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^S"] 
 
ELEMEI^TS 
 
 AGEICULTTJKAL CHEMISTKY 
 
ELEMENTS 
 
 AGEICULTUEAL CHEMISTRY 
 
 THOMAS AJ^TDERSON, 
 
 F.R.B.E., P.C.S. 
 
 PROFESSOR OF CHEMIBTBT IN THE DNIVERSITT OF GLASGOW, AND 
 
 CHEMIST TO THE HIGHLAND AND AGRICULTURAL 
 
 SOCIETY OF SCOTLAND. , 
 
 EDINBURGH: 
 
 ADAM AND CHARLES BLACK. 
 
 1860, 
 
s 
 
 5§S" 
 A 55 \ 
 
 374426 
 
 ERRATUM. 
 Page 190, line 11, for "gallon" read "ton.' 
 
 r'RINTED BT n. AND K. CLARK, EDlNuUKOH. 
 
PREFACE. 
 
 The object of the present work is to offer to the 
 farmer a concise outline of the general principles of 
 Agricultural Chemistry. It has no pretensions to be 
 considered a complete treatise on the subject. On 
 the contrary, its aim is strictly elementary, and with 
 this view I have endeavoured, as far as possible, to 
 avoid unnecessary technicalities so as to make it intel- 
 ligible to those who are unacquainted with the details 
 of chemical science, although I have not hesitated to 
 discuss such points as appeared essential to the proper 
 understanding of any particular subject. 
 
 The rapid progress of agricultural chemistry, and 
 the numerous researches prosecuted under the auspices 
 of agricultural societies and private experimenters in 
 this and other countries, render it by no means an easy 
 task to make a proper selection from the mass of facts 
 
 8213- 
 
PREFACE. 
 
 which is being daily accumulated. In doing this, 
 however, I have been guided by a pretty iutimate 
 knowledge of the wants of the farmer, which has in- 
 duced me to enlarge on those departments of the 
 subject which bear more immediately on the every- 
 day practice of agriculture ; and for this reason the 
 composition and properties of soils, the nature of 
 manures, and the principles by which their applica- 
 tion ought to be governed, have been somewhat 
 minutely treated. 
 
 In all cases numerical details have been given as 
 fully as is consistent with the Umits of the work; and 
 it may be right to state that a considerable number 
 of the analyses contained in it have been made in my 
 own laboratory, and that even when I have preferred to 
 quote the results of other chemists, they have not un- 
 frequently been confirmed by my own experiments. 
 
 Univeksity of Glasgow, 
 1st November 1860. 
 
CONTENTS. 
 
 Page 
 
 Introduction .... .1 
 
 CHAPTER I. 
 
 The Organic Constituents op Plants. 
 
 Carbon... Carbonic Acid. ..Hydrogen. ..Nitrogen. ..Nitric Acid... 
 Ammonia.. .Oxygen. ..Sources whence obtained. ..The At- 
 mosphere. ..The Soil. ..Source of the Inorganic Constituents 
 of Plants... Manner in which the Constituents of Plants are 
 absorbed ... 8 
 
 CHAPTER n. 
 
 The Proximate Constituents of Plants. 
 
 The Saccharine and Amylaceous Constituents... Cellulose... 
 Incrusting Matter. ..Starch. ..Lichen Starch. ..Inuline... 
 Gum. ..Dextrine. ..Sugar... Mucilage. ..Pectine and Peotic 
 Acid.. .Oily or Fatty Matters. ..Margaric, Stearic, and Oleic 
 Acids. ..Wax. ..Nitrogenous or Albuminous Constituents 
 of Plants and Animals. .. Albumen. ..Fibvine... Casein... 
 Diastase ... . 40 
 
 CHAPTER HI. 
 
 The Changes which take place in the Food of 
 Plants during their Growth. 
 
 Changes occurring during Germination. ..Changes daring the 
 After-Growth of the Plant. ..Decomposition of Carbonic 
 Acid. ..Decomposition of Water. ..Decomposition of Am- 
 monia. ..Decomposition of Nitric Acid 54 
 
VI • CONTENTS. 
 
 CJHAPTER IV. 
 
 The Inorganic Constituents of Plants. 
 
 The Amount of Inorganic Matters in Different Plants. ..The 
 Relative Proportions of Ash in the Different Parts of 
 Plants. ..Influence of the Nature of the Soil on the Propor- 
 tion of Mineral Matters in the Plant. ..The Composition of 
 the Ashes of Plants. ..Classification of Different Plants 63 
 
 CHAPTER V. 
 
 The Soil — Its Chemical and Physical Charactees. 
 
 The Origin of Soils... Composition of Crystalline and Sedimen- 
 tary Rooks. ..their Disintegration. ..Chemical Composition 
 of the Soil... Fertile and Barren Soils. ..Mechanical Texture 
 of Soils.. .Absorbent Action of Soils.. .their Physical Cha- 
 racters... Relation to Heat and Moisture. ..The Subsoil... 
 Classification of Soils . 83 
 
 CHAPTER VI. 
 
 The Improvement of the Soil- by Mechanical 
 Processes. 
 
 Draining. . .Its Advantageous Effects. . . Subsoil and Deep Plough- 
 ing.. .Improving the Soil by Paring and Burning. ..Warp- 
 ing. ..Mixing of Soils. ..Chalking . . . 137 
 
 CHAPTER VII. 
 The Genekal Principles of Manuring. 
 
 Fundamental Principles upon which Manures are applied... 
 Special and General Manures. ..Importance of this dis- 
 tinction. ..Views regarding the Theory of Manures. ..Re- 
 marks on Special Manures. ..Action of Manures on the 
 Chemical and Physical Properties of a Soil... Remarks on 
 the Application of Manures . 152 
 
CONTENTS. VU 
 
 Page 
 
 CHAPTER VIII. 
 The Composition and Properties of Farm-yard 
 AND Liquid Manures. 
 
 Farm-yard Manure . . . Urine . . . Composition of . . . Duag. . .Com- 
 poBition of... Farm yard Manure... Composition of.. .Man- 
 agement of Dung-Heaps. ..Box-feeding. ..Fermentation and 
 application of Manure... Liquid Manure... Composition and 
 application of.. .Sewage Manure. ..Its composition and ap- 
 plication ... . . 166 
 
 CHAPTER IX. 
 
 The Composition and Properties of Vegetable 
 
 Manures. 
 
 Rape-Dust, Mustard, Cotton and Castor Cake. ..Composition of 
 various Oil-Cakes... Malt-Dust, Bran, Chaff, etc.. ..Straw 
 and Sawdust. ..Manuring with Fresh Vegetable Matter... 
 Green Manuring. ..SearWeed... Composition of various Sea- 
 Weeds. ..Leaves. ..Peat . . . 196 
 
 CHAPTER X. 
 
 The Composition and Properties of Animal 
 
 Manures. 
 
 Guano, different varieties of...Avei'age composition of... Division 
 into Ammoniacal and Phosphatic... Characters of...Adulter- 
 tion of... Application of.. .Pigeons' Dung.. .Urate and Sul- 
 phated Urine, ..Night-Soil and Poudrette...Hair, Skin, 
 Horn, Wool, etc.... Blood... Fish... "Fish-Guano"— Bones . 204 
 
 CHAPTER XL 
 
 The Composition and Properties of Mineral 
 
 Manures. 
 
 Mineral Manures. ..Sulphate and Muriate of Ammonia.. .Sulpho- 
 rauriate of Ammonia... Ammoniacal Liquor. ..Nitrates of 
 
CONTENTS. 
 
 Page 
 
 Potash and Soda.. .Muriate and Sulphate of Potash... Chlo- 
 ride of Sodium, or Common Salt. ..Carbonates of Potash 
 and Soda.. .Silicates of Potash and Soda... Sulphate of Mag- 
 nesia. ..Phosphate of Lime. ..Bone-ash. ..Coprolites... Apa- 
 tite... Sombrero Guano. ..Superphosphates and Dissolved 
 Bones. ..Biphosphate of Lime or Soluble Phosphates. ..Phos- 
 pho-Peruvian Guano. ..Lime. ..Chalk. ..Marl. ..Application 
 and Action of Lime on Soils. ..Sulphate of Lime or Gyp- 
 sum . .226 
 
 CHAPTER XII. 
 The Valuation of Manures. 
 
 The Principle on which Manures are valued.. .Its application to 
 different simple and complex Manures... Method of Calcu- 
 lation... General Remarks . . . 255 
 
 CHAPTER Xin. 
 
 The Rotation op Ceops. 
 
 Its necessity explained.. .Quantity of Mineral Matters in the 
 produce of an Acre of Different Crops. ..The Theory of 
 Rotation . . 266 
 
 CHAPTER XIV. 
 The Feeding of Farm Stock. 
 
 The Principles of Feeding... The Composition of different 
 Animals in different stages of Fattening... The Composition 
 of the Food of Animals. ..Milk.. .The Principal Varieties of 
 Cattle Food. ..General Observations on Feeding . . 276 
 
AGKICULTUKAL CHEMISTRY. 
 
 INTRODUCTION. 
 
 That the phenomena of vegetation are dependent on 
 certain chemical changes occurring in the plant, by which 
 the various elements of its food are elaborated and con- 
 verted into vegetable matter, was very early recognised by 
 chemists ; and long before the correct principles of that 
 science were established. Van Helmont maintained that 
 plants derived their nourishment from water, while Sir 
 Kenelm Digby, Hook, Bradley, and others, attributed an 
 equally exclusive influence to air, and enlarged on the 
 practical importance of the conclusions to be deduced from 
 their views. These opinions, which were little better than 
 hypotheses, and founded on very imperfect chemical data, 
 are mentioned by Jethro Tull, the father of modern agri- 
 culture, only to deny their accuracy ; and he contended that 
 the plants absorb and digest the finer particles of the earth, 
 and attributed the success of the particular system of 
 husbandry he advocated to the comminution of the soil, 
 
 B 
 
2 , INTRODUCTION. 
 
 by. which- a larger number of its particles are rendered 
 sufficiently small to permit their ready absorption by the 
 roots. Popular opinion at that time was in favour of the 
 mechanical rather than the chemical explanation of agri- 
 cultural facts, and Tull's work had the effect of confirming 
 this opinion, and turning attention away from the appli- 
 cation of chemistry to agriculture. Indeed, no good results 
 could have followed its study at that time, for chemistry, 
 especially in those departments bearing more immediately 
 on agriculture, was much too imperfect, and it was only 
 towards the close of the last century, when Lavoisier 
 established its true principles, that it became possible to 
 pursue it with any prospect of success. 
 
 Very soon after Lavoisier's system was made known, 
 Lord Dundonald published his " Treatise on the Intimate 
 Connexion between Chemistry and Agriculture," in which 
 the important bearings of the recent chemical discoveries 
 on the practice of agriculture were brought prominently 
 under the notice of the farmer, and almost at the same 
 time De Saussure commenced those remarkable researches, 
 which extended over a long series of years, and laid the 
 foundation of almost all our accurate knowledge of the 
 chemistry of vegetation. Saussure traced with singular 
 care and accuracy the whole phenomena of the life of 
 plants, and indicated the mode in which the facts he 
 established might be taken advantage of in improving the 
 cultivation of the soil. But neither his researches, nor 
 Lord Dundonald's more direct appeal to the farmer, excited 
 the attention they deserved, or produced any immediate 
 
IIMRODUCTION. 3 
 
 effect on the progress of agriculture. It was not till ^;h"e 
 year 1812 that the interest of practical men was fairly- 
 awakened by a course of lectures given by Sir Humphrey 
 Davy, at the instance of Sir John Sinclair, who was at that 
 time president of the Board of Agriculture. In these 
 lectures, written with all the clearness and precision which 
 characterised their author's style, the results of De 
 Saussure's experiments were for the first time presented to 
 the farmer in a form in which they could be easily under- 
 stood by him, the conclusions to which they led were 
 distinctly indicated, and a number of useful practical 
 suggestions made, many of which have been adopted into 
 every-day practice, and become so thoroughly incorporated 
 with it, that their scientific origin has been altogether 
 forgotten. A lively interest was excited by the publica- 
 tion of Davy's work, but it soon died out, and the subject 
 lay in almost complete abeyance for a considerable number 
 of years. Nor could any other result be well expected, 
 for at that time agriculture was not ripe for chemistry, 
 nor chemistry ripe for agriculture. The necessities of a 
 rapidly increasing population had not yet begun to compel 
 the farmer to use every means adapted to increase the 
 amount of production to its utmost limit ; and though the 
 fundamental principles of chemistry had been established, 
 its details, especially in that department which treats of 
 the constituents of plants and animals, were very imper- 
 fectly known. It is not surprising, therefore, that matters 
 should have remained almost unchanged for the compa- 
 ratively long period of nearly thirty years. Indeed, with 
 
4 . INTRODUCTION. 
 
 the- exception of the investigation of soils by Schiibler, 
 and some other inquiries of minor importance, and which, 
 in this country at least, excited no attention on the part 
 of the agriculturist, nothing was done until the year 1840, 
 ■when Liebig published his treatise on Chemistry, in its 
 application to Agriculture and Physiology. 
 
 Saussure's researches formed the main groundwork of 
 Liebig's treatise, as they had before done for Davy's ; but 
 the progress of science had supplied many new facts 
 which confirmed the opinions of the older chemists in most 
 respects, and enabled Liebig to generalise with greater 
 confidence, and illustrate more fully the principles upon 
 which chemistry ought to be applied to agriculture. Few 
 works have ever produced a more profound impression. 
 Written in a clear and forcible style, dealing with scientific 
 truths in a bold and original manner, and producing a 
 strong impression, as well by its earnestness as by the 
 importance of its conclusions, it was received by the 
 agricultural public with the full conviction that the 
 application of its principles was to be immediately followed 
 by the production of immensely increased crops, and by a 
 rapid advance in every branch of practical agriculture. 
 The disappointment of these extravagant expectations, 
 which chemists themselves foresaw, and for which they 
 vainly attempted to prepare the agriculturist, was followed 
 by an equally rapid reaction ; and those who had embraced 
 Liebig's views, and lauded them as the commencement of 
 a new era, but who had absurdly expected an instantaneous 
 efiect, changed their opinion, and contemned, as strongly 
 
I»TEODUCTION. O 
 
 as they had before supported, the application of chemistry 
 to agriculture. 
 
 That this effect should have been produced is not 
 unnatural ; for practical men, having at that time little 
 or no knowledge of chemistry, were necessarily unable to 
 estimate its true position in relation to agriculture, and 
 forgetting that this department of science was still in its 
 early youth, and burthened with all the faults and errors 
 of youth, they treated it as if it were already perfect in all 
 its parts. Neither could they distinguish between the 
 fully demonstrated scientific truths, and the uncertain, 
 though probable conclusions deduced from them ; and when 
 the latter, as occasionally happened, proved to be at 
 variance with practice, it is not surprising that this should 
 have produced a feeling of distrust on the part of persons 
 incapable, from an imperfect, and still oftener from no 
 knowledge of science, of drawing the line of demarcation, 
 which Liebig frequently omitted to do, between the positive 
 fact and the hypothetical inference, which, however probable, 
 is, after all, merely a suggestion requiring to be substantiated 
 by experiment. This omission, which the scientific reader 
 can supply for himself, becomes a source of serious mis- 
 apprehension in a work addressed to persons unacquainted 
 with science, who adopt indiscriminately both the facts 
 and the hypotheses of the author. And this is no doubt 
 the cause of the very different estimation in which the 
 work of the Giessen Professor was held by scientific and 
 practical men. 
 
 Liebig's treatise was followed, in the year 1844, by 
 
b . INTKODUCTION. 
 
 the publication of Boussingault's Economie Rurale, a -work 
 wliich excited at the time infinitely less interest than 
 Liebig's, although it is really quite as important a contri- 
 bution to scientific agriculture. It is distinguished by 
 entering more fully into the special details of the appli- 
 cation of chemistry to agriculture, and contains the results 
 of the author's numerous researches both in the laboratory 
 and the field. Boussingault possesses the qualification, at 
 present somewhat rare, of combining a thorough knowledge 
 of practical agriculture with extended scientific attainments; 
 and his investigations, which have been made with direct 
 reference to practice, and their results tested in the field, 
 are the largest and most valuable contribution to the exact 
 data of scientific agriculture which has yet been made public. 
 The year 1844 was also distinguished by the foundation 
 of the Agricultural Chemistry Association of Scotland, an 
 event of no small importance in the history of scientific 
 agriculture. That association was instituted through the 
 exertions of a small number of practical farmers, for the 
 purpose of pursuing investigations in agricultural chemistry, 
 and affording to its members assistance in all matters con- 
 nected with the cultivation of the soil, and has formed the 
 model of similar establishments in London, Dublin, and 
 Belfast, as well as in Germany; and it is peculiarly credit- 
 able to the intelligence and energy of the practical farmers 
 of Scotland, that with them commenced a movement, which 
 has already found imitators in so many quarters, and con- 
 ferred such great benefits on agriculture. Within the last 
 ten or twelve years, and mainly owing to the establishment 
 
INTBODOCTION. 7 
 
 of agricultural laboratories, great progress has been made 
 in accumulating facts on which to found an accurate know- 
 ledge of the principles of agricultural chemistry, and the 
 number of chemists who have devoted themselves to this 
 subject has considerably increased, though still greatly less 
 than its exigencies require. 
 
 Notwithstanding all that has recently been done, it 
 must not be forgotten that we have scarcely advanced 
 beyond the threshold, and that it is only by numerous 
 and frequently repeated experiments that it is possible to 
 arrive at satisfactory results. Agricultural inquiries are 
 liable to peculiar fallacies due to the perturbing influence 
 of climate, season, and many other causes, the individual 
 effects of which can only be eliminated with difficulty, and 
 much error has been introduced, by hastily generalising 
 from single experiments, in place of awaiting the results of 
 repeated trials. Hence it is that the progress of scientific 
 agriculture must necessarily be slow and gradual, and is 
 not likely to be marked by any great or startling dis- 
 coveries. Now that the relations of science to practice are 
 better understood, the extravagant expectations at one time 
 entertained have been abandoned, and, as a necessary con- 
 sequence, the interest in agricultural chemistry has again 
 increased, and the conviction daily gains ground that no one 
 who wishes to farm with success, can afford to be without 
 some knowledge of the scientific principles of his art. 
 
CHAPTEE I. 
 
 THE ORGANIC CONSTITUENTS OF PLANTS. 
 
 When the water naturally existing in plants is expelled 
 by exposure to the air or a gentle heat, the residual dry 
 matter is found to be composed of a considerable number 
 of different substances, which have been divided into two 
 great classes, called the organic and the inorganic, or 
 mineral constituents of plants. The former are readily 
 combustible, and on the application of heat, catch fire, 
 and are entirely consumed, leaving the inorganic matters 
 in the form of a white residuum or ash. All plants con- 
 tain both classes of substances ; and though their relative 
 proportions vary within very wide limits, the former always 
 greatly exceed the latter, which in many cases form only 
 a very minute proportion of the whole weight of the plant. 
 Owing to the great preponderance of the organic or com- 
 bustible matters, it was at one time believed that the 
 inorganic substances formed no part of the true structure 
 of plants, and consisted only of a small portion of the 
 mineral matters of the soil, which had been absorbed along 
 with their organic food ; but this opinion, which probably 
 was never universally entertained, is now entirely aban- 
 doned, and it is no longer doubted that both classes of sub- 
 stances are equally essential to their existence. 
 
 Although they form so large a proportion of the plant, 
 
OKGANIC CONSTITUENTS OF PLANTS. 9 
 
 its organic constituents are composed of no more than four 
 elements, viz : — 
 
 Carbon. Nitrogen. 
 
 Hydrogen. Oxygen. 
 
 The inorganic constituents are much more numerous, 
 not less than thirteen substances, which appear to be 
 essential, having been observed. These are — 
 
 Potash. 
 
 Silicic Acid. 
 
 Soda. 
 
 Phosphoric Acid. 
 
 Lime. 
 
 Sulphuric Acid. 
 
 Magnesia. 
 
 Chlorine. 
 
 Peroxide of Iron. 
 
 
 more rarely 
 
 
 Manganese. 
 
 Bromine. 
 
 Iodine. 
 
 Fluorine. 
 
 Several other substances, among which may be mentioned 
 alumina and copper, have also been enumerated ; but there 
 is every reason to believe that they are not essential, and 
 the i-ases in which they have been found are quite excep- 
 tional. 
 
 It is to be especially noticed that none of these sub- 
 stances occur in plants in the free or uncombined state, 
 but always in the form of compounds of greater or less 
 complexity, and extremely varied both in their properties 
 and composition. 
 
 It would be out of place, in a work like the present, to 
 enter into complete details of the properties of the ele- 
 ments of which plants are composed, which belongs strictly 
 to pure chemistry, but it is necessary to premise a few 
 observations regarding the organic elements, and their 
 more important compounds. 
 
10 .AttRICULTUKAL CHEMISTRY. 
 
 Carbon. — When a piece of wood is heated in a close 
 vessel, it is charred, and converted into charcoal. This 
 charcoal is the most familiar form of carbon, but it is not 
 absolutely pure, as it necessarily contains the ash of the 
 wood from which it was made. In its purest form it 
 occurs in the diamond, which is "believed to be produced 
 by the decomposition of vegetable matters, and it is there 
 crystallized and remarkably transparent ; but when pro- 
 duced by artificial processes, carbon is always black, more 
 or less porous, and soils the fingers. It is insoluble in 
 water, burns readily, and is converted into carbonic acid. 
 Carbon is the largest constituent of plants, and forms, in 
 round numbers, about 50 per cent of their weight when dry. 
 
 Carbonic Acid. — This, the most important compound 
 of carbon and oxygen, is best obtained by pouring a 
 strong aciil upon chalk or limestone, when it escapes with 
 effervescence. It is a colourless gas, extinguishing fame, 
 incapable of supporting respiration, much heavier than 
 atmospheric air, and slightly soluble in water, which 
 takes up its own volume of the gas. It is produced abun- 
 dantly when vegetable matters are burnt, as also during 
 respiration, fermentation, and many other processes. It is 
 likewise formed during the decay of animal and vegetable 
 matters, and is consequently evolved from dung and com- 
 post heaps. 
 
 Hydrogen occurs in nature only in combination. Its 
 principal compound is water, from which it is separated by 
 the simultaneous action of an acid, such as sulphuric acid 
 and a metal, in the form of a transparent gas, lighter than 
 any other substance. It is very combustible, burns with 
 a pale blue flame, and is converted into water. It is found 
 in all plants, although in comparatively small quantity, 
 for, when dry, they rarely contain more than four or five per 
 
ORGANIC CONSTITUENTS OF PLANTS 11 
 
 cent. Its most important compound is water, of which it 
 forms one-ninth, the other eight-ninths consisting of oxygen. 
 
 Nitrogen exists abundantly in the atmosphere, of which 
 it forms nearly four-fifths, or, more exactly, 79 per cent. 
 It is there mixed, but not combined with oxygen ; and when 
 the latter gas is removed, by introducing into a bottle of 
 air some substance for which the former has an afSnity, 
 the nitrogen is left in a state of purity. It is a transparent 
 gas, which is incombustible, and extinguishes flame. It 
 is a singularly inert substance, and is incapable of directly 
 entering into union with any other element except oxygen, 
 and with that it combines with the greatest difficulty, and 
 only by the action of the electric spark — a peculiarity which 
 has very important bearings on many points we shall 
 afterwards have to discuss. Nitrogen is found in plants 
 to the extent of from 1 to 4 per cent. 
 
 Nitric Acid. — This, the most important compound of 
 nitrogen and oxygen, can be produced by sending a current 
 of electric sparks through a mixture of its constituents, 
 but in this way it can be obtained only in extremely small 
 quantity. It is much more abundantly produced when 
 organic matters are decomposed with free access of air, 
 in wliich case the greater proportion of their nitrogen 
 combines with the atmospheric oxygen. This process, 
 which is known by the name of nitrification, is greatly 
 promoted by the presence of lime or some other substance, 
 with which the nitric acid may combine in proportion as 
 it is formed. It takes place, to a great extent, in the soil 
 in India and other hot climates ; and our chief supplies of 
 saltpetre, or nitrate of potash, are derived from the soil in 
 these countries, where it has been formed in this manner. 
 The same change occurs, though to a much smaller extent, 
 in the soil in temperate climates. 
 
12 , AGRICULTURAL CHEMISTRY. 
 
 Ammonia is a compound of nitrogen and hydrogen, 
 but it cannot be formed by the direct union of these gases. 
 It is a product of the decomposition of organic substances 
 containing nitrogen, and is produced when they are dis- 
 tilled at a high temperature, or allowed to putrefy out of 
 contact of the air. In its pure state it is a transparent and 
 colourless gas, having a peculiar pungent smell, and highly 
 soluble in water. It is an alkali resembling potash and 
 soda, and, like these substances, unites with the acids and 
 forms salts, of which the sulphate and muriate are the 
 most familiar. In these salts it is fixed, and does not 
 escape from them unless they be mixed with lime, or some 
 other substance possessing a more powerful affinity for the 
 acid with which it is united. 
 
 Oxygen is one of the most widely distributed of all the 
 elements, and, owing to its powerful affinities, is the most 
 important agent in almost all natural changes. It is 
 found in the air, of which it forms 21 per cent, and in 
 combination with hydrogen, and almost all the other che- 
 mical elements. In the pure state it possesses very remark- 
 able properties. All substances burn in it with greater 
 brilliancy than they do in atmospheric air, and its affi- 
 nity for most of the elements is extremely powerful. 
 When diluted with nitrogen, it supports the respiration 
 of animals ; but in the pure state it pr<)ves fatal after the 
 lapse of an hour or two. It is found in plants, in quanti- 
 ties varying from 30 to 36 per cent. 
 
 It is worthy of observation, that of the four organic 
 elements, carbon only is fixed, and the other three are 
 gases ; and likewise, when any two of them unite, their 
 compound is either a gaseous or a volatile substance. The 
 charring of organic substances, which is one of their most 
 characteristic properties, and constantly made use of by 
 
THE ORGANIC COJISTITUENTS OF PLANTS. 13 
 
 chemists as a distinctive reaction, is due to this peculiarity ; 
 for when they are heated, a simpler arrangement of their 
 particles takes. place, the hydrogen, nitrogen, and oxy- 
 gen imite among themselves, and carry off a small quan- 
 tity of carbon, while the remainder is left behind in the 
 form of charcoal, and is only consumed when access of the 
 external air is permitted. 
 
 Now, in order that a plant may grow, its four organic 
 constituents must be absorbed by it, and that this absorp- 
 tion may take place, it is essential that they be presented 
 to it in suitable forms. A seed may be planted in pure 
 carbon, and supplied with unlimited quantities of hydrogen, 
 nitrogen, oxygen, and inorganic substances, and it will not 
 germinate ; and a plant, when placed in similar circum- 
 stances, shows no disposition to increase, but rapidly lan- 
 guishes and dies. The obvious inference from these facts 
 is, that these substances cannot be absorbed when in the 
 elementary state, but that it is only after they have entered 
 into certain forms of combination that they acquire the 
 property of being readily taken up, and assimilated by the 
 organs of the plant. 
 
 It was at one time believed that many different com- 
 pounds of these elements might be absorbed and elaborated, 
 but later and more accurate experiments have reduced the 
 number to four — namely, carbonic acid, water, ammonia, and 
 nitric acid. The first supplies carbon, the second hydrogen, 
 the two last nitrogen, while all of them, with the exception 
 of ammonia, may supply the plant with oxygen as well as 
 with that element of which it is the particular source. 
 
 There are only two sources from which these substances 
 can be obtained by the plant, viz. the atmosphere and the 
 soil, and it is necessary that we should here cbnsider the 
 mode in which they may be obtained from each. 
 
14 AGKICULTUEAL CHEMCSTRY. 
 
 The Atmosphere as a source of the Organic Constituents q/ 
 Plants. — Atmospheric air consists of a mixture of nitrogen 
 and oxygen gases, watery vapour, carbonic acid, ammonia, 
 and nitric acid. The two first are the largest constituents, 
 and the others, though equally essential, are presentin small, 
 and some of them in extremely minute quantity. When 
 deprived of moisture and its minor constituents, 100 
 volumes of air are found to contain 21 of oxygen and 79 
 of nitrogen. Although these gases are not chemically 
 combined in the air, but only mechanically mixed, their 
 proportion is exceedingly uniform, for analyses completely 
 corresponding with these numbers have been made by 
 Humboldt, Gay-Lussac, and Dumas at Paris, by Saussure 
 at Geneva, and by Lewy at Copenhagen ; and similar 
 results have also been obtained from air collected by Gay- 
 Lussac during his ascent in a balloon at the height of 
 21,430 feet, and by Humboldt on the mountain of Antisano 
 in South America at a height of 16,640 feet. In short, 
 under all circumstances, and in all places, the relation 
 subsisting between the oxygen and nitrogen is constant ; 
 and though, no doubt, many local circumstances exist which 
 may tend to modify their proportions, these are so slow 
 and partial in their operations, and so counterbalanced by 
 others acting in an opposite direction, as to retain a uni- 
 form proportion between the main constituents of the 
 atmosphere, and to prevent the undue accumulation of 
 one or other of them at any one point. 
 
 No such uniformity exists in the proportion of the 
 minor constituents. The variation in the quantity of 
 watery vapour is a familiar fact, the difference between a 
 dry and moist atmosphere being known to the most careless 
 observer, and the proportions of the other constituents are 
 also liable to considerable variations. , 
 
ORGANIC CONSTITUENTS OF PLANTS. l5 
 
 Carbonic Acid. — The proportion of carbonic acid in 
 the air has been investigated by Saussure. Prom his 
 experiments, made at the village of Chambeisy, near 
 Geneva, it appears that the quantity is not constant, but 
 varies from 3-15 to 5-75 volumes in 10,000 ; the mean 
 being 4.-15. These variations are dependent on different 
 circumstances. It was found that the carbonic acid was 
 always more abundant during the night than during the 
 day — the mean quantity in the former case being 4-32, in 
 the latter 3-38. The largest quantity found during the 
 night was 5-74:, during the day 5"4. Heavy and continued 
 rain diminishes the quantity of carbonic acid, by dissolving 
 and carrying it down into the soil. Saussure found that 
 in the month of July 1827, during the time when nine 
 millimetres of rain fell, the average quantity of carbonic 
 acid amounted to 5-18 volumes in 10,000; while in Sep- 
 tember 1829, when 254 millimetres fell, it was only 3-57. 
 A moist state of the soil, which is favourable to the absorp- 
 tion of carbonic acid, also diminishes the quantity contained 
 in the air, while, on the other hand, continued frosts, by 
 retaining the atmosphere and soil in a dry state, have an 
 opposite effect. High winds increase the carbonic acid to 
 a small extent. It was also found to be greater over the 
 cultivated lands than over the lake of Geneva ; at the tops 
 of mountains than at the level of the sea ; in towns than in 
 the country. The differences observed in all these cases, 
 though small, are quite distinct, and have been confirmed 
 by subsequent experimenters. 
 
 Ammonia. — The presence of ammonia in the atmo- 
 sphere appears to have been first observed by Saussure, 
 who found that when the sulphate of alumina is exposed 
 to the air, it is gradually converted into the double sulphate 
 of alumina and ammonia. Liebig more recently showed 
 
16 AGKICULTURAL CHEMISTRY. 
 
 that ammonia can always be detected in rain and snow 
 water, and it could not be doubted that it had been ab- 
 sorbed from the atmosphere. Experiments have since been 
 made by different observers with the view of determining 
 the quantity of atmospheric ammonia, and their results are 
 contained in the subjoined table, which gives the quantity 
 found in a million parts of air. 
 
 Kemp 3-6800 
 
 p. ( 12 feet above the surface 3"5000 
 
 ™ \25feet do. do 0-5000 
 
 Graeger 03230 
 
 ("By day 00980 
 
 ". By night 0-1690 
 
 TMaximum 0-0317 
 
 In Paris -< Minimum 00177 
 
 (Mean 0-0237 
 
 „ . ("Maximum 0-0276 
 
 linvirons ) t.^. ■ ^ „,„, 
 
 „ -r, . -< Minimum 0-0165 
 
 01 iaris J -,, . ^„,„ 
 
 (Mean 0-0210 
 
 Of these results, the earlier ones of Kemp, Pierre, and 
 Graeger are undoubtedly erroneous, as they were made 
 without those precautions which subsequent experience has 
 shown to be necessary. Even those of the other observers 
 must be taken as giving only a very general idea of the 
 quantity of ammonia in the air, for a proportion so minute 
 as one fifty-millionth cannot be accurately determined 
 even by the most delicate experiments. For this reason, 
 more recent experimenters have endeavoured to arrive at 
 conclusions bearing more immediately upon agricultural 
 questions, by determining the qiiantity of ammonia brought 
 down by the rain. The first observations on this subject 
 were made by Barral in 1851, and they have been repeated 
 during the years 1855 and 1856 by Mr. Way. In 1853, 
 
 Fresenius 
 
 Ville. 
 
ORGANIC CONSTITUENTS OF PLANTS. 17 
 
 Boussingault also made numerous experiments on the 
 quantity of ammonia in the rain falling at different places, 
 as well as in dew and the moisture of fogs. He found in 
 the imperial gallon — 
 
 Gra. 
 
 jjj^j^ / Paris 0-2100 
 
 (. Liebfrauenberg .' 0-0350 
 
 Dew, Liebfrauenbergjj;™^ ;;; lf^\l 
 
 ■p ^ f Liebfrauenberg 0-1790 
 
 ° (.Paris 9-6000 
 
 It thus appears that in Paris the quantity of ammonia 
 in rain-water is just six times as great as it is in the coun- 
 try, a result, no doubt, due to the ammonia evolved during 
 the combustion of fuel, and to anim.al exhalations, and to 
 the same cause, the large quantity contained in the mois- 
 ture of fogs in Paris may also be attributed. Barral and 
 Way have made determinations of the quantity of ammonia 
 carried down by the rain in each month of the year, the 
 former using for this purpose the water collected in the 
 rain-gauges of the Paris Observatory, and representing, 
 therefore, a town atmosphere ; the latter, that from a large 
 rain-gauge at Rothamsted, at a distance from any town. 
 According to Barral the ammonia annually deposited on 
 an acre of land amounts to 12-28 lbs., a quantity consider- 
 ably exceeding that obtained by Way, whose experiments 
 being made at a distance from towns, must be considered 
 as representing more accurately the normal condition of 
 the air. His results for the years 1855 and 1856 are 
 given below, along with the quantities of nitric acid found 
 at the same time. 
 
 Nitric Acid. — The presence of nitric acid ■ in the air 
 appears to have been first observed by Priestley at the 
 
18 
 
 , AGRICULTURAL CHEMISTRY. 
 
 end of the last century, but Liebig, in 1825, showed that it 
 was always to be found after thunder-storms, although he 
 failed to detect it at other times. In 1851 Barral proved 
 that it is invariably present in rain-water, and stated the 
 quantity annually carried down to an acre of land at no 
 less than 41-29 lbs. But at the time his experiments 
 were made, the methods of determining very minute quan- 
 tities of nitric acid were exceedingly defective, and "Way, 
 by the adoption of an improved process, has shown that 
 the quantity is very much smaller than Barral supposed, 
 and really falls short of three pounds. His results for 
 ammonia, as well as nitric acid, are given in the subjoined 
 table. 
 
 
 Nitiic 
 
 Acid in 
 
 Ammonia in 
 
 Total Nitrogen in 
 
 
 Grains. 
 
 Grains. 
 
 Grains. 
 
 1855. 
 
 1856. 
 
 1855. 
 
 1856. 
 
 1853. 
 
 1856. 
 
 January . 
 
 230 
 
 1564 
 
 1244 
 
 5,005 
 
 1084 
 
 4,526 
 
 February 
 
 944 
 
 544 
 
 2337 
 
 4,175 
 
 2169 
 
 3,579 
 
 March 
 
 UC2 
 
 866 
 
 4513 
 
 2,108 
 
 3995 
 
 1,945 
 
 April 
 
 325 
 
 1063 
 
 1141 
 
 8,614 
 
 1024 
 
 7,369 
 
 May . . 
 
 1840 
 
 3024 
 
 4206 
 
 18,313 
 
 3939 
 
 15,863 
 
 June 
 
 3303 
 
 2046 
 
 5574 
 
 4,870 
 
 6447 
 
 4,540 
 
 July 
 
 2680 
 
 1191 
 
 9620 
 
 2,869 
 
 8615 
 
 2,670 
 
 August . 
 
 3577 
 
 2125 
 
 4769 
 
 4,214 
 
 4870 
 
 4,021 
 
 September 
 
 732 
 
 1756 
 
 3313 
 
 5,972 
 
 2917 
 
 5,373 
 
 October . 
 
 4480 
 
 2075 
 
 7592 
 
 3,921 
 
 7414 
 
 3,767 
 
 November 
 
 1007 
 
 1371 
 
 3021 
 
 2,591 
 
 2749 
 
 2,489 
 
 December 
 
 664 
 
 2035 
 
 2438 
 
 4,070 
 
 2180 
 
 3,352 
 
 Total in pounds for) 
 the whole year J 
 
 2-98 
 
 •280 
 
 711 
 
 9-53 
 
 6-63 
 
 8-31 
 
 No attempts have been made to determine the propor- 
 tion of nitric acid in air, but its quantity is undoubtedly 
 excessively minute, and materially smaller than that of 
 ammonia. At least this conclusion seems to be a fair 
 inference from Way's researches, as well as the recent 
 
ORGANIC CONSTITUENTS OF PLANTS. 19 
 
 experiments of Boussingault on the proportion of nitric 
 acid contained in rain, dew, and fog, made in a manner 
 exactly similar to those on the ammonia, already quoted. 
 According to his experiments an imperial gallon contains — 
 
 Grs. 
 
 jj^jjj fParis 0-0708 
 
 ' ( Liebfrauenberg 0-0140 
 
 jj /Maximum 0-0785 
 
 ^^■^ Minimum 0-0030 
 
 FocT j P*"« 0-7092 
 
 "■ (^Liebfrauenberg 0-0718 
 
 Although it thus appears that Barral's results have 
 been only partially confirmed, enough has been ascertained 
 to show that the quantity of ammonia and nitric acid in 
 the air is sufficient to produce a material influence in the 
 growth of plants. The large amount of these substances 
 contained in the dew is also particularly worthy of notice, 
 and may serve to some extent to explain its remarkably 
 invigorating effect on vegetation. 
 
 Carhureited Hydrogen. — Gay-Lussac, Humboldt, and 
 Boussingault have shown, that when the whole of the 
 moisture and carbonic acid have been removed from the 
 air, it still contains a small quantity of carbon and hydro- 
 gen ; and Saussure has rendered it probable that they exist 
 in a state of combination as carburetted hydrogen gas. 
 No definite proof of this position has, however, as yet been 
 adduced, and the function of the compound is entirely 
 unknown. It is possible that the presence of carbon and 
 hydrogen may be due to a small quantity of organic matter; 
 but, whatever be its source, its amount is certainly 
 extremely small. 
 
 Sulphuretted Hydrogen and Phosphuretted Hydrogen. 
 — The proportion of these substances is almost infini- 
 
20 . AGRICULTURAL CHEMISTRY. 
 
 tesimal ; but they are pretty general constituents of the 
 atmosphere, and are apparently derived from the decom- 
 position of animal and vegetable matters. 
 
 The preceding statements lead to the important con- 
 clusion, that the atmosphere is capable of affording an 
 abundant supply of all the organic elements of plants, 
 because it not only contains nitrogen and oxygen in the 
 free state, but also in those forms of combination in which 
 they are most readily absorbed, as well as a large quantity 
 of carbonic acid, from which their carbon may be derived. 
 At first sight it may indeed appear that the quantity of 
 the latter compound, and still more that of ammonia, is so 
 trifling as to be of little practical importance. But a very 
 simple calculation serves to show that, though relatively 
 small, they are absolutely large, for the carbonic acid 
 contained in the whole atmosphere amounts in round 
 numbers to 
 
 2,400,000,000,000 tons, 
 
 and the ammonia, assuming it not to exceed one part in 
 fifty millions, must weigh 
 
 74,000,000 tons, 
 quantities amply sufficient to afford an abundant supply of 
 these elements to the whole vegetation of our globe. 
 
 The Soil as a Source of the Organic Constituents of 
 Plants. — When a portion of soil is subjected to heat, it is 
 found that it, like the plant, consists of a combustible and 
 an incombustible part ; but while in the plant the incom- 
 bustible part or ash is small, and the combustible large, 
 these proportions are reversed in the soil, which consists 
 chiefly of inorganic or mineral matters, mixed with a 
 quantity of combustible or organic substances, rarely ex- 
 ceeding 8 or 10 per cent, and often falling considerably 
 short of this quantity. 
 
ORGANIC CONSTITUENTS OP PLANTS. 21 
 
 The organic matter exists in the form of a substance 
 called humus, which must be considered here as a source 
 of the organic constituents of plants, independently of the 
 general composition of the soil, which will be afterwards 
 discussed. 
 
 The term humus is generic, and applied by chemists 
 to a rather numerous group of substances, very closely 
 allied in their properties, several of which are generally 
 present in all fertile soils. They have been submitted to 
 examination by various chemists, but by none more accu- 
 rately than by Mulder and Herman, to whom, indeed, we 
 owe almost all the precise information we possess on the 
 subject. The organic matters of the soil may be divided 
 into three great classes ; the first containing those sub- 
 stances which are soluble in water ; the second, those 
 extracted by means of caustic potash ; and the third, those 
 insoluble in all menstrua. When a soil is boiled with a 
 solution of caustic potash, a deep brown fluid is obtained, 
 from which acids precipitate a dark brown flocculent sub- 
 stance, consisting of a mixture of at least three diflferent 
 acids, to which the names of humic, ulmic, and geic acids 
 have been applied. The fluid from which they have been 
 precipitated contains two substances, crenic and apocrenic 
 acids, while the soil still retains what has been called in- 
 soluble humus. 
 
 The acids above named do not differ greatly in chemical 
 characters, but they have been subdivided into the humic, 
 geic, and crenic groups, which present some differences in 
 properties and composition. They are compounds of car- 
 bon, hydrogen, and oxygen, and are characterised by so 
 powerful an affinity for ammonia that they are with diffi- 
 culty obtained free from that substance, and generally exist 
 in the soil in combination with it. They are all products 
 
22 - AGRICULTURAL CHEMISTEY. 
 
 of the decomposition of vegetable matters in the soil, and 
 are formed during their decay by a succession of changes, 
 which may be easily traced by observing the course ot 
 events when a piece of wood or any other vegetable sub- 
 stance is exposed for a length of time to air and moisture. 
 It is then found gradually to disintegrate with the evolution 
 of carbonic acid, acquiring first a brown and finally a black 
 colour. At one particular stage of the process it is con- 
 vetted into one or other of two substances, called humin 
 and ulmin, both insoluble in alkalies, and apparently 
 identical with the insoluble humus of the soil ; but when 
 the decomposition is more advanced the products become 
 soluble ia alkalies, and then contain humic, ulmic, and 
 geic acids, and finally, by a still further progress, crenic 
 and apocrenic acids are formed as the result of an oxidation 
 occurring at certain periods of the decay. 
 
 The roots and other vegetable debris remaining in the 
 soil undergo a similar series of changes, and form the 
 humus, which is found only in the surface soil, that is to 
 say, in the portion which is now or has at some previous 
 period been occupied by plants, and the quantity of humus 
 contained in any soil is mainly dependent on the activity 
 of vegetation on it. Numerous analyses of humus com- 
 pounds extracted from the soil have been made, and have 
 served to establish a number of minor differences in the 
 composition even of those to which the same name has been 
 applied, due manifestly to the fact that their production 
 is the result of a gradual decomposition, which renders it 
 impossible to extract from the soil one pure substance, but 
 only a variable mixture of several, so similar to one another 
 in properties, that their separation is very difficult, if not 
 impossible. For this reason great discrepancies exist in 
 the statements made regarding them by different observers, 
 
OBQANIC COKariTUENTS OF PLANTS. 23 
 
 but this is a matter of comparatively small importance, as 
 their exact composition has no very direct bearing on 
 agricultural questions, and it will suffice to give the names 
 and chemical formulae of those which have been analysed 
 and described, — 
 
 Ulmic acid from long Frisian turf C40 Hjs Oie 
 
 Humic acid from hard turf C40 H15 O15 
 
 Humic acid from arable soil C40 Hig Oie 
 
 Humic acid from a pasture field C40 H14 Ou 
 
 Geic acid C40 Hjs O17 
 
 Apocrenic acid C48 H12 O24 
 
 Crenic acid C24 Hx2 Oie 
 
 It is only necessary to observe further, that these 
 formulae indicate a close connection with woody fibre, and 
 the continuous diminution of the hydrogen and increase of 
 oxygen shows that they must have been produced by a 
 gradually advancing decay. 
 
 The earlier chemists and vegetable physiologists attri- 
 buted to the humus of the soil a much more important 
 function than it is now believed to possess. 
 
 It was formerly considered to be the exclusive, or at 
 least the chief source of the organic constituents of plants, 
 and by absorption through the roots to yield to them the 
 greater part of their nutriment. But though this view 
 has still some supporters, among whom Mulder is the most 
 distinguished, it is now generally admitted that humus is 
 not a direct source of the organic constituents of plants, 
 and is not absorbed as such by their roots, although it is. 
 so indirectly, in as far as the decomposition which it is 
 constantly undergoing in the soil yields carbonic acid, 
 which can be absorbed. The older opinioft is refuted by 
 many well-ascertained facts. As regards the exclusive 
 
24 .AGRICULTURAL CHEMISTRY. 
 
 origin of the carbon of plants from humus, it is easy 
 to see that this at least cannot be true, for humus, as 
 already stated, is itself derived solely from the decom- 
 position of vegetable and animal mMters ; and if the 
 plants on the earth's surface were to be supported by it 
 alone, the whole of their substance would have to return 
 to the soil in the same form, in order to supply the gene- 
 ration which succeeds them. But this is very far from 
 being the case, for the respiration of animals, the combus- 
 tion of fuel, and many other processes, are annually convert- 
 ing a large quantity of these matters into carbonic acid ; 
 and if there were no other source of carbon but the humus 
 of the soil, the amount of vegetable life would gradually 
 diminish, and at length become entirely extinct. Schleiden, 
 who has discussed this subject very fully, has made an 
 approximative calculation of the total quantity of humus 
 on the earth's surface, and of the carbon annually converted 
 into carbonic acid by the respiration of man and animals, 
 the combustion of wood for fuel, and other minor processes; 
 and he draws the conclusion that, if there were no other 
 source of carbon except humus, the quantity of that sub- 
 stance existing in the soil would only support vegetation for 
 a period of sixty years. 
 
 The particular phenomena of vegetation also afford 
 abundant evidence that humus cannot be the only source 
 of carbon. Thus Boussingault has shown that on the 
 average of years, the crops cultivated on an acre of: land 
 remove from it about one ton more organic matter than 
 they receive in the manure applied to them, although 
 there is no corresponding diminution in the quantity of 
 humus contained in the soil. An instance which leads 
 still more unequivocally to the same conclusion is given 
 by Humboldt. He states that an acre of land, planted 
 
ORGANIC CONSTITUENTS OF PLANTS. 25 
 
 with bananas, yields annually about 152,000 pounds 
 weight of fruit, containing about 32,000 pounds, or almost 
 exactly 14 tons of carbon ; and as this production goes on 
 during a period of twenty years, there must be withdrawn 
 in that time no less than 280 tons of carbon. But the 
 soil on an acre of land weighs, iu round numbers, 1000 
 tons, and supposing it to contain 4 per cent of humus, the 
 total weight of carbon in it would amount to little more 
 than 20 tons. 
 
 It is obvious from these and many other analogous 
 facts that humus cannot be the only or even a considerable 
 source of the carbon of plants, although it is still contended 
 by some chemists thiit it may be absorbed to a small extent. 
 But even this is at variance with many well-known facts. 
 For if humus were absorbed, it might be expected that 
 vegetation would be most luxuriant on soils containing 
 abundance of that substance, especially if it existed in a 
 soluble and readily absorbable form ; but so far from this 
 being the case, nothing is more certain than that peat, in 
 which these conditions are fulfilled, is positively injurious 
 to most plants. On the other hand, our daily experience 
 affords innumerable examples of plants growing luxuriantly 
 in soils and places where no humus exists. The sands of 
 the sea-shore, and the most barren rocks, have their vege- 
 tation, and the red-hot ashes which are thrown out by 
 active volcanoes are no sooner cool than a crop of plants 
 springs np on them. 
 
 The conclusions to be drawn from these considerations 
 have been fiirther confirmed by the direct experiments of 
 different observers. Boussingault sowed peas, weighing 
 15'60 grains, in a soil composed of a mixture of sand and 
 clay, which had been heated red-liot, and consequently 
 contained no humus, and after 99 days' growth, during 
 
26 _ AGRICULTURAL CHEMISTRY. 
 
 which they had been watered with distilled water, he found 
 the crop to weigh 68"72 grains, so that there had been 
 a fourfold increase. Similar experiments have been made 
 by Prince Salm Horstmar, on oats and rape sown in a soil 
 deprived of organic matter by ignition, in which they 
 grew readily, and arrived at complete maturity. One oat 
 straw attained a height of three feet, and bore 78 grains ; 
 another bore 47 ; and a third 28 — in all 153. These when 
 dried at 212° weighed 46-302 grains, and the straw 45-6 
 grains. The most satisfactory experiments, however, are 
 those of Weigman and Polstorf, these observers having 
 found that it was possible to obtain a two-hundred-fold 
 produce of barley in an entirely artificial soil, provided 
 care was taken to give it the physical characters of a fer- 
 tile soil. They prepared a mixture of six parts of sand, 
 two of chalk, one of white bole, and one of wood charcoal ; 
 to which was added a small quantity of felspar, previously 
 fused with marble and some soluble salts, so as to imitate 
 as closely as possible the inorganic parts of a soil, and in 
 it they planted twelve barley pickles. The plants grew 
 luxuriantly, reaching a height of three feet, and each bear- 
 ing nine ears, containing 22 pickles. The grain of the 
 twelve plants weighed 2040 grains. 
 
 These experiments show that plants can grow and 
 produce seed when the most scrupulous care is taken to 
 deprive them of every trace of humus. But Saussure has 
 gone further, and shown that even when present, humus 
 is not absorbed. He allowed plants of the common bean 
 and the Polygonum Persicaria to grow in solutions of 
 humate of potash, and found a very trifling diminution in 
 the quantity of humic acid present ; but the value of his 
 experiments is invalidated by his having omitted to ascer- 
 tain whether the diminution of humic acid which he 
 
ORGANIC CONBTITDENTS OF PLANTS. 27 
 
 observed was really due to absorption by the plant. This 
 omission has been supplied by Weigman and Polstorf. 
 They grew plants of mint (Mentha undulata) and of Polygo- 
 num Persicaria in solutions of humate of potash, and placed 
 beside the glass containing the plant, another perfectly simi- 
 lar, and containing only the solution of humate of potash. 
 The solution, which contained in every 100 grains, 0*148 
 grains of solid matter, consisting of humate of potash, etc. 
 was found to become gradually paler, and at the end of a 
 month, during which time the plants had increased by 6i^ 
 inches, the quantity of solid matter in 100 grains had 
 diminished to 0'132. But the solution contained in the 
 other glass, and in which no plant had grown, bad dimi- 
 nished to 0*136, so that the absorption could not have 
 amounted to more than 0004 grains for every 100 grains 
 of solution employed. This quantity is so small as to be 
 within the limits of error of experiment, and we are conse- 
 quently entitled to draw the conclusion that humus, even 
 under the most favourable circumstances, is not absorbed 
 by plants. 
 
 But though not directly capable of affording nutriment 
 to plants, it must not, on that account, be supposed that 
 humus is altogether devoid of importance, for it is con- 
 stantly undergoing decomposition in the soil, and thus 
 becomes a source of carbonic acid which can be absorbed, 
 and, as we shall afterwards more particularly see, it exer- 
 cises very important functions in bringing the other con- 
 stituents of the soil into readily available forms of combi- 
 nation. 
 
 It has been already observed that carbon, hydrogen, 
 nitrogen, and oxygen, cannot be absorbed by plants when 
 uncombined, but only in the forms of water, carbonic acid, 
 ammonia, and nitric acid. It is scarcely necessary to 
 
28 .AGRICULTURAL CHEMISTEY. 
 
 detail the grounds on which this conclusion has been 
 arrived at in regard to carbon and hydrogen, for practi- 
 cally it is of little importance whether they can be absorbed 
 or not, as the former is rarely, the latter never, found un- 
 combined in nature. Neither can there be any doubt that 
 water and carbonic acid are the only substances from 
 which these elements can be obtained. Every- day expe- 
 rience convinces us that water is essential to vegetation ; 
 and Saussure, and other observers, have shown that plants 
 will not grow if they are deprived of carbonic acid, and 
 that they actually absorb that substance abundantly from 
 the atmosphere. The evidence for the non-absorption of 
 oxygen lies chiefly in the fact that plants obtain, in the 
 form of water and carbonic acid, a larger quantity of that 
 element than they require, and in place of absorbing, are 
 constantly exhaling it. The form in which nitrogen may 
 be absorbed has given rise to much difference of opinion. 
 In the year 1779, Priestley commenced the examination of 
 this subject, and drew from his experiments the conclu- 
 sion, that plants absorb the nitrogen of the air. Saussure 
 shortly afterwards examined the same subject, and having 
 found, that when grown in a confined space of air, and 
 watered with pure water, the nitrogen of the plants under- 
 went no increase, he inferred that they derived their entire 
 supplies of that element from ammonia, or the soluble 
 nitrogenous constituents of the soil or manure. Botissin- 
 giinlt has since re-examined this question, and by a most 
 elaborate series of experiments, in which the utmost care 
 was taken to avoid every source of fallacy, he was led to 
 the conclusion, that when haricots, oats, lupins, and cresses 
 were grown in calcined pumice-stone, mixed with the ash 
 of plants, and supplied with air deprived of ammonia and 
 nitric acid, their nitrogen underwent no increase. It 
 
ORGANIC CONS.TITUENTS OF PLANTS. 29 
 
 has been objected to these experiments, that the plants 
 being confined in a limited bulk of air, were placed in an 
 unnatural condition, and Ville has recently repeated them 
 with a current of air passing through the apparatus, and 
 found a slight increase in the nitrogen, due, as he thinks, 
 to direct absorption. It is much more probable, however, 
 that it depends on small quantities of ammonia or nitric 
 acid which had not been completely removed from the air 
 by the means employed for that purpose, for nothing is 
 more difficult than the complete abstraction of these sub- 
 Btances, and as the gain of nitrogen was only 0-8 grains, 
 while 60,000 gallons of air, and 13 of water, were em- 
 ployed in the experiment, which lasted for a considerable 
 time, it is reasonable to suppose that a sufficient quantity 
 may have remained to produce this trifling increase. 
 
