THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID RURAL CHEMISTRY. Digitized by tine Internet Arcinive in 2008 with funding from IVIicrosoft Corporation http://www.arcliive.org/details/cliemistryruralOOsollricli RUEAL CHEMISTRY: (Khmntartt Sntrnitrrtinn TO THE STUDY OF THE SCIENCE IN ITS RELATION TO AGRICULTURE AND THE ARTS OF LIFE. BY EDWAED SOLLY, F.R.S., F.L.S., F.G.S., HON. MEMB. ROY. AGB. SOC. ENG. Fellow of the Chemical Society, the Society for the Encouragement of Arts and Manufactures, and the Society of Antiquaries ; Hon. Memb. of the Royal Polytechnic Society of Cornwall, the Ipswich Museum, and the Poole Scientific Institution ; Professor of Chemistry to the Horticultural Society of London, Lecturer on Chemistry in the lion. E. I. Co.'s Military Seminary at Addiscomhe, &c. &c. FROM THE THIRD ENGLISH EDITION, REVISED AND ENLARGED. PHILADELPHIA: HENRY CAREY BAIRD, SUCCESSOR TO E. L. CAREY. 1852. ka. PHILADELPHIA: T. K. AND P. G. COLLINS, PRINTERS. PREFACE TO THE FIRST EDITION. The following pages formed the substance of a short series of articles on Chemistry, which origi- nally appeared in the columns of the Gardeners' Chronicle. The interest which they excited in the readers of that journal, has led to their republica- tion in a separate and more complete form. It would have been easy to have greatly increased the size of the book; and indeed it was frequently very difficult to select from the mass of information which exists those facts which appeared most worthy of notice. The original object of the Author was to give such an elementary sketch of the science as should enable those ignorant of the subject more readily to comprehend the works of the various authors who have written on Agricultural Chemistry. ^^6264.1 VI PREFACE. As a general rule, care has been taken, as much as possible, merely to give well-esta])lished facts, or, when doubtful theories are mentioned, to state dis- tinctly that they are more or less problematical. PREFACE TO THE THIRD EDITION. In accordance with numerous suggestions, very considerable additions have been made to this little book, in preparing it for a new edition; several important practical matters, not treated of in the former editions, having been introduced. Brief descriptions of the more important of the domestic arts, such as wine and vinegar making, brewing, the manufacture of spirits, baking, cheese-making, cookery, &c., have been added; together with some account of the scientific principles involved in those arts. Numerous recent analyses of agricultural crops have likewise been given, and the whole has been carefully revised and corrected. E. SOLLY. Tavistock Square, London, Nov. 1, 1850. CONTENTS. PAGE Introduction 13 CHAPTER I. Objects of chemistry — Affinity — Nature of combination and decomposition — The elements — The air, its pro- perties and composition — Oxygen and nitrogen — Com- bustion, results of combustion — Carbonic acid gas — Water, ice, and steam — Effects of frost — Latent heat — Composition of water — Hydrogen ... 25 CHAPTER II. Carbon, its different forms — Cohesion — Combustion and decay — Carbonic acid gas, produced by respiration, combustion, fermentation, &c. — Nature of acids and salts — Carbonic oxide — Carburetted hydrogen, fire damp, coal gas — Compounds all definite — Combining weights — Nitrogen combined with hydrogen forms ammonia — Carbonate, sulphate, muriate, and phosphate of ammonia — Nitric acid — Nitrates — Sulphur, sulphu- rous acid — Sulphuric acid, sulphates — Sulphuretted hydrogen — Chlorine, muriatic acid — Iodine, bromine — Phosphorus, phosphoric acid .... 58 CONTENTS. CHAPTER III. Metals — Bases — Alkalies — Potash-, its properties — Carbo- nate and nitrate of potash, gunpowder — Soda, common salt, sulphate, carbonate, and nitrate of soda — The alkaline earths — Lime, its nature and properties — Car- bonate, sulphate, and phosphate of, lime — Magnesia, its carbonate, sulphate, muriate, and phosphate . 97 CHAPTER IV. The earths — Alumina, its properties — Alum — Silica, or silicic acid — Silicates of potash and soda — Glass — Sili- cates in the soil, in plants — The metals, their oxides and salts — Iron, its oxides — Rusting of iron — Pyrites — Sul- phate of iron, or green vitriol — Gold — Silver — Mercury — Copper — Sulphate of copper, or blue vitriol — Zinc — Tin — Manganese — Lead Metallic alloys . . . 118 CHAPTER V. Organic matter — Vegetable substances — Lignin, or woody fibre — Starch, varieties of starch — Gum, soluble and in- soluble — Sugar, cane and grape, its manufacture — Glu- ten, albumen, legumine, fibrin, gliadine — Chemical Transformations — Formation of gum, sugar, &c. — Fer- mentation — Lactic acid — Manufacture of wine — Alco- hol — Brandy and grain spirit — Brewing — Bread-mak- ing — Vinegar or acetic acid 139 CHAPTER VI. Vegetable principles — Vegetable acids — Citric, tartaric, malic, and oxalic acids — Oils, fixed and volatile, manu- facture of soap — Resins, pitch, and tar — Coloring mat- ters, dyeing — Inorganic constituents of plants — Animal CONTENTS. XI PAGE matter — Albumen — Fibrin— Caseine, milk, butter, and cheese — Gelatine — Tanning, leather — Fat — Bone — Pro- tein — Food of animals— Respiration — Circulation of the blood — Digestion -^ Formation of fat — Cookery, roasting and boiling — Action of medicines . . 199 CHAPTER VII. The food of plants — Substances derived from the air — Sources of oxygen, hydrogen, nitrogen, and carbon — Substances derived from the soil — Sources of earthy substances — Composition of soils, their formation — De- composition of silicates — Mechanical structure of soils — The saline constituents of soils — Organic matters in soils, humus, humic acid ; their use in soils — Germina- tion, malting — Moisture, air and warmth — Influence of light — Office of the leaves — Roots — Formation of or- ganic matter — Flowers, fruit, seeds — Organic and organized matter — Vitality of embryo — Nature of seeds — Earthy substances in plants — Effects of climate — Action of plants on the air 246 CHAPTER VIII. Deterioration of soils, its cause — Modes of maintaining the fertility of the soil — Theory of fallowing — Rotation of crops — Subsoil ploughing — Draining — Manure — Organic manure — Animal manure, contains nitrogen — Results of putrefaction — Sulphuretted hydrogen — Loss of manure — Liquid manure — Animal excre- ments, guano — Modes of fixing ammonia, by acids, by gypsum, &o. — Strong manures — Wool, rags, oil — Bones — ^^Super-phosphate of lime — Vegetable manures — Sawdust, seaweed — Green manures — Irrigation — Inorganic manures — Lime, chalk, marl, shell sand — Xn CONTENTS. PAGE Gypsum — Phosphate of lime — Ashes — Burnt clay — Soot, charcoal — Gas liquor — Potash — Alkaline salts — Nitrates, common salt — Salt and lime . . . 284 CHAPTER IX. Composition of particular crops — Composition of wheat — Barley — Oats — Rye — Maize — Rice — Buckwheat — Lin- seed — Hempseed — Oil-seeds — Beans — Peas — Lentils — Vetches — Potatoes — Batatas, Jerusalem artichoke — ■ Oxalis — Cabbage — Turnips — Mangel-Wurzel — Carrot — Parsnip — Clover — Lucern — Saintfoin — Composition of particular manures — Cows' urine — Horse-dung — Pigs' dung — Night-soil — Urine — Bones of oxen — Cows — Horses — Pigs — Farmyard dung — Guano — Wood- ashes — Lixiviated ashes — Peat ashes — Kelp . 333 Index 379 INTRODUCTION No branch of knowledge has made more rapid pro- gress, during the last hundred years, than chemistry. From being merely a confused collection of marvel- lous facts and incomprehensible phenomena, it has become a definite and methodical science : no longer mysterious and full of uncertainty, but based on clear and simple laws, the knowledge of chemistry at once gives us the key to a great number of natural changes and phenomena, which without it, would be quite unintelligible. Chemistry is intimately connected with all other sciences; for it embraces the study of the various forms and conditions of matter, tjieir nature and pro- perties, and the changes which, either from natural or artificial causes, they undergo. The study of chemistry is of the greatest importance in relation to the arts of life, which all depend more or less on 1 XIV INTRODUCTION. chemical principles. Hence, a knowledge of this science enables us more readily to understand the processes of the manufacturer, points out the best and most economical mode of effecting his objects, and teaches how that which was before useless and of no value, may be converted into sources of wealth and happiness. It is needless to point out examples of the influence which the progress of chemistry has had on our manufactures ; for every one of them owes, more or less directly, its present improved condition to the labors of the chemist. Such being the case, it be- comes interesting to inquire. What has chemistry done for agriculture, the most important, because the most necessary, and most extensively practised, of all the arts? It is remarkable that agriculture should have received infinitely less assistance from the labors of chemists, than any other art ; but this ceases to be surprising, when we consider how little attention was paid by the ancient chemists to that subject. — The chemistry of the earthy and metallic substances presented to them easier and more attract- ive objects of inquiry; they were led away by the visionary hope of discovering a mode of making gold ; and they consequently neglected everything, in order to try all sorts of experiments, in the vain idea INTRODUCTION. XV of converting lead, iron, &c., or the base metals as they called them, into gold. Hence, it is not to be wondered at, that the chemistry of the metals was studied and investigated, long before the nature and properties of vegetable and animal substances were examined. The labors of the alchemists brought to light many valuable discoveries respecting the uses, nature, and properties, of earthy and metallic sub- stances; but it was only in the last century, when the constitution of the air and other gaseous bodies was discovered, that anything approaching to correct ideas respecting the nature of animal and vegetable substances was entertained. The important discoveries of Dr. Priestley led the way to a complete revolution in the science, and may almost be said to have laid the foundation of agricul- tural chemistry. It is true that, before his time, there had been many careful and accurate observers, and multitudes of laborious and valuable experiments have been made on plants, by such men as Yan Hel- mont — Evelyn — Boyle — Hales, and others ; but, be- fore the time of Priestley and his contemporaries, Bonnet, Ingenhousz, Henry, and Percival, little pro- gress had been made in studying the chemical changes on which the growth of plants depends. We are indebted to Hales for much curious information XYl INTRODUCTION. respecting the rise and motion of the sap in plants, the perspiration, or evaporation, which is constantly going on to a greater or less extent, from the surface of the leaves, and the effects of various substances on plants; his chemical speculations, however, are for the most part, of little value, though he was often apparently on the point of making important disco- veries. The discovery of carbonic acid gas, or fixed air, by Dr. Black, and the beautiful experiments of Priestley, opened a new field of inquiry and research : he observed that plants possessed the property of purifying the air; in fact, that they were able to decompose the carbonic acid gas which it always con- tains in small quantity; appropriating the carbon, and restoring back to the atmosphere the oxygen, or vital air, so necessary to the processes of respiration and combustion. The knowledge of this great fact, necessarily led to many minor discoveries respecting the growth of plants, and the sources of their food. After this period. Organic Chemistry began to attract a large share of the attention of chemists, the com- position of vegetable substances was carefully inves- tigated, new modes of analysis were discovered, and an immense mass of curious and useful facts was col- lected. A great number of chemists occupied them- selves with researches in Vegetable Chemistry, but INTRODUCTION, XVll for the most part they were employed in examining the innumerable substances which plants produce; whilst the great questions as to the food of plants, their growth, and nourishment, were left very nearly in the same state which the experiments of Priestley and Ingenhousz had brought them to. At the end of the last century, and in the com- mencement of the present. Organic Chemistry made rapid advances ; the labors of Hassenfratz, -Hum- boldt, Berzelius, Saussure, Senebier, Einhof, and Davy, contributed to throw light on many parts of the subject ; whilst the investigations of Gay-Lussac, Hatchett, Lampadius, Lavoisier, Marcet, Prout, Thompson, Yauquelin, Thdnard, and others, in all parts of Europe, led to a more complete and accurate knowledge of the nature, composition, and properties of organic matter. The first chemist who wrote on agriculture appears to have been J. G. Wallerius, who, in 1754, published a book on the Cause of Fertility. Even before this time, however, several books had been written on agriculture, in which attempts were made to explain the operations of farming on chemical principles; such, for example, were The Rational Farjner, 1743, a curious book, containing numerous accounts of rude chemical experiments, together with a num- 1* xviii ' INTRODUCTION. ber of sound practical facts: the author, however, was evidently not a chemist. Wallerius was suc- ceeded by several other authors, amongst whom ought