Rural Chemistry: An Elementary Introduction to the Science in Its Relation ...

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Preface

The following pages formed the substance of a short series of articles on Chemistry, which originally appeared in the columns of the Gardeners^ Chronicle. The interest which they excited in the readers of that journal has led to their republication 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 a2

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IV PREFACE.

the works of the various authors, who have written on Agricultural Chemistry. As a general rule, care has been taken, as much as possible, merely to give well established facts, or, when doubtful theories are mentioned, to state distinctly that they are more or less problematical.

Contents

PAGK

Introduction ......... vii

Chapter I

Objects of Chemigtry — AflBnity — Nature of combination, and decomposition — The Elements — Air, its properties and composition — Oxygen and nitrogen — Combustion, results of combustion — Carbonic-acid -gas — Water, ice^ and steam — latent beat — composition of crater — Hydrogen 1

Chapter II

Carbon, its different forms^-Cohesion — Combustion and decay — Carbonic-acid-gas, produced by respiration, combustion, fermentation, &c. — Nature of acids — Carburetted bydrogen or fire-damp — Compounds all definite in composition — Carbonic oxide — Nitrogen, combined with hydrogen forms ammonia — Nature and properties of ammonia, nitrogen, and oxygen — Nitric acid — Sulphur, sulphurous acid, sulphuric acid, sulphuretted hydrogen---Chlorine, muriatic acid — Phosphorus^ phosphoric acid 19

Chapter III

Bases — Potash, its properties — Carbonate and nitrate of potash. Gunpowder — Soda, common salt, sulphate, carbonate and nitrate of Soda — Ammonia, its carbonate, sulphate, and muriate — Lime, its nature and compounds, carbonate, sulphate, and phosphate of lime — Magnesia, its carbonate, sulphate, muriate, and phosphate — Alumina, its properties — Alum — Silica or silicic acid — Silicates of potash and soda — Glass — Silicates in the soil, in plants — The metals, their oxides — Iron, its oxides, and sulphuret— Sulphate of iron or green vitriol — Manganese — Metallic salts 43

CONTENTS.

Chapter IV

Organic matter — Vegetable substances-— Lignin, or woody fibre- Starch, varieties of starch — Gum, soluble, and insoluble — Sugar, Cane sugar and Grape sugar — Gluten and albumen — nature, properties, and composition of these substances- Vegetable acids. Oils, Resins, Gum-resins, and colouring matters — Chemical Changes — Fermentation — Inorganic constituents of plants, ashes of plants — Animal substances— Albumen, Fibrin, Blood, and Muscle — Gelatin— Fat — Bones, teeth, horn, &c. — Composition of Animal substances — Food of animals . 75

Chapter V

The food of plants — Substances di-rived from the air — Sources of oxygen, hydrogen, nitrogen, and carbon— Substances derived from the soil — Sources of earthy substances — Composition of soils, their formation — Decomposition of silicates — Mechanical structure of soils — The saline constituents of soils — ^Organic . matters in soils, humus, humic acid, their use in soils— Ger^ miuation— Moisture, air and warmth — Influence of light-^ Office of the leaves — Roots — Formation of organic matter — Flowers, fruit, seeds — Organic, and organised matter — Vitality of embryo — Nature of seeds— Earthy substances in plants — Effects of climate — Action of plants on the air . . 93

Chapter VI

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 niauui-e — Liquid manure — Animal excrements, guano — Modes of .fixing ammonia, by acids, by gypsum, &c. — Strong manures — Bones — Vegetable manures — Wood ashes — Green manures — Inorganic manures — Lime, chalk, marl, shell sand — Gypsum — Phosphate of lime — Ashes — Burnt clay — Soot — Gas-liquor — Potash — Alkaline nitrates —Salt 121

Appendix

Composition of substances — Chemical equivalents* or proportions — Tables of equivalents of simple and compound substances- Composition of the principal varieties of organic matter— Tables of the inorganic constituents of plants — Composition of soils — Salts in sea-watex^-Composition of Guano and Urine . .149

Introduction

No branch of knowledge has made more rapid progress during the last hundred years than chemistry. From being merely a confused collection of marvellous 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 which 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, their nature, properties, 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 chemical principles. Hence, a knowledge of this science enables us more

VIU INTRODUCTION.

