansing 366 EXPBEIMBNTAL CHEMISTET. of coloured fabrics. If train oil, temp-seed oil, or Enseed oil is used instead of olive oil, a darker-coloured soft soap is obtained, which is usually coloured green by indigo and turmeric (green and black soap). Ammonia acts far more feebly than potash and soda upon fats. If some oils are shaken up with ammonia, thick white mixtures, called liniments, are obtained, which are often applied by friction to the skin. Experiment 4. — The action of common salt in soap-makiirg may be seen by trying to dissolve hard soap in salt water ; no solution takes place, not even on boiling, for soap is insoluble in salt water, and likewise in strong lye ; therefore soap may be precipitated from a solution in water by the addition of common salt. This method of separation is usually employed on the large scale, since it yields a purer soap than when the water is removed by evaj)oration ; for, in the latter case, glycerin, surplus of lye, and the impurities contained in the lye or fat, remain mixed with the soap, while by the former method they are retained in the liquid (wnder-lye). Conversion of Potash soap into Soda soap. — Experiment 5. — Dissolve some of the soft soap obtained in Experiment 3 in boiling water, and sprinkle in some salt; the soap separates, and collects upon the surface of the water, yet, when cold, it will no longer be soft, but hard. The salt here acts in another manner ; it occasions an interchange of the constituent parts — namely, from the potassium-saU; ; of the fatty acid and chloride of sodium are formed chloride of potassium and the sodium-salt of the fatty acid (soda soap). This process was formerly much used in Germany. Experiment 6. — Dissolve some hard soap in hot soft water, and add white vinegar, a drop at a time, till the liquid is tho- roughly turbid. The acetic acid liberates the fatty acids of the soap, which after a time rise to the surface of the liquid and float there, being insoluble in water. The liquid now contains sodium acetate. Washing with soaps. — Soaps have two important pro- perties ; — 1st, they dissolve fat and oils ; 2nd, they are very easily resolved, merely by mixing with much water, into an acid salt and free alkali; the latter dissolves, as is well SAPONinOATION. SOAP. 367- known, most organic substances, wliile the former effects by its lubricity an easy washing away of the dissolved matter from other substances. On these two properties depends the application of soap in washing. The separated acid salt of the fatty acids both diminishes the action of the free alkali, and keeps the articles pliant which are washed with soap, while they would become rigid if they were cleansed with caustic alkalies alone. To prevent the shrinking of woollen articles, wash them with a weak solution of sodium carbonate instead of with soap. Soap and Alcohol. — Experiment 7. — Pour one ounce of alcohol upon one ounce of the shavings of tallow soap ; the soap is completely dissolved on heating in the water-bath, but the solution congeals on cooling to a transparent jelly. This jelly-like soap, mixed with camphor and ammonia, is called opodeldoc. The white stars separating from this consist of crystallized sodium stearate. All soaps prepared from solid fats (rich in stearin) behave like tallow soap. HxperimentS. — Dissolve one drachm of Naples soap in half an ounce of alcohol ; this solution does not coagulate on cooling ; it forms a tincture of soap. By evaporation, a diaphanous soap is obtained (transparent soap). All the soaps made from the fluid fats (rich in olein) act like the Naples soap. Mcperiment 9. — If some lime-water is added to a solution of soap in water, a precipitate of insoluble calcium soap is formed; this explains why spring-water, which generally contains calcium and magnesium salts (hard water), neither dissolves soap nor lathers with it, and accordingly cannot economically be used for washing. Hard water may, how- ever, be softened by the addition of sodium carbonate (common washing soda), which precipitates the calcium and magnesium as insoluble carbonates. Of course the metals can also be removed by soap, if enough is used, but washer- women use soda instead because it is much cheaper. TeUow soap. — The tallow and palm oil used' in soap- making is often mixed with half its weight of common rosin, which at a high temperature combines with alkalies even more easily than the fats. The soap so obtained is called yellow soap. It is cheap, but has a disagreeable odour. Marine soap is made from cocoa-nut oil. It is soluble in 368 EXPERIMENTAL OHEMISTET. somewhat dilute brine, and is therefore used for washing in sea-water. Glycerin. — Experiment 10. — In a deep basin, heat together 9 parts of olive oil (or any other glyceride), 5 parts of finely-powdered litharge and a little water. A little more water must be added from time to time to replace the loss from evaporation. After a time the oil disappears, and a firm mass insoluble in water is obtained and a watery liquid. The mass is the insoluble lead soap generally known as lead plaster. It consists, if olive oil has been used, chiefly of lead oleate. The watery liquid is a solution of glycerin containing some dissolved lead. It must be separated from the liquid, and the latter thoroughly saturated with sulphuretted hydrogen by passing a stream of the gas through it. This throws down the lead as sulphide, and the filtered liquid, evaporated to a syrup on the water bath, yields glycerin. It generally retains, however, a small quantity of l^td. A much better process for the preparation of glycerin is generally adopted on the large scale. It depends on the fact that superheated steam decomposes glycerides into glycerin and the fatty acids, both of which are carried over with the steam and readily condense in separate layers. The process is usually applied to solid fat (tallow, palm oil, &c.), and the solid fatty acids,' stearic and palmitic, are used for the manu- facture of the so-called stearin, palm, or composite candles, now so largely used. Properties of Glycerin. — Pure glycerin is a colourless syrupy liquid of sp. gr. 1-26. It mixes with water and alcohol in all proportions, but is insoluble in ether. It has a very sweet taste, whence its name (from yXvKo^, sweet). Distilled with steam, or at a reduced pressure, it passes over unchanged, but under ordinary circumstances the greater part is decomposed, and a substance of pungent and irritating odour, called acrolein, C3H4O, is produced. Experiment 11. — Boil a little glycerin in a test-tube, the irritating odour of acrolein will soon be perceived. If some hydrogen potassium sulphate is mixed with the glycerin, acrolein is produced in much larger quantities, but, unless elaborate precautions are taken, it is impossible to remain in the laboratory while the experiment is in progress, as the vapour, even in very minute quantity, irritates the eyes insupportahly. DKYING OE VARNISH OILS. ^69 Acrolein, treated with silver oxide, yields the silver salt of acrylic acid, AgCsHsOa (page 300), of which acid acrolein is the aldehyde. When glycerin is heated with fatty acids under pressure, oils or fats identical with the proximate constituents of the natural fats and oils (page 360) are obtained, water being formed at the same time. Geoup ii — Drying or Varnish Oils. We have seen that many seeds, when submitted to pressure, yield fixed oils analogous ia their nature to the animal fats and oils. A certain number of these oils possess the property of drying, that is, of becoming solid and hard when exposed to the air. The change is attended with the absorp- tion of oxygen, but is not well understood. It renders them very valuable in the manufacture of paints and varnishes. The oils of linseed, hemp-seed, and poppy-seed, and the oil of walnut kernels (nut oil), are among the most important of, this class. Linseed oil, which is more largely used than the others, is the only one which need be studied here. All the drying oils are mixtures of glycerides. Linseed oil contains the glyceride of a peculiar acid, linoleie acid. They are, of course, all capable of saponification. 'Linseed oil. — The well-loiown linseed, the seed of common flax, yields, on being subjected to pressure, a yellow oil, equal to one-fitfth of its own weight, which is gradually bleached by long exposure to the surdight. It is most frequently used in oil varnishes. Experiment 1. — Add to an ounce of linseed oil a quarter of a drachm of litharge, and half a drachm of acetate of lead ; put the mixture in a warm place, and frequently shake it. The liquid, clarified by settling, now dries much quicker than it would have done before ; it is used in the manufacture of the common linseed oil varnish, which, mixed with colours, is generally used for imparting a gloss to wood, metal, &c. The so-called oil-cloth is cotton cloth smeared with coloured Un- seed oil ; oil-silk is varnished silk. The oil is commonly prepared, on a large scale, by heating one hundred pounds of linseed oil with one pound of litharge, and maintaining the mixture for an hour at a temperature of 212° F. (100° C). A stronger heat renders the varnish darker and thicker, and, 2 B 370 EXPEBIMBNTAL CHEMISTRY. besides, might easily cause it to boil over and take fire. The slimy, dingy white sediment which remains after both pro- cesses is a combination of mucilaginous substances with oxide of lead. All oils contain, in the unpurified state, mucilaginous (gummy and albuminous) substances, which retard the drying; these are rendered insoluble by oxide of lead. Varnish is, accordingly, linseed oil free from mucilage. jExperiment 2. — The difference between the drying and non-drying oils may be shown by smearing two pennies, one with olive, the oth«r with linseed oil, and allowing them to remain for several days in a warm place. The linseed oil wlU dry up into a thin transparent solid layer. Experiment 3. — Heat some linseed oil over a lamp, and test the temperature of it occasionally by a thermometer. At ■pj J2Q first the heat rapidly rises to 212° F. (100° C), and remains for some J time at that temperature, during which time the oil boils moderately ; this behaviour is occasioned by all crude oil containing watery particles, which evaporate at 212° F. (100° C). As soon as these have volatilised, the temperature soon rises to 300° C. (572° F.), or even higher, when the oil begins to boil for the second time, but emits now a white smoke having a very disagreeable odour. This vapour consists principally of illuminating gas, from the decomposed oil, and burns, when kindled, with a brisk flame. The oil at last acquires a treacle-like consistence and a brown colour. It is called hoiled oil. Printing ink is made with boiled oil, lamp-black, and a little yellow soap. Putty is a mixture of linseed oil and whiting. Group iii. — The Waxes and Spermaceti. These substances differ from the glycerides inasmuch as their essential constituents are salts, not of the triad radical glyceryl (CsHg)"', but of. some of the mcmad alcohol radicals homologous with methyl and ethyl (page 297). The acid radicals are those of the fatty acids, therefore they are homologues of the radicals of formic and acetic acids, so that the proximate constituents of these substances are WAXES AND SPERMACETI. 371 true hdmologues of the formate or acetate of methyl or ethyl. Spermaceti, fovmd in cavities in the head of the sperm whale, consists chiefly of cetin ; Chinese wax, obtained from the branches of certain trees in China, contains ceryl cerotate ; and hees-wax contains myricin, with two or more other consti- tuents. Other vegetal waxes are known. The following table will show the constitution of these proximate constituents, and their relationship to the simplest series of alcohols and fatty acids. Methyl formate, the lowest possible member of the series, is placed at the head for com- parison : Cetin Chinese wax Myricin C^HA Methyl Formate. = CH3JGHO2. Cetyl Palmitate. Ceryl Cerotate. Myricyl Palraitate. C46H92O2 - CgoH6i,Ci6H3i02. These compounds are decomposed by caustic alkalies just as the glycerides are, the products being an alcohol, or hydrate of the basic radical, and a compound of the acid radical with potassium, or sodium ; Myricin. CsoHeijCieHgiOg -|- KHO Myricyl Alcohol. Polassium P&lmitate. : Cs„He,HO + KCieHsiOj. This is, in truth, a process of saponification. 