to be mentioned Cullen, Pearson, Gyllenborg, De Beunie, Riickert, Einhof, and Dundonald ; but the speculations of these authors (though ingenious) were, for the most part, crude and incomplete. The writings of Einhof were valuable for the numerous accounts of careful experiments which they contain ; the analyses, though not carried to that degree of minuteness which subsequent discoveries led to, were trustworthy and accurate, and, as such, will always continue of value. Humboldt's Sheteh of the Chemical Physiology of Vegetation, which appeared at this time, is a book of far higher talent than those just mentioned, and contains enlarged views and cautious generalizations, which the subsequent pro- gress of science has in most cases confirmed. At the commencement of the present century, when Organic Chemistry was rapidly advancing, Berzelius and Davy endeavored to apply the conclusions to be derived from chemical experiments, to agriculture. If the deductions which they made were not always correct, and if the plans which they proposed did not always produce the effects which the authors anticipated, it must be remembered that they were INTRODUCTION. XIX amongst the first to take the subject up, and that though they did so under far more favorable circum- stances than their predecessors did, yet that even then the science of organic chemistry was in many respects very imperfect and incomplete. During the last forty years, many important additions have been made to this department of Chemistry; improved and more accurate modes of chemical investigation have enabled more exact ana- lyses to be made of the different varieties of organic matter; the composition of those substances which constitute the bodies of animals and plants has been accurately and carefully ascertained. At the same time, many valuable observations have been made respecting the functions of plants, the conditions requisite to germination, the formation of flowers and seed, the chemical changes attendant on the ripening of fruit, the office performed by roots and leaves, and a variety of other important subjects of inquiry. The names of Liebig, Schiibler, and Sprengel, in Germany; Braconnot, Boussingault, Chevreul, Colin, Chaptal, Dumas, Edwards, and Payen, in France ; and of Daubeny, Fownes, John- ston, Pepys, Turner, Christison, and "Way, in our own country, deserve especial mention. Even in so short a sketch of the subject as this, it XX INTRODUCTION. would not be right to omit altogether the name of Grisenthwaite, whose book on the theory of Agricul- ture (1819) is remarkable for the enlarged and ex- tended views which it contains. It is true that the author falls into many errors ; but, at the same time, he was the first who entertained correct views of the importance of nitrogen as an element of manure, and of the necessity of supplying phosphates, as well as substances containing nitrogen, to plants, like wheat, chiefly cultivated for the sake of the azotized princi- ple which renders them valuable as food. Intimately connected with the progress of Vege- table Chemistry, is the study of Vegetable Physio- logy: a knowledge of the one is essential to a perfect comprehension of the other; for it is impossible well to understand the chemical changes going on in the organs of plants, if we are wholly ignorant of the forms and structure of those organs; and, on the other hand, the most complete knowledge of the anatomy of vegetables could never lead any one to sound and correct conclusions respecting the nutri- tion of plants. It is rather to be regretted that both Chemists and Physiologists have appeared to avoid availing themselves of the advantages which each might have derived by studying the results that the others had obtained ; it is only by comparing INTRODUCTION. XXI togetlier the observations of both, that correct con- clusions can be formed. The observations made by the older physiologists, like those of their chemical contemporaries, were mostly imperfect, and the deduc- tions they formed, were, in consequence, very fre- quently erroneous ; the modes of examination, and the instruments which they employed, were far less per- fect than those which have been used in more recent times. Nevertheless, the observations recorded by Grew, Malpighi, and Duhamel, are of considerable value ; they may be said, indeed, to have laid the foundation of Vegetable Physiology. As the study of Botany itself advanced, greater care was bestowed in examining the structure and anatomy of plants ; and, from the labors of many zealous and careful observers, there has resulted a tolerably complete system of Vegetable Physiology. In recent years, De Candolle, Brongniart, Decaisne, Dutrochet, and Mirbel, in France; Link, Mohl, Meyen, and Schlei- den, in Germany; Amici, in Italy; and Brown, Griffiths, Henslow, Knight, and Lindley, in England, have, besides many others, made valuable additions to Vegetable Physiology. The relations of plants to climate, and the influence of heat, light, and moist- ure, have also been studied ; especially by Daniell and Royle in our own country. XXll INTRODUCTION. Amongst the names of those who have contributed to the. science of Agricultural Chemistry, that of Liebig stands pre-eminent. The thanks of all are due to him, both for the valuable and laborious ex- periments he has performed, and likewise for the exertions which he has made to remove the many- doubts and uncertainties that surrounded the very elements of the subject. But little has been done since the days of Priestley and Ingenhousz to prove how plants obtained their food, what were the sources whence they derived the elements of organic matter, and the nature of the office performed by manures. Chemists, and likewise physiologists, had formed many ingenious speculations; but they had not em- ployed the only real mode of getting at the truth, namely, well-selected and carefully performed expe- riments. Liebig, in his Organic Chemistry applied to Agriculture and Physiology, has strongly drawn attention to these important questions ; he has exposed the fallacy of many of the theories which had been formed to explain them, and has established, on good evidence, the simple chemical rules which regulate the growth of plants. Although the experiments of Priestley and Ingen- housz had shown that plants possess the power of decomposing Carbonic Acid ; and, although they had IXTKODUCTION. XXlll advanced numerous arguments to prove that plants derive the carbon which they contain from the de- composition of that gas; yet this doctrine, although admitted by many physiologists, was by no means universally believed by chemists. M. Hassenfratz, in particular, opposed these views, asserting that plants did not derive their carbon from the decom- position of carbonic acid existing in the air, bjit absorbed it direct from the soil, in a state of suspen- sion or solution; he gives the name of carbon to the brown substance left on the evaporation of dung water, and, in fact, to the various modifications of decaying organic matter, subsequently described under the general name of Humus. Few experi- ments, indeed, were made to show that the explana- tion of Priestley and Ingenhousz was improbable; but "it was conceived that plants must derive their carbon from the soil, and many theories were formed to explain the mode in which they might be supposed to obtain it. These theories have been rigidly ex- amined by Liebig, and the results of his investigation have shown, that the old views put forth by Priestley and Ingenhousz were in truth correct. It has long been known that plants consist of Carbon, Oxygen, Hydrogen, and Nitrogen, and also that they invariably contain a small quantity of inor- XXIV INTRODUCTION. ganic, or earthy and saline matters. The presence of Nitrogen was formerly greatly overlooked, in analyses of vegetable substances ; it is contained in less quantity than the other three elements of organic matter, and was very commonly regarded as being merely accidental, and not a necessary consti- tuent of plants. Improved modes of analysis have proved that nitrogen always exists in the same pro- portion, in certain constituents of plants; -and, as it appears that these substances are also those which form the most valuable part of food, it becomes a question of the first importance — Whence do the plants derive their Nitrogen? They obtain it, prin- cipally, if not wholly, from the air; they do not absorb it in the free and uncombined form, but they absorb it combined with Hydrogen and with Oxygen, in the states of Ammonia and Nitric Acid. "The importance of the earthy substances in plants was, likewise, greatly overlooked formerly. It has been proved, by repeated experiments, that these sub- stances are of the greatest importance in the growth of plants, being quite essential to their development. Although much has been done, and although- che- mists have labored to remove the perplexities which encompassed the subject, there is still a very great deal which requires investigation; many important INTRODUCTION. XXV points. are as yet imperfectly, or even not at all, explained, and many questions must be satisfactorily settled before a complete system of Agricultural Chemistry can be established. Till these difficulties are removed, it is premature to expect that Chemistry can be of more than partial assistance to Agricul- ture; for, whilst many of the fundamental laws of Agricultural Chemistry are still scarcely understood, all attempts to apply them to practice must be in- complete, and liable to error. The composition of the principal varieties of organic matter is well known ; the substances which, by combining together, form the various constituents of plants, have been ascertained. The food of plants, the great , sources whence they derive it, and the manner in which they absorb it, are known. The various changes which organic matter undergoes, the conversion of one substance into another, and the influence which these changes have on the growth of plants, is likewise easily understood ; nearly all the purely chemical operations which are concerned in their nutrition, can be explained by reference to simple chemical laws; but there are many most im- portant phenomena which are as yet wholly in the dark. Thus, for example, the manner in which wood is formed ; and, indeed, all those natural operations XXVI INTRODUCTION. in "vtliich cellular or organized matter is generated under the influence of light and heat, are but very imperfectly explained. A knowledge of the chemical composition of soils, and the various substances em- ployed as manures, enables us to comprehend the mode in which the latter act ; and a knowledge of the nature of those substances which plants require, points out the best and most economical methods of restoring to the soil, by manures, those substances which plants remove from it: but our knowledge of this part of the subject is very far from being com- plete; for although it is certain that, in addition to the great elements of organic matter, which plants derive from both air and soil, they likewise absorb small quantities of inorganic or mineral substances from the soil exclusively, the office performed by the latter in the vegetable economy is not yet well under- stood. Many theories, indeed, have been formed respecting their use, but very little is positively known on the subject. Although Agricultural Chemistry is in this imper- fect state, and though much still remains to be done in that branch of science, yet it is so far advanced as to be able to render substantial assistance to the practical agriculturist. It can teach him the princi- ples which govern the growth of plants, and, conse- INTRODUCTION. XXVll quentlj, guide him in the application of artificial means to produce the most beneficial results. He must, however, not expect too much from the aid of Chemistry, nor give himself blindly up to specula- tions or theories. Whilst he gives due credit and belief to well-authenticated facts, he must always receive theories with caution and doubt. Perhaps the most important advantage which a practical man may at present derive from a know- ledge of Agricultural Chemistry, is connected with the use of manure. If he knows what it is that gives the fertilizing powers to manure, and is aware of the nature of those substances, he will soon learn the best method of preserving and using them; he will then understand how to make the most of the various sources of manure at his disposal, and he will be enabled readily to save much, that, for the want of such knowledge, would otherwise be lost. RUEAL CHEMISTRY CHAPTER I. COMBINATION — DECOMPOSITION — AIR— WATER. 1. The object of Chemistry is to determine accu- rately the properties ' of all natural substances, to study the changes which are going on in Nature, to find out the rules which govern them, and the manner in which these natural operations are influenced by circumstances. 