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 yalue, 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 eyery one of them owes, more or less directly, its present improved condition to the labours of the chemist. Such being the case, it becomes 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 labours 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 attractive 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 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

INTRODUCTION. IX

chemistry of the metals was studied and investigated, long before the nature and properties of vegetable and animal substances were examined. The labours of the alchemists brought to light many valuable discoveries respecting the uses, nature, and properties of earthy and metallic substances ; 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 agricultural chemistry. It is true that before his time there had been many careful and accurate observers, and multitudes of laborious and valuable experiments had been made on plants, by such men as Van Helmont — Evelyn — Boyle — Hales^ and others ; but before the time of Priestley, and his contemporaries, Ingenhousz and Bonnet, little progress had been made in studying the chemical changes on which the growth of plants depends. We are indebted to Hales for much curious information 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

X INTRODUCTION.

efFects of yarious 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 discoYeries. 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 contains 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 composition of vegetable substances was carefully investigated, new modes of analysis were discovered, and an immense mass of curious and useful facts was collected. A great number of chemists occupied themselves with researches in Vegetable Chemistry, but 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

INTRODUCTION, XI

left very nearly in the same state which the experiments of Priestley and Ingenhonsz had brought them to.

At the end of the last oentnry, and in the commencement of the present. Organic Chemistry made rapid advances ; the labours of Humboldt, Berzelius, Saussure, Sennebier^ Einhof, and Dayy, contributed to throw light on many parts of the subject ; whilst the investigations of Gay-Lussac, Hatchett, Lampadius, Lavoisier, Marcet, Prout, Thomson, Yauquelin, Th^nard, 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 was, I believe, J. G. Wallerius, who, in 1754, published a book on the Cause of Fertility. He was succeeded by several other authors, amongst whom ought to be mentioned Gyllenborg, Einhof, and Dundonald ; but the speculations of these authors (though ingenious), were for the most part crude and incomplete. At the commencement of the present century, when Organic Chemistry was rapidly advancing, Berzelius and Davy endeavoured to apply the conclusions to be derived from chemical ex* periments^ 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

Xll INTRODUCTION.

they anticipated, it must be remembered that they were amongst the first to take the subject up, and that though they did so under far more favourable circumstances 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 analyses 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, Ghevreul, Colin, ChaptaU Dumas, Edwards, and Payen^ in France ; and of Daubeny, Johnson, Pepys, Turner, and Christison, in our own country, deserve especial mention.

Intimately connected with the progress of Vegetable

INTRODUCTION. Xlll

Chemistry, is the study of Vegetable Physiology ; 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 their organs ; and, on the other hand, the most complete knowledge of the anatomy of yegetables, could never lead any one to sound and correct conclusions respecting the nutrition of plants. It is rather to be regretted that both Chemists and Physiologists have appeared to avoid availing themselves of the advantages which both might have derived by studying the results which the others had obtained ; it is only by comparing together the observations of both that correct conclusions can be formed. The observations made by the older physiologists, like those of their chemical contemporaries, were mostly imperfect, and the deductions they formed were, in consequence, very frequently erroneous ; the modes of examination^ and the instruments which they employed, were far less perfect than those which have been used in more recent times. Nevertheless, the observations recorded by Grew, Malpighi, and Duhamel, are of considerable value; they maybe said indeed to have laid the foundation of Vegetable Physiology. As the study of Botany itself advanced, greater care was be-

XIV INTRODUCTION.

Bio wed in examining the structure and anatomy of plants, and from the labours of many zealous and careful observers, there has resulted a tolerably complete system of Vegetable Physiology. In recent years, Decandolle, Brongniart, Decaisne,Dutrochet, and Mirbel, in France; Link, Mohl, Meyen, and Schleiden, 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 moisture, have also been studied ; especially by Daniell and Boyle in our own country.

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 experiments 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 had been done since tjie 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

INTRODUCTION* XY

had not employed the only real mode of getting at the truth, namely, well selected and carefully performed experiments. 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 eyidenoe the simple chemical rules which regulate the growth of plants.

Although the experiments of Priestley and Ingenhousz had shown that plants possess the power of decomposing Carbonic Acid, and although they had advanced numerous arguments to prove that plants derive the carbon which they contain from the decomposition of that gas ; yet this doctrine, although admitted by many physiologists, was by no means universally believed by chemists. Few experiments, mdeed, were made to shew that this explanation 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 examined by Liebig, and the results of his investigation have shown, that the old views put forth by Priestley and Ingenhousz, were in truth correct.

INTRODUCTION.