372 EXPERIMENTAL CHBMISTET. CHAPTEE VIII. VOLATILE OILS, RESINS, AND ALLIED BODIES. The compounds enumerated in this chapter are closely allied to one another. Many of them (the pure volatile oils, caoutchouc, &c.) are hydrocarbons ; the rest are compounds of carbon, hydrogen, and oxygen. The constitution is not thoroughly understood, even of the best known members of the different groups. The phenomenon of isomerism (p. 293) is very common among them, many of the volatile ©ils having the same formula as that of oil of turpentine, CioHu. A few are derived from the animal kingdom (ambergris, castoreum, civet), but the great majority are the produce of plants. The following classification will be found useful. Group I. Volatile, or Essential Oils. — Exist in several parts of many plants, either alone or mixed with resin, &c. They often separate by cold into two portions, one solid and camphor-like, which contains oxygen, and is called the stear- opten; the other liquid, and free from oxygen, called the elceopten. They are commonly obtained by distilliag the plant, or portion of the plant, with water. The oil comes over with the water and floats on its surface when it con- denses. The liquid oUs of lemon and orange peel, anise, cloves, lavender, thyme, and wormwood, are among those isomeric with oil of turpentine. Whenever we perceive an odour in a plant, we may pre- sume that a volatile oil is present, which gradually evapo- rates. But how incredibly diffused and diluted this must be in many plants, may be inferred from the fact that scarcely a quarter of an ounce of volatile oil is contained in one hundred pounds of fresh roses, or orange-flowers. We most frequently find the volatile oils in the flowers and seeds, sometimes in the stalks and leaves, and more rarely in the VOLATILE OILS. 373 roots. The oils procured from the peel of certain fruits, as the lemon, citron, bergamot-pear, &c., are obtained by ex- pression from the fresh rind. An immense number of volatile oils are known. The following are among the most important : — a.) From the flower : Oil of roses, a yellowish, thick fluid, with flakes resembling tallow floating in it. Oil of orange-flowers (oil of neroli), colourless; becomes reddish on exposure to the light. Oil of chamomile, a dark blue, thick liquid; becomes green, and finally brown, by age and light. Oil of lavender, a yellowish, thin liquid. Oil of doves, yellowish, soon becomes brown ; a somewhat thick fluid, heavier than water. Oil of hops, greenish yellow. h. ) From seeds and fruits : Oil of cumin, colourless ; becomes yellowish, and finally brown, by age. Oil of anise-seed, yellowish. Oil of fennel, colourless or yellowish. Oil of dill, yellow; becomes brown in the light. Oil of nutmeg, a pale yellow, thin liquid ; has the smell of nutmegs. Oil of hitter almonds, yellow ; heavier than water ; consists chiefly of henzoyl-hydride, C7H50,H, but contains hydro- cyanic acid, and consequently is very poisonous. Oil of mustard, yellowish, of an extremely pungent smell, causing lachrymation ; contains sulphur. Oil of juniper, colourless. Oil of savin, colourless, or yellowish ; a thin fluid. Oil of parsley, pale yellow ; yields much stearopten. OH of lemons, fifom lemon-peel. Oil of orange peel, very like oil of lemons. Oil of hergamot, from the rind of the bergamot orange, a pale yellow, very thin liquid. c.) From the leaves and branches : Oil of peppermint, colourless or yellowish, a very thin liquid. Oil of halm, pale yellow, has an odour like that of lemons. Oil ofma/rjoram, yellowish or brownish. 374 EXPERIMENTAL OHEMISTET. Oil of thyme, when fresh, yellowish or greenish; when old, brownish-red. Oil of sage, when fresh, yellowish or greenish ; when old, brownish-red. Oil of wormwood, dark green; soon becomes brown or yellow, and viscous in the light. Oil of rosemary, colourless and very thin. Cajeput oil, from the leaves of a tree growing in the Moluccas ; the oil, when pure, is colourless ; the crude oil is commonly green, and often contains camphor; it has a camphorated odour. Oil of rue, pale yellow or greenish. Oil of cinnamon, yellow ; soon becomes brown in the air ; heavier than water. Oil of turpentine, the most common of the volatile oils, is contained in all our fir-trees, and exudes from them, mixed with resin, as turpentine. When purified, it is colourless and thin, and has an agreeable, penetrating odour. An ordinary sort, possessing a disagreeable, empyreumatic odour, obtained in the preparation of pitch from pine resin, is crude oil of turpentine. d.) From roots : Oil of aeorus, yellow or brownish. Oil of valerian, pale yellow or greenish ; becomes rapidly brown and viscous on exposure to the air. It is very remarkable, that we sometimes find several sorts of oil in one and the same plant. Thus, for example, we find in the orange-tree three different kinds of oil ; one in the leaves, another in the blossom, and a third in the rind of the fruit. Geodp II. Besins. —Solid bodies containing oxygen. They have faint acid properties. Common colophony, or rosin, which accompanies oil of turpentine, is a good example. It consists chiefly of ahietic anhydride, C^HejOi. Other resins are animS, copal, lac, and mastic. Amber is a fossil resin. Gkoup III. Balsams. — Semi-solid masses. Some are mix- tures of resins and volatile oils. Of these the most important are the different varieties of turpentine, including Canada halsam and frankincense, from which Burgundy pitch is obtained ; halsam of Copaiba, used in medicine, and balsam VOLATILE OILS. 375 of Mecca, or halm of Gilead, of which the finest kind is hardly known in this country ; others contain cinnamie aeid (balsam of Peru, storax, tolu), or benzoic acid (gvm benzoin, dragon's blood), A few curious and highly valuable animal substances, remarkable for their odour, may be included among the balsams ; namely, ambergris, found in the head of certain whales; castoreum, obtained from the beaver; and duet, from the civet cat. Group IV. Gum Mesins are mixtures containing resin gum and other ingredients. The niost important are, — Asafoetida, from the' root of a plant growing in Persia. Its disgusting odour is due to the presence of about three per cent, of a sulphuretted oil. Gamboge, from the leaves and branches of a tree which grows, in Cambogia and Ceylon. Myrrh, from Arabia and Abyssinia. Imported in the form of reddish tears. Olibanum, or incense. Burnt in religious ceremonies. Brought from Arabia. Scammony-, from Syria and Asia Minor. Aleppo scammony is the best. It has a strong odour and is used in medicine. Group V. Camphors. — Solid volatile bodies of peculiar pungent odour. They contain carbon, hydrogen and oxygen. Common, or laurel camphor, CioH^O, obtained from Laurus camphora, a tree which grows in the East Indian islands, is the most important. Borneo camphor, CuHuO, is similar to common camphor. The stearoptens of some volatile oils are closely allied to the camphors. Group VI. Caoutchouc and GvMa-percha. — These sub- stances, though so different in properties, are allied in com- position to oil of turpentine. When pure they contain no oxygen, and are said to have the formula CuHis. VOLATILE OILS. Preparation of Volatile Oils. — Hxperiment 1. — Put one ounce of turpentine in a dish in a warm place, and when it has become liquid transfer it to a capacious flask ; pour upon it four ounces of water, and distil until about threer fourths of the water have passed over. Pour the residue, whilst still hot, into cold water, in which the non-volatile portion of the turpentine will soon congeal into a solid mass 376 EXPERIMENTAL OHKUISTBY. (resin). A strongly smelliag, colourless liquid — a volatile oil, commonly known under the name of oil of turpentine — floats on the surface of the water. Turpentine is the juice which exudes from pines and some either trees when the inner bark is cut through. We see from this experiment that it is a mixture of resin and volatile oil, which latter is carried over as vapour with the water and afterwards condensed. If the distilled liquid is received in a pipette (p. 367), the lower end of which dips in water, the oil will collect in it and may easily be separated from the water. Pig. 121. Pig. 122. Experiment 2. — Distil in the same manner half an ounce of cumin-seeds (which have been previously bruised in a mortar) in a retort containing four ounces of water, until two ounces of water have passed over. The drops floating upon the water consist of a vola- tile oil, oU of cumin ; they have the smell and taste of the cumin-seeds, but in a stronger degree, while the residue remaining in the retort has scarcely the least smell or taste of them. All volatile oils possess a burning taste, and are somewhat rough to VOLATILE OILS. 377 the touch ; but the fat oils have a mild taste and an unctuous feel. Experiment 3. — ^Pour a drop of some volatile oil upon a sheet of paper, and let it remain exposed to the air; the paper at first receives an apparent grease-spot, but this dis- appears after a time, because the oH gradually evaporates. If the oiled paper is placed upon a warm stove, evaporation takes place much more rapidly. Aromatic oils are employed in this way for perfuming apartments. Usually a quantity of flowers, woods, and barks, finely cut up, are moistened with the oil, and scattered as a fumigating powder upon the stove. Experiment 4. — Heat a quarter of an ounce of oil of turpentine in a vessel to boiling. A thermometer introduced into the liquid will indicate a temperature of about 328° F. (160° C). Other oils boil with even jnore difficulty. The vapour may be inflamed by a taper, when it will burn with an intense sooty flame. It is easily extinguished by covering the vessel with a board ; but water must on no account he employed for extinguishing burning oils. Then remove the oil from the fire. After it is cold, mix it with some water, and again heat it ; as long as any water is present the tem- perature of the fluid wHl not rise above 212° F. (100° C). The ascending vapour is a mixture of the vapours of water and oil. The same thing, occurs here as previously men- tioned ; the less volatile oil evaporates with the more easily volatile water. The oils remain unchanged at the boiling point of water, but at their own boiling point, from 284° F. (140° G.) to 392° F. (200° C), they become not unfrequently somewhat empyreumatic : this is the reason why water is always added in the preparation of oils, and also in the redistillation of them (rectification). Experiment 5. — Inflame some drops of oil of turpentine put upon a shaving, and also a piece of camphor laid upon water; both bodies wiU ignite, and burn with a highly luminous and sooty flame. The volatile oils are far more easily combustible than the fat oils, which in order to burn with a flame must be heated to 662° F. (350° C.). We have consequently in oil of turpentine a convenient means for speedily lighting oil-lamps; it being merely necessary to smear the wick with a few drops of it. 378 EXPERIMENTAL CHEMISTRY. Experiment 6. — Pour a mixture of half an ounce of absolute alcohol with half a drachm of oil of turpentine into a spirit- lamp ; the mixture gives, when lighted, a strongly illumina- ting, but no longer a sooty flame, since all the carbon of the oil of turpentine is converted by the heat of the burning alcohol, rich in hydrogen, into Oluminatiug gas, and then into carbonic anhydride and water. This mixture has some- times been used in lamps constructed for the purpose, and which are so made that the liquid evaporates in them, and the vapour ignites as it issues from several small openings. Volatile Oils and Water. — Ea^eriment 7. — Drop some oil of cumin upon water ; the oil floats on the surface without mixing with the water, for most of the volatile oils are lighter than water ; but there are some, such as oil of cinnamon, oil of cloves, and oil of bitter almonds, which are heavier than water, and sink in it. If the mixture is briskly shaken, the water becomes turbid, because the oil is thus divided into small, invisible globules, which are kept suspended in the water. The water may be again clarified by filtration, but it retains the smell and taste of the oil, since a small quantity of it remains dissolved. Many such solutions are kept in the apothecaries' shops, under the name of medicated or distilled waters. It is well to keep them protected from the light, and in full vessels, — both light and air having a decomposing action on the volatile oils. They are commonly prepared by distilling with water the vegetable substance containing the oil, as thereby a more intimate combination of the water with the oil is effected than by merely shaking it up. Volatile Oils and Alcohol. — Experiment 8. — Add a drop of oil of cumin to one ounce of strong alcohol. It dissolves readily and entirely. All the volatile oils are soluble in alcohol, most of them even in alcohol of eighty per cent. ; but the non-oxygenated oils, such as oil of turpentine, oil of lemons, &c., only in absolute alcohol. H an ounce of water, in which half an ounce of sugar has previously been dis- solved, is added to the solution, we obtain cumin-cordiaL In this manner, by the aid of various aromatic oils, the innumerable cordials or liqueurs occurring in commerce can be prepared. They were formerly manufactured from aromatic seeds, flowers, herbs, &c., by pouring brandy over VOLATILE OILS. 379 them, the brandy being afterwards distilled or drawn off, whereby a spirituous solution of the volatile oils was likewise obtained. Experiment 9. — If some drops of oil of bergamot, orange- flower, lavender, or rosemary, are dissolved in half an ounce of strong alcohol, we obtain a spirit of a very pleasant odour. In a similar way the innumerable kinds of perfumed waters are prepared, at the head of which stands the well-known eau de Cologne. The fumigating spirit also, which, instead of the fumigating powder, is often sprinkled on a warm stove, has a similar composition. Camphorated spirit, much used in medicine, is a solution of camphor in alcohol. The volatile oils are not only dissolved by alcohol, but also by ether and concentrated acetic add. A solution of oil of cloves, cinnamon, bergamot, and thyme, in acetic acid, is used as aromatic vinegar, on account of its refreshing odour. The volatile oils may also be mixed with fat oils, and with some kinds of tallow and lard ; hence by means of them an agreeable odour may be imparted to the latter, as, for instance, in hair oils, pomatum, &c., or grease-spots be dissolved and removed by them from various articles. Volatile oils mixed with alcohol yield, when shaken up with olive oil, a turbid, milky liquid, because the alcohol does not dissolve the olive oil ; this behaviour may be taken advantage of for testing the purity of commercial oils. Experiment 10. — If you add some drops of oil of turpen- tine to iodine, a brisk emission of sparks ensues, sinCe a part of the hydrogen is expelled and replaced by the iodine. The same phenomenon is occasioned by all non-oxidised oils, but not by those oxidised ; therefore iodine may serve as a