 While these experiments show that plants maintain 
 only a languid existence when grown in air deprived of 
 ammonia and nitric acid, and hence, that the direct absorp- 
 tion of nitrogen, if it occur at all, must do so to a very 
 small extent, the addition of a very minute quantity of the 
 former substance immediately produces an active vegeta- 
 tion and rapid increase in size of the plants. Among the 
 most striking proofs of this are the experiments of Wolff, 
 made by growing barley and vetches in a soil calcined so 
 as to destroy organic matters, and then mixed with small 
 quantities of different compounds of ammonia. He found 
 that when the produce from the calcined soil was repre- 
 sented by 100, that from the different ammoniacal salts 
 was — 
 
 Barley. Vetches. 
 
 Muriate of Ammonia 257'2 176-4 
 
 Carbonate of Ammonia 123-6 173'8 
 
 Sulpliaie of Ammonia 203'6 12.0-2 
 
30 ^GEICULTURAL CHEMISTRY. 
 
 These experiments not only prove that ammonia can 
 be absorbed, but they also indirectly confirm the statement 
 already made, that humus is not necessary ; for in some 
 instances the produce was higher than that obtained from 
 the uncalcined soil with the same manures, although it 
 contained four per cent of humus. 
 
 On such experiments Liebig rests his opinion that 
 ammonia is the exclusive source of the nitrogen of plants, 
 and although he has recently admitted that it may be 
 replaced by nitric acid, it is obvious that he considers this 
 a rare and exceptional occurrence. The evidence, how- 
 ever, for the absorption of nitric acid appears to rest on 
 as good grounds as that of ammonia, for experience has 
 shown that nitrate of soda acts powerfully as a manure, 
 and its efiect must be due to the nitric acid, and not 
 to the soda, for the other compounds of that alkali have 
 no such effect. Wolff has illustrated this point by a 
 series of experiments on the sunflower, of which we shall 
 quote one. He took two seeds of that plant, and sowed them 
 on the 10th May, in a soil composed of calcined sand, mixed 
 with a small quantity of the ash of plants, and added at 
 intervals during the progress of the experiment, a quantity 
 of nitrate of potash, amounting in all to 17 '13 grains. 
 The plants were watered with distilled water, containing 
 carbonic acid in solution, and the pot in which they grew 
 was protected from rain and dew by a glass cover. On the 
 19th August one of the plants had attained a height of 
 above 28 inches, and had nine fine leaves and a flower- 
 bud ; the other was about 20 inches high, and had ten 
 leaves. On the 22d August, one of the plants having been 
 accidentally injured, the experiment was terminated. The 
 plants, which contained 103'16 grains of dry matter, were 
 then carefully analysed, and the quantity of nitrogen con- 
 
ORGANIC CONSTITUENTS OP PLANTS. 31 
 
 tained in the soil after the experiment and in the seed was 
 determined. 
 
 Grains. 
 
 Nitrogen in the dry plants 1-737 \a.,Qi 
 
 „ remaining in the soil ...0-697 J 
 
 in the nitrate of potash 2-370 [„.„„„ 
 in the seeds /^.AL,n 
 
 2-370 7 „.„ 
 .0-029 ]■'''' 
 
 Difference 0-035 
 
 Hence, the nitrogen contained in the plants must, in 
 this instance, have been obtained entirely from the nitrate 
 of potash, for the quantity contained in it and in the seeds 
 is exactly equal to that in the plants and the soil, the dif- 
 ference of 0-03 grains being so small that it may be safely 
 attributed to the errors inseparable from such experiments. 
 For the sake of comparison, an exactly similar experiment 
 was made on two seeds grown without nitrate of potash, 
 and in this instance, after an equally long period of growth, 
 the largest plant had only attained a height of 7-5 inches, 
 and had three small pale and imperfectly developed leaves. 
 They contained only 0-033 grains of nitrogen, while the 
 seeds contained 0-032 — indicating that, under these cir- 
 cumstances, there was no increase in the quantity of that 
 element. 
 
 But, independently of these experimental results, it 
 may be inferred from general considerations, that nitric 
 acid must be one of the sources from which plants derive 
 their nitrogen. It has been already stated, that the humus 
 contained in the soil consists of the remains of decayed 
 plants, and there is every reason to suppose that the pri- 
 meval soil contained no organic matters, and that the first 
 generation of plants must have derived the whole of their 
 nitrogen from the atmosphere. If, therefore, it be assumed 
 
32 ^ AGRICULTUKAL CHEMISTKY. 
 
 that ammbnia is the only source of the nitrogen of plants, 
 it would follow, that as that substance cannot be produced 
 by the direct union of its elements, the quantity of ammo- 
 nia in the air could only remain undiminished in the event 
 of the whole'of the nitrogen of decaying plants returning 
 into that form. But this is certainly not the case, for 
 every time a vegetable substance is burned, part of its 
 nitrogen is liberated in the free state, and in certain con- 
 ditions of putrefaction, nitric acid is produced. Now, if 
 ammonia be the only form in which nitrogen is absorbed, 
 there must be a gradual diminution of the quantity con- 
 tained in the air ; and further, there must either be some 
 continuous source of supply by which its quantity is main- 
 tained, or there must be some other substance capable of 
 affording nitrogen in a form fitted for the maintenance of 
 plant life. As regards the first alternative, it must be 
 stated that we know of no source other than the decom- 
 position of plants from which ammonia can be derived, 
 and we are therefore compelled to adopt the second alter- 
 native, and to admit that there must be some other source 
 of nitrogen, and it cannot be doubted, from what has been 
 already stated, that it is from nitric acid only that it can 
 be obtained. 
 
 It must be admitted, then, that carbonic acid, ammonia, 
 nitric acid, and water, are the great organic foods of plants. 
 But while they have afforded to them an inexhaustible 
 supply of the last, the quantity of the other three available 
 for food are limited, and insufficient to sustain their life for 
 a prolonged period. It has been shown by Chevandrier, 
 that an acre of land under beech wood accumulates 
 annually about 1650 lb. of carbon. Now, the column of 
 air resting upon an acre of land contains only about 
 ] 5,500 lb. of carbon, and the soil may be estimated to 
 
ORGANIC CON^ITUENTS OF PLANTS. 33 
 
 contain 1 per cent, or 22,400 lb. per acre, and the whole 
 of this carbon would therefore be removed, both from the 
 air and the soil, in the course of little more than 23 years. 
 But it is a familiar fact, that plants continue to grow with 
 undiminished luxuriance year after year in the same soil, 
 and they do so because neither their carbon nor their 
 nitrogen are permanently absorbed ; they are there only 
 for a period, and when the plant has finished its functions, 
 and dies, they sooner or later return into their original 
 state. Either the plant decays, in which case its carbon 
 and nitrogen pass more or less rapidly into their original 
 state, or it becomes the food of animals, and by the pro- 
 cesses of respiration and secretion, the same change is 
 indirectly effected. In this way a sort of balance is sus- 
 tained ; the carbon, which at one moment is absorbed by 
 the plant, passes in the next into the tissues of the animal, 
 only to be again expired in that state in which it is fitted 
 to commence again its round of changes. 
 
 But while there is thus a continuous circulation of these 
 constituents through both plants and animals, there are vari- 
 ous changes which tend to liberate in the free state a certain 
 quantity both of the carbon and nitrogen of plants, and these 
 being thus removed from the sphere of organic life, there 
 would be a gradual diminution in the amount of vegetation 
 at the earth's surface, unless this loss were counterbalanced 
 by some corresponding source of gain. In regard to carbonic 
 acid the most important source is volcanic action, but the 
 loss of nitrogen, which is far more iipportant and consider- 
 able, is restored by the direct combination of its elements. 
 The formation of nitric acid during thunder storms has 
 been long familiar ; but it would appear from the recent 
 experiments of Cloez, which, should they be confirmed 
 by farther enquiry, will be of much importance, that this 
 
 D 
 
34 AGRICULTURAL CHEMISTRY. 
 
 compound is also produced without electrical action when 
 air is passed over certain porous substances, saturated with 
 alkaline and earthy compounds. Fragments of calcined 
 brick and pumice stone were saturated with solution of 
 carbonate of potash, with carbonates of lime and magnesia 
 and other mixtures, and a current of air freed from nitric 
 acid and ammonia passed over them for a long period, at 
 the end of which notable quantities of nitric acid were 
 detected. 
 
 Source of the Inorganic Constituents of Plants. — The 
 inorganic constituents of plants being all fixed substances, 
 it is sufficiently obvious that they can only be obtained 
 from the soil, which, as we shall afterwards see, contains 
 all of them in greater or less abundance, and has always 
 been admitted to be the only substance capable of supply- 
 ing them. The older chemists and physiologists, however, 
 attributed no importance to these substances, and from the 
 small quantities in which they are found in plants, imagined 
 that they were there merely accidental impurities absorbed 
 from the soil along with the humus, which was at that 
 time considered to be their organic food. This opinion, 
 sufficiently disproved by the constant occurrence of the same 
 substances in nearly the same proportions, in the ash of 
 each individual plant, has been further refuted by the experi- 
 ments of Prince Salm Horstmar, who has established their 
 importance to vegetation, by experiments upon oats grown 
 on artificial soils, in each of which one inorganic constituent 
 was omitted. He found that, without silica, the grain 
 vegetated, but remained small, pale in colour, and so weak 
 as to be incapable of supporting itself; without lime, it 
 died when it had produced its second leaf; without potash 
 and soda, it grew only to the height of three inches ; 
 without magnesia, it was weak and incapable of supporting 
 
OEGANIC CONSI'ITUENTS OF PLANTS. 35 
 
 itself ; without phosphoric acid, weak but upright ; and 
 without sulphuric acid, though normal in form, the plant 
 was feeble, and produced no fruit. 
 
 Manner in which the Constituents of Plants are absorbed. 
 — Having treated of the sources of the elements of plants, 
 it is necessary to direct attention to the mode in which 
 they enter their system. 
 
 Water. — The absorption of water by plants takes 
 place in great abundance, and is connected with many of 
 the most important phenomena of vegetation. It is prin- 
 cipally absorbed by the roots, and passes into the tissues 
 of the plant, where a part of it is decomposed, and goes 
 to the formation of certain of its organic compounds ; 
 while by far the larger quantity, in place of remaining 
 in it, is again exhaled by the leaves. The extent to 
 which this takes place is very large. Hales found that a 
 sunflower exhaled in twelve hours about 1 lb. ooz. of water, 
 but this quantity was liable to considerable variation, 
 being greater in dry, and less in wet weather, and 
 much diminished during the night. Saussure made 
 similar experiments, and observed that the quantity of 
 water exhaled by a sunflower amounted to about 2201b. in 
 four months. The exhalation of plants has recently been 
 examined with great accuracy by Lawes. His experi- 
 ments were made by planting single plants of wheat, 
 barley, beans, peas, and clover, in large glass jars capable 
 of holding about 421b. of soil, and covered with glass 
 plates, furnished with a hole in the centre for the passage 
 of the stem of the plant. Water was supplied to the soil 
 at certain intervals, and the jars were carefully weighed. 
 The result of the experiments, continued during a period 
 of 172 days, is given in the following table, which shows 
 the total quantity of water exhaled in grains : — 
 
36 
 
 AGRICULTURAL CHEMISTRY. 
 
 Wheat 113,527 
 
 Barley 120,025 
 
 Beans 112,231 
 
 Peas 109,082 
 
 Closer, cut 28th June 55,093 
 
 It further appears, that the exhalation is not uniform, but 
 increases during the active growth of the plant, and dimi- 
 nishes again when that period is passed. These variations 
 are shown by the subjoined tables, of which the first gives 
 the total exhalation, and the second the average daily loss 
 of water during certain periods. 
 
 Table I. — Showing the Number of Grains of Water given 
 off by the Plants during stated divisional Periods of their 
 Growth. 
 
 
 9 Days. 
 
 From 
 Mar. 19 
 
 to 
 M3r.28. 
 
 31 Days. 
 
 27 Days. 
 
 34 Days. 
 
 30 Days. 
 
 14 Days. 
 
 27 Days. 
 
 ' Description 
 ■ of Plant. 
 
 Prom 
 Mar. 28 
 
 to 
 Apr. 28. 
 
 Prom 
 Apr. 28 
 
 to 
 May 25. 
 
 ftom 
 May 25 
 
 to 
 June 28 
 
 From 
 June 28 
 
 to 
 July 28. 
 
 From 
 July 28 
 
 to 
 Aug. 11. 
 
 From 
 Aug. 11 
 
 to 
 Sept. 7. 
 
 j Wheat 
 i Barley 
 i Beans . 
 i Pease 
 ; Clover 
 
 129 
 129 
 88 
 101 
 400 
 
 1268 
 1867 
 1854 
 1332 
 1645 
 
 4,385 
 12,029 
 4,846 
 2,873 
 2,948 
 
 40,030 
 37,480 
 30,110 
 36,715 
 50,100 
 
 46,060 
 45,060 
 58,950 
 62,780 
 
 15,420 
 
 17,046 
 
 12,626 
 
 5,281 
 
 6235 
 6414 
 3657 
 
 Table II. — Showing the average daily Loss of Water (in 
 Grains) by the Plants, within several stated divisional Periods 
 of their Growth. 
 
 Description 
 
 9 Days. 
 
 31 Days. 
 
 27 Days. 
 
 34 Days. 
 
 30 Days. 
 
 14 Days. 
 
 27 Days. 
 
 Trom 
 
 From 
 
 From 
 
 From 
 
 I'rom 
 
 From 
 
 From 
 
 of Plant 
 
 Mar. 19 
 
 Mar. 28 
 
 Apr. 28 
 
 May 26 
 
 June 28 
 
 July 28 
 
 Aug. 11 
 
 
 to 
 
 to 
 
 to 
 
 to 
 
 to 
 
 to 
 
 8) 
 
 
 Mai. 28. 
 
 Apr. 28. 
 
 May 25. 
 
 June 28. 
 
 July 2a 
 
 Aug. 11. 
 
 Sept. 7. 
 
 Wheat 
 
 14-3 
 
 40-9 
 
 162-4 
 
 1177-4 
 
 1535-3 
 
 1101-4 
 
 230-9 
 
 Barley . 
 
 14-3 
 
 60-2 
 
 445-5 
 
 1102-3 
 
 1502-0 
 
 1217-6 
 
 237-5 
 
 Beans . 
 
 9-7 
 
 59-8 
 
 179-5 
 
 885-6 
 
 1965-0 
 
 901-8 
 
 135-4 
 
 Peas . 
 
 112 
 
 42-9 
 
 106-4 
 
 ] 079-8 
 
 2092-7 
 
 377-2 
 
 .•. 
 
 Clover 
 
 44-4 
 
 530 
 
 109-2 
 
 1473-5 
 
 
 
 ... 
 
ORGANIC CONSTITOENTS OF PLANTS. 37 
 
 Similar experiments were made with the same plants 
 in soils to which certain manures had been added, and 
 with results generally similar. Calculating from these 
 experiments, we are led to the apparently anomalous con- 
 clusion that the quantity of water exhaled by the plants 
 growing on an acre of land greatly exceeds the annual 
 fall of rain ; although it is obvious that of all the rain 
 which falls, only a small proportion can be absorbed by 
 the plants growing on the soil, for a large quantity is 
 carried off by the rivers, and never reaches their roots. 
 It has been calculated, for instance, that the Thames 
 carries off in this way at least one-third of the annual rain 
 that falls in the district watered by it, and the Rhine 
 nearly four-fifths. Of course this large exhalation must 
 depend on the repeated absorption of the same quantity of 
 water, which, after being exhaled, is again deposited on 
 the soil in the form of dew, and passes repeatedly through 
 the plant. This constant percolation of water is of im- 
 mense importance to the plant, as it forms the channel 
 through which some of its other constituents are carried 
 to it. 
 
 Carbonic Acid. — While the larger part of the water 
 which a plant requires is absorted by its roots, the reverse is 
 the case with carbonic acid. A certain proportion no doubt 
 is carried up through the roots by the water, which always 
 contains a quantity of that gas in solution, but by far the 
 larger proportion is directly absorbed from the air by the 
 leaves. A simple experiment of Boussingault's illustrates 
 this absorption very strikingly. He took a large glass globe 
 having three apertures, through one of which he introduced 
 the branch of a vine, with twenty leaves on it. With one 
 of the side apertures a tube was connected, by means of 
 which the air could be drawn slowly through the globe, 
 
38 •AGRICULTURAL CHEMISTRY. 
 
 and into an apparatus in which its carbonic acid was 
 accurately determined. He found, in this way, that while 
 the air which entered the globe contained 0'0004 of 
 carbonic acid, that which escaped contained only 0*0001, 
 so that three-fourths of the carbonic acid had been absorbed. 
 
 Ammonia and Nitric Acid. — Little is known regarding 
 the mode in which these substances enter the plant. It 
 is usually supposed that they are entirely absorbed by the 
 roots, and no doubt the greater proportion is taken up in 
 this way, but it is very probable that they may also be 
 absorbed by the leaves, at least the addition of ammonia 
 to the air in which plants are grown, materially accelerates 
 vegetation. It is probable, however, that the rain carries 
 down the ammonia to the roots, and there is no doubt that 
 that derived from the decomposition of the nitrogenous 
 matters in the soil is so absorbed. 
 
 Inorganic Constituents. — The inorganic constituents of 
 course are entirely absorbed by the roots ; and it is as a 
 solvent for them that the large quantity of water con- 
 tinually passing through the plants is so important. 
 They exist in the soil in particular states of combination, 
 in which they are scarcely soluble in water. But their 
 solubility is increased by the presence of carbonic acid 
 contained in the water, and which causes it to dissolve, to 
 some extent, substances otherwise insoluble. It is in this 
 way that lime, which occurs in the soil principally as the 
 insoluble carbonate, is dissolved and absorbed. And 
 phosphate of lime is also taken iip by water containing 
 carbonic acid, or even common salt in solution. The 
 amount of solubility produced by these substances is 
 extremely small ; but it is sufficient for the purpose of 
 supplying to the plant as much of its mineral constituents 
 as are required, for the quantity of water which, as we 
 
ORGANIC CONSTITUENTS OF PLANTS. 39 
 
 have already seen, passes througt a plant is very large 
 when compared with the amount of inorganic matters 
 absorbed. It has been shown by Lawes and Gilbert, that 
 about 2000 grains of water pass through a plant for every 
 grain of mineral matter fixed in it, so that there is no 
 difficulty in understanding how the absorption takes place. 
 It is worthy of notice, however, that the absorption of 
 the elements of plants takes place even though they may 
 not be in solution in the soil, the roots apparently possess- 
 ing the power of directly acting on and dissolving insoluble 
 matters ; but a distinction must be drawn between this 
 and the view entertained by Jethro Tull, who supposed 
 that they might be absorbed in the solid state, provided 
 they were reduced to a state of sufficient comminution. 
 It is now no longer doubted that, whatever action the 
 roots may exert, the constituents of the plant must be in 
 solution before they can pass into it — experiment having 
 distinctly shown that the spongioles or apertures through 
 which this absorption takes place are too minute to admit 
 even the smallest solid particle. 
 
CHAPTEE IL 
 
 THE PROXIMATE CONSTITUENTS OF PLANTS. 
 
 The substances absorbed by the plant, which are of simple 
 composition, and contain only two elements, are elaborated 
 within it, and converted into the many complicated com- 
 pounds of which its mass is composed. Some of these, as, 
 for example, the colouring matters of madder and indigo, 
 the narcotic principle of the poppy, &c., are confined to a 
 single species, or small group of plants, while others are 
 found in all plants, and form the main bulk of their tissues. 
 The latter are the only substances which claim notice in 
 a treatise like the present. They have been divided into 
 three great classes, of widely different properties, com- 
 position, and functions. 
 
 Is*. The Saccharine and Amylaceous Constituents. — 
 These substances are compounds of carbon, hydrogen, and 
 oxygen, and all possess a certain degree of similarity in 
 composition, the quantities of hydrogen and oxygen they 
 contain being always in the proportion required to form 
 water, so that they may be considered as compounds of 
 carbon and water ; not that it can be asserted that they 
 actually do contain water, as such, for of that there is no 
 evidence, but only that its elements are present in the 
 proportion to form it. 
 
 Cellulose. — This substance forms the fundamental part 
 
PROXIMATE CONSTITUENTS OP PLANTS. 41 
 
 of all plants. It is the principal constituent of woody fibre, 
 and is found in a state of purity in the fibre of cotton and 
 flax, and in the pith of plants ; but in wood it is generally 
 contaminated with another substance, which has received 
 the name incrusting matter, because it is deposited in and 
 around the cells of which the plant is in part composed. 
 Cellulose is insoluble in all menstrua, but, when boiled for 
 a long time with sulphuric acid, is converted iuto a sub- 
 stance called dextrine. Cellulose consists of — 
 
 Prom pith of Elder-tree. Spon^oles of roots. 
 
 Carbon 43-37 43-00 
 
 Hydrogen 6-04 6-18 
 
 Oxygen..., 50-59 50-82 
 
 100-00 10000 
 
 It is represented chemically by the formula, C24 Hji O21, 
 which shows it to be a compound of 24 atoms of carbon 
 with 21 of hydrogen and 21 of oxygen. 
 
 Incrusting matter. — Large quantities of this substance 
 enter into the composition of all plants. Of its chemical 
 nature little is known, as it cannot be obtained separate 
 from cellulose, but it is analogous to that substance in its 
 composition, and probably contains hydrogen and oxygen 
 in the proportion to form water. 
 
 Starch. — Starch is one of the most abundant constitu- 
 ents of plants, and is found in most seeds, as those of the 
 cereals and the leguminous plants ; in the tubers of the 
 potatoe, the bulbs of tulips, &c. &c. It is obtained by 
 placing a quantity of wheat flour in a bag, and kneading 
 it under a gentle stream of water. When the water is 
 allowed to stand, it deposits the starch as a fine white 
 powder, which, when examined by the microscope, is 
 found to be composed of minute grains, formed of concentric 
 
42 . AGRICULTUKAL CHEMISTRY. 
 
 layers deposited on one another. These grains vary con- 
 siderably in size and structure in different plants ; but in 
 the same plant they are generally so much alike as to 
 admit of their recognition by a practised observer. They 
 were formerly believed to be composed of an external 
 coating of a substance insoluble in water, and containing 
 in their interior a soluble kernel ; but this opinion has 
 been refuted, and distinct evidence been brought to show 
 that the exterior and interior of the globules are identical 
 in chemical properties. Starch is insoluble in cold water, 
 but by boiling, it dissolves, forming a thick paste. By 
 long continued boiling with water containing a small 
 quantity of acid, it is completely dissolved and converted 
 into dextrine, and eventually into sugar. The same change 
 is produced by the action of fermenting substances, such 
 as the extract of malt ; when heated in the dry state to a 
 temperature of about 390 Fahr., it becomes soluble in cold 
 water. It is distinguished by giving a brilliant blue com- 
 pound with iodine. Starch contains — 
 
 Carbon 44'47 
 
 Hydrogen 6-28 
 
 Oxygen 49-25 
 
 100-00 
 and its composition is represented by the formula C12 
 Hio Oio, so that it differs but little from cellulose in com- 
 position, although its chemical functions in the plant are 
 extremely different. It is connected with some of the 
 most important changes which occur in the growing plants, 
 and by a series of remarkable transformations is converted 
 into sugar and other important compounds. 
 
 Lichen Starch is found in most species of lichens, and 
 is distinguished from common starch by producing a green 
 
PROXIMATE CONSTITUENTS OP PLANTS. 43 
 
 colour with iodine. Its composition is the same as that of 
 ordinary starch. 
 
 Inuline. — The species of starch to which this name is 
 given is characterised by its dissolving in boiling water, 
 and giving a white pulverulent deposit in cooling. It is 
 found in the tuber of the dahlia, in the dandelion, and 
 some other plants. Its composition is identical with that 
 of cellulose, and its formula is C24 H21 O21. 
 
 Gum is excreted from various plants as a thick fluid, 
 which dries up into transparent masses. Its composition 
 is identical with that of starch. It dissolves readily in 
 cold water, and is converted into sugar by long continued 
 boiling with acids. Its properties are best marked in gum 
 arabic, which is obtained from various species of acacia ; 
 that from other plants differs to some extent, although its 
 chemical composition is the same. 
 
 Dextrine. — When starch is exposed to a heat of about 
 400°, or when treated with sulphuric acid, or with a sub- 
 stance extracted from malt called diastase, it is converted 
 into dextrine. It may also be obtained from cellulose by 
 a similar treatment. The dextrine so obtained has the 
 same composition as the starch from which it is produced, 
 but its properties more nearly resemble those of gum. It 
 plays a very important part in the process of germination, 
 and may be converted into sugar on the one hand, and 
 apparently also into starch on the other. 
 
 Sugar. — Under this name are included four or five 
 distinct substances, of which the most important are, cane 
 sugar, grape sugar, and the uncrystallisable sugar found in 
 many plants. 
 
 Cane Sugar. — This variety of sugar, as its name implies, 
 is found most abundantly in the sugar cane, but it occurs 
 also in the maple, beet-foot, and various species of palms. 
 
44 AGRICULTURAL CHEMISTRY. 
 
 from all of which it is extracted on the large scale. It is 
 extremely soluble in water, and can be obtained in large 
 transparent prismatic crystals, as in common sugar-candy. 
 It swells up, and is converted into a brown substance 
 called caramel, when heated, and by contact with fer- 
 menting substances, yields alcohol and carbonic acid. It 
 contains — 
 
 Carbon 42-22 
 
 Hydrogen 6-60 
 
 Oxygen 5118 
 
 10000 
 
 and its chemical formula is C12 Hn On. 
 
 Crrape Sugar is met with in the grape, and most other 
 fruits, as well as in honey. It is produced artificially 
 when starch is boiled for a long time with sulphuric acid, 
 or treated with a large quantity of diastase. It is less 
 soluble in water than cane sugar, and crystallises in small 
 round grains. Its composition, when dried at 284°, is — 
 
 Carbon 40-00 
 
 Hydrogen , 6-66 
 
 Oxygen 53-34 
 
 100-00 
 
 and its formula is C12 Hi2 O12 ; but when crystallised it 
 contains two equivalents of water, and is then represented 
 by the formula C12 Ha2 O12 -f 2 HO. 
 
 The uncrystallisable sugar of plants is closely allied to 
 grape sugar, and, so far as at present known, has the same 
 composition, although, from the difficulty of obtaining it 
 quite free from crystallised sugar, this is still uncertain. 
 
 Mtidlage is the name applied to the substance existing 
 
PROXIMATK CONgTITUENTS OF PLANTS. 45 
 
 in linseed, and in many other seeds, and which communicates 
 to them the property of swelling up and becoming gelatin- 
 ous when treated with water. It is found in a state of 
 considerable purity in gum tragacanth and some other gums. 
 Its composition is not fenown with absolute certainty, 
 but it is either C24 Hjg O19, or Ci2 Hio Oio ; and in the 
 latter case it must be identical with starch and gum. 
 
 It will be observed that all the substances belonging 
 to this class are very closely related in chemical composi- 
 tion, some of them, as starch and gum, though easily dis- 
 tinguished by their properties, being identical in constitu- 
 tion, while others only differ in the quantity of water, or 
 of its elements which they contain. In fact, they may 
 all be considered as compounds of carbon and water, and 
 their relations are, perhaps, more distinctly seen when 
 their formulae are written so as to show this, as is done in 
 the following table, in the second column of which those 
 containing twelve equivalents of carbon are doubled, so as 
 to make them comparable with cellulose : — 
 
 
 
 
 Water. 
 
 Grape sugar, 
 
 C12 H12 O12 
 
 C24 H24 O24 
 
 C24 + 24 
 
 Cane sugar. 
 
 Ci2 Hii Oil 
 
 C24 H22 O22 
 
 C24 + 22 
 
 Cellulose, . 
 
 C24 H21 O21 
 
 C24 H21 O21 
 
 C24 + 21 
 
 Inuline, 
 
 C24 H21 021 
 
 C24 H21 O21 
 
 C24 + 21 
 
 Starch, 
 
 C12 Hio Oio 
 
 C24 H20 O20 
 
 C24, + 20 
 
 Dextrine, . 
 
 C12 Hio Oio 
 
 O24 H20 O20 
 
 Gii + 20 
 
 Gum, 
 
 Ci3 Hio Oio 
 
 C24 H20 O30 
 
 C24 + 20 
 
 Mucilage, . 
 
 Ci3 Hio Oio 
 
 C24 H30 O20 
 
 C34 + 20 
 
 The relation between these substances being so close, it 
 is not difficult to understand how one may be converted 
 into another by the addition or subtraction of water. 
 Thus, cellulose has only to absorb an equivalent of water 
 to become grape sugar, or to lose an equivalent in order 
 
46 AGRICULTURAL CHEMISTRY. 
 
 to be converted into starch, and we shall afterwards see 
 that such changes do actually occur in the plant during 
 the process of germination. 
 
 Pectine and Pectic Acid. — These substances are met 
 with in many fruits and roots, as, for instance, in the apple, 
 the carrot, and the turnip. They differ from the starch 
 group in containing more oxygen than is required to form 
 water along with their hydrogen ; but their exact compo- 
 sition is still uncertain, and they undergo numerous changes 
 during the ripening of the fruit. 
 
 2d. Oily or Fatty Matters. — The oily constituents of 
 plants form a rather extensive group of substances all 
 closely allied, but distinguished by minor differences in 
 properties and constitution. Some of them are very widely 
 distributed throughout the vegetable kingdom, but others 
 are almost peculiar to individual plants. They are all 
 compounds of carbon, hydrogen, and oxygen, and are at 
 once distinguished from the preceding class, by containing 
 much less oxygen than is required to form water with 
 their hydrogen. The principal constituents of the fatty 
 matters and oils of plants are three substances, called 
 stearine, margarine, and oleine, the two former solids, the 
 latter a fluid ; and they rarely, if ever, occur alone, but are 
 mixed together in variable proportions, and the fluidity of 
 the oils is due principally to the quantity of the last which 
 they contain. If olive oil be exposed to cold, it is seen 
 to become partially solid; and if it be then pressed, a 
 fluid flows out, and a crystalline substance remains ; the 
 former is oleine, though not absolutely pure, and the latter 
 margarine. The perfect separation of these substances 
 involves a variety of troublesome chemical processes ; and 
 when it has been effected, it is found that each of them is 
 a compound of a peculiar acid, with another substance 
 
PROXIMATE CONSTITUENTS OP PLANTS. 47 
 
 having a sweet taste, and which has received the name of 
 glycerine, or the sweet principle of oil. Glycerine, as it 
 exists in the fats, appears to be a compound of C3 Hg 0, 
 and its properties are the same from whatever source it is 
 obtained. The acids separated from it are known by the 
 names of margaric, stearic, and oleic acids. 
 
 Margaric Acid is best obtained pure by boiling olive 
 oil with an alkali until it is saponified, and decomposing 
 the soap with an acid, expressing the margaric acid, 
 which separates, and crystallising it from alcohol. It is a 
 white crystalline fusible solid, insoluble in water, but 
 soluble in alcohol and in solutions of the alkalies. Its 
 composition is — 
 
 Carbon 75-56 
 
 Hydrogen 12-59 
 
 Oxygen 11-85 
 
 100-00 
 and its formula C34 H34 O4. 
 
 Stearic Acid. — Although this acid exists in many 
 plants, it is most conveniently extracted from lard. It is 
 a crystalline solid less fusible than margaric acid, but 
 closely resembling it in its other properties. Its formula 
 is C36 Has O4. 
 
 Oleic Acid. — Under this name two different substances 
 appear to be included. It has been applied generally to 
 the fluid acids of all oils, while it would appear that the 
 drying and non-drying oils actually contain substances of 
 different composition. The acid extracted from olive oil 
 appears to have the formula C36 H34 O4, while that from 
 linseed oil is C46 H38 Og, but this is still doubtful. 
 
 Other fatty acids have been detected in palm oil, 
 cocoa-nut oil, &c. &c., which so closely resemble margaric 
 
48 ^ AGEICULTTJBAL CHEMISTEY. 
 
 and stearic acids as to be easily confounded with them. 
 Though presenting many points of interest, it is imneces 
 sary to describe them in detail here. 
 
 Wax is a substance closely allied to the oils. It con 
 sists of two substances, cerine and myricine, which arc 
 separated from one another by boiling alcohol, in which 
 the former is more soluble. They are extremely complex 
 in composition, the former consisting principally of an acid 
 similar to the fatty acids, called cerotic acid, and containing 
 C54 H54 O4. The latter has the formula C92 H92 O4. The 
 wax found in the leaves of the lilac and other plants 
 appears to consist of myricine, while that extracted from 
 the sugar-cane is said to be different, and to have the 
 formula C48 H50 O2. It is probable that other plants con- 
 tain different sorts of wax, but their investigation is still 
 so incomplete, that nothing definite can be said regarding 
 them. Wax and fats appear to be produced in the plant 
 from starch and sugar ; at least it is unquestionable that 
 the bee is capable of producing the former from sugar, and 
 we shall afterwards see that a similar change is most pro- 
 bably produced in the plant. The fatty matters contained 
 in animals are identical with those of plants. 
 
 3d. Nitrogenous or Albuminous Constituents of Plants 
 and Animals. — The nitrogenous constituents of plants and 
 animals are so closely allied, both in properties and com- 
 position, that they may be most advantageously considered 
 together. 
 
 Albumen. — Vegetable albumen is found dissolved in 
 the juices of most plants, and is abundant in that of the 
 potato, the turnip, and wheat. In these juices it exists in a 
 soluble state, btit when its solution is heated to about 150°, 
 it coagulates into a flocky insoluble Substance. It is also 
 thrown down by acids and alcohol Coagulated albumen 
 
PROXIMATE CONSTITUENTS OF PLANTS. 49 
 
 is soluble in alkalies and in nitric acid. Animal albumen 
 exists in the white of eggs, the serum of blood, and the 
 juice of flesh ; and from all these sources is scarcely dis- 
 tinguishable in its properties from vegetable albumen. 
 
 It is a substance of very complicated composition, and 
 chemists are not agreed as to the formula by which its 
 constitution is to be expressed, a difficulty which occurs 
 also with most of the other nitrogenous compounds. The 
 results of the analyses of albumen from different sources 
 are however quite identical, as may be seen from those 
 subjoined — 
 
 I'rom From From From 
 
 Wheat. Potatoes. Blood. White ot Egg. 
 
 Carbon 537 53-1 53-4 53-0 
 
 Hydrogen.. 7-1 7-2 7-0 7-1 
 
 Nitrogen... 15-6 ... 15-5 15-6 
 
 Oxygen ■) ( ... 221 229 
 
 Sulphur V 23-6 ■< 0-97 1-6 1-1 
 
 Phosphorus ) ( ... 04 03 
 
 1000 1000 100-0 
 
 Closely allied to vegetable albumen is the substance 
 known by the name of glutin, which is obtained by boil- 
 ing the gluten of wheat with alcohol. It appears to be a 
 sort of coagulated albumen, with which its composition 
 completely agrees. 
 
 Vegetable Fibrine. — If a quantity of wheat flour be 
 tied up in a piece of cloth, and kneaded for some time 
 under water, the starch it contains is gradually washed 
 out, and there remains a quantity of a glutinous substance 
 called gluten. When this is boiled with alcohol, the 
 glutin above referred to is extracted, and vegetable fibrine 
 is left. It dissolves in dilute potash, and on the addition 
 of acetic acid is deposited in a pure state. Treated with 
 hydrochloric acid, diluted with ten times its weight of 
 
 E 
 
50 , AGEICULTnEAL CHEMISTRY. 
 
 water, it swells up into a jelly-like mass. When boiled 
 or preserved for a long time under water, it cannot be dis- 
 tinguished from coagulated albumen. 
 
 Animal Fibrine exists in the blood and the muscles, 
 and agrees in all its characters and composition with 
 vegetable fibrine, as is shown by the subjoined analyses — 
 
 Wheat Flonr. Blood. Resh. 
 
 Carbon 531 52-5 53-3 
 
 Hydrogen 7-0 6-9 7-1 
 
 Nitrogen 15-6 15-5 15-3 
 
 Oxygen 23-2 24-0 23-1 
 
 Sulphur 1-1 1-1 1-2 
 
 100-0 100-0 lOO-O 
 
 Caseine. — Vegetable caseine exists abundantly in most 
 plants, especially in the seeds, and remains in the juice 
 after albumen has been precipitated by heat, from which 
 it may be separated in flocks by the addition of an acid. 
 It has been obtained for chemical examination, principally 
 from peas and beans, and from the almond and oats. 
 When prepared from the pea it has been called legumine, 
 from almonds emulsine, and from oats avenine ; but they 
 are all three identical in their properties, although for- 
 merly believed to be different, and distinguished by these 
 names. Vegetable caseine is best obtaiued by treating 
 peas or beans with hot water, and straining the fluid. 
 On standing, the starch held in suspension is deposited, 
 and the caseine is retained in solution in the alkaline 
 fluid ; by the addition of an acid it is precipitated as a 
 thick curd. Caseine is insoluble in water, but dissolves 
 readily in alkalies ; its solution is not coagulated by heat, 
 but, on evaporation, becomes covered with a thin pellicle, 
 which is renewed as often as it is removed. 
 
PROXIMATE CONSTITUENTS OF PLANTS. 51 
 
 Animal Caseine is the principal constituent of milk, and 
 is obtained by the cautious addition of an acid to skimmed 
 milk, by which it is precipitated as a thick white curd. It 
 is also obtained by the use of rennet, and the process of 
 curding milk is simply the coagulation of its caseine. It 
 is soluble in alkalies, and precipitated from its solution by 
 acids, and in all other respects agrees with vegetable 
 caseine. 
 
 The composition of animal caseine has been well ascer- 
 tained, but considerable doubt still exists as to that of 
 vegetable caseine, owing to the difficulty of obtaining it 
 absolutely pure. The analyses of different chemists give 
 rather discordant results, but we have given those which 
 appear most trustworthy — 
 
 Fiom Peas. 
 
 Carbon 50-6 50-7 
 
 Hydrogen 6'8 6'6 
 
 Nitrogen 16"5 15'8 
 
 Oxygen 25-6 23-8 
 
 Sulphur 0-5 0-8 
 
 Phosphorus 2-3 
 
 100-0 100-0 
 Other results differ considerably from these, and some 
 observers have even obtained as much as eighteen per cent 
 of nitrogen and fifty- three of carbon. 
 
 The composition of animal caseine differs from this 
 principally in the amount of carbon. Its composition is — 
 
 Carbon 53-6 
 
 Hydrogen 7-1 
 
 Nitrogen 15'8 
 
 Oxygen 22-5 
 
 Sulphur 1-0 
 
 100-0 
 
52 AGKICtTLTURAL CHEMISTRY. 
 
 The most cursory examination of these analytical num- 
 bers is sufficient to show that a very close relation subsists 
 between the different substances just described. Indeed, 
 with the exception of vegetable caseine, they may be said 
 all to present the same composition ; and, as already men- 
 tioned, there are analyses of it which would class it com- 
 pletely with the others. While, however, the quantities 
 of carbon, hydrogen, nitrogen, and oxygen are the same, 
 differences exist in the sulphur and phosphorus they 
 contain, and which, though very small in quantity, are 
 indubitably essential to them. Much importance has been 
 attributed to these constituents by various chemists, and 
 especially by Mulder, who has endeavoured to make out 
 that all the albuminous substances are compounds of a 
 substance to which he has given the name oi proteine, with 
 different quantities of sulphur and phosphorus. The com- 
 position of proteine, according to his newest experiments, 
 is — 
 
 Carbon 54-0 
 
 Hydrogen 7-1 
 
 Nitrogen 16-0 
 
 Oxygen 21"4 
 
 Sulphur 1"5 
 
 1000 
 
 and is exactly the same from whatever albuminous com- 
 pound it is obtained. Although the importance of proteine 
 is probably not so great as Mulder supposed, it affords an 
 important illustration of the close similarity of the different 
 substances from which it is obtained, the more especially 
 as there is every reason to believe that the different albu- 
 minous compounds are capable of changing into one 
 another, just as starch and sugar are mutually convertible ; 
 
PROXIMATE CONMITDENTS OF PLANTS. 53 
 
 and the possibility of this change throws much light on 
 many of the phenomena of nutrition in plants and animals. 
 Indeed, it would seem probable that these compounds are 
 formed from their elements by plants only, and are merely 
 assimilated by animals to produce the nitrogenous con- 
 stituents they contain. 
 
 Diastase is the name applied to a substance existing 
 in malt, and obtained by macerating that substance with 
 cold water, and adding a quantity of alcohol to the fluid, 
 when the diastase is immediately precipitated in white 
 flocks. It is produced during the malting process, and is 
 not found in the unmalted barley. Its chemical composi- 
 tion is unknown, but it is nitrogenous, and is believed to 
 be produced by the decomposition of gluten. If a very 
 small quantity of diastase be mixed with starch suspended 
 in hot water, the starch is found gradually to dissolve, 
 and to pass first into the state of dextrine, then into that 
 of sugar. The change thus efiected takes place also in a 
 precisely similar manner in the plant, diastase being pro- 
 duced during the process of germination of all seeds and 
 tubers, for the purpose of effecting this change, and to fulfil 
 other functions less understood, but no doubt equally im- 
 portant. Diastase is found in the seeds only during the 
 period when the starch they contain is passing into sugar ; 
 as soon as that change has taken place, its function is ended, 
 and it disappears. 
 
CHAPTER III. 
 
 THE CHANGES WHICH TAKE PLACE IN THE FOOD OF 
 PLANTS DURING THEIR GROWTH. 
 
 The simple compounds which the plant absorbs from the 
 atmosphere and soil are elaborated within its system, and 
 converted into the various complex substances of which 
 its tissues are composed, by a series of changes, the details 
 of which are still in some respects imperfectly known, al- 
 though their general nature is sufficiently well understood. 
 They may be best rendered intelligible by reference, in 
 the first instance, to the changes occurring during germi- 
 nation, when the young plant is nourished by a supply 
 of food stored up in the seed, in sufficient quantity to 
 maintain its existence until the organs by which it is 
 afterwards to draw its nutriment from the air and soil are 
 sufficiently developed to serve that purpose. 
 
 Changes occurring during Germination. — When a seed 
 is placed in the soil under favourable circumstances, it 
 becomes the seat of an important and remarkable series 
 of chemical changes, which result in the production of the 
 young plant. Experiment and observation have shown 
 that heat, moisture, and air, are necessary to the produc- 
 tion of these changes, and though probably not absolutely 
 essential, the absence of light is favourable in the early 
 stages. The temperature required for germination varies 
 
CHANGES IN FOOD OP PLANTS DURING GROWTH. 55 
 
 greatly in different seeds, some germinating readily at a 
 few degrees above the freezing point, and others requiring 
 a tolerably high temperature. The rapidity with which 
 it takes place appears to increase with the temperature ; 
 but this is true only within very narrow limits, for beyond 
 a certain point heat is injurious, and when it exceeds 120° 
 or 130° Fahrenheit, entirely prevents the process. The 
 presence of oxygen is also essential, for it has been shown 
 that if seeds are placed in a soil exposed to an atmos- 
 phere deprived of that element, or if they be buried so 
 deep that the air does not reach them, they may lie with- 
 out change for an unlimited period ; but so soon as they 
 are exposed to the air, germination immediately com- 
 mences. Illustrations of this fact are frequently observed 
 where earth from a considerable depth has been thrown 
 up to the surface, when it often becomes covered with 
 plants not usually seen in the neighbourhood, which have 
 sprung from buried seeds. When all the necessary condi- 
 tions for germination are fulfilled, the seed absorbs mois- 
 ture, swells up, and sends out a shoot which rises to the 
 surface, and a radicle which descends — the one destined to 
 develope the leaves, the other the roots, by which the plant 
 is afterwards to derive its nutriment from the air and the 
 soil. But until these organs are properly developed, the 
 plant is dependent on the matters contained in the seed 
 itself. These substances are mostly insoluble, but are 
 brought into solution by the atmospheric oxygen acting 
 upon the gluten, and converting it into a soluble sub- 
 stance called diastase, which in its turn reacts upon the 
 starch, converting it first into dextrine, and then into 
 cellulose, and the latter is finally deposited in the form of 
 organised cells, and produces the first little shoot of the 
 plant. At the first moment of germination, the oxygen 
 
56 * AGRICULTURAL CHEMISTRY. 
 
 absorbed appears simply to oxidize the constituents of the 
 seed, but this condition exists only for a very limited 
 period, and is soon followed by the evolution of carbonic 
 acid, water being at the same time formed from the 
 organic constituents of the seed, which gradually dimi- 
 nishes in weight. The amount of this diminution is 
 different with different plants, but always considerable. 
 Boussingault found that the loss of dry substance in the 
 pea amounted in 26 days to 52 per cent, and in wheat to 
 
 57 per cent in 51 days. Against this, of course, is to be 
 put the weight of the young plant produced ; but this is 
 never sufficient to counterbalance the diminished weight 
 of the seed, for Saussure found that a horse bean and the 
 plant produced from it weighed, after 16 days, less by 
 29 per cent than the seed before germination. The same 
 phenomenon is observed in the process of malting, which 
 is in fact the artificial germination of barley, the malt 
 produced always weighing considerably less than the grain 
 from which it was obtained. It was believed by Saus- 
 sure, and the older investigators, that the carbonic acid 
 evolved was entirely produced from starch and sugar ; and 
 as these substances may be viewed as compounds of carbon 
 and water, the change was very simply explained by sup- 
 posing that the carbon was oxidised and converted into 
 carbonic acid and its water eliminated. But this hypo- 
 thesis is incapable of explaining all the phenomena 
 observed ; for woody fibre, which is one of the chief consti- 
 tuents of the young plant, contains more carbon than the 
 starch and sugar from which it must have been produced, 
 and we are, therefore, forced to admit that the action must 
 be more complicated. There is eve^y reason to believe 
 that the nitrogenous constituents of the seed are most 
 abundantly oxidized, for they are remarkably prone to 
 
CHANGES IN FOOD OP PLANTS DURING GROWTH. 57 
 
 change ; but the action of the air is not confined to them, 
 and it appears most probable that all the substances take 
 part in the decomposition, and the process of germination 
 may, in some respects, be compared to decay or putrefac- 
 tion, which, like it, is attended by the absorption of oxy- 
 gen and evolution of carbonic acid; but while in the 
 latter case the residual substances remain in a useless 
 state, in the former they at once become part of a new 
 organism. 
 
 Ghanges occurring during the After-growth of the Plant. 
 — When the plant has developed its roots and leaves, 
 and exhausted the store of materials laid up for it in the 
 seed, it begins to derive its subsistence from the surround- 
 ing air, and to absorb carbonic acid, water, ammonia, and 
 nitric acid, and to decompose and convert them into the 
 different constituents of its tissues. These changes take 
 place slowly at first, and more rapidly as the organs 
 fitted for the elaboration of its food are developed. The 
 roots and the leaves are equally active in performing this 
 duty, the former absorbing the mineral matters along with 
 the carbonic acid, ammonia, nitric acid, and moisture in 
 the soil, or the manure added to it ; the latter gathering 
 the gaseous substances existing in the air. Each of these 
 undergoes a series of changes claiming our consideration. 
 
 Decomposition of Carbonic Acid. — Carbonic acid, which 
 appears to be absorbed with equal readiness by the roots, 
 leaves, and stems, undergoes immediate decomposition, its 
 carbon being retained, and its oxygen, in whole or in 
 part, evolved into the air. This decomposition occurs 
 only under the action of the sun's rays, and has been 
 foimd to be proportionate to the amount of light to which 
 the plant is exposed. It takes place only in the green 
 parts of plants, for though the roots absorb carbonic acid, 
 
58 - AGRICULTURAL CHEMISTRY. 
 
 they cannot decompose it, or evolve oxygen ; and the 
 coloured parts, the flowers, fruits, etc., have an entirely 
 opposite effect, absorbing oxygen and giving off carbonic 
 acid. The absorption of carbonic acid and escape of 
 oxygen has been proved by numerous direct experiments 
 by Saussure and others, in which both atmospheric air 
 and artificial mixtures containing an increased quantity 
 of carbonic acid have been employed. Saussure allowed 
 seven plants of periwinkle ( Vinca minor) to vegetate in 
 an atmosphere containing 7-5 per cent of carbonic acid 
 for six days, during each of which the apparatus was 
 exposed for sis hours to the sun's rays. The air was 
 analysed both before and after the experiment, and the 
 results obtained were — 
 
 Volume " Tw-t- r. Carbonic 
 
 of the air. Nitrogen. Oxygen. ^^ 
 
 Before the experiment, 5746 4199 1116 431 
 
 After „ 5746 4338 1408 
 
 Nitrogen. 
 
 Oxygen. 
 
 4199 
 
 1116 
 
 4338 
 
 1408 
 
 Difference, +139 + 292 -431 
 
 In» this experiment the whole of the carbonic acid, 
 amounting to 431 volumes, was absorbed, but only 292 
 volumes of oxygen were given off Had the carbonic 
 acid been entirely decomposed, and all its oxygen elimi- 
 nated, its volume would have been equal to that of the 
 acid, or 431, so that in this instance 139 volumes of the 
 oxygen of the carbonic acid have been retained to form 
 part of the tissues of the plant. On the other hand, the 
 nitrogen is found to be increased after the experiment. 
 It might be supposed that the nitrogen evolved had been 
 derived from the decomposition of the nitrogenous consti- 
 tuents of the plant, but this cannot be the true explana- 
 tion, because in this particular case it greatly exceeded 
 
CHANGES IN FOOD OF PLANTS DURING GROWTH. 59 
 
 the whole nitrogen contained in the plants experimented 
 on. Its source is not well understood, but Boussingault 
 supposes it to have existed in the interstices of the plant, 
 and to have escaped during the course of the experiment. 
 Saussure found that the oak, the horse-chestnut, and other 
 plants, absorb oxygen and give off carbonic acid in less 
 volumes than the oxygen, while the house-leek and the 
 cactus absorb oxygen without evolving carbonic acid. 
 The absorption and decomposition of carbonic acid takes 
 place only during the day, and matters are entirely re- 
 versed during the night, when oxygen is absorbed and 
 carbonic acid eliminated from all parts of the plants. 
 
 Although the action occurring during the night is the 
 reverse of that which takes place during the day, it is in 
 no degree to be attributed to a re-oxidation of the carbon 
 which had been deposited in the tissues of the plant. It 
 appears, on the contrary, to be a purely mechanical, and 
 not a chemical process. During the night the sap con- 
 tinues to circulate through the vessels of the plant, and 
 moisture, carrying with it carbonic acid in solution, is 
 absorbed by the roots ; but when it reaches the leaves, 
 where the sun's light would have caused its decomposi- 
 tion during the day, it is again exhaled unchanged. The 
 oxygen absorbed during the night must, however, take 
 part in some chemical processes, for if it were merely 
 mechanical, the absorption would not be confined to that 
 gas alone, but would be participated in by the other con- 
 stituents of the air. Moreover, the amount of absorption 
 varies greatly in dififerent plants — being scarcely appreci- 
 able in some, and very abundant in others. Plants con- 
 taining volatile oils, which are readily converted into 
 resins by the action of oxygen, or those containing tannin 
 or other readily oxidizable substances, take up the largest 
 
60 .ASRICULTURAL CHEMISTRY. 
 
 quantity. This is remarkably illustrated by an experi- 
 ment in which the leaves of the Agave americana, after 
 twenty-four hours' exposure in the dark, were found to have 
 absorbed only 0'3 of their volume of oxygen, while those 
 of the fir, in which volatile oil is abundant, bad taken up 
 twice, and those of the oak, containing tannin, eighteen 
 times as much oxygen. 
 
 In the flowers, both by day and night, there is a con- 
 stant absorption of oxygen, and evolution of carbonic acid. 
 In fact, an active oxidation is going on, attended by the 
 evolution of heat, which, in the Arum maculatum and 
 some other plants, is so great as to raise the temperature 
 of the flower 10° or 12° above that of the surrounding 
 air. 
 