2. In pursuing these inquiries, the chemist is obliged to proceed slowly and with great caution ; it is quite impossible for him to predict beforehand the result of a new experiment; he must try it, and then, if it has been properly conducted, it always furnishes him with a new fact, for he is sure that, on repeating it in the same manner, he will obtain the same result. Hence Chemistry is purely an experimental science ; every fact is the result of careful experiment, and every theory is deduced from the study of such facts. The greatest care must be taken to distinguish facts from theories; the former are well-established and 3 26 COMBINATION. unquestionable truths, the latter are plausible con- jectures, to which we are led by the attentive study of facts. When a chemist has made a number of experiments, or has observed many phenomena, he endeavors to ascertain the causes of the effects he has been studying. lie selects the most probable explanation, and adopting it as a theory or view, to be confirmed or disproved by future experiments, proceeds to try in all possible ways the truth of his conclusion. By thus forming a theory he is enabled to arrive at the truth more easily than if he were merely to continue making experiments at random. It is by reasoning on the results of thousands of ex- periments that chemists have been enabled to reduce the science into a useful form, as they have thus been led to discover certain great leading laws, which govern all chemical changes or operations. 3. Nearly all the changes which are going on in Nature may be classed under two heads. The one kind of change is that which takes place when two substances come together which have, as it were, an attraction or afiinity for each other. As a familiar example of what then happens, we may take the com- mon process of soap-boiling. When an alkaline or caustic lye is boiled with tallow or fat, soap is formed. The alkali which is contained in the lye has an attrac- tion for the fat; the two become thoroughly mixed, and combine or unite together, and form a new sub- stance, quite different from either the fat or the alkali^ which new substance is called soap. CHEMICAL AFFINITY. 2T 4. This kind of action is quite distinct from simple mixture. When we mix together two substances — such as, for example, brown sugar and sand, no change takes place, however long they are kept together, or in whatever way they are treated, for they have no affinity or attraction for each other; and, therefore, if boiling water is poured upon the mixture, it will soon dissolve out all the sugar and leave the sand, and neither the sugar nor the sand will be at all altered by having been mixed. 5. When we mix two substances which have an attraction for each other, they are both changed, and the new substance formed by their union is quite dif- ferent from either ; and when two substances are thus united or combined together, they are not so easily separated as when merely mixed, because they require the exertion of some attraction more powerful than that which made them combine, to cause their sepa- ration. In the case of the soap just mentioned, the compound of fat and alkali does not resemble either of its components ; it is different from the ley in not being caustic, and differs from the fat in being easily soluble in water. 6. It is a rule which holds good in all cases, that whenever two substances combine or unite together, and form a new substance, the properties of the new substance are quite different from those of either of its components; but when two substances are only mixed, the properties of the mixture are intermediate, or half-way, between those of its two components : 28 DECOMPOSITION. thus, in the mixture of sand and sugar, we may easily recognize both substances, for the characters of neither are altered by being brought together. 7. Another common case of affinity is observed •when we slake quicklime. Quicklime has a strong affinity for water, and when it is wetted, it becomes very hot; the lime combines with a quantity of water, and when is has cooled, we find that the lime is much altered, having to a great extent lost its strong caustic properties, and become slaked, as it is termed. Here again we observe that the properties of the com- pound differ remarkably from its components. Dry caustic lime, in combining with water, forms a dry compound of lime and water, the water becomes solid, 'entering into the composition of a dry solid powder, whilst the lime no longer possesses the power of heat- ing when water is poured over it, and has become less caustic (235). 8. It may perhaps seem as if these two examples of the change produced by attraction or affinity were processes of Art, and not of Nature. They will, how- ever, serve as examples of what is going on in a great many natural operations ; and as we proceed with the subject, it will be evident that this kind of change, by which two or more difi'erent substances unite and form one new substance, is exceedingly common throughout Nature. 9. The second kind of change which we shall have to consider, is that which goes on whenever anything decays. This change is quite opposite in its nature DECOMPOSITION. 29 to that which we have just been describing. It takes place whenever any substance is separated or divided into its component parts. Thus, to return again to the quicklime, which is made by burning chalk or limestone, we say that the chalk or limestone is decom- posed, when, by burning or heating it in a very hot fire, whatever it contains which can be roasted out by fire, is driven off, and the lime only remains (118). 10. The decomposition of a substance is also effect- ed when it is mixed with anything which has a very strong attraction for one of its components. Soap is made by the attraction which the alkali has for fat (3) ; but if we add to a solution of soap in w^ater, any- thing which has a stronger attraction for the alkali than the latter has for the fat, we shall decompose the soap : there are many substances which have the power of doing this, but it is sufficient now to mention one. If vinegar is poured into a solution of soap, the soap is decomposed ; the fat is separated and floats on the surface, and the vinegar combines with the alkali of the soap. 11. This kind of change is always going on when anything decays or putrefies, and therefore is of con- siderable interest in connection with manures ; but in fact, combination and decomposition are almost always going on at the same time in most natural changes, for when a compound consisting of several different substances is decomposed, it is generally found that 3* 30 ' DECOMPOSITION. these substances again combine together, one with another, to form various other compounds (105, 145). 12. Combination takes place whenever substances are brought together which have an affinity for each other, under suitable circumstances ; chemical action then takes place, and a compound is formed. De- composition of a compound is caused either by the influence of some external power, the presence of some substance capable of acting on one of the ele- ments of the compound, or some influence able to weaken the chemical affinity which binds these ele- ments together. - 13. Combination is often modified and controlled in a very remarkable manner by circumstances, ac- cordingly as they are favorable or unfavorable to the union of the substances brought together. Fine division, or any other method whereby the particles are enabled readily to mix or come in contact, gener- ally assist combination. When two solid lumps are placed in contact with each other, they are only able to touch by a very few points, and hence in many cases do not combine even though they have an affinity for each other. If they are finely powdered and well mixed they are much more able to combine ; and for the same reason if they are fusible, heat, by rendering them fluid, and thus enabling the particles more easily to mix, assists their combination, 14. A similar eff*ect is produced by solution in water. In a common Seidlitz powder or saline THE ELEMENTS. 31 draught, wc have two solutions mixed together, which are able to act on each other, but cannot do so in the dry state ; when water is added they are brought thoroughly in contact, and chemical action at once takes place. In many cases combination is greatly assisted by heat, which exalts the chemical affinity that the substances have for each other (35). 15. Precisely in the same way decomposition is often curiously affected by various circumstances. Some compounds decompose spontaneously ; they cannot be kept any time, and without any external influence they undergo decomposition ; this is espe- cially the case with many animal and vegetable substances (354). Decomposition is frequently caused by the influence of light (187, 295, 699), or heat (9, 119, 233). The decomposition of many compounds, likewise, is caused by the presence of particular sub- stances. A great number of different organic sub- stances are decomposed when a small, quantity of some other substance in an active state of decom- position is mixed with them ; this may be called decomposition by example ; it is a very singular form of decomposition, and is termed fermentation (365). A similar change is sometimes caused by the mere presence of a particular substance, even though it is not itself undergoing any change whatever at the time (361). 16. It is a common saying that there are only four elements ; air, earth, fire, and water ; and many 82 THE ELEMENTS. people believe that all things are composed or made up of these four elements. This is very incorrect, because there are many substances which do not con- tain any of these so-called elements ; and they are, besides, themselves compounded of many different substances. The term elements, in the sense in which it is used by chemists, means a certain set of simple substances, which, by combining or uniting together, form all the various matters that occur in Nature. 17. To return once more to the example of soap, we may say that the elements of soap are alkali and tallow ; but then the question will arise, what are the elements of tallow and alkali ? which can only be ascertained by chemical experiments. In this way, then, we may analyze, or as it were pull to pieces, different substances, till at last we find that we are unable to separate or decompose them any further, and the substances which then remain are called ele- ments, or simple substances. It is possible that chemists may hereafter discover that some of the substances now called elements are really compounds, and of course it is impossible to prove that they are not so; all therefore that is meant by the term ele- ment, or elementary substance, is that chemists have not yet been able to prove them to be compounds. 18. There are upwards of sixty of these elements, but it will not be necessary to study the nature and properties of the whole series, because many of them are of very rare occurrence, and found only in small quantities. ELEMENTARY SUBSTANCES. 33 19. The following is a list of all the substances which are at present considered as being simple, or elementary : — 1. Aluminum 2. Antimony 3. Arsenic 4. Barium 5. Bismuth *6. Boron 7. Bromine 8. Cadmium 9. Calcicum 10. Carbon 11. Cerium 12. Chlorine 13. Chromium 14. Cobalt 15. Columbium 16. Copper 17. Didymium 18. Erbium 19. Fluorine 20. Glucinum 21. Gold 22. Hydrogen 23. Iodine 24. Iridium 25. Iron 26. Lantanum 27. Lead 28. Lithium 29. Magnesium 30. Manganese 31. Mercury 32. Molybdenum 33. Nickel 34. Niobium 35. Nitrogen 36. Osmium 37. Oxygen 38. Palladium 39. Pelopium 40. Phosphorus 41. Platinum 42. Potassium 43. Rhodium 44. Ruthenium 45. Selenium 46. Silicon 47. Silver 48. Sodium 49. Strontium 50. Sulphur 51. Tellurium 52. Terbium 53. Thorium 54. Tin 55. Titanium 56. Tungsten 57. Uranium 58. Vanadium 59. Yttrium 60. Zinc 61. Zirconium. 20. We will commence with those substances which are of the greatest importance, whether simple or com- pound, and gradually go through them, before enter- ing upon the Chemistry of Vegetation. Foremost in importance, of the substances whose properties we are about to study, stands the Air. 21. We are too apt to think of the Air as being merely empty space; we move about through it with- 34 AIR — COMBUSTION. out feeling any resistance, and, from its being invisible and totally unlike anything else we know, many for- get its existence altogether. The fact is, that every part of the surface of the globe is surrounded by air, which floats on its surface almost like water. 22. It is easy to prove that the air is really a sub- stance. When we try to squeeze together the sides of an inflated bladder, the mouth of which is tightly tied up, we feel that the bladder is full of something which resists the pressure ; this something is the air which it contains, and which, though so easily dis- placed, or pushed aside, by anything moving through it, resists strongly any force applied to it when thus confined in a limited space ; and if whilst we are press- ing the bladder we prick a hole in it, the air then rushes out, we feel that the resistance is gone, and the sides of the bladder are easily squeezed together. 23. And again, when working a pair of bellows, it is the resistance of the air which we have to overcome by the force of the arms, which constitutes the labor of working the bellows ; and if the nozzle of the bel- lows is stopped up, we presently find that it is impos- sible to go on working the bellows any longer, because having forced in as much air as it can hold, the natu- ral tendency of the air to resist compression prevents any more from entering. 24. Although we are so forgetful of the very exist- ence of the air, it is of the greatest importance to all our daily occupations, and even to life itself. With- out air nothing could burn; we could have neither COMBUSTION. 35 fires nor lights ; and, indeed, without air neither ani- mals nor plants could live, for it is just as essential to the life of animals as it is to the growth of plants and the burning of coals and candles. 