test, although not a very delicate one, for ascertaining whether oils of the latter class have been adulterated with oil of turpentine. Conversion of the Volatile Oils into Besins. — Experiment 11. — Let some oil of turpentine remain exposed to the air for some weeks, in a cup covered with paper, and afterwards put the cup in a warm place to evaporate the oil ; it will not entirely volatilise, but will leave at first a viscous, and after- wards a vitreous residue. This residue is a kind of resin, obtained by the absorption of oxygen. ' Eesins are often produced by the spontaneous oxidation of volatile oils. For 380 EXPBBIMBNTAL OHEMISTET. this reason, old oil of turpentine is not suitable for removing grease spots, paint, &o., from clothing. BESINS. Preparation of the Sesins. — -Ua^eriment 1. — Spread a little turpentine upon a board, and put the board for some time near a heated stove ; the oil of turpentine evaporates, but the resin remains behind as an amorphous brittle mass. In some countries, incisions are made through the bark of fir- trees, and the turpentine which exudes is allowed to evapo- rate on the trees themselves, and after it has been purified, by melting and straining through a colander, from the woody particles adhering to it, it is brought into market under the name of rodn, white pitch, or Burgundy pitch. Large quantities of such resin are now exported from the forests of America (American rosin). Eesinous juices, which harden in the air, forming solid resins, exude, either spontaneously or through incisions made for the purpose, not only from our fir-trees, but also from many other trees and shrubs, particularly those of hot climates. Almost all the resins occurring in commerce are procured in this manner. Experiment 2. — Besin is deposited most abundantly in Fig. 123. those parts of the trees where the branches join the trunk ; wood impregnated with such 'resin is called resinous wood. If a piece of resinous wood is lighted at the upper end, and held by a wire in an oblique position over a basin of water, one portion of the resin burns up with a sooty flame, while another part is melted by the heat, and runs down into the vessel beneath. Besin is not soluble in water ; hence it hardens in the latter without mixing with it. In this manner, hy roasting, resins may be prepared from many plants ; but the colour of the resins thus prepared is usually dark, because some of the resin has become burnt, and is thereby richer in carbon, according to the general law, that hydrogen is always burnt before carbon. Experiment 3. — Pour strong alcohol upon some resinous wood, and let it remain for a day in a warm place ; the resin EESINS. 381 is dissolved, and the woody fibre remains behind. The solution is poured into eight times its quantity of water, which is thereby rendered milky, because the resin is pre- cipitated, but in such a state of fine division, that it floats about in the water in the form of small globules. If this milky fluid is heated to the boiling point, the resinous particles soften and unite with each other in small lumps, which may be taken out and pressed together in larger masses. This is a third method of extracting resin from vegetable substances. Besin qid Water. — The resins as a general rule are inso- luble in water, and therefore tasteless ; but some of them in very small quantities may be dissolved, and these usually have a bitter taste. But many of the resins which occur in commerce contain some water in a state of minute division, and are thereby rendered dull and opaque ; common pine- resin and boiled tm-pentine furnish examples of this. Colophony, or Bosin. — Experiment 4. — Heat a piece of solid turpentine, or else some pine-resin, -pj ^24 in a spoon, till all the water is evaporated ; the anhydrous resin will now appear perfectly trans- parent. In this state it is called colopJumy, or rosin, being white when it is moderately heated, but h'oten when the heat is so strong as to convert a part of the resin into black pitch. Colophony is so brittle, that it may easily be re- duced to a powder. When the bow of a violin , is rubbed with it, the rosin powder formed remains adherent to the hairs, and these then again adhere better to the strings of the violin. A similar effect is produced on the cords which sustain the weights in clocks when they are rubbed vnth rosin to prevent their slipping. The resins, accordingly, exert an effect contrary to that of oil ; by resin, a rough, uneven surface is produced ; by oU, a smooth, slippery surface. Action of Seat on Begins. — The experiment first performed reveals at the same time another property of resin ; namely, its easy fusibility. Most of the resins require, in order to 382 EXPERIMENTAL CHEMISTRY. become fluid, a heat which is somewhat higher than that of boiling water. If melted rosin is poured upon a board, it spreads, and forms after hardening a solid, brilliant coating on the wood. The resins are hereby well adapted for pro- tecting wood or metal from the penetration of air or water. For this reason, iron rails and iron ornaments are covered with a coating of pitch, to prevent them from being so quicHy oxidised by the oxygen of the air ; for the same reason, also, wine-casks and beer-barrels are smeared with pitch, that no air may penetrate into the casks, and that no beer may penetrate into the staves. The wood-work of ships, the hatches, &c., are covered with tar, to keep out the sea-water and rain ; and finally, also, the solid and tenacious resin, shell-lac, which is formed by insects on the twigs of certain trees growing in the East Indies, is employed in the form of sealing-wax, as a protection against curiosity. Sealing-wax. — Experiment 5. — Melt together in a small ladle one-fourth of an ounce of pale shell-lac, one drachm of turpentine, one drachm of cinnabar, and three-fourths of a drachm of prepared chalk ; scrape out the mass while yet soft, and roll it out into sticks by the hands, moistened with water. The turpentine renders the sealing-wax more in- flammable, and the cinnabar imparts to it the favourite red colour. Various other colours are given to it by chrome- yellow, ultramarine, Brunswick-green, lamp-black, bronze- powder, &c. Mosin-gas. — Experiment 6. — When rosin is heated above its melting point, it kindles and hums with a luminous and sooty flame, leaving behind some charcoal. Therefooe pow- dered rosin, when blown into the flame of a lamp, burns vividly. In some places illuminating gas is prepared from it, by letting it drop in a melted state upon coke, which is heated to redness in an iron cylinder (rosin-gas). Burnt Pitch. — If the rosin, after it has burnt for some time, is extinguished by putting a board over it, we shall have as a residuum a black, burnt resin, ship-pitch, and cobbler s wax, possessing great tenacity. Lam,p-blacle. — Ea^eriment 7. — If you hold a cone made of blotting-paper over burning pine-wood, it will soon become lined with soot. The well-known lamp-hlach is prepared on a large scale by a similar method. Besinous wood, or the BESINS. 383 resin itself, is burnt with an insufficient supply of air in a stove furnished with long flues, or with a chamber in which the smoke deposits its carbon on its passage through. ' Experiment 8. — If some amber is scattered on glowing charcoal, a vapour having a pleasant balsamic odour is emitted from it as it smoulders away. Amber, frankincense, benzoin, and mastic are on this account frequently used for fumigating purposes. Mesin and Alcohol. — Experiment 9. — Wrap half an ounce of sandarach (a resin which comes from Barbary) in paper, and break it with a hammer into smaller pieces ; then mix it with a drachm of sand, which has been previously freed from its finer particles by washing, and afterwards thoroughly dried, and pour the mixture into a glass vessel, with two ounces of strong alcohol. Tie a piece of bladder over the vessel, and let it remain for several days in a warm place, frequently stirring it round. The clear solution of resin thus obtained is called lac-varnish, because, when smeared over metal, wood, or paper, it leaves behind, after the alcohol has evaporated, a varnished, shining coat. If alcohol is poured upon the sandarach, unmixed with sand, the resinous powder will cake together on the bottom of the vessel, forming a tenacious mass of resin, which dissolves much more slowly. To lacquer or varnish, then, is to coat the surface of anything with resin. By this coat of varnish, articles not only acquire a beautiful brilliancy, but are rendered at the same time impervious to air and water. When" paper articles, as drawings, maps, &c., are to .receive a coat of varnish, size or a solution of gum must previously be spread over them several times, as the solution of resin would otherwise penetrate into the fibres of the paper, and render it grey and transparent. This imbibition is usually prevented in wooden articles by smearing them with linseed oil before putting on the varnish. When the varnish is applied on places that are wet, white opaque spots are formed, because the resin is separated by the water as a dull white powder. Experiment 10. — Dissolve half an ounce of sheU-lac in strong alcohol ; a turbid liquid is obtained, as the shell-lac contains, besides the resin, small quantities of wax and mucilaginous substances, which float about undissolved in 384 EXPERIMENTAL OHEMISTKT. the solution of resin. This solution is also employed as a lac-varnish, but much more frequently as the so-called French polish of the cabinet-makers ; that is, as a solution of resin, which they rub continuously upon the wood with a ball of linen, until the alcohol has evaporated. By this means a still smoother and finer polish is obtained than by merely applying the resinous solution with a brush, the marks of which frequently remain visible. The finer articles of furniture are usually French polished, the more common ones varnished. Resins and Oils. — Experiment 11. — Mix half an ounce of dammara resin with some sand, and pour over the mixture two ounces of oil of turpentine ; after a few days you will obtain an almost complete solution, for all the resins are soluble in the volatile oils. These solutions are also frequently employed as lac-varnishes ; they dry, indeed, more slowly, but form a more tenacious coating, which is less liable to crack. The paler and finer varieties of varnish are principally prepared from amber, copal, dammara, shell-lac, sandarach, and mastic ; the inferior and darker kinds, from amber-colophony, common colophony, turpentine, asphal- tum, &c. A yellow colour is sometimes given to the pale varnishes by the addition of dragon's-blood, or gamboge. The resins are likewise soluble in fat oils. Many of the ointments and plasters of the apothecaries consist of mixtures of fats and resins, and it is the latter which communicate to the former the property of adhering to the skin. Turpentine is usually employed for this purpose. The use of resins in soap-making has already been noticed (page 367). They are also used by paper-makers, to prevent the porosity of the paper and the consequent running of the ink. CA0T7TCH0U0 AND GUTTA-PERCHA. Caoutchouc, or India-rubber. — When incisions are made in the bark of certain large trees, of which the Siphonia elastica of South America and Java, and the Ficus elastica of Assam, are the most important, a milky juice exudes, which dries in the air to ordinary caoutchouc. It is often imported in the form of bottles, which are made by spreading the milky juice on clay moulds and drying it over a fire. OAOUTOHOUC AND GUTTA-PEECHA. 385 Experiment 1. — Caoutcliouc at the ordinary temperature is hard and stiff, but it becomes soft when it is put into hot water or held near the ^^^- ^^^■ &e. Cut from a piece of thin sheet fire. Uut trom a piece of thin sheet I b caoutchouc, softened by heat, a square ( f '"■ ■, f" piece,. apply it evenly round the ends of ' 33 two glass tubes, and then clip off with a pair of scissors the ends of the strip in the direction marked out in the annexed figure : the fresh surfaces of the caoutchouc adhere firmly to each other (but stUl more closely when they are pressed together with the nail, _ ^'g- ^^6- yet without touching the freshly ctit^^^^^^^^l^^B surfaces), and thus is formed a tube, ^^^^^^^^^^ which, firmly tied at' both ends, connects the two glass tubes air-tight to each other. To the chemist, tubes made of caoutchouc are of the utmost value. They are sold of all sizes, and at a very moderate price. Caoutchouc corks also have recently been introduced into laboratories. They are very useful, and may readily be bored with ordinary brass-tube cork- borers. Caoutchouc is perfectly insoluble in water and alcohol, but pure ether, benzol (the lightest portion of coal-tar naphtha), and some volatile oils, including turpentine, dissolve it more or less perfectly. The best solvents are caoutchoucine (vide infra) and a mixture of carbon disulphide, with about 8 per cent, of absolute alcohol. When the solvent evaporates, the caoutchouc is left unaltered, and solutions of this kind are therefore largely used to render fabrics water- proof (the Mackintosh process). The gas bags used by chemists are made in this way. Experiment 2. — Digest some india-rubber in a stoppered bottle with one of the solvents named above. The i^olution so obtained may be used for waterproofing, and in the laboratory for a variety of useful purposes. Caustic alkalies, cold or hot, have no action on caoutchouc. It is affected by strong nitric and sulphuric acids and by chlorine, but not by the majority of acids. The xohole of the caoutchouc does not dissolve in the above experiment, for caoutchouc appears to be a mixture of .two substances, one of which is sparingly soluble. 