 Decomposition of Water in the Plant. — In addition to 
 the function which water performs in the plant, as the 
 solvent of the different substances which form its nutri- 
 ment, and hence as the medium through which they pass 
 into its organs, it serves also as a direct food, undergoing 
 decomposition, and yielding hydrogen to the organic sub- 
 stances. Its constituents, along with those of the car- 
 bonic acid absorbed, undergo a variety of transformations, 
 and form the principal part of the non-nitrogenous con- 
 stituents. It has been already observed that starch, 
 sugar, and the other allied substances, may be considered 
 as compounds of carbon with water ; and they might be 
 supposed to owe their origin to the carbonic acid losing 
 the whole of its oxygen, and direct combination then 
 ensuing between the residual carbon and a certain pro- 
 portion of water ; but this would imply that the latter 
 substance undergoes no decomposition, and though undoubt- 
 edly the simplest view of the case, it is by no means the 
 most probable. It is much more likely that the carbonic 
 
CHANGES IN FOOD QF PLANTS DURING GROWTH. 61 
 
 acid is only partially decomposed, half its oxygen being 
 separated, and replaced by hydrogen, produced by the 
 decomposition of a certain quantity of water into its ele- 
 ments. Thus, for instance, sugar may be produced from 
 twelve equivalents of carbonic acid and twelve equivalents 
 of water, twenty-four equivalents of oxygen being elimi- 
 nated, as thus represented : 
 
 12 equivalents of carbonic acid, C13 O12 O12 
 
 12 „ water, H13 O12 
 
 1 „ sugar, and 24 of ox. C12 H12 O13 +O24 
 
 It must not be supposed that we are in a condition to 
 assert that sugar is really produced in the manner here 
 shown, the illustration being given merely for the purpose 
 of pointing out how it may be supposed to occur, and on 
 a similar principle it is possible to explain the formation 
 of most other vegetable compounds ; and this subject has 
 been very fully discussed by the late Dr. Gregory, in his 
 " Handbook of Organic Chemistry." That water must 
 be decomposed, is evident from the fact, established by 
 analysis, that the hydrogen of the plant generally exceeds 
 the quantity required to form water with its oxygen, so 
 that this excess at least must be produced by the decom- 
 position of water. The hydrogen of the volatile oils, 
 many of which contain no oxygen, and that of the fats, 
 which contain only a small quantity, must manifestly be 
 obtained in a similar manner. 
 
 Decomposition of Ammonia. — The nitrogenous or albu- 
 minous compounds of vegetables must necessarily obtain 
 their nitrogen from the decomposition either of ammonia 
 or nitric acid, experiment having distinctly shown that 
 they are incapable of absorbing it in the free state from 
 the atmosphere. It has been clearly ascertained that the 
 
62 ^ AGRICULTUEAL CHEMISTRY. 
 
 albuminous substances do not contain ammonia, and it is 
 hence apparent that a complete decomposition of that sub- 
 stance must take place in the plant. No doubt carbonic 
 acid and water take part with it in these changes, which 
 must be of a very complex character, and in the present 
 state of our knowledge it seems hopeless to attempt any 
 explanation of them. 
 
 Decomposition of Nitric Acid. — Chemists are not en- 
 tirely at one as to whether nitric acid is directly absorbed 
 by the plant, or is first converted into ammonia. But 
 there are certain facts connected with the chemistry of 
 the soil, to be afterwards referred to, which seem to us to 
 leave no doubt that it may be directly absorbed ; and in 
 that case it must be decomposed, its oxygen being elimi- 
 nated, and the nitrogen taking part with carbon and 
 hydrogen in the formation of the organic compounds. It 
 must be clearly understood that while such changes as 
 those described manifestly must take place, the explana- 
 tions of them which have been attempted by various che- 
 mists are not to be accepted as determinately established 
 facts; they are at present no more than hypothetical 
 views which have been expressed chiefly with the inten- 
 tion of presenting some definite idea to the mind, and are 
 unsupported by absolute proof; they are only inferences 
 drawn from the general bearings of known facts, and not 
 facts themselves. Although, therefore, they are to be 
 received with caution, they have advantages in so far as 
 they present the matter to us in a somewhat more tangible 
 form than the vague general statements which are all 
 that could otherwise be made. 
 
CHAPTER IV. 
 
 THE INORGANIC CONSTITUENTS OF PLANTS. 
 
 When treating of the general constituents of plants, it has 
 been already stated that the older chemists and vegetable 
 physiologists, misled by the small quantity of ash found in 
 them, entertained the opinion that mineral matters were 
 purely fortuitous components of vegetables, and were pre- 
 sent merely because they had been dissolved and absorbed 
 along with the humus, which was then supposed to enter 
 the roots in solution, and to form the chief food of the 
 plant. This supposition, which could only be sustained at 
 a time when analysis was imperfect, has been long since 
 disproved and abandoned, and it has been distinctly shown 
 by repeated experiment that not only are these inorganic 
 substances necessary to the plant, but that every one of 
 them, however small its quantity, must be present if it is 
 to grow luxuriantly and arrive at a healthy maturity. 
 The experiments of Prince Salm Horstmar, before alluded 
 to, have established beyond a doubt, that while a seed may 
 germinate, and even grow, to a certain extent, in absence 
 of one or more of the constituents of its ash, it remains 
 sickly and stunted, and is incapable of producing either 
 flower or seed. 
 
 Of late years the analysis of the ash of different plants 
 has formed the subject of a large number of laborious in- 
 vestigations, by which our knowledge of this subject has 
 
64 
 
 AGEICULTURAL CHEMISTRY. 
 
 been greatly extended. From these it appears that the 
 quantity of ash contained in each plant or part of a plan! 
 is tolerably uniform, differing only within comparativelj^ 
 narrow limits, and that there is a special proportion belong 
 ing to each individual organ of the plant. This fact may 
 be best rendered obvious by the subjoined table, showing 
 the quantity of ash contained in a hundred parts of the 
 different substances dried at 212°. Most of these numbere 
 are the mean of several experiments : — 
 
 Table showing the quantity of inorganic matters in 1 00 
 parts of different plants dried at 212". 
 
 SEEDS. 
 
 Wheat 1-97 
 
 Barley 248 
 
 Oata (with husk) SSO 
 
 Oats (without husk) 206 
 
 Eye 200 
 
 Millet 3-60 
 
 Eice 0-37 
 
 Maize 120 
 
 Peas 2-88 
 
 Beans 322 
 
 Kidney Beans 409 
 
 Lentils 2-51 
 
 Tares 260 
 
 Buckwheat 213 
 
 Linseed 4"40 
 
 Hemp seed 5'60 
 
 Eape seed 4'35 
 
 Indian Eape-seed* 406 
 
 Sunflower 8-26 
 
 Cotton seed 593 
 
 Guinea Com 1 99 
 
 Gold of Pleasure 410 
 
 White Mustard 415 
 
 Black Mustard 431 
 
 Poppy 656 
 
 Niger seed ( G-uizotia oleifera) 7 00 
 
 Earth nut 3 88 
 
 Sweet Ahnond 490 
 
 Horse-chesnut 281 
 
 Grape 2 76 
 
 CloTer 6-19 
 
 Turnip 398 
 
 Carrot 1003 
 
 Sainfoin 5"27 
 
 Italian Eyegrass 6'91 
 
 Mangold-Wurzel 658 
 
 STKAWS AND STEMS. 
 
 Wheat 4-54 
 
 Barley 499 
 
 Oat 7-24 
 
 Winter Eye 515 
 
 Summer Eye 5'78 
 
 Millet 8-32 
 
 Maize 3'60 
 
 Pea 4-81 
 
 Bean 659 
 
 Tares 6-00 
 
 Lentil 538 
 
 Buckwheat 450 
 
 Hops 4-42 
 
 Flax straw 4-25 
 
 Hemp 4"14 
 
 Gold of Pleasure 605 
 
 Eape 4'41 
 
 Potato 14-90 
 
 Jerusalem Artichoke 4-40 
 
 EMTIBE FLANT. 
 
 Potato 17-70 
 
 Spurry., 1006 
 
 Eed Clover 879 
 
 * Apparently a species of Sinapis. 
 
INORGANIC CO;JSTITnENTS OF PLANTS. 
 
 65 
 
 White Clover 8'72 
 
 Yellow Clover 806 
 
 Crimson Clover (T. incama- 
 
 „'«"?) 10-81 
 
 Cow Grass {T. medium) 11-31 
 
 Sainfoin g-^j 
 
 Ryegrass 6-42 
 
 Meadow Foxtail {Alopecvr- 
 
 rus pratemia) 7-81 
 
 Sweet-scented Vernal Grass 
 
 {Aiithoxanthum odoratum) 6-32 
 Downy Oat Grass (Avena 
 
 piibescens) 522 
 
 Bromus erectus 6-21 
 
 Bromus mollis 5-82 
 
 Cynosurus cristatus 6-38 
 
 Dactylis glomeratus 5-31 
 
 Festnca duriuscula 5-42 
 
 Holcus lanatus 6-37 
 
 Hordeum pratense 5-67 
 
 Lolium perenne 7-54 
 
 Foa annua 283 
 
 Poa pratensis 5-94 
 
 Poa trivialis 833 
 
 Phleum pratense 529 
 
 Plantago lanceolata 8 68 
 
 Poterium Sangnisorba 797 
 
 Yarrow 1345 
 
 Bape Kale 8-00 
 
 Cow Cabbage 1000 
 
 Asparagus 6.40 
 
 Parsley 110 
 
 Furze 311 
 
 Chamomile (Anthemis ar- 
 
 vensia) 966 
 
 Wild Chamomile (Matricaria 
 
 . ChamomiUa) g-lO 
 
 Corn Cockle [Agroatemma 
 
 Githago) 13-20 
 
 Corn Blue Bottle (Centaurea 
 
 Cyanui) 732 
 
 Foxglove 10 89 
 
 Hemlock (Conium macula- 
 
 tum) 12-80 
 
 SweetRush [Acorus Calamus) 6-90 
 Common Reed {AruTido 
 
 Phragmites) 1-44 
 
 Celandine (Chelidonium 
 
 majvs) 685 
 
 Equisetum fluviatile 2360 
 
 Equisetum hyemale 11-80 
 
 „ arvense 13-80 
 
 „ linosum 16-50 
 
 Fucus nodosus 1903 
 
 Fucus vesiculoaus 27-63 
 
 Lamiuaria digitata 39-68 
 
 LEAVES. 
 
 Turnip 9-37 
 
 Beet 20-30 
 
 Kohl-rabi 1854 
 
 Carrot 10 95 
 
 Jerusalem Artichoke 2830 
 
 Hemp 2200 
 
 Hop 17-25 
 
 Tobacco 2262 
 
 Spinach 19-76 
 
 Chicory 16-67 
 
 Poplar 23-00 
 
 Red Beech 600 
 
 White Beech 10-5] 
 
 Oak 9-80 
 
 Elm , 16-33 
 
 Horse-chesnut 908 
 
 Maple 2806 
 
 Ash 14-76 
 
 Fir 2-31 
 
 Acacia 1820 
 
 Olive 6-45 
 
 Orange 1373 
 
 Potato 15-10 
 
 Tussac Grass 715 
 
 HOOTS AND TDBEES. 
 
 Potato 4-16 
 
 Jerusalem Artichoke 538 
 
 Turnip 13-64 
 
 Beet 827 
 
 Kohl-rabi 608 
 
 Rutabaga 7-34 
 
 Carrot 580 
 
 Belgian White Carrot 622 
 
 Maiigold-Wurzel 8-78 
 
 Parsnip 552 
 
 Radish 7-35 
 
 Chicory 5-21 
 
 Madder 8-33 
 
 Beech 038 
 
 Apple 1-29 
 
66 
 
 *GRICULTUEAL CHEMISTRY. 
 
 Cherry 0-28 
 
 Birch 100 
 
 Oak 2-50 
 
 Walnut 1-57 
 
 Lime 500 
 
 Horse-chesnut 1'05 
 
 Olive 0-58 
 
 Mahogany 081 
 
 Vine 2-57 
 
 Larch 0'32 
 
 Fir 014 
 
 ScotchFir 0-17 
 
 Filbert 050 
 
 Chesnut 350 
 
 Poplar 080 
 
 Hazel 0-50 
 
 Orange 2-74 
 
 Vine 2-57 
 
 Beech 6-62 
 
 Cherry 10-37 
 
 Fir 1-79 
 
 Oak 600 
 
 Horse-chesnut 7'85 
 
 Filbert 6-20 
 
 Cork 112 
 
 FEUITS. 
 
 Plum 0-40 
 
 Cherry 0-43 
 
 Strawberry 0'41 
 
 Pear 0-41 
 
 Apple 0-27 
 
 Chesnut 099 
 
 Cucumber 0'63 
 
 Vegetable Marrow 5"10 
 
 On examining this table it may be observed that, not- 
 withstanding the very great variety in the proportion of ash 
 in dififerent plants, some general relations may be traced. 
 A certain similarity may be observed between those belong- 
 ing to the same natural family, the seeds of all the cereal 
 grains, for instance, containing in round numbers two 
 per cent of inorganic matters. Leguminous seeds (peas 
 and beans) contain about three per cent, while in rape- 
 seed, linseed, and the other oily seeds, it reaches four per 
 cent. In the stems and straws less uniformity exists, but 
 with the exception of a few extreme cases, the quantity of 
 ash in general approaches pretty closely to £ve per cent. 
 Still more diversified results are obtained from the entire 
 plants ; but this diversity is probably much more apparent 
 than real, and must be, in part at least, dependent on the 
 proportion existing between the stem and leaves, for the 
 leaves are peculiarly rich in ash, and a leafy plant must 
 necessarily yield a higher total percentage of ash, although, 
 if stems and leaves were separately examined, they might 
 not show so conspicuous a difference. 
 
INORGANIC CgNSTITUENTS OF PLANTS. 67 
 
 The leaves surpass all other parts of plants, in the pro- 
 portion of inorganic constit'ients they contain, the table 
 showing that in some instances, as in the maple and Jeru- 
 salem artichoke, they exceed one-fourth of the whole 
 weight of the dry matter. In other leaves, and more 
 especially in those of the coniferse, the proportion is much 
 smaller. Taking the average of all the analyses hitherto 
 made, it appears that leaves contain about thirteen per 
 cent of ash, but the variations on either side are so large 
 that little value is to be attached to it except as an indi- 
 cation of the general abundance of mineral matters. 
 
 In roots and tubers the variations are less, and all, 
 except the potato and the turnip, contain about seven per 
 cent of ash. 
 
 The smallest proportion of mineral matter is found in 
 wood. In one case only does the proportion reach five 
 per cent, while the average scarcely exceeds one, and in 
 the fir the quantity amounts to no more than one six- 
 hundredth of the dry matter. In the bark the quantity is 
 much larger, and may be stated at seven per cent. 
 
 The general proportion of ash found in different parts 
 of plants is given in round numbers in the subjoined 
 table :— 
 
 Wood 1 
 
 Seeds 3 
 
 Stems and straws 5 
 
 Boots and tubers 7 
 
 Bark 7 
 
 Leaves 13 
 
 The differences in the quantity of ash contained in 
 different parts of plants are obviously intended to serve a 
 useful purpose, and it is interesting to observe that the 
 wood which is destined to remain for a long period, some- 
 
68 
 
 ^GEICDLTUKAL CHEMISTRY. 
 
 times for several centuries, a part of the plant, contains the 
 smallest proportion, and it is not improhable that what it 
 does contain is really due, not to the actual woody matter 
 itself, but to the sap which permeates its vessels. By this 
 arrangement but a small proportion of these important 
 mineral matters, which the soil supplies in very limited 
 quantity, is locked up within the plant, and those which 
 are absorbed, after circulating through it, and fulfilling 
 their allotted functions, are accumulated in the leaves, and 
 annually returned to the soil. 
 
 The different proportions of mineral matters contained in 
 the individual organs of plants is most strikingly illustrated 
 when parallel experiments are made on the same species; but 
 the number of instances in which a sufficiently extensive 
 series of analyses has been made to show this, is compara- 
 tively limited, and is confined to the oat, the orange-tree, ■ 
 and the horse chesnut — each of which has formed the 
 subject of a very elaborate investigation. The following 
 table gives the results obtained on the oat : — 
 
 
 
 
 i 
 
 
 
 
 
 la — 
 
 
 
 
 
 
 
 o 5 
 
 o 
 
 £-1 
 
 _ 
 
 ^ 
 
 
 
 Jl 
 
 ll 
 
 11 
 
 If 
 
 u 
 
 Mean. 
 
 
 li 
 
 1-81 
 
 II 
 
 k 
 
 KH 
 
 M 
 
 
 Grain 
 
 214 
 
 i2-22 
 
 211 
 
 1-76 
 
 200 
 
 Husk 
 
 6-47 
 
 603 
 
 6-99 
 
 8-24 
 
 603 
 
 6-75 
 
 Chaff 
 
 16-53 
 
 17-23 
 
 15-59 
 
 1919 
 
 18-97 
 
 16-06 
 
 Leaves 
 
 8-44 
 
 719 
 
 14-59 
 
 10-29 
 
 15-92 
 
 10-88 
 
 Upper part of' 
 Btraw f 
 
 4-95 
 
 5-44 
 
 9-22 
 
 8-25 
 
 11-0 
 
 7-77 
 
 Middle part of" 
 Btraw 1 ' 
 
 611 
 
 5-23 
 
 7-41 
 
 6-53 
 
 9-01 
 
 6-66 
 
 Lower part ot\ 
 straw j 
 
 5-33 
 
 518 
 
 9-76 
 
 7-11 
 
 7-30 
 
 6-93 
 
INORGANIC CONSTITUENTS OF PLANTS. 69 
 
 The specimens of oats on which these analyses were 
 made were from different districts of country, grown on 
 soils of different quality, and were, further, of different 
 varieties ; and yet they show, on the whole, a remarkable 
 similarity in the proportion of ash in each part, and indi- 
 cate that there is a normal quantity belonging to it. Such 
 a series of analyses also affords the most convincing proof 
 that the inorganic matters cannot be fortuitous, and merely 
 absorbed from the soil along with their organic food, 
 as the old chemists supposed, because, in that case, they 
 ought to be uniformly distributed throughout the entire 
 plant, and not accumulated in particular proportions in 
 each individual organ. 
 
 Not only does the proportion of ash vary in the dif- 
 ferent parts of a plant, but even in the same part it is 
 greatly influenced by its period of growth. The laws 
 which regulate these variations are very imperfectly known, 
 but in general it is observed that during the period of 
 active growth the quantity of ash is largest. Thus, it 
 has been found that in early spring the wood of the young 
 shoots of the horse-chesnut contains 9'9 per cent of ash. 
 In autumn this has diminished to 3'4, and the last year's 
 twigs contain only 1"1 per cent, while in the old wood 
 the quantity does not exceed 0'5. Saussure has also 
 observed that the quantity of ash diminishes in certain 
 plants when the seed has ripened. Thus, he found that 
 the percentages of ash, before flowering, and after seeding, 
 were as follows : — 
 
 Before flowering. With ripe seed. 
 
 Sunflower 14-7 93 
 
 Wheat 7-9 3-3 
 
 Maize 12-2 4-6 
 
 On the other hand, the quantity of ash in the leaves 
 
70 ASEICULTURAL CHEMISTRY. 
 
 of trees increases considerably in autumn, as shown by 
 this table : — 
 
 Fex-centagz ot ash IK 
 May. September. 
 
 Oak leaves 5'3 5-5 
 
 Poplar 6-6 9-3 
 
 Hazel 61 7-0 
 
 Horse-chesnut 7*2 8"6 
 
 In general, the proportion of ash appears to increase 
 as the plant reaches maturity, and this is particularly 
 seen in the oat, of which very complete analyses have 
 been made at different periods of its growth : — 
 
 Proportion of Ash in different parts of the Oat at 
 different periods of its growth. 
 
 
 
 
 
 
 Date. 
 
 Stalks. 
 
 Leaves. 
 
 Chaff. 
 
 with husk. 
 
 2d July - 
 
 7-83 
 
 11-35 
 
 
 4-91 
 
 9tliJuly - 
 
 7-80 
 
 12-20 
 
 
 4-36 
 
 16th July- - - 
 
 7 94 
 
 12-61 
 
 600 
 
 3-38 
 
 23d July - - 
 
 7-99 
 
 16-45 
 
 9-11 
 
 3-62 
 
 SOth July - 
 
 7-45 
 
 16-44 
 
 12-28 
 
 4-22 
 
 6th August 
 
 7-63 
 
 16-05 
 
 13-75 
 
 4-31 
 
 13th August - 
 
 6-62 
 
 20-47 
 
 18-68 
 
 4-07 
 
 20th August - 
 
 6-66 
 
 21-14 
 
 2107 
 
 3-64 
 
 27th August - - 
 
 7-71 
 
 22-13 
 
 22-46 • 
 
 3-51 
 
 3d September - - 
 
 8-35 
 
 20-90 
 
 27-47 
 
 3-65 
 
 The increase is here principally confined to the leaves 
 and chaff, while the stalks, which owe their strength to a 
 considerable extent to the inorganic matters they contain, 
 are equally supplied at all periods of their growth. In 
 the grain only is there a diminution, but this is apparent 
 and not real, and is due to the fact that the determination 
 of the quantity of ash, as made on the grain with its husk, 
 and the former, which contains only a small quantity of 
 
INOEGANIC CqUBTITUENTS OF PLANTS. 
 
 7] 
 
 mineral matters, increases much more rapidly in weight 
 than the latter, when it approaches the period of ripening, 
 and it is accordingly during the last three weeks of its 
 growth that this diminution becomes apparent. 
 
 The nature of the soil has also a very important in- 
 fluence on the proportion of mineral matters, and of this 
 an interesting illustration is given in the following table, 
 which shows the quantities found in the grain and straw of 
 the same variety of the pea grown on fourteen different 
 soils : — 
 
 
 Seed. 
 
 Straw. 
 
 
 Seed. 
 
 Straw. 
 
 1 
 
 2-30 
 
 
 8 
 
 2-27 
 
 6-59 
 
 2 
 
 3-25 
 
 3-43 
 
 9 
 
 2-69 
 
 3-49 
 
 3 
 
 4-27 
 
 3-62 
 
 10 
 
 1-61 
 
 3-91 
 
 4 
 
 3-40 
 
 3-39 
 
 11 
 
 311 
 
 5-28 
 
 5 
 
 2-99 
 
 3-90 
 
 12 
 
 3-34 
 
 7-57 
 
 6 
 
 319 
 
 6-80 
 
 13 
 
 2-78 
 
 3-76 
 
 7 
 
 253 
 
 3-90 
 
 14 
 
 301 
 
 3-38 
 
 Although those differences are very large, especially 
 in the straw, and must be attributed to the soil, it has 
 hitherto been found impossible to ascertain the nature of 
 the relation subsisting between it and the crops it yields ; 
 indeed, it must obviously be dependent on very compli- 
 cated questions, which cannot at present be solved, for 
 it may be observed that the increase in the grain does not 
 occur simultaneously with that in the straw, and in seve- 
 ral cases a large proportion of ash in the former is asso- 
 ciated with an unusually small amount in the latter. 
 A priori, it might be expected that those soils which are 
 especially rich in the more important constituents of the 
 ash should yield a produce containing more than the 
 average quantity, but this is very far from being an 
 
72 AGRICULTURAL CHEMISTRY. 
 
 invariable occurrence, and not unfrequently the very re- 
 verse is the case. In some instances the variations may 
 be. traced to the soil, as in the following analyses of the 
 fruit of the horse-chesnut, grown on an ordinary forest 
 soil, and on a rich soil, produced by the disintegration of 
 porphyritic rock, in which the latter yields a much larger 
 quantity of ash : — 
 
 Kernel of seed. Green husk. Brown husk. 
 
 Forest soil 226 4'5.3 1-70 
 
 Porphyry soil 3-36 729 2-20 
 
 In the majority of instances we fail to establish any 
 connection between the nature of the soil and the plants 
 it yields, chiefly because we are still very deficient in 
 analyses of those grown on uncultivated soils ; and on cul- 
 tivated land it is impossible to draw conclusions, because 
 the nature of the manure exerts an influence quite as 
 great, if not greater, than that of the soil itself 
 
 The relative proportion in which the difierent mineral 
 matters enter into the composition of the ash varies within 
 very wide limits, as will be apparent from the following 
 table, containing a selection of the best analyses of our 
 common cultivated and a few uncultivated plants. 
 
INORGANIC CDNSTITDENTS OF PLANTS. 
 
 73 
 
 
 o — ■ 
 
 is 
 
 •-« M 
 
 o' S " 
 
 -S -so 
 
 e g.2 
 
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 8 c 
 
 g)^ 
 
 55 S 
 o* o 
 
 
 1 
 
 
 o>04iNeoooeo*oc«o»ocr)0'r-QoeoD*»-'Cor- 
 
 s 
 
 00£X)OICO»n'^»OCOC^»0»OCiCT30CDC*»^(004»p 
 
 i^ 
 
 CO«^000'*J*CSC^O'^»-<t- 
 
 1- CO o CO o e< w «o 
 
 m 
 
 OCOCOO rfc- tD CI 
 
 
 u 
 
 CO c- 
 
 r* c* CO ci ci CO r* 
 
 Sa 
 
 CO .... 00 
 
 . CO CO -^ ■t' CO t»- CO 
 
 t< 
 
 : : z : I '. ^ I I '. '. zo 
 
 : b b N CO ihoo b 
 
 
 
 CI M <N 1-H C* 
 
 £ 
 
 
 
 j,_; 
 
 a> i-HCi »c— «t>-o o 
 
 r>- e» CO o o c» i> 
 
 ^"i* 
 
 .o ,oo . « o .-. » .--1 
 
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 Ceo '. ^ ^ :«c;oo :o 
 
 : -^ -if do CO ^ c) Tf 
 
 ■ u . 
 
 0»0"eoO'^l"--:rc»OCiOeo-«J*00(MCsCs^ 
 
 S'ga 
 
 r-c-««pc^'*oooi<»«»Oo*eoO'pr--<j'Oeo 
 
 t^< 
 
 O(N'^00D-O»b-HOD0TOQQC'iOo4l<a0O3O 
 
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 ■^Ot-COOiOOOO-l*Ot^COC^ OOf- '-'»C 
 
 U 5 
 
 CS-«a<?0'^CQC0-ttCJO-*-*(M 
 
 -^ . " o .coco . 
 
 
 ob 6 
 
 CI f— CO '-' •-r 
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 1-1 — o C4 w :o^ :oo : 
 
 
 C3 -^ t* 
 
 -^OOCJ«3OC0t*OC0^«D 
 
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 TOOc^c^i;-<»r-OT«-voowor*^o»pcotD 
 
 
 cb^-^t-c^t-coboacJcoiOTf^iOc»?bw»0" 
 
 •A s 
 
 ^ « ^ 
 
 
 
 »oc^QO»nciao^»o^ cxt* ctco— *cot*o»oaO'^ 
 
 c3 
 
 «yC0Ol;-9lOC5O--<iC'O 
 
 i-.D-r-wOJQpl^l^ 
 
 3 
 
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 c*>bTfr-ibbb*b 
 
 3 
 
 ^ ^ 
 
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 ■w^' t--<14 OoCS IO-* -^coo 
 
 1-a 
 
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 C« Cl c- *-■ 
 
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 :::o:^c4::b:. 
 
 : c* CO : : : co t- 
 
 O o 
 
 
 
 
 <N t- O CO CO CI -^ 
 
 o d -^ r- 
 
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 CO-Tt^ . . .CiCaCO .t- 
 
 t . . c«o c- . . 
 
 o 
 
 IX. 
 
 n ^ ^ ' ' ' ^ en <-: : ^ 
 
 (N : :-^ bc< : : 
 
 J 
 
 c*co-^*-<«"cMcoocoeoot*o^^oo«»oc»c» 
 
 
 oci^^^^c4COTfeoooe*coo)C<t^t-eor-coooi> 
 
 bc^cs'^^boatDwr-QOob^^^'^^caW'^ 
 
 co-^ c4,_,cMi— C0'-<c4coe*eo-*04»ococoeo 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 S='=, 
 
 cc 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 t»T "iT- "- 
 
 
 „-i; » -C-0-- 
 
 
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74 
 
 AGRICULTURAL CHEMISTRY. 
 
 
 
 oeMCDcocoiotOoooo-^^iOeo^moicoeooca 
 
 g 
 
 ■^f Ci ClOD — 
 
 .Oi*-'t^t*COCOC*CM'^CO.-icOiOCO»-it*OOHO<^ 
 
 « 
 
 '•-4 t« 0» i-t rH 
 
 :,-,^,_i,_iMQooo<baocoocb6ooot*^cbcMt-*-i 
 
 « 
 
 r-( tH 
 
 CMTOCOeOCOTCMC»CMCM-^»-<COCOCO 
 
 .H 
 
 
 OCD — -"^-^CDO »Ot- CiOOC^Ca osocac4 
 
 g-a 
 
 CM P- ■<*< O ec 
 
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 O O »0 CO t- 
 
 : doo -^ o lb »-^ o iocs : CM t-( ,-t o .cocotj* 
 
 6-^ 
 
 1-1 <N C<l 
 
 " CM CM « 
 
 =^ 
 
 CD Oi OO O C 
 
 CDCDCM»OOCSCDt^CD»— OCM»0*-<Otr>00Or-CD 
 
 •^ u 
 
 O CO CO over- 
 
 .ooaocMaoeot-tcoTPCicMtO'*'*cM-*»-'CM-4'co 
 
 
 T-. CO lOOQ ^ 
 
 -CMCM'^co-il^cbcjcbibrj'eocbca'^iocoo*^'^'")' 
 
 
 
 
 s-g.< 
 
 o lo OS toes 
 
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 00 t* — Tt< C 
 
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 CO CO *-H 
 
 f-H »-l -^ ^^ .-1 ,-1 
 
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 oco o>o 
 
 CDCSO— «COOOt^CMCDOOCOOiQO""OOt-OOOSe" 1 
 
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 .CMO'^J'C-CM— ■«*t>.CMd.--<*Or»CQCMCM«OCMCMCM 
 
 32 
 
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 T-« o o tN 00 r- CO OS «-• ca CO 00 t* c» o CO (N CO *-« »o o> '^ -- o o i 
 
 bus 
 
 ^CMOOCiOO . ■<*' 00 CO o o* u3 M -^ ca CD ** CM QO ■«# CO »o --r t- ca CO 1 
 
 sg 
 
 CO-^dONOO :COG0d0'^>bc4<--l«-^CMC4C4C4«ir«C4C4C4COtH 
 
 
 ooo^o t^ c» CO CO o ^ o CM 00 -<J" CD CM w w.t CM o> ro O "* 
 
 
 •*eMCO«f3-tJ* .iO"*CM00COCMOaC-COCD»—a0COCOCD00CDCDa0Ci 
 
 
 oowdoi-irt* . -^ -^ e- oo osM -^ ocDo ih o do 6i<x>i^ tboo '**' 
 
 
 OJ CM W CM CM ^ CM CM ^ „ ^ ^ ,-. . 
 
 
 CD" coco OOOCM coco lO -* O CO00*< O^CMCOlO^kO^ "* 
 
 eo CMCiio Ci ciooo — ' o Cics . co co ^ , o co cocm ^ co co .cm 
 
 o o3 
 
 ooaocM doc* oi-i 00 " 1-t -^ iih^oo : coo«>t*»b CO w :« 
 
 •3 2 - 
 
 
 CM CO Oi CM OS ■* CO O 1ft CO O CD t> ^ o t-»ooo 
 
 ~se 
 
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 osc CO t- '>> eDO»o 0«D .cooo^osoo .-<*CMOir- 
 
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 CD CD CO »0 — 1 ....,,,,, , CO . , , , .00 .... 
 
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 -1 COOO^ 
 
 
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 S, 
 
 TJ^-HO^«^OTt^»bc«l^^6>^-CM^-1-*0 0"^C>".'iJ^TJ«aO^-^"0>-^ 
 
 COea»-i^C4COCMNC«CMCMCOCOCOCMCOCMCMeOCOCMCM'«*'COCMCO 
 
 
 
 
 
 
 
 
 1 
 
 
 
 1 
 
 1 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 * 
 
 t 
 
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 1. 
 
 
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 ? 
 
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 E g g « 
 
 lit 
 
 C g »! = 
 
 E 
 
 K 
 
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 15'- = 
 
 C P HJ — 
 
 ii 
 
 J 53 = 
 
 •5 
 
 1 
 
 c 
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 c 
 
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 c 
 
 g 
 
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 8 
 
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IKORGANIC CONETITITENTS OF PLANTS. 
 
 75 
 
 C^QOiy-iC*fSr^*-*t^^ C«00 >^C<.-ii-«O0i^H»-ie0--*H00'-'OO»-1 
 
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 ^i^ih-^ooebibodoeoodotbcD 
 
 ''-(■^Tt'^«or-t*co*HOcoco-^Tt<tooococot*i-<<NOO>'-HCsr*«-«co 
 
 
 
 1 
 
 |2 
 
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 o> to CO d CO t« ooe« »o-^.-t«D d o CD oO'^'-t t^-Hco^-* 
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 do^cot-o^ t-il**^ ^t-dcsr* : CO ^ CD : C4 ^ (N ^r-ea-^-^o 
 
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 . . .oo . .cDt-d^-Tt^^dT^QDoo*. -^p . .eo . .«3p - 
 
 li 
 
 11 
 
 cotoi>oocor-aiO»-«*— ocDao^eoot*»HCDcoOc-ooo«^eoio«o 
 c4e>lCOr-lOc>lOO^aoo)c^tOcocot-*->e4eoaoaa•-ieo^»*-lCOO^>*H 
 
 raoocoor-ibdo<0^m^i^dodr«oc»ooo>oo^oooiN 
 
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7G AGRICULTURAL CHEMISTRY. 
 
 A simple inspection of this table leads to various in- 
 teresting conclusions. It is particularly to be observed 
 that some of the constituents of the ash are not invari- 
 ably present, and two at least — namely, alumina and 
 manganese — are found so rarely as to justify the inference 
 that they are not indis^nsable. Of the other substances, 
 iodine is restricted exclusively to sea-plants, but to them 
 it appears to be essential. Oxide of iron, which occurs 
 only in small quantities, has sometimes been considered 
 fortuitous, but it is almost invariably present, and the 
 experiments of Prince Salm Horstmar leave no doubt that 
 it is essential to the plant. Its function Ls unknown, but 
 it is an important constituent of the blood of herbivorous 
 animals, and may be present in the plant, less for its own 
 benefit than for that of the animal of which it is destined 
 to become the food. 
 
 Soda appears to be a comparatively unimportant con- 
 stituent of the ash, of •which it generally forms but a small 
 proportion, although the instances of its entire absence are 
 rare. In the cruciferous plants (turnip, rape, etc.) it is 
 found abundantly, and to them it appears indispensable, 
 but in most other plants it admits of replacement by 
 potash. It seems probable that where the soil is rich in 
 the latter substance, plants will select that alkali in pre- 
 ference to soda ; but as they must have a certain quantity 
 of alkali, the latter may supply the place of the former 
 where it is deficient. Cultivation, probably by enriching 
 the soil in that element, increases the proportion of potash 
 found in the ash of plants, as is remarkably seen in the 
 asparagus, which gave the following quantities of alkalies 
 and chlorine : — 
 
INORGANIC COMSTITCENTS OP PLANTS. 77 
 
 Potash , 
 
 VIM. 
 
 18-8 
 
 Cultivated. 
 
 50-5 
 
 Soda 
 
 Chlorine 
 
 16-2 
 
 16-5 
 
 trace. 
 
 8.3 
 
 The soda having almost entirely disappeared in the cul- 
 tivated plant, while a corresponding increase had taken 
 place in the quantity of potash. 
 
 Potash is one of the most important elements of the 
 ash of all plants, rarely forming less than 20, and 
 sometimes more than 50 per cent of its weight. The 
 latter proportion occurs chiefly in the roots and tubers, 
 but it is also abundant in all seeds and in the grasses. 
 The straw, and particularly the chaff of the cereals, and 
 the leaves of most plants, contain it in smaller quantity, 
 although exceptions to this are not unfrequent, one of the 
 most curious being the case of poppy-seed, which con- 
 tains only about 12 per cent, while the leaves yield up- 
 wards of 37 per cent. 
 
 The proportion of lime varies within very wide limits, 
 being sometimes as low as 1, and in other plants reaching 
 40 per cent of their ash. The former proportion occurs 
 in the grains of the cerealia, and the latter in the leaves 
 of some plants, and more especially in the Jerusalem 
 artichoke. The turnip and some of the leguminous plants 
 also contain it abundantly. 
 
 Magnesia is generally found in small quantity. It is 
 largest in the grains, amounting in them to about 12 or 
 13 per cent of the ash, but in other plants it varies from 
 2. to 4 per cent. Although small in quantity, it is an 
 important substance, and apparently cannot be dispensed 
 with ; at least there is no instance known of its entire 
 absence. 
 
78 . AGEICDLTURAL CEEMISTET. 
 
 Chlorine is by no means an invariable constituent of 
 the asb, although it is generally present, and sometimes 
 in considerable quantity. It is most abundant when the 
 proportion of soda is large, and exists in the ash prin- 
 cipally in combination with that base as common salt. 
 The relation between these two elements may be traced 
 more or less distinctly throughout the whole table of 
 analyses, and conspicuously in that of mangold-wurzel, 
 where the common salt amounts to almost exactly one- 
 half of the whole mineral matter. The analyses of the 
 cultivated and uncultivated asparagus also show that a 
 diminution in the soda is accompanied by a reduction in 
 the proportion of chlorine. 
 
 Sulphuric Acid is an essential constituent of the ash. 
 But it is to be observed that it is in some instances 
 entirely, and in all partially, a product of the combustion 
 to which the plant has been submitted in order to obtain 
 the ash. It is partly derived from the sulphur contained 
 in the albuminous compounds, which is oxidised and con- 
 verted into sulphuric acid during the process of burning 
 the organic matter, and remains in the asL The quantity 
 of sulphuric acid found in the ash is, however, no criterion 
 of that existing in the plant, for a considerable quantity 
 of it escapes during burning. The extent to which this 
 occurs in particular instances is well illustrated by refer- 
 ence to the case of white mustard, which yields an ash 
 containing only 2-19 of sulphuric acid, equivalent to 0-9 
 of sulphur ; and if calculated on the seed itself, this will 
 amount to no more than 0-039 per cent, while experiments 
 made in another manner prove it to cqptain about thirty 
 times as much, or more than 1 per cent. For the purpose 
 of determining the total quantity of sulphur which the 
 
INORGANIC CONSTITUENTS OF PLANTS. 
 
 79 
 
 plants contain in their natural state, it is necessary to 
 oxidise them by means of nitric acid ; and from such ex- 
 periments the following table, showing the total amount 
 of sulphur contained in 100 parts of different plants, dried 
 at 212", has been constructed : — 
 
 Fob palustris ■ 0°165 
 
 Lolium perenne - 0310 
 
 Italian Byegrase - 0329 
 
 TrifoHum pratense 01 07 
 
 repens - 0.099 
 
 Lucerne 0-336 
 
 Vetch - 0178 
 
 Potato tuber 0082 
 
 tops 0-206 
 
 Carrot, root - 0092 
 
 tops 0-745 
 Mangold- Wurzel, root - 0058 
 
 tops - - 0-502 
 
 Swede, root - - 0.435 
 
 tops - 0-458 
 
 Bape . 0-448 
 
 Drumhead Cabbage 
 
 0-431 
 
 Wheat, grain 
 
 0.068 
 
 straw 
 
 - 0-245 
 
 Barley, grain, 
 
 0-053 
 
 straw - 
 
 - 0.191 
 
 Oats, grain 
 
 0-103 
 
 straw - • 
 
 0-289 
 
 Eve, grain 
 
 - 0051 
 
 Beans 
 
 0-056 
 
 Peas - 
 
 0-127 
 
 Lentils - 
 
 - 0.110 
 
 Hops 
 
 1-063 
 
 Gold of Pleasure 
 
 0-253 
 
 Black Mustard 
 
 1-170 
 
 White Mustard 
 
 1-050 
 
 Phosphoric acid, which may be looked upon as the 
 most important mineral constituent of plants, is found to 
 be present in very variable proportions. The straws, 
 stems, and leaves contain it in comparatively small quan- 
 tity, but in the seeds of all plants it is very abundant. 
 In those of the cereals it constitutes nearly half of their 
 whole mineral components, and it rarely falls below 30 
 per cent. 
 
 Carbonic acid occurs in very variable quantities in 
 the ash. It is of comparatively little importance in itself, 
 and is really produced by the oxidation of part of the 
 carbonaceous masters of the plant ; but it has a special 
 interest, in so far as it shows that part of the bases con- 
 tained in the plant must in its natural state have been in 
 
80 AGEICULTUEAL CHEMISTRY. 
 
 union witli organic acids, or combined in some way with 
 the organic constituents of the plant. 
 
 Silica is an invariable constituent of the ash, but in 
 most plants occurs but in small quantity. The cereals 
 and grasses form an exception to this rule, for in them it 
 is an abundant and important element. It is not, how- 
 ever, uniformly distributed through them, but is accumu- 
 lated to a large extent in the stem, to the strength and 
 rigidity of which it greatly contributes. The hard shin- 
 ing layer which coats the exterior of straw, and which is 
 still more remarkably seen on the surface of the bamboo, 
 consists chiefly of silica ; and in the latter plant this ele- 
 ment is sometimes so largely accumulated, that concre- 
 tions resembling opal, and composed entirely of it, are 
 found loose within its joints. The necessity for a large 
 supply of silica in the stems of other plants does not exist, 
 and in them it rarely exceeds 5 or 6 per cent, but in some 
 leaves it is more abundant. 
 
 A knowledge of the composition of the ash of plants is 
 of considerable importance in a practical point of view, 
 and enables us in many instances to explain why some 
 plants will not grow upon particular soils on which others 
 flourish. Thus, for instance, a plant which contains a 
 large quantity of lime, such as the bean or turnip, will 
 not grow in a soil in which that element is deficient, 
 although wheat or barley, which require but little lime, 
 may yield excellent crops. Again, if the soil be deficient 
 in phosphoric acid, those plants only will grow luxuriantly 
 which require but a small quantity of that element, and 
 hence it follows that on such a soil plants cultivated for 
 the sake of their stems, roots, or leaves, in which the 
 quantity of phosphoric acid is small, may yield a good 
 
INORGANIC COSSTITUENTS OP PLANTS. 8] 
 
 return ; while others, cultivated for the sake of their seed, 
 in which the great proportion of that constituent of the 
 ash is accumulated, may yield a very small crop. It is 
 obvious also that even where a soil contains a proper 
 quantity of all its ingredients, the repeated cultivation of 
 a plant which removes a large quantity of any individual 
 element, may, in the course of time, so far reduce the 
 amount of that substance as to render the soil incapable 
 of any longer producing that plant, although, if it be 
 replaced by another which requires but little of the 
 element thus removed, it may again produce an abundant 
 crop. On this principle also, attempts have been made to 
 explain the rotation of crops, which has been supposed to 
 depend on the cultivation in successive years of plants 
 which abstract from the soil preijonderating quantities of 
 different mineral matters. But though this has unques- 
 tionably a certain influence, we shall afterwards see reason 
 to doubt whether it affords a sufficient explanation of all 
 the observed phenomena. 
 
 It may be observed, on examining the table of the per- 
 centage and position of the ash, that some plants are 
 especially rich in alkalies, while in others lime or silica 
 preponderate, and it would therefore be the object of the 
 farmer to employ, in succession, crops containing these 
 elements in different proportions. In carrying out this 
 view, attempts have been made to classify different plants 
 under the heads of silica plants, lime plants, and potash 
 plants ; and the following table, extracted from Liebig's 
 Agricultural Chemistry, in which the constituents of the 
 ash are grouped .under the three heads of salts of potash 
 and soda, lime and magnesia, and silica, gives such a 
 classification as far as it is at present possible : — 
 
 G 
 
82 
 
 . AGRICULTURAL CHEMISTRY. 
 
 
 Salts of 
 
 Potash and 
 
 Soda. 
 
 Salts of 
 Lime and 
 Magnesia. 
 
 Silica. 
 
 a- 
 
 a. a. 
 
 Oat straw with seeds... 
 
 Wheat straw 
 
 Barley straw with seeds 
 Kye straw 
 
 3400 
 22-50 
 1900 
 18-65 
 
 6-00 
 24-34 
 27-82 
 
 4-20 
 3920 
 72-45 
 81-60 
 88-00 
 85-81 
 84-30 
 
 4-00 
 7-20 
 25-70 
 16-52 
 34-00 
 67-44 
 63-74 
 59-40 
 56-00 
 6-50 
 18-40 
 12-00 
 14-19 
 15-70 
 
 62-00 
 
 61-50 
 
 65-30 
 
 63-89 
 
 60-00 
 
 8-30 
 
 7-81 
 
 36-40 
 
 4-90 
 
 18-00 
 
 Good hay 
 
 I Tobacco 
 
 Pea straw 
 
 Potato plant 
 
 Meadow Clover 
 
 Maize straw 
 
 Turnips 
 
 Beet root 
 
 Potatoes 
 
 ^ Jerusalem Artichoke ... 
 
 The special application of these facts must be reserved 
 till we come to treat of the rotation of crops. 
 
 It is manifest that, as the crops removed from the soil 
 all contain a greater or less amount of inorganic matters, 
 they must be continually undergoing diminution, and at 
 length be completely exhausted unless their quantity is 
 maintained from some external source. In many cases 
 the supply of these substances is so large that ages may 
 elapse before this becomes apparent, but -where the quantity 
 is small, a system of reckless cropping may reduce a soil 
 to a state of absolute sterility. A remarkable illustration 
 of this fact is found in the virgin soils of America, from 
 which the early settlers reaped almost unheard-of crops, 
 but, by injudicious cultivation, they were soon exhausted 
 and abandoned, new tracts being brought in and cultivated 
 only to be in their turn abandoned. The knowledge of the 
 composition of the ash of plants assists ns in ascertaining 
 how this exhaustion may be avoided, and indicates the mode 
 in which such soils may be preserved in a fertile state. 
 
CHAPTER V. 
 
 THE SOIL ITS CHEMICAL AND PHYSICAL CHARACTERS. 
 
 No department of agricultural chemistry is surrounded 
 with greater difficulties and uncertainties than that relating 
 to the properties of the soil. When chemistry began to 
 be applied to agriculture, it was not unnaturally supposed 
 that the examination of the soil would enable us to 
 ascertain with certainty the mode in which it might be 
 most advantageously improved and cultivated, and when, 
 as occasionally happened, analysis revealed the absence of 
 one or more of the essential constituents of the plant in a 
 barren soil, it indicated at once the cause and the cure of 
 the defect. But the expectations naturally formed from 
 the facts then observed have been as yet very partially 
 fulfilled ; for, as our knowledge has advanced, it has 
 become apparent that it is only in rare instances that it is 
 possible satisfactorily to connect together the composition 
 and the properties of a soil, and with each advancement 
 in the accuracy and minuteness of our analysis the diffi- 
 culties have been rather increased than diminished. 
 Although it is occasionally possible to predicate from its 
 composition that a particular soil will be incapable of 
 supporting vegetation, it not unfrequently happens that a 
 fruitful and a, barren soil are so similar that it is impos- 
 
8-1: 4GKICULTUEAL CHEMISTRY. 
 
 sible to distingnisli them from one another, and cases even 
 occur in which the barren appears superior to the fertile 
 soil. The cause of this apparently anomalous phenome- 
 non lies in the fact that analysis, however minute, is 
 unable to disclose all the conditions of fertility, and that 
 it must be supplemented by an examination of its physical 
 and other chemical properties, which are not indicated by 
 ordinary experiments. Of late years very considerable 
 progress has been made in the investigation of the 
 properties of the soil, and many facts of great importance 
 have been discovered, but we are still unable to assert 
 that all the conditions of fertility are yet known, and the 
 practical application of those recently discovered is still 
 very imperfectly understood. 
 
 It must not be supposed that a careful analysis of a- 
 soil is without value, for very important practical deduc- 
 tions may often be drawn from it, and when this is not 
 practicable it is not unfrequently due to its being imperfect 
 or incomplete, for it is so complex that the cases in which 
 all the necessary details have been eliminated are even 
 now by no means numerous. In fact, the want of a large 
 number of thorough analyses of soils of different kinds is 
 a matter of some difiSculty, and so soon as a satisfac- 
 tory mode of investigation can be determined upon, a 
 full examination of this subject would be of much import- 
 ance. 
 
 Origin of Soils. — The constituents of the soil, like 
 those of the plant, may be divided into the great classes of 
 organic and inorganic. The origin of the former has 
 been already discussed : they are derived from the decay 
 of plants which have already grown upon the soil, and 
 which, in various stages of decomposition, form the nume- 
 rous class of substances grouped together under the name 
 
CHEMICAL AND PHY6ICAL CHARACTERS OF SOIL. 85 
 
 of humus. The organic substances may therefore be con- 
 sidered as in a manner secondary constituents of the soil, 
 which have been accumulated in it as the consequence of 
 the growth and decay of successive generations of plants, 
 while the primeval soil consisted of inorganic substances 
 only. 
 
 The inorganic constituents of the soil are obtained as 
 the result of a succession of chemical changes going on in 
 the rocks which protrude through the surface of the earth. 
 We have only to examine one of these rocks to observe 
 that it is constantly undergoing a series of important 
 changes. Under the influence of air and moisture, aided 
 by the powerful agency of frost, it is seen to become 
 soft, and gradually to disintegrate, until it is finally con- 
 verted into an uniform powder, in which the structure of 
 the original rock is with difficulty, if at all distinguishable. 
 The rapidity with which these changes take place is very 
 variable ; in the harder rocks, such as granite and mica 
 slate it is so slow as to be scarcely perceptible, while in 
 others, such as the shales of the coal formation, a very few 
 years' exposure is sufficient for the purpose. These actions, 
 operating through a long series of years, are the source of 
 the inorganic constituents of all soils. 
 
 Geology points to a period at which the earth's sur- 
 face must have been altogether devoid of soil, and have 
 consisted entirely of hard crystalline rocks, such as granite 
 and trap, by the disintegration of which, slowly proceed- 
 ing from the creation down to the present time, all the 
 soils which now cover the surface have been formed. But 
 they have been produced by a succession of very compli- 
 cated processes ; for these disintegrated rocks being 
 washed away in the form of fine mud, or at least of 
 minute particles, and being deposited at the bottom of the 
 
86 .AGRICTJLTUEAL CHEMISTRY. 
 
 primeval seas, have there hardened into what are called 
 sedimentary rocks, which being raised above the surface 
 by volcanic action or other great geological forces, have 
 been again disintegrated to yield different soils. Thus, 
 then, all soils are directly or indirectly derived from the 
 crystalline rocks, those overlying them being formed im- 
 mediately by their decomposition, while those found above 
 the sedimentary rocks may be traced back through them 
 to the crystalline rocks from which they were originally 
 formed. 
 
 Such being the case, the composition of different soils 
 must manifestly depend on that of the crystalline rocks 
 from which they have been derived. Their number is by 
 no means large, and they all consist of mixtures in variable 
 proportions of quartz, felspar, mica, hornblende, augite, 
 and zeolites. With the exception of quartz and augite, 
 these names are, however, representatives of different 
 classes of minerals. There are, for instance, several diffe- 
 rent minerals commonly classified under the name of fel- 
 spar, which have been distinguished by mineralogists by 
 the names of orthoclase, albite, oligoclase, and labradorite ; 
 and there are at least two sorts of mica, two of hornblende, 
 and many varieties of zeolites. 
 
 Quartz consists of pure silica, and when in large 
 masses is one of the most indestructible rocks. It 
 occurs, however, intermixed with other minerals in small 
 crystals, or irregular fragments, and forms the entire mass 
 of pure sand. 
 
 The four kinds of felspar which have been already 
 named are compounds of silica with alumina, and another 
 base which is either potash, soda, or lime. Their composi- 
 tion is as follows, two examples of each being given — 
 
CHEMICAL AND PHYSICAL CHAEACTEUS OF SOIL. 
 
 87 
 
 Silica 
 
 Alumina 
 
 Peroxide of 
 iron 
 
 Oxide of man- 
 ganese 
 
 Lime 
 
 Magnesia 
 
 Potash 
 
 Soda 
 
 Orthoclaae. 
 
 Albite. 
 
 Oligoclase. 
 
 Labradorite. 
 
 65-72 
 
 6500 
 
 67-99 
 
 68-23 
 
 62-70 
 
 63-51 
 
 54-66 
 
 54-67 
 
 18-57 
 
 18-64 
 
 19-61 
 
 18-30 
 
 23-80 
 
 23-09 
 
 27-87 
 
 27-89 
 
 traces 
 
 0-83 
 
 0-70 
 
 101 
 
 0-62 
 
 — 
 
 — 
 
 0-31 
 
 traces 
 
 0-13 
 
 
 
 
 
 
 
 
 
 
 
 
 
 0-34 
 
 1-23 
 
 0-66 
 
 1-26 
 
 4-60 
 
 2-44 
 
 12-01 
 
 10-60 
 
 0-10 
 
 103 
 
 — 
 
 0.51 
 
 0-02 
 
 0-77 
 
 — 
 
 0-18 
 
 14-02 
 
 9-12 
 
 — 
 
 2-53 
 
 105 
 
 219 
 
 — 
 
 0-49 
 
 1-25 
 
 3-49 
 99-47 
 
 11-12 
 
 7-99 
 99-83 
 
 8-00 
 
 937 
 
 5-46 
 
 5-05 
 
 10000 
 
 100-08 
 
 100-79 
 
 101-37 
 
 100-00 
 
 99-19 
 
 It is obvious that soils produced by the disintegration 
 of these minerals must differ materially in quality. Those 
 yielded by orthoclase must generally abound in potash, 
 while albite and labradorite, containing little or none of 
 that element, must produce soils in -which it is deficient. 
 The quality of the soil they yield is not however entirely 
 dependent on the nature of the particular felspar which 
 yields it, but is also intimately connected with the extent 
 to which the decomposition has advanced. It is observed 
 that different felspars undergo decomposition with different 
 degrees of rapidity but after a certain time they all begin 
 to lose their peculiar lustre, acquire a dull and earthy 
 appearance, and at length fall into a more or less white 
 and soft powder. During this change water is absorbed, 
 and, by the decomposing action of the air, the alkaline sili- 
 cate is gradually rendered soluble, and at length entirely 
 washed away, leaving a substance which, when mixed 
 with water, becomes plastic, and has all the characters of 
 common clay. The nature of this change will be best 
 seen by the following analysis of the clay produced during 
 this composition, which is employed in the maliufacture of 
 porcelain under the name of kaolin, or china clay — 
 
88 AGRICULTURAL CHEMISTRY. 
 
 Silica 46-80 
 
 Alumina 36-83 
 
 Peroxide of iron 3"11 
 
 Carbonate of lime 0'55 
 
 Potash 0-27 
 
 Water 12-44 
 
 100-00 
 In this instance the decomposition of the felspar had 
 reached its limit, a mere trace of potash being left, bnt if 
 taken at different stages of the process, variable proportions 
 of that alkali are met with. This decomposition of felspar 
 is the source of the great deposits of clay which are so 
 abundantly distributed over the globe, and it takes place 
 with nearly equal rapidity with potash and soda felspar. 
 It is rarely complete, and the soils produced from it 
 frequently contain a considerable proportion of the unde- 
 composed mineral, which continues for a long period to 
 yield a supply of alkalies to the plants which grow on them. 
 Mica is a very widely distributed mineral, and two 
 varieties of it are distinguished by mineralogists, one of 
 which is characterised by the large quantity of magnesia 
 it contains. Different specimens are found to vary very 
 greatly in composition, but the following analyses may 
 
 represent their most usual composition : 
 
 Mica. 
 