25. If a lighted candle is put into a large glass bot- tle, and the mouth of the bottle is then stopped up, the candle soon gets dim, and in a short time goes out : the air is no longer able to keep it alight. If we put a second lighted candle into the bottle it will go out immediately. Were a living animal substitut- ed for the lighted candle, after living for a certain time in a confined portion of air, it would die, and a second animal placed in the air would immediately expire. 26. The question now will naturally arise : Is the whole of the air, then, spoiled or used up ; and if it is, why does not fresh air enter the bottle and supply its place? The truth is, only a small portion, about one- fifth of the bulk of the air, is able to feed the flame of a candle; the remainder, which cannot feed flame nor the life of an animal, is of a different kind from the air which can ; and we find that the common air which we breathe is a mixture of two kinds of air, or GAS, as it is called by chemists ; — the one kind, which we might call good air, which supports the life of animals, and is essential to the burning of fires and candles: and the other, or bad air, in which animals cannot live, and which immediately puts out fire and lights. ^7. Chemists call the good air Oxygen, and the 36 OXYGEN — NITROGEN. bad air Nitrogen, or Azote: but we must not suppose that, because the nitrogen appears thus useless, it is really so ; for it is, in fact, of very great importance, as we shall hereafter see. In the experiment just mentioned, of burning the candle in a large bottle, the oxygen is all combined with the elements of the tallow, for which they have a strong affinity, whilst the nitrogen is left unchanged because it cannot com- bine with them ; for the same reason, also, it puts out a fresh-lighted candle plunged into it. 28. Oxygen, when obtained pure, and separate from any other substance, is a gas like common air in its ordinary characters, but remarkable for the very brilliant manner in which all kinds of combus- tible matter burn in it. Oxygen may be breathed with safety, but it causes all the functions of the ani- mal system to be carried on with great vigor and rapidity, so much so, that an animal breathing pure oxygen would be soon destroyed, from the very power- ful effect which the gas would have on its organs. Oxygen has a strong affinity for most of the other elements, and combines with them to form a numerous and important series of compounds. 29. Nitrogen, though it resembles oxygen in ap- pearance, yet differs from it very remarkably in chemical characters; it extinguishes flame, and can- not support the combustion of any substance ; it is irrespirable, suffocating animals if they attempt to breathe it pure, and seeming to have very little affi- nity for other elements ; at least under ordinary mv- COMBUSTION. 37 cumstances, it shows very little tendency to combine with them ; under particular circumstances, however, it does form compounds (147, 163), and some of them are very curious and important. Common air consists of one part of oxygen to four parts of nitrogen : it is a mixture, not a compound. 30. When a candle burns, it gradually disappears ; it grows shorter and shorter, and at last, when all the tallow is burnt, the candle goes out ; but we must not therefore suppose that it is utterly destroyed. A change has taken place ; the tallow, or rather its ele- ments, have combined with the oxygen of a portion of air, and two new compounds, one of which is a gas or kind of air, are produced. If we put a piece of salt into water, it will get less and less, and at last will disappear altogether, having wholly dissolved ; but the salt is not destroyed, it is only dissolved in the water. 31. Now we may compare the burning of a candle to dissolving a piece of salt ; for all the solid matter of the candle remains diffused throughout the air, after it is burnt, just as the salt remains dissolved in the water; but with this difference, the salt is dissolved in the water, but not combined with it. The elements of the tallow are dissolved in the air, but they have combined with a quantity of oxygen, because they have a strong affinity or attraction for it. If the solution of salt is left for some time in a warm place, the water evaporates, and we get the salt again vtn- chunged ; but in the case of the candle its elements 4 38 KESULTS OF COMBUSTION. have combined with oxygen, and they cannot be sep- arated again from it except by the action of something which, having a more powerful attraction for the oxy- gen than it has for the elements of the candle, causes it to relinquish them. 32. There are substances which have suflficient attraction for the oxygen to effect this : we cannot get back the tallow, it is true, but we may obtain its elements, or the simple substances of which it was composed. What has been said with regard to the burning of a candle is equally applicable to the burn- ing of wood, coal, or in fact any combustible matter. In all ordinary cases they burn in consequence of their affinity for the oxygen of the air, and they are never destroyed when burnt, for their elements may always afterwards be found combined with oxygen, in the air in which they have been burnt. 33. It must also be remembered that when the candle goes out for want of air, it does not do so because all the oxygen is burnt, but because the elements of the candle having combined with all the oxygen of the air, or, as it were, saturated it, there is no more free oxygen left to keep up the combustion of the candle. 34. The changes occasioned by chemical action fre- quently proceed slowly and quietly, but in many cases, and especially when substances combine together which have a strong affinity for each other, a great deal of heat is given out. Sometimes, as soon as two substances are brought together, they combine di- CARBONIC ACID GAS IN AIR. 39 rectly, and become very hot ; this is the case in the slaking of lime ; but it most usually happens that the mere bringing together of two substances, even though they have an affinity for each other, is not sufficient to cause them to combine. 35. In these cases combination cannot take place until the substances are heated up to a certain point. Thus, charcoal has a strong affinity for the oxygen of the air, yet it cannot combine with it whilst both are cold ; but as soon as a part of the charcoal is heated redhot, combination commences, and this very act evolves so much heat that the surrounding parts of the charcoal soon begin to burn, and thus the com- bustion, or combination of the charcoal with oxygen, continues and increases, until either the charcoal is all burnt, or the oxygen in the surrounding air is saturated with carbon, and therefore unable to cause the combustion any more. 36. The common operation of lighting a fire is a daily illustration of this. The fuel contains carbon, or charcoal, ready to combine with the oxygen of the air, but unable to do so, until, by applying a light to it, we heat a portion up to the point required to com- mence combination : after which the heat given out by the chemical action going on, keeps it alight, and causes the combustion to spread to the surrounding fuel. 37. The atmosphere is composed chiefly of two different gases, called oxygen and nitrogen : but besides this, it also contains a small quantity of a 40 CARBONIC ACID GAS IN AIR. third gas or kind of air, which is not simple, like oxygen and nitrogen, but a compound of charcoal (bj chemists named carbon) with oxygen, and called CARBONIC ACID GAS (108). 38. It is known that all things containing carbon will produce a quantity of this gas whilst burning ; and hence we can have no difficulty in accounting for its presence in the air. Indeed, we might at first sup- pose that it must be always increasing in quantity ; this, however, is not the case, for we always find ex- actly the same quantity in any portion of air that we analyze. The cause of this is, that all plants con- tain substances which have a very strong affinity for carbon, but which cannot combine with it in its solid forms, because they are unable to come in contact with it ; but which, when the carbon has combined with oxygen and become a part of the air, are able, in consequence of their having a more powerful at- traction for it, to seize upon the carbon of the car- bonic acid gas thus difi'used throughout the air and cause it to relinquish the oxygen, with which it was previously combined (697, 708). 39. These facts show us a new use of plants, for we learn that the objects which we have only admired for their beauty, or valued for their utility as pro- ducing articles of food ; that even weeds themselves, and things we usually consider as wholly useless, are all constantly, by the agency of attraction or chemi- cal affinity, decomposing carbonic acid gas, and thus keeping the air in an uniform and healthy state (745). VAPOR IN THE AIR. 41 40. The air then always contains a regular propor- tion of carhonic acid gas, which is constantly pro- duced by the burning of combustibles, and in many other ways, and as constantly decomposed by the action of plants. As we are now only considering the properties and nature of the air, we will, for the present, pass over further consideration of carbonic acid gas, to which we shall shortly return (108) when studying the nature of carbon, and merely mention now that it is of the greatest importance to the life of plants, being the principal source from whence they derive the carbon necessary for their growth. 41. The air always contains dissolved in it some water, or rather vapor, which varies in quantity ac- cording as the air is hotter or colder. When it is hot, a larger quantity of water is evaporated or con- verted into vapor, and dissolved in the air, which in consequence becomes more damp; whilst, on the other hand, when the air becomes cold, the vapor in the air is condensed, returning to the state of water, and the air becomes drier. 42. This, of course, is modijSed according to cir- cumstances; thus, in dry barren countries, where the ground contains but little moisture, the air, when it becomes hot, remains comparatively dry; whilst in moist or swampy countries, under similar circum- stances, the air becomes damp from the abundance of vapor given off; and thus some of the principal differences of climate depend mainly upon the quan- tity of water dissolved in the air. 4* 42 WATER. 43. The solution of water in the air may easily be seen, by observing the steam issuing from the spout of a teakettle. "When the water boils strongly, and there is a large volume of steam coming out of the spout, we observe that just where it comes out, the steam is almost invisible ; at a little distance it be- comes white and cloudy, and when it gets further out into the air it soon disappears and is again invisible. The reason of this is, that hot steam is quite colorless and invisible^ like air ; and it only becomes apparent to us when it is partly cooled by rushing out into the cold air, and therefore is beginning to condense, and it would fall to the ground in a shower of little drops like rain, if it were not dissolved and carried away by the air, as fast as it issues from the teakettle. When a large quantity of steam is quickly cooled, as in escaping from the funnel of a steam-boat, it is con- densed, and falls in the form of water. 44. The quantity of moisture in the air is also ren- dered apparent to us, whenever a cold substance is exposed to it; this cools the vapor in the air so much, that it is condensed and appears again as water, in little drops on the cold surface: thus a bottle of cold water brought into warm damp air, speedily be- comes covered on the outside with dew, or water thus condensed from the air. 45/ The substance next in importance to air is WATER, which exists naturally in three different states: namely, in the solid state as ice; in the fluid state in its ordinary condition; and lastly, as vapor LATENT HEAT. 43 or steam. These three states of water are familiar to every one, but few are aware what causes the great difference between them. 46. When ice is placed before the fire, or exposed to the sunshine, or in any other way warmed, it ab- sorbs heat, it melts and becomes water; and when water is heated, it assumes the form of steam or vapor. The difference between these three forms of water is entirely caused by the quantity of heat they contain ; and we may truly say that water is a com- pound of ice and heat, and that steam is a compound of water and heat. 47. Although this seems very like chemical action, it is really quite different, and must not be confounded with it. Chemical action can only take place between material substances, or those that have weight; now heat is not a substance — it is not a thing we are able to weigh, like all the chemical elements, and conse- quently when it combines with any substance it only alters the appearance and outward characters of that substance, but does not at all change its chemical properties or nature. 48. When heat is thus combined with a substance, it is said to be latent (hidden), which means that it is not sensible to the feel. This will be easily under- stood from a very simple experiment. If we put some water in a kettle on the fire, we find that it will soon begin to feel warm to the hand if immersed in it; the warmth which we then feel is called free or sensible heat: but if we put some ice into the kettle in place 44 LATENT HEAT — STEAM. of water, it will not become warm so soon ; the ice melts, but the water thus formed will remain ice-cold until the whole of the ice is melted, because all the heat supplied to it by the fire is absorbed or combined with the ice in melting; and therefore as the heat so absorbed does not make the melting ice any warmer, it is called latent. When all the ice is melted, the water will begin to get warm. 49. In the same way heat is absorbed, or rendered latent, when water is converted into steam. If a kettle full of cold water is placed on the fire it rapidly beomes hot until it begins to boil ; but as soon as that is the case it remains constant at the same tempera- ture. The fire of course continues to give out as much heat as it did before, but the water does not become any hotter ; the only change is that a small portion of it is converted into steam, and this steam is not apparently any hotter than the boiling water itself was. All the heat of the fire, therefore, be- comes latent, and is combined withr the water in thus changing it into steam. 