2 386 BXPEEIMENTAL CHEMISTRY. Experimeni 3. — Allow a little of the solutioB obtained in E-xperiment 2 to evaporate on a slip of grass. The residue will be seen to be ^perfectly transparent and colourless (pure caoutchouc), for the colour of ordinary india-rubber is due entirely to impurities. ■ Experiraent 4. — Heat a little caoutchouc in an iron spoon over a lamp, very gently. It will melt to a viscid mass, which does not recover its elasticity on cooling. Experiment 5. — Marine Glue. — Dissolve halfan-ounce of caoutchouc in two ounces of coal-tar, with the assistance of heat, then add one ounce of shell-lac, and heat the whole till it is homogeneous. A very powerful cement is obtained, which is readily melted by heat. Experiment 6. — Gaovichmcine. — Distil a little caoutchouc in a Florence flask with a.large bent tube, keeping the receives as cool as possible. A volatile oil of strong empyreumatio odour comes over, and can be rendered colourless by re- distillation. This is called caoutchoudne. It is a mixture of various, hydrocarbons, which are isomeric with one another and perhaps with caoutchouc itself. It is an excellent solvent for caoutchouc and resins. Vulcanized Caoutchouc. — When caoutchouc is mixed with flowers of sulphur, or red antimonious sulphide, and the mixture kneaded in an iron vessel at a temperature of about 250° F. (121° 0.), the mineral substance is taken up in a very curious manner. The caoutchouc acquires additional elasticity; it no longer hardens with cold, and may be heated to a much higher temperature than ordinary caout- chouc without becoming sticky. This is the so-called vulcanized ca^mtchoue, which is applied to so many useful purposes. The kind made with antimony is called red rubber. Ebonite. — When the mixture of caoutchouc and sulphur is heated for four hours to 302° F. (150° C), a further change takes place, and the beautiful black substance called ebonite is obtained. At the temperature named it is soft, and can be moulded, but when cold it is as hard as horn, and can readily be cut and polished. Combs, beads, and many other articles are now made of it. It is of great value to the electrician, as it developes an amazing quantity of electricity when rubbed. It is insoluble, even in carbon disulphide. GUTTA-PBROHA. 387 Guttorfercha. — The juice of the Isonarda percha, a tree which grows in Malacca and the islands of the Indian archi- pelago, is obtained like caoutchouc, which it ' resembles in many respects. It is imported in rough masses. Grutta-percha dissolves easily, with - the aid of heat, in benzol, oil of turpentine, and carbon disulphide. Oh allowing the solution to evaporate, the gutta remains as a brownish-red porous film. Gutta differs in several important particulars from caoutchouc, with which however it appears to be identical in composition. At ordinary temperatures, it is tough and flexible, but not elastic. At low temperatures it is very hard and brittle, but at about 100° F. (38° C.) it becomes so soft that it can readily be welded or pressed into any desired form. It is a non-conductor of electricity, and is therefore largely used for coating telegraph wires. When exposed to the air, gutta-percha undergoes slow oxidation and becomes brittle. A resin is formed. Vul- canized caoutchouc often undergoes a similar change. Gutta-percha is attacked by strong nitric and sulphuric acids. Hydrofluoric acid has no action on it, and it is therefore used for making bottles to contain that acid. 388 EXPEEIMENTAIi OHEMISTKT. CHAPTEE IX. DEEIVATIYES OF AMMONIA. ALKALOmS. Wb have already seen (p. 301) that a large number of com- pounds can be formed, which may be regarded as ammonia, in which the hydrogen is partly or entirely replaced by alcohol radicals (amines), or acid radicals (amides). The amides are true analogues of ammonia, and, like ammomaf, combine with acids to form salts, which are called compo/UriA ammonium salts. The great majority of these artificial ammonia derivatives can only be prepared by difficult pro- cesses, and their description is therefore left to more advanced manuals of chemistry. The very important an^ interesting body called aniline will serve as a type of the amines. ANIUNB, OK PHBNTLAMINB. Experiment 1. — Take some powdered indigo ; add to it abont an equal quantity of very strong solution of potash, and distil in a retort as long as any - brown oil comes over. Separate the oil from the ammoniacal water which accom- panies it, and distil it again at as low a temperature as possible. The distillate is now colourless, and consists of aniline. This process is expensive, as it involves the loss of a good deal of indigo. Experiment 2. — -The hydro-carbon called benzol, or benzine, CsHj, is now prepared in very large quantities from coal-tar. Take half an ounce of fuming nitric acid in a small beaker glass, or large test-tube, warm it slightly, and add, in very small quantities at a time, about an equal quantity of benzoL A curious change takes place, whereby the benzol is con- verted to nitrobenzol, CeH^NOa (p. 304). On adding a little ANILINE OE PHENTLAMINE. 389 water, the nitrobenzol falls to the bottom as a heavy yellow oil, which possesses a smell closely resembling that of bitter almond oil. Agitate with ether, which dissolves the nitro- benzol; draw off the ethereal solution, and add to it some alcohol and about an equal quantity of strong hydrochloric acid. Then add small fragments of granulated zinc from time to time, until the smell of bitter almonds has dis- appeared, and a new and peculiar odour (that of aniline) is perceived. The nascent hydrogen (that is, hydrogen in the act of leaving its combination) combines with the oxygen of the nitrobenzol, and at the same time another portion takes its place : NitrobenzoL Aniline. CeH^NO^ 4- 6H = CHaNHa -f 4S.fi. The aniline exists in the solution as hydrochlorate, C6H5NH2,H01, but may be liberated by the addition of potash. On once more shaking the liquid with ether, the aniline is dissolved, and may be obtained by allowing the ether to evaporate on a watch-glass. Aniline is very little heavier than water (sp. gr. 1-02). It is sparingly soluble in water, readily in alcohol and ether. It boils at 360° P. (182° C). Its aqueous solution is feebly alkaline. When exposed to the action of oxidizing agents, aniline yields a series of colours, which for brilliancy and variety are unrivalled. The manufacture of these so-called aniline, or eoal-tar colours is now an important branch of industry. Their discovery is a remarkable example of the benefits which science confers on civilization and commerce. . Baeperiimewt 3. — Add a little solution of bleaching powder to a few drops of aniline on a white plate. A beautiful, though evanescent, violet colour will be produced. This is an excellent test for aniline. Experiment 4. — When sulphuric aeid is added to aniline, a crystalline mass of sulphate of aniline, (C8H,N)2H2SOi, or (C!5H8N)2S04, is formed, which is very soluble in water, and may be purified by recrystallization. Take a cold and somewhat dilute solution of this salt, and add to it a cold solution, also somewhat dilute, of potassium dichromate. Stir at intervals for ten or twelve hours. At the end of that time a black mass will have formed, which may be washed, first with water, and afterwards with boiling 390 EXPERIMENTAL CHEMISTRY. benzol, which last dissolves out a tarry substance. The residue is the beautiful aniline purple, or mauve. It dis- solves easily in alcohol, and the solution may be used idi dyeing silk or woollen goods. Vegetable fabrics, Buch as cotton, do not hold the colour, but require the assistance of some mordard. Experiment 5. — Add to a little aniline, in a test-tube, several grains of dry mercuric chloride, and boil the mixture for a quarter of an hour. The liquid gradually becomes almost black : allow it to cool, and pour it into a large quantity of boiling water, which immediately acquires a magnificent criinson colour, and may be used for dyeing silk and wood. This is the colour generally known as roseine, or magenta. It is the hydrochlorate of a colourless base called rosanUine, C2oHi9N3,HCl. The base may be thrown down by potash. Many salts of aniline besides the sulphate can be prepared. Most of them can easily be purified by crystallization. UEEA, Carbamide, or Carbonyl diamide, COS.^^ =f CO^HaN)^. This important body may be viewed as an amide, although it differs from most amines in that it combines with acids. Its constitution has already been explained (p. 303). Ea^eriment 1. — Evaporate a pint of fresh urine on a water, bath* to about one-eighth of its bulk: allow it to cool. Eeserve a small portion, and mix the rest with about an equal volume of a saturated solution of oxalic acid. A crystalline precipitate of oxalate of urea, rCOH4N2)2H2C204, will form before long. When it has stood for a few hours, the liquid may be poured ofi', and the crystals pressed with blotting-paper, and dissolved in the smallest possible quantity of warm water. Chalk is now added in excess, when the oxalic acid is thrown down as the insoluble calcium oxalate (p.. 354), and, together with the excess of chalk, may be removed by filtration. The clear liquid is now to be con- centrated to a small bulk on the water-bath, when it will * A common saucepan without the cover makes a most excellent water-bath. It should be two-thirds fiUed with water, and the basin containing the substance to be heated rested on its mouth, the basin being of course somewhat wider than the saucepan. NATURAL ALKALOIDS. 391 jrield on cooling beautiful crystals of urea, slightly coloured^ however, by the pigment of the urine. Experiment 2. — The other portion of the concentrated urine may be mixed with strong nitric acid. Beautiful pearly crystals of nitrate of urea, COH4N2HNO3, will separate. ■ ■ Escperiment 3. — When urine putrefies, a kind of fermenta- tion takes place, and the urea is converted to ammonium carbonate : COH,N2+2H20 = (]SrH,),C03. The smell of ammonia in putrid urine is well known. Experiment 4. — Synthesis of urea. — Melt some potassium cyanide in a porcelain crucible, and add red lead, or litharge, in small portions at a time until it ceases to be reduced by the cyanide, and a little remains unchanged. Allow the crucible to cool, dissolve the mass in water, and add dry ammonium sulphate equal to twice the weight of the original cyanide. Evaporate to dryness on a water-bath, boil the dry mass with strong alcohol (methylated spirit), and filter. The filtered liquid will, on evaporation, yield colourless crystals of pure urea. This process, discovered by Wohler, in 1828, is of great interest, because it afforded the first example of the synthesis of an organic compound (p. 100). Its details may be ex- plained as follows : — The cyanide is first converted into cyanate by the oxygen of the lead-oxide : Potassium Potassium Cyanide. Cyanate, KCN + PbO = K0NO+Pb. When ammonium sulphate is added, ammonium cyanate and potassium sulphate are formed by double decomposition. But ammonium cyanate is instantly changed by heat into urea, which is isomeric with it : Ammonium tt Cyanate. ^rea. NH^CNO = OOH4N2. NATUEAL ALKALOIDS. A large and important class of compounds containing nitrogen exists in different plants, to which the name of alkaloids, or natural bases, is applied. They are commonly 392 EXPERIMENTAL OHBMISTET. bitter in taste, and exceedingly active in properties, some of them being among the most virulent of known poisons. A few of them (nicotine, conine) are volatile liquids, con- taining only carbon hydrogen and nitrogen, but the majority are crystalline solids, which contain oxygen as well. Many of them have an alkaline reaction, and all are capable of combining with acids and forming definite salts. There can be no doubt that the alkaloids belong to the class of ammonia derivatives, although only one of them, conine, has as yet been prepared synthetically, TOBACCO — NICOTINE. Experiment. — Boil a quarter of a pound of common shag tobacco for a short time vdth a pint of water. Pour off the brown extract, and press the tobacco in calico. The liquid contains nicotine in combination with malic acid, the acid contained in apples. Evaporate it down on the watei;-batli ' imtil it has the consistence of oil ; put it into a small stoppered bottle with about an equal quantity of _ strong potash solution and some ether or benzol, shaking the bottle at intervals for an hour. The potash liberates the nicotine from its combination, and the ether dissolves it. The ethereal solution may then be drawn off into a basin, and the ether allowed to evaporate, when nicotine in a somewhat impure state will remain. It may be purified by distUlationj but as the boiling point is high (250° C. = 482° F.), a portion is destroyed by the heat. This may be avoided by distilling in a current of hydrogen, when the alkaloid is obtained as a colourless oil, of sp. gr. 1-027. Nicotine has the formula C10H14N2. It is a deadly poison, and possesses a terribly acrid and burning taste. _ It is strongly alkaline, and forms a definite series of salts. It is very soluble in water, alcohol, ether,' and benzol. Strong; tobaccos sometimes contain as much as eight per cent. ofJ nicotine. Tobacco smohe is a complex and imperfectly known mixture. It contains some permament gases, CO2, &o., and some empyreumatic oils, &c., in a state of vapour. The tobacco oil which collects in pipes, and which is often mistaken for nicotine, is an acid, tarry oil, analogous to that formed PERUVIAN BAEK — QUININE. 