 Potash. Magnesia. 
 
 Silica 46-36 42-65 
 
 Alumina 36-80 12-96 
 
 Peroxide of iron 4-53 — 
 
 Protoxide of iron — 7.11 
 
 Oxide of manganese 0-02 1-06 
 
 Magnesia — 25-75 
 
 Potash 9-22 603 
 
 Hydrofluoric acid 0-70 0-62 
 
 Water 1-84 3-17 
 
 99^ 9^35 
 
CHEMICAL AND PHYglCAL CHARACTERS OF SOIL. 89 
 
 Mica undergoes decomposition with extreme slowness, 
 as is at once illustrated by the fact that its shining scales 
 may frequently be met with entirely unchanged in the soil. 
 Its persistence is dependent on the small quantity of 
 alkaline constituents which it contains ; and for this 
 reason it is observed that the magnesian micas undergo 
 decomposition less rapidly than those containing the 
 larger quantity of potash. Eventually, however, both 
 varieties become converted into clay, their magnesia and 
 potash passing gradually into soluble forms. 
 
 Hornblende and augite are two widely distributed 
 minerals, which are so similar in composition and properties 
 that they may be considered together. Of the former two 
 varieties, basaltic and common have been distinguished, and 
 their composition is given below : — 
 
 Horublende. 
 Common. Basaltic. Augite. 
 
 Silica 41-50 42-24 50-12 
 
 Alumina 1575 1392 4-20 
 
 Protoxide of iron... 7-75 14-59 11-60 
 Oxide 
 ganese 
 
 Lime 14-09 1224 2055 
 
 Magnesia 19-40 13 74 1370 
 
 Water 0-50 — — 
 
 of man- 1 ^,^^ (, 33 
 se J 
 
 99-24 97-05 99-67 
 
 In these minerals alkalies are entirely absent, and their 
 decomposition is due to the presence of protoxide of iron, 
 which readily absorbs oxygen from the air, when the 
 magnesia is separated and a ferruginous clay left. 
 
 The minerals just referred to, constitute the great 
 bulk of the mountain masses, but they are associated with 
 
90 ^ AGRICULTURAL CHEMISTRY. 
 
 maBy others which take part in the formation of the soil. 
 Of these the most important are the zeolites which do not 
 occur in large masses but are disseminated through the 
 other rocks in small quantity. They form a large class 
 of minerals of which Thomsonite and natrolite may be 
 selected as examples — 
 
 Thomfionite. Natrolite. 
 
 Silica 38-73 4868 
 
 Alumina 30 84 2636 
 
 Lime 13 43 — 
 
 Potash 0-54 023 
 
 Soda 3-85 1600 
 
 Water 1309 9-55 
 
 100-48 100-83 
 
 They are chiefly characterized by containing their silica 
 in a soluble state, and hence may yield that substance to the 
 plants in a condition particularly favourable for absorption. 
 
 It is obvious from what has been stated that all these 
 minerals are capable, by their decomposition, of yielding 
 soft porous masses having the physical properties of 
 soils, but most of them would be devoid of many essential 
 ingredients, while not one of them would yield either phos- 
 phoric acid, sulphuric acid, or chlorine. It has, however, 
 been recently ascertained that certain of these minerals, or 
 at least the rocks formed from them, contain minute, but 
 distinctly appreciable traces of phosphoric acid, although 
 in too small quantity to be detected by ordinary analysis ; 
 and small quantities of chlorine and sulphuric acid may 
 also in most instances be found. 
 
 Still it will be observed that most of these minerals 
 would yield a soil containing only two or three of those 
 substances, which, as we have already learned, are essen- 
 tial to the plant. Thus, potash felspar, while it would 
 
CHEMICAL AND PHYSICAL CHAEACTEES OF SOIL. 91 
 
 give abundance of potash, would be but an inefBcient 
 source of lime and magnesia; and labradorite, which 
 contains abundance of lime, is altogether deficient in mag- 
 nesia and potash. 
 
 Nature has, however, provided against this difficulty, 
 for she has so arranged it that these minerals rarely occur 
 alone, the rocks which form our great mountain masses 
 being composed of intimate mixtures of two or more of 
 them, and that in such a manner that the deficiencies of 
 the one compensate those of the other. We shall shortly 
 mention the composition of these rocks. 
 
 Granite is a mixture of quartz, felspar, and mica in 
 variable proportions, and the quality of the soil it yields 
 depends on whether the variety of felspar present be 
 orthoclase or albite. When the former is the constituent, 
 granite yields soils of tolerable fertility, provided their 
 climatic conditions be favourable ; but it frequently occurs 
 in high and exposed situations which are unfavourable to 
 the growth of plants. Gneiss is a similar mixture, but 
 characterised by the predominance of mica, and by its 
 banded structure. Owing to the small quantity of felspar 
 which it contains, and the abundance of the difficulty 
 decomposable mica, the soils formed by its disintegration 
 are generally inferior. Mica slate is also a mixture of 
 quartz, felspar, and mica, but consisting almost entirely of 
 the latter ingredient, and consequently presenting an 
 extreme infertility. The position of the granite, gneiss, 
 and mica slate soils in this country is such that very few 
 of them are of much value ; but in warm climates they 
 not unfrequently produce abundant crops of grain. Syenite 
 is a rock similar in composition to granite, but having the 
 mica replaced by hornblende, which by its decomposition 
 yields supplies of lime and magnesia more readily than 
 
92 . AGKICULTCRAL CHEMISTRY. 
 
 they can be obtained from the less easily disintegrated 
 mica. For this reason soils produced from the syenitic 
 rocks are frequently possessed of considerable fertility. 
 
 The series of rocks of which greenstone and trap are 
 types, and which are very widely distributed, differ greatly 
 in composition from those already mentioned. They are 
 divisible into two great classes, which have received the 
 names of diorite and dolerite, the former a mixture of 
 albite and hornblende, the latter of augite and labrador- 
 ite, sometimes with considerable quantities of a sort of 
 oligoclase containing both soda and lime, and of different 
 kinds of zeolitic minerals. Generally speaking, the soils 
 produced from diorite are superior to those from dolerite. 
 The albite which the former contains undergoes a rapid 
 decomposition, and yields abundance of soda along with 
 some potash, which is seldom altogether wanting, while 
 the hornblende supplies both lime and magnesia. Dolerite, 
 when composed entirely of augite and labradorite, produces 
 rather inferior soils ; but when it contains oligoclase and 
 zeolites, and comes under the head of basalt, its disintegra- 
 tion is the source of soils remarkable for their fertility ; 
 for these latter substances undergoing rapid decomposition 
 furnish the plants with abundant supplies of alkalies and 
 lime, while the more slowly decomposing hornblende 
 affords the necessary quantity of magnesia. In addition 
 to these, the basaltic rocks are found to contain appreciable 
 quantities of phosphoric acid, so that they are in a con- 
 dition to yield to the plant almost all its necessary con- 
 stituents. 
 
 The different rocks now mentioned, with a few others 
 of less general distribution, constitute the whole of our 
 great mountain masses ; and while their general composi- 
 tion is such as has been stated, they frequently contain 
 
CHEMICAL AND PHYSICAL CHARACTEES OF SOIL. 93 
 
 disseminated through them quantities of other minerals 
 which, though in trifling quantity, nevertheless add their 
 quota of valuable constituents to the soils. Moreover, the 
 exact composition of the minerals of which the great 
 masses of rocks are composed is liable to some variety. 
 Those which we have taken as illustrations have been 
 selected as typical of the minerals ; but it is not uncommon 
 to find albite containing 2 or 3 per cent of potash, labra- 
 dorite with a considerable proportion of soda, and zeolitic 
 minerals containing several per cent of potash, the pre- 
 sence of which must of course considerably modify the 
 properties of the soils produced from them. They are 
 also greatly affected by the mechanical influences to 
 which the rocks are exposed; and being situated for 
 the most part in elevated positions, they are no sooner 
 disintegrated than they are washed down by the rains. 
 A granite, for instance, as the result of disintegration, has 
 its felspar reduced to an impalpable powder, while its 
 quartz and mica remain, the former entirely, the latter in 
 great part, in the crystalline grains which existed originally 
 in the granite. If such a disintegrated granite remains 
 on the spot, it is easy to see what its composition must be ; 
 but if exposed to the action of running water, by which 
 it is washed away from its original site, a process of 
 separation takes place, the heavy grains of quartz are first 
 deposited, then the lighter mica, and lastly the felspar. 
 Thus there may be produced from the same granite, soils 
 of very different nature and composition, from a pure and 
 barren sand to a rich clay formed entirely of felspathic debris. 
 The sedimentary or stratified rocks are formed of 
 particles carried down by water and deposited at the 
 bottom of the primeval seas from which they have been 
 upheaved in the course of geological changes. The 
 
94 , AGRICULTURAL CHEMISTRY. 
 
 process of their formation may be watched at the present 
 day at the mouths of all great rivers, where a delta com- 
 posed of the suspended matters carried down by the waters 
 is slowly formed. The nature of these rocks must there- 
 fore depend entirely on that of the country through which 
 the river flows. If its course runs through a country in 
 which lime is abundant, calcareous rocks will be deposited, 
 and if it passes through districts of different geological 
 characters the deposit must necessarily consist of a mix- 
 ture of the disintegrated particles of the different rocks 
 the river has encountered. Eor this reason it is im- 
 possible to enter upon a detailed account of their com- 
 position. It is to be observed, however, that the particles 
 of which they are composed, though originally derived 
 from the crystalline rocks, have generally undergone a 
 complex series of changes, geology teaching that, after 
 deposition, they may in their turn undergo disintegration 
 and be carried away by water, to be again deposited. 
 Their composition must therefore vary not merely accor- 
 ding to the nature of the rock from which they have been 
 formed, but also according to the extent 'to which the 
 decomposition has gone, and the successive changes to 
 which they have been exposed. They may be reduced to 
 the three great classes of clays, including the different 
 kinds of clay slates, shales, etc., sandstone and limestone. 
 It must be added also, that many of them contain carbon- 
 aceous matters produced by the decomposition of early races 
 of plants and animals, and that mixtures of two or more 
 of the different classes are frequent. 
 
 The purest clays are produced by the decomposition of 
 felspar, but almost all the crystalline rocks may produce 
 them by the removal of their alkalies, iron, lime, etc. 
 Where circumstances have been favourable, the whole of 
 
CHEMICAL AND PHYSICAL CHAKACTERS OF SOIL. 95 
 
 these substances are removed, and the clay which remains 
 consists almost entirely of silica and alumina, and yields 
 a soil which is almost barren, not merely on account of 
 the deficiency of many of the necessary elements of plants, 
 but because it is so stiff and impenetrable that the roots 
 find their way into it with difficulty. It rarely happens, 
 however, that decomposition has advanced so far as to 
 remove the whole of the alkalies, which is exemplified by 
 the following analyses of the fire clay of the coal formation, 
 and of transition clay slate : — 
 
 Transition -e.. o. 
 
 Clay Slate. F"-« Clay. 
 
 Silica 60-03 54-77 
 
 Alumina 14-91 28-61 
 
 Peroxide of iron 8-94 4-92 
 
 Lime 208 0-58 
 
 Magnesia 4-22 1-14 
 
 Potash 3-87 100 
 
 Soda — 0-24 
 
 Carbonic acid 
 
 } 
 
 Wft, i '■" «■« 
 
 99-72 99-50 
 
 The sandstones are derived from the siliceous particles 
 of granite and other rocks, and consist in many cases of 
 nearly pare silica, in which case their disintegration 
 produces a barren sand, but they more frequently contain 
 an admixture of clay and micaceous scales, which some- 
 times form a by no means inconsiderable portion of them. 
 Such sandstones yield soils of better quality, but they are 
 always light and poor. Where they occur interstratified 
 with clays, still better soils are produced, the mutual 
 admixture of the disintegrated rocks affording a substance 
 of intermediate properties, in which the heaviness of the 
 clay is tempered by the lightness of the sandstone. 
 
96 . AGEICTJLTURAL CHEMSTEY. 
 
 Limestone is one of the most widely distributed of tte 
 stratified rocks, and in different localities occurs of very 
 different composition. Limestones are divided into two 
 classes, common and magnesian ; the former a nearly pure 
 carbonate of lime, the latter a mixture of that substance 
 with carbonate of magnesia. But while these are the 
 principal constituents, it is not imcommon to find small 
 quantities of phosphate and sulphate of lime, which, how- 
 ever trifling their proportions, are not unimportant in an 
 agricultural point of view. The following analyses will 
 serve to illustrate the general composition of these two 
 sorts of limestone as they occur in the early geological 
 formations : — 
 
 COMMOS. MAONE3IAK. 
 
 
 'Mid- 
 
 Suther- 
 
 Suther- 
 
 Dum- 
 
 
 Lothian. 
 
 land. 
 
 land. 
 
 fries. 
 
 Silica 
 
 2-00 
 
 7-42 
 
 6-00 
 
 2-31 
 
 Peroxide of iron \ 
 and alumina j 
 
 0-45 
 
 0-76 
 
 1-57 
 
 2-00 
 
 Carbonate of lime 
 
 93-61 
 
 84-11 
 
 50-21 
 
 58-81 
 
 Carbonate of ") 
 magnesia.... j 
 
 1-62 
 
 7-45 
 
 41-22 
 
 36-41 
 
 
 
 
 
 Phosphate of lime 
 
 0-56 
 
 ■ •• 
 
 • .. 
 
 
 Sulphate of lime 
 
 0-92 
 
 ... 
 
 
 0-10 
 
 Organic matter.... 
 
 0-20 
 
 ... 
 
 • .. 
 
 • •- 
 
 Water 
 
 0-50 
 
 ... 
 
 0-69 
 
 ... 
 
 99-86 99-74 99-69 9963 
 
 These limestones are hard and possess to a greater or 
 less extent a crystalline texture. They are replaced in 
 later geological periods by others which are much softer, 
 and often purer, of which the oolitic limestones, so called 
 from their resemblance to the roe of a fish, and chalk are 
 the most important. Other limestones are also known 
 
CHEMICAL AND PHY«ICAL CHAKACTEES OF SOIL. 97 
 
 which contain an admixture of clay. The soils produced 
 by the disintegration of limestone and chalk are generally 
 light and porous, but when mixed with clay, possess a very 
 high degree of fertility, and this is particularly the case 
 with chalk, which yields some of the most valuable of all 
 soils. But it is true only of the common limestones, for 
 experience has shown that those which contain magnesia 
 in large quantity are often prejudical to vegetation, and 
 sometimes yield barren or inferior soils. 
 
 Such are the general characters of the three great 
 classes of stratified rocks ; any attempt to particularise the 
 numerous varieties of each would lead us far beyond the 
 limits of the present work. It is necessary, however, to 
 remark, that in many instances one variety passes into 
 the other, or, more correctly speaking, sedimentary rooks 
 occur, which are mixtures of two, or more of the three 
 great classes. In fact, the name given to each really 
 expresses only the preponderating ingredient, and many 
 sandstones contain much clay, shales and clay slates 
 abound in lime, and limestones in sand or clay, so that it 
 may sometimes be a matter of some difficulty to decide to 
 which class they belong. Such mixtures usually produce 
 better soils than either of their constituents separately, and 
 accordingly, in those geological formations in which they 
 occur, the soils are generally of excellent quality. The 
 same effect is produced where numerous thin beds of mem- 
 bers of the different classes are interstratified, the disin- 
 tegrated portions being gradually intermixed, and valuable 
 soils formed. 
 
 The fertility of the soils formed from the stratified rocks 
 is also increased by the presence of organic remains which 
 afford a supply of phosphoric acid, and which are sometimes 
 so abundant as to form a by no means unimportant part of 
 
 H 
 
98 • AGRICULTtTRAL CHEMISTKT. 
 
 their mass. They do not occur in the oldest sedimentary 
 rocks, but as we ascend to the more recent geological 
 epochs, they increase in abundance, until, in the greensands 
 and other recent formations, whole beds of coprolites and 
 other organic remains are met with. Great differences 
 are observed in the quality of the soils yielded by different 
 rocks. In general, those formed by the disintegration of 
 clay slates are cold, heavy, and very difficult and expensive 
 to work ; those of sandstone light and poor, and of lime- 
 stone often poor and thin. These statements must, however, 
 be considered as very general ; for individual cases occur in 
 which some of these substances may produce good soils, re- 
 markable exceptions being offered by the lower chalk and 
 some of the shales of the coal formation. Little is at pre- 
 sent known regarding the peculiar nature of many of these 
 rocks, or their composition ; and the cause of the differences 
 in the fertility of the soil produced from them is a subject 
 worthy of minute investigation. 
 
 Chemical Composition of the Soil. — Keference has been 
 already made to the division of the constituents of the soil 
 into the two great classes of organic and inorganic. And 
 when treating of the sources of the organic constituents of 
 plants, we entered with some degree of minuteness into the 
 composition and relations of the different members of the 
 former class, and expressed the opinion that they did not 
 admit of being directly absorbed by the plant. But though 
 the parts then stated lead to the inference that, as a direct 
 source of these substances, humus is unimportant, it has 
 other functions to perform which render it an essential con- 
 stituent of all fertile soils. These functions are dependent 
 partly on the power which it has of absorbing and entering 
 into chemical composition with ammonia, and with certain 
 of the soluble inorganic substances, and partly on the effect 
 
CHEMICAL AND PHYSICAL CHARACTERS OF SOIL. 99 
 
 which the carbonic acid produced by its decomposition 
 exerts on the mineral matters of the soil. In the former 
 way, its effects are strikingly seen in the manner in which 
 ammonia is absorbed by peat ; for it suffices merely to pour 
 upon some dried peat a small quantity of a dilute solu- 
 tion of ammonia to find its smell immediately disappear. 
 This peculiar absorptive power extends also to the fixed 
 alkalies, potash and soda, as well as to lime and magnesia, 
 and has an important effect in preventing these substances 
 being washed out of the soil — a property which, as we 
 shall afterwards see, is possessed also by the clay con- 
 tained in greater or less quantity in most soils. On the 
 other hand, the air and moisture which penetrate the soil 
 cause its decomposition, and the carbonic acid so produced 
 attacks the undecomposed minerals existing in it, and 
 liberate the valuable substances they contain. 
 
 In considering the composition of a soil, it is important 
 to bear in mind that it is a substance of great complexity, 
 not merely because it contains a large number of chemical 
 elements, but also because it is made up of a mixture of 
 several minerals in a more or less decomposed state. The 
 most cursory examination shows that it almost invariably 
 contains sand and scales of mica, and other substances can 
 often be detected in it. Now it has been already observed 
 that the minerals of which soils are composed, differ to a 
 remarkable extent in the facility with which they undergo 
 decomposition, and the bearing of this fact on its fertility is 
 a matter of the highest importance, for it has been found 
 that the mere presence of an abundant supply of all the 
 essential constituents of plants is not always sufficient to 
 constitute a fertile soil. Two soils, for instapce, may be 
 found on analysis to have exactly the same composition, 
 although in practice one proves barren and the other fertile. 
 
100 iGEICUIiTURAL CHEMSTEY. 
 
 The cause of this difference lies in the particular state of 
 combination in which the elements are contained in them, 
 and unless this be such that the plant is capable of absorb- 
 ing them, it is immaterial in what quantity they are present, 
 for they are thus locked up from use, and condemn the soil 
 to hopeless infertility. 
 
 It is admitted that unless the substances be present in 
 a state in which they can be dissolved, the plant is incap- 
 able of absorbing them ; but it is a matter of doubt whether 
 it is necessary that they be actually dissolved in the water 
 which permeates the soil, or whether the plant is capable 
 of exercising a directly solvent action. The latter view 
 is the most probable, but at the same time it cannot be 
 doubted, that if they are presented to the plant in solution, 
 they will be absorbed in that state in preference to any 
 other. Hence it has been considered important in the 
 analysis of a soil, not to rest content with the determina- 
 tion of the quantity of each element it contains, but to 
 obtain some indication of the state of combination in which 
 it exists, so as to have some idea of the ease or difSculty 
 with which they may be absorbed. For this purpose it is 
 necessary to determine, 1st, The substances soluble in 
 water ; 2d, Those insoluble in water, but soluble in acids ; 
 3d, Those insoluble both in water and acids ; and if to 
 these the organic constituents be added, there are four sepa- 
 rate heads under which the components of a soil ought to 
 be classified. This classification is accordingly adopted in 
 the most careful and minute analyses ; but the difSculty 
 and labour attending them has hitherto precluded the 
 possibility of making them except in a few instances ; and, 
 generally speaking, chemists have been contented with 
 treating the soil with an acid, and determining in the solu- 
 tion all that is dissolved. Such analyses are often useful 
 
CHEMICAL AND PHYSICAL CHAEACTERS OF SOIL. 101 
 
 for practical purposes, as for example, when they show the 
 absence of lime, or any other individual substance, by the 
 addition of which we may rectify the deficiency of the soil ; 
 but they are of comparatively little scientific value, and 
 throw but little light on the true constitution of the soil, 
 and the sources of its fertility. Nor is it likely that much 
 satisfactory information will be obtained until the number 
 of minute analyses is so far extended as to establish the 
 fundamental principles on which the various properties of 
 the soil depends. 
 
 The separation of the constituents of a soil into the 
 four great groups already mentioned, is effected in the fol- 
 lowing manner : — A given quantity of the soil is boiled 
 with three or four successive quantities of water, which 
 dissolves out all the soluble matters. These generally 
 amount to about one-half per cent of the whole soil, and 
 consist of nearly equal proportions of organic and 
 inorganic substances. In very light and sandy soils, it 
 occasionally happens that not more than one or two-tenths 
 per cent dissolve in water, and in peaty soils, on the other ' 
 hand, the proportion is sometimes considerably increased, 
 principally owing to the abundance of soluble organic 
 matters. 
 
 When the residue of this operation is treated with 
 dilute hydrochloric acid, the matters soluble in acids are 
 obtained in the fluid. The proportion of these substances 
 is liable to very great variations, and in some soils 
 of excellent quality, and well adapted to the growth of 
 wheat, it does not exceed 3 per cent ; while in cal- 
 careous soils, such as those of the chalk formation, it may 
 reach as much as 50 or 60 per cent. In general, 
 however, it amounts to about 10 per cent. The organic 
 constituents are also very variable in amount ; ordinary 
 
102 
 
 4GWCULTDKAL CHEMISTKT. 
 
 soils of good quality containing from 2 to 10 per cent, 
 while in peat soils they not unfrequently reach 30 or 
 even 50 per cent. But these cannot be considered fertile 
 soils. The insoluble constituents are likewise subject to 
 great variations, but, in the ordinary clay and sandy soils 
 of this country, they generally form from 70 to 85 per 
 cent of the whole. 
 
 The distribution of the constituents under these diffe- 
 rent heads will be best illustrated by a few analyses of 
 soils of good quality, and for this purpose we shall select 
 two, noted for the excellent crops of wheat they produce, 
 and for their general fertility. The analyses were made 
 from the upper 10 inches, and a quantity of the 10 inches 
 immediately subjacent was analysed as subsoil. The first 
 is the ordinary wheat soil of the county of Mid-Lothian, 
 the other the alluvial soil of the Carse of Gowrie in 
 Perthshire, so celebrated for the abundance and luxuriance 
 of the crops it produces. 
 
 SDBSTANCES SOLUBLE 
 IH WATER. 
 
 Silica 
 
 Lime ... 
 
 Magnesia - 
 
 Chlor. of magnesium 
 I Potash - 
 I Soda - - - 
 I Chloride of potassium 
 I Chloride of sodium - 
 
 Sulphuric acid 
 
 Chlorine 
 
 Organic matters 
 
 Mid-LothiRn. 
 
 Perthshire. 
 
 Soil. 
 
 Subsoil. 
 
 SoiL 
 
 Subsoil. 
 
 0-0149 
 
 00104 
 
 00072 
 
 0-0461 
 
 00300 
 
 00072 
 
 0-0184 
 
 0-0306 
 
 00097 
 
 00016 
 
 0-0040 
 
 0-0034 
 
 — 
 
 — 
 
 — 
 
 0-0033 
 
 00034 
 
 00037 
 
 — 
 
 — 
 
 00065 
 
 00049 
 
 — 
 
 — 
 
 — 
 
 — 
 
 00088 
 
 00080 
 
 — 
 
 — 
 
 0-0110 
 
 00166 
 
 00193 
 
 00124 
 
 0-0089 
 
 0-0239 
 
 trace 
 
 trace 
 
 — 
 
 — 
 
 01481 
 
 0-2228 
 
 0-0608 
 
 0-1342 
 
 0-2319 
 
 0-2630 
 
 01191 
 
 0-2661 
 
CHEMICAL AND PHYSICAL CHARACTEES OF SOIL. 103 
 
 
 Mid-Lothian. 
 
 Fetthsliiie. 
 
 Sott. 
 
 Subsoil. 
 
 , Sou. 
 
 Subsoil. 
 
 SOLUBLE in ACIDS. 
 
 
 
 
 
 Silica - - 
 
 01490 
 
 0-0680 
 
 00482 
 
 0-1697 
 
 Peroxide of iron 
 
 51730 
 
 3-4820 
 
 4-8700 
 
 4-6633 
 
 Alumina 
 
 21540 
 
 1-8130 
 
 2-6900 
 
 3-9070 
 
 Lime - - 
 
 0-4470 
 
 0-3810 
 
 0-3616 
 
 0-5050 
 
 Magnesia - 
 
 0-4120 
 
 0-2850 
 
 0-3960 
 
 0-9420 
 
 Potash - 
 
 00650 
 
 01650 
 
 0-3445 
 
 01670 
 
 Soda - 
 
 0-0050 
 
 0-0560 
 
 0-1242 
 
 0-1920 
 
 Snlpliuric acid 
 
 0-0250 
 
 00850 
 
 0-0911 
 
 0-0160 
 
 Phosphoric acid - 
 
 0-4300 
 
 0-1970 
 
 0-2400 
 
 0-2680 
 
 Carbonic acid 
 
 INSOLUBLE IK ACIDS. 
 
 — 
 
 — 
 
 00500 
 
 
 8-8600 
 
 6-5320 
 
 9-2156 
 
 10-8300 
 
 
 
 
 
 Silica 
 
 71-3890 
 
 82-5090 
 
 63-1400 
 
 61-4200 
 
 Alumina - 
 
 4-7810 
 
 3-5120 
 
 11-3500 
 
 10-3400 
 
 Peroxide of iron 
 
 trace 
 
 trace 
 
 — 
 
 1-5670 
 
 Lime - - 
 
 0-7520 
 
 0-5500 
 
 0-4500 
 
 a-7400 
 a-4450 
 
 Magnesia - 
 
 0-6610 
 
 0-5500 
 
 0-6200 
 
 Potash - 
 
 0-2860 
 
 — 
 
 2-4500 
 
 2-0030 
 
 Soda . 
 
 0-4220 
 
 — 
 
 1-3100 
 
 0-8440 
 
 78-2910 
 
 87-1210 
 
 79-3200 
 
 77-3590 
 
 
 
 
 
 Insoluble organic') 
 matter - / 
 
 8-8777 
 
 4-2370 
 
 7-7400 
 
 6-2910 
 
 Humine - 
 
 0-8850 
 
 0-3450 
 
 0-0700 
 
 00840 
 
 Humic acid - 
 
 0-1340 
 
 0-0310 
 
 0-6800 
 
 0-3600 
 
 Apocrenic acid 
 Water - 
 
 Sum of all the con- \ 
 stituents - j 
 
 0-1533 
 
 — 
 
 — 
 
 0-0929 
 
 2-6840 
 
 1-7670 
 
 2-7000 
 
 4-5750 
 
 12.7340 
 
 6.3800 
 
 n-1900 
 
 11-4020 
 
 
 
 
 
 100-1169 
 
 100.2960 
 
 99-8447 
 
 99-8571 
 
 AMOUNT OF CAKBO 
 
 N, HYDBOeE 
 
 N, NITEOOEN 
 
 , AND OXY 
 
 GEN 
 
 CONTAIHE 
 
 D IH 100 PA 
 
 KTS OF EACH 
 
 SOIL. 
 
 
 Carbon 
 
 4-510 
 
 1-3060 
 
 2-55 
 
 203 
 
 Hydrogen 
 
 0-550 
 
 0-3324 
 
 0-71 
 
 0-53 
 
 Nitrogen 
 
 0220 
 
 0-0973 
 
 21 
 
 017 
 
 Oxygen 
 
 4-918 
 
 3-1001 
 
 5-08 
 
 4-09 
 
 10-198 
 
 4-8358 
 
 8-55 
 
 6-82 
 
104 AGRICITLTURAL CHEMISTRY. 
 
 In examining these analyses, it is particularly worthy 
 of notice that by far the larger proportion of the sub- 
 stances soluble in water consists of organic matter, lime, 
 and sulphuric acid, the two last being in combination as 
 sulphate of lime, while some of those substances which are 
 usually considered to be the most important mineral con- 
 stituents of plants are present in very small quantity — 
 potash, for instance, forming not more than l-25,000th of 
 the whole soil, and phosphoric acid being entirely absent. 
 On the other hand, this portion contains the whole of the 
 chlorine which exists in the soil, and this might be antici- 
 pated from the ready solubility in water of the compounds 
 of that substance. 
 
 The portion soluble in acids consists of alumina and 
 oxide jf iron, both of which are comparatively unimpor- 
 tant to the plant, but very important, as we shall after- 
 wards see, in relation to the physical properties of the 
 soil. The remainder of the substances soluble in acids, 
 amounting to from 1 and 2 per cent, is composed of some of 
 the most essential constituents of plants. Lime, magnesia, 
 potash, and soda, appear again in larger quantity than in 
 the soluble part, and along with them we have the phos- 
 phoric acid to the amount of from 0'2 to 0'4 per cent of 
 the whole soil, and sulphuric acid in much smaller 
 quantity. 
 
 The insoluble matters differ remarkably in the two 
 soils, that from the Carse of Gowrie being characterised 
 by a large quantity of potash and soda, indicating an 
 important difference in the materials from which they 
 have been formed. In the Perthshire soil it is obvious 
 that the felspathic element has been abundant, and that 
 its decomposition has been arrested at a time, when it still 
 
CHEMICAL AND PHXSICAL CHAEACTERS OF SOIL. 105 
 
 contained a large quantity of alkalies. And this diffe- 
 rence is of great practical importance, because those soils, 
 which contain a large quantity of potash in their in- 
 soluble portion, have within them a source of permanent 
 fertility, the alkali being gradually liberated by the de- 
 composition which is constantly in progress, owing to the 
 air and moisture permeating the soil. As regards the 
 special distribution of the inorganic matters, it is to be 
 observed that some of them occur in each of the three 
 heads under which they are arranged, while others are 
 confined to one or two. Silica and the alkalies occur 
 generally, though not invariably, in all three. Chlorine 
 is met with only in the part soluble in water, phosphoric 
 acid only in that soluble in acids, while sulphuric acid 
 occurs in both the last-named divisions. j 
 
 The greater part of the organic matters are insoluble 
 both in water and acids. At least it is generally believed 
 that any portion dissolved by strong acids, in the course 
 of analysis, has been entirely decomposed, and is in a 
 completely different state from that in which it existed 
 actually in the soil. 
 
 As an example of a calcareous soil, forming a striking 
 contrast to those given above, we select one from the 
 island of Antigua, from which very large crops of sugar- 
 cane are obtained. The soil is of great depth, and ana- 
 lyses of the subsoil at the depth of 18 inches and 5 feet 
 are given. These last analyses are not so minute as that 
 of the soil itself, the soluble matters not having been 
 separately determined, but included in that soluble in 
 acids. 
 
106 
 
 AGRICCLTUEAL CHEMISTRY. 
 
 SOLUBLE IN -WATER. 
 
 Lime 
 
 Magnesia 
 
 Potash 
 
 Soda 
 
 Chlorine 
 
 Organic matter 
 
 SOLUBLE IN ACIDS. 
 
 Silica 
 
 Peroxide of iron 
 
 Protoxide of iron 
 
 Alumina 
 
 Lime 
 
 Magnesia , . 
 
 Potash 
 
 Soda 
 
 Sulphuric acid 
 
 Phosphoric acid 
 
 Carbonic acid 
 
 INSOLUBLE IN ACIDS. 
 
 Silica 
 
 Protoxide of iron 
 
 Alumina 
 
 Lime 
 
 Magnesia 
 
 Potash 
 
 Soda 
 
 ORGANIC MATTERS. 
 
 Humine 
 
 Humic acid 
 
 Insoluble organic matters 
 Water 
 
 Sum of all the constituents. 
 
 Surface soil. 
 
 0-07 
 trace 
 0-06 
 0-04 
 0-05 
 0-15 
 
 0-37 
 
 0-74 
 2-22 
 0-77 
 1-90 
 
 10-43 
 0-20 
 0-03 
 0-02 
 
 trace 
 014 
 7-38 
 
 23-83 
 
 41-44 
 3-24 
 9-00 
 0-08 
 0-80 
 
 54-56 
 1-58 
 
 1-J)8 } 
 
 1-15 y 
 
 7-66 J 
 
 11-13 
 21-52 
 
 100-28 
 
 18 inclies 
 deep. 
 
 5 feet deep. 
 
 1-67 
 9-05 
 2-52 
 3-04 
 0-54 
 0-29 
 0-11 
 0-02 
 trace 
 0-82 
 
 18-06 
 
 51-24 
 0-26 
 1-50 
 0-88 
 0-54 
 0-74 
 0-25 
 
 55-41 
 
 12-05 
 14-69 
 26-74 
 
 100-21 
 
 1-87 
 3-10 
 4-21 
 
 25-75 
 0-51 
 0-28 
 0-16 
 0.13 
 0-04 
 
 20-23 
 
 56-28 
 
 27-67 
 1-40 
 1-00 
 trace 
 trace 
 
 30-07 
 
 7-49 
 
 6-06 
 
 13-55 
 
 99-90 
 
CHEMICAL AND PHYSICAL CHAEACTEES OF SOIL. 107 
 
 In this soil there is a general resemblance in the com- 
 position of the portion soluble in water to those of the 
 wheat soils. But the part soluble in acids is distinguished 
 by the great abundance of carbonate of lime. 
 
 The subsoil contains also a large quantity of pro- 
 toxide of iron, a substance frequently found in subsoils 
 containing much organic matter, and to which the air has 
 imperfect access. Under these circumstances peroxide of 
 iron is reduced to protoxide ; and when present abun- 
 dantly in the soil in that form, iron has been found to 
 exercise a very injurious influence on vegetation ; and 
 it has frequently happened that when subsoils containing 
 it have been brought up to the surface, they have in the 
 first instance caused a manifest deterioration of the soil, 
 although after some time, when it had become peroxidised 
 by the action of the air, it ceased to be injurious. 
 
 The soil of Holland, from the neighbourhood of the 
 Zuider Zee, which is an alluvial deposit from the waters 
 of the Bhine, and produces large crops, gave the results 
 which foUow — 
 
 Insoluble silica 
 
 Soluble silica 
 
 Alumina 
 
 Peroxide of iron .... 
 Protoxide of iron ... 
 Oxide of manganese 
 
 Lime 
 
 Magnesia 
 
 Potash 
 
 Soda 
 
 Ammonia 
 
 Phosphoric acid 
 
 Surface. 
 
 15 inches 
 deep. 
 
 30 inches 
 deep. 
 
 67-646 
 
 51.706 
 
 55-372 
 
 2-340 
 
 2-496 
 
 2-286 
 
 1-830 
 
 2-900 
 
 2-888 
 
 9-039 
 
 10-305 
 
 11-864 
 
 0-350 
 
 0-563 
 
 0-200 
 
 0-288 
 
 0-354 
 
 0-284 
 
 4-092 
 
 5-096 
 
 . 2-480 
 
 0-1.30 
 
 0140 
 
 0-128 
 
 1-026 
 
 1-430 
 
 1-521 
 
 1-972 
 
 2-069 
 
 1-937 
 
 0-060 
 
 0-078 
 
 0-075 
 
 0-466 
 
 0-324 
 
 0-478 
 
108 
 
 AGRICULTURAL CHEMISTRY. 
 
 
 Surface. 
 
 IS inclies 
 deep. 
 
 30 mches 
 deep. 
 
 
 0-896 
 6-085 
 1-240 
 2-798 
 0-771 
 0-107 
 
 8-324 
 
 0-540 
 
 1-104 
 6-940 
 1-302 
 3-991 
 0-731 
 0-160 
 
 7-700 
 
 0-611 
 
 0-576 
 4-775 
 1-418 
 3-428 
 0-037 
 0-152 
 
 9-348 
 
 0-753 
 
 
 Chlorine .. 
 
 Hiimic acid 
 
 Crenic acid 
 
 Other organic matters and "| 
 
 Combined water / 
 
 Loss 
 
 
 100-000 
 
 100-000 
 
 100-000 
 
 
 
 
 It is unnecessary to multiply analyses of fertile soils, 
 those now given being sufficient to show their general 
 composition. ■ They are all characterised by the presence, 
 in considerable quantity, of all the essential constituents of 
 plants, in a state in which they may be readily absorbed. 
 The absence of one or more of these substances imme- 
 diately diminishes or altogether destroys the fertility of 
 the soil ; and the extent to which this occurs is illustrated 
 by the following analysis of a soil from Pumpherston, 
 Mid-Lothian, forming a small patch in tie lower part of 
 a field, and on which nothing would grow. Being 
 naturally wet, it had been drained and sowed with oats, 
 which died out about six weeks after sowing, and left a 
 bare soil on which weeds did not show the slightest dis- 
 position to grow. 
 
 SOLUBLE IN ACIDS. 
 
 Soluble silica 0-173 
 
 Peroxide of iron 6'775 
 
 Alumina .., ri50 
 
CHEMICAL AND PHYSICAL CHARACTERS OP SOIL. 109 
 
 Oxide of manganese ,..,, trace 
 
 Carbonate of lime 0-856 
 
 Magnesia 0-099 
 
 Potash 0-132 
 
 Soda 0123 
 
 Phosphoric acid trace 
 
 Chlorine trace 
 
 9-308 
 
 Silica 73096 
 
 Peroxide of iron 1-371 
 
 Alumina 4-363 
 
 Lime 0-858 
 
 Magnesia 0-520 
 
 80-108 
 
 Organic matter 8-012 
 
 Water 2391 
 
 10-403 
 
 99-819 
 
 In this instance the barrenness of the soil is distinctly 
 traceable to the deficiency of phosphoric acid, sulphuric 
 acid, and chlorine. There is also a remarkably large 
 quantity of oxide of iron, which, when acted on by the 
 humic acid, is well known to be highly prejudicial to vege- 
 tation, and that this took place was shown by the fact 
 that the drains, a couple of months after being laid, were 
 almost stopped up by humate of iron. Still more striking 
 are the following analyses : — 
 
110 
 
 AGKICDLTURAL CHEMISTET. 
 
 Silica and sand 
 
 Alumina 
 
 Oxide of iron 
 
 Oxide of manganese.. 1 
 
 Lime f 
 
 Magnesia 
 
 Potash ■) 
 
 Soda 1 
 
 Phosphoric acid 
 
 Sulphuric acid J 
 
 MoorlHnd soil 
 
 near Aurich, 
 
 East Fheslaud. 
 
 Sandy soil 
 
 near 
 Wettingen. 
 
 Soil from 
 
 near Uuhl- 
 
 hansea. 
 
 70-576 
 
 1-050 
 
 ■ 0-252 
 
 ti-ace 
 
 0-012- 
 
 trace 
 
 ■ 
 
 96-000 
 
 0-500 
 
 2-000 
 
 (■ trace 
 
 1 0-001 
 
 trace 
 
 trace 
 
 0-200 
 
 1-299 
 
 77-780 
 9-490 
 5-800 
 0-105 
 0-866 
 0-728 
 
 < trace 
 
 0-003 
 trace 
 0-200 
 trace 
 0-732 
 0-200 
 4-096 
 
 100-000 
 
 Chlorine 
 
 trace 
 11-910 
 16-200 
 
 Insoluble humus 
 
 Water 
 
 100000 
 
 100-000 
 
 The results contained in these analyses are peculiarly 
 remarkable, for they indicate the almost total absence of 
 all those substances which the plant requires. They must, 
 however, be considered as in a great measure exceptional 
 cases, as it is but rarely that so large a number of consti- 
 tuents is absent, and it is much more frequent to find the 
 deficiency restricted to one or two substances. They are 
 illustrations of barrenness dependent on difierent circum- 
 stances. The first shows the unimportance of the organic 
 matters of the soil, which are here unusually abundant, 
 ■without in any way counteracting the infertility depend- 
 ent on the absence of the other constituents. The second 
 is that of a nearly pure sand ; and the third, though it 
 contains a greater number of the essential ingredients of 
 the ash, is still rendered unfruitful by the deficiency of 
 alkalies, sulphuric acid, and chlorine. 
 
 An examination of the foregoing analyses indicates 
 pretty clearly some of the conditions of fertility of the 
 
CHEMICAL AND PHTSICAL CHARACTERS OF SOIL. Ill 
 
 soil, which must obviously contain all the constituents of 
 the plants destined to grow upon it. But it by no means 
 exhausts the subject, for numerous instances are known of 
 soils containing all the essential elements of plants in 
 abundance, but on which they nevertheless refuse to 
 grow. In these instances the defect is due either to the 
 presence of some substance injurious to the plant, or to 
 the state of combination of those it requires being such as 
 to prevent their absorption. Eeference has been already 
 made to the bad effects of protoxide of iron, and it would 
 appear that organic matter is sometimes injurious. Even 
 water, by excluding air, and so preventing those decom- 
 positions which play so important a part in liberating the 
 essential elements from their more permanent compounds, 
 although it cannot render a soil absolutely barren, not 
 unfrequently materially diminishes its fertility. 
 
 Tie state of combination of the soil constituents un- 
 questionably exercise a most important influence on its 
 fertility. That this must be the case is an inference 
 which may be easily drawn from the statements already 
 made regarding the different minerals from which it is 
 directly or indirectly produced. If, for instance, a soil 
 consist to a large extent of mica, it would be found on 
 analysis to contain abundance of potash and some other 
 matters, and yet our knowledge of the difficulty with 
 which that mineral is decomposed, would enable us to 
 pronounce unfavourably of the soil ; and practical experi- 
 ence here fully confirms the scientific inference. 
 
 The forms of combination most favourable to fertility 
 is a subject on which our information is at present compa- 
 ratively limited. It was at one time believed that solu- 
 bility in water was an indispensable requisite, but recent 
 investigations appear to lead to a directly contrary con- 
 
Il2 
 
 AGEICULTURAL CHEMISTKY. 
 
 elusion. The analyses of soils already given, show that 
 the part directly soluble in water embraces only a certain 
 number of the constituents of the plant, and of those dis- 
 solved the quantity is very small. This becomes still 
 more apparent if we estimate from the analyses the actual 
 quantities of those substances contained in an acre of soil. 
 It is generally assumed that the soil on an imperial acre 
 of land 10 inches deep weighs in round numbers about 
 1000 tons ; and calculating from this, we find that the 
 quantity of potash soluble in water in the Mid-Lothian 
 wheat soil, amounts to no more than 70 lb. per acre. But 
 a crop of hay carries off from the soil about 38 lb. of 
 potash, and one of turnips, including tops, not less than 
 200 lb., so that if only the matters soluble in water could 
 be taken up by the plant, such soils could not possess the 
 amount of fertility which they are actually found to have. 
 It is to be remembered, also, that in these analyses the 
 experiment is made under the most favourable circumstances 
 for ascertaining the whole quantity of matters which are 
 capable of dissolving in water ; that practically dissolved 
 is very different. The recent analysis by Krocker and Way 
 of the drainage water of soils afford a means of estimating 
 this. Way found in one gallon of the drainage water from 
 seven different fields, collected in the end of December — 
 
 
 1 
 
 -2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 Potash, 
 
 trace 
 
 trace 
 
 002 
 
 0-05 
 
 trace 
 
 0-22 
 
 trace 
 
 Soda, 
 
 1-00 
 
 217 
 
 2-26 
 
 0-87 
 
 1-42 
 
 1-40 
 
 3-20 
 
 Lime, . . 
 
 4-85 
 
 719 
 
 605 
 
 2-26 
 
 2-52 
 
 5-82 
 
 1300 
 
 Magnesia, 
 
 068 
 
 2-32 
 
 2-48 
 
 0-41 
 
 0-21 
 
 0-93 
 
 2-50 
 
 
 0-40 
 
 005 
 
 010 
 
 none 
 
 130 
 
 0-35 
 
 0-60 
 
 Silica. 
 
 095 
 
 0-45 
 
 0-55 
 
 1-20 
 
 1-80 
 
 0-65 
 
 0-85 
 
 Chlorine, ... 
 
 0-70 
 
 110 
 
 1-27 
 
 0-81 
 
 1-26 
 
 1-21 
 
 2-62 
 
 Sulphuric acid, . 
 
 1-65 
 
 515 
 
 4-40 
 
 1-71 
 
 1-29 
 
 3-12 
 
 9-61 
 
 Phosphoric acid, . . 
 
 trace 
 
 0-12 
 
 trace 
 
 trace 
 
 0-08 
 
 0-06 
 
 012 
 
 Amrnn^i^ 
 
 0-018 
 
 0-018 
 
 0-018 
 
 0-U12 
 
 0-018 
 
 0^)06 
 
 0-018 
 
 Nitric add, . . 
 
 7 17 
 
 14-74 
 
 12-72 
 
 1-95 
 
 3-45 
 
 8-05 
 
 1145 
 
 Organic matter, 
 
 700 
 
 7-40 
 
 12-50 
 
 5-60 
 
 6-70 
 
 5-80 
 
 7-40 
 
CHEMICAL AND PIUfSICAL CHAEACTEES OF SOIL. 113 
 
 Some of the 
 tained had been 
 of nitrogenous 
 amount of nitric 
 has extracted, 
 soils less highly 
 summer. 
 
 soils from which these waters were ob- 
 manured with unusually large quantities 
 matters, which accounts for the large 
 acid, as well as the lime which that acid 
 Dr. Krocker's analyses were made on 
 manured, and the water was collected in 
 
 
 IN 10.000 rAETS. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 Organic matter , . . 
 Carbonate of lime 
 Sulphate of lime . . 
 Nitrate of lime . . . 
 Carbonate of magnesia 
 Carbonate of iron . ... 
 
 Potash 
 
 Soda 
 
 Chloride of sodium . . 
 Silica 
 
 0-26 
 0-84 
 2-08 
 002 
 0-70 
 0-04 
 002 
 Oil 
 008 
 007 
 
 024 
 0-84 
 2-lU 
 002 
 0-69 
 0-04 
 002 
 0-lB 
 008 
 0-07 
 
 0-16 
 1-27 
 114 
 001 
 0-47 
 0-04 
 0-02 
 1,3 
 0-07 
 0.06 
 
 0.06 
 0'79 
 017 
 002 
 0-27 
 002 
 002 
 010 
 003 
 0-05 
 
 O'es 
 
 0-71 
 0-77 
 002 
 0-27 
 002 
 004 
 0-05 
 0-01 
 006 
 
 0-56 
 0-84 
 0-72 
 0-02 
 016 
 0-01 
 006 
 0-04 
 0-Ul 
 005 
 
 In order to obtain from these experiments an estimate 
 of the quantity of the substances actually dissolved, we shall 
 select the results obtained by Way. The average rain- 
 fall in Kent, where the waters he examined were obtained, 
 is 25 inches. Now, it appears that about two-fifths of 
 all the rain which falls escapes through the drains, and the 
 rest is got rid of by evaporation. An inch of rain falling on 
 an imperial acre weighs rather more than a hundred tons ; 
 hence, in the course of a year, there must pass off by the 
 drains about 1000 tons of drainage water, carrying with 
 it, out of the reach of the plants, such substances as it has 
 dissolved, and 1500 tons must remain to give to the plant 
 all that it holds in solution. These 1500 tons of water 
 must, if they have the same composition as that which 
 escapes, contain only two and a half pounds of potash, and 
 less than a pound of ammonia. It may be alleged that 
 
114 AGRICULTURAL CHEMISTRY. 
 
 the water which remains, lying longer in contact with the 
 soil, may contain a larger quantity of matters in solution ; 
 but even admitting this to be the case, it cannot for a 
 moment be supposed that they can ever amount to more than 
 a very small fraction of what is required for a single crop. 
 It may therefore be stated with certainty that solubility 
 in water is not essential to the absorption of substances by 
 the plant, which must possess the power of itself directly 
 attacking, acting chemically on, and dissolving them. 
 The mode in which it does this is entirely unknown, but 
 it in all probability depends on very feeble chemical 
 actions, and hence the importance of having the soil con- 
 stituents, not in solution, but in such a state that they 
 may be readily made soluble by the plants. Many of the 
 minerals from which fertile soils are formed are probably 
 not attackable by plants when in their natural condition, 
 and even after disintegration the quantity of the essential 
 elements of their food, which are present in an easily 
 assimilable state, is at no one time very large. But this 
 is of comparatively little importance, for the soil is not an 
 inert unchangeable substance ; it is the theatre of an im- 
 portant series of chemical changes effected by the action 
 of air and moisture, and producing a continued liberation 
 of its constituents. This decomposition is effected partly 
 by the carbonic acid of the atmosphere, but to a much 
 larger extent by its oxygen acting upon the organic matters 
 of the soil, and causing a constant though slow evolution 
 of that acid, which in its turn attacks the mineral matters. 
 Boussingault and Levy have illustrated the extent of this 
 action by examining the composition of the air contained 
 in the pores of different soils, and have obtained the follow- 
 in? results : — 
 
CHEMICAL AND PHYSICAL CHARACTERS OF SOIL. 115 
 
 
 
 h^ 
 
 100 VOLUMES 07 AIS 
 
 Natdrb or Soil. 
 
 Ckop. 
 
 •a si 
 g.s| 
 
 COMTAIK 
 
 a 
 
 s 
 
 c 
 
 
 
 *3'a a 
 do' 
 
 Id 
 
 ■e " 
 
 
 1 
 
 
 
 a° 
 
 a 
 
 O 
 
 K 
 
 light sandy soil, newly manured 
 
 
 80 
 
 2-17 
 
 Do. shortly after rain . 
 
 
 — 
 
 9-74 
 
 10-35 
 
 79-91 
 
 Do. long after manuring 
 
 Yellow turnip 
 
 79 
 
 0-93 
 
 19-50 
 
 79-57 
 
 Very sandy .... 
 
 Vineyard 
 
 9-6 
 
 106 
 
 19-72 
 
 79-22 
 
 Sandy, with many stones . . 
 
 Forest 
 
 40 
 
 0-87 
 
 19-61 
 
 79-52 
 
 Loamy 
 
 
 2-4 
 
 0-46 
 
 ... 
 
 ... 
 
 Sandy, subsoil of the last . . 
 
 
 30 
 
 0-24 
 
 
 ... 
 
 Sandy soil, long after manuring 
 
 Trefoil' 
 
 76 
 
 0-74 
 
 19-'62 
 
 80-24 
 
 Do. recently manured 
 
 ... 
 
 ... 
 
 085 
 
 19-41 
 
 79-74 
 
 Do. manured 8 days before 
 
 ... 
 
 
 1-54 
 
 18-80 79-66 
 
 Heavy clay . . . . . 
 
 Jerusalem 
 artichoke 
 
 7.0 
 
 0-66 
 
 19-99 79 35 
 
 Fertile soil (moist) . . . 
 
 Meadow 
 
 5-5 
 
 1-79 
 
 19-41 78-80 
 
 From these analyses it appears that the air contained 
 in the pores of the soil is much richer in carbonic acid 
 than the atmosphere, the poorest soil containing about 
 25 times, and a recently manured soil 250 times as much. 
 This carbonic acid, which is obviously produced by the 
 decomposition of the vegetable matters and manure, acting 
 partly as gas and partly dissolved in the soil -water, exerts 
 a solvent action on its constituents. And, though a very 
 feeble acid, its continuous action produces in the course 
 of time a large effect ; -while, during the interval, the 
 constituents of the soil are safely stored up, and liberated 
 only as the plant requires them, by -which bountiful pro- 
 -vision of nature they are exposed to fewer risks of loss 
 than if they had been all along in a state in -which they 
 could be absorbed. Carbonic acid not only assists in 
 effecting the decomposition of the minerals of the soil, 
 but its aqueous solution acts as a solvent of many sub- 
 
116 -AGRICULTUBAL CHEMISTRY. 
 
 stances, which are quite insoluble in pure water. It is in 
 this way that much of the lime contained in natural waters 
 is held in solution, and it has been ascertained that mag- 
 nesia, iron, and even phosphate of lime, may also be dis- 
 solved by it. It is probable that when these substances 
 are dissolved, the plants will take them from solution in 
 place of themselves attacking the insoluble matters ; but of 
 the extent to which this may occur nothing is yet known — 
 the action of solvents on the soil being a subject which is 
 as yet scarcely examined. 
 