50. When steam is condensed, all that heat which became latent during its formation, is given out again in the free and sensible form. This fact is well shown in all stills, in which we see how large a quantity of cold water is necessary to cool and condense a com- paratively small quantity of any steam or vapor. If a gallon of water is converted into steam, the steam formed will not be sensibly any hotter than boiling water, yet it contains so much latent heat that, if it is EFFECTS OF HEAT. 45 condensed into the liquid form again, we shall obtain a gallon of boiling hot water, and heat enough will be given out during its condensation to raise seven gallons more of cold water to the boiling point. 51. The very large proportion of heat which steam therefore contains in this latent state, shows why steam is such an excellent means of conveying heat about from place to place, as in the arrangements for warming buildings, heating coppers, &c. It is quite as hot as so much boiling water, and, in addi- tion, has nearly seven times as much heat thus stored up in the latent form, which becomes sensible, how- ever, as soon as it is condensed. 52. The general effect of heat upon substances, whether solid, liquid, or gaseous, is to expand or make them larger ; thus whenever we heat a portion of water or any other fluid, it increases in size : upon this fact the construction of the common thermometer depends, which consists of a bulb and tube containing a certain bulk of mercury, or quicksilver ; when this is heated it becomes larger, and when cooled, the mercury shrinks, or occupies less space than it did before. 53. When a substance expands, or becomes larger, it of course becomes lighter. If ten measures are expanded by heat to eleven, it follows that ten mea- sures of the heated substance must weigh one eleventh less than ten measures of it when cold. For example, air, when heated, becomes lighter, and consequently rises, because, becoming larger, it weighs compara- tively, bulk for bulk, less than the cool air around. 46 WEIGHT OF THE ATMOSPHERE. 54. Air, like water and solid substances, has weight or gravity ; it presses downwards towards the centre of the earth ; and, as the bulk of the air is very great, the whole weight of it pressing on the surface of the globe must be enormous. It is important to dis- tinguish between the weight of air, and the weight of the atmosphere. By means of a light glass globe, an air-pump, and a good pair of scales, we can readily ascertain the weight of a cubic foot of air, and we find that, under ordinary circumstances, it weighs thirty-one grains. 55. The weight of the atmosphere is, however, the accumulated weight of many thousand cubic feet of air, for the air surrounds the earth to a height of many miles, floating upon its surface, and pressing downwards in consequence of its weight or gravity. The weight of the column of air which rests upon any given space or surface, may be known by the use of the barometer : and is found to be about two thousand pounds on the square foot. 56. The barometer consists of a glass tube nearly a yard long, closed at one end, filled with mercury, and inserted in a cup of the same heavy liquid. The height which the mercury stands in the tube, is an exact measure of the weight of a column of air of the same size as the diameter of the tube, but as high as the whole atmosphere. The mercury in the tube being very heavy, presses downwards, and tends to fall in the tube ; but the air without, which also press- es downwards, resting on the mercury in the cup, WEIGHT OP THE ATMOSPHERE. 47 exactly counterbalances the weight of the mercury in the tube, and so keeps it from falling. 57. When from any circumstance the weight of the atmosphere is for a time diminished, it counterbalances a less weight of mercury, and the column of mercury in the tube of the barometer falls ; on the other hand, when the weight of the air increases, the mer- cury rises. These fluctuations in the weight of the air are constantly going on with the changes of the weather, and consequently the barometer is a most valuable instrument, because it renders evident to us the changes in the air, which being invisible we should not otherwise know of. 58. The higher we ascend in the air, either by going up a hill or by means of a balloon, the less weight of air shall we have above us, and consequently the shorter will be the column in the barometer. Hence the use of that instrument in measuring heights. The mercury falls about one inch for every thousand feet as we ascend from the level of the sea. 59. We do not feel the weight of the air at all, because it presses equally in all directions, and com- pletely surrounds us. The weight of a column of air resting on a table four feet square, is about four- teen tons ; but this weight does not press upon the table, it is met by a corresponding pressure upwards, from the air below the table, due to the weight of all the surrounding air. 60. In moving through the air, therefore, we merely displace it, or move it aside ; but as we do not disturb 48 FREEZING OF WATER. this equilibrium, or the equal pressure in all directions, we do not feel its weight. On plunging the hand into a pailful of water, we feel very little of its weight, only in fact that of the small portion which we displace, because it is much heavier than air is ; but if we attempt to lift up the whole pailful, we then feel the weight of the whole bulk of water. 61. Flame seems to ascend in the air ; this is not because heat has any tendency to ascend, but because it expands the surrounding air, makes it larger, and therefore specifically lighter than the cold air is, and the latter, therefore, displaces it and causes it to rise. Hot air, though it rises in the air, nevertheless has weight, though it is not so heavy as cold air. A piece of cork falls through the air towards the surface of the earth, it has weight ; yet the same piece of cork rises upwards through water till it reaches the surface. As the cork does not fall downwards in water, but rises upwards, so heated air ascends in the atmosphere; not because it has no weight or gravity, but merely because, bulk for bulk, it has less weight than the sur- rounding cold air. It is for precisely the same reason that a balloon rises in the atmosphere. 62. It is, in fact, a general rule that, when sub- stances are heated, they expand; when water is heated, it becomes larger and lighter, and consequently rises through the cooler portions above it. Just the re- verse of this happens when substances are cooled; they then become smaller and heavier. 63. There is one remarkable exception to this rule FREEZING OF WATER. 49 in the case of water ; when water is cooled it con- tracts, and this goes on till very near the freezing point ; but then the water begins to expand, and in place of continuing to contract, as all other liquids do, it becomes larger; this leads to a very important result in Nature. When the air above the surface of a lake or pond becomes cold, as towards the end of autumn, it gradually cools the surface of the water ; the upper part becoming cold, shrinks, and conse- quently becomes heavier, it therefore sinks through the warmer "water. This circulation or gradual sinking of the cooled water goes on, if the air continues cold, until the whole of the water is very near freezing, but then it stops ; because if the surface still goes on cooling, the water begins to expand, becoming larger again, and consequently lighter ; the surface, there- fore, gets colder and freezes, whilst the lower part of the water remains considerably above the freezing point. If it were not for this curious fact, water would continue to become colder, until the whole of it froze together. 64. In passing from the liquid to the solid state, some substances contract, such as melted lead, for ex- ample, whilst others expand; thus ice-cold water, in freezing, expands very considerably, and therefore ice is even lighter than the water on which it is formed. It is for this reason that ice floats on water, and if the ice did not expand in forming, the curious fact just mentioned would not prevent lakes and ponds from freezing entirely, because the ice, if it contracted in 5 5^ FREEZING OF WATER. forming, would then sink through the water to the bottom, and thus soon cool the whole mass of water. 65. This expansion of water in the act of freezing, takes place with immense force, giving rise to the bursting of water-pipes and vessels full of water, in cold weather. It is often supposed that this effect is occasioned by the thaw, and not by the frost. This is a mistake; the mischief is caused by expansion at the moment of freezing, though we only discover it on the approach of warm weather, when the ice begins to melt. Another, and very important natural result of this power, is the disintegration or breaking up of rocks, stones, and soils by frost, during winter. A few drops of water, in freezing, are able to break asunder the hardest rocks, and this effect year after year, gradually destroys them, causing them to crum- ble down into powder (647). 66. It has already been stated that water is not an elementary or simple substance; it is a compound, and consists of two gases. This fact at first seems incomprehensible, for we can hardly believe it possi- ble that a hard and solid substance like ice, or a weighty fluid like water, is composed of colorless and invisible gas. The difficulty, however, greatly diminishes when we remember that heat alone, with- out adding anything to the weight of ice, converts it into water, and that a little more heat will convert that water into an invisible colorless vapor; for, as has already been said (43), pure hot steam is quite invisible, and only becomes visible to us when partly COMPOSITION OF WATER. 51 Condensed by the contact of the colder air, which deprives it of the heat necessary to keep it in a state of vapor (43, 73). 67. The consideration of these facts makes the com- position of water appear far less wonderful ; for we have little difficulty in believing that steam is com- posed of two gases, and we know that steam, water, and ice, are, chemically speaking, the same. 68. One element of water is oxygen gas (28), that part of the air which is so essential to life and com- bustion : it constitutes eight-ninths of the weight of ice, water, and steam. One thousand parts of water, therefore, consist of 889 parts of Oxygen 111 *' Hydrogen 1000 " Water. 69. The other element, or the remaining one-ninth, is called hydrogen gas, or inflammable air, because it is very combustible, being the basis of the common coal gas used for lighting the streets, and entering into the composition of the inflammable air or fire- damp of mines, and many other combustible sub- stances (82). 70. Water is not, like common air, a mere mixture of two gases: it is a compound, and therefore is quite different in its properties from either of its two ele- ments. The very inflammable gas, hydrogen, having combined with a certain quantity of oxygen, which 62 SEA-WATER. is the great promoter of combustion, forms water, a compound which we always regard as the greatest enemy to fire or combustion. 71. The purest kind of water which occurs naturally is rain-water, for all others, such as spring, river, or sea-water, are more or less contaminated or rendered impure by substances dissolved in them. Thus sea- water contains, along with other matters, a large quantity of common salt, which in some places is pro- cured from it by exposing it in shallow pits to the heat of the sun : this causes the water to evaporate, and leaves the salt behind. 72. The composition of sea-water from different parts of the world is found to vary slightly. The following table shows the composition of 100,000 parts of sea-water from the English Channel. (Schweit- zer.) Water 96,474 Common Salt 2,706 Chloride of Potassium . 76 Choloride of Magnesium 366 Bromide of Magnesium 3 Sulphate of Magnesia . 229 Sulphate of Lime . 140 Carbonate of Lime 3 Iodine .... traces Ammonia traces 100,000 73. Water may be artificially purified by distil- lation; when heated and raised into vapor, all the SPRING-WATER. 53 impurities are left behind, and accordingly condensed steam is perfectly pure water; there are numerous contrivances for thus purifying water. The common still, which consists of a vessel to generate steam in, and a pipe, passing through a tub of cold water, to condense the steam, is a familiar example. 