393 during the imperfect combtistioii of wood, &c. It contains some nicotine, but only a small quantity. • During tte burning of tobacco, a slight deflagration is often noticed. This is due to nitre, which is always present in tobacco. Conine is a volatile alkaloid, analogous to nicotine. It is contained in hemlock, and has the formula CgHuN. PERUVIAN BARK QUININE. This celebrated bark, from which one of the most valuable of medicines is obtained, has sometimes been called Jesuits' bark, because its medicinal value was believed to have been first made known to Europeans by the Jesuits. It occurs on several, species of the cinchona-tree, which flourishes in Peru, but is now cultivated with great success at Ootacamund in the Madras Presidency. It contains several alkaloids, of which quinine, CjoHj^NjOg, and einchonine, C2oH24N20, are the most important, in combination with a peculiar acid, called quinic, or Mnic acid, C7H12O6. Experiment 1. — Into the percolating apparatus used in preparing tannin (p. 357), introduce some yellow cinchona bark (the yellow is the best kind) in fine powder, and pour on it some very dilute hydrochloric acid (1 of acid to 24 water). As the acid passes through, it combines with the alkaloids, and the liquid so obtained contains the hydro- chlorates of quinine and einchonine, together with a good deal of the colouring matter of the bark. The addition of acid may be repeated three or four times. To the acid solution, sodium carbonate is now added to alkaline reaction, which throws down the alkaloids, together with some colour- ing matter. After standing for some time, pour off the greater part of the liquid and evaporate the remainder, con- taining the alkaloids, to dryness on a water-bath. The dry mass may now be shaken up with ether in a small stoppered bottle. This takes up the quinine, which can be obtained as a resinous mass by evaporating the ethet. After pouring off the ethereal solution of quinine, the residue may be digested with warm and strong alcohol. This takes up the einchonine, and on allowing the alcohol to evaporate spontaiieously, einchonine separates in colourless anhydrous prisms. Neither alkaloid is quite pure when prepared by this process. 394 EXPEEIMBNTAl CHEMISTRY. Experiment 2. — Both alkaloids dissolve very easily in dilnte sulphuric and other acids. The substance generally sold as quinine is the neutral sulphate. Dilute sulphuric acid dissolves it easily. From all acid solutions the alkaloid may be precipitated by the addition of an alkali. Experiment 3. — -When quinine or any of its salts (acid solution of the sulphate answers well) is treated with chlorine water, and afterwards with solution of ammonia, a beautiful green colour is produced. This is the best test for quiaine. Experiment 4. — Commercial sulphate of quinine is some- times adulterated with salicin (the bitter principle of willow bark). This may be detected by rubbing the dry salt with a drop of strong sulphuric acid. If salicin be present in any quantity, a bright red colour will be produced. • OPIUM — MORPHINB. Opium is the dried juice of the unripe capsules of the white poppy, a plant which is extensively cultivated in the East. It contains six or eight different alkaloids, together with a peculiar acid, meconic add, C7H4O7. The most important of the alkaloids is morphine, CnHigNOs. The complete separation of the opium alkaloids is a matter of great difficulty, but the following experiment will illustrate the method. Experiment 1. — Digest some opium, cut in thin slices, in lukewarm water for some time till a strong decoction is obtained ; pour off the solution, and add a little chalk to neutralize free acid. Evaporate on a water-bath to a small bulk, and then add excess of calcium chloride. Calcium, meconate is precipitated while the alkaloids remain in solution as hydrochlorates. Filter and again concentrate, when more of the meconate will separate : after it has been filtered off, the hot solution will, on cooling, deposit crystals of the hydrochlorates of morphine and codeine. These crystals may be dissolved in a little water and treated with ammonia, which throws down morphine. It is slightly coloured, but its solution may be purified by agitation with animal charcoal, which removes the colour. Experiment 2. — From the calcium meconate formed in the above process, meconic acid may be prepared as follows : wash the calcium meconate and dissolve it in the smallest OTHEE ALKALOIDS. 395 possible quantity of warm and very dilute hydrochloric acid. Add potash until a faint cloudiness appears, filter and con- centrate to a small bulk. Somewhat coloured crystals of meconic acid will separate. Eayperiment' 3. — An aqueous solution of morphine or any of its salts gives, with neutra,l ferric chloride, a blue colour. Experiment 4. — Put a minute particle of morphine, or one of its salts, on a white plate, and touch it with a drop of solution of iodic acid. Iodine will at once be liberated, and its presence is shown by its brown colour and the violet compound formed on the addition of starch paste. This is an excellent test for morphine. Experiment 5. — Solution of meconic acid gives, with ferric salts, a blood-red colour. This test is so delicate, that meconic acid can sometimes be detected where the quantity of opium present is too small to allow of the detection of morphine. The red colour is much like that given by iron salts with sulphocyanates, but the latter is instantly destroyed by solution of corrosive sublimate. NUX VOMICA STEYOHNINE. The beans of nux vomica and St. Ignatius, and some other products of the order sirychnos, contain two alkaloids^ strychnine and hrucine, both of which, especially the former, are deadly poisons. They cannot easily be prepared on a small scale. Experiment. — Dissolve a minute crystal of strychnine on a white plate with a drop of strong sulphuric acid. Then rub with it an equally minute quantity of potassium di- ehromate. A beautiful blue colour, quickly fading to brick- red, is produced. Other oxidizing agents added to the siilphuric solution produce the same effect. This is an exceedingly delicate test for strychnine. OTHER ALKALOIDS. The following are some of the more important vegetable alkaloids, which have not been noticed in the preceding sections : Aeonitine, found in monkshood (Aconitum napellus). Said to be the most intensely poisonous of all the alkaloids. 396 EXPERIMENTAL CHEMISTRY. Asparagine, in asparagus. Atropine, in deadly nigMshade {Atropa belladonna) and thorn-apple (Datura stramonium). Berberine, in the barberry (Berberig vulgaris). Caffeine, or Theine, in coffee and tea. Colchicine, in colchicum. Byoscyamine, in henbane (Hyoscyamus niger). Piperine, in pepper. Sicinine, in castor seed (Micinus communis). Sinapine, in mustard. Solanine, in the potato, &c. Theobromine, in cacao beans. Veratrine, in white hellebore (Verairum album). ( 397 ) CHAPTEE X. COLOTTEING MATTEES. Or the pigments used in painting, dyeing and colour- printing, a good many haye already been described. Of mineral pigments the following are a few of the most important : Seda. — Vermilion (HgS) ; red lead (PbsOi) ; Venetian red (FeA). FeHoJcs.-T-Chrome yellow (PbCrO^) ; orpiment, or king's yellow (AsjSg) ; yellow ochre (clay coloured by FojOs). Greens. — Chrome green (CrgOs) ; Schweinfurt, or imperial green (cupric aceto-arsenite). ^ Blue&. — Ultramarine (a complex double silicate, containing a polysulphide of sodium) ; Prussian blue (ferric ferro- cyanide) ; cobalt blue (a compound of cobalt oxide and almnina). Among organic colours, some can only be prepared by artificial methods. To this class belong the splendid colours of almost every conceivable shade which are prepared fr6m aniline and its congeners (p. 390). A beautiful crimson colour, called murexide, can be prepared from uric acid, which in its turn is obtained from urine or guano. The term coloilring matter is generally restricted to those colours which are obtained directly from animals and vegetables. To those we shall confine our attention here. OOLOUEING MATTEES OF FLOWBES. The beautiful and various tints of colour that we see in flowers are due to colouring matters which are very imper- fectly understood. The reds and blues are generally soluble in water, the yellows only in alcohol. They are very evanescent, fading rapidly when exposed to light. 398 EXPERIMENTAL CHEMISTRY. Eayperiment 1. — Digest some of the flowers of the blue iris, lobelia, or almost any blue flower, with a small quantity of warm alcohol. Pour off the alcohol and press the flowers in muslin. A blue solution will be obtained, which will yield a blue pigment when evaporated on the water-bath. Flowers of other colours will yield their colouring matters in the same way. Experimeni 2. — The colouring matter obtained in an impure state in the last experiment is called cyanin. Dis- solve a little in water, and add to one portion of the solution a drop of acid. The blue colour changes to red. To another portion add a drop of soda. The blue changes to green. The red may be changed to green, and the green to red, by the addition of alkali or acid. Such a solution may therefore be used as a substitute for litmus. Tinclwre of roses is sometimes used for this purpose. Experiment 3. — On adding a drop of solution of sulphu- rous acid to the aqueous solution the colour wiU first change to red, and then disappear. On standing, however, the acid will pass away and the colour return. It is believed by some that the colour of most red flowers is due to cyanin reddened by an acid. Experiment 4. — The red cabbage yields to water a colour- ing matter similar to, if not identical vrith, cyanin. The aqueous decoction yields a red with acids, a green with alkalies, and a purple with solution of alum ; so that four different colours may be produced from the same solution. Eayperiment §. — Take the flowers of the orange-coloured tropxolum majus, or the brown calceolaria, and digest them with boiling water. A purple colouring matter will be dissolved out. Pour off the water, press the flowers, and digest them again with alcohol. A yellow colour will now be obtained, and both may be separated from their solutions by evaporation. The flower is thus rendered white. - '^ Some flowers therefore contain more than one colouring' matter. COLOUR OP LEAVES — CHLOBOPHYLL. Experiment 1. — Digest some fresh grass or other leaves with alcohol. A beautiful green solution is obtained, which contains chlorophyll. In the solid state it is a dark green INDIGO. 399 powder, whicli is insoluble in water, but soluble in alcohol and ether. Neither acids nor alkalies change its colour. INDIGO. A number of plants which grow in the East and West Indies contain an almost colourless substance called indican, CjsHjiNOi,. When the leaves are macerated with water arid allowed to ferment, the indican is decomposed and indigo blue, CftFIsNO, is formed. Indigo usually occurs in commerce in deep blue, friable cakes, which exhibit, when rubbed by the nail, a coppery colour and lustre. Its brilliant blue colouring matter is called indigo-blue ; but besides this, the crude indigo contains other foreign substances, such as indigo-gluten, indigo- brown, indigo-red. Indigo is quite insoluble in water, alcohol, ether, &c. ; there is only one liquid known which can dissolve it, except in minute quantities, namely, concentrated sulphuric acid. The Nordhausen, or fuming acid, is the kind generally used, as six parts of it will dissolve as much as fifteen parts of the common acid. The ' indigo-blue chemically combines with the sulphuric acid, forming a blue compound soluble in water, which is called sulpMndigotic acid. What we call tincture of indigo is principally a mixture of water, sulph- indigotic acid, and free sulphuric acid. - The sulphindigotic acid combines with bases like a simple acid, forming salts. The best known of these salts is suJjoMndigotate of potassium (blue carmine), which is obtained as a deep blue precipitate when the sulphindigotic acid is neutralised by potassa. The blue carmine is indeed soluble in, pure water, but not in water containing a salt in solution. Indigo-white. — We can also, but in a very different way, render indigo soluble, by mixing it with bodies which, by taking oxygen from water, will impart hydrogen to it; for instance, with ferrous or stannous salts. Experiment 1. — Triturate half a drachm of finely-powdered indigo with one and a half drachm of green vitriol and two drachms of slaked lime; shake up the mixture in a four- ounce bottle ; then, having filled the bottle with water and closed it tightly, let it stand for several days ; the indigo gradually loses its blue colour, and dissolves into a clear 400 EXPERIMENTAL CHEMISTRY. yellowisli liquid. The body which effects the decolouration is the ferrous hydrate, which is separated by means of the lime from the green vitriol. The solution now contains the so-called wMte, or reduced indigo, CgHgNO. As soon as the clear liquid is exposed to the air, the extra atom of hydrogen is oxidized, and it again becomes blue. If you saturate a piece pf blotting-paper or linen with the liquid, and then dry it in the air, it first . becomes green, and then blue, and the blue colour formed adheres quite firmly, since it has not only settled upon but in the fibres of the paper. In dyeing establishments, such a solution of indigo is called the cold vat. A third method of rendering indigo soluble is by adding it, together with hot watet, to a mixture of bran, woad, madder, &c., which (potassium and calcium carbonates being present) passes into fermentation. The fermentation is partly acid, and partly putrefactive; in both processes hydrogen is liberated and combines with the indigo. The colourless indigo dissolves in the alkaline liquid (warm vat). By treating indigo with powerful reagents, such as nitric acid, chlorine, potash, &c., many interesting compounds can be obtained. Experiment 2. — Heat a little indigo carefully in a watch- glass over which another watch-glass is inverted. A portion of the indigo will sublime in beautiful crystals. Woad is a European plant, which likewise contains indican and yields indigo, but in far less quantities than the foreign indigo plants. HABDER. This important dye-stuff is the root of the BiMa titictorum, a plant which is extensively cultivated in many parts of Europe. In its natural state, the root appears to contain a glucoside, that is, a substance which is readily decomposed into glucose and something else. This compound is called rtibian. It is analogous to the indican of the indigo plant. It readily yields two colouring matters, alizarin and purpurin, the former of which is much the most valuable of the con- stituents of madder. Experiment 1. — Digest some ground madder with warm water. A dark brown muddy liquid is obtained. This MADDER. 