 Carbonic acid is, however, a most important agent in 
 producing the chemical changes in the soil, and ihe par- 
 ticular value of humus lies in its affording a supply of that 
 substance exactly when it is wanted ; but the carbonic 
 acid of the atmosphere also takes part in these changes, 
 although with different degrees of rapidity according to 
 the character of the soil, acting rapidly in light, and slowly 
 in stiff, clay soils. The solvent action of the carbonic 
 acid is, no doubt, principally exerted on the substances 
 soluble in acids, but not entirely, for it is known that the 
 insoluble part is gradually being disintegrated and made 
 soluble ; and hence it is that the composition of that part 
 of the soil which resists the action of acids, and which at 
 first sight might appear of no moment, is really important. 
 It is obvious that this circumstance must at once confer on 
 the soil of the Carse of Gowrie a great superiority over 
 those of Mid-Lothian and most other districts ; for it con- 
 tains in its insoluble part a quantity of alkalies which 
 must necessarily form a source of continued fertility. Ac- 
 cordingly, experience has all along shown the great supe- 
 riority of that soil, and of alluvial soils generally, which 
 are all more or less similar to it. The facility with which 
 these matters are attackable by carbonic acid is also an 
 
CHEMICAL AND PH'JfSICAL CHARACTERS OF SOIL. 117 
 
 important element of the fertility of a soil, and it is to 
 the existence of compounds which are readily decom- 
 posed by it that we attribute the high fertility of the 
 trap soils. 
 
 By a further examination of the analyses of fertile 
 soils, it is at once apparent that the most essential con- 
 stituents of plants are by no means very abundant in 
 them. In fact, phosphoric and sulphuric acids, lime, 
 magnesia, and the alkalies, which in most instances make 
 up nine-tenths of the ash of plants, form but a small por- 
 tion of even the most fertile soils ; while silica, which, ex- 
 cept in the grasses, occurs in small quantity, oxide of iron 
 which is a limited, and alumina a rare, constituent of the 
 ash, constitute by far their larger part. Thus the total 
 amount of potash, soda, lime, magnesia, phosphoric and 
 sulphuric acids and chlorine, contained in the Mid-Lothian 
 wheat soil amounts only to 3"5888 per cent, and in the 
 Perthshire to 6'4385, the entire remainder being substances 
 which enter into the plant for the most part in much smal- 
 ler quantity. And, as these small quantities of the more 
 important substances are capable of supplying the wants 
 of the plant, it must be obvious that a very small fraction 
 of the silica, oxide of iron, and alumina, which the soils 
 contain, would afford to it the whole quantity of these 
 substances it requires, and that the remainder must have 
 some other functions to perform. 
 
 The soil must be considered not merely as the source of 
 the inorganic food of plants, for it has to act also as a 
 support for them while growing, and to retain a sufficient 
 quantity of moisture to support their life ; and unless it 
 possess the properties which fit it for this purpose, it may 
 contain all the elements of the food of plants, and yet be 
 nearly or altogether barren. 
 
118 iGKICULTUEAL CHEMISTKT. 
 
 The adaptation of the soil to this function is depen- 
 dent to a great extent on its mechanical texture, and on 
 this considerable light is frequently thrown by a kind of 
 mechanical analysis. 
 
 If a soil be shaken up with water and allowed to 
 stand for a few minutes, it rapidly deposits a quantity 
 of grains which are at once recognised as common sand ; 
 and if the water be then poured off into another vessel 
 and allowed to stand for a longer time, a fine soft 
 powder, having the properties and composition of common 
 clay, is deposited, while the clear fluid retains the soluble 
 matters. By a more careful treatment it is possible 
 to distinguish and separate humus, and in soils lying 
 on chalk or limestone, calcareous matter or carbonate of 
 lime. 
 
 In this way the components can be classified into four 
 groups, a mixture of two or more of which in variable pro- 
 portions is found in all soils. 
 
 The relative proportions in which these substances 
 exist in soils are, as we shall afterwards see, the founda- 
 tion of their classification into the light, heavy, calcareous, 
 and other sub-divisions. But they are also intimately 
 connected with certain chemical and mechanical peculiari- 
 ties which have an important bearing on its fertility. It 
 is a familiar fact, that particular soils are specially adapted 
 to the growth of certain crops ; and we talk of a wheat or 
 a turnip soil as readily distinguishable. It is to be ob- 
 served, however, that in many such instances the mere 
 analysis may show no difference, or, at least, none sufficient 
 to account for the peculiarity. A remarkable illustration 
 is offered by the following analyses of two soils, on one of 
 which red clover grows luxuriantly, while on the other it 
 invariably fails. 
 
CHEMICAL AND PHYSICAL CHAKACTEIJS OF SOIL. 119 
 Clover fails. Clover succeeds. 
 
 Insoluble silicates 83-90 81-34 
 
 Soluble silica 0-08 0*02 
 
 Peroxide of iron 4-45 6-68 
 
 Alumina 2-40 3-00 
 
 Lime 123 133 
 
 Magnesia 0-45 025 
 
 Potash 0-20 0-22 
 
 Soda 007 009 
 
 Sulphuric acid 0-05 0-08 
 
 Phosphoric acid 0-38 0-07 
 
 Carbonic acid 0-09 0-34 
 
 Chlorine trace trace 
 
 Humic acid 042 0-43 
 
 Humine " ... 0-10 
 
 Insoluble organic matters 3-70 3-61 
 
 Water 2-54 2-52 
 
 99-96 100-08 
 
 Nitrogen 015 1-15 
 
 In this instance such difference as exists is rather in 
 favour of the soil on which clover fails, but it is exceedingly 
 trifling ; and it is necessary to seek an explanation in the 
 special properties of its mechanical constituents. 
 
 These properties are partly mechanical and partly 
 chemical, and in both ways exercise an important influence 
 on the fertility of the soil. 
 
 Sand and clay, the most important of the mechanical 
 constituents, confer on the soil diametrically opposite pro- 
 perties ; the former, when present in large quantity, pro- 
 ducing what are designated as light, the latter stifif or 
 heavy soils. The hard indestructible siliceous grains, of 
 which sand is composed, form a soil of an open texture, 
 through which water readily permeates ; while clay, from 
 its fine state of division, and peculiar adhesiveness or plas- 
 
120 AGRICULTURAL CHEMISTRY. 
 
 ticity, gives it a close-textured and retentive character, 
 and their proper intermixture produces a light fertile loam, 
 each tempering the peculiar properties of the other. In- 
 deed, their mixture is manifestly essential, for sand alone 
 contains little or none of the essential ingredients of plants ; 
 and if present in large quantity, the openness of the soil is 
 excessive, water flows through it with rapidity, manures 
 are rapidly wasted, and on the accession of drought, the 
 plants growing upon it soon languish and die. Clay, on 
 the other hand, is by itself equally objectionable ; the 
 closeness of its texture prevents the spreading of the roots 
 of plants, and the access of carbonic acid, which, as we 
 have already seen, is so important an agent in the changes 
 occurring in the soil. In fact, a pure clay, that is to say, 
 a clay unmixed with sand, even though it may contain all 
 the essential constituents of the plant, is for this reason 
 unfertile. Practically, of course, these extreme cases 
 rarely occur ; the heaviest clay soils being mixtures of 
 true clay with sand, and the most sandy containing their 
 proportion of clay ; but frequently the preponderance of 
 the one over the other is so great, as to produce soils 
 greatly inferior to those in which the mixture is more 
 uniform. 
 
 It is easy to understand how the proportions in which 
 sand and clay are mixed must affect the suitability of soils 
 to particular crops, and that an open soil must be favour- 
 able to the turnip, and a heavy clay, owing to the resis- 
 tance it offers to the expansion of the bulbs, unfavour- 
 able. But these substances also exercise an important 
 chemical action on the soluble constituents of the food of 
 plants, combining with them, and converting them into 
 an insoluble, or nearly insoluble state, so as to prevent 
 their being washed away by the rain or other water which 
 
CHEMICAL AND PHYSICAL CHAEACTEES OF SOIL. 12] 
 
 percolates through the soil. It has long been known to 
 chemists that clay has a tendency to absorb a small pro- 
 portion of ammonia, and even when brought up from a 
 great depth frequently contains that substance. It is to 
 Mr. Thompson of Moat Hall, however, that we owe the 
 important observation, that arable soils rapidly remove 
 ammonia from solution, and Way, who pursued this inves- 
 tigation, showed that not only ammonia, but potash, and 
 several of the other important elements of the food of 
 plants, are thus absorbed. The removal of these sub- 
 stances from solution is easily illustrated by a simple expe- 
 riment. It suffices to take a tall cylindrical vessel open 
 at both ends, and filled with the soil to be operated upon, 
 which is retained by a piece of rag tied over its lower end. 
 A quantity of a dilute solution of ammopia being then 
 poured upon the surface of the soil, and allowed to per- 
 colate, the first quantity which flows away is found to 
 have entirely lost its peculiar smell and taste ; and in a 
 similar manner the removal of potash may be illustrated. 
 This action is by no means confined to those substances 
 when in the free state, but is equally marked when they 
 are combined with acids in the form of salts, and in the 
 latter case the absorption is attended with a true chemical 
 decomposition, the base only being retained, and the acid 
 escaping most commonly in combination with lime. Thus, 
 if sulphate of ammonia be employed, the water which 
 flows from the soil contains sulphate of lime, and if 
 muriate of ammonia be used, it is muriate of lime which 
 escapes. 
 
 This absorbent action is most remarkably manifested 
 in the case of ammonia and potash, but it takes place also 
 with magnesia and soda. With the latter, however, it is 
 incomplete, only a half or a fourth of the soda being 
 
1^ 
 
 ■ AGKICULTUEAL CHEMISTEY. 
 
 removed from solution, the difference depending to some 
 extent on the acid with which it is in combination. The 
 extent to which absorption takes place varies also with 
 the nature of the soil, and the state of combination of the 
 substance used. Exact experiments have hitherto been 
 chiefly confined to ammonia, potash, and lime in the free 
 state, and as bicarbonate ; and the following table gives 
 the results obtained by Way, with solutions containing 
 about 1 per cent of these substances in solution : — 
 
 
 Loam; 
 
 soil, 
 Dorset- 
 
 sliire. 
 
 Red soil, 
 Berk- 
 sllire. 
 
 Pnre 
 clay. 
 
 Subsoil 
 clay, 
 Somer- 
 setshire. 
 
 AmtnoTii^ij cf^nf^'^ .--- 
 
 0-3438 
 0-3478 
 
 0-1570 
 0-1966 
 
 0-2847 
 
 1-050 
 
 0-4980 
 
 1-468 
 
 0-731 
 
 0-0818 
 2-087 
 
 „ from muriate . 
 Potash, caustic 
 
 „ from nitrate 
 
 Lime, caustic 
 
 „ from bicarbonate . . 
 
 From these numbers it appears that very great differ- 
 ences exist in the absorbent power of different soils, the 
 first of those experimented on being capable of taking 
 more than twice as much ammonia as the second, and 
 nearly four times as much as the subsoil cl^y. It appears 
 also, as far as absorption goes, to be immaterial whether 
 the ammonia is free or combined. But it is different 
 with potash, which is absorbed from the nitrate to the 
 extent of about 0-6 per cent, and from a caustic solution 
 of potash to double that amount. 
 
 The circumstances under which absorption takes place 
 modify, in a manner which cannot well be explained, the 
 amount absorbed by the same soil. It is found generally 
 to be most complete with very dilute solutions, and if a 
 soil be agitated with a quantity of ammonia larger than it 
 
CHEMICAL AND PHYSICAL CHAKACTEBS OF fiDtL. 123 
 
 can take up, it will absorb only a certain amount of that 
 substance, but by a further increase of the amount of 
 ammonia a still larger quantity will be absorbed. 
 
 It is important to observe that whoa a salt is used, 
 the base only is absorbed, and the acid escapes in com- 
 bination with lime ; even nitric acid, notwithstanding its 
 importance as a food of plants, being in this predicament. 
 From this it may be gathered that lime is not readily 
 absorbed from solutions of its salts ; indeed, it would 
 appear that the only salt of that substance liable to absorp- 
 tion is the bicarbonate, from which it is taken to the extent 
 of 1 "4 per cent by the soil. The absorption of lime from 
 this salt, and that of phosphoric acid, which takes place to 
 a considerable extent, probably occurs, however, quite inde- 
 pendently of the clay present in the soil, and is occasioned by 
 its Ume, which forms an insoluble compound with phos- 
 phoric acid, and by removing half the carbonic acid of the 
 bicarbonate of lime converts it also into an insoluble state. 
 
 In addition to these mineral substances, organic mat- 
 ters are also removed from solution. This is conspicu- 
 ously seen in the case of putrid urine, which not only 
 loses its ammonia, but also its smell and colour, when 
 allowed to percolate through soil ; and an equally marked 
 result was obtained with flax water, from which the 
 organic matter was entirely abstracted. 
 
 The cause of this absorptive power is still very imper- 
 fectly known. Mr. Way having observed that sand has 
 no such property, while clay, even when obtained from a 
 considerable depth, always possesses it, supposed that the 
 absorption was entirely due to that substance. A diffi- 
 culty, however, presents itself in explaining how it should 
 happen that while a pure clay absorbs only 0"2847 of 
 ammonia, a loamy soil, of which one-half probably is 
 
124 AGKICTJLTURAL CHEMISTKY. 
 
 sand, should absorb a larger quantity. The inference is, 
 that the effect cannot be due to the clay as a whole, and 
 Mr. Way has sought to explain it by supposing that there 
 exist in the soil particular double silicates of alumina and 
 lime. He has shown that felspar and the other minerals 
 from which the soil is produced have no absorbent power, 
 but that artificial compounds can be formed which act upon 
 solutions of ammonia and potash in a manner very similar 
 to the soil ; but there is not the slightest evidence that 
 these compounds exist in the soil, and in the year 1853* 
 I pointed out the probability that clay is not the only 
 agent at work, but that the organic matters take part in 
 the process. So powerful indeed is the affinity of these 
 substances for ammonia, that chemists are at one as to 
 the difficulty of obtaining humic and other similar acids 
 pure, owing to the obstinacy with which they retain it ; 
 and there cannot be a doubt that in many soils these sub- 
 stances are in this point of view of much importance. 
 This is particularly the case in peat soils, which, though 
 naturally barren, may be made to produce good crops by 
 the application of sand or gravel ; and as neither of these 
 can cause any absorption of the valuable matters, we must 
 attribute this effect to the organic matter. Eeferring to 
 an earlier series of experiments made in 1850, I showed 
 that, if a quantity of dry peat be taken and ammonia 
 poured on it, its smell disappears ; and this may be con- 
 tinued until upwards of 1'5 per cent of dry ammonia 
 has been absorbed, and this quantity is retained by the 
 peat. 
 
 In this case pure ammonia was used, but Way's 
 experiments having shown that this alkali is not absorbed 
 
 * Transactions of the Highland and Agricultural Society, vol. 
 vi., p. 317. 
 
CHEMICAL AND PHYSICAL CHARACTERS OF SOIL. 125 
 
 from its salts by organic matters, I expressed the opinion 
 that humate of lime (which certainly exists in most soUs) 
 ought on chemical grounds to decompose the salts of 
 ammonia and cause the retention of their base. The 
 recent researches of Brustlein have shown that lime does 
 cause the organic matters to absorb ammonia from its salts. 
 He confirms the fact that pure ammonia is absorbed by 
 peat, and shows that decayed wood has the same efiect, 
 although both are without action on solutions of its salts. 
 A stiff clay, on the other hand, containing organic matters 
 and much carbonate of lime, readily absorbed ammonia, 
 both when pure and combined ; but after extracting the 
 lime by means of a dilute acid, it lost the power of taking 
 it from its salts, although it retained the free alkali as 
 completely as before. On the addition of a small quantity 
 of lime, it again acquired the power of withdrawing 
 ammonia from its compounds. These experiments may be 
 explained, either on the supposition of the presence of 
 humate of lime, or by supposing that the carbonate of lime 
 first decomposed the salts of ammonia, and that the 
 liberated alkali combined with the organic matter. It 
 must be admitted, however, that it is very doubtful whether 
 the ammonia and other substances are fixed in the soil by 
 a true chemical combination. They are certainly retained 
 by a very feeble attraction, for it appears from Brustlein's 
 experiments that ammonia may be, to a considerable extent, 
 removed by washing with abundance of water, and that 
 if the soil which has absorbed ammonia be allowed to 
 become dry in the air, it loses half its ammonia, and after 
 four times moistening and drying, three-fourths have 
 disappeared. These facts are certainly not incompatible 
 with the presence of a true chemical compound, for the 
 humate of ammonia is not absolutely insoluble, and many 
 
126 AGEICULTUBAL CHEMISTRY. 
 
 cases occnr of actions taJdng place in the presence of water, 
 •which are entirely reversed ■when that fluid is removed ; 
 and it is quite possible that when humate of ammonia is 
 dried in contact with carbonate of lime, it may be decom- 
 posed, and carbonate of ammonia escape. There are other 
 circumstances, however, which render it, on the whole, 
 most probable that the combination is not wholly chemical, 
 but rather of a physical character, among which may be 
 more especially mentioned the fact, that the quantity of 
 the substances retained by the soil is dependent on the 
 degree of dilution of the fluid from which they are taken ; 
 and that the quantity absorbed never exceeds a very 
 small fraction of the weight of the soil. 
 
 The practical inferences to be drawn from these facts 
 regarding the value of soils are of the highest importance. 
 It is obvious that two soils having exactly the same 
 chemical composition may dififer widely in absorptive 
 power, and that which possesses it most largely must 
 have the highest agricultural value. The examination of 
 different soils, in this point of view, is a subject of much 
 importance, and deserves the best attention of both farmers 
 and chemists, although little has as yet been done in 
 regard to it, and the results which have been obtained 
 are not of a very satisfactory character. Liebig states, that 
 in his experiments, all the arable soils examined possessed 
 the same absorptive power, whether they contained a large 
 or a small proportion of lime or alumina. It can scarcely 
 be expected, however, that this should be true in all 
 cases, and there are many facts which seem to indicate 
 that differences must exist. It is well known that there 
 are some soils in which the manure is very rapidly ex- 
 hausted, and it is more than probable that this effect is 
 due to deficient absorptive power, which leaves the soluble 
 
CHEMICAL AND PHYSICAL CHAEACTEES OF SOIL. 127 
 
 matters at the mercy of the weather, and liable at any 
 moment to be washed out by a heavy fall of rain. 
 
 The more strictly mechanical properties of the soil, 
 such as its relations to heat and moisture, are not less 
 important than its chemical composition. It is known that 
 soils differ so greatly in these respects as sometimes mate- 
 rially to affect their productive capacity. Thus, for instance, 
 two soils may be identical iu composition, but one may be 
 highly hygrometric, that is, may absorb moisture readily 
 from the air, while the other may be very deficient in that 
 property. Under ordinary circumstances no difference 
 will be apparent in their produce, but in a dry season the 
 crop upon the former may be in a flourishing condition, 
 while that on the latter is languishing and enfeebled, 
 merely from its inability to absorb from the air, and supply 
 to the plant the quantity of water required for its growth. 
 In the same way, a soil which absorbs much heat from 
 the sun's rays surpasses another which has not that 
 property ; and though in many cases this effect is compa- 
 ratively unimportant, in others it may make the difference 
 between successful and unsuccessful cultivation in soils 
 which lie in an unfavourable climate or exposure. 
 
 The investigation of the physical characters of soils 
 has attracted little attention, and we owe all our present 
 knowledge of the subject to a very elaborate series of re- 
 searches on this subject, published by Schiibler, nearly 
 thirty years ago. He determined 1st, The specific gravity 
 of the soils ; 2d, The quantity of water which they are 
 capable of imbibing ; Sd, The rapidity with which they 
 give off by evaporation the water they have imbibed ; that 
 is, their tendency to become dry ; ith. The extent to which 
 they shrink in drying ; 5th, Their hygrometric power ; 6th, 
 The extent to which they are heated by the sun's rays ; 
 
128 AGRICULTURAL CHEMISTRY. 
 
 1th, The rapidity with -which a heated soil cools down, 
 which indicates its power of retaining heat ; 8iA, Their 
 tenacity, or the resistance they offer to the passage of 
 agricultural implements ; %th, Their power of absorbing 
 oxygen from the air. Each of these experiments was 
 performed on several different soils, and on their mechani- 
 cal constituents. Schiibler's experiments are undoubtedly 
 important, and though the methods employed are some of 
 them not altogether beyond cavil, they have apparently 
 been performed with great care. It is nevertheless desir- 
 able that they should be repeated, for such facts ought 
 not to rest on the authority of one experimenter, however 
 skilful and conscientious, nor on a single series of soils, 
 which may not give a fair representation of their general 
 physical properties. In fact, Schtibler appears to imagine 
 that having once determined the extent to which the sand, 
 clay, and other mechanical constituents of the soil possess 
 these properties, we are in a condition to predicate the 
 effect of their mixture in variable proportions, although this 
 is by no means probable. 
 
 In examining these properties, Schiibler selected for 
 experiment, pure siliceous sand, calcareous sand (carbonate 
 of lime in coarse grains), finely powdered carbonate of 
 lime, pure clay, humus, and powdered gypsum. He used 
 also a heavy clay consisting of 1 1 per cent of sand and 
 89 of pure clay, a somewhat stiff clay containing 24 per 
 cent of sand and 76 of clay, a light clay with 40 per 
 cent of sand and 60 of pure clay, a garden soil consisting 
 of 52'4 per cent of clay, 36'5 of siliceous sand, 1-8 of cal- 
 careous saiid, 2 per cent of finely divided carbonate of lime, 
 and 7*2 of humus, and two arable soils, one from Hoffwyl, 
 and one from a valley in the Jura, the former a somewhat 
 stiff^, the latter a light soil. 
 
CHEMICAL AND PHYSICAL CHARACTEES OF SOIL. 129 
 
 3 OO^V:- 
 
 J" HI-SI'S 
 
 OOi-tTH{N(NT^COOCNNCN 
 
 cpopCpOOt^CpCDOO 
 lO CO 00 O 00 (N 
 
 Power of 
 retaining 
 
 heat. 
 Calcare- 
 ous sand. 
 
 100. 
 
 
 CpOOS*;H-^t-COOCNQOT7*Cp 
 
 *oocbT^do'i'T^a5cb'^o-4j< 
 1— i 
 
 
 1- 
 
 1=3 g 
 
 ■855 
 
 ■Iss; 
 
 s 
 
 r-lCOvOt^Cf3lOOt>'<*t-HO 
 
 •t^ 
 
 1 
 5 
 
 T-HilDOOOOiOOl>Oi-iO 
 0(>lT7^COCpCpC£)rJ10(»t>lO 
 
 § 
 
 1 
 
 ocoOi-Hi^-aococoi^-cor-o 
 
 
 et 
 
 (— .Oi-HtMr-crffOCOt^CsCOI:^ 
 ^T--iCf)0iC0C0Ot-.O«DCqO 
 
 B.S'g.S'^-S 
 
 oocboDTHOOiiaoo'^fJflbs 
 
 
 »**' 
 
 . « E -K * 
 
 ■^o:>000:>cr50iOb-oOi-i 
 
 
 
 "S-c 
 
 *oojour5oai<xi<Niccoo<N 
 
 t>OOI^-OCOm*^<MCCC(OTt<iO 
 
 H CO 
 
 
 >.3 
 
 , ;^- - rt c3 
 
 -fj o C* ^ O ^ 
 
 
 Is 
 
 o S 
 
 jUi-a 
 
 I- H S 
 
 S !3. o O 
 r*^ iS O O 
 
 CSCSccoo 
 
130 AGKICULTUEAL CHEMISTKY. 
 
 The experiments detailed in the preceding table speak 
 in a great measure for themselves, and scarcely require 
 detailed comment. It may be remarked, however, that 
 the columns illustrating the relations of the soil to water 
 are probably more important than the others. The superi- 
 ority of a retentive over an open soil is sufficiently fami- 
 liar in practice, and though this is no doubt partly due to 
 the former absorbing and retaining more completely the 
 ammonia and other valuable constituents of the manures 
 applied to it, it is also dependent to an equal if not greater 
 extent upon the power it possesses of retaining moisture. 
 A reference to the table makes it apparent that this power 
 is presented under three different heads, which are cer- 
 tainly related to one another, but are not identical. In 
 the second column of the table is given the quantity of 
 water absorbed by the soil, determined by placing a given 
 weight of the perfectly dry soil in a funnel, the neck of 
 which is partially stopped with a small piece of sponge or 
 wool, pouring water upon it, and weighing it after the 
 water has ceased to drop from it. This may be considered 
 as representing the quantity of water retained by these 
 different soils when thoroughly saturated by long con- 
 tinued rains. The column immediately succeeding gives 
 the quantity of that water which escapes by evaporation 
 from the same soil after exposure for four hours to dry 
 air at the temperature of 66°. The fifth, sixth, seventh, 
 and eighth columns indicate the quantity of moisture 
 absorbed, when the soil, previously artificially dried, is 
 exposed to moist air for different periods. These charac- 
 ters are dependent principally, though not entirely, on the 
 porosity of the soil. The last may also be in some measure 
 due to the presence of particular salts, such as common 
 salt, which has a great affinity for moisture, but is chiefly 
 
CHEMICAL AND PHYSICAL CHARACTERS OF SOIL. 131 
 \ 
 
 occasioned by their peculiar structure. It is to be re- 
 marked that clay and humus are two of the most highly 
 hygrometric substances known, and it is peculiarly in- 
 teresting to observe, that by a beneficent provision of 
 nature, they also form a principal part of all fertile soils. 
 The quantity of water imbibed by the soil is important to 
 its fertility, in so far as it prevents it becoming rapidly 
 dry after having been moistened by the rains. It is valu- 
 able also in another point of view, because if the soil be 
 incapable of absorbing much water, it becomes saturated 
 by a moderate fall of rain, and when a larger quantity 
 falls, the excess of necessity percolates through the soil, 
 and carries off with it a certain quantity of the soluble 
 salts. Important as this property is, however, it must not 
 be possessed in too high a degree, but must permit the 
 evaporation of the water retained with a certain degree of 
 rapidity. Soils which do not admit of this taking place 
 are the cause of much inconvenience and injury in practice. 
 By becoming thoroughly saturated with moisture during 
 winter, they remain for a long time in a wet and unwork- 
 able condition, in consequence of which they cannot be 
 prepared and sown until late in the season, and though 
 chemically unexceptionable, they are always disadvan- 
 tageous, and in some seasons greatly disappoint the hopes 
 of the farmer. 
 
 The extent to which the imbibition and evaporation 
 of water takes place is very variable, but they are obvi- 
 ously related to one another, the soils which absorb it 
 least abimdantly parting with it again with the greatest . 
 facility ; for it appears that siliceous sand absorbs only 
 one-fourth of its weight of water, and again gives off in 
 the course of four hours four-fifths of that it had taken 
 up, while humus, which imbibes nearly twice its weight, 
 
132 AGRICULTURAL CHEMISTRY. 
 
 retains nine-tenths of that quantity after four hours' ex- 
 posure. Long-continued and slow evaporation of the water 
 absorbed by a soil is injurious in another way, for it makes 
 the soil " cold " — a term of practical origin, but which very 
 correctly expresses the peculiarity in question. It is due 
 to the fact, that when water evaporates it absorbs a very 
 large quantity of heat, which prevents the soil acquiring 
 a sufiSciently high temperature from the sun's rays. The 
 soils which have absorbed a large quantity of moisture 
 shrink more or less in the process of drying, and form 
 cracks, which often break the delicate fibres of the roots 
 of the plants, and cause considerable injury : the extent of 
 this shrinking is given in the fourth column. 
 
 The relation of the soils to heat divides itself into two 
 considerations : the amount of heat absorbed by the soil, 
 and the degree in which it is retained. Of these the latter 
 only is illustrated in the table. The former is dependent 
 on so many special considerations, that the results cannot 
 be tabulated in a satisfactory manner. It is independent 
 of the chemical nature of the soil, but varies to a great 
 extent according to its colour, the angle of incidence of 
 the sun's rays, and its state of moisture. It is, how- 
 ever, an important character, and has been found by 
 Girardin to exercise a considerable influence on the 
 rapidity with which the crop ripens. He found in a par- 
 ticular year that, on the 25th of August, 26 varieties of 
 potatoes were ripe on a very dark-coloured sandy vegetable 
 mould, 20 on an ordinary sandy soil, 19 on a loamy soil, 
 and only 16 on a nearly white calcareous soil. 
 
 The tenacity of the soil is very variable, and indicates 
 the great differences in the amount of power which must 
 he expended in working them. According to Schiibler, 
 a soil whose tenacity does not exceed 10, is easily, tilled, 
 
CHEMICAL AND PHYSICAL CHAKACTEES OF SOIL. 133 
 
 but when it reaches 40 it becomes very difficult and heavy 
 to work. 
 
 On examining the table it becomes manifest, that as 
 far as its mechanical properties are concerned, humus is a 
 substance of the very highest importance, for it confers on 
 the soil, in a high degree, the power of absorbing and 
 retaining water, diminishes its tenacity and permits its 
 being more easily worked, adds to its hygrometric power 
 and property of absorbing oxygen from the air, and 
 finally, from its dark colour, causes the more rapid absorp- 
 tion of heat from the sun's rays. It will be thus under- 
 stood, that though it does not directly supply food to the 
 plant, it ministers indirectly in a most important manner 
 to its well-being, and that to so great an extent that it 
 must be considered an indispensable constituent of a fertile 
 soil. But it is important to observe that it must not be 
 present in too large a quantity, for an excess does away 
 with all the good effects of a smaller supply, and produces 
 soils notorious for their infertility. 
 
 Such are the important physical properties of the soil, 
 and it is greatly to be desired that they should be more 
 extensively examined. The great labour which this in- 
 volves has, however, hitherto prevented its being done, 
 and will, in all probability, render it impossible except in 
 a limited number of cases. Some of these characters are, 
 however, of minor importance, and for ordinary purposes it 
 might be sufScient to determine the specific gravity of the 
 soil in the dry and moist state, the power of imbibing and 
 retaining water, its hygrometric power, its tenacity, and 
 its colour. With these data we should be in a condition 
 to draw probable conclusions regarding the others; for 
 the higher the specific gravity in the dry state, the greater 
 is the power of the soil to retain heat, and the darker its 
 
134 AGRICULTURAL CHEMISTRY. 
 
 colour the more readily does it absorb it. The greater its 
 tenacity the more difficult is it to work, and the greater 
 difficulty will the roots of the young plant find in pushing 
 their way through it. The greater the power of imbibing 
 water, the more it shrinks in drying ; and the more slowly 
 the water evaporates, the colder is the soil produced. The 
 hygrometric power is so important a character that Davy 
 and other chemists have even believed it possible to make 
 it the measure of the fertility of a soil ; but though this 
 may be true within certain limits, it must not be too 
 broadly assumed, the results of recent experiments by no 
 means confirming the opinion in its integrity, but indi- 
 cating only some relation between the two. 
 
 Tlie Subsoil. — The term soil is strictly confined to that 
 portion of the surface turned over by the plough working 
 at ordinary depth ; which, as a general rule, may be taken 
 at 10 inches. The portion immediately subjacent is called 
 the subsoil, and it has considerable agricultural importance, 
 and requires a short notice. In many instances, soil and 
 subsoil are separated by a purely imaginary line, and no 
 striking difference can be observed either in their chemical 
 or physical characters. In such cases it has been the 
 practice with some persons not to limit ' the term soil to 
 the upper portion, but to apply it to the whole depth, 
 however great it may be, which agrees in characters with 
 the upper part, and only to call that subsoil which mani- 
 festly differs from it. This principle is perhaps theoreti- 
 cally the more correct, but great practical advantages are 
 derived from limiting the name of soil to the depth actu- 
 ally worked in common agricultural operations. The sub- 
 soil is always analogous in its general characters to a soil, 
 but it may be either identical with that which overlies 
 it or not. Of the former, striking illustrations are seen in 
 
CHEMICAL AND PHYSICAL CHAEACTERS OP SOIL. 135 
 
 the wheat subsoils,, the analyses of which have been, 
 already given. In the latter case great differences may 
 exist, and a heavy clay is often found lying on an open 
 and porous sand, or on peat, and vice versa. Even where 
 the characters of the subsoil appear the same as those of 
 the soil, appreciable chemical differences are generally ob- 
 served, especially in the quantity of organic matter, which 
 is increased in the soil by the decay of plants growing 
 upon it and by the manure added. In general, then, all 
 that we have said regarding the characters of soils both 
 chemically and physically, will apply to the subsoils, ex- 
 cept that, owing to the difficulty with which the air 
 reaches the latter, some minor peculiarities are observed. 
 The most important is the effect of the decay of vegetable 
 matter, without access of air, which is attended by the 
 reduction of the peroxide of iron to the state of protoxide, 
 and not unfrequently by the production of sulphuret of 
 iron, compounds which are extremely prejudicial to vege- 
 tation, and occasionally give rise to some difficulties when 
 the subsoil is brought to the surface, as we shall after- 
 wards have to notice. 
 
 The physical characters of the subsoil are often of 
 much importance to the soil itself. As, for instance, 
 where a light soil lies on a clay subsoil, in which case its 
 value is much higher than if it reposed on an open or 
 sandy subsoil. And in many similar modes an important 
 influence is exerted ; but these belong more strictly to 
 the practical department of agriculture, and need not be 
 mentioned here. 
 
 Classification of Soils. — Numerous attempts have been 
 made to form a classification of soils according to their 
 characters and value, but they have not hitherto proved 
 very successful ; and the result of more recent chemical 
 
136 AGEICULTUKAL CHEMISTRY. 
 
 investigations has not been such as to encourage a far- 
 ther attempt. We have not at present data sufficient 
 for the purpose, nor, if we had, would it be possible to 
 arrange any soil in its class except after an elaborate 
 chemical examination. The only classification at present 
 possible must be founded on the general physical cha- 
 racters of the soil ; and the ordinary mode followed in 
 practice of dividing them into clays, loams, etc. etc., 
 which we need not here particularize, fulfils all that can 
 be done until we have more minute information regard- 
 ing a large number of soils. Those of our readers who 
 desire more full information on this point are referred to 
 the works of Thaer, Schiibler, and others, where the 
 subject is minutely discussed. 
 
CHAPTEE VI. 
 
 THE IMPROVEMENT OF THE SOIL BY MECHANICAL PE0CES8ES. 
 
 Comparatively few uncultivated soils possess the physical 
 properties or chemical composition required for the pro- 
 duction of the most abundant crops. Either one or more 
 of the substances essential to the growth of plants are 
 absent, or, if present, they are deficient in quantity, or 
 exist in some state in which they cannot be absorbed. 
 Such defects, whether mechanical or chemical, admit of 
 diminution, or even entire removal, by certain methods of 
 treatment, the adaptation of which to particular cases is 
 necessarily one of the most important branches of agricul- 
 tural practice, as the elucidation of their mode of action 
 is of its theory. The observations already made with 
 regard to the characters of fertile soils must have prepared 
 the reader for the statement that these defects may be 
 removed, either by mechanical or chemical processes. The 
 former method of improvement may at first sight appear 
 to fiill more strictly under the head of practical agriculture, 
 of which the mechanical treatment of the soil forms so 
 important a part, and that their improvement by chemical 
 means should form the sole subject of our consideration in 
 a treatise on agricultural chemistry. But the line of 
 demarcation between the mechanical and the chemical, 
 which seems so marked, disappears on more minute obser- 
 
138 AGEICULTURAL CHEMISTRY. 
 
 vation, and we find that the mechanical methods of 
 improvement are frequently dependent on chemical prin- 
 ciples ; and those which, at first sight, appear to be entirely 
 chemical, are also in reality partly mechanical. It will 
 be necessary for ns, therefore, to consider shortly the 
 mechanical methods of improving the soil. 
 
 Draining. — By far the most important method of 
 mechanically improving the soil is by draining — a practice 
 the beneficial action of which is dependent on a great 
 variety of circumstances. It is unnecessary lo insist on 
 the advantage derived from the rapid removal of moisture, 
 which enables the soil to be worked at times when this 
 used to be almost impossible, and other direct practical 
 benefits. Of its more strictly chemical effects, the most 
 important is probably that which it produces on the tem- 
 perature of the soil. It has been already remarked that 
 the germination of a seed is dependent on the soil in which 
 it is sown acquiring a certain temperature, and the rapidity 
 of the after-growth of the plant is, in part at least, depen- 
 dent on the same circumstance. The necessary tempera- 
 ture is speedily attained by the heating action of the sun's 
 rays, when the soil is dry ; but when it is wet, the heat is 
 expended in evaporating the moisture with which it is 
 saturated ; and it is only after this has been effected that 
 it acquires a sufficiently high temperature to produce the 
 rapid growth of the seeds committed to it. 
 
 The extent to which this effect occurs may be best 
 illustrated by reference to some experiments made by 
 Schiibler, in which he determined the temperature attained 
 by different soils, in the wet and dry state, when exposed 
 to the sun's rays, from 11 till 3 o'clock, in the latter part 
 of August, when the temperature in the shade varied from 
 72° to 77°. 
 
UrPROVEMENT OF SOIL BT MECHANICAL PROCESSES. 139 
 
 Description of Soil. 
 
 Wet. 
 
 Dry. 
 
 Siliceous sand 
 
 Degs. 
 99-1 
 99-3 
 98-2 
 99-1 
 99-3 
 99-5 
 99-5 
 97-7 
 lOt-8 
 
 Degs. 
 112-6 
 112-1 
 111-4 
 112-1 
 112-3 
 113-0 
 113-5 
 111-7 
 115-3 
 
 Calcareous sand 
 
 
 Loam V clav 
 
 stiff clay 
 
 
 Garden mould 
 
 Arable soil 
 
 Slaty marl 
 
 
 In a soil which is naturally dry or has been drained, 
 the superfluous moisture escapes by the drains, and only 
 that comparatively small quantity which is retained by 
 capillary attraction is evaporated, and hence the soil is 
 more frequently and for a longer period in a condition to 
 take advantage of the heating effect of the sun's rays, 
 and in this way the period of germination, and, by conse- 
 quence also, that of ripening is advanced. The extent 
 of this influence is necessarily variable, but it is generally 
 considerable, and in some districts of Scotland the exten- 
 sive introduction of draining has made the harvest, on the 
 average of years, from ten to fourteen days earlier than it 
 was before. It is unnecessary to insist on the importance 
 of such a change, which in upland districts may make 
 cultivation successful when it was previously almost 
 impossible. The removal of moisture by drainage affects 
 the physical characters of the soil in another manner ; it 
 makes it lighter, more friable, and more easily worked ; 
 and this change is occasioned by the downward flow of 
 the water carrying with it to the lower part of the soil 
 
140 AGRICULTURAL CHEMISTRY. 
 
 the finer argillaceous particles, leaving the coarser and 
 sandy matters above, and in this way a marked improve- 
 ment is produced on heavy and retentive clays. The 
 access of air to the soil is also greatly promoted by drain- 
 ing. In wet soils the pores are filled with water, and 
 hence the air, which is so important an agent in their 
 amelioration, is excluded ; but so soon as this is removed, 
 the air is enabled to reach and act upon the organic 
 matters and other decomposable constituents present. In 
 this way also provision is made for the frequent change of 
 the air which permeates the soil ; for every shower that 
 falls expels from it a quantity of that which it contains, 
 and as the moisture flows off by the drains, a new supply 
 enters to take its place, and thus the important changes 
 which the atmospheric oxygen produces on the soil are 
 promoted in a high degree. The air which thus enters 
 acts on the organic matters of the soil, producing car- 
 bonic acid, which we have already seen is so intimately 
 connected with many of its chemical changes. In its 
 absence the organic matters undergo different decomposi- 
 tions, and pass into states in which they are slowly acted 
 on, and are incapable of supplying a sufficient quantity of 
 carbonic acid to the soil ; and they thus exercise an 
 action on the peroxide of iron, contained in all soils, 
 reduce it to the state of protoxide, or, with the simultane- 
 ous reduction of the sulphuric acid, they produce sulphnret 
 of iron, forms of combination which are well known to be 
 most injurious to vegetation. 
 
 The removal of water from the lower part of the soil, 
 and the admission of air, which is the consequence of 
 draining, submits that part of it to the same changes which 
 take place in its upper portion, and has the effect of prac- 
 tically deepening the soil to the extent to which it is thus 
 
IMPROVEMENT OP SOIL BY MECHANICAL PROCESSES. 141 
 
 laid dry. The roots of the plants growing on the soU, 
 which stop as soon as they reach the moist part, now 
 descend to a lower level, and derive from that part of it 
 supplies of nourishment formerly unavailable. The deep- 
 ening of the soil has further the efiFect of making the plants 
 which grow upon it less liable to be burned up in seasons 
 of drought, a somewhat unexpected result of making a soil 
 drier, but which manifestly depends on its permitting the 
 roots to penetrate to a greater depth, and so to get beyond 
 the surface portion, which is rapidly dried up, and to 
 which they were formerly confined. 
 
 It may be added also that the abundant escape of 
 water from the drains acts chemically by removing any 
 noxious matters the soil may contain, and by diminishing 
 the amount of soluble saline matters, which sometimes 
 produce injurious effects. It thus prevents the saline 
 incrustation frequently seen in dry seasons on soils which 
 are naturally wet, and which is produced by the water 
 rising to the surface by capillary attraction, and, as it 
 evaporates, depositing the soluble substances it contained, 
 as a hard crust which prevents the access of air to the 
 interior of the soil. 
 
 It is thus obvious that the drainage of the soil modifies 
 its properties both mechanically and chemically. It exerts 
 also various other actions in particular cases which we 
 cannot here stop to particularize. It ameliorates the 
 climate of districts in which it is extensively carried out, 
 and even affects the health of the population in a favour- 
 able manner. The sum of its effects must necessarily 
 differ greatly in different soils, and in different districts ; 
 bat a competent authority* has estimated, that, on the 
 
 • Mr. Dudgeon, Spylaw. Transactions of the Highland Society, 
 Tol. czxix., p. 505. 
 
142 AGRICULTURAL CHEMISTRY. 
 
 average, land which has been drained produces a quarter 
 more grain per acre than that which is undrained. But 
 this by no means exhausts the benefits derived from it, 
 draining being merely the precursor of further improve- 
 ment. It is only after it has been carried out that the 
 farmer derives the full benefit of the manures which he 
 applies. He gains also by the increased facility of work- 
 ing the soil, and by the rapidity with which it dries after- 
 continued rain, thus enabling him to proceed at their 
 proper season with agricultural operations, which would 
 otherwise have to be postponed for a considerable time. 
 
 It would be out of place to enlarge here upon the 
 mode in which draining ought to be carried out ; it may 
 be remarked, however, that much inconvenience and loss 
 has occasionally been produced by too close adherence to 
 particular systems. No rules can be laid down as to the 
 depth or distance between the drains which can be uni- 
 versally applicable, but the intelligent drainer will seek 
 to modify his practice according to the circumstances of 
 the case. As a general rule, the drains ought to be as 
 deep as possible, but in numerous instances it may be more 
 advantageous to curtail their depth and increase their 
 number. If, for instance, a thick impervious pan resting 
 on a clay were found at the depth of three feet below the 
 surface, it would serve no good purpose to make the 
 drains deeper ; but if the pan were thin, and the subjacent 
 layer readily permeable by water, it might be advantageous 
 to go down to the depth of four feet, trusting to the pos- 
 sible action of the air which would thus be admitted, 
 gradually to disintegrate the pan, and increase the depth 
 of soil above it. It is a common opinion that if we reach, 
 at a moderate depth, a tenacious and little permeable clay, 
 no advantage is obtained by sinking the drains into it ; 
 
IMPROVEMENT OF SOIL BY MECHANICAL PROCESSES. 143 
 
 but this is an opinion which should be adopted with 
 caution, both because no clay is absolutely impermeable, 
 even the most tenacious permitting to a certain extent the 
 passage of water, and because the clay may have been 
 brought down by water from the upper part of the soil, 
 and may have stopped there merely for want of some 
 deeper escape for the water, and which drains at a lower 
 level might supply. In some cases it may even be advis- 
 able to vary the depth of the drains in different parts of 
 the same field, and the judicious drainer may sometimes 
 save a considerable sum by a careful observation of the 
 peculiarities of the different parts of the ground to be 
 drained. 
 
 Subsoil and Deep Ploughing. — It frequently happens, 
 when a soil is drained, that the subsoil is so stiff as to per- 
 mit the passage of water imperfectly, and to prevent the 
 tender roots of the plant from penetrating it, and reaching 
 the new supplies of nourishment which are laid open to 
 them. In such cases the benefits of subsoil ploughing and 
 deep ploughing are conspicuous. The mode of action of 
 these two methods of treatment is similar but not identical. 
 The subsoil plough merely stirs and opens the subsoil, and 
 permits the more ready passage of water and the access of 
 air and of the roots of plants — the former to effect tne 
 necessary decompositions, the latter to avail themselves of 
 the valuable matters set free. But deep ploughing pro- 
 duces more extensive changes ; it raises new soil to the 
 surface, mixes it with the original soil, and thus not only 
 brings up fresh supplies of valuable matters to it, but 
 frequently changes its chemical and mechanical characters, 
 rendering a heavy soil lighter by the admixture of a light 
 subsoil, and vice versa. Both are operations which are 
 useless unless they are combined with draining, for it must 
 
144 AGKICtJLTUEAL CHEMISTEY. 
 
 manifestly serve no good purpose to attempt to open tip a 
 soil unless the water which lies in it be previously removed. 
 In fact, subsoiling is useless unless the subsoil has been 
 made thoroughly dry ; and it has been found by experience 
 that no good effects are obtained if it be attempted imme- 
 diately after draining, but that a sufiBcient time must 
 elapse, in order to permit the escape of the accumulated 
 moisture, which often takes place very slowly. Without 
 this precaution, the subsoil, after (being opened by the 
 plough, soon sinks together, and the good effects antici- 
 pated are not realized. The necessity for allowing some 
 time to elapse between draining and further operations is 
 stUl more apparent in deep ploughing, when the soil is 
 actually brought to the surface. In that case it requires 
 to be left for a longer period after draining, in order that 
 the air may produce the necessary changes on the subsoil ; 
 for if it be brought up after having been for a long time 
 saturated with moisture, and containing its iron as pro- 
 toxide, and the organic matter in a state in which it is not 
 readily acted upon by the air, the immediate effect of the 
 operation is frequently injurious in place of being advan- 
 tageous. One of the best methods of treating a soil in 
 this way is to make the operation a gradual one, and by 
 deepening an inch or two every year gradually to mix the 
 soil and subsoil ; as in this way from a small quantity 
 being brought up at a time no injurious effects are pro- 
 duced. Deep ploughing may be said to act in two ways, 
 firstly, by again bringing to the surface the manures which 
 have a tendency to sink to the lower part of the soil, and, 
 secondly, by bringing up a soil which has not been ex- 
 hausted by previous cropping — ^in fact a virgin soiL 
 
 The success which attends the operation of subsoiling 
 or deep ploughing must manifestly be greatly dependent 
 
IMPROVEMENT OF SOIL BY MECHANICAL PROCESSES. 145 
 
 on the character of the subsoil, and good effects can only 
 be obtained when its chemical composition is such as to 
 supply in increased quantity the essential constituents, of 
 the plant; and it is no doubt owing to this that the 
 opinions entertained by practical men, each of whom speaks 
 from the results of his own experience, are so varied. 
 The effects produced by deep ploughing on the estates of 
 the Marquis of Tweeddale, are familiarly known to most 
 Scottish agriculturists, and they are at once explained by 
 the analyses of the soil and subsoil here given, which show 
 that the latter, though poor in some important constituents, 
 contains more than twice as much potash as the soil. 
 
 Soil. Sabsoil, 
 
 Insoluble silicates 87-623 82-72 
 
 Soluble silica 0-393 0-12 
 
 Alumina and peroxide of iron 4-129 8-60 
 
 Lime 0-341 0-18 
 
 Magnesia 0-290 0-24 
 
 Sulphuric acid 0-027 0-03 
 
 Phosphoric acid 0-240 trace 
 
 Potash 0-052 0-12 
 
 Soda 0050 0-04 
 
 Water .^ 1-956 3-26 
 
 Organic matter....'. 5-220 4*02 
 
 100-321 99-33 
 
 In addition to the difference in the amount of potash, 
 something is probably due to the large proportion of 
 alumina and oxide of iron in the subsoil, which for this 
 reason must be more tenacious than the soil itself, which 
 appears to be rather light. In other instances, the use of 
 the subsoil plough has occasioned much disappointment, 
 and has led to its being decried by many practical men ; 
 but of late years its use having become better understood, its 
 
 L 
 
146 AGEICULTDEAL CHEMISTRY. 
 
 merits are more generally admitted. We believe, that in 
 all cases in which the soil is deep, more or less marked 
 good effects must be produced by its use, but of course 
 there must be cases in which, from the defective composi- 
 tion of the subsoil or other causes, it must fail. It may 
 sometimes be possible a priori to detect these cases, but 
 in a large majority of them our knowledge is stUl too 
 limited to admit of satisfactory conclusions being arrived 
 at. 
 
 Improving the Soil hy Paring and Burning. — It has 
 long been familiarly known, that a decided improvement 
 has been produced on some soils by burning. Its advan- 
 tages have chiefly been observed on two sorts, heavy clays 
 and peat soUs, on both of which it has been practised to 
 a great extent. The action of heat on the heavy clays 
 appears to be of a twofold character, depending partly on 
 the change effected in its physical properties, and partly 
 on a chemical decomposition produced by the heat. The 
 operation of burning is effected by mixing the clsty with 
 brushwood and vegetable refuse, and allowing it to 
 smoulder in small heaps for some time. It is a process 
 of some nicety, and its success is greatly dependent on 
 the care which has been taken to keep the temperature 
 as low as possible during the whole course of the burning. 
 
 Experience has shown that burning is by no means 
 equally advantageous to all clays, but is most beneficial 
 on those containing a considerable quantity of calcareous 
 matter, and of silicates of potash. In such clays heat 
 operates by causing the lime to decompose the alkaline 
 silicates, and liberate a quantity of the potash which was 
 previously in an unavailable state. Its effect may be best 
 illustrated by the following analyses by Dr. Voelcker of 
 a soil, and the red ash produced in burning it. 
 
IMPROVEMENT OF SOIL BY MECHANICAL PKOCESSES. 147 
 
 Soil. Red Ash. 
 
 Water 0-93 1-18 
 
 Organic matter 10.67 3-32 
 
 Oxides of iron and alumina 13-40 18"42 
 
 Carbonate of lime 23-90 8-83 
 
 Sulphate of lime trace 1-15 
 
 Carbonate of magnesia .. . 1*10 „ 
 
 Magnesia „ 1-76 
 
 Phosphoric acid trace 0*71 
 
 Potash 0-38 1-08 
 
 Soda ;... 013 „ 
 
 Chloride of sodium „ 1-03 
 
 Insoluble matter, chiefly clay 49-66 62-52 
 
 100-17 10000 
 In this instance the quantity of burned soil amounted 
 to about fifteen tons per acre, and it is obvious that the 
 quantity of potash which had been liberated from the 
 insoluble day and the phosphoric acid are equal to that 
 contained in a considerable manuring. In order to obtain 
 these results, it is necessary, as has been already observed, 
 to keep the temperature as low as possible during the 
 process of burning, direct experiment having shown that 
 when this precaution is not observed another change 
 occurs, whereby the potash, which at low temperatures 
 becomes soluble, passes again into an insoluble stat«. A 
 part of the beneficial effect is no doubt also due to the 
 change produced in the physical characters of the clay by 
 burning, which makes it lighter and more friable, and by 
 mixture with the unburnt clay ameliorates the whole. This 
 improvement in the physical characters of the clay also re- 
 quires that it shall be burnt with as low a heat as possible ; 
 for if it rises too high, the clay coheres into hard masses 
 which cannot again be reduced to powder, and the success 
 of the operation of burning may always be judged of by the 
 readiness with which it falls into a uniform friable powder. 
 
148 AGEICULTUKAL CHEMISTRY. 
 
 The improvement of peat by burning has been practised 
 to some extent in Scotland, though less frequently of late 
 years than formerly ; but it is still the principal method of 
 reclaiming peat soils in many countries, and particularly in 
 Finland, where large breadths of land have been brought 
 into profitable cultivation by means of it. The modus 
 operandi of burning peat is very simple ; it acts by dimi- 
 nishing the superabundant quantity of humus or other 
 organic matters, which, in the previous section we have 
 seen to be so injurious to the fertility of the soil. It may 
 act also in the same way as it does on clay, by making 
 part of the inorganic constituents more really soluble, 
 although it is not probable that its effect in this way can 
 be very marked. Its chief action is certainly by destroy- 
 ing the organic matters, and by thus improving the phy- 
 sical character of the peat, and causing it to absorb and 
 retain a smaller quantity of water than it naturally does. 
 For this reason it is that it proves successful only on thin 
 peat bogs, for if they be deep, the inorganic matters soon 
 sink into the lower part, and the surface relapses into its 
 old state of infertility. It is probably for this reason that 
 the practice has been so much abandoned in Scotland, 
 more especially as other and more economical modes of 
 treating peat soils have come into use. 
 