74. This explains why rain-water is much purer than other sorts of water, because when the heat of the sun evaporates water from the surface of the earth, all the impurities which it contains are left behind; and of course when this vapor is cooled and falls down in the form of rain, it must be very nearly pure. 75. Springs, which rise from the ground, always contain earthy matters dissolved in them, which vary in nature and quantity, with the soil through which the springs rise. The presence of these impurities in water in any quantity gives to it that peculiar* character which is termed hardness. Sometimes springs contain a small quantity of iron or sulphur, and other substances, which constitute the many varieties of mineral waters. These matters, like the more common earthy impurities, are all derived from the beds of stone, sand, or clay, through which the springs rise; because the source of all springs is rain-water, which, falling pure from the clouds, becomes contaminated by filtering through the earth, and collects in holes and cavities, or porous beds of sand, constituting springs and wells. 5 54 PHOSPHORIC ACID IN WATER. 76. The quantity of saline and earthy matter in spring-water varies from about 20 grains to 1800 grains in the gallon ; when above 100 grains per gal- lon, it constitutes a mineral water. The average quantity in ordinary spring-water is from 20 to 80 grains. The most common salts are Sulphate and Carbonate of Lime (230), Sulphate, Muriate, and Carbonate of Potash and Soda. 77. Thames-water contains usually from seventeen to twenty-four grains of earthy and saline matter per gallon, and of this at least fifteen grains consist of carbonate of lime. The same quantity of New River water contains about nineteen grains of solid matter, and that of the River Lea nearly twenty-four grains. The chief constitutent in both these waters is also carbonate of lime. 78. The proportion of solid matter is almost al- ways greater in well-water than in that of rivers. A great number of other substances besides those just mentioned are occasionally found in mineral springs; amongst these are silica, alumina, oxides of iron, and manganese, salts of baryta, strontia, magnesia, am- monia, &c. 79. The presence of phosphoric acid in some Vaters has recently been discovered (194). The following analysis of the deep well-water from below the Lon- don clay, shows the presence of a considerable quan- tity of phosphoric acid. Ten gallons of the water contained five hundred and sixty-four grains of saline matter, consisting of HYDROGEN. Carbonate of Soda . 116 Sulphate of Soda . 242 Choloride of Sodium 127 Carbonate of Lime 62 Carbonate of Magnesia . 10 Phosphate of Lime 1 Phosphate of Iron . 2 Silica . . 4 In ten gallons 564^ 55 80. Besides these saline and earthy substances, water always contains atmospheric air dissolved in it. This is essential to the life of fishes, and to the growth of water-plants, which could not exist if they were not thus supplied with common air. 81. Water is essential to the existence of all plants and animals : it constitutes a large proportion of all animal and vegetable substances, it is the principal component of -the blood of animals, and the sap of plants, and is of the greatest importance, as being the means of introducing into their systems many soluble matters, necessary for their healthy growth. 82. Hydrogen, the inflammable element of water, is a substance of considerable interest ; it is true, it is never found in Nature in a pure and separate state, but its compounds are abundant, and some of them very important ; when pure, hydrogen is an invisible transparent gas, like the air; very combustible, burn- ing readily when once inflamed, and remarkable for being so much lighter than common air, that a thin bladder, filled with this gas, would rise through the 56 HYDROGEN. air in the same manner that a bubble of common air rises through water. Balloons are sometimes filled with pure hydrogen gas, but more commonly carbu- retted hydrogen is employed, which, as it consists in great part of hydrogen, is much lighter than common air. 83. The most important of its compounds are water, which is formed by its union with oxygen; ammonia, a gas which it forms by combining with nitrogen; and carburetted hydrogen or coal-gas, an inflammable gas consisting of hydrogen and carbon. The two latter will shortly come under notice (131, 148). 84. As hydrogen is the lightest gas known, it is often employed by chemists as a standard of com- parison in expressing the relative weight of all other gases. By weighing a thin glass glpbe filled with hydrogen, and then having pumped that gas out of it by means of an air-pump, and filled the globe again with any other sort of gas, a second weighing gives us the comparative weight or specific gravity of the gas as compared with hydrogen. Suppose, for ex- ample, that the globe held exactly ten grains of hy- drogen and twenty-five grains of the second gas, then it is plain that the latter is twice and a half as heavy as hydrogen is; or, that taking equal volumes of both, that of the gas would weigh twice and a half as much as the hydrogen would. We should say, then, that the specific gravity of that gas was 2J or 2.5, taking hydrogen as the standard of unity. HYDROGEN. 57 85. The following table shows the weight in grains of several gases which a bottle containing one hundred cubic inches, or about three pints, would hold; and also the specific gravity or relative weight of the same gases compared to hydrogen, and also to common air, as a standard : — Weight in Specific gravity Specific gravity grains of 100 compared to compared to air, cubic inches. hydrogen, taken as 1000. taken as 1000. Hydrogen . . . 2 1,000 69 Common Air . . 31 15,200 1.000 Oxygen .... 34 16,000 1,109 Nitrogen . . . 30 14,000 971 Carbonic Acid Gas 47 22,000 1,520 Ammonia . . . 18 8,500 589 Chlorine . . . 76 36,000 2,470 58 CHAPTER II, CARBON — NITROGEN — SULPHUR — CHLORINE — PHOSPHORUS. 86. We now come to the consideration of an ele- mentary or simple substance, -which has been already more than once alluded to, namely, carbon or charcoal. Carbon is the name applied to the pure element, but common charcoal is so nearly pure, that we may con- sider the two words as meaning the same thing ; it is an essential part of all kinds of fuel or combustible substances, during the burning of which it combines with oxygen, and forms carbonic acid gas, the sub- stance before adverted to as always existing in the atmosphere (37). 87. The forms of carbon which we are accustomed to see, are almost all black, like common charcoal; but this is not the case with all the varieties of car- bon, for we know that the brilliant transparent gem called the diamond, is really pure carbon, there being no chemical difference between that gem and common charcoal. 88. There are many substances in Nature which exist in two or more different states, presenting very dissimilar appearances, but being really chemically COHESION. 59 the same. Thus, chalk and marble are very different looking substances, but they are composed of precisely the same elements ; the difference between them is not caused by heat, like the difference between the three states of water, but is wholly of a mechanical nature. The particles composing a piece of chalk are much smaller than those composing a piece of marble, which are in fact compound particles, consisting of many joined together, and hence a piece of marble appears made of many little grains, whilst chalk is composed of particles so small that we are unable to distinguish them, and therefore appears to be a uni- form substance. 89. The power which holds together the little par- ticles composing the piece of marble or chalk, or any other substance, is called cohesion, and this power varies in strength in different substances ; thus it is far stronger in marble than in chalk, and hence a piece of marble requires a much harder blow to break it, than a piece of chalk. In the same way, we say that the particles composing the diamond are held together more firmly by cohesion than the particles composing a piece of charcoal. Cohesion is, of course, quite independent of chemical attraction, for it holds the different particles of a substance together, con- stituting its mechanical strength ; whilst chemical affinity binds together particles of two different sub- stances, forming a compound substance, but does not in any way affect the strength of the compound to resist mechanical force applied to it. 60 CARBON IN PLANTS. 90. Under common circumstances, carbon is one of the most unchangeable things we know ; neither air, water, nor any of the substances commonly found in nature, have any action upon it ; and hence the prac- tice of charring the lower parts of wooden posts, which are intended to be driven into the ground ; the coat of charcoal thus formed, protects the wood from decay for a much longer period than if not charred (882). When, however, carbon is heated, its chemical affi- nity for oxygen is greatly increased, and it no longer appears to be the unchangeable substance which it is whilst cold. 91. Carbon has been already stated to be a neces- sary element of plants, which, though so various in form and color, are nevertheless composed of very few elements. They consist almost wholly of oxygen, hydrogen, nitrogen, and carbon, which, by combining in different proportions, form all the principal parts of both plants and animals. 92. The greater number of vegetable substances consist whoUyof oxygen, hydrogen, and carbon; whilst animal matters mostly contain, in addition to these three elements, a quantity of nitrogen: some of the compounds of plants, however, resemble animal mat- ter in containing nitrogen. When wood is charred, or decomposed by heat, its elements are separated from each other; the hydrogen and oxygen combine together and form water, whilst the carbon is left behind. When wood is burnt in the open air both its hydrogen and carbon combine with oxygen, caus- COMBUSTION. 61 ing flame; the combination of carbon with oxygen proceeds slowly and steadily, the carbon continuing to glow until all is consumed ; hydrogen, on the other hand, being a gas, mixes and combines with oxygen more rapidly, burning at once, with a flame. 93. All organic substances burn with a flame, and this alone is a proof that they contain hydrogen, because under ordinary circumstances the other ele- ments of vegetable matter could not cause flame ; and whenever the flame is bright, we are sure that it con- tains a good deal of carbon, for the flame of pure hydrogen is very pale indeed, and the brightness of a flame, such as that of a candle, is entirely due to the carbon contained in the tallow, which is burned at the same time with the hydrogen, both combining with oxygen. 94. As the products of the combustion of a candle are carbonic acid gas and water, it would be natural to expect that a cold substance held over the flame of a candle would take from the vapor of water thus formed, the heat necessary to its existence in the state of vapor, and consequently condense it into the fluid form. This is an experiment which may very easily be made, for we have only to hold a cold glass at a little distance above the flame of the candle, and we shall soon find it lined with a fine dew of water condensed in this manner. 95. There are several important facts to be ob- served connected with the combustion of a lamp or candle. The wax, tallow, or other combustible sub- 6 62 FLAME. stance, is undergoing decomposition; and its elements, the combustible substances of which they are com- posed, are combining with the oxygen of the surround- ing air to form new compounds; heat is necessary to both of these two changes, and this heat is evolved by the very changes themselves. 96. When a candle is lighted a portion of the fuel is melted, drawn up by capillary action through the wick, and decomposed and converted into combustible vapor; this vapor burns as its elements combine with the surrounding oxygen, and the heat which re- sults from this chemical action renders the process continuous, by causing the decomposition of fresh portions of the tallow, &c., and the consequent pro- duction of more combustible vapor. 97. In ordinary flame, therefore, several things are necessary: air and heat are of course quite essential. The heat evolved by the flame itself, causes a circu- lation of air (61), provides a sort of natural ventila- tion, and insures a constant supply of fresh air to the burning vapors; on the other hand, this circula- tion of air, by bringing fresh oxygen to the burning combustible vapors, causes the evolution of heat enough to insure the combustion of the fresh vapors, which are about to be given out. 98. Every one knows well how necessary fresh air is to perfect combustion ; the importance of heat is not so evident, though it is really quite as essential. The flame of a candle may be extinguished by a coil of wire, or by bringing a piece of cold metal in • FLAME. 63 contact with its outer edge, and is frequently "snuiFed out" merely in consequence of its being cooled. A candle, moved quickly through the air, flares and smokes, and its combustion becomes im- perfect, because it is cooled. 99. It is a necessary consequence of this fact, that flame cannot pass through a piece of wire-gauze, and the miner's safety-lamp merely consists of a lamp surrounded with a cylinder of wire-gauze. A lamp thus protected, may safely be taken into an explosive mixture of air and carburetted hydrogen, the flame may be put out, the explosive gas may burn within the cylinder, but the flame cannot pass through the wire gauze to set fire to the explosive atmosphere without, because it is too much cooled by contact with the wire gauze. 