401 ■with dilute sulphuric acid yields a brown precipitate consist- ing of alizarin and purpurin with foreign bodies. The clear yellow liquid which remains contains nothing of importance. It may be removed by filtration, and the colouring matters washed with water. The precipitate is then to be boiled with concentrated solution of aluminium chloride (prepared by saturating strong hydrochloric acid with aluminium hydrate), which dissolves alizarin and purpurin but leaves a brown residue of impurities. On adding hydrochloric acid to the filtered liquid a red precipitate of the two colouring matters is obtained. If it be desired to separate them, dissolve them, while moist, in dilute ammonia, and digest for some time with moist aluminium hydrate. They both combine with the metal, forming compounds called lakes (vide infra). The mixed lakes are then boiled with sodium carbonate, which dissolves out the purpurin. The residue is then boiled with hydrochloric acid, which leaves the yellowish-red alizarin. When pure, alizarin and purpurin resemble one another closely. Both form yellowish-red crystals, which may to a great extent be sublimed unchanged. Both are sparingly soluble in water, more soluble in alcohol. Both are insoluble in acids, but easily soluble in alkalies, being thrown down unchanged when the alkali is neutralized. Both combine with the oxides of many metals (aluminium, iron, tin, lead, &c.), forming insoluble compounds called lakes. It appears, however, that the colours produced by dyeing fabrics with madder are mainly compounds of alizarin. AHzarin has the formula CiiHgOi. It has lately been fornied synthetically from anthracin (p. 409), and it appears probable that the artificial compound will supersede the root altogether. The formula for purpurin is Ci^HgOj. Madder lake. — A beautiful pigment bearing this name is used by artists. The following is said to be the best receipt for it : Experiment 2.'^Enclose two troy ounces of the best ground madder in a strong calico bag capable of holding three times as much. Macerate the bag with one pint of cold soft water in a basin or mortar, pressing and twisting the bag as much as possible. Pour off the coloured liquid, and repeat the process until five pints of liquid are obtained. 2 J) 402 EXPERIMENTAL OHEMISTET. Nearly boil the liquid in an earthen vessel or large beaker, and pour it into another vessel containing 1 ounce of alnm dissolved in 1 pint of boiling soft water. Stir and add IJ ounce of a saturated solution of potassium carbonate. When cool, pour off the liquid and add to the precipitated lake 1 quart of boiling soft water. When cold, pour off the washings and collect the lake, which should weigh half-an- ounce, on a filter. If required for water-colour painting it may be dried at a gentle heat and mixed with a little glycerine. Paints so prepared are called moist colours. Dyeing loith Madder. — ^Madder is a good example of what is sometimes called an adjective, as distinguished &om a substantive colour. Substantive colours adhere to, or combine with the fibre of a fabric, and do not require any separate process to fix them. Adjective colours, on the contrary, have no power of fixing themselves to a fabric, but require the aid of some other substance, which, either by rendering them insoluble or by some other means, fixes them to the fabric. Such substances are called mordants. The following simple experiments illustrate their use in the case of madder : Experiment 3. — Madder red. — Soak a piece of calico in the solution of impure aluminium acetate, which is obtained by mixing equal weights of alum and lead acetate (both in solution) and filtering from the insoluble lead sulphate. Let it hang in the air for a couple of days, and then soak it for two or three hours in a strong decoction of madder. It may then be removed and thoroughly washed, when it will be foun^ to be dyed a fast and very permanent red. Instead of soaking the calico in the mordant, the latter may be printed on in any required pattern (calico-printing). The red dye wUl only appear on the parts where tibe mordant has been applied. The action of the mordant here is obvious. The alizarin combines with the aluminium and fotms the insoluble red madder lake. Aluminium acetate is called by dyers red liquor. Experiment 4. — Various shades of violet and purple can be produced by using the mordant called iron liquor instead of red liquor. Iron liquor is prepared like red liquor, by mixing equal weights of green vitriol (FeSOjVAq) and lead acetate. It consists, of course, of ferrous acetate. OTHER COLOUEINO MATTERS. 403 Experiment 5. — Mixtures of the above two mordants yield various shades of brown. COOHINEAL. A. curious Kttle insect, called the cochineal insect (Coccus cacti), is known, which lives exclusively on certain species of cactus. It was first discovered in Mexico in 1578, but is now cultivated in many tropical places. This insect contains about half its weight of a beautiful red colouring mattei called carmine, or carminie acid. The female insects only are used. They are imported in the dry state. Experiment 1. — Boil some powdered cochineal insects with soft water for a quarter of an hour. A splendid red solution will be obtained, for carminie acid is very soluble in water. It is equally soluble in alcohol, but almost insoluble in ether. Experiment 2. — Add some moist aluminium hydrate to the above solution (cold). The alumina will combine with the colouring matter, and a beautiful crimson lake will be obtained. Experiment 3. — To other portions of the solution add very small quantities of alum and stannic chloride, re- spectively. The former will yield a crimson, the latter a fine scarlet colour. If these liquids are allowed to stand for a time beautiful precipitates are deposited which are used by artists under the name of carmine. The precipitation appears to be due to the coagulation of the albuminoid matters of the cochineal. Experiment 4. — The two liquids from which, in the last experiment, carmine was obtained may be cautibusly treated with sodium carbonate. The whole of the colour vrill now be thrown down as lakes, and, if excess of base has been avoided, they will possess brilliant colours. Experiment 5. — Silk and wool may be dyed by immersing them in the solutions of Experiment 3. The colour adheres very strongly to the fabrics, but it slowly fades when exposed to light. OTHER COLOTJEING MATTERS. Brazil-wood, from the heart- wood of several trees growing in South America, imparts to different materials a beautiful but not very permanent red colour. It is employed also 404 EXPEEIMENTAL CHEMISTBT, in the preparation of red ink, of drop-lake, &c. Peach-wood, Nicaragva-wood, Sapan-wood, &c., differ but slightly from Brazil-wood. (Colouring matter, Braziltn, crystallies in orange-coloured needles, easily 'soluble in water.) Safflower, the flowers of the dyer's saffi-on, are used for obtaining a brilliant rose-colour (for pink-saucers). (Colour-r ing matter, Garthamin, soluble in water.) The alhmet-root contains in its bark a resinous colouring matter, which is not soluble in water ; silk is dyed violet with it, but alcohol, oils (as petroleum), and fats (as lip- salve), are coloured pink with it. Sandal-wood (red sanders-wood), the rasped blood-red wood of a tree growing in the East Indies, contains likewise a red, resinous colouring matter (Santalin), The red dyes occurring in manj fruits, as, for instance, cherries, raspberries, &c., are but slightly durable, and only used for colouring confectionery, cordials, &c. Lac-dye is a red colouring matter very similar to cochineal, which is deposited with shell-lac (page 374) on the twigs of certain East Indian trees. The twigs with their coating are known as stidc-lac. Fustic is the rasped trunk- wood of a mulberry-tree growing in the West Indies. It yields a yellow dye. Quercitron, a nankeen-yellow powder, mixed with fibrous fragments, is obtained from the bark of the black oak, a tree of North America. (^Quercitrin, a yellow powder, soluble in water.) Buckthorn, Persian, or yellow terries, the fruit of the buckthorn and other species of Shamnus, growing in warm countries. (Phamnin, little known.) Weld and dyer's weed are the names given to the Eeseda luteola, dried after it has done blooming. (Luteolin, crystal- lizes in yellow needles, soluble in water.) The four last-mentioned colouring substances are prin- cipally used for dyeing silk, wool, cotton, and other materials, yellow, Annotto occurs as a brownish-red paste, which is pre- pared from, the pulp surrounding the seeds of the Bixa Orellana, and contains two colouring principles, a yellow and a red. The former is dissolved when the annotto is boiled with water, the latter on boiling it with a weak lye. OTHEK COLOURING MATTERS. 405 TMrmeric, the root of a plant growing in the East Indies, is very rich in a resinous yellow dye, which is coloured brownish-red by alkalies. Paper stained with it may there- fore be used like red litmus-paper for detecting alkalies. (Curcumin, an amorphous yellow mass.) Saffron consists of the dried stigmas of the flowers of the Crocus sativus. Its application, in colouring articles of food and cordials yellow, is well known. Logwood, or Cam/peachy-wood, the reddish-brown interior wood of a tree of tropical America, is one of the most com- mon colouring matters for dyeing blue, violet, and black. (HdBmatoxylin, in colourless crystals, which become speedily violet and blue in the air, owing to the ammonia always contained in the latter.) Archil. — Several species of lichens, growing on the rocks in England and France, contain peculiar substances, which, although in themselves colourless, acquire a beautiful purple-red colour when they are acted upon by ammonia and air. It is common to putrefy the bruised lichens with urine, and then a red or violet-coloured paste is obtained {cudbear, orchil). By the addition of lime or potash, this red is changed into blue [litmus). We have examples of both these colouring matters in red and blue test-paper. Experiments with the above Substances. Experiment 1. — Take up some sandal- wood on the point of a kmfe and put it on a filter, and pour over it some alcohol ; the alcohol which passes through has a red colour, and, when poured upon a piece of wood, imparts to it an intense blood-red colour. Cabinet-makers frequently employ this solution for staining furniture. Alcohol acquires a pink colour when a small piece of alhanet-root is put into it. Water will not extract a red dye from either of these substances. Those colouring matters which are uncrystal- lizable, and soluble only in alcohol, are called resinous. Experiment 2. — Boil for some time in a jar, — 1st, either fustic, or yellow berries ; 2nd, Brazil-wood ; and 3rd, log-wood ; each separately, with twelve times its amount of water ; the decanted decoction of the first is yellow, of the second reddish-yellow, and of the third brownish-red ; a sufBcient proof that the colouring matters contained in these substances 406 EXPERIMENTAL CHEMISTRY. have been dissolved in the water. Dyers call these colonred Fig. 127. decoctions hatha. Eseperiment 3. — Divide these colouring decoctions into two equal parts. Dissolve a quarter of an ounce of alum in one part of each, and then add to these a solution of potassium carbonate, as long as any precipitate subsides. Aluminium hydrate ' is precipitated ; but with it the colouring matter, and hence the precipitates are coloured. These precipitates are called lakes. The lake obtained from the yellow berries occurs in commerce under the name of yellow lake, that from Brazil-wood as drop-lake. Experiment 4. — Prepare a solution of alum (a), another of stannous chloride (6), a third of ferrous sulphate (c-), a fourth of potassiiun carbonate (d), a fifth of tartaric acid (e), and saturate a sheet of white blotting-paper with each solution. When dry, cut each sheet into three strips, smear one of the strips from each sheet with the fustic, another of them with the Brazil-wood, and the third set with the logwood decoction, and again dry them. You will find that one and the same colouring matter produces a different colour, or shade of colour, upon each of the five sheets. This colour will be very slight when the coloured decoctions are applied to mere blotting-paper (f). If you now immerse the coloured and dried strips in warm water, the colours will be for the most part dissolved from the three last tests (d, e, /), but not from the former (a, 6, c), on which the metallic bases act as mordants. These simple experiments give some idea of the interesting and complex arts of dyeing and taMco-printing. ( 407 ) CHAPTEE XI. PRODtrCTS OF DESTETJOTIVE DISTILLATION. The general nature of the interesting and important process of destructive distillation has already been explained (p. 185). We have