 Warping. — This name has been given to a method of 
 improving soils by causing the water of rivers to deposit 
 the mud it carries in suspension upon them, and which has 
 been largely practised in the low lying lands of Lincoln 
 and Yorkshire, where it was introduced about a century 
 ago. It it most beneficial on sandy or peaty soil, and by 
 its means large tracts of worthless land have been brought 
 under profitable cultivation. It requires that the land to 
 be 80 treated shall be under the level of the river at full 
 tide, and it is managed by providing a sluice through 
 
IMPROVEMENT OF SOIL BY MECHANICAL PROCESSES. 149 
 
 which the river water is allowed to flood the land at high 
 tide, and again to escape at ebb, leaving a layer of mud 
 generally about a tenth of an inch in thickness, which it 
 brought along with it. By the repetition of this process, 
 a layer of several feet in thickness, of an excellent soil, is 
 accumulated on the surface. Herapath, who has carefully 
 examined this subject chemically, has shown that in one 
 experiment where the water used contained 233 grains of 
 mud per gallon, 210 were deposited during the warping. 
 The following analyses will show the general nature of the 
 matters deposited, and the change which they produce on 
 the soil : — No. 1 is the mud from the Humber in its natural 
 state, No. 2 a specimen of warp of average quality artifi- 
 cially dried. No. 3 a sandy soil before warping, and No. 
 4, the same fifteen years after having received a coating of 
 1 1 inches of mud. 
 
 Water , 
 
 Organic matter 
 
 Cloride of Calcium 
 
 Magnesium.. 
 
 Sodium 
 
 Potassium .. 
 
 Sulpliate of Soda 
 
 Magnesia .. 
 
 Lime 
 
 Carbonate of Magnesia 
 
 Lime 
 
 Potash and Soda 
 
 Magnesia 
 
 Ijime 
 
 Peroxide of Iron 
 
 Alumina 
 
 Phosphate of Iron 
 
 Silica 
 
 Sand and Stones 
 
 1 
 
 2 
 
 3 
 
 4 
 
 47-49 
 
 
 106 
 
 2-00 
 
 6-94 
 
 6-93 
 
 2-20 
 
 7-61 
 
 
 0-10 
 
 ... 
 
 
 1 1-G6 
 
 I 0-94 
 0-31 
 
 \ 0-14 
 
 016 
 
 
 ... 
 
 ... 
 
 ... 
 
 1-18 
 
 J - 
 
 
 trace 
 
 1-10 
 
 trace 
 
 trace 
 
 2-60 
 
 0-31 
 
 trace 
 
 0-29 
 
 3-59 
 
 8-18 
 
 trace 
 
 0-46 
 
 018 
 
 0-47 
 
 trace 
 
 0-17 
 
 1-69 
 
 2-60 
 
 trace 
 
 0-26 
 
 039 
 
 0-68 
 
 trace 
 
 0-14 
 
 1 6-63 
 
 5-05 
 
 0-os 
 
 1-17 
 
 8-18 
 
 0-39 
 
 0-41 
 
 0-58 
 
 1-04 
 
 trace 
 
 0-28 
 
 
 905 
 
 0-14 
 
 2-77 
 
 2915 
 
 55-87 
 
 95-91 
 
 84-97 
 
 100-00 
 
 100-00 
 
 10000 
 
 100-00 
 
150 AGRIC0LTtrRAL CHEMISTRY. 
 
 It is easy to understand the importance of the effects 
 produced by adding to any soil large quantities of a mud 
 containing upwards of one per cent of phosphate of iron; and 
 in point of fact, Herapath has calculated that in one par- 
 ticular instance the quantity of phosphoric acid brought by 
 warping upon an acre of land, exceeded seven tons per acre. 
 As, moreover, the matters are all in a high state of divi- 
 sion, they must exist in a condition peculiarly favourable 
 to the plant. The overflow of the Nile is only an instance 
 of warping on the large scale, with this difference, that it 
 is repeated once only in every year, whereas, in this country, 
 the operation is repeated at every tide until a deposit some- 
 times of several feet in thickness is obtained, after which 
 it is stopped, and the soil brought under ordinary cultiva- 
 tion. 
 
 An operation which is, in some respects, the converse 
 of warping, has been carried out on Blair-Drummond 
 Moss, where the peat has been dislodged and carried off 
 by the action of water, leaving the subjacent soil in a 
 state fitted for cropping. Of course both this and warp- 
 ing are restricted to special localities, but they are most 
 important means of ameliorating the soil when circum- 
 stances admit of their being carried out. 
 
 Mixing of Soils. — When soils possess conspicuous 
 defects in their physical, and even in their chemical pro- 
 perties, great advantages may, in some instances, be 
 derived from their proper admixture. A light sandy soil, 
 for instance, is greatly improved by the addition of clay, 
 and vice versa ; so that, when two soils of opposite pro- 
 perties occur near to one another, both may be improved 
 by mixture. It has been applied to the improvement of 
 heavy clay soil and of peat, the former being mixed with 
 sand or marl so as to diminish its tenacity ; the latter 
 
IMPROVEMENT OF SOIL BY MECHANICAL PROCESSES. 151 
 
 ■with clay or gravel to add to its inorganic matters, and in 
 both instances it has proved successful. 
 
 The process of chalking, which has heen carried out 
 on a large scale in some parts of England, and which 
 consists in bringing up the chalk from pits, penetrating 
 through the overlying tenacious clay, and mixing it with 
 the soil, operates, to some extent, in a similar manner, 
 though no doubt the lime also exercises a strictly chemical 
 action. It is probable that the mixing of soils might be 
 advantageously extended, and it merits more minute study 
 than it has yet obtained. Its use is obviously limited 
 by the expense, because, of course, where good effects _are 
 to be obtained, it is necessary to remove large quantities 
 of soil, in some instances as much as 50 or 100 tons per 
 acre, but the expense might be much diminished if it were 
 carried out methodically, and on a considerable scale. 
 The admixture of highly fertile soils with others of inferior 
 quality is also worthy of attention ; indeed, it is under- 
 stood that this has been done, to some extent, with the 
 rich trap soils of some parts of Scotland, but the extent 
 of the benefit derived from it has not been made public. 
 
CHAPTER VII. 
 
 THE GENERAL PEINCIPLES OP MANUEING, 
 
 In their natural condition all soils not absolutely barren 
 are capable of supporting a certain amount of vegetation, 
 and they continue to do so for an unlimited period, because 
 the whole of the substances extracted from them are again 
 restored, either directly by the decay of the plants, or 
 indirectly by the droppings of the wild animals which 
 have browzed upon them. Under these circumstances, a 
 soil yields what may be called its normal produce, which 
 varies within comparatively narrow limits, according to the 
 nature of the season, temperature, and other climatic con- 
 ditions. But the case is completely altered if the crop, in 
 place of being allowed to decay on the soil, is removed 
 from it, for, though the air will continue to afford an 
 undiminished supply of those elements of the food of 
 plants which may be derived from it, the fixed substances, 
 which can only be obtained from the soil, decrease in 
 quantity, and are at length entirely exhausted. In this 
 way a gradual diminution of the fertility of the soil takes 
 place, until, after the lapse of a period, longer or shorter, 
 according to its natural resources, it will become entirely 
 incapable of maintaining a crop, and fall into absolute 
 infertility unless the substances removed from it are 
 restored from some other source in the form of manure. 
 
GENERAL PEINCIPLES OF MANUKING. 153 
 
 When this is done, the fertility of the soil may not only 
 be sustained but greatly increased, and, in point of fact, 
 all cultivated soils, by the use of manure, are made to 
 yield a much larger crop than they can do in their natural 
 condition. 
 
 The fundamental principle upon which a manure is 
 employed is that of adding to the soil an abundant supply 
 of the elements removed from it by plants in the condi- 
 tion best fitted for absorption by their roots ; but looked 
 at in its broadest point of view, it acts not merely in this 
 way, but also by promoting the decomposition of the 
 already partially disintegrated rocks of which the soil is 
 composed, setting free those substances it already con- 
 tains, and facilitating their absorption by the plants. 
 
 In considering the practical applications of the broad 
 general principle just stated, it might be assumed that a 
 manure ought invariably to contain all the elements of 
 plants in the quantities in which they are removed by the 
 crops, and that when this has been accurately ascertained 
 by analysis, it would only be necessary to use the various 
 substances in the proportions thus indicated. But this, 
 though a very important, and no doubt in many cases 
 essential condition, is by no means the only matter which 
 requires to be taken into consideration in the economical 
 application of manures. And this becomes sufficiently 
 obvious when the circumstances attending the exhaustion 
 of the soil are minutely examined. When a soil is cropped 
 during a succession of years with the same plant, and at 
 length becomes incapable of longer maintaining it, the 
 exhaustion is rarely, if ever, due to the simultaneous con- 
 sumption of all its different constituents, but generally 
 depends upon that of one individual substance, which, from 
 its having originally existed in the soil in comparatively 
 
154 AGEICULTUKAL CHEMISTRY. 
 
 small quantity, is removed in a shorter time than the 
 others. To restore the fertility of a soil in this condition, 
 it is by no means necessary to supply all the different sub- 
 stances required by the plant, for it will sufBce to add that 
 which has been entirely removed. On the other hand, if 
 an ordinary soil be supplied with a manure containing a 
 very small quantity of one of the elements of plant food, 
 along with abundance of all the others, the amount of in- 
 crease which it yields must obviously be measured, not by 
 those which are abundant, but by that which is deficient; for 
 the crop which grows luxuriantly so long as it obtains a sup- 
 ply of all its constituents, is arrested as effectually by the 
 want of one as of all, as has been proved by the experiments 
 of Prince Salm Horstmar and others, referred to in a pre- 
 vious chapter ; and hence, in order to obtain a good crop, it 
 would be necessary to use the manure in such abundance as 
 to supply a sufficiency of the deficient element for that pur- 
 pose. If this course were persevered in for a succession of 
 years, the other substances which would have been used in 
 much more than the quantity required by the crops, must 
 either have been entirely lost or have accumulated in the 
 soil. In the latter case it is sufficiently obvious that the 
 soil must have been gradually acquiring an amount of 
 resources which must remain dormant until the system of 
 manuring is changed. To render them available, it is only 
 necessary to add to it a quantity of the particular substance 
 in which the manure hitherto employed has been deficient, 
 so as to restore the lost balance, and enable the plant to 
 make use of those which have been stored up within it. 
 The substance so used is called a special manure ; that con- 
 taining all the constituents of the crop is a general manure. 
 The distinction of these two classes of manures is very 
 important in a practical point of view, because a special 
 
GENERAL PRINCIPLES OP MANURING. 155 
 
 manure is not by itself capable of maintaining the life of 
 plants, but is only a means of bringing into use the natural 
 and acquired resources of the soil. In place of preventing 
 or retarding its exhaustion, it rather accelerates it by caus- 
 ing the increased crops to consume more abundantly, and 
 Tvithin a shorter period of time, those substances which it 
 contains. On the other hand, a general manure prevents 
 or diminishes the consumption of the elements of plant- 
 food contained in the soil, and if added in sufficient abun- 
 dance, may cause them to accumulate in it, and even enable 
 an almost absolutely barren soil to yield a tolerable crop. 
 General manures must therefore always be the most im- 
 portant and essential, and no others would be used if 
 it were possible to obtain them of a composition exactly 
 suited to the requirements of the crop to be raised. Prac- 
 tically, however, this condition cannot be fulfilled, because 
 all the substances available for the purpose, and particularly 
 farm-yard manure, are refuse matters, the exact composi- 
 tion of which is not under our control, and they do not 
 necessarily contain their constituents either in the most 
 suitable proportions, or the most available forms, and con- 
 sequently when they are used during a succession of years, 
 certain of their constituents may accumulate in the soil, 
 and it is under such circumstances that special manures are 
 both necessary and advantageous. 
 
 Several diflferent substances, but more especially farm- 
 yard manure, fulfil in a very remarkable manner the con- 
 ditions of a general manure, and supply abundantly, not 
 merely the mineral, but also the carbonaceous and nitro- 
 genous matters necessary for building up the organic part 
 of the plant ; and hence its use is governed by principles of 
 comparative simplicity, and really resolves itself into deter- 
 mining the best mode of managing it so as effectually to 
 
156 AGEICULTUKAL CHEMISTEY, 
 
 preserve its useful constituents, and, at the same time, to 
 bring them into those forms of combination in which they 
 are most available to the plant. But the employment of a 
 special manure opens up nice questions as to the relative 
 importance of the different elements of plants which have 
 given rise to much controversy and difference of opinion. 
 
 In treating of the food of plants, it has been already 
 observed that the fixed or mineral constituents which are 
 contained in their ash, are necessarily derived exclusively 
 from the soil, but that the carbon, hydrogen, nitrogen, and 
 oxygen, of which their organic part is composed, may be 
 obtained either from that source or from the air. The 
 important distinction which thus exists between these two 
 classes of substances, has given rise to two different views 
 regarding the tlieory of manures. Basing his views on the 
 presence of the organic elements in the air, Liebig has 
 maintained that it is unnecessary to supply them in 
 the manure, while others, among whom Messrs. Lawes 
 and Gilbert have taken a prominent position, hold that, 
 as a rule, fertile soils, cultivated in the ordinary man- 
 ner, contain a sufficient supply of mineral matters for 
 the production of the largest possible crops, but that the 
 quantity of ammonia and nitric acid which the plants are 
 capable of extracting from the air is insufficient, and 
 must be supplemented by manures containing them. A 
 large number of experiments have been made in support 
 of these views, but the inferences which can be drawn 
 from them are not absolutely conclusive on either side, 
 and it is necessary to consider the matter in a general 
 point of view. 
 
 Setting out from the proposition already so frequently 
 referred to, that the plant cannot grow unless it receives 
 a supply of all its elements, it must be obvious that if, 
 
GENERAL PRINCIPLES OF MANURING. 157 
 
 to a soil containing a sufficiency of mineral matters to raise 
 a given number of crops, a supply of ammonia be added, 
 its total productive capacity cannot be thus increased ; 
 and though it may yield larger crops than it would have 
 done without that substance, this can only be accom- 
 plished by a proportionate diminution of their number. In 
 either case, the same quantity of vegetable matter will 
 be produced, but the time within which it is obtained 
 will be regulated by the supply of ammonia. That sub- 
 stance differs in no respect from any other element of 
 plant-food, and used in this way is to all intents and pur- 
 poses a special manure, and acts merely by bringing into 
 play those substances which the soil already contains. Its 
 effect may not be apparent until after the lapse of a very 
 long period of time, but it ultimately leads to the exhaus- 
 tion of the soil. If, on the other hand, a soil be continu- 
 ously cropped until it ceases to yield any produce, it is 
 manifest that the exhaustion must in this instance be 
 entirely due to the removal of its available mineral nutri- 
 ment, because the superincumbent air constantly changed 
 by the winds must continue to afford the same unvarying 
 supply of the organic elements, and the power of sup- 
 porting vegetation would be restored to it, by adding the 
 necessary inorganic matters. Hence when a soil, which in its 
 natural condition is capable of yielding a certain amount 
 of vegetable matter, is rendered barren by the removal 
 of the crop, it may be laid down as an incontrovertible 
 position, that its infertility is due to the loss of mineral 
 matters, and that it may be restored to its pristine con- 
 dition by the use of them, and of them only. 
 
 But the case is materially altered when we come to 
 consider the course of events in a cultivated soil. The 
 object of agriculture is to cause the soil, by appropriate 
 
158 AGEICULTtmAL CHEraSTKY. 
 
 treatment, to yield much more than its normal produce, 
 and the question is, how this can be best and most econo- 
 mically effected in practice. According to Liebig, it is 
 attained by adding to the soil a liberal supply of those 
 mineral substances required by the plant, and that it is 
 unnecessary to use any of the organic elements, because 
 they are supplied by the air in sufBcient quantity to meet 
 the requirements of the most abundant crops. Other 
 chemists and vegetable physiologists again hold that 
 though a certain increase may be obtained in this way, a 
 point is soon reached beyond which mineral matters will 
 not cause the plant to absorb more ammonia from the air, 
 although a further increase may be obtained by the addi- 
 tion of nitrogen in that or some other available form. 
 
 It is admitted on both sides, that all the elements of 
 plant food are equally essential, and the controversy really 
 lies in determining what practically limits the crop pro- 
 ducible on any soil. The point at issue may be put in a 
 clear point of view by considering the course of events on 
 a soil altogether devoid of the elements of plants. If a 
 small quantity of mineral matters be added to such a soil, 
 it immediately becomes capable of supporting a certain 
 amount of vegetation, deriving from the air the organic 
 elements necessary for this purpose, and with every in- 
 crease of the former, the air will be laid under a larger 
 contribution of the latter, to support the increased growth, 
 and this must proceed until the limit of supply firomthe 
 atmosphere is reached. At this point a further supply 
 of mineral matters alone must obviously be incapable of 
 again increasing the crop, and it would thus be absolutely 
 necessary to conjoin them with a proportionate quantity of 
 organic substances. Liebig maintains that this limit is 
 never attained in practice, but that the air affords ammonia 
 
GENERAL PRINCIPLES OP MANURING. 159 
 
 and the other organic elements in excess of the require- 
 ments of the largest crop, while mineral matters are gene- 
 rally though not invariably present in the soil in insufS- 
 cient quantity. Messrs. Lawes and Gilbert, on the other 
 hand, believe that the soil generally contains an excess of 
 mineral matters, and that a manure which is to bring out 
 their full effect must contain ammonia, or some other nitro- 
 genous substance fitted to supplement the deficient supply 
 afforded by the atmosphere. In short, the question at 
 issue is, whether there is or is not a sufficiency of atmo- 
 spheric food to meet the demands of the largest crop which 
 can practically be produced. 
 
 An absolutely conclusive reply to this question is by 
 no means easy. The experiments by which it is to be 
 resolved are complicated by the fact, that all soils capable 
 of supporting anything like a crop, contain not only the 
 mineral, but the organic elements of its food in large and 
 generally in greatly superabundant quantity, and it is impos- 
 sible satisfactorily to ascertain how much is derived fi:om 
 this source, and how much from the atmosphere. There 
 are in fact no experiments in which the effects of a purely 
 mineral soil have been ascertained. The important and 
 carefully performed researches of Messrs. Lawes and 
 Gilbert were made upon a soil which had been long 
 under cultivation, and contained decaying vegetable mat- 
 ters in sufficient abundance to supply nitrogen to many 
 successive crops, and it would be most unreasonable 
 to assert that the produce they did obtain by means of 
 mineral manures, drew the whole of its nitrogen from 
 the air. On the contrary, it may be fairly assumed that 
 the soil did yield a certain quantity of its nitrogenous 
 compounds, but to what extent this occurs, it is impos- 
 sible to determine. This difficulty is encountered more 
 
160 AGEICULXnRAL CHEMISTRY. 
 
 or less in all the other experiments, and precludes absolute 
 conclusioDS. The same fallacy also hesets the arguments 
 of Liebig when he holds that the crop, increased by means 
 of mineral manures alone, must derive the whole of the 
 additional quantity of nitrogen which it contains from the 
 air, as appears to be tacitly assumed throughoat the whole 
 discussion. So far from this being the case, it is just as 
 likely that the mineral matters should cause the plants to 
 take it from the soil, if it is there, as from the atmosphere. 
 Taking a general view of the whole question, it is 
 evident that a certain amount of vegetation may always 
 be produced by means of mineral manures, and the quan- 
 tity obtained is generally much beyond the normal produce 
 of the soil. But it is still open to doubt whether the 
 largest possible crop can be thus obtained, although the 
 balance of evidence is against it, and "in favour of the 
 addition of ammonia, and other nitrogenous and organic 
 substances, to the soil. In actual practice manures con- 
 taining nitrogen are more important, and more extensively 
 applied than any others, and the quantity of that element 
 thus used is very much larger than is generally supposed. 
 Twenty tons of farm-yard manure, a quantity commonly 
 applied, and often exceeded on well cultivated land, con- 
 tain a sufficiency of organic matters to yield about 2i- 
 cwt. of nitrogen. A complete rotation, according to the 
 six-course shift, contains almost exactly the same quantity 
 of nitrogen, when we assume average crops throughout the 
 whole, and it is thus made up.* 
 
 • The quantities here taken are the averages deduced from the 
 agricultural statistics taken in Scotland some years since, with the 
 exception of hay and straw, which are not included in them. I have 
 therefore assumed a reasonahle quantity in these cases. 
 
GENERAL PRINCIPLES OP MANURING. 161 
 
 Lba. of Nitrogen. 
 
 1. Turnips (13^ tons) 60 
 
 2 f Wheat (28 bushels at 60 lbs.) 29 
 
 ■ Istraw 16^ 
 
 3. Hay (2i tons) 56 
 
 ^ (■ Oats (34 bushels at 40 lbs.) 27 
 
 t Straw 14 
 
 6. Potatoes (3 tons) 27 
 
 6. Wheat and straw as before 45 
 
 Total 274 
 
 The supply is therefore quite sufficient for the require- 
 ments of the crop ; and when it is borne in mind that a 
 considerable quantity of ammonia and nitric acid is annu- 
 ally carried down by the rain, and that during a long 
 rotation other substances are very generally used in addi- 
 tion to farm-yard manure, it is obvious that the crop need 
 not depend to any extent upon what it derives from the 
 air. What is true of the nitrogenous matters applies with 
 still greater force to the mineral constituents of the manure. 
 Twenty tons of farm-yard manure contain 32 cwt. of 
 mineral matters, while the average crops of a six course- 
 shift contain only 1088 lbs., or less than one-third of this 
 quantity. It is obvious, therefore, that in well manured 
 land there must be a gradual increase of all the consti- 
 tuents of plants, but that of the mineral matters is rela- 
 tively much greater than that of the nitrogenous. If 
 therefore from any cause the crop produced on a soil to 
 which farm-yard manure had been applied were greatly 
 to exceed the average, the amount of produce, so far as 
 the soil is concerned, would be limited not by deficiency 
 of mineral, but of nitrogenous food. Hence also when 
 farm-yard manure is liberally applied, there is a gradual 
 
 M 
 
162 AGEICULTtJKAL CHEMISTET. 
 
 accumulation of valuable matters, and a progreBsiTe 
 improvement of the productive capacity of the BoU. 
 
 It is far otherwise, however, if a special manure is 
 employed, because in that case the crop is thrown upon 
 the resources of the soil itself for all its constituents except 
 those contained in the substance employed, and by per- 
 sisting in its exclusive use exhaustion is the inevitable 
 result. It would he wrong, however, to infer &om this, 
 that special manures are to be avoided. On the contrary, 
 great benefits are derived from their judicious employment, 
 and the circumstances under which they are admissible 
 may be readily gathered from what has already been said. 
 They are agents which bring into useful activity the dor- 
 mant resources of the soil, they restore the proper balance 
 between its different constituents, and supply the excessive 
 demand of some particular elements. Thus, for instance, in 
 a soil containing an abundant supply of mineral matters, a 
 salt of ammonia or nitric acid increases the crop, by pro- 
 moting the absorption of the substances already present. 
 So likewise a soil on which young cattle and milch cows 
 have been long pastured has its fertility restored by phos- 
 phate of lime, because that substance is removed in the 
 bones and milk in relatively much larger proportion than 
 any Others. 
 
 The choice of a special manure is necessarily dependent 
 on a great variety of circumstances, and is governed partly 
 by the nature of the soil, and partly by that of the crop. 
 It is obvious that cases may occur in which any individual 
 element of the plant may be deficient, and ought to be 
 supplied, but experience has shown that, as a rule, nitrogen 
 and phosphoric acid are the substances which it is most 
 necessary to furnish in this way, and which in all but excep- 
 tional cases produce a marked effect on the crop. The other 
 
GENERAL PRINCIPLES OF MANURING. 163 
 
 substances, such as potash, soda, magnesia, etc., occasion- 
 ally act beneficially, but the results obtained from them 
 are very uncertain, and frequently entirely negative. 
 
 It has been commonly asserted that phosphates are 
 specially adapted to root crops, and ammonia or nitrates to 
 the cereals, and this statement is so far true, that the 
 former are used with advantage on the turnip, while the 
 latter act with great benefit on grain crops and more 
 especially on oats and barley. The effect of the latter, 
 however, is more or less apparent in all crops and on all 
 soils, because it promotes the assimilation of the mineral 
 matters already present. But its peculiar importance lies 
 in the power which it has of promoting the rapid develop- 
 ment of the young plant, causing it to send its roots out into 
 the soil, and to spread its leaves into the air, thus enabling 
 it to take from those two sources, abundance of the useful 
 substances existing in them. But it ought to be dis- 
 tinctly understood, that the statement that particular 
 manures are specially suited to particular crops must be 
 assumed with some reservation, because everything depends 
 upon the nature of the food contained in the soil. It is 
 well known that there are many soils in which ammonia 
 acts more favourably on the turnip than phosphates, and 
 vice versa, and the difference is often due to the previous 
 treatment. In many cases in which ammonia when first 
 used proved most beneficial, it now begins to lose its 
 effect, and the reason no doubt is, that by its means the 
 phosphates existing in these soils have been reduced in 
 amount, while the ammonia has accumulated, so that a 
 change in the system of manuring becomes necessary. A 
 general manure may be used year after year in a perfectly 
 routine manner, but where a special manure is employed, 
 the importance of watching its effects, and altering it as 
 
164 AGKICULTOEAL CHEMISTET. 
 
 circumstances indicate, cannot be over-estimated. The 
 length of time during which special manures have been 
 extensively used has not been sufficient to bring this pro- 
 minently before the agriculturist, but its importance must 
 sooner or later force itself upon him, and he will then see 
 the necessity for studying the succession of manures as 
 well as that of crops. 
 
 Hitherto we have considered a manure merely as a 
 source from which plants derive their food, but it exercises 
 a scarcely less important action on the chemical and phy- 
 sical properties of the soil. Farm-yard manure, which, as 
 we shall afterwards see, contains a large amount of decom- 
 posing vegetable and animal matters, yields a supply of 
 carbonic acid, which operates on the mineral constituents, 
 promotes their further disintegration, and thus liberates 
 their useful elements. It affects also their physical 
 properties, for it diminishes the tenacity of heavy clays ; 
 each straw as it decomposes forming a channel through 
 which the roots of plants, air, and moisture can penetrate 
 more readily than through the stiff clay itself. On the 
 other hand, it diminishes the porosity of light sandy 
 soils, causes them to retain moisture, and generally makes 
 their texture more suitable to the plant. Special manures 
 probably act to some extent chemically on the soil, but 
 the nature of the changes they produce is as yet imper- 
 fectly understood. Superphosphates which are highly acid 
 in all probability act powerfully on the mineral substances, 
 and common salt, which, though of little importance to 
 the plant, occasionally produces very striking effects, 
 appears to exercise some decomposing action on the soil. 
 It is difficult, however, to trace the mode in which they 
 operate on a substance of such complexity as the soil. 
 Lime, as we shall afterwards see, acts by promoting the 
 
GENEEAL PRINCIPLES OP MANUEING. 165 
 
 decomi)osition of the vegetable matters on the soil, and 
 possibly some other substances may have a similar effect. 
 In the application of manures to the soil there are 
 several circumstances which must be taken into considera- 
 tion. It is generally stated that they ought to be dis- 
 tributed as uniformly as possible, but this is not always 
 necessary nor even advisable, and certainly is not acted 
 on in practice. Much must depend upon the nature both 
 of crop and soil. When the former throws out long and 
 widely penetrating roots, the more uniformly the manure 
 is distributed the better ; but if the rootlets are short, it is 
 clearly more advisable that it should be deposited at no 
 great distance from the seed. Practically this is observed 
 in the case of the potato and turnip, which are short rooted, 
 and where the manure is generally deposited close to the 
 seed. But this course is never adopted with the long 
 rooted cereals, the manure being nsually applied to the 
 previous crop, so that the repeated ploughings to which 
 the soU is subjected in the interval may distribute what 
 remains as widely and uniformly as possible. In soils 
 which are either excessively tenacious or light, the accu- 
 mulation of the manure close to the plants has also the 
 effect of producing an artificial soil in their immediate 
 neighbourhood, containing abundance of plant-food, and 
 having physical properties better fitted for the support of 
 the plant. On the other hand, when a special manure is 
 used alone, and with the view of promoting the assimila- 
 tion of substances already existing in the soil, the more 
 imiform its distribution the better, because it is essential 
 that the roots which penetrate through it should find at 
 every point they reach not only the original soil consti- 
 tuents, but also the substances used to supplement their 
 deficiencies. 
 
CHAPTER VIII. 
 
 THE COMPOSITION AND PKOPERTIES OF FARM-YAED AND 
 LIQUID MANURES. 
 
 In the preceding chapter, a general manure has been 
 defined as one containing all the constituents of the crop 
 to which it is to be applied, in a state fitted for assimilation. 
 This condition is fulfilled only by substances derived from 
 the vegetable and animal kingdoms, and most efiectually 
 by a mixture of both. On this account, and also because 
 its properties are such as enable it to act powerfully on 
 the soil, farm-yard manure must always be of the highest 
 importance. It is, in fact, the typical manure, and in 
 proportion as other substances approach it in properties 
 and composition, is their value for general purposes on the 
 farm. 
 
 Farm-yard manure is a mixture of the dung and urine 
 of domestic animals, with the straw used as litter ; and its 
 value and composition must necessarily depend upon that 
 of these substances, as well as on the proportion in which 
 they are mixed. The dung of animals consists of that 
 pare of their food which passes through the intestinal 
 canal without undergoing assimilation ; the urine con- 
 taining the portion which has been assimilated and is 
 again excreted, in consequence of the changes which are 
 proceeding in the tissues of the animal. Their compo- 
 
FARM-YAKD AND LIQUID MAKUEES. 167 
 
 sition is naturally very different, and must be separately 
 considered. 
 
 Urine. — Urine consists of a variety of earthy and alka- 
 line salts, and of certain organic substances, generally rich 
 in nitrogen, dissolved in a large quantity of water. That 
 of the different domestic animals has been frequently 
 examined, but the analyses of Fromberg give the most 
 complete view of their manurial value : — 
 
 Hone. Swine. Ox. Goat. Sheep. 
 
 Extractive matter, ^.^gg o-142 2-248 0-100 0-340 
 soluble m water J 
 
 Extractive matter) 3.550 0-387 1-421 0-454 3-330 
 soluble in spirit ) 
 
 Salts soluble in) 2-340 0-909 2-442 0-850 1-957 
 
 water > 
 
 Salts insoluble in) ^.gg^ ^.^gg ^.^55 qq^q q.q^^ 
 
 water ) 
 
 Urea 1-244 0-273 1-976 0-378 1-262 
 
 Hippuricacid 1-260 ... 0-550 0-125 
 
 Mucus 0-005 0-005 0.007 0-006 0-025 
 
 Water 88-589 98-196 91-201 98-007 92-897 
 
 100-000 100-000 100-000 100-000 99-863 
 Composition of the Ask of these Urines. 
 
 Horse. Swine. Ox. Goat. Sheep. 
 
 Carbonate of lime 12-50 ... 1-07 trace 0-82 
 
 Carbonate of magnesia 9-46 ... 6-93 7-3 0-46 
 
 Carbonate of potash... 46-09 12-10 77-28 trace 
 
 Carbonate of soda 10-33 53-0 42-25 
 
 Sulphate of potash ... 13-30 ... 2-98 
 
 Sulphate of soda 13-04 7-00 ... 25-0 7-72 
 
 Phosphate of soda 19-00 
 
 Phosphate of lime f 
 
 Phosphate of mag-[- ... 8-80 0-70 
 
 nesia ) 
 
 Carryforward 91-42 46-90 98-58 85-3 54-93 
 
168 AGRICULTURAL CHEMISTRY. 
 
 
 Horse. 
 
 Swine. 
 
 Ox. 
 
 Goat. 
 
 Sheep. 
 
 Brought forward 
 
 91-42 
 
 46-90 
 
 98-58 
 
 85.3 
 
 54.93 
 
 Chloride of sodram 
 
 6-94 
 
 53-10 
 
 0-30 
 
 14-7 
 
 32-01 
 
 Chloride of potassium 
 
 ... 
 
 trace 
 
 ... 
 
 ... 
 
 12-00 
 
 Silica 
 
 0-55 
 1-09 
 
 
 0-35 
 0-77 
 
 
 1-06 
 
 Oxide of iron and loss 
 
 
 100-00 100-00 100-00 100-00 100-00 
 
 Human urine has been accurately examined, by Berze- 
 lius, although his estimate of the proportion of urea is 
 generally admitted to be above the average. His analysis 
 gives the following numbers : — 
 
 Natural. Dry Residae. 
 
 Urea 3-010 44-70 
 
 Lactic acid, lactate of ammonia, 
 
 ■} 
 
 1-714 25-58 
 and extractive matter 
 
 Uric acid 0100 1-49 
 
 Mucus 0032 0-48 
 
 Sulphate of potash 0-371 5-64 
 
 Sulphate of soda 0-316 4-72 
 
 Phosphate of soda 0-294 4-39 
 
 Biphosphate of ammonia 0.165 2-46 
 
 Chloride of sodium 0-445 6-64 
 
 Muriate of ammonia 0-150 2-46 
 
 Phosphates of magnesia and lime .... 0-100 1-49 
 
 Silica 0-003 0-05 
 
 Water 93-300 
 
 100-000 100-00 
 
 Among the special organic constituents of the urine 
 are three substances, urea, uric acid, and hippuric acid, 
 which are of much importance in a manurial point of 
 view. The first of these is found in considerable quantity 
 in the urine of all animals, but is especially abundant in 
 the camivora. Uric acid is found only in these ani- 
 mals, and is the most remarkable constituent of the 
 
FAEM-TAED AND LIQUID MANDEES. 169 
 
 excrement of birds, serpents, and many of the lower 
 animals. Hippuric acid is most abundant in tbe her- 
 bivora. These substances are all highly nitrogenous. 
 They contain — 
 
 Urea, Uric Acid. Hippuric Acid. 
 
 Carbon 20-00 36-0 607 
 
 Hydrogen 6-60 2-4 5-0 
 
 Nitrogen 46-70 33-4 8-0 
 
 Oxygen 26-70 28-2 26-3 
 
 100-00 100-0 100-0 
 
 They are extremely prone to change, and in presence 
 of animal matters readily ferment, and are converted into 
 salts of ammonia. Thug human urine, which, at the time 
 of emission is free from smell of ammonia, and has a 
 slightly acid reaction, becomes highly ammoniacal if it be 
 kept for a few days. This is due to the conversion of 
 urea into carbonate of ammonia; and the same change 
 takes place, though more slowly, with uric and hippuric 
 acids. 
 
 It is obvious, from the foregoing analyses, that great 
 differences must exist in the manurial value of the urine 
 of different animals. Not only do they vary greatly in 
 the proportion of solid matters which they contain, but 
 also in the kind and quantity of their nitrogenous consti- 
 tuents. They differ also in regard to their saline ingre- 
 dients; and while salts of potash and soda form the 
 principal part of the ash of the urine' of the ox, sheep, 
 goat, and horse, and phosphoric acid and phosphates are 
 entirely absent, that of the pig contains a considerable 
 quantity of the latter substances, and in this respect more 
 nearly resembles the urine of man. Human urine is also 
 much richer in urea and nitrogenous constituents generally, 
 and has a higher value than any of the others. 
 
170 AGEICULTnKAL CHEMISTRY. 
 
 It is especially worthy of notice that the nrine of the 
 purely herbivorous animals (with the exception of the 
 sheep, which contains a small quantity), are devoid of 
 phosphates and nrea ; and consequently, when employed 
 alone, they are not general manures — a matter of some 
 importance in relation to the subject of liquid manuring, 
 which will be afterwards discussed. 
 
 Dung. — The solid excrement of animals is equally 
 variable in composition. That of the domestic animals 
 which had the ordinary winter food was found to have the 
 following composition : — 
 
 Horse. Cow. Sheep. Swine. 
 
 Per-centageofwaterinthel ^^.25 33.45 55.47 77.13 
 
 fresh excrement J 
 
 Ash in the dry excrement 13-36 15-23 13-49 37-17 
 
 100 parts of ash contained — 
 
 Horse. Cow. Sheep. Swine. 
 
 Silica 62-40 62-54 50-11 13-19 
 
 Potash 11-30 2-91 832 360 
 
 Soda 1.98 0-98 3-28 3-44 
 
 Chloride of sodium 0-03 0-23 0-14 0-89 
 
 Phosphate of iron , 2-73 8-93 398 10-55 
 
 Lime 463 5-71 1815 2-63 
 
 Magnesia 3-84 11-47 5-45 2-24 
 
 Phosphoric Acid 8-93 4-75 7-52 0-41 
 
 Sulphuric acid 1-83 1-77 2-69 0-90 
 
 Carbonic acid trace trace 0-60 
 
 Oxide of manganese •- 2-13 ... 
 
 Sand 61-37 
 
 99-80 99-29 99-64 99-82 
 
 Human foeces contain about 75 per cent of water ; 
 and their dry residue was found by Way to have the fol- 
 lowing composition : — 
 
FARM- YARD AND LIQUID MANURES. 171 
 
 Organic matter 88-52 
 
 Insoluble siliceous matters 1-48 
 
 Oxideofiron 0-54 
 
 Lime 1-72 
 
 Magnesia 1-55 
 
 Phosphoric acid 4-27 
 
 Sulphuric acid 0-24 
 
 Potash 1-19 
 
 Soda 0-31 
 
 Chloride of sodium 0-18 
 
 100-00 
 
 In a sample analyzed by myself there were found — 
 
 Organic matter 86-75 
 
 Phosphates 8-19 
 
 Alkaline salts, containing 1-18 of phos- ) „ r„ 
 
 phoric acid J 
 
 Insoluble matters 2-53 
 
 100-00 
 
 Nitrogen 4-59 
 
 Equal to ammonia 5-57 
 
 It is to be observed that the urine and dung of ani- 
 mals differ conspicuously in the composition of their ash, 
 the former being characterized by the abundance of alka- 
 line salts, while the latter contains these substances in 
 small proportion, but is rich in earthy matters, and espe- 
 cially in phosphoric acid. Salts of potash, for example, 
 form nine-tenths of the inorganic part of the urine of the 
 ox, while less than three per cent of that alkali is found 
 in its dung. Phosphoric acid, on the other band, is not 
 met with in the urine, but forms about ten per cent of the 
 dung. Silica is the most abundant constituent of the 
 
172 
 
 AGBICTJLTUEAI, CHEMISTRY. 
 
 dung, but a large proportion of that found on analysis has 
 been swallowed in the shape of grains of sand and particles 
 of soil mechanically mixed with the food, although part is 
 also derived from the straw and grains, which contain 
 that substance in great abundance. The difference in the 
 quantity of nitrogen they contain is also very marked, and 
 is distinctly shown by the following analyses by Boussin- 
 gault, which give the quantity of carbon, hydrogen, ni- 
 trogen, oxygen, and ash in the dung and urine of the 
 horse and the cow in their natural state, and after drying 
 at 212°. 
 
 Carbon 
 
 Hydrogen... 
 Nitrogen ... 
 Oxygen ... 
 
 Ash 
 
 Water 
 
 HOBSE. 
 
 Cow. 
 
 Natural. 
 
 Dry. 
 
 Natural. 
 
 Dry. 
 
 Urine. 
 
 Dnn?. 
 
 Urine. 
 
 Dung. 
 
 Urine. 
 
 Duug. 
 
 Urine. 
 
 Dung. 
 
 4-46 
 0-47 
 1-55 
 1-40 
 4-51 
 87-61 
 
 9-56 
 1-26 
 0-54 
 9-31 
 4-02 
 75-31 
 
 360 
 3-8 
 12-5 
 11-3 
 36-4 
 00 
 
 38-7 
 
 5-1 
 
 2-2 
 
 37-7 
 
 16-3 
 
 0-0 
 
 3-18 
 0-30 
 0-44 
 3-09 
 4-68 
 88-31 
 
 4-02 
 0-49 
 0-22 
 3-54 
 1-13 
 90-60 
 
 27-2 
 
 2-6 
 
 3-8 
 
 26-4 
 
 40-0 
 
 0-0 
 
 42-8 
 
 5-2 
 
 2-3 
 
 37-7 
 
 12-0 
 
 0-0 
 
 100-00 
 
 100-00 
 
 100-0 
 
 100-0 
 
 100-00 
 
 100-00 
 
 100-0 
 
 100-0 
 
 Hence, weight for weight, the urine of the horse, in 
 its natural state, contains three times as much nitrogen as 
 its dung ; that of the cow twice as much ; and the dif- 
 ference, especially in the horse, is still more conspicuous 
 when they are dry. 
 
 It is obvious that the quality of farm-yard manure 
 must depend — 1. On the kind of animal from which it is 
 produced ; 2. On the quantity of straw which has been 
 used as litter ; 3. On the nature of the food with which 
 the animals have been supplied ; 4. On the extent to 
 which its valuable constituents have been rendered avail- 
 
FARM- YARD AND LIQUID MANURES. 173 
 
 able by the treatment to which it has been subjected ; and 
 5. On the care which has been taken to prevent the 
 escape of the mine, or of the ammonia produced by its 
 decomposition. 
 
 The composition of farm-yard manure has engaged the 
 attention of several chemists ; but there are still many 
 points on which our information regarding it is less com- 
 plete than might be desired. Its investigation is sur- 
 rounded with peculiar difficulties, not merely on account 
 of its complexity, but because its properties render it 
 exceedingly difficult to obtain a sample which fairly repre- 
 sents its average composition. In the case of long dung, 
 these difficulties are so great that it is scarcely possible to 
 overcome them ; and hence, discrepancies are occasionally 
 to be met with in the analyses of the most careful experi- 
 menters. The most minute and careful analyses yet made 
 are those of Voelcker, who has compared the composition 
 of fresh and rotten dung, and studied the changes which 
 the former undergoes when preserved in different ways. 
 He employed in his experiments both fresh apd rotten 
 dung, and subjected them to different methods of treat- 
 ment. His analyses are given in the accompanying table, 
 in which column 1 gives the composition of fresh long 
 dung, composed of cow and pig dung. 2. Is dung of the 
 same kind, after having lain in a heap against a wall, but 
 otherwise unprotected from the weather for three months 
 and eleven days in winter, during which time little rain 
 fell, 3, The same manure, kept for the same time under 
 a shed. 4. Well rotten dung, which had been kept in 
 the manure heap upwards of six months. 5. The same, 
 after having lain against a wall for two months and nine 
 days longer. 
 
174 
 
 AGKICDLTURAL CHEmSTET. 
 
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PAEM-YAED AND LIQOTD MANURES. 
 
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176 AGEICDLTUEAL CHEMISTRY. 
 
 On examining and comparing these analyses, it appears 
 that the differences are by no means great, although, on 
 the whole, they tend to show that, weight for weight, 
 well-rotten dung is superior to fresh, provided it has been 
 properly treated. Not only is the quantity of valuable 
 matters existing in the soluble state materially increased, 
 whereby the dung is enabled to act with greater rapidity, 
 but, owing to evaporation and the escape of carbonic acid, 
 produced by the decomposition of the organic substances, 
 the proportion of those constituents which are most im- 
 portant to the plant is increased. This is particularly 
 to be noticed, in regard to the nitrogen, which has dis- 
 tinctly increased in all cases in which the dung has 
 been kept for some time ; and the practical importance 
 of this observation is very great, because it has been 
 commonly supposed that, during the process of fermen- 
 tation, ammonia is liable to escape into the air. It would 
 appear, however, that there is but little risk of loss in 
 this way, so long as the dung-heap is left undisturbed ; 
 and it is only when it is turned that any appreciable quan- 
 tity of ammonia volatilizes. It is different, however, with 
 the action of rain, which soon removes, by solution, a con- 
 siderable quantity of the nitrogen contained in farm-yard 
 manure ; and the deterioration must necessarily be most 
 conspicuous in rotten dung, which sometimes contains 
 nearly half of its nitrogen in a soluble condition. The 
 effect produced in this way is conspicuously seen, by the 
 results of weighings and analyses of small experimental 
 dung-heaps, made by Dr. Voelcker at different periods. 
 The subjoined table shows the composition of the heap, 
 lying against a wall, and exposed to the weather at dif- 
 ferent periods: — 
 
FARM- YARD AND LIQUID MANURES. 
 
 177 
 
 Weight of manure in lbs 
 
 Water 
 
 When Put up. 
 
 Nov. 3d 
 1854. 
 
 April 30th 
 1655. 
 
 Aug. 23d 
 1856. 
 
 Not. 16th 
 1855. 
 
 2838 
 
 2026 
 
 1994 
 
 1974 
 
 1877-9 
 960-1 
 
 1336-1 
 689-9 
 
 1505-3 
 
 488-7 
 
 1466-5 
 507-5 
 
 Dry matter 
 
 Coneisting of— 
 Soluble organic matter 
 
 70-38 
 
 43-71 
 
 731-07 
 
 114-94 
 
 86-51 
 
 57-88 
 
 389-74 
 
 156-77 
 
 58-83 
 
 39-16 
 
 243-22 
 
 147-49 
 
 64-04 
 
 36-89 
 
 214-92 
 
 201-67 
 
 „ mineral matter 
 
 Insoluble organic matter 
 
 „ mineral matter 
 
 Total nitrogen 
 
 18-23 
 22-14 
 
 18-14 
 22-02 
 
 13-14 
 15-96 
 
 13-03 
 15-75 
 
 £qual to ammonia 
 
 
 In this case, during the winter six months, -which were 
 very dry, the manure lost 541-8 lbs. of -water and 270-2 
 lbs. of dry matter, but the nitrogen remained completely 
 unchanged. But during the succeeding semi-annual 
 period, -when rain fell abundantly, the quantity of nitrogen 
 is diminished by nearly a third, -while the water has in- 
 creased, and the loss of dry matter by fermentation, not- 
 -withstanding the high temperature of the summer months, 
 was only 182-4 lbs. The soluble mineral matters also, 
 which increased during the first period, are again reduced 
 during the second, until they also fall to about two-thirds 
 of their maximum quantity. That this effect is to be 
 attributed to the solvent action of rain is sufficiently 
 obvious, from a comparison of the results afforded by the 
 other heaps, which had been kept under^ cover during 
 the same period, as shown below. 
 
178 
 
 AGKICULTUEAL CHEMISTRY. 
 
 Weight of manure in lbs 
 
 Water 
 
 When Put dp. 
 
 Not. 3d, 
 1854. 
 
 April 30th 
 1855. 
 
 Ang. 23d 
 1855. 
 
 Not. 15th 
 1866. 
 
 3258 
 
 1613 
 
 1297 
 
 1235 
 
 2156-0 
 1102-0 
 
 917-6 
 695-4 
 
 563-2 
 733-8 
 
 514-5 
 720-5 
 
 
 Consisting of — 
 Soluble organic matter 
 
 „ mineral matter 
 
 Insoluble organic matter 
 
 „ mineral matter 
 
 80-77 
 60 14 
 
 839-17. 
 
 131-92 
 
 74-68 
 
 54-51 
 
 410-24 
 
 155-97 
 
 53-56 
 
 39-55 
 
 337-32 
 
 303-37 
 
 66-28 
 
 54-68 
 
 341-97 
 
 257-57 
 
 20-93 
 25-40 
 
 19-26 
 23-33 
 
 16-54 
 20-08 
 
 1-79 
 2-81 
 
 
 
 The loss of nitrogen is here comparatively trifling, and 
 during the -whole year, but little exceeds two pounds, of 
 which the gi'eater part escapes during the first six months, 
 and the soluble inorganic matters are almost unchanged. 
 The total weight of the manure, however, undergoes a very 
 great reduction, due chiefly to evaporation of water, but 
 in part also to the loss of organic matters evolved in the 
 form of carbonic acid during fermentation. 
 
 When the manure is spread out, as it is usually found 
 under cattle in open yards, the deterioration is very great, 
 a quantity thus treated ha-ving lost, in the course of a 
 year, nearly two-thirds of its nitrogen, and four-fifths of its 
 soluble inorganic matters. 
 
 The general conclusion deducible from these analyses 
 is that, pro-vided it be carefully prepared, farm-yard manure 
 does not diSier very largely in value, although the balance 
 is in favour of the well-rotten dung. This result is 
 in accordance with that obtained by other experimenters, 
 who have generally found from 0'5 to 0'6 per cent of 
 
FARM-YARD AND LIQUID MANURES. 17ft 
 
 nitrogen, and 1 or 2 per cent of phosphates. But when 
 carelessly managed, it may fall greatly short of this stan- 
 dard, as is particularly seen in a sample examined by 
 Cameron, which had been so effectually washed out by 
 the rain, as to retain only 0'15 per cent of ammonia. 
 These cases, however, are exceptional, and well made and 
 well preserved farm-yard manure will generally be found to 
 differ comparatively little in value ; and when bought at 
 the ordinary price, the purchaser, as we shall afterwards 
 more particularly see, is pretty sure to get full value for 
 his money, and the specialities of its management are of 
 comparatively little moment to him. But the case is very 
 different when the person who uses the manure has also to 
 manufacture it. The experiments already quoted have 
 shown that, though the manure made in the ordinary 
 manner may, weight for weight, be as valuable as at first, 
 the loss during the period of its preservation is usually very 
 large, and it becomes extremely important to determine 
 the mode in which it may be reduced to the minimum. 
 
 In the production of farm-yard manure of the highest 
 quality, the object to be held in view is to retain, as effec- 
 tually as possible, all the valuable constituents of the dung 
 and urine. But in considering the question here, it will be 
 sufficient to refer exclusively to its nitrogen, both because 
 it is the most important, and also because the circum- 
 stances which favour its preservation are most advanta- 
 geous to the other constituents. In the management of 
 the dung-heap, there are three things to be kept in view : — 
 First, To obtain a manure containing the largest possible 
 amount of nitrogen ; secondly. To convert that nitrogen 
 more or less completely into ammonia ; and thirdly, To 
 retain it effectually. 
 
 As far as the first of these points is concerned, it must 
 
180 AGEICULTCEAL CHEMISTEY. 
 
 be obvious that much will depend on the nature and 
 quantity of the food with which the animals yielding the 
 dung are supplied, and the period of the fattening process 
 at which it is collected. When lean beasts are put up 
 to feed, they at first exhaust the food much more com- 
 pletely than they do when they are nearly fattened, and 
 the manure produced is very inferior at first, and goes on 
 gradually improving in quality as the animal becomes fat. 
 
 When the food is rich in nitrogenous compounds, the 
 value of the manure is considerably increased. It has 
 been ascertained, for instance, that when oU-cake has been 
 used, not less than seven-eighths of the valuable matters 
 contained in it reappear in the excrements ; and as that 
 substance is highly nitrogenoQS, the dung ought, weight 
 for weight, to contain a larger amount of that element. 
 That it actually does so, I satisfied myself by experiments, 
 made some years since, when the dung and urine of animals 
 fed on turnips, with and without oil-cake, were examined ; 
 but unfortunately, no determination of the total quantity 
 of the excretions could be made, so that it was impossible 
 to estimate the increased value. It has been commonly 
 supposed that when cattle are fed with oil-cake, the 
 increased value of the manure is equal to from one-half to 
 two-thirds the price of the oil-cake ; but this is a rather 
 exaggerated estimate as regards linseed-cake, although it 
 falls short of the truth in the case of rape, as we shall 
 afterwards more particularly see. 
 
 Although it may be possible, in this way, to increase 
 the quantity of nitrogen as a manure, there is a limit to its 
 accumulation, due to the fact, that it is contained most 
 abundantly in the urine, which can only be retained by the 
 use of a sufficient supply of litter. Where that is deficient, 
 the dung-heap becomes too moist, and the fluid and most 
 
FARM-YAUD AND LIQUID MANURES. 181 
 
 valuable part drains off, either to be lost, or to be collected 
 in the liquid manure-tank. In the well managed manure- 
 heap, the quantity of litter should be sufficient to retain 
 the greater part of the liquid manure, and to admit of 
 only a small quantity draining from it, which should be 
 pumped up at intervals, so as to keep the whole in a proper 
 state of moisture. Attention to this point is of great 
 moment, and materially affects the fermentation. When 
 it is too moist or too dry, that process is equally checked ; 
 in the former case by the exclusion of air, which is essen- 
 tial to it ; and in the latter, by the want of water, without 
 which the air cannot act. The exact mode in which 
 the manure is to be managed must greatly depend on 
 whether the supply of litter is large or small. In the latter 
 case the urine escapes, and is collected in the liquid 
 manure-tank, and must be used by irrigation, and in some 
 cases this mode of application has advantages, but in 
 general, it is preferable to avoid it, and have recourse to 
 substances which increase the bulk of the heap sufficiently 
 to make it retain the whole of the liquid. For this pur- 
 pose, clay, or still better, the vegetable refuse of the farm, 
 such as weeds, ditch cleanings, leaves, and, in short, any 
 porous matters, may be used. But by far the best sub- 
 stance, when it can be obtained, is dry peat, which not 
 only absorbs the fluid, but fixes the ammonia, by convert- 
 ing it more or less completely into humate. Reference 
 has been already made to the absorbent power of peat in 
 the section on soils, but it may be mentioned here that 
 accurate experiment has shown that a good peat will 
 absorb about 2 per cent* of ammonia, and when dry will 
 still retain from 1 to 1"5 per cent, or nearly twice as 
 
 * Report on the economic uses of peat. Highland Society's Trans- 
 actions, N.S., vol. iv. p. 549. 
 
183 AGRICULTURAL CHEMISTRY. 
 
 much as would be yielded by the whole nitrogen of an 
 equal weight of farm-yard manure. Peat charcoal has 
 been recommended for the same purpose, but careful ex- 
 periment has shown that it does not absorb aramonia, 
 although it removes putrid odour ; and though it may be 
 usefully employed when it is wished to deodorize the manure 
 heap, it must not be trusted to for fixing the ammonia. 
 