100. It is evident that the combustion of a flame can only take place on its outside, or at that part at which it is in contact with the air, and, as a necessary consequence of this, it follows that flame is hollow. It is only the outside of the flame of a candle that gives out light, the inside is dark, because no com- bustion is there going on. In a large flame this is easily shown, because, as no combustion is going on, no heat is given out, and consequently the inner part of such a flame is comparatively cool; a small piece of wood or paper may be held in the centre of such a flame, and it will hardly be singed, or a small spoon containing a portion of gunpowder may be 64 SMOKE. placed in the centre of the flame, and the powder ■will not be fired. 101. The wick of a common candle requires con- stant snuflSng, because, being in the very centre of the flame, it is in fact deprived of two necessary conditions to combustion, namely, heat and fresh air ; composition candles with twisted wicks, on the other hand, do not require snuffing, because, as the candle burns, the wick constantly twists outwards towards the edge of the flame; it is thus brought into the hottest part of it, and at the same time is supplied with fresh air, which causes it to burn. 102. Smoke is merely combustible matter which is unable to burn, because it cannot come in contact with free oxygen, or does not reach it till it is too cold to burn. The production of smoke from a fire- place or furnace, may always be prevented, and in so doing a loss of heat is obviated. A great deal is often said about the burning of smoke ; this is a very difficult thing ; it is far more easy to prevent its formation than to burn it when once formed. It requires, however, constant care and attention to prevent the production of smoke ; there is no reason to doubt that at least nine-tenths of the dense black smoke which contaminates the air of large towns might be altogether prevented. 103. Carbon is unable to combine with oxygen at common temperatures; it requires to be heated before it can enter into combination with that substance; but when a compound substance containing carbon is CARBONIC ACID GAS. 65 exposed to the air, it usually happens that, if the other elements which it contains combine with oxy- gen, the carbon also is then able to combine with oxygen, and forms carbonic acid gas. 104. Thus when a plant dies and decays, its ele- ments separate and form new compounds ; but the carbon is not set free in the form of black charcoal — it is slowly combined with oxygen to form carbonic acid gas (767). 105. Hence we see that decay is very like burning, similar effects being produced by both; only that the change which is effected by combustion in a short time, and accompanied with a great deal of heat, is very slowly and gradually effected by decay, very little heat being at the same time evolved. In both cases carbonic acid gas is produced. 106. This explains one great use of decaying vege- table substances in manures ; they, of course, con- tain carbon, which is slowly combining with oxygen, and therefore always supplying the growing plants with carbonic acid gas, which is essential to their growth, as they, being able to decompose it, thus obtain carbon (698, 708). 107. Carbonic acid gas is produced in large quan- tity by the breathing of animals. A constant supply of fresh air is requisite for the support of life, and we know that if an animal is prevented from breath- ing or inhaling fresh air, it will very soon be suffo- cated. The chemical action which goes on in the lungs of an animal, is just the reverse of that which 6* bb ACIDS AND BASES. takes place in the organs of plants : in the latter case, carbonic acid gas in the air is decomposed, and the carbon which it contained is appropriated by the plant; whilst in the lungs of an animal, carbonic acid is formed ; for the oxygen of the air is found, on being expelled from the lungs, to have combined with carbon, and become converted into carbonic acid gas. In fact, the process of breathing is very similar to that of combustion, the same results being produced in either case (605). 108. Carbonic acid gas is invisible and transparent like common air, slightly soluble in water, and re- moj-kable for being much heavier than air, and for extinguishing flame and destroying animal life ; it is called an acid, although it certainly is not acid or sour to the taste, like vinegar and the other common acids we are acquainted with; it will, therefore, be proper, before proceeding any further, to explain why it is called an acid, and in fact what is meant by that term. 109. There exists in Nature a numerous class of substances which are called bases; amongst which are potash, soda, and lime, &c. Now an acid is a sub- stance that has a strong affinity for these bases, and which in combining with one of them forms a neutral compound, possessing none of the properties of either. 110. Some acids are exceedingly sour, and very corrosive substances, like oil of vitriol, and aqua- fortis; but when poured upon a base, such as potash or soda, they combine with it directly, and both the NATURE OF SALTS. 67 acid and the base lose their caustic and corrosive qualities. 111. These compounds of acids and bases are usually called Salts, or saline compounds, and are very numerous ; for there are many acids, and many bases. Most of the acids combine with bases in two or three different proportions, forming sub-salts, neu- tral salts, and acid, or super-salts. In the sub-salts, the proportion of acid is not enough to more than half neutralize the base; in the super-salts it is twice as much as is required to neutralize the base; and in the neutral salts, as the name indicates, the acid and base are combined in single proportionals, or per- fectly equal quantities (139, 141). 112. There is also a great number of salts called double salts: these are compounds of two similar salts; thus there are double sulphates, like alum, the sulphate of alumina and potash (267) ; and double phosphates, like the phosphate of ammonia and mag- nesia (253). These double salts are distinct com- pounds of the salts of which they consist, and possess perfectly different properties from either of their constituents; they may generally be made by merely mixing together solutions of their two components. The number of double salts is very considerable, but there is also an immense number of salts which do not thus combine together. 113. Acids have a curious property of changing certain vegetable colors. The greater number of vegetable blue colors are by acids changed to red, 68 TEST PAPERS. and this property is therefore made use of by the chemist, to detect the presence of a free acid ; for this power of acid ceases immediately, when they are combined with bases : because their powers are then neutralized (110). 114. A very common illustration of this change of color may be seen in the pickling of red cabbage. Every one knows that red cabbages, as they are called, are really dark purple or blue, whilst growing, and they only become red by the action of the acid vin- egar employed in pickling them; the same effect would be produced if any other acid was employed. 115. If now we add to some cabbage thus reddened by acid, a little alkali, either potash, soda, or ammo- nia, or indeed a portion of any base, the color will soon be restored to its original blue ; because the acid is neutralized by the base. And if the base employed be one of the three alkalies, or their car- bonates, such as common pearlash, which is the car- bonate of potash, the solution of cabbage will become green, because free alkalies, and likewise their car- bonates, have the power of turning vegetable blues green. 116. Alkaline solutions have also the property of turning certain vegetable yellows red, such, for ex- ample, as common turmeric ; these tests, as they are termed, are very easily applied, and papers stained with blue or yellow vegetable colors, are consequently most useful indicators of the presence either of free acid, or free alkali, in a solution. CARBONIC ACID GAS. 69 117. Although carbonic acid, being a gas. is not perceptibly sour to the taste, like the strong acids just mentioned, it nevertheless combines with bases, and in so doing neutralizes, or at least weakens to a considerable extent, their caustic properties ; but as it has a far less powerful attraction for bases than most other acids have, it is very easily expelled from compounds containing it, by the action of another acid, which seizes upon the base, and sets the car- bonic acid gas at liberty. 118. "VVe have already spoken of the conversion of chalk into lime by heat, in which process the chalk is decomposed, certain matters being expelled or driven off, and the lime left caustic. Chalk or limestone is a compound of carbonic acid gas and caustic lime, and is called a carbonate of lime (233). 119. The carbonic acid is combined with the lime by so weak an attraction, that heat alone is sufficient to expel the acid, together with a small quantity of water which the chalk always contains. If a piece of chalk is put into some vinegar, or indeed into any sour liquid, the chalk will be decomposed, and the car- bonic acid will bubble through the fluid, until the vine- gar or other acid is fully combined with lime, and its acid powers entirely neutralized. The same will happen with any other carbonate. 120. In consequence of this gas being considerably heavier than common air (85), it frequently collects in caverns, cellars, and other similar situations, and often occasions fatal accidents, suffocating those who 70 CARBONIC ACID. unfortunately enter the places thus filled with car- bonic acid. Its presence in such places in the air, in any quantity, may always be easily ascertained, by letting down a lighted candle into the well or cellar: if the candle continues to burn, we know that there is enough oxygen present to support the life of an animal ; whilst if the candle is extinguished, we are certain that the place is full of carbonic acid gas, and therefore that it must not be entered until the heavy gas has been dispersed by proper ventilation. 121. Carbonic acid is also evolved in large quan- tities during the process of fermentation, and occa- sions the pricking taste and effervescence of cider, bottled ale, and other liquors. Common ale is allowed to ferment in open vessels, so that nearly all the car- bonic acid formed during that process (424) is dis- persed ; but bottled ale being confined in close vessels before its fermentation is completed, much of the carbonic acid evolved subsequently is pent up in the liquor, and escapes from it in innumerable small bubbles, when the cork of the bottle is removed. 122. Carbonic acid, then, is constantly being form- ed in several different ways ; it is produced during the combustion of all substances containing carbon, during the respiration of animals, during the decay of almost all vegetable and animal substances, and during the process of fermentation. It is likewise, in many situations, naturally given out by the earth in large quantities. 123. To counterbalance all these sources of in- CARBONIC ACID. 71 crease, there is only the power of plants already mentioned of decomposing it, by abstracting its carbon and setting free the oxygen again (106, 698, 710, 745). 124. When two substances combine together and form a compound, they unite in definite and invari- able proportions. A given weight of carbon, in burn- ing, always combines with a uniform quantity of oxygen, to produce a certain weight of carbonic acid gas ; and this rule holds good in all cases of chemi- cal combination, for it is one of the distinctions between mixture and combination, that we are able to mix two substances together, in any relative propor- tion we like ; but we are only able to make sub- stances combine in certain fixed proportions. 125. Compounds do not always consist of equal parts of their elements, for they can consist of one part of one element, and one, two, three, or more parts of another element; and, indeed, there can frequently be formed several difi'erent compounds, by the union of two elements in various proportions. When, how- ever, we mix together two substances which can unite together, they always combine in one of these fixed proportions; and if there is more of the one element than is requisite to form the compound, it is left un- altered. 126. Thus we know that every six grains of car- bon, or pure charcoal, require sixteen grains of oxy- gen to burn them perfectly, and convert them into carbonic acid ; and exactly the same quantity will be 72 CARBONIC OXIDE. required whether the carbon is burnt in a few seconds, or slowly combined with oxygen by the gradual pro- cess of decay. If we were to try to combine six grains of carbon with twenty grains of oxygen, we should find that only sixteen grains of the oxygen would combine with the charcoal, and the remaining four grains of oxygen would be left unchanged. 127. When we try to burn charcoal so that it shall get less oxygen than is requisite to convert it into carbonic acid, we find that it is possible to do so, but that the gas produced is not carbonic acid. Carbon and oxygen are able to combine together in more than one proportion ; and consequently, though when carbon is burnt in the air, or where it can get abundance of oxygen, it always forms carbonic acid, yet when burnt so that it cannot combine with a suffi- cient quantity of oxygen to form that gas, it forms a different compound containing less oxygen, which is called carbonic oxide. 