seen that coal and many other non-volatile carbon compounds when heated in close vessels are decomposed ; a portion of their carbon remains in the retort (coke, charcoal, bone-black, &c.), whilst a number of new and volatile bodies are formed which can be distilled over and collected. Of these, some at ordinary temperatures are gases, some liquids, and some solids. The manufacture of coal gas is a typical, and by far the most important example of destructive distil- lation. A reference to the table on page 186 will show how the products of the distillation of coal divide themselves into gases of various kinds which can be purified and collected, ammoniacaJ water, the chief source of the ammonium salts (p. 208), and tar, which collects below the water, and can easily be removed from it. It is with the very complex and valuable liquid tak, and a class of substances allied to it, that we have to deal in this chapter. COAL TAB. A gallon of coal tar may be procured for a mere trifle at any gas-works. It is black, viscid, like treacle, and has a very disagreeable smell. A portion of the ammoniacal liquor often floats on it and may be poured off and tested for ammonia, ammonium sulphide, carbonate, &c. Distillation of Tar. — Experiment 1. — Introduce a pint of the tar into a retort, connect the neck of the retort, with a re- ceiver kept very cold, and apply a gentle heat to the retort. As soon as an ounce of liquid (naphtha) has distilled over, remove the receiver and replace it by another, which it is no longer 408 EXPBEIMBNTAL CHEMISTET. necessary to cool artificially, l^he heat must now be increased and the distillation continued until yellow scales begin to solidify in the long neck of the retqrt. A heavy oily liquid (dead oils) is obtained in this stage of the distil- lation. The receiver is now again changed and the tempera ■ ture raised. The distillation may now be continued very carefully until it is thought that the retort wUl no longer bear the heat. In this last stage the distillate solidifies into a yellow, butter-like mass as it drops into the receiver. The neck of the retort may be warmed with a spirit-lamp from time to time to melt the solid that accumulates in it, and cause it to drop into the receiver. The black residue left in the retort must be poured out while still hot on to a stone or iron slab. When cold it appears as a hard, shining, brittle mass; the pitch, or CLsphM, now so largely used for covering woodwork and making pavements. By this mode of conducting the distillation (fractional dis- tillation) the tar is separated into four portions, namely, naphtha, or light oils, dead, or heavy oils, a solid portion, and pitch. Each of these is a very complex mixture. The constituents of these mixtures can only be separated on the large scale, and with great difficulty. 1. Naphtha. — Goal-tar Naphtha. — The portion which first comes over in the distillation of tar is very volatile, and is lighter than water. It consists chiefly of the hydrocarbon benzol, with its homologues, toluol, xylol, and cumol (p. 296). It contains also in minute quantity certain hoses, namely, aniline and its homologues (pp. 302, 388), and a series isomeric with the anilines called the pyridine series ; and an acid portion, consisting of phenol or carbolic acid (p. 297), and its homologues, cresylic and xylylic phenols (or acids). Coal-tar naphtha also contains a little naphthaUn (p. 296). The bases are first removed by agitating the naphtha with dilute sulphuric acid; the phenols are then removed by agitating with caustic soda, and finally the hydrocarbons, chiefly benzol and toluol, are removed by rectification nearly in the same manner as alcohol. 2. Heavy oils. — Dead oils. — The heavy oils of coal tar contain many hydrocarbons, some of which (notably naphthalin) are, when pure, solid at ordinary temperatures. But they are chiefly valuable as containing the imperfectly COAL TAB. 409 acid bodies called phenols in considerable quantity. Ordinary phenol, or carbolic acid, is now prepared on a very large scale from this portion of coal tar. 3. Solid portion. — This often amounts to a very large proportion of the whole products of distillation. The most important of its constituents are naphthalin and anthracin. From anthracin, alizarin, the chief colouring matter of madder, can be prepared. 4. Pitch. — Gas-tar Asphalt. — The nature of pitch is not yet well known. At a bright red heat, anthracin and other solid hydrocarbons can be distilled from it, and a coke remains which consists mainly of carbon. PBOXIMATB CONSTITUENTS OF COAL TAR. Several of the constituents of coal tar are now important articles of commerce, and the student can therefore undertake a simple experimental study of them although he may not be able to prepare them from the tar. Benzol, or Benzine, CjHg. — Experiment 1. — Distil a mixture of one part benzoic acid (p. 351) and three parts slaked lime. Benzol and water pass over. The former has a specific gravity of only 0'85, and therefore floats on the water. Add some pieces of caustic potash to the mixture to absorb traces of acid. After standing some time, decant the benzol into a small flask containing solid calcium chloride. Cork and allow the mixture to stand twenty-four hours ; then distil off the perfectly pure benzol by means of a water bath and bent tube, taking care to keep the receiver very cold and to prevent the vapour from coming near a light. The formula which describes the formation of benzol in this experiment is as follows : O^HsOa+CaO = CaCOa -^G^B.^. Commercial benzol is obtained as above described from gas tar. It is never pure, but contains many higher hydro- carbons, of which the most important is toluol, C,H8, the homologue next above benzol. Nevertheless, when carefully rectified from a water bath, the less volatile portions being rejected, it will do very well for the following experiments. Pure benzol boils at 80° C. (176° F.). It has a peculiar, but not unpleasant odour. 410 EXPERIMENTAL OHEMIBTET. Experiment 2. — Benzol ignites very easily when a light is applied, and bums with a bright smoky flame. Ea^etiment 3. — Benzol evaporates very easily at ordinary temperatures, and the vapour is very inflammable. Shake a few drops of the liquid in a small bottle of oxygen and apply a light. An explosion will be produced. Eayperiment 4. — Put some cotton wool into a tube drawn to a jet at one end. Pour a few drops of benzol on the cotton, blow gently through the tube, and apply a light to the jet. The mixture of air and benzol vapour will burn with a luminous flame. Experiment 5. — Benzol is a powerful solvent of oils and fats. Shake a known weight of oil with benzol in a test tube. It will dissolve in considerable quantity. On allowing the benzol to evaporate on a basin the oil will be recovered unchanged. If the basin is heated on a water bath for some time and again weighed, the increase of weight will correspond with that of the oil employed. This experiment shows how benzol may be employed in estimating the quantity of oil or fat present in any substance. It also illustrates the use of benzol in removing grease-stains from articles of clothing. Experiment 6. — Immerse a beaker or tumbler containing benzol in a mixture of snow or crushed ice and salt. The benzol crystallizes and may be separated from other sub- stances by pressing it rapidly in a cloth. Toluol does not soHdify at -20° 0. (-4° F.). At 5°-5 C. (42° T.), the benzol, now very pure, once more becomes liquid. The conversions of benzol into niiro-benzol, and of nitro- benzol into aniline, have already been explained (p. 388). Pure aniline does not yield the beautiful aniline colours, but only a mixture of aniline and toluidine. Toluidine, CyH^NHj, is a homologue of aniline, prepared from toluol as aniline is from benzol. Phenol, or Carbolic Acid, C5H5O = C^HgHO. — This valuable and interestiog compound is now prepared on a large scale from coal tar, and may be purchased in the pure state at a cheap rate. When pure it crystallizes in colourless deli- quescent needles, which melt at 34° C. (93° F.) and boil at 184° C. (363° F.). It has a peculiar tar-like odour. Experiment 1. — If the heavy oil of coal tar is distilled by OOAL IAS. 411 itself, and the portion ■whicli comes over between 150° and 200° C. (302° and 392° F.) is collected by itself, this portion will contain the great bulk of the phenol of the tar. When a concentrated solution of potash and a little solid potash in powder is added to it, the liquid becomes semi-solid from the formation of the white crystalline potassium phenate. This is dissolved in hot water, the neutral oil removed from the surface, and the salt neutralized with hydrochloric acid. Impure phenol rises to the surface as an oil, and may be washed, dried by agitation with calcium chloride, and purified by repeated distillations and crystallizations. The purification is, however, a difficult process, and for many purposes is not necessary. JExperiment 2. — Dissolve some pure phenol in water, and observe that it is sparingly soluble in cold, but somewhat more in hot water. It dissolves easily in alcohol and ether. The solutions, when pure, have a neutral reaction, although phenol combines with bases, and so far has an acid character. The salts are, however, somewhat indefinite. Experiment 3. — Phenol and its homologues are among the most powerful of antiseptics. Suspend a piece of fresh meat above a little phenol in a bottle. The vapour of the phenol will entirely prevent the putrefaction of the meat, which will in time dry up into a horny mass. For this reason phenol is often used in preserving anatomical specimens. Its action in disinfecting, which is its most important use, is probably due to its power of destroying the organized germs which appear to be the active agents of contagion in some zymotic diseases. Trinitrophenic, Picric, or Garhazoiic Acid, C8H3(N02)30 = HC5H2(N02)30. — Experiment 1. — Add fuming nitric acid, a drop at a time, to a small quantity of phenol in a large test tube. Violent action takes place. When this begins to diminish, the mixture must be warmed and ultimately boiled, for otherwise mono- and dinitrophenic acid will be formed. On concentrating the acid liquid, beautiful yellow crystals of trinitrophenic, or, as it is more often called, picric acid are obtained, and may be purified by recrystallization from water : CeHiOe-l- 3HNO3 = CeHaCNOOaO + SH^O. 412 EXPEEIMENTAL CHEMISTRY. The same compound may be formed by the action of nitric acid on indigo, silt, and other substances. The dying of animal substances by nitric acid (p. 160) is probably due to the formation of this compound. Experiment 2. — Picric acid is sparingly soluble in cold water, but the solution, even when it contains only 1 part acid in 10,000 of water, has an intense yellow colour. It is very soluble in alcohol. The solutions are used for im- parting a beautiful and permanent colour to silk. Ea^eriment 3. — Neutralize a warm and moderately con- centrated solution of sodium carbonate with picric acid. Sodium picrate separates in yellow crystals as the solution cools. Other picrates may be formed by double decomposi- tion with the sodium salt. Potassium picrate requires 260 parts of cold water (15° C. = 59° F.) for solution, and for this reason sodium picrate, which is soluble in about 12 parts of water, is sometimes used as a test for potassium. Experim,ent 4. — Heat a little potassium picrate on a slip of plantinum foil. It burns with explosion. In a close vessel the explosion is violent, and the salt has even been proposed as a substitute for gunpowder. PARAITIN PARAFFIN OIL PETROLEUM. When coal, peat, lignite, bituminous shales, &c., are exposed to destructive distillation at a temperature which is not allowed to rise above low redness, very little gas is obtained, but instead, a considerable quantity of tar or oil, which differs in composition from the tar obtained in the manufacture of gas. This tar is called crude paraffin oil, because it contains in solution the solid hydrocarbons which are grouped together under the name of paraffin (p. 296). A kind of coal, called boghead coal, found at Bathgate, near Edinburgh, is the best material for the preparation of paraffin oil. It is said to yield as much as 100 gallons of crude oil per ton. The crude oil is purified in much the same manner as gas tar. It is freed from basic and acid constituents by treat- ment vnth sulphuric acid and caustic soda. The remaining oil consists entirely of hydrocarbons and it is separated by distillation into a light and very volatile spirit, or naphtha, a burning oil, and a heavy, or lubricating oil. The heavier PARAFFIN PARAFFIN OIL — PETROLEUM. 