It has long been known^ that plants consist of Carbon, Oxygen, Hydrogen, and Nitrogen, and also that they invariably contain a small quantity of inorganic, 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 constituent of plants. Improved modes of analysis have established that it always exists in the same proportion, 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 principally, if not wholly, from the air ; they do not absorb it in the free and uncombined form, but they absorb it combined with Hydrogen, in the state of Ammonia. The importance of the earthy substances in plants was, likewise, greatly overlooked formerly. It has been proved, by repeated experiments, that these substances are of the greatest importance in the growth of plants, being quite essential to their developement.

Although much has been done, and although chemists have laboured to remove the perplexities which encom-

INTRODUCTION. ZVU

passed the subject, there is still a very great deal which requires investigation ; many important points are as yet imperfectly, or eyen 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 Agriculture, for whilst many of the fundamental laws of Agricultural Chemistry are still scarcely understood, all attempts to apply them to practice must be incomplete, and liable to error.

The composition of the principal varieties of organic matter is well known ; the substances which, by com^ bining 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 important phenomena which are as yet wholly in the dark. Thus, for example^ the manner in

b

XTUl INTRODUCTION.

which wood is formed, and, indeed, all those natnial operations in which cellular or organised 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 yarious substances employed 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 remoYe from it ; but our knowledge of this part of the subject is very far from being complete, 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 yegetable economy is not yet well understood. Many theoriqa indeed have been formed respecting their use, but very little is positively known on the subject.

Although Agricultural Chemistry is in this imperfect 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 prin-

INTRODUCTION. XIX

ciples which govern the growth of plants, and, consequently, 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 speculations 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 knowledge of Agricultural Chemistry, is connected with the use of manure. If he knows what it is that gives the fertilising 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.

ERRATA.

Page 21, line 28, for " whenever" read " whenever on organic' Page 41, line 12, for ** continuing" rtai "combining."

RURAL CHEM'fStfet'

Chapter I. Combination — Decomposition— Air — Water

1. The object of ChemiBtry is to determine accurately 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 an experiment ; he must try it, and then, if it has been properly conducted, the result 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 repeated 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 unquestionable truths^ the

^ COMBINATION.

latter are plausible coDJectures, 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 endeavours to ascertain the cause of the offsets ;he has'.bi^eSi: stiodying. He selects the most probable 'Explanation', 'an*d adopting it as a theory or view, to be /Co^/ioiediccr dt3irtOye<£ 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 result of thousands of experiments 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 affinity for each other. As a familiar example of what then happens, we may take the common process of soap-boiling. When an alkaline or caustic ley is boiled ynth tallow or fat, soap is formed. The alkali which is contained in the ley has an attraction for the fat ; the two become thoroughly mixed, and combine or unite together, and form a new substance, quite different from either the fat or the alkali, which new substance is called soap.

CHEMICAL AFFINITY. O

4. This kind of action is quite distinct from simple mixture. When we mix together two substancessuch as, for example, brown sugar and sand — no change takes place, 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 different 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 separation. In the case of the soap just mentioned, 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 halfway, between those of its two components.

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 ;

b2

4 DECOMPOSITION.

the lime combines with a quantity of water, and when it has cooled, we find that the lime is much altered, having lost its strong caustic properties, and become mild or slaked.

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, however, 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 different 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 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 decomposed, when, by burning or heating it in a very hot fire, all the water, or whatever else it contains^ which can be roasted out by fire, is driven ofi^, and the lime only remains. (74.)

10. The decomposition of a substance is also effected 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 hi ; but if we add to a solution of soap in water an3rthing

THE ELEMENTS. 5

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 haye 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 yinegar combines with the alkali of the soap. This kind of change is always going on when anything decays or putrifies^ and therefore is of considerable interest in connexion with manures.

11. It is a yery common saying that there are four elements, abr, earth, fire, and water ; and many people belieye that all things are composed or made up of these four elements. This is yery incorrect, because there are many substances which do not contain any of these so-called dements ; 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.

12. 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 analyse, or pull to pieces, different substances, till at last we find that we axe unable to separate or decompose them any farther,—- and the substances

6 AIR.

which then remain are called elements, or simple substances.

13. There are upwards of fifty 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. We will commence with those substances which are of the greatest importance, whether simple or compound, and gradually go through them, before entering upon the chemistry of vegetation. Foremost in importance, of the substances whose properties we ate about to study, stands the air.

14. We are too apt to think of the air as being merely empty space ; We move about through it without feeling any resistance, and from its being invisible and totally unlike anything else we know, many forget 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.