128. This compound is a transparent colorless gas, like carbonic acid, and resembles it also in being totally unfit to support animal life; indeed, it appears to be far more dangerous than carbonic acid when taken into the lungs, even though considerably di- luted with common air. It extinguishes flame, as might be expected, but it is itself combustible, burn- ing with a pale blue flame, and at the same time is converted into carbonic acid, in consequence of having acquired more oxygen from the air in which it has burnt. OXALIC ACID. 73 129. We frequently see on the top of charcoal or coke fires a pale blue flame, quite different in appear- ance from the usual bright flame of wood or coal ; this is occasioned by carbonic oxide, which is formed in the midst of the mass of burning fuel, where the carbon, being unable to get enough oxygen to form carbonic acid, produces this gas, which, when it reaches the top of the fuel, meets with fresh air, and combines with a further quantity of oxygen. When, however, a charcoal fire is burning slowly, a quantity of carbonic oxide escapes into the air without being burnt into carbonic acid ; and its poisonous nature is often shown, when persons have foolishly placed a pan of burning charcoal in a close bedroom. The charcoal is not only abstracting the oxygen of the air, and converting it into carbonic acid, which can- not support life, but is also forming quantities of the highly poisonous gas, carbonic oxide, the presence of which in a room, in any considerable quantity, is sure to destroy life. 130. Besides these two compounds of carbon, there is yet a third, intermediate in composition between carbonic oxide and carbonic acid, though very differ- ent from either in its properties ; this substance is oxalic acid, a strong, and very poisonous acid. Oxalic acid occurs in many plants, and may be easily form- ed artificially (503); it is a white solid substance, soluble in water, in which it forms a very sour solu- tion ; and has a strong affinity for bases. It has never been formed direct from carbon and oxygen. 7 74 CARBURETTED HYDROGEN. 131. Although when carbon burns in the air it only combines with oxygen, it can, under some cir- cumstances, combine with nitrogen and also hydro- gen. Thus when vegetable matters decay under water, we find that a gas is given off in bubbles which consist of hydrogen and carbon, and is there- fore called carburetted hydrogen. 132. This gas is, as may be supposed, inflamma- ble; burning in the air with a tolerably bright flame, and forming, by the combustion of its two elements, water and carbonic acid. This gas is found in very large quantity in coal mines, where it is called fire- damp, and occasions violent explosions, when a light is incautiously brought into a mixture of it and com- mon air. 133. In these cases the gas is mixed with a quantity of atmospheric air, but the affinity of the carbon and hydrogen, of which it consists, for the oxygen of the air, is not powerful enough to cause combination. "When, however, a lighted candle or lamp is brought into the mixture, that part is immediately raised to the temperature at which combination can take place, the mixture takes fire, the flame spreads with very great rapidity, and in a few seconds the mixed gases are changed from air and carburetted hydrogen, into carbonic acid gas, steam, and nitrogen. At the mo- ment of explosion the gases are very greatly expanded by the heat of the flame, and subsequently they are suddenly condensed, as the steam is cooled and con- verted into water. Carbonic acid and nitrogen alone CARBURETTED HYDROGEN. 75 being left, many of the dreadful accidents which occur in coal mines are less caused by the violence of the explosion, than by the suflfocating effects of the after-damp, as the foul air left in the mines after the explosion is termed. 134. There are also many other compounds of car- bon and hydrogen, in which different proportions of the two elements give rise to a great variety of differ- ent substances: one of the most important of these is the common coal gas, obtained by distilling or roast- ing coals in close iron vessels, and which is used for lighting the streets; it differs from the fire-damp of mines, in containing rather more carbon. India-rub- ber, gutta-percha, coal-tar naphtha, oil of turpentine, &c., are also compounds of carbon and hydrogen. 135. In expressing the composition of any sub- stance, chemists are in the habit of saying that it con- sists of such and such proportions of its elements; whatever quantity they may have taken for analysis, they generally calculate the proportion which a hun- dred or a thousand parts would consist of. Thus, for example, 550 grains of pure carbonate of lime contain 308 grains of lime, and 222 grains of carbonic acid; hence 1000 grains must contain 560 grains of lime, and 440 grains of carbonic acid ; and 100 grains of carbonate of lime contain bQ grains of lime, and 44 grains of carbonic acid. 136. This is a very sini^le example, but it con- stantly happens that the composition of substances is not so easily expressed. 1000 grains of dry gypsum, or sulphate of lime, consist of 412 grains of lime, and 76 DEFINITE PROPORTIONS. 588 grains of sulphuric acid. The composition of 100 grains of such a suhstance is represented thus : — Lime 41.2 Sulphuric Acid . . . . . 58.8 This merely means that one hundred grains contain 41 and two-tenths of a grain of lime, and 58 and eight- tenths of a grain of sulphuric acid : hence there is no real difference whether we put the dot or not : if it is used, the figures behind are known to be fractions ; if not they are whole grains. 137. Sulphate of lime may be expressed either as Lime 0.412 4.12 41.2 412 Sulphuric Acid 0.588 5.88 58.8 588 1 grain. 10 grains. 100 grains. 1000 grains. In all the analyses given in the following pages, no fractions are used ; the composition of everything is given as it would be obtained if 10,000 or 100,000 grains were analyzed. 138. Chemists are constantly in the habit of speak- ing of atoms, proportions, combining numbers, and similar terms ; it will be well briefly to describe what is meant by these words. It has been already stated that the composition of all compound substances is de- finite (124); that a certain weight of carbon, for ex- ample, can only combine with a fixed quantity of oxygen, to form carbonic «-cid (126). 139. Let us observe what relation there exists be- tween the quantity of different substances which can COMBININa WEIGHTS. 77 combine together. It is found that one grain of hy- drogen (for hydrogen, thaugh a gas, can be readily weighed) will combine with eight grains of oxygen, to form nine grains of steam, and this relative propor- tion between the two elements of water is perfectly invariable. One grain of hydrogen can combine with exactly sixteen grains of sulphur, to form seventeen grains of sulphuretted hydrogen (182), a compound shortly to be described, or, with six grains of carbon, to form seven grains of carburetted hydrogen (131). 140. These numbers, then, express the quantity of each of these substances which can combine with one another, for, of course, it is perfectly the same whether we take a grain, an ounce, a pound, or any other weight. But this is not all ; the number thus found for carbon, namely six, is not merely the quantity of that substance which could combine with one of hy- drogen, but represents the quantity of carbon which can combine with eight parts of oxygen, to form car- bonic oxide (127), or twice eight, 16, parts of oxygen to form carbonic acid ; and, again, eight parts of oxygen is not merely the quantity which can combine with one part of hydrogen, or with six parts of carbon, but is exactly the quantity which is able to combine with a definite proportion or equivalent, of any other substance. 141. The numbers which are in this manner ob- tained, are called combining weights, proportionals, equivalents, &c, ; they express the relative proportions in which substances combine together. Some com- 7* 78 COMBINING WEIGHTS. ' pounds consist of a single proportional of each of these elements, but more commonly they contain one of one element, and two, three, or more of the other; of-ganic substances, for the most part, consist of nearly ten or a dozen proportionals of each of their elements (316, 369). 142. The following table shows the proportions or combining weights of the most important simple sub- stances. Oxygen 8 Hydrogen 1 Carbon * 6 Nitrogen . . . . . . . 14 Chlorine 35 Phosphorus 31 Sulphur . . . . . . .16 Iron 27 143. When a compound is formed by the union of two elements, the equivalent or combining proportion of the compound is exactly the sum of the equivalent of its elements; thus, for example, carbonic acid con- sists of one equivalent of carbon, the number of which is 6, and two equivalents of oxygen, weighing 16 ; the sum of 6 and 16, is 22 ; this, then, is the equivalent of carbonic acid, the quantity which will combine with an equivalent weight of any base, for example, with 28 parts of lime, 47 of potash, and so on. 144. In the following table the combining weight of some of the most important compounds is exhi- bited : — NITROGEN. 79 Water . . . . . . .9 Nitric Acid 54 Carbonic Oxide 14 Carbonic Acid 22 Sulphurous Acid 32 Sulphuric Acid .40 Phosphoric Acid 71 Muriatic Acid .*.... 36 Sulphuretted Hydrogen . . . ,17 Carburetted Hydrogen .... 8 Ammonia 17 Potash 47 Soda 31 Lime ^28 Magnesia 20 Silica 46 Alumina .51 Prot-oxide of Iron 35 145. When plants or vegetable substances consist- ing of oxygen, hydrogen, and carbon, decay, their elements form new compounds, the principal of which are carbonic acid and water. We must now consider what are the products resulting from the decay of animal matters, and of those vegetable substances which, like them, consist of oxygen, hydrogen, car- bon, and nitrogen; these are water, carbonic acid, and ammonia. 146. Nitrogen or azote differs from most other substances in appearing to be remarkably inert; it seems to have little or no affinity for any other sub- stance. It is always mixed with oxygen in the air, but it appears to have no inclination to combine with it ; 80 AMMONIA. and when carbon, or substances containing it, are burnt, they combine only with the oxygen, and never with the nitrogen of the air : so that it would appear as if the chief use of nitrogen in the air was to dilute the oxygen, and prevent it from combining too ra- pidly with carbon, and other substances. 147. Under some circumstances, however, nitrogen does combine with other elements, and its compounds are amongst the most curious and important sub- stances we know. When animal or vegetable matters containing nitrogen decay, we find that it, like the carbon, is not set free in its simple and uncombined form, but that during decay it combines with a por- tion of hydrogen. 148. Therefore, in addition to water and carbonic acid, the two principal substances arising from the decay of ordinary vegetable matters, we find a pun- gent, strong-smelling gas, composed of nitrogen and hydrogen, which is called Ammonia. 149. This substance, though a transparent invisible gas, is, like potash and soda, a base; like them it has a strong affinity for acids, and when combined with them neutralizes their powers; and, therefore, as it is evolved at the same time with carbonic acid, it com- bines with that acid and produces a solid salt, which is called a carbonate of ammonia, just as the com- pound of carbonic acid ns are established. NORRIS'S HAND-BOOK FOR LOCOMOTIVE ENGI- NEERS AND MACHINISTS: Comprising the Calculations for Constructing Locomotives. Manner of setting Valves, &c. &c. By Septimus Norris, Civil and Mechanical Engineer. In One Volume, 12mo., with illus- to'ations • $1.60 I A COMPLETE TREATISE ON TAI^NII-TG, CITRRYING AND EVERY BRANCH OF LEATilER-DRESSING. From the French and from original sources. By Campbell MoRFiT, one of the Editors of the "• Encyclopedia of Chemistry," Author of " Chemistry Applied to the Manufacture of Soap and Candles," and other Scientific Treatises. 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This works contains a Comprehensive System of Calculations for Mill Gearing and Machinery, from the first moving power through the diff"erent processes of Carding, Drawing, Slabbing, Roving, Spinning, and Weaving, adapted to American Machinery, Practice, and Usages. Compendious Tables of Yarns and Reeds are added. Illustrated by large Working-drawings of the most approved American Cotton Machinery. Complete in One Volume, octavo $3.50 This edition of Scott's Cotton-Spinner, by Oliver Byrne, is designed for the American Operative. It will be found intensely practical, and will be of the greatest possible value to the Manager, Overseer, and Workman. THE PRACTICAL METAL-WORKER'S ASSISTANT, For Tin-Plate Workers, Brasiers, Coppersmiths, Zinc-Plate Ornamenters and Workers, Wire Workers, Whitesmiths, Black- smiths, Bell Hangers, Jewellers, Silver and Gold Smiths, Elec- trotypers, and all other Workers in Alloys and Metals. By Charles Holtzappfel. Edited, with important additions, by Oliver Byrne. Complete in One Volume, octavo $4.00 It will treat of Casting, Founding, and Forcing; of Tongs and other Tools; Degrees of Heat and Mauagemnet of Fires; Welding; of Heading and Swa;re Tools; of Punches and Anvils; of Hardening and Tempering; of Malleable Iron Castings, Case Hardening, Wrought and Cast Iron. The management and ma- nipulation of 3Ietals and Alloys, 3Ieltiug and Mixing. The management of Fui^ naces, Casting and Founding with Metallic ^Moulds, Joining and Working Sheet Metal. Peculiarities of the different Tools employed. Processes dependent on the ductility of Metals. Wire Drawing. Drawing Metal Tubes, Soldering. The use of the Blowpipe, and every other known "Metal-Worker's Tool. To the works of Holtzappfel, Oliver Btrne has added all that is useful and peculiax 10 th« American Metal- Worker. 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