413 portions of the oil deposit solid paraffin on cooling, and this paraffin is purified and applied to the manufacture of candles and other useful purposes. After the paraffin has been separated, the oil is again distilled with other portions of the oil, and a large proportion of oil, suitable for burning in lamps, is thereby obtained. The lighter portions of the oil cannot be used with safety in ordinary lamps, as the vapour, mixed with air, is very explosive. Terrible accidents often occur from the use in lamps of oil which contains too large a proportion of the lighter constituents. The safety of paraffin or petroleum oil may be tested in the following manner. Experiment. — Fill a beaker two-thirds full of the oil and cover it with a card, and immerse it in boiling water tUl the temperature of the oil rises to 100° F. (38° C), taking care to avoid draughts of air, which might blow away the vapour. Then bring a taper very near to the surface of the oil. If a flash of flame appears the oil is unsafe, and ought on no account to be used. In short, the flash point of the oil ought to be above 100° F. Pure paraffin oil is a very complex mixture of hydrocarbons, the greater number of which appear to belong to the saturated, or marsh gas series, CuETj^j. Petroleum. — In many parts of the world, as, for instance, in North America, Burmah, Persia, and the West Indies, hydrocarbon oils, known variously as petroleum, rock oil, mineral tar, or naphtha, &o., are found in great abundance below the soil, and can be obtained by sinking wells. These oils are very similar to paraffin oil, and some of them yield a great deal of solid paraffin. Eangoon tar yields as much as eleven per cent, of this substance. The petroleum of Pennsylvania has been found to yield at least twelve homo- logous liquid hydrocarbons, besides gases and solid paraffins. They all appear to belong to the CoH2„+2 series. Asphalt. — Compact Bitumen. — A solid black substance, between coal and petroleum in composition and properties. It melts at about 100° C, and burns with a smoky flame. It is found in considerable quantities in soine parts of the world, notably on the shores of the Dead Sea and in the celebrated bitumen lake — one mile and a half in circum- ference — of Trinidad. There are also small deposits of asphalt in Cornwall, Derbyshire, and other parts of England. ( 414 ) INDEX. ACETIO ACtD, 347. Acetylene, 182, 296. Acids, 95. basity of, 96. organic, 298. Aconitine, 395. Acrolein, 368. Acrylic acid, 369. Adhesion, 3! AfSnity, chemical, 5. Air-balloons, 46. Air, composition of, 154. currents of, 45. Air-pump, 57. Albumin, 825. Albuminoid substances, 313, 824. Alcohol, 342. Alcohols, 296. Aldehyde, 850. Alizarin, 400. Alkaloids, 388. ALkanet, 404. AUotropio states, 166. Alum, 259. Aluminium, 257. compounds of, 258. Amalgams, 230. Amides, 303. Amines, 301. Ammonia, 155. derivatives of, 301. Ammonium amalgam, 157. carbonate, 209. chloride, 208. -— sulpljide, 209. Ammoniums, compound, 802. Analysis, 15. Analysis of carbon compounds, 293. Aniline, 388. Annotto, 404. Anthracin, 296, 409. Antictdor, 110. Antimony, 280. compounds of, 281. Antiseptic?, 201, 411. Aqua fortis, 159. regia, 278. Archil, 405. Argand burner, 190. Argol, 354. Arrowroot, 314. Arsenic, 275. compounds of, 276. white, 275. Arsine, or arseniuretted hydrogen, 278. Artiad, 85. Asafoetida, 375. Asparagine, 396. Asphalt, 409, 413. Atmosphere, pressure of, 53. Atomic theory, 88. weiglits, 77. modes of fixing, 78. Atomicity, 84. hypothesis to account for, 91. modes of fixing, 85. explains homology, 288. Atoms, 69. Atropine, 396. Aureus and avu:ic salts, 273. Avogadro and Ampere's bypothesifi, 89. Azote, or nitrogen, 153. INDEX. 415 Balance, 19, Balsams, 374. Barium, 216. salts of, 216. Barometer, 55. Bases, 95. Bassorln, 319. Bast, 308. Battery, voltaic, 4. Beer, 334. Bell-metal, 222. Benzoic aoid, 851. Benzol, 296, 409. Berberine, 396. Bessemer process, 243. Bismuth, 283. compounds of, 284. glance, 285. Bittern, 116. Bitumen, 413. Blast furnace, 239. Bleaching, 307. by chlorine, 109. powder, 134. by sulphur, 144. Blood, 326. Blowpipe, 188. Boghead coal, 412. Boiling, 37. Bone, 329. Bone-black, 175. Boracic acid, 171. i Borax, 172, 206. Boric acid, 171. anhydride, 171. Boron, 171. • Brandy, 324. Brass, 221. Brassic acid, 363. Brazil-wood, 403. Brazilin, 404. Bread, 339. Brimstone, 139. Bromine, 116. Bronze, 221. Brucine, 395. Buckthorn, 404. Bunsen-bumer, 27. Burgundy pitch, 380. Burnett's disinfecting fluid, 220. Butter, 329, 362. Cadmium, 220. Caffeine, 396. Calcium, 213. carbonate, 214. chloride, 215. fluoride, 215. oxide, 213. sulphate, 214. Calomel, 228. Camphor, 375. Caoutchouc, 384. Caramel, 322. Carbazotic aoid, 411. Carbohydrates, 305. Carbolic acid, 410. Carbon, 173. compounds, structure of, 286. disulphide, 182. oxides of, 177. Carbonates, 179. Carbonic anhydride, 177. oxide, 179. Carmine, 408. Case-hardening, 244. Casein, 327. Castor oU, 364., Oelestine, 215. Cellulin, 306. Cetin, 371. Chalk, 214. Chameleon mineral, 256. Changes of state by heat, 35. Charcoal, 174. absorption of gases by, 174. animal, 175. Cheese, 328. Chemistry, applied, 17. uses of, 17. Chloric acid, 135. Chlorides, test for, 116. Chlorine, 108. oxides of, 133. peroxide, 135. Chloro compounds, 303. Chlorophyll, 398. Clioke damp, 181. Chrome iron ore, 249. yellow, 252. Chromium, 249. compounds of, 250. Cinchonlae, 393, 416 INDEX. Citric acid, 356. Clark's process, 21i. Classification of carbon compounds, 295. Clay, 257. Clouds, 40. Coal, distillation of, 186. Cobalt, 261. Cochineal, 403. Cohesion, 2. Coke, 175. Colchicine, 396. Collodion, 310. Colophony, 381. Colouring matter of flowers, 397. — : of leaves, 398. matters, mineral, 397. Colours, coal tar, 389. Combination, 60. by weight and volume, 63. Combining weights, 77, Combustion, 126. Composition, per centage, 74. Condy's fluids, 256. Conine, 393. Copper, 220. ores of, 220. oxides of, 222. salts of, 223. smeltin? of, 220. Copperas, 247. Cordials, 378. Corrosive sublimate, 228. Corundum, 257. Cotton, 308. Cream, 328, 362. Crystallization, 51. Cudbear, 405. Cumin-seeds, 376. Cumol, 408. Cupellation, 210. Cuicumin, 405. Cyanides, 184. Cyanin, 398. Cyanogen, 183. Dalton's atomic theory, 88. Davy lamp, 189. Decantation, 49. Decomposition, 61. double, 62. Deflagration, 127. Destructive distillation, 185. Dew, 47. Dextrin, 315. Diamond, 176. Diastase, 316. Diffusion of gases, 178. Dimorphism, 137. Disinfection by chlorine, 110. Distillation, 42. destructive, 407. Dohbereiner's lamp, 107. Dragon's blood, 375. Drying oils, 369. Dutch liquid, 182. Eau de Cologne, 379. Ebonite, 386. Eggs, 325. Electricity, 3. decomposition by, 12. Electro-plating, 11. Electrotyping, 225. Elements and compounds, 15. classification of, by atomicity. 84. the ancient, 18. Eliquation, 283. Emery, 257. Equations, 92. Equivalents, 79. Ether, 344. Ethers, 298. compound, 298. Ethylene, 181. chloride, 182. Evaporation, 40. Expansion by heat, 28. Fatty acids, 299. .Fermentation, 331. acetous, 347. butyric, 351. lactic, 351. Ferrous and ferric salts, 245. Fibrin, 326. Filtration, 49. Fii-e-damp, 181. Flame, 187. Flax, 307. Flour, wheat, 313. INDEX. 417 Fluor Bpar, 215. Fluorine, 120. Force, chemical, 5. conaervation of, 8. forms of, 2. rays of, 10. Forces, correlation of, 8. relation to one another, 7. FormulsB, 66. glyptic, 289. French polish, 384. Fusible metal, 283. Fustic, 404. Galena, 231. GaU-nuts, 357. Gallic acid, 357. Galvanic battery, 4. Gamboge, 375. Gases, collection of, 104. constitution of; 64, 68. correction for pressure, 57. correction for temperature, 34. elasticity of, 56. Gas manufacture, 186. rosia, 882. Gases, standard of volume for, 66. , structure of, 90. Gelatm, 329. German silver, 222. Glass, 207. etching on, 120. soluble, 190. Glauber's salt, 202. Glucose, 319. Glucosides, 358. Glue, 329. marine, 386. Glntin, 325. Glyceridea, 361. Glycerin, 368. Glycerins, 297. Glycols, 297. Gold, 271. compounds of, 273. Goulard water, 234. Graphite, 175. Gravity, 2-19. specific, 22. Gum Arabic, 318. British, 315. Gum, Senegal, 318. tragacanth, 319. resins, 375. Gun cotton, 309. Gunpowder, 197. Gutta-percha, 387. Gypsum, 214. Hsematoxylin, 405. Halogens, 108. Hartshorn, 156. Heat, 27. conduction of, 43. convection of, 44. latent, 36, 38. radiation Of, 46. specific, 81. Homologues, 287. Hydriodio acid, 119. Hydrobromic acid, 119. Hydrocarbons, 295. structure of, 286. saturated and unsaturated, 287. Hydrochloric acid, 112. Hydrocyanic acid, 184. Hydiofluoric acid, 120. Hydrofluosilicio acid, 192. Hydrogen, 102. peroxide, 133. Hydrometer, 25. Hydrosulphmic acid, 141. Hygrometers, 41. Hygroscopic bodies, 41. Hyoacyamine, 396. Hypochlorous anhydride, 134. India-rubber, 384. Indigo, 399. Ink, 358. printing, 370. Iodine, 118. Iron, 239. oast, 24] . compounds of, 245. ores of, 239. pyrites, 248. refining, 243. slag, 241. smelting of, 239. wrought, 242. 2 K 418 INDEX. Isinglass, 329. Isomerism, 293. Isomorphism, 83, 26,0. King's yellow, 278. Lac-dye, 404. Lactic acid, 329, 351. Lacquering, 383. Lactose, 323. Lakes, 260, 401. Lamp-black, 175, 382. Lard, 361. Laughing gas, 162. Law of combination by weight, 76. of constant composition, 63. of gaseous volumes, 64. Lead, 231. chromate, 252. compounds of, 232. tree, 235. Leather, 357. Leaven, 340. Legumin, 327. Light, its chemical effects, 3, 10, 115. Lime, 213. chloride of, 134. light, 131. water, 49. Linen, 307. Liniments, 366. Linoleio acid, 369. Linseed oil, 369. Litharge, 232. Litmus, 405. paper, 50. Liver of sulphur, 200. Logwood, 405. Lunar caustic, 211. Madder, 400. Magnesium, 216. salts of, 217. Magnetism, 5. Malt, 316. Manganese, 253. compounds of, 254. Manuite, 323. Marsh's test for arsenic, 279. Mashing, 317. Matter, 1. Mauve, 390. Mead, 332. Measures, 22. Meeonic acid, 394. Melting, 35. Mercury, 225. oxides of, 227. salts of, 228. Meta-phosphorlc acid, 170. Methene, or marsh gas, 180. Metrical system, 20. MUk, 327. Minium, 233. Mispickel, 275. Mixture and compound, 15. Moire metallique, 264. Molecules, 89, 91. Mordants, 260, 402. Morphine, 394. Mosaic gold, 268. Motion, 2. Muroxide, 397. Myricin, 371. Myrrh, 375. Naphth4., coal tar, 408. Naphthalin, 296, 409. Nickel, 261. Nicotine, 392. Nitrates, 161. Nitre, 197. Nitric oxide, 162. acid, 158. peroxide, 163. Nitrogen, 152. oxides of, 158. Nitro-benzol, 388. Nitro-oompounds, 303. Nitrous anhydride, 163. oxide, 161. Nomenclature, 87, 292. Nordhausen sulphuric acid, 147. Nux vomica, 395. Oak-baik, 357. Oil, almond, 363. cocoa-nut, 363. cod-liver, 362. colza and rape, 363. olive, 363. palm, 363. INDEX. 419 Oil, rook, 413. train, 362. OUs, volatile, 372. Olefiaut gas, 181. , Oleic acid, 361. Olein, .S61. Olibaaum, 375. Opium, 394. Organic compounds, 100. Orpiment, 278. Ossein, 329. Oxalic acid, 352. Oxides, 125. Oxygen, 121. Oxy-hydrogeu blowpipe, 181. Ozone, 128. Palmitic acid, 361. Palmitin, 360. Paper, 308. Papin's digfester, 59. Paracyanogen, 184. Paraffin, 412. Parchment, vegetable, 309. Pattinson's process, 210. Pearl white, 284. Pearlash, 195. Perissiad, 85. Persian berries, 404. Peruvian bark, 393. Petroleum, 413. Phenol, 410. Phenols, 297. Phenylamine, 388. Phosphates, 168. Phosphine, or phosphuretted hy- drogen, 166. Phosphoric acid, 168. anhydride, 168. Phosphorus, 163. oxides of, 168. Photography, 10. Picric acid, 411. Piperine, 396. Pipettes, 357. Pitch, 409.- Plaster of Paris, 215. Platinum, 268. - — black, 270. — — compounds of, 269. oxidation by, 108. Platinum, spongy, 270. Plumbago, 175. Pneumatic trough, 104. Potash, caustic, 194. Potassium, 193. carbonate, 195. chlorate, 198. chloride, 199. hydrate, 194. iodide, 199. nitrate, 197. oxide, 194. ■ sulphate, 196. sulphide, 199. Pressure, 52. effect of, on boiling, 58. Prusaic acid, 184. Puddling of iron, 243. Purple of Oassius, 275. Purpurin, 40O. Putrefaction, 331. Putty, 370. powder, 266. Pyridine bases, 408. Pyrogallic acid, 359. Pyroligneous acid, 350, Pyrolusite, 254. Pyrophorus, lead, 236. Pyro-phosphoric acid, 170 Pyroxylin, 809. Quantivalence, 84. Quartation, 273. Quercitron, 404. QuioksUver, 225. Quinic acid, 393. Quinine, 393. Radicals, 85. atomicity of, 86. hydrocarbon, 289. table of, 87. Eats, poison for, 163. Eennet, 328. Eeains, 374. Eespiration, 127. Eeverberatory furnace, 205. Eiciaine, 396. Eosaniline, 890. Eoseine, 390. Eose's metal. 284. 420 INDEX. Bubian, 400. Euby, 257. Safety tube, 51. Safflower, 404. Saffron, 405. Sal ammoniac, 208. Salioin, 394. Salt, common, 201. Saltpetre, 197. ChiU, 206. Salts, 95. formation ot 99. of hydrocarbon radicals, 298. Sandal wood, 404. Sandarach, 383. Sapphire, 257. Scammony, 375. Scheele's green, 277. Sealing-wax, 382. Selenium, 151. Serum, 326. SheUa«, 404. SiUoa, 190. Silicates, 192. Silicic anhydride, 190. Silicon, 190. — ^- fluoride, 192. Silver, 210. chloride, 212. fulminating, 212. glance, 212. nitrate, 211. sulphide, 212. Slnapine, 396. Smalt, 260. Smelling-salts, 209. Soap, 364. Soda, caustic, 200. Sodium, 200. borate, 206. carbonate, 204. chloride, 201. hydrate, 200. nitrate, 206. phospbate, 206. ; silicates, 207. sulphate, 202. sulphide, 204. Solanine, 396. Solder, 264. Solution, 48. saturated, 50. Soot, 175. Specific gravity, 22. calculation of, 72. Speiss, 262. Spermaceti, 371. Spirits, 336. methylated, 343. Stannous and stannic salts, 265. Starch, 310. Stearic acid, 861. Stearin, 360. Steel, 243. Stibine, or antimoniuretted hydro- gen, 282. Strontium, 215. salts of, ^15. Strychnine, 3&5. Sublimation, 138. Substitution, 62. Sugar-candy, 321. Sugar, cane, 320. grape, 319. mill, 323. Sulphindigotic acid, 399. Sulphides, 140. Sulphites, 145. Sulphur, 136. oxides of, 143. Sulphuretted hydrogen, 141. Sulphureous waters, 143. Sulphuric add, 145. anhydride, 145. Sulphurous acid, 143. anhydride, 143. Symbols, 66. use of, 78. Synthesis, 16. Tallow, 361. Tannin, 357. Tar, coal, 407. Tariai, cream of, 356. emetic, 282. Tartaric acid, 854. Tellurium, 151. Test-tubes, 45. Theobromine, 396. Theory, 16. Thermometer, 29. INDEX. 421 Tin, 263. compounds of, 265. plate, 264. stone, 263. Tiuoal, 171. Tobacco, 392. Toluidine, 410. Toluol, 408. Turmeric, 405. Turpentine, 375. oil of, 296. Type metal, 280. Ultramarine, 260. Urea, 390. Vacuum, Torricellian, 55. Vapour, aqueous, 40. Varnish, 383. Ventilation, 46. Veratrine, 396. Vinegar, 347. aromatic, 379. wood, 350. Vitriol, blue, 224. green, 247. oil of, or sulphuric acid, 147. Vitriol, white, 219. Washing-bottle, 57. Washing with soap, 366. Water, 130. oompositiou of, 132. expansion of, 33. — — hardness of, 214. of crystallization, 202. Wax, 370. Weighing, 19. Weights and measures, 20. Weld, 404. White lead, 234. precipitate, 229. Wine, 333. Woad, 400. Wood, 306. Woulfe's bottles, 114. Xylol, 408. Yeast, 332. Zinc, 217. granulated, 104. salts of, 219. LONDON : PBINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET AND CHARING CROSS.