 Much stress has frequently been laid on the advantage 
 to be derived from the use of substances capable of com- 
 bining chemically with the ammonia produced during the 
 fermentation of dung and gypsum, sulphate of iron, chloride 
 of manganese, sulphate of magnesia, and sulphuric acid, 
 have been proposed for this purpose, and have been used 
 occasionally, though not extensively. They all answer 
 the purpose of fixing the ammonia, that is, of preventing 
 its escaping into the air ; but the risk of loss in this way 
 appears to have been much exaggerated, for a delicate test- 
 paper, held over a manure-heap, is not affected ; and 
 during fermentation, humic acid is produced in such abun-' 
 dance, as to combine with the greater part of the ammonia. 
 The real source of deterioration is the escape of the soluble 
 matters in the drainings from the manure-heap, which is 
 not prevented by any of these substances ; and where 
 no means are taken to preserve or retain this portion, 
 the loss is extremely large, and amounts, under ordinary 
 circumstances, to from a third to a half of the whole 
 value of the manure. Manure, therefore, cannot be 
 exposed to the weather without losing a proportion of 
 its valuable matters, depending upon the quantity of rain 
 which falls upon it. Hence it is obvious that great advan- 
 tage must be derived, especially in rainy districts, from 
 covered manure-pits. This plan has been introduced on 
 some farms with good effect ; but the expense and doubts 
 
FARM- YARD AND LIQUID MANUEES. 183 
 
 as to the benefits derived from it, have hitherto prevented 
 the practice becoming general. The principal difficulty 
 experienced in the use of the covered dung-pit is, that, 
 where the litter is abundant, the urine does not supply a 
 sufficiency of moisture to promote the active fermentation 
 of the dung, and it becomes necessary to pump water over 
 it at intervals ; but when this is properly done, the quality 
 of the manure is excellent, and its valuable matters are 
 most thoroughly economized. 
 
 Although covered dung-pits have been but little 
 used, their benefits have been indirectly obtained by the 
 method of box-feeding, one of the great advantages of 
 which is held to be the production of a manure of superior 
 quality to that obtained in the old way. In box-feeding 
 none of the dung or urine is removed from under the 
 animals, but is trampled down by their feet, and new 
 quantities of litter being constantly added, the whole is 
 consolidated into a compact mass, by which the urine is 
 entirely retained. Whatever objection may be taken to 
 this system, so far as the health of the animals is con- 
 cerned, there is no doubt as to the complete economy of the 
 manure, provided the quantity of litter used be sufficient to 
 retain the whole of the liquid. But its advantage is entirely 
 dependent on the possibility of fulfilling this condition. 
 
 Whether box manure is really superior to that which 
 can be prepared by the ordinary method is very question- 
 able, but it undoubtedly surpasses a large proportion of 
 that actually produced. It is more than probable, how- 
 ever, that the careful management of the manure-heap 
 would yield an equally good product. It is manifest that 
 the same number of cattle, fed in the same way, on the 
 same food, and supplied with the same quantity of litter, 
 must always excrete the same quantities of valuable mat- 
 
184 AGKICtTLTUEAL CHEMISTET. 
 
 ters ; and the only question to be solved is, whether thej" 
 are more effectually preserved in the one way than the 
 other ? It will be readily seen that this cannot be done 
 by analysis alone, but that it is necessary to conjoin with 
 it a determination of the total weight of manure produced ; 
 for though, weight for weight, box manure may be better 
 than ordinary farm-yard manure, the total quantity obtained 
 by the latter method, from a given number of cattle, may 
 be BO much greater, that the deficiency in quality may be 
 compensated for. At the present time our knowledge is 
 too limited to admit of a definite opinion od this subject, 
 but it is highly deserving of the combined investigation of 
 the fanner and the chemist. 
 
 Supposing the conditions which produce the manure 
 containing the largest quantity of nitrogen to have been 
 fulfilled, we have now to consider those which affect its 
 evolution in the form of ammonia. This change is effected 
 hj fermentation. When a quantity of manure is left to 
 itself it becomes hot, and gradually diminishes in bulk, 
 and if it be turned over after some time, the smell of 
 ammonia may be more or less distinctly observed. This 
 ammonia is produced, in the first instance, from the 
 urine, the nitrogenous constituents of which are rapidly 
 decomposed, and the fermentation thus set up in the mass 
 of manure extends first to the solid dung, and then to the 
 straw of the litter, and gradually proceeds until a large 
 quantity of ammonia is produced. 
 
 When fresh manure is deposited in the soil, the same 
 changes occur, but they then proceed more slowly, 
 and experience has shown that a much smaller effect is 
 produced on the crop to which it has been applied than 
 when it has been well fermented in the heap. This effect 
 is consistent with theory, which would further indicate 
 
FARM- YARD AND LIQUID MANURES. 185 
 
 that well-fermented dung must be especially advantageous 
 when applied to quick-growing crops, and less necessary 
 to those which come slowly to maturity. As a rule, well 
 fermented manure is to be preferred, provided it has been 
 well managed and carefully prepared ; but when this has 
 not been done, and the manure has been exposed to the 
 weather, or made in open courts or hammels, the econo- 
 mic advantages are all on the side of the fresh dung. It 
 may be questioned also whether, now that there are so 
 many other available sources of ammonia, it may not in 
 many instances be advantageous to use the dang fresh, 
 conjoined with a sufScient quantity of some salt of am- 
 monia, or other substance fitted to supply the quantity of 
 that element necessary for the requirements of the crop. 
 
 After the farm-yard manure has been prepared at the 
 homestead, it is often necessary to cart it out to the field 
 some time before it is to be applied, and it is a question 
 of some importance to determine how it may be best pre- 
 served there. The general practice is to store it in heaps 
 in the corners of the fields, but some difference of opinion 
 exists as to whether it should be lightly thrown up so as 
 to leave it in a porous state, and so promote its further fer- 
 mentation, or whether it should be consolidated as much 
 as possible by driving the carts on to the top of the heap 
 during its construction. Considering the risks to which 
 the manure is exposed on the field, the latter plan would 
 appear to be the best. It is advisable also to interstratify 
 the dung with dry soil, so as to absorb any liquid which 
 may tend to escape from it, and it should also be covered 
 with a well-beaten layer of earth, in order to exclude the 
 rain. Although these precautions must not be omitted if 
 the manure is to be stored in heaps, it will probably be 
 often found quite as advantageous to spread it at once, 
 
186 AGElCULTtlKAL CHEMISTRY. 
 
 and leave it lying on the surface nntil it is convenient to 
 plough it. The loss of ammonia by volatilization will, 
 under such circumstances, especially in the cold season of 
 the year, be very trifling, and the rain which falls will 
 only serve to incorporate the soluble matters with the soil, 
 where they will be retained by its absorptive power. 
 
 In the actual application of the manure to the crop, 
 several points require consideration. It is especially im- 
 portant to determine whether it ought to be uniformly dis- 
 tributed through the soil, or be kept near the roots of the 
 plants. Both systems have their advocates, and each has 
 advantages in particular cases. The choice between the 
 two must greatly depend upon the nature of the crop and 
 the soil. When the former is of a kind which spreads its 
 roots wide and deep through the soil, the more uniformly 
 the manure can be distributed the better ; but when it is 
 used with plants whose roots do not travel far, it is more 
 advantageous to accumulate it near the seeds. Obvious 
 advantages also attend this practice in soils which are 
 either too heavy or too light. When, for example, it is 
 necessary to cultivate turnips in a heavy clay, the manure 
 put into the drills produces a kind of artificial soil in 
 the neighbourhood of the plants, in which the bulbs ex- 
 pand more readily than in the clay itself. On the other 
 hand, when a large quantity of dung, in a state of active 
 fermentation, comes into immediate contact with the roots, 
 its efiect is not unfrequently injurious. These and many 
 other points, which will readily suggest themselves to any 
 one who studies the composition and properties of farm- 
 yard manure, belong more strictly to the subject of prac- 
 tical agriculture, and need not be enlarged on here. 
 
 In the present state of agriculture, a proper estimate of 
 the money value of farm-yard manure is of much import- 
 
FARM-YAKD AND LIQUID MANtTKES. 187 
 
 ance in an economic point of view, and many matters 
 connected with the profitable management of a farm must 
 hinge upon it. If an estimate be made upon the prin- 
 ciple which will be explained when we come to treat of 
 artificial manures, it appears that fresh farm-yard manure 
 of good quality is worth from 12s. to 15s. per ton, and 
 well-rotted dung rather more. It is questionable, how- 
 ever, whether the system of valuation which is accu- 
 rate in the case of a guano or other rapidly acting sub- 
 stance, is applicable to farm-yard manure, the effects of 
 which extend over some years. A deduction must be 
 made for the years during which the manure remains un- 
 productive, and also for the additional expense incurred in 
 carting and distributing a substance so much more bulky 
 than the so-called portable manures, and it would not be 
 safe to estimate its value at more than 7s. or 8s. per ton. 
 
 Liquid Manure. — This term is applied to the urine of 
 the animals fed on the farm, and to the drainings from the 
 manure-heap, which, in place of being returned to it, are 
 allowed to flow away, and collected in tanks, from which 
 they are distributed by a watering-cart, or according to 
 the method recently introduced in Ayrshire, and since 
 adopted in other places, by pipes laid under-ground in the 
 fields, and through which the manure is either pumped by 
 steam-power, or, where the necessary inclination can be 
 obtained, is distributed by gravitation. That liquid manure 
 must necessarily be valuable, is an inference which may be 
 at once drawn from the analyses of the urine of different 
 animals already given, and of which it chiefly consists. In 
 addition to the urine, however, it contains also the soluble 
 organic and mineral matters of the dung, as well as a 
 quantity of solid matters in suspension, amiong which 
 phosphates are found, and thus it possesses a supply of an 
 
188 AGEICULT0EAL CHEMISTKY. 
 
 element which would be almost entirely deficient if it were 
 composed of nrine alone. In the following analyses by 
 Professor Johnston, No. 1 is the drainings of the manure- 
 heap when exposed to rain ; and No. 2 the same, when 
 moistened with cows' urine pumped over it, the results 
 being expressed in grains per gallon : — 
 
 No. 1. No. 3. 
 
 Ammonia 9'6 21'5 
 
 Organic matter 200-8 77-6 
 
 Ash 268-8 518-4 
 
 Total solids in a gallon 479-2 617-5 
 
 The ash contained — 
 
 Alkaline salts 207-8 420-4 
 
 Phosphates 25-1 44-5 
 
 Carbonate of lime 18-2 31-1 
 
 Carbonate of magnesia, and loss 4-3 3-4 
 
 Silica and almnina 134 19-0 
 
 268-8 618-4 
 
 More elaborate analyses of the same fluid have since 
 
 been made by Dr. Voelcker, with the subjoined results per 
 gallon : — 
 
 1. 2. 3. 
 
 Organic matters and ammo- 1 263-80 250-63 70-121 
 
 niacal salts 3 
 
 Silica 2-49 9-98 1-154 
 
 Oxide of iron 0-70 0-68 
 
 Lime 5-34 25-18 13-011 
 
 Magnesia 2-96 15-33 1-660 
 
 Potash 103-23 112-26 13-411 
 
 Chloride of potassium 72-00 77-38 7-712 
 
 Chloride of sodinm 17-18 46-03 17-258 
 
 Phosphoric acid 2-70 9-51 2-304 
 
 Sulphuric acid 22-31 37-60 3-408 
 
 Carbonic acid, and loss 33-90 27-95 14-025 
 
 Total sohds 526-61 612-53 144-064 
 
 Atomonia 114-16 22-31 26-647 
 
FARM- YARD AND LIQUID MANURES. 189 
 
 The differences are here very remarkable, especially in 
 the quantity of ammonia, which is exceedingly large in 
 the first sample. All of them are particularly rich in 
 potash, and contain but a small proportion of phosphoric 
 acid. The general inference to be deduced from them is, 
 that liquid manure is a most important source of the 
 alkalis and ammonia, and must be peculiarly valuable on 
 soils in -which these substances are deficient. 
 
 The system of liquid manuring, originally introduced 
 by Mr. Kennedy of Myremill, Ayrshire, and which has 
 since been adopted in some other places, differs from liquid 
 manuring in its strict sense, for not only are the drainings 
 of the manure-heap employed, but the whole solid excre- 
 ments are mixed with water in a tank, and rape-dust 
 and other substances occasionally added, and distributed 
 through the pipes. 
 
 It has been abandoned on Mr. Kennedy's farm, but is 
 in use at Tiptree Hall, and on the farm of Mr. Balston, 
 Lagg, where the fluid is distributed by gravitation. 
 
 The arrangements employed by Mr. Mechi are iden- 
 tical with those formerly in use at Myremill. The greater 
 part of the stock is kept on boards, and the liquid and solid 
 excrements are collected together in the tank, and largely 
 diluted before distribution. The liquid from the tanks has 
 been recently examined by Dr. Voelcker, who found it to 
 contain per gallon — 
 
 Organic matter and ammoniacal salts 53'03 
 
 Soluble silica 6-47 
 
 Insoluble siliceous matter (clay) 15'17 
 
 Oxide of iron and alumina 2'36 
 
 Lime 6-60 
 
 Magnesia 1"73 
 
 Carry forward 85*36 
 
190 AGEICULTUEAL CHEMISTRY. 
 
 Brought forward 85-36 
 
 Potash 0-35 
 
 Chloride of potassium 1-95 
 
 Chloride of sodium 4'81 
 
 Phosphoric acid 3'72 
 
 Sulphuric acid 1-94 
 
 Carbonic acid, and loss 0-47 
 
 Total solids 96-60 
 
 Ammonia 8-10 
 
 The quantity of this liquid distributed per acre is about 
 50,000 gallons, at a cost of 2d. per gallon. As this quan- 
 tity contains about 39 lbs. of ammonia, it must be nearly 
 equivalent to 2 cwt. of Peruvian guano, which costs, with 
 the expense of spreading, from 28s. to 30s. per acre, while 
 the cost of distributing the liquid exceeds £1 : 17s. per 
 acre. On the other hand, the rapidity with which liquid 
 manure produces its effect must be taken into account. It 
 is on this that its chief value depends, and especially when 
 applied to grass land in early spring, it produces an abun- 
 dant crop just when turnips and other winter food are 
 exhausted. Mr. Telfer, Cunning Park, who has used 
 this system for a good many years, has come to the con- 
 elusion that it is only in this way that it can be made 
 profitable ; and though pipes are laid all over his farm, he 
 has latterly restricted the use of the liquid manure entirely 
 to Italian rye-grass. Its effect on the cereals is much less 
 marked, and it can scarcely be considered as capable of 
 advantageous application to the general operations of the 
 farm. Neither can liquid manure be applied to all soils. 
 It fails entirely on heavy clays, but is peculiarly adapted 
 to light sandy soils ; and even barren sand may by its 
 repeated application, be made to yield luxuriant crops. 
 It is not likely that the system of liquid manuring will 
 
FAHM-YARD AND LIQUID MANUBES. 191 
 
 extend, except in localities where it is possible to distri- 
 bute it by gravitation ; and even then, it will probably be 
 found most economical to restrict its use to one portion of 
 the farm ; and for that purpose, the poorest and most 
 sandy soil ought to be selected. 
 
 Sewage Manure. — The use of the sewage of towns as 
 a manure is closely connected with that of the liquid 
 manure produced on the farm. Its application must take 
 place in a similar manner, and be governed by the same 
 principles. Although numerous attempts have been made 
 to convert it into a solid form, or to precipitate its valu- 
 able matter, none of them have succeeded ; nor can it be 
 expected that any plan can be devised for the purpose, 
 because the most important manurial constituents are 
 chiefly soluble, and cannot be converted into an insoluble 
 state, or precipitated from their solution. In its liquid form, 
 however, sewage manure has been employed with the best 
 possible effect in the cultivation of meadows. The most 
 important instance of its application is in the neighbour- 
 hood of Edinburgh, where 325 acres receive the sewage 
 of nearly half the town, and have been converted from 
 barren sand into land which yields from £20 to £30 per 
 acre. The contents of the sewer, taken just before it 
 flows into the first irrigated meadow, near Lochend, were 
 found to contain per gallon — 
 
 Soluble organic matter 21'90 
 
 Insoluble organic matter 21'70 
 
 Peroxide of iron and alumina 2'01 
 
 Lime 10-50 
 
 Magnesia 2-00 
 
 Sulphuric acid 6'09 
 
 Phosphoric acid 6."14 
 
 Carry forward 70.34 
 
192 AGRICtrLTUEAL CHEMISTRY. 
 
 Brought forward 70-34 
 
 Chlorine 12-20 
 
 Potash 2-89 
 
 Soda 13-27 
 
 Silica 6-50 
 
 105-20 
 Ammonia 14'90 
 
 It is interesting to notice that this sewage is superior 
 in every respect to the liquid manure used at Tiptree 
 Hall ; and the good effects obtained from its application, 
 in the large quantities in which it is used in the Craigen- 
 tinny meadows, may be well imagined. It operates, not 
 merely by the substances which it holds in solution, but 
 also by depositing a large quantity of matters carried 
 along in suspension, and is in reality warping with a sub- 
 stance greatly superior to river-mud. A deposit collected 
 in a tank, where the sewage passes through a farm, is 
 used as a manure, and contains — 
 
 Peroxide of iron and alumina 4-45 
 
 Lime 1-74 
 
 Magnesia 0-39 
 
 Potash 010 
 
 Soda 0-06 
 
 Phosphoric acid 1-08 
 
 Sulphuric acid 0-16 
 
 Organic matter 17-95 
 
 Sand 20-51 
 
 "Water 5356 
 
 100-00 
 Ammonia 0-93 
 
 And even, though containing more than half its weight of 
 
FAKM-YARD AND LIQUID MANDBES. 193 
 
 water and 20 per cent of sand, this substance has con- 
 siderable value as a manure. 
 
 The growing evils of the existing system of sewage, 
 and the enormous waste of a manurial matter, which the 
 experience of the Craigentinny meadows has shewn to be 
 productive of the most important effects, has recently 
 directed much attention to the conversion of the contents 
 of our sewers into a useful manure. Numerous plans for 
 its precipitation and conversion into a solid manure have 
 been proposed, but most of these have shewn an entire 
 ignorance of the fundamental principles of chemistry, and 
 the best only succeed in precipitating a very small propor- 
 tion of its valuable matters, and leave almost the whole of 
 the ammonia, as well as the greater part of the fixed alka- 
 lies, in solution. Nor is it to be expected that any process 
 will be discovered by which these substances can be precipi- 
 tated, because solubility is the special characteristic of their 
 compounds, and no means is known by which it is possible 
 to convert them into an insoluble form. If sewage is to be 
 used at all, there seems little doubt that it must be by apply- 
 ing it entire, and in the liquid state. But here again, the 
 expense of conveying it on to the land becomes an obstacle 
 ■which it must frequently be impossible to overcome. 
 When it can be conveyed by gravitation, as is the case 
 in the neighbourhood of Edinburgh, it may undoubtedly 
 be used with the utmost advantage, and with the very 
 best economic results. But when it requires to be carried 
 to a great distance through pipes, and raised to a high 
 level by pumping, all these advantages disappear. If the 
 cost of application amounts to 2d. a gallon, as in Mr. 
 Mechi's case, or even to half that sum, it may be fairly 
 concluded that it cannot be used with any great prospect 
 of large economic results, and that, unless under very 
 exceptional cases, it must be unprofitable. 
 
194 AGEICULTUKAL CHEMISTEY. 
 
 The chances of success must also greatly depend upon 
 the kind of soil on which it is used. Experience has 
 shewn that its effects are most beneficial on light and 
 deep sandy soils, but that on heavy retentive clays it is 
 without effect, or even absolutely injurious. In clay soils 
 it is important to use every means of getting rid of mois- 
 ture, and any plan which adds 200 or 300 tons of water 
 to them, only aggravates their natural defects to an extent 
 which more than counterbalances the benefits derived from 
 the manurial matter it contains. "Whatever the ultimate 
 result of the use of town sewage in the liquid form may 
 be, it is unlikely that it will be employed in general agri- 
 cultural practice. It is more probable that it will be 
 found necessary to set apart a certain breadth of land to 
 be treated by it exclusively. Many plans have been pro- 
 posed for conveying it through considerable districts, and 
 selling to the surrounding farmers the quantities which 
 they require, but wherever large sewage-works are estab- 
 lished, it will be impossible to depend on a precarious 
 demand, and the promoters of such schemes will be com- 
 pelled, as part of their speculation, to supply not only the 
 manure, but the land on which it is to be used. Indeed, 
 the difficulties attending the whole question are so formid- 
 able, that even those who are most anxious to see a stop 
 put to the waste of manurial matter must admit that the 
 prospect of a successful economic result is not encouraging. 
 Nor is it likely that anything will be done until the whole 
 system of managing town refuse is changed, and in place 
 of deluging it with water, some plan can be contrived 
 which, while fulfilling sanatory requirements, shall pre- 
 serve it in a concentrated fonn, or convert it into a dry and 
 inodorous substance. 
 
CHAPTER IX. 
 
 COMPOSITION AND PROPBETIES OP VEGETABLE MANURES. 
 
 Many vegetable substances have been employed as man- 
 ures, either alone or as auxiliaries to farm-yard manure. 
 Like that substance, they are general manures, and contain 
 all the constituents of ordinary crops ; but, owing to the 
 absence of animal matter, they in general imdergo decom- 
 positi(m and fermentation much more slowly, although 
 some of them contain a so largely preponderating propor- 
 tion of nitrogen, that they may in some respects be com- 
 pared to the strictly nitrogenous manures. 
 
 Mape-dust, Mustard, Cotton and Castor Cake, — Eape- 
 dust has long been employed as a manure, and the suc- 
 cess which has attended its use has led to the introduction 
 of the refuse cake from some other oil seeds, such as 
 those of mustard and castor-oil, which cannot be em- 
 ployed for feeding. Like the seeds of all plants, these 
 substances are rich in nitrogen, and their ash, containing 
 of course all the constituents of the plant, supplies the 
 necessary inorganic elements. The following are analyses' 
 of these substances, which, in addition to the amount of 
 nitrogen and phosphates, shew also that of water and 
 oil, to which reference will be made in a future chapter, 
 in relation to the feeding value of some of them. The 
 detailed composition of their ash may be judged of from 
 
196 
 
 AGRICULTOEAL CHEMISTKY. 
 
 that of the seeds from which they are made, and which 
 have been given under that head. 
 
 Water . 
 
 Rape-Cake. 
 
 Poppy-Cake. 
 
 Cotton-seed 
 Cake. 
 
 Castor-Cake. 
 
 10-68 
 
 11-63 
 
 11-19 
 
 12-31 
 
 Oil . . 
 
 11-10 
 
 5-95 
 
 9-08 
 
 24-32 
 
 Albuminous com- ) 
 pounds . . j 
 
 29-53 
 
 31-16 
 
 25-16 
 
 21-91 
 
 Ash 
 
 7-79 
 
 12-98 
 
 5-64 
 
 6-08 ' 
 
 Other constituents 
 
 40-90 
 
 38-18 
 
 48-93 
 
 35-38 1 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 j 
 
 Nitrogen 
 
 4-38 
 
 4-94 
 
 3-95 
 
 3-20 ; 
 
 Silica . . . 
 
 1-18 
 
 3-36 
 
 1-32 
 
 1-96 
 
 Phosphates . . 
 
 3-87 
 
 69-3 
 
 2-19 
 
 2-81 ' 
 
 Phosphoric acid l 
 
 
 
 
 
 in combination >- 
 
 0-39 
 
 3-27 
 
 015 
 
 0-64 
 
 with alkalies ) 
 
 
 
 
 1 
 
 A general similarity may be observed in the composi- 
 tion of all these substances ; they are rich in nitrogen, 
 and contain as much of that element as is found in six 
 or seven times their weight of farm-yard manure, and a 
 somewhat similar proportion exists in the amount of phos- 
 phates, and probably of their other constituents. They 
 have all been employed with success, but the most ac- 
 curate observations have been made with rape-dust, which 
 has been longer and more extensively used than any of 
 the others. It has been employed alone for turnips, or 
 mixed with farm-yard manure, and also as a top-dressing 
 to cereals. But the most marked advantage is derived 
 from it when applied in the latter way on land which has 
 been much exhausted, and its efifects are then very strik- 
 ing. An adequate supply of moisture is essential to the 
 production of its full effects, and hence it often proves a 
 
COMPOSITION OP VEGETABLE MANURES. 197 
 
 failure in very dry seasons, and on dry soils. It must not 
 be applied in too great abundance, experience having 
 shewn that after a certain point has been reached, an in- 
 crease in the quantity produces no benefit, and even some- 
 times positively diminishes the crop. The other substances 
 of the same class, in all probability, act in the same 
 way, but as their introduction is recent, and their use 
 limited, less is known regarding their effects. 
 
 Malt- Dust, Bran, Chaff, etc. — The value of these sub- 
 stances as manures is chiefly dependent on the nitrogen 
 they contain, though to some extent also on their inor- 
 ganic constituents. Malt-dust contains about 4*5 per 
 cent, and bran 3 "2 per cent of nitrogen. But they are' 
 little used as manures, as they can generally be more 
 advantageously employed for feeding. The value of chaff 
 more nearly resembles that of straw. 
 
 Straw is occasionally employed as a manure, and 
 sometimes even as a top-dressing for grass land. It is 
 generally admitted, however, that its application in the 
 dry State, and especially as a top-dressing, is a practice 
 not to be recommended, as it decomposes too slowly in the 
 soil ; and it is always desirable to ferment it in the 
 manure heap, so as to facilitate the production of ammonia 
 from its nitrogen. Still circumstances may occur in which 
 it becomes necessary to employ it in the dry state, and it 
 will generally prove most valuable on heavy soils, which 
 it serves to keep open, and so promotes the access of air, 
 and enables it to act on the soil. On light sandy soils it 
 generally proves less advantageous, as its tendency of 
 course is to increase the openness of the soil, and render 
 it less able to retain the essential constituents of the 
 plant. 
 
 The quantity of nitrogen in straw does not exceed 0'2 
 
198 AGRICOLTURAL CHEMISTRY. 
 
 per cent, and its value is mainly due to its inorgsipic 
 constituents and to its mechanical effect on the soil. 
 
 Saw-dust has little value as a manure, as it undergoes 
 decomposition with extreme slowness. It is a good me- 
 chanical addition to heavy soils, and diminishes their 
 tenacity ; and though its manurial effects are small, it 
 sooner or later undergoes decomposition, and yields what 
 valuable matters it contains. The saw-dust of hard wood 
 is to be preferred, both because it contains more valuable 
 matters than that of soft wood, and because the absence 
 of resinous matters permits its more rapid decomposition. 
 It is a useftd absorbent of liquid manure, and may be 
 advantageously added to the dung-heap for that pur- 
 pose. 
 
 Manuring with Fresh Vegetable Mattel Green 
 
 Manuring. — The term green manuring is applied to the 
 system of sowing some rapidly growing plant, and plough- 
 ing it in when it has attained a certain size, and the 
 success attending it, especially on boUs poor in organic 
 matters, is very marked. It is obvious that this mode of 
 manuring can add nothing to the mineral matters contained 
 in the soil, and its utility must therefore be due to the 
 plant gathering organic matters from the air, which, by 
 their decomposition, yield nitrogen and carbonic acid — 
 the former to be directly made use of by subsequent crops, 
 the lattet, in all probability, acting also on the soil, and 
 setting free its useful constituents. Hence those plants 
 which obtain the largest quantity of their organic elements 
 from the air ought to be most advantageous for green 
 manuring. The plants used for this purpose act also as a 
 means of bringing up from the lower parts of the soil the 
 valuable matters which exist in it out of reach of ordinary 
 crops, and mixing them again with the surface part. 
 
COMPOSITION OP VEGETABLE MANURES. 199 
 
 Many of the plants found most useful for green manuring 
 send down their roots to a considerable depth ; and when 
 they are ploughed in, all the substances which they have 
 brought up are of course deposited in the upper few 
 inches of the soil. Vegetable matter when ploughed in 
 in the fresh state, also decomposes rapidly, and is therefore 
 able immediately to improve the subsequent crop ; and as 
 this decomposition takes place in the soil without the loss 
 of ammonia and other valuable matters, which is liable to 
 occur to a greater or less extent when they are fermented 
 on the dung-heap, it will be obvious that in no other 
 mode can equally good results be obtained by its use. 
 
 Many plants have been employed as green manure, 
 and different opinions have been expressed as to their re- 
 lative values. In the selection of any one for the pur- 
 pose, that should of course be taken which grows most 
 rapidly, and produces within a given time the largest 
 quantity of valuable matters, but no general rule can be 
 given for the selection, as the plant which fulfils those 
 conditions best will differ in different soils and climates. 
 The plants most commonly employed in this country are 
 spurry, white mustard, and turnips. Eye, clover, buck- 
 wheat, white lupins, rape, borage, and some others, have 
 been largely employed abroad. Some of these are ob- 
 viously mifitted for the climate of the British Islands ; and 
 the others, although they have been tried occasionally, do 
 not appear to have been very extensively employed. The 
 turnip is sown broadcast at the end of harvest, and 
 ploughed in after two months. White mustard and spurry 
 are employed in the same way as a preparation for winter 
 wheat, and with the best results. The latter is some- 
 times sown as a spring crop in March, ploughed in in May, 
 and another crop sown which is ploughed in in June, and 
 
•200 AGRICULTURAL CHEMISTRY. 
 
 immediately followed by a third. The effect of this treat- 
 ment is such that the worst sands may be made to bear a 
 remunerative crop of rye.. 
 
 It is not easy to estimate the addition made by green 
 manuring to the yaluable matters contained in the soil, 
 but it is probably far from inconsiderable. A crop of 
 turnips, cultivated on the ordinary agriculttiral system, 
 after two months' growth, weighs between five and seven 
 tons per acre, and contains nitrogen equivalent to about 
 48 lbs. of ammonia, and half a ton of organic matters ; 
 but nothing is known as to the quantity produced when 
 it is sown broadcast, and is not thinned, although it 
 must materially esceed this. Neither is it possible to 
 determine the relative proportions derived from the soil 
 and the air, although it is, in all probability, dependent 
 on the resources of the soil itself, — ^plants grown on a 
 rich soil obtaining their chief supplies from it, while, 
 on poorer soils, a larger proportion is drawn from the 
 atmosphere. Hence light and sandy soils are most bene- 
 fited by green manuring, partly on this account, and 
 partly also, no doubt, because the valuable inorganic 
 matters, which are so liable to be washed out of these 
 soils, are accumulated by the plants and retained in them 
 in a state in which they are readily available for the sub- 
 sequent crop. 
 
 Sea- Weed. — Sea- weeds have been employed from time 
 immemorial as a manure on the coasts of Scotland and 
 iJngland, in quantities varying from 10 to 20 tons per 
 acre. Their action is necessarily similar to that of green 
 manure ploughed in, as they contain all the ordinary con- 
 stituents of land plants. 
 
 The subjoined analyses of three of the most abundant 
 species will sufficiently indicate their general composition. 
 
COMPOSITION OF VEGETABLK MANURES. 
 
 201 
 
 
 ^S33 
 
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202 AGRICULTTJEAL CHEmSTRY. 
 
 The first four analyses give the composition of the 
 weeds after they have been separated from all foreign 
 substances ; the last, that of the mixture taken from the 
 heap just as it is used in Orkney ; and its value is then 
 enhanced by small shells and marine animals adhering to 
 the plants, which increase the amount of phosphoric acid 
 and nitrogen- 
 
 The ease with which all sea-weeds pass into a state 
 of putrefaction, adapts them in a peculiar manner to the 
 manurial requirements of a cold and damp climate. The 
 rapidity of their decomposition is such, that when spread 
 on the land they are seen to soften and disappear in a 
 short time. They form therefore a rapid manure, and 
 their effects are said to be confined to the crop to which 
 they are applied ; but this is probably due to the fact, 
 that they are chiefly used in inferior sandy soils, in which 
 any manure is rapidly exhausted. In good soils there is 
 no reason why their effect should not be as lasting as that 
 of farm-yard manure, which, in many particulars, they 
 considerably resemble. The method of applying sea-' 
 weeds most generally in use, is to spread them on the 
 soil, and plough them in after putrefaction has commenced, 
 and it is on the whole the most advantageous. But they 
 are sometimes composted with lime and earth, or mixed 
 with farm-yard manure, and occasionally, also, they are 
 used as a top-dressing to grass land. 
 
 On some parts of the western coast of Scotland and in 
 the Hebrides, sea- weed is the chief manure. It gives ex- 
 cellent crops of potatoes, but they are said to be of inferior 
 quality, unless marl or shell-sand is employed at the same 
 time. 
 
 Leaves may be used as a manure, simply by ploughing 
 
COMPOSITION OP VEGETABLE MANURES. 203 
 
 them in, by composting them with lime, or by adding them 
 to the manure heap. 
 
 Peat. — As a source of organic matter, peat may be 
 used with advantage, especially on soils in which it is 
 naturally deficient. Dry peat of good quality contains 
 about one per cent of nitrogen, and a quantity of ash 
 varying from five to twenty per cent. These substances, 
 however, become available very slowly, owing to the tardy 
 decay of peat in its natural state ; and in order to make it 
 useful, it is necessary to compost it with lime, or to mix it 
 with farm-yard manure, or some readily putrescible sub- 
 stance, so that its decomposition may be accelerated. It may 
 be most advantageously used as an absorbent of liquid man- 
 ure, and on this account, forms a useful addition to the 
 manure heap. 
 
 The observations which have been made regarding the 
 use of these substances, lead directly to the inference that 
 all vegetable matters possess a certain manurial value, and 
 that they ought to be carefully collected and preserved. 
 In fact, the careful farmer adds everything of the sort to 
 his manure heap, where, by undergoing fermentation along 
 with the manure, their nitrogen becomes immediately 
 available to the plant ; while the seeds of weeds are 
 destroyed during the fermentation, and the risk of the land 
 being rendered dirty by their springing up when the man- 
 ure comes to be used is prevented. 
 
CHAPTER X. 
 
 COMPOSITION AND PROPERTIES OF ANIMAL MANURES. 
 
 Manures of animal origin are generally characterized by 
 the large quantity of nitrogen they contain, which causes 
 them to undergo decomposition with great rapidity, and to 
 yield the greater part of their valuable matters to the crop 
 to which they are applied. 
 
 Guano. — By far the most important animal manure is 
 guano, which is composed of the solid excrements of carni- 
 vorous birds in a more or less completely decomposed state, 
 and is accumulated in immense quantities on the coasts of 
 South America and other tropical countries. It has been 
 used as a manure in Peru from time immemorial, but the 
 accounts given by the older travellers of its marvellous 
 effects were considered to be fabulous, until Humboldt, 
 from personal observation, confirmed their statements. It 
 was first imported into this country in 1840, in which year 
 a few barrels of it were brought home ; and from that time 
 its importation rapidly increased. Soon after large deposits 
 of it were found in Ichaboe ; and it has since been brought 
 from many other localities. The quantity of guanos of 
 all kinds imported into this country and retained for home 
 consumption now exceeds 240,000 tons a year. 
 
 The value of guano differs greatly according to the 
 extent to which its decomposition has gone, and this is 
 chiefly dependent on the climate of the locality from which 
 
COMPOSITION OF ANIMAL MANURES. 205 
 
 it is obtained. When deposited in the rainless districts of 
 Peru it still retains some of the uric acid and the greater part 
 of the ammonia naturally existing in it, and the quantity 
 which has escaped by decomposition is unimportant. But 
 that obtained from other districts has suffered a more or 
 less complete decomposition according to the humidity of 
 the climate, which reduces the quantity of organic matters 
 and ammonia, until, in some varieties, they are so small 
 as to be of little importance. The following are minute 
 analyses of three specimens of Peruvian guano, shewing 
 all the different constituents it contains, and the amount 
 of difference which may exist : — 
 
 I. U. III. 
 
 Urate of ammonia 10-70 9-0 3-24 
 
 Oxalate of ammonia 12-38 10-6 13-35 
 
 Oxalate of lime 5-44 7-0 1636 
 
 Phosphate of ammonia 19-25 6-0 6-45 
 
 Phosphate of magnesia and ammonia 2-6 4-20 
 
 Sulphate of potash 4-50 5-5 4-23 
 
 Sulphate of soda 1-95 3-8 1-12 
 
 Sulphate of ammonia 3-36 
 
 Muriate of ammonia 4-81 4-2 6-50 
 
 Phosphate of soda ... 5-29 
 
 Chloride of sodium ... 0-10 
 
 Phosphate of lime 15-56 14-3 9-94 
 
 Carbonate of lime 1-80 
 
 Sand and alumina 1-59 47 5-80 
 
 Water 9-14 ^ 
 
 Undetermined humus-like organic ) j^q-qo r ^^'^ 23-42 
 
 matters J J 
 
 100-48 100-0 100-00 
 
 These analyses illustrate two ])oinis— first, that in 
 some samples the decomposition has advanced to a greater 
 extent than in others ; for we observe that the quantity of 
 
206 AGRICULTURAL CHEMISTRY. 
 
 uric acid, or rather of urate of ammonia, is greatly less in 
 the last analysis than in the other two, and much smaller 
 than in the fresh dung, which contains from 50 to 70 per 
 cent of uric acid ; and secondly, that guano is rich in all 
 the constituents of the plant, hut especially in ammonia, 
 the best form in which nitrogen can be supplied, in uric 
 acid which by decomposition yields ammonia, and in 
 phosphoric acid. But such analyses are too elaborate for 
 ordinary purposes, and much less convenient for comparison 
 and for estimating the value of the guano than the shorter 
 analysis commonly in use, which gives the water, the 
 loss by ignition (that is, the sum -of the organic matters 
 and ammoniacal salts), the phosphates, the alkaline salts, 
 and the quantity of phosphoric acid contained in them, and 
 existing there in a state similar to that in which it is found 
 in the soluble phosphates of a superphosphate. In addi- 
 tion to these, the quantities of sand and other less 
 valuable ingredients are also stated. 
 
 In the subjoined tables the composition of a great 
 variety of different kinds of guano is given. Most of 
 these are averages deduced from a considerable number of 
 analyses of good samples. Those of some kinds of guano, 
 such as Peruvian, which present a considerable amount of 
 uniformity, afford a sufficiently accurate idea of the general 
 composition of the variety, but in other cases they are of 
 less value, because the imports of different seasons, and even 
 of different cargoes, differ so greatly in composition that 
 no proper average can be made. Several of these varieties 
 are already exhausted, the importation of others has 
 ceased, and new varieties are constantly being introduced. 
 
COMPOSITION OP ASlHAh MANURES. 
 
 207 
 
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COMPOSITION OF ANIMAL MANURES. 209 
 
 On examining the tables given above, it is obvious 
 that guanos may be divided into two classes, the one 
 characterized by the abundance of ammonia, the other by 
 that of phosphates ; and which, for convenience sake, 
 may be called ammoniacal and phosphatic guanos. Peru- 
 vian and Angamos are characteristic of the former, and 
 Saldanha Bay and Bolivian of the latter class. The 
 value of these two classes of guano dififers materially, 
 and they are also applicable under different circum- 
 stances, but to these points reference will afterwards be 
 made. 
 
 Very special precautions are necessary on the part of 
 the farmer in order to insure his obtaining a guano which 
 is not adulterated, and of good quality if genuine. In 
 the case of Peruvian guano, which is tolerably uniform in 
 its qualities, it is possible to form some opinion by careful 
 examination, and the following points ought to be at- 
 tended to : 
 
 1st, The guano should be light coloured. If it is 
 dark, the chances are that it has been damaged by water. 
 
 2d, It should be dry, and when a handful is well 
 squeezed together it should cohere very slightly. 
 w 3d, It should not have too powerful an ammoniacal 
 odour. 
 
 4th, It should contain lumps, which, when broken, 
 appear of a paler colour than the powdery part of the 
 sample. 
 
 5lh, When rubbed between the fingers it should not 
 be gritty. 
 
 6th, A bushel of the guano should not weigh more 
 than from 56 to 60 lbs. 
 
 These characters must not, however, be to6 implicitly 
 relied on, for they are all imitated with wonderful inge- 
 
210 
 
 AGRICtTLTUEAL CHEMISTRY. 
 
 nuity by the skilful adulterator, and they are applicable 
 only to Peruvian guano ; the others being so variable 
 that no general rules can be given for determining whether 
 they are genuine. Neither are they so precise as to en- 
 able us to give any opinion regarding the relative values 
 of several samples where all are genuine. The only way 
 in which adulteration can with certainty be detected, and 
 the value of different guanos be determined, is by analysis, 
 and the importance of this can easily be illustrated. 
 
 In the table above, the average composition of the 
 different guanos is given ; but in order to shew how much 
 individual cargos may differ from the mean, we give here 
 analyses of samples of the highest and lowest quality of 
 the genuine guanos of most importance : 
 
 Water . . . . 
 
 Angamos. 
 
 PerUTian. 
 
 Bolivian. 
 
 Highest. 
 
 Lowest. 
 
 Highest. 
 
 Iiowest. 
 
 Highest. 
 
 Lowest. 
 
 12 60 
 
 7-09 
 
 10-37 
 
 21-49 
 
 11-53 
 
 16-20 
 
 Organic matter i 
 
 
 
 
 
 
 
 and ammoniacal V 
 
 6562 
 
 60-83 
 
 55-73 
 
 46-26 
 
 11-17 
 
 12-86 
 
 salta ... I 
 
 
 
 
 
 
 
 Phosphates . . . 
 
 10-83 
 
 870 
 
 25-20 
 
 18-93 
 
 62-99 
 
 52-95 
 
 Alkaline salts . 
 
 7-50 
 
 1030 
 
 7-50 
 
 10-64 
 
 9-93 
 
 13-83 
 
 Sand 
 
 3-45 
 
 17 08 
 
 1-20 
 
 2-68 
 100-00 
 
 4-38 
 
 416- 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 10000 
 
 Ammonia . . . 
 
 25-33 
 
 17-15 
 
 18-95 
 
 14-65 
 
 1-89 
 
 2-23 
 
 The differences are here exceedingly large ; and 
 when the values of the two Pemviaa guanos are calcu- 
 lated according to the method to be afterwards described, 
 it appears that the highest exceeds the lowest in value 
 by nearly £3 per ton. Of course, this is an extreme 
 case, but it is no uncommon occurrence to find a dif- 
 
COMPOSITION OP ANIMAL MANURES. 211 
 
 ference of £1 or even £2 per ton bet weep the values of 
 cargos of Peruvian guano, which are sold at the same 
 price. 
 
 The adulteration of guano is carried on to a very large 
 extent ; and though perhaps not quite so extensively now 
 as it was some years since, it is only kept in check by the 
 utmost vigilance on the part of the purchaser. The chief 
 adulterations are a sort of yellow loam very similar in 
 appearance to guano, sand, gypsum, common salt, and 
 occasionally also ground coprolites and inferior guano. 
 These substances are, rarely used singly^ but are com- 
 monly mixed in such proportions as most closely to imitate 
 the colour and general appearance of the genuine article. 
 The extent to which the adulteration is carried may be 
 judged of from the following analyses taken at random 
 from those of a large number of guanos, all of which 
 were sold as first-class Peruvian, 
 
 Water . ... 12-85 15-19 12-06 27-86 6-32 
 
 Orga^c matter and. 26-84 44-31 34-14 30-41 27-42 
 
 ammomacal salts . ) 
 
 Phosphates .... 15-54 20-95 22-08 22-17 33-61 
 
 Sulphate of lime 11-08 ... 22-11 
 
 Alkaline salts . . . 6-07 9-40 12-81 7-92 22-50 
 
 Sand ... . 38-70 10-15 7-83 1-64 10-15 
 
 100-00 100-00 100-00 100-00 100-00 
 
 Ammonia 934 13-90 9-77 8-64 9-76 
 
 In all those cases a very large depreciation in the 
 value has taken place, and several of them are worth con- 
 siderably less than half the price of the genuine guano, 
 while they are generally offered for sale at about £1 
 under the usual price. The adulteration is chiefly prac- 
 tised in London, and cases occasionally occur which cau 
 
212 AGKICULTURAL CHEMISTRY. 
 
 be traced to Liverpool and other places ; but it always 
 takes place in the large towns, because it is only there 
 that facilities exist for obtaining the necessary materials 
 and carrying it out without exciting suspicion. The 
 sophisticated article then passes into the hands of the 
 small country dealers, to whom it is sold with the assur- 
 ance that it is genuine, and analysis quite unnecessary. 
 In other instances, adulterated and inferior guanos are 
 sold by the analysis of a genuine sample, and sometimes 
 an analysis is made to do duty for many successive cargos 
 of a guano which, though all obtained from one deposit, 
 may differ excessively in composition. In order to insure 
 obtaining a genuine guano, it is above all things impor- 
 tant to deal only with a person of established character, 
 who will generally, for his own sake, satisfy himself that 
 the article he vends is genuine and of good quality ; and 
 it is always important that the buyer should examine the 
 analysis, and in all cases where there is the slightest 
 doubt, should ascertain that the bulk sent corresponds 
 with it. In the case of a Peruvian guano, a complete 
 analysis is not necessary for this pui"pose ; but an ex- 
 perienced chemist, by the application of a few tests, can 
 readily ascertain whether the sample is genuine. Where 
 the difference in value between different samples is re- 
 quired, a complete analysis is necessary, and this is indis- 
 pensable in the case of the inferior guanos. Many of 
 these are obtained from deposits of limited extent, and 
 in loading it considerable quantities of the subjacent soil 
 are taken up, so that very great differences may exist 
 even in different parts of the same cargo. Nor must it be 
 forgotten that, except in the case of Peruvian, the name 
 is no guarantee for the quality of the guano, even if 
 genuine. Peruvian guano is all obtained from the same 
 
COMPOSITION OF ANIMAL MANURES. 213 
 
 deposits, those of the Chiiicha Islands, but the guanos 
 which are brought into the market under the name of Fata- 
 gonian, Chilian, etc., are obtained from a great variety 
 of deposits scattered along the coasts of these countries, 
 sometimes at a distance of several hundred miles from 
 each other, and which have been accumulated under 
 totally different circumstances. In illustration of this, it 
 is only necessary to refer to the subjoined analysis of 
 samples, all of which I believe to be genuine as im- 
 ported, and which were sold under the name of Upper 
 Peruvian Guano. 
 
 I. II. III. 
 
 Water 7-80 6-65 8-85 
 
 Organic matter and ammoniacal salts 10-85 19-16 10-20 
 
 Phosphates . . • 67-00 20-41 17-10 
 
 Carbonate of lime ... 21-15 
 
 Alkaline salts IMO 5-31 61-30 
 
 Sand 3-25 27-32 2-55 
 
 100-00 10000 100-00 
 
 Ammonia 2-29 6-73 1-48 
 
 Phosphoric acid in the alkaline salts . 224 ... 1-70 
 
 Equal to phosphate of lime . . . . 4-89 ... 3-70 
 
 With the exception of Peruvian, the supply of good 
 guanos of uniform composition is by no means large, and 
 phosphatic guanos of good quality are now especially 
 rare. The Saldanha Bay, and other similar deposits, have 
 been exhausted, and few guanos of equally good quality 
 have been lately discovered. There is no doubt, however, 
 that such guanos are very useful, and if obtained in large 
 quantity, and of uniform composition, would be used to a 
 much larger extent than they at present are. 
 
 The value and use of guano are now so well under- 
 
214 AGRICULTURAL CHEMISTRY/ 
 
 stood, that it is scarcely necessary to enlarge on the mode- 
 of its application. Peruvian guano owes its chief value 
 to its ammonia and phosphates, but it also contains potash, 
 soda, and all the other constituents of plants in small 
 quantity, although in a readily available condition, as is 
 seen in the detailed analysis given in page 205. 
 
 In other guanos which have undergone more complete 
 decomposition, and irom which the soluble matters have been 
 more or less completely exhausted by rain, the alkaline 
 salts, or at least the potash they originally contained, have 
 almost entirely disappeared. Hence an important differ- 
 ence between Peruvian guano and most other varieties. 
 The former can be used as a complete substitute for farm- 
 yard manure, and excellent crops of turnips and potatoes 
 can be raised by means of it alone, and at a less cost than 
 with ordinary dung. But though this may be done, and 
 in many cases is attended with great economic advantages, 
 it is a practice that cannot be recommended for general 
 use, because the quantity of valuable matters contained in 
 the usual application of guano is much smaller than in 
 farm-yard manure, and the probability is that it would not, 
 if used alone during a succession of years, be sufficient to 
 maintain the soil permanently in a high state of fertility. 
 Five cwt. of Peruvian guano, which is a liberal application 
 per acre, contains about 95 lbs. of ammonia, and 130 of 
 phosphates, while 20 tons of good farm-yard manure con- 
 tain 312 of ammonia, and about the same quantity of 
 phosphates, and when the other constituents, such as 
 potash and soda, are compared with those in guano, the 
 difference is still more striking. On the other hand, 
 gnano is a rapidly acting manure ; its constituents are in 
 a condition in which they are more immediately accessible 
 by the plant, and its immediate effect is far more marked. 
 
COMPOSITION OP ANIMAL MANURES. 215 
 
 as it is chiefly expended on the crop to which it is 
 applied. It has indeed been alleged that it produces Ho 
 effects on the subsequent crops, but this opinion can scarcely 
 be considered as well founded. In no case does the crop 
 raised by means of it contain the whole of the ammonia 
 or phosphates present in the manure, and the unappropri- 
 ated quantity, though it may, and probably does, escape 
 from the lighter soils, must be retained and preserved for 
 the use of subsequent crops by heavy and retentive clay 
 soils. The general inference is, that though guano may 
 at an emergency be used as an entire substitute for farm- 
 yard manure, the practice is one to be generally avoided. 
 When, however, as occasionally happens after a long con- 
 tinued use of farm-yard manure, organic matters have 
 accumulated in the soil, and passed into an inert condition, 
 then Peruvian guano may be used alone with very great 
 advantage. In all cases the rapidity of the action of 
 guano makes it an important auxiliary of farm-yard 
 manure, and it is in this way that it may be most advan- 
 tageously employed. Experience has shewn that one- 
 half the farm-yard manure may be replaced by guano 
 with the production of a larger crop than by the former 
 alone in its full quantity. The proportion of guano 
 usually employed is from three to five cwt, and it is alleged 
 that a much larger quantity produces prejudicial effects on 
 the subsequent crop, although it is not very easy to see on 
 what this depends. 
 
 The variety of guano to be selected must depend to a 
 great extent on the use to which it is to be put. Peruvian 
 guano is most advantageously applied as a top-dressing to 
 young com and particularly to oats. For the turnip, the 
 ammoniacal guanos were formerly preferred, and on strong 
 soils, under good cultivation, their effects are excellent,lrat 
 
216 AGRICULTURAL CHEMISTRY. 
 
 on light soils they are less applicable, their soluble salts 
 being more rapidly washed out, and their effects lost, and 
 in these cases they are surpassed by the phosphatic gnanos. 
 
 No definite rules can be given for determining the 
 soils on which these different varieties are most applicable, 
 hut each individual must determine by experiment that 
 which best suits his own farm ; and the inquiry is of much 
 importance to him, as, of course, if the phosphatic guanos 
 will answer as well as the ammoniacal, there is a large 
 saving in the cost of the manure. A very excellent 
 practice is to employ a mixture of equal parts of the two 
 sorts of guano. 
 
 Pigeons' Dung. — The dnng of all birds, which more or 
 less closely resembles guano, may be employed with much 
 advantage as a manure, but that of the pigeon and the 
 common fowl are the only ones which can be got in quan- 
 tity. Pigeons' dung, according to Boussingault, contains 
 8-3 per cent of nitrogen, equivalent to lO'O of ammonia. 
 Its value, therefore, will be more than half that of guano, 
 but it varies greatly, and a sample imported from Egypt 
 into this country, and analysed by Professor Johnston, con- 
 tained only 5*4 per cent of ammonia. Hens' dnng has 
 not been accurately analysed, but its value must be about 
 the same as pigeons'. 
 
 Urate and Sulphated Urine. — We have already dis- 
 cussed the urine of animals, in reference to farm-yard 
 manure. But human urine, the composition of which was 
 then stated, is of much higher value than that of the 
 lower animals, and many attempts have been made to 
 preserve and convert it into a dry manure. Urate is pre- 
 pared by adding gypsum to urine, and collecting and dry- 
 ing the precipitate produced. It contains a considerable 
 quantity of the phosphoric acid of the urine, but very 
 
COMPOSITION OF ANIMAL MANDEES 217 
 
 little of its ammonia ; and as the principal value of urine 
 depends on the latter, it is necessarily a very inefficient 
 method of turning it to account. A better method has 
 been proposed by Dr. Stenhouse, who adds lime-water to 
 the urine, and collects the precipitate, which, when dried 
 in the air, contains 1'91 per cent of nitrogen, and about 
 41 per cent of phosphates. This method is subject to the 
 same objection as that by which urate is made, namely, 
 that the greater part of the ammonia is not precipitated. 
 This might probably be got over to some extent by the 
 addition of sulphate of magnesia, or, still better, of chloride 
 of magnesium, which would throw down the phosphate of 
 magnesia and ammonia. By much the best mode of 
 employing urine is in the form of sulphated urine, which 
 is made by adding to it a sufficient quantity of sulphuric 
 acid to neutralize its ammonia, and evaporating to dryness. 
 In this form all the valuable constituents are retained, and 
 excellent results are obtained from it. Its effects, though 
 mainly attributable to its ammonia, are also in part de- 
 pendent on the phosphates and alkaline salts which it 
 contains ; and it is therefore capable of supplying to the 
 plant a larger number of its constituents than the animal 
 matters already mentioned. 
 
 Niffht-Soil and Poudrette. — The value of night-soil, 
 which is well known, depends partly on the uriue, and 
 partly on the faeces of which it is formed. Its disagreeable 
 odour has prevented its general use, and various methods 
 have been contrived both for deodorising and converting 
 it into a solid and portable form. The same difficulties 
 which beset the conversion of urine into the solid form 
 occur here, and in most of the methods employed the loss 
 of ammonia is great. It is sometimes mixed with lime 
 or gypsum, and dried with heat, and sometimes with 
 
218 AGRICULTDKAI, CHEMISTRY. 
 
 animal charcoal or peat charcoal. The ijianufacttire of a 
 manure from night-soil, called " poudrette," has long been 
 practised in the neighbonrhood of Paris and other con- 
 tinental towns. The process employed at Montfangon 
 and at Bondy is very simple. The contents of the cess- 
 pools are conveyed to the work in large barrels, which are 
 then emptied into tanks capable of containing the accu- 
 mulation of several months. "When filled they are allowed 
 to stand for some time, during which the smell diminishes 
 and the contents become nearly dry. The residue is then 
 dug out and mixed with ashes, dry loam, charcoal powder, 
 peat, peat^charcoal, saw-dust, and other matters, so as 
 to deodorize it, and render it sufficiently dry for transport. 
 Its general composition may be judged of from the sub- 
 joined analyses of samples from different places : — 
 
 MontfauqoQ. Bondy. Dresden. American. 
 
 Water 28-00 13-60 19-50 39-97 
 
 Organic matters 29-00 24-10 20-80 20-57- 
 
 Phosphates 7-65 4-96 5-40 1-88 
 
 Carbonates of lime and ") 
 
 Magnesia, alkaline >■ 7-35 14-14 11-30 7-63 
 
 salts, etc ) 
 
 Sand 28-00 48-20 43-00 29-95 
 
 100-00 100-00 100-00 100-00 
 
 Ammonia 1-54 1-98 2-60 1-23 
 
 These analyses shew su£Sciently the extent to which 
 the animal matters have been mixed with valueless driers, 
 the second and third samples containing considerably more 
 than half their weight of worthless matters. 
 
 Hair, Skin, and Horn, — The refuse of manufactories 
 in which these substances are employed, are frequently 
 used as manures. They are highly nitrogenous substances, 
 
COMPOSITION OP ANIMAL MAN0EES. 219 
 
 and owe their entire value to the nitrogen they contain, 
 their inorganic constituents being in too small quantity to 
 be of any importance, wool and hair having only 2 per 
 cent, and horn 0*7 per cent of ash. In the pure and dry 
 state, and after subtraction of the ash, their composition 
 
 IS. 
 
 Skin. Bomanhair. Wool Horn. 
 
 Carbon 50-99 50-65 50-65 51-99 
 
 Hydrogen 7-07 6-36 7-03 6-72 
 
 Nitrogen 18-72 17-14 17-71 17-28 
 
 Oxygen 23-22 20-85", 
 
 Sulphur 5-00 ; 24-61 24-01 
 
 100-00 100-00 100-00 100-00 
 
 It rarelySif ever happens, however, that the refuse 
 o£fered for sale as a manure is pure. It always contains 
 water, sand, and other foreign matters. Woollen rags are 
 mixed with cotton which has no manurial value, and the 
 skin refuse from tan-works contains much lime. Due 
 allowance must therefore be made for such impurities 
 which are sometimes present in very large quantity. 
 
 Befuse horse hair generally contains 11 or 12 per 
 cent of nitrogen. Woollen rags of good quality contain 
 12-7 per cent of nitrogen; wooUen cuttings about 14; 
 and what is called shoddy only 5*5 per cent. Horn 
 shavings are extremely variable in their amount of nitrogen ; 
 when pure, they sometimes contain as much as 12 '5 per 
 cent, but a great deal of the horn shavings from comb 
 manufactories, etc., contain much sand and bone dust, by 
 which their percentage of nitrogen is greatly diminished, 
 and it sometimes does not exceed 5 or 6 per cent. 
 
 All these substances are highly valuable ifis manures, 
 but it must be borne in mind that they undergo decompo- 
 
220 AGKICULTURAL CHEMISTRY. 
 
 sition very slowly in the soil, and hence are chiefly 
 applicable to slow growing crops, and to those which 
 require a strong soil. Woollen rags have been largely 
 employed as a manure for hops, and are believed to sur- 
 pass every other substance for that crop. As a manure 
 applicable to the ordinary purposes of the farm they have 
 scarcely met with that attention which they deserve, pro- 
 bably because their first action is slow and the fanner is 
 more accustomed to look to immediate than to future 
 results ; but they possess the important qualification of 
 adding permanently to the fertility of the soil. 
 
 Blood is a most valuable manure, but it is not much 
 employed in this country, at least in the neighbourhood of 
 large towns, as there is a demand for it for other purposes, 
 and it can rarely be obtained by the farmer in large quan- 
 tity, and at a sufficiently low price. In its natural state 
 it contains about 3 per cent of nitrogen, and after being 
 dried up, the residue contains about 15 per cent. It is 
 best used in the form of a compost with peat or mould, and 
 this forms an excellent manure for turnips, and is also 
 advantageously applied as a top-dressing to wheat. 
 
 Flesh. — The flesh of all animals is useful as a 
 manure, and is especially distinguished by the rapidity 
 with which it undergoes decomposition, and yields up its 
 valuable matters to the plant. It is rarely employed in 
 its natural state, but horse flesh was at one time converted 
 into a dry and portable manure, although, I understand, 
 this manufacture is not now prosecuted. The dead 
 animal after being skinned is cut up and boiled in large 
 cauldrons until the flesh is separated from the bones. The 
 latter are removed, and the flesh dried upon a flat stove. 
 The flesh as sold has the following composition : — 
 
COMPOSITION OP ANIMAL MANBEES. 
 
 221 
 
 Water 
 
 Organic matter 
 Phosphate of lime, etc. 
 Alkaline salts 
 Sand 
 
 Nitrogenj .... 
 Ammonia to which the nitrogen is ) 
 
 equivalent 
 
 12-17 
 
 78-44 
 3-82 
 3-64 
 1-93 
 
 100-00 
 922 
 
 11-20 
 
 The dried flesh and small bones of cattle, from the 
 great slaughtering establishments of South America, was at 
 one time imported into this country under the name of 
 flesh manure. Its composition was — 
 
 Water 
 
 
 9-05 
 
 Fat 
 
 
 11-13 
 
 Animal matter 
 
 
 39-52 
 
 Phosphate of lime 
 
 
 28-74 
 
 Carbonate of lime 
 
 
 3-81 
 
 Alkaline salts 
 
 
 0-57 
 
 Sand .... 
 
 
 7-18 
 
 
 100-00 
 
 Nitrogen 
 
 
 5-56 
 
 Ammonia to which the nitrogen 
 
 ':} 
 
 
 equivalent . 
 
 6-67 
 
 But owing to the large proportion of phosphates contained 
 in it, it may be most fairly compared with bones. It is not 
 now imported, the results obtained from its use being said 
 not to have proved satisfactory, although this statement 
 appears very paradoxical. 
 
 Fish have been employed in considerable quantity 
 as a manure. That most extensively employed in this 
 country is the sprat, which is occasionally caiight in enor- 
 mous quantities on the Norfolk coast, and used as an ap- 
 
222 AGRICULTDEAL CHEMISTRY. 
 
 plication for turnips. They are sold at 8d. per bushel, 
 and their composition is — 
 
 Water 64-6 
 
 Organic matter . . . 33"3 
 
 Ash 2-1 
 
 100-0 
 
 Nitrogen 1-90 
 
 Phosphoric acid .... 0-91 
 
 The refuse of herring and other fish-curing establish- 
 ments, whales' blubber, and similar fish refuse, are all 
 useful as manure, and are employed whenever they can be 
 obtained. They are not usually employed alone, but are 
 more advantageously made into composts with their own 
 weight of soil, and allowed to ferment thoroughly before 
 being applied. 
 
 Many attempts have been made to convert the oflfal 
 of the great fish-curing establishments, and the inedible 
 fish, of which large quantities are often caught, into a dry 
 manure, which has received the name of " fish guano." 
 The processes employed have consisted in boiling with 
 sulphuric acid and other agents, and then evaporating, or 
 sometimes by simply drying up the refuse by steam heat. 
 A manure made in this way proved to have the following 
 composition : — 
 
 Water .... 
 
 8-00 
 
 Fatty matters 
 
 7-20 
 
 Nitrogeneous organic matters 
 
 7:-46 
 
 Phosphate of lime 
 
 8-70 
 
 Alkaline salts 
 
 3-80 
 
 Sand .... 
 
 0-84 
 
 100-00 
 
COMPOSITION OP ANIMAL MANURES. 223 
 
 Nitrogen 11-25 
 
 Equal to ammonia . , . 13' 68 
 
 Phosphoric acid in the alkaline salts, ■» 
 equal to 1'41 phosphate of lime j 
 
 The expense of manufacturing manures of this de- 
 scription has hitherto acted as a barrier to their intro- 
 duction. In this country several manufactories have been 
 established, but either owing to this cause, or to the difiS- 
 culty of obtaining sufficiently large and uniform supplies of 
 the -raw material, some of them have not proved successfiil, 
 but a manufactory is now in operation in Norway, which 
 exports the manure to Germany. It is probable that most 
 of the processes used in this country failed because they 
 were too costly, and it. is much to be desired that the 
 subject should be actively taken up. It is said that the 
 refuse from the Newfoundland fisheries is capable of yield- 
 ing about 10,000 tons of fish guano annually ; and the 
 quantity obtainable on our own coasts is also very con- 
 siderable. 
 
 Bones. — Bones have been used as a manure for a long 
 period, but they first attracted the particular attention of 
 agriculturists from the remarkable effects produced by their 
 application on the exhausted pasture lands of Cheshire. 
 During the present century they came into general use on 
 arable land, and especially as a manure for turnips ; and 
 they are now imported in large quantities from the conti- 
 nent of Europe. The bones used in agriculture are chiefly 
 those of cattle, but sheep and horse bones are also em- 
 ployed. They do not differ much in quality when genuine. 
 The subjoined analysis is that of a good sample. 
 
 Water . . . . 6-20 
 
 Organic matter . . 39-13 
 
 Phosphate of lime . . - 48-95 
 
224 AGRICULTURAL CHEMISTRY. 
 
 Lime . . . 2-57 
 
 Magnesia .... 0'30 
 
 Sulphuric acid .... 255 
 
 Silica 0-30 
 
 100-00 
 Ammonia which the organic matter ") 
 is capable of yielding . . j 
 
 In general, bones may be said to contain abont half 
 their weight of phosphate of lime, and 10 or 12 per cent 
 of water. But, in addition to their natural state, they are 
 met with in other forms in commerce, in which their or- 
 ganic matter has been extracted either by boiling or burn- 
 ing. The latter is especially common in the form of the 
 spent animal charcoal of the sugar refiners, which usually 
 contains from 70 to 80 per cent of phosphate of lime, but 
 when deprived of their organic matter, they may be more 
 correctly considered under the head of mineral manures. 
 
 From the analysis given above, it is obvious that the 
 manurial value of bones is dependent partly on their phos- 
 phates and partly on the ammonia they yield. It has 
 been common to attribute their entire effects to the former, 
 but this is manifestly erroneous ; and although there are 
 no doubt cases in which the former act most powerfully, 
 the benefit derived from the ammonia yielded by the 
 organic matter is unequivocal. When the phosphates only 
 are of use, burnt bones or the spent animal charcoal of 
 the sugar refiners are to be preferred. 
 
 At their first introduction, bones were applied in large 
 fragments, and in quantities of from 20 to 30 cwt., or even 
 more, per acre, but as their use became more general they 
 were gradually employed in smaller pieces, until at last 
 they were reduced to dust, and it was found that, in a fine 
 state of division, a few hundredweights produced as great 
 
COMPOSITION OF ANIMAL MANURES. 225 
 
 an effect as the larger quantity of the unground bones. 
 Even the most complete grinding which can be attained, 
 however, leaves the bones in a much less minute state of 
 division than guano, and they necessarily act more slowly 
 than it does, the more especially as they contain no ready- 
 formed ammonia. They may be still further reduced by 
 fermentation, which acts by decomposing the organic 
 matter, and causing the production of ammonia ; but not 
 as is frequently, though erroneously supposed, by converting 
 the phosphates into a soluble condition, for this does not 
 occur to any extent, and their more rapid action is solely 
 due to the partial decomposition of the organic matter, by 
 which it is brought into a condition capable of undergoing 
 a more rapid change in the soil. The rapidity of action of 
 bones is still more promoted by solution in sulphuric acid, by 
 which they are converted into the form of dissolved bones 
 or superphosphate. At the present moment, however, 
 very little of the superphosphates sold in the market are 
 made exclusively from bones in their natural state, by 
 far the larger portion being manufactured from mineral 
 phosphates, or from bones after destruction of their organic 
 matter, sometimes with the addition of small quantities of 
 unbumt bones, but more frequently of sulphate of ammonia, 
 to yield the requisite quantity of ammonia. These sub- 
 stances may therefore be best considered under the head of 
 mineral manures. 
 
CHAPTER XL 
 
 COMPOSITION AND PROPERTIES OF MINERAL MAN0RES. 
 
 Mineral manure is a term which is now used with 
 great laxity. In its strict sense, it means manures which 
 contain only, and owe their exclusive value to the presence 
 of, those substances which go to make up the inorganic part 
 or ash of plants. It has, however, been usually taken to 
 inclnde all saline matters, and especially the compoiuids of 
 ammonia and nitric acid, which are indebted for their 
 manorial effects to the nitrogen they contain ; and thus is so 
 far incorrect. It would, however, be manifestly impossible 
 to arrange these compounds with any degree of accuracy 
 among either animal or vegetable manures, and hence the 
 necessity of including them amongst those which are strictly 
 mineral. The most important practical distinction between 
 them and the substances discussed in the two preceding 
 chapters is, that the latter generally contain the whole or 
 the greater part of the constituents of plants. Even bones 
 yield a certain quantity of alkalies, magnesia, sulphuric acid, 
 and chlorine, and may in some sense be considered as a 
 general manure. But those to which the term mineral 
 manure is applied for the most part contain only one or 
 two of the essential elements of plants, and hence cannot 
 be applied as substitutes for the substances already dis- 
 cussed, although they are frequently most important addi- 
 tions to them. 
 
COMPOSITION OP MINERAL MANURES. 227 
 
 Sulphate and Muriate of Ammonia. — These and other 
 salts of ammonia have been tried experimentally as man- 
 ures, and it has been ascertained that they may all be used 
 with equal success ; but as the sulphate is by much cheaper, 
 it is that which probably will always be employed to the 
 exclusion of every other. It contains, when pure, 25"7 
 per cent ammonia. 
 
 It is now manufactured of excellent quality for agri- 
 cultural use, and when good, contains from 95 to 97 per 
 cent of actual sulphate, the remainder consisting chiefly of 
 moisture and a small quantity of fixed residue ; but speci- 
 mens are occasionally met with containing as much as 10 
 per cent of impurities, which, as its price is high, makes 
 a material difference in its value. Inferior descriptions 
 are also occasionally sold, among which is a variety dis- 
 tinguished by containing a large quantity of water and 
 fixed salts, although it appears to the eye a good article. 
 Its composition is — 
 
 
 I. 
 
 II. 
 
 Water . 
 
 9-05 
 
 5-77 
 
 Sulphate of ammonia 
 
 . 79-63 
 
 85-21 
 
 Fixed salts 
 
 . 11-17 
 
 9-02 
 
 
 100-00 
 
 100-00 
 
 Ammonia 
 
 . 20-55 
 
 21-94 
 
 An article called sulpho- muriate of ammonia is also sold 
 for agricultural use. It is obtained as a refuse product 
 in the manufacture of magnesia, and is a mixture of 
 sulphate and muriate of ammonia, with various alkaline 
 salts. It differs somewhat in quality, and is sold by 
 analysis at a price dependent on the ammonia it contains. 
 
228 AQEICULTUKAL CHEMISTEY. 
 
 
 I. 
 
 11. 
 
 Water 
 
 14-49 
 
 25-39 
 
 Sulphate of ammonia 
 
 62-55 
 
 47-79 
 
 Muriate of ammonia . 
 
 15-3 
 
 ... 
 
 Sulphate of soda 
 
 ... 
 
 9-12 
 
 Sulphate of magnesia 
 
 ... 
 
 18-38 
 
 Chloride of potassium 
 
 4-75 
 
 2-94 
 
 Chloride of sodium 
 
 17-35 
 
 0-35 
 
 
 100-00 
 
 10000 
 
 Ammonia 
 
 16-50 
 
 11-28 
 
 The quality of sulphate of ammonia may generally be 
 judged of from its dry and uniformly crystalline appearance, 
 and it may be tested by heating a small quantity on a 
 shovel over a clear fire, when it ought to volatilize com- 
 pletely, or leave only a trifling residue. Some care, how- 
 ever, is necessary in applying this test, as in the hands of 
 inexperienced persons it is sometimes fallacious. The 
 salts of ammonia may be applied in the same way as 
 guano ; but they are most advantageously employed as a 
 top-dressing, and principally to grass lands. In this way 
 very remarkable effects are produced, and within a week 
 after the application, the difference between the dressed, 
 and undressed portions of a field is already conspicuous. 
 Experience has shewn that success is best insured when 
 the salt is applied during or immediately before rain, so 
 that it may be at once incorporated with the soil ; as when 
 used in dry weather little or no benefit is derived from it. 
 It seems also to exert a peculiarly beneficial effect upon 
 clover ; and hence it ought to be employed only on clover- 
 hay, as where rye-grass or other grasses form the whole of 
 the crop we have better manures. 
 
COMPOSITION OF MINERAL MANURES. 229 
 
 Ammoniacal Liquor of the Gas-Works, and of tJie 
 Animal Charcoal Manufacturers. — Both of these are 
 excellent forms in which to apply ammonia, when they 
 can be obtained. The ammoniacal liquor of the gas-works 
 is very variable in quality, but contains generally from 
 4 to 8 ounces of dry ammonia per gallon, which corresponds 
 in round numbers to from 1 to 2 lb. of sulphate of ammonia. 
 It is best applied with the watering-cart, but must be 
 diluted before use with three or four times its bulk of 
 water, as if concentrated it burns up the grass, and it is 
 alsoadvisable to use it during wet weather. The ammoniacal 
 liquor of the ivory-black works contains about 12 per cent 
 of ammonia, or about four or five times as much as gas 
 liquor. It has been used in some parts of England, made 
 into a compost, and applied to the turnip and other crops, 
 and, it is said, with good effect. Bone oil, which distils 
 over along with it, has also been used in the form of a 
 compost ; it contains a large quantity of ammonia and of 
 nitrogen in other forms of combination ; the total quantity 
 of nitrogen it contains being 9 "04 per cent, which is equiva- 
 lent to 10'98 of ammonia. Only part of this nitrogen is 
 actually in the state of ammonia ; and some circumstances 
 connected with the chemical relations of the other nitro- 
 genous compounds in this substance render it probable .that 
 they may pass very slowly into ammonia, and may there- 
 fore be of inferior value ; but the substance deserves a 
 trial, as it is very cheap. It must be carefully composted 
 with peat, and turned over several times before being used. 
 
 Nitrates of Potash and Soda. — Nitrate of potash 
 has long been used as a manure, but its high price has 
 prevented its general application, and its place has now 
 been almost entirely taken by nitrate of soda, which is 
 much cheaper and contains weight for weight a larger 
 
230 AGKICULTUKAL CHEMISTRY. 
 
 quantity of nitrogea Both these salts are employed as 
 sources of nitrogen; but nitrate of potash owes also a 
 certain proportion of its value to the potash it contains. 
 Nitrate of soda, on the other hand, must be considered to 
 owe its entire value to its nitric acid, as soda' is of little 
 value to the plant ; and, moreover, can be obtained in 
 common salt at a price so low, as to make it a matter of 
 no moment in the valuation of the nitrate. In its ordinary 
 state, as imported from Peru, nitrate of soda contains from 
 5 to 10 per cent of impurities, and it bears a price pro- 
 portionate to the quantity of the pure salt present in it. 
 When of good quality it contains about 15 per cent of 
 nitrogen, equivalent to 18 of ammonia, and is, therefore, 
 richer in that constituent of plants than Peruvian guano. 
 It is essentially a rapidly acting manure, and produces a 
 marked effect within a very few days after its application ; 
 but owing to the fact that nitric acid cannot be absorbed 
 and retained by the soil in the same manner as ammonia, 
 it is liable to be lost unless it can be at once assimilated 
 by the plant. For this reason it acts best when applied 
 in small quantity as a top-dressing to grass-land, and to 
 young corn. A large application has no advantages, 
 and there can be no doubt that the best effect would be 
 produced by several very small quantities, applied at 
 intervals. In one experiment, Mr, Pusey found 42 lb. 
 per acre to increase the produce of barley by 7 bufihels, 
 and very favourable results have been obtained by other 
 experimenters. The beneficial effects of nitrate of soda 
 appear to be almost entirely confined to the grasses and 
 cereals. At least experience here has shewn that it pro- 
 duces little or no effect on clover ; and one fanner has 
 stated, that having recently adopted the practice of sowing 
 clover with a very small proportion of rye-grass only, he 
 
COMPOSITION OP MINERAL MANURES. 231 
 
 has been led to abandon the use of nitrate of soda, which 
 he formerly employed abundantly, when ryegrass formed a 
 principal part of his crop. The action of nitrate of soda is 
 very remarkable, not only in this respect, but also because 
 a given quantity of nitrogen in it appears to produce a 
 greater effect than the same quantity in sulphate of ammonia 
 or gaano. At the same time this statement must be taken 
 as very general, definite experiments being still too few 
 to admit of its being stated as an absolute fact. The pro- 
 bability is, that the same quantity of nitrogen, in the form 
 either of ammonia or nitrate of soda, will produce the same 
 effect, although the conditions necessary for its successful 
 action may not be the same with the two manures. It is 
 alleged that nitrate of soda is advantageously conjoined 
 with common salt, which is said to check its tendency to 
 make the grain crops run to straw, and to prevent their 
 lodging, as they are apt to do, when it is employed 
 alone. But considerable difference of opinion exists in this 
 point, many farmers believing that salt produces no effect. 
 When employed for hay, especially when mixed with clover, 
 it is advisable to use it along with an equal quantity of 
 sulphate of ammonia, which gives a better result than 
 either separately. 
 
 Salts of Potash and Soda. — The substances just men- 
 tioned must be considered to owe their chief manurial 
 value to nitric acid; but other salts have been used as 
 manures in which the effect is undoubtedly due to the alka- 
 lies themselves. With the exception of common salt, most 
 of the alkaline salts have only been used to a limited extent; 
 and it is remarkable that, so far as our present experience 
 goes, there is no class of substances from which more un- 
 certain results are obtained. 
 
 Muriate and Sulphate of Potash have both been used. 
 
232 AGEICULTURAL CHEMISTEY. 
 
 and the former has in some cases, and in particular seasons, " 
 produced a very remarkable effect in the potato ; but in 
 other instances it has proved quite useless. The cause of 
 this difference has not been ascertained. Sulphate of soda 
 has also been used to some extent, but apparently without 
 much benefit ; and there is no reason to expect that it should 
 act better than common salt, which can be obtained at a 
 much lower price. 
 
 Chloride of Sodium, or Common Salt, has at different 
 times been employed as a manure, but its effects are so 
 variable and uncertain, that its use, in place of increasing, 
 has of late years rather diminished, it having frequently 
 been found that on soils in all respects similar, or even 
 on the same soil, in different years, it sometimes proves 
 advantageous, at others positively injurious. Its use as an 
 addition to nitrate of soda has been already alluded to, 
 and it is said that it produces the same effect when mixed 
 with guano and salts of ammonia. The accuracy of this 
 statement is doubted by many persons, and the explanation 
 which has been given of the cause of its action is more than 
 dubious. It is supposed to enable the plant to absorb more 
 silica from the soil ; but this is a speculative explanation 
 of its action, and has not been supported by definite 
 experiment. Although little effect has been observed from 
 salt, it deserves a more accurate investigation, as not with- 
 standing the extent to which it has been employed, we are 
 singularly deficient in definite experiments with it. 
 
 Carbonates of Potash and Soda have only been tried 
 experimentally, and that to a small extent, nor is it likely 
 that they will ever come into use, owing to their high 
 price. The remarks we have made in the section on the 
 ashes of plants regarding the subordinate value of soda, 
 will enable the reader to see that greater effects are to be 
 
COMPOSITION OF MINEEAL MANUBBS. 233 
 
 anticipated from the former than from the latter of these 
 salts. They may, however, exert a chemical action on the 
 soil, altogether independent of their absorption by the plant, 
 but its nature and amount are still to determine. 
 
 Silicates of Potash and Soda have been employed with 
 the view of supplying silica to the plant, but the results 
 have been far from satisfactory. This may perhaps have 
 been due to the doubtful nature of the commercial article, 
 but now that silicate of soda can be obtained of good quality, 
 it is desirable that the experiments should be repeated. 
 It is said to have produced good effects on the potato. 
 
 Sulphate of Magnesia can be obtained at a low cost, 
 and has been used as a manure in some instances with 
 very marked success. It has been chiefly applied as a top- 
 dressing to clover hay, but it seems probable that it might 
 prove a useful application to the cereals, the ash of which 
 is peculiarly rich in magnesia. 
 
 Many other saline substances have been tried as man- 
 ures ; but in most instances on too limited a scale to permit 
 any definite conclusions as to their value. The experi- 
 ments have also been too frequently performed without 
 the precautions necessary to exclude fallacy, so that the 
 results already arrived at must not be accepted as esta- 
 blished facts, but rather as indications of the direction in 
 which further investigation would be valuable. There is 
 little doubt that many of these substances might be usefully 
 employed, if the conditions necessary for their successfril 
 application were eliminated ; and no subject is at present 
 more deserving of elucidation by careful and well-devised 
 field experiments. 
 
 Phosphate of Lime. — The use of bones in their natural 
 state as a manure has been already adverted- to, and it 
 was stated, that though their value depended mainly on 
 
234 
 
 ASEICCLTUKAL CHEMISTRY. 
 
 the phosphates, the animal matters and other sntstances 
 contained in them were not without effect. The action of 
 phosphates is greatly promoted by solution in sulphuric 
 acid, and the application of the acid has brought into use 
 many varieties of phosphates of purely mineral origin, or 
 which have been deprived of their organic matters by artifi- 
 cial processes. Of these, the spent animal charcoal of 
 the sugar-refiners, usually containing about 70 per cent 
 of phosphates, and South American bone ash, are the most 
 important. The latter is now imported in very large 
 quantity, and has the composition shewn in the following 
 analyses : — 
 
 I. 
 
 610 
 
 5-05 
 79-20 
 
 4-05 
 
 0-15 
 
 5-45 
 
 Water 
 Charcoal 
 Phosphates 
 Carbonate of lime 
 Alkaline salts 
 Sand . 
 
 100-00 
 
 II. 
 
 III. 
 
 6-28 
 
 3-03 
 
 2-19 
 
 2-02 
 
 71-10 
 
 88-55 
 
 3-55 
 
 5-60 
 
 traces 
 
 ... 
 
 16-90 
 
 0-80 
 
 100-00 
 
 100-00 
 
 Bone ash has hitherto been almost entirely consumed as 
 a raw material for the manufacture of superphosphates ; 
 but as it is sold at from £4 : 10s. to £5 : 10s. per ton when 
 containing 70 per cent of phosphates, it is, in reality, a 
 very cheap source of these substances, and merits the atten- 
 tion of the farmer as an application in its ordinary state. 
 
 Of strictly mineral phosphates, a considerable variety 
 is now in use, but they are employed exclusively ia the 
 manufacture of superphosphates, as in their natural state 
 they are so hard and insoluble, that the plant is incapable 
 of availing itself of them. 
 
COMPOSITION OP MINERAL MANURES. 
 
 235 
 
 Coprolites. — This_ name was originally applied by Dr. 
 Buckland to substances found in many geological strata, 
 and which he believed to be the dung of fossil animals. 
 It has since been given to phosphatic concretions found 
 chiefly in the greensand in Suffolk and Cambridgeshire, 
 which are certainly not the same as those described by 
 Dr. Buckland, but consist of fragments of bones, ammonites, 
 and other fossils. Coprolites are now collected in very 
 large quantities, and about 43,000 tons are annually em- 
 ployed. They are extremely hard, and require powerful 
 machinery to reduce them to powder, and hence their price 
 is considerable, being about £2 : 10s. per ton. Their 
 composition varies somewhat according to the care taken 
 in selecting them, and the locality from which they have 
 been obtained. A general idea of their composition may 
 be derived from the subjoined analyses : — 
 
 Water 
 
 1-95 
 
 1-90 
 
 Organic matter 
 
 2-59 
 
 6-85 
 
 Phosphate of lime 
 
 55-21 ■> 
 3-84 J 
 
 6115 
 
 Phosphate of iron 
 
 Carbonate of lime 
 
 26-70 
 
 16-20 
 
 Sulphate of lime 
 
 1-97 
 
 »J 
 
 Alkaline salts 
 
 1-85 
 
 3-21 
 
 Sand . 
 
 5-89 
 
 11-65 
 
 100-00 
 
 100-00 
 
 Within the last two or three years, coprolites have 
 been found in great abundance in France, but they are of 
 inferior quality, and rarely contain more than 40 per cent 
 of phosphates. 
 
 Apatite, or mineral phosphate of lime, is found in 
 
236 AGRICULTUEAL CHEMISTRY. 
 
 large deposits in dififerent places. It is particularly abun- 
 dant in Spain, and occurs also in America and Norway. 
 From the latter country it has been imported to some ex- 
 tent ; and during the last year considerable quantities 
 have been brought from Spain, and the importations will 
 undoubtedly increase very largely as the means of trans- 
 port improve in that country. Spanish apatite contains — 
 
 Water . 
 
 0-80 
 
 Phosphate of lime 
 
 93-30 
 
 Carbonate of lime 
 
 0-50 
 
 Chlorine, etc. 
 
 traces 
 
 Sand . 
 
 4-70 
 
 99-30 
 
 Several other varieties of mineral phosphates have 
 been imported under the name of guano. The most im- 
 portant is Sombrero Island guano, which is found on a 
 small island in the Gulf of Mexico, where it occurs in a 
 layer said to be forty feet thick. It contains — 
 
 Water 
 
 , 
 
 8-96 
 
 Phosphate of lime 
 
 , 
 
 37-71 
 
 Phosphates of alumina 
 
 and iron 
 
 44-21 
 
 Phosphate of magnesia 
 
 . 
 
 4-20 
 
 Sulphate of lime 
 
 
 0-86 
 
 Carbonate of lime 
 
 
 3-36 
 
 Sand 
 
 • 
 
 0-70 
 
 100-00 
 A somewhat similar substance, but in hard crnsts, 
 
COMPOSITION OP MINERAL MANURES. 
 
 237 
 
 has been imported, under the names of Maracaybo guano, 
 Pyroguanite, etc., which contains — 
 
 Water 
 
 Organic matter 
 Phosphates 
 Alkaline salts 
 Sand 
 
 Phosphoric acid in the alkaline "> 
 salts = 1"68 phosphate of lime j 
 
 103 
 6-78 
 
 75-69 
 4-91 
 
 11-64 
 
 100-00 
 0-78 
 
 These substances are all excellent sources of phos- 
 phates, but they are so hard that the plants cannot ex- 
 tract phosphoric acid from them, and they are only useful 
 when made soluble by chemical processes. 
 
 Superphosphate; Dissolved Bones. — These names were 
 at first applied to bones which had been treated with 
 sulphuric acid ; but superphosphates are now rarely made 
 from bones alone, but bone ash and some of the mineral 
 phosphates just described are employed, either along with 
 them, or very frequently alone. The manufacture of 
 superphosphates depends on the existence of two different 
 compounds of phosphoric acid and lime, one of which con- 
 tains three times as much lime as the other. That which 
 contains the larger quantity of lime is found in the bones 
 and all other natural phosphates, and is quite insoluble 
 in water ; but when two-thirds of its lime are removed, 
 it is converted into the other compound, which is exceed- 
 ingly soluble. This change is effected by the use of 
 sulphuric acid, which combines with two-thirds of the 
 lime of the ordinary insoluble phosphate of lime, and con- 
 verts it into the hiphosphate of lime, which is soluble. 
 
238 AGRICULTURAL CHEMISTRY. 
 
 When, therefore, we add to 100 lbs. of common phosphate 
 of lime the necessary quantity of sulphuric acid, it yields 
 64 lbs. of biphosphate, containing the whole of the phos- 
 phoric acid, which is the valuable constituent, the diminu- 
 tion in weight being due to the removal of the valueless 
 lime. Hence it follows, also, that as the lime so removed 
 is converted into sulphate, there must, for every 100 lbs. 
 of phosphate of lime converted into biphosphate, be pro- 
 duced 87 lbs. of dry sulphate of lime, or 110 of the 
 ordinary sulphate called gypsum. This is the minimum 
 quantity which can be present, but in actual practice it is 
 liable to be greatly exceeded, more especially where cop- 
 rolites are used, owing to the large amount of carbonate 
 of lime they contain, which is also converted into sulphate 
 by the action of the acid, so that it is far from uncommon 
 to find the gypsum twice as great as it would be if materials 
 free from carbonates could be obtained. By employing a 
 sufficiency of sulphuric acid, the whole quantity of phos- 
 phoric acid in the bones may be thus brought into a soluble 
 state, but in actual practice it is found preferable to leave 
 part of it in the insoluble condition ; as where it is entirely 
 soluble, its effect is too great during the early part of the 
 season, and deficient at its end. In order to dissolve 
 bones, bone ash, or mineral phosphates, they are mixed 
 with from a third to half their weight of sulphuric acid, 
 of specific gravity 1 70 or 1 40° Twaddell. When mine- 
 ral phosphates, and particularly coprolites, are used, the 
 quantity of sulphuric acid must be increased so as to 
 compensate for the loss of that which is consumed in de- 
 composing the carbonate of lime they contain. When 
 operating on the small scale, the materials are put into a 
 vessel of wood, stone, or lead (iron is to be avoided, as it 
 is rapidly corroded by the acid), and mixed with from a 
 
COMPOSITION OF MINERAL MANURES. 239 
 
 sixth to a fourtli of their weight of water, which may 
 with advantage be used hot. The sulphuric acid is then 
 added, and mixed as uniformly as possible with the bones. 
 Considerable effervescence takes place, and the mass be- 
 comes extremely hot. At the end of two or three days 
 it is turned over with the spade, and after standing for 
 some days longer, generally becomes pretty dry. Should 
 it still be too moist to be sown, it must be again turned 
 over, and mixed with some dry substance to absorb the 
 moisture. For this purpose everything containing lime 
 or its carbonate must be carefully avoided, as they bring 
 back the phosphates into the insoluble state, and undo 
 what the sulphuric acid has done. Peat, sawdust, sand, 
 decaying leaves, or similar substances, will answer the 
 purpose, and they should all be made thoroughly dry 
 before being used. An excellent plan is to sift the bones 
 before dissolving, to apply the acid to the coarser part, and 
 afterwards to mix in the fine dust which has passed through 
 the sieve, to dry up the mass ; or a small quantity of bone 
 ash, of good quality, or Peruvian guano, may be Hsed, 
 On the large scale, mechanical arrangements are employed 
 for mixing the materials, so as to economise labour, and 
 mineral phosphates, such as apatite, can then be used 
 with advantage. In such cases, blood, sulphate of am- 
 monia, soot, and other refuse matters, are occasionally 
 used to supply the requisite quantity of nitrogenous sub- 
 stances, but large quantities are also made from bone ash, 
 etc., without these additions. 
 
 The composition of superphosphates must necessarily 
 vary to a great extent, and depends not only on the 
 materials, but on the proportion of acid used for solution. 
 The following analysis illustrates the composition of good 
 samples made from different substances — 
 
240 
 
 AGRICULTURAL CHEMISTRY. 
 
 o 
 
 1.11 
 
 11 
 
 t> t>CCO"Ol>CDO 
 1-1 iM '-^ "<t 
 
 o >o 
 o »o 
 
 o ^ 
 
 o 
 
 O CO 
 O IN 
 
 DQ 
 
 S 
 o 
 
 1 
 
 o 
 
 *-< ■r-i cq • CD 
 
 1-t W T-i O 
 
 o S 
 
 g ^ 
 
 o 
 
 O (N CT) C? 00 CO O 
 ■^ OS O O O t- M 
 
 o Tt* « o OD r- -^ 
 
 i-H (M CO •<** . 
 
 — (1) 
 
 1 :;: = !§: 
 
 CO '*IOCO(MCD*^CO 
 CY3 a» CO CO Oi «-! c^ 
 
 lb <i5 1^ CO »b <i> -^ 
 
 (N CO, "^ 
 
 O CO 
 
 1 ^ 
 
 O CO 
 O (N 
 
 O O 
 
 o 
 
 c 
 o 
 
 g 
 
 t- tDOOcOT-MOiO 
 
 t- '^dsici'-*»boco 
 01 _. ca CO 
 
 -* COQOt^-HOCOOO 
 t- cp -^ ic cfi <p 'f -^ 
 
 C r»COoO(LOrHCO 
 — < ^ (M i-H ■* 
 
 o ^ 
 
 o o 
 
 O CO 
 
 o 
 
 O CI 
 
 o 
 
 
 Water-, .... 
 Organic matters and ammoniacal 
 
 salts, 
 Biphosphate of lime. 
 Equivalent to soluble phosphates. 
 Insoluble phosphates, . 
 Sulphate of lime, 
 Alkaline salts. 
 Sand, 
 
 Ammonia, 
 
COMPOSITION OF MINEEAL MANURES. 241 
 
 Superphosphates made from bones alone are generally 
 distinguished by a large quantity of ammonia, and a rather 
 low per centage of biphosphate of lime. This is oWing to 
 the difficulty experienced in making the acid react in a 
 satisfactory manner on bones, the phosphates being pro- 
 tected from its action by the large quantity of animal 
 matter which, when moistened, swells up, fills the pores, 
 and prevents the ready access of the acid to the interior 
 of the fragments. Superphosphates from bone-ash, on 
 the other hand, contain a mere trifle of ammonia, and 
 when well made a very large quantity of biphosphate 
 of lime. Their quality differs very greatly, and depends, of 
 course, on that of the bone-ash employed, which can rarely 
 be obtained of quality sufficient to yield more than 30 or 
 35 per cent of soluble phosphates. Coprolites are seldom 
 used alone for the manufacture of superphosphates, but are 
 generally mixed with bone-ash and bone dust. Mixtures 
 containing salts of ammonia, flesh, blood, etc., are also 
 largely manufactpred, and some are now produced con- 
 taining as much as four or five per cent of ammonia, and 
 the consumption of such articles is largely increasing. 
 
 The analyses above given are all those of good super- 
 phosphates, in which abundance of acid has been used so 
 as to convert a large proportion of insoluble into soluble 
 phosphates; but there are many samples of very inferior 
 quality to be met with in the market, in which the pro- 
 portion of acid has been reduced, and the quantity of phos- 
 phates made soluble is consequently much lower than it 
 ought to be. The following analyses illustrate the com- 
 position of such manures, which are all very inferior 
 and generally worth much less than the price asked for 
 them. 
 
242 
 
 AGRICULTURAL CHEMISTRY. 
 
 Water 
 
 21-60 
 
 5-37 
 
 7-19 
 
 Organic matter and am- 
 
 
 
 
 moniacal salts, 
 
 11-62 
 
 13-91 
 
 8-80 
 
 Biphosphate of lime 
 
 298 
 
 2-02 
 
 6-42 
 
 Equivalent to soluble . 
 
 
 
 
 phosphates 
 
 (4-65) 
 
 (315) 
 
 (10-02) 
 
 Insoluble phosphates 
 
 25-70 
 
 15-80 
 
 14-03 
 
 Sulphate of lime 
 
 23-66 
 
 47-52 
 
 51-93 
 
 Alkaline salts 
 
 10-70 
 
 3-73 
 
 3-43 
 
 Sand 
 
 3-80 
 
 11-65 
 
 8-20 
 
 
 100-00 
 
 10000 
 
 100-00 
 
 Ammonia, 
 
 1-32 
 
 0-59 
 
 0-33 
 
 The deliberate adulteration of superphosphate, that 
 is, the addition to it of sand or similar worthless materials, 
 I believe to be but little practised. The most common 
 fraud consists in selling as pure dissolved bones, articles 
 made in part, and sometimes almost entirely, from copro- 
 lites. Occasionally refuse matters are used, but less with 
 the intention of actually diminishing the valne of the 
 manure as for the purpose of acting as driers. It is said 
 that sulphate of lime is sometimes employed for this pur- 
 pose, but this is rarely done, because that substance is 
 always a necessary constituent of superphosphate in very 
 large quantities ; and as farmers look upon it with 
 great suspicion, all the efforts of the manufacturers are 
 directed towards reducing its quantity as much as possible. 
 It is very commonly supposed by farmers that the sulphate 
 of lime found in so large quantity in all superphosphates, 
 and often amounting to as much as fifty per cent, has been 
 added to the materials in the process of manufacture, but 
 this is a mistake ; it is a necessary and inevitable product 
 of the chemical action by which the phosphates are ran- 
 
COMPOSITION OP MINERAL MANURES. 243 
 
 dered soluble, although its quantity depends on the mate- 
 rials from which the manure is made. When pure bones 
 are used its quantity is small, and it does not greatly exceed 
 twice that of the biphosphate of lime ; but in a manure 
 made from coprolites, or other substances containing a 
 large proportion of carbonate of lime, which must in the 
 process of manufacture be converted into sulphate, it may 
 be four or five times as much. 
 
 Although there is no manure which varies more in 
 quality, or requires greater vigilance on the part of the 
 purchaser, in order to obtain a good article, there is no 
 doubt that superphosphates, owing to the process of manu- 
 facture being better understood, and to increased competi- 
 tion, have considerably improved in quality. Six or eight 
 years since a manure containing thirty per cent of phos- 
 phates, of which twelve or fifteen had been converted into 
 biphosphate, was considered a fair sample, but now the 
 proportion rendered soluble is greatly increased ; and 
 where bone ash alone is employed, as much as thirty and 
 even forty per cent of soluble phosphates is occasionally 
 found. This, of course, is an exceptional case, and great 
 attention and care in the selection of materials are necessary 
 to obtain so large a proportion. The analyses already 
 given will shew the farmer what he has to expect in good 
 superphosphates, but it is very necessary that he should 
 take care to obtain from the manufacturer a manure equal 
 to the guarantee ; and he ought to bear in mind that, 
 owing to the difficulty of getting materials of constant com- 
 position, variations often take place to a considerable 
 extent in manures which are supposed to be made in ex- 
 actly the same manner. 
 
 Phospho-Peruvian Guano. — Under this name a kind 
 of superphosphate, which is understood to be made by 
 
244 
 
 AGRICULTURAL CHEMISTRY. 
 
 9-54 
 
 . 21-38 
 
 . 16-81 
 
 . 10-88 
 
 . 37-21 
 
 . 2-22 
 
 . 1-81 
 
 100-00 
 
 3-50 
 
 dissolving a native " rock guano," has recently attracted 
 
 considerable attention, and is used to a large extent. Its 
 
 composition is — 
 
 Water 
 
 Organic matter 
 
 Biphosphate of lime, equivalent to 25-22 soluble 
 
 phosphates 
 Insoluble phosphates 
 Sulphate of lime 
 Alkaline salts, containing 1-32 of phosphoric acid, 
 
 and equivalent to 2-86 soluble phosphates 
 Sand .... 
 
 Ammonia, 
 
 It is chiefly distinguished by the large proportion of 
 valuable ingredients it contains, and the care taken to 
 secure uniformity of composition. 
 
 A variety of substances are sold under the name of 
 nitTophosphate, potato manure, cereal manure, etc. etc. 
 which are all superphosphates, differing only in the pro- 
 portion of their ingredients, and in the addition of small 
 quantities of alkaline salts, sulphate of magnesia, and other 
 substances, but they present little difference from ordinary 
 superphosphates in their effects. 
 
 The use of superphosphate has greatly extended of late 
 j-ears, and its consumption has increased in a greatly more 
 rapid ratio than that of guano or any other manure. 
 Ten or twelve years since it was comparatively little known, 
 but it has now come to be used in many cases in which 
 Peruvian guano was formerly employed. It produces a 
 better effect than that manure on light soils, although in 
 general a mixture of the two answers better than either 
 
COMPOSITION OF MINERAL MANURHS. 245 
 
 separately. When Peruvian guano is to be applied along 
 with it, 'the farmer will naturally select a superphosphate 
 made from bone ash, and containing the largest obtainable 
 quantity of soluble phosphates ; but when it is to be used 
 alone, it is advisable to take one made from bones, or at all 
 events one containing a considerable quantity of nitrogenous 
 matter or ammonia. The kind to be selected must, how- 
 ever, be greatly dependent on the particular soil, and the 
 situation in which it is to be used. 
 
 Lime. — Lime is by far the most important of the mine- 
 ral manures, and an almost indispensable agent of agri- 
 cultural improvement. It has been used as chalk, marl, 
 shell and coral sand, ground limestcme, and as quick and 
 slaked lime, and its action varies according as it is applied 
 in any of its natural forms, or after being burnt. In all 
 of its native forms the lime is combined with carbonic 
 acid in the proportion of fifty-six parts of lime to forty- 
 four of carbonic acid, and the carbonate is generally mixed 
 with variable quantities of earthy ingredients, which in 
 some instances are important additions to it, and affect its 
 utility as a manure. 
 
 Chalk is a very pure form of carbonate of lime, and 
 where it abounds has been largely employed as an appli- 
 cation on the soil. It is dug out of pits and exposed to 
 the action of the winter's frost, by which it is thoroughly 
 disintegrated, and in spring it is applied in quantities, 
 which, in many instances, are only limited by the question 
 of cost. 
 
 Marl is a name given to a mixture of finely-divided 
 carbonate of lime, with variable proportions of clay and 
 siliceous matters, which is found at the bottom of valleys 
 and in hollow places in beds often of considerable extent 
 and thickness, where it is deposited from the waters of 
 
246 
 
 AGRICULTUEAL CHEMISTEY. 
 
 lakes holding lime in solution, fed by streams passing over 
 limestone, or rocks rich in lime. The composition of marls 
 differs greatly in different districts, and they have been 
 divided into true marls, and clay marls, according as the 
 carbonate of lime or clay is the preponderating ingredient. 
 The following table illustrates the composition of different 
 varieties : — 
 
 
 Barbadoes. 
 
 Luneburg, 
 
 Ayrshire, 
 
 Wesermarsh. 
 
 Carbonate of lime 
 
 93-2 
 
 85-4 
 
 8-4 
 
 8-2 
 
 Carbooate of magnesia 
 
 
 1-3 
 
 
 30 
 
 Sulphate of lime 
 
 
 01 
 
 
 0-5 
 
 Phosphate of lime 
 
 01 
 
 2-3 
 
 
 1-2 
 
 Aluminaand oxide of iron 
 
 1-6 
 
 4-6 
 
 2-2 
 
 7-2 
 
 Alkaline salts 
 
 ... 
 
 01 
 
 
 10 
 
 Silica and clay 
 
 4-6 
 
 5-6 
 
 84-9 
 
 789 
 
 Organic matter 
 
 0-5 
 
 0-6 
 
 2-8 
 
 
 Water 
 
 
 
 1-4 
 
 
 
 100-00 
 
 100-00 
 
 99-7 
 
 10000 
 
 The true marls, that is those in -which carbonate of 
 lime abounds, are greatly preferable to clay marls, the 
 latter, indeed, operate chiefly mechanically, by altering 
 the texture of the soil — the lime they contain being fre- 
 quently too small to exercise much appreciable effect. 
 
 Shell and coral sands consist chiefly of fragments of 
 shells and coral disintegrated by the action of the waves, 
 and mixed with more or less siliceons sand, and contain- 
 ing small quantities of phosphate of lime. They occur to 
 a considerable extent both on our own coasts and those of 
 France, and have been used with good effect on some 
 descriptions of soil. 
 
 The general composition of limestones has been already 
 
COMPOSITION OF MINERAL MANURES. 247 
 
 adverted to, when treating of the origin of soils, and a 
 distinction drawn between the common limestones and 
 dolomite or magnesian limestone. Few limestones can 
 be considered as even approaching to purity, and they 
 almost all contain a small quantity of carbonate of mag- 
 nesia as well as earthy matters, and occasionally a little 
 phosphate of lime. In good specimens the quantities of 
 these substances are generally small, and they usually 
 contain about half their weight of lime. When lime- 
 stone is burnt in the kiln, the change which ensues con- 
 sists in the expulsion of the carbonic acid, and the conse- 
 quent conversion of the lime into the uncombined or quick 
 state. If water be thrown upon it when in this condi- 
 tion, it becomes hot, swells up, and falls to a fine soft 
 powder, and has then entered into combination with 
 water. If it be exposed to the air, the same action takes 
 place, although, of course, more slowly; and if it be left 
 for a sufficient time, it at length absorbs carbonic acid,' 
 and reverts to its original form of carbonate of lime, 
 although now in a state of very fine division. 
 
 While lime may be applied in the state of carbonate, 
 either as chalk, marl, or pounded limestone, and with a 
 certain amount of advantage, much greater effects are 
 obtained from the use of lime itself in the quick or slaked 
 state. These advantages are dependent partly on the 
 mechanical effect of the burning and slaking, which 
 enable us to reduce the lime to a much more minute 
 state of division, and consequently to incorporate it more 
 uniformly and thoroughly with the soil, and partly on the 
 more powerful chemical action which it exists when in 
 the quick or caustic state. Other minor advantages are 
 also secured, such as the production of a certain quantity 
 of sulphate of lime, produced by the oxidation of the sul- 
 
248 AGRICULTURAL CHEMISTRY. 
 
 phnr of the coal used in burning, etc., which, though 
 comparatively trifling, may, under particular circumstances 
 and in some soils, be of considerable importance. 
 
 The action of lime is of a complicated character. 
 Where the soil is deficient in lime, it must necessarily 
 act by supplying that substance to the plants growing 
 in it. But this is manifestly a very subordinate part of 
 its action, — 1st, Because no soil exists which does not 
 contain lime in sufficient quantity to supply that element 
 to the plants. 2d, Because its effects are not restricted to 
 those soils in which it exists naturally in small quantity ; 
 and, 3d, Because it is found that a small application, such 
 as would suffice for the wants of the crops, is not sufficient 
 to produce its best effects. 
 
 It is a familiar fact that the quantity of lime applied 
 to the soil for agricultural purposes is very large, as much 
 as ten, and even twenty tons per acre having been used, 
 while the smallest application is exceedingly large when 
 compared with the mere requirements of the crops. Of 
 late years the very large applications once in use have 
 become less common, as it has been found preferable to 
 employ smaller doses more frequently repeated. The 
 quantity used depends, however, to a great extent, on the 
 nature and condition of the soil, heavy clays, especially 
 if undrained, and soils of a peaty nature, requiring a large 
 application ; while on well drained and light soils a 
 smaller quantity suffices. Thin soils also require only a 
 small application. The geological origin of the soil is 
 also not without its influence, and its beneficial effect is 
 peculiarly seen on granite, porphyry, and gneiss soils, 
 both because these are naturally deficient in lime, and 
 because the decompositions by which their valuable con- 
 stituents are liberated take place with extreme slowness. 
 
COMPOSITION OF MINEEAL MANURES. 249 
 
 The greater part of the action of lime is unquestion- 
 ably dependent on its exerting a chemical decomposition 
 on the soil ; and it acts equally on both the great divi- 
 sions of its constituents, the inorganic and the organic. 
 On the former, it operates by decomposing the silicates, 
 which form the main part of the soil, and the alkalies 
 they contain being thus set free, a larger supply becomes 
 available to the plant. On the organic constituents its 
 effects are principally expended in promoting the decom- 
 position which converts their nitrogen into ammonia; 
 and thus a supply of food, which might remain for a long 
 period locked up, is set free in a state in which the plant 
 can at once absorb it. But these chemical decompositions 
 are attended by a corresponding change in the mechanicar 
 characters of the soil. Heavy clays are observed to be- 
 come lighter and more open in their texture; and those 
 which are too rich in organic matter have it rapidly re- 
 duced in quantity, and the excessive lightness which it 
 occasions diminished. 
 
 The effects of an application of lime are not generally 
 observed immediately, but become apparent in the course 
 of one or two years, when it has had time to exert its 
 chemical influence on the soil ; but from that time its 
 effects are seen gradually to diminish and finally to cease 
 entirely. The period within which this occurs necessarily 
 varies with the amount of the application and the nature 
 of the soil, but it may be said generally that lime will 
 last from ten to fifteen years. The cessation of its effects 
 is due to several circumstances, partly of course to the 
 absoi-ption of lime by the plants, partly to its being 
 washed out of the soil by the rains, and partly to its 
 tendency to sink to a lower level, a tendency which most 
 practical men have had opportunities of observing. In 
 
250 AGRICULTURAL CHEMISTRY. 
 
 the latter case, deep-ploughing often produces a marked 
 effect, and sometimes makes it possible to postpone for a 
 year or two the reapplication of lime. All these cir- ■ 
 cumstances have their influence in bringing its action 
 to an end, but the most important is, that after a time it 
 has exhausted its decomposing effect on the soil, having 
 destroyed all the organic matter, or liberated all the in- 
 soluble mineral substances which the quantity added is 
 competent to do, and so the soil passes back to its old 
 state. It does even more, for unless active measures are- 
 taken to sustain it by other means, it is found that the 
 fertility of the soil is apt to become less than it was before 
 the use of lime. And that it should be so is manifest, if 
 we consider that the lime added has liberated a quantity 
 of inorganic matter, which, in the natural state of the 
 soil, would have become slowly available to the plant, 
 and that it must have acted chiefly in those very por- 
 tions which, from having already undergone a partial 
 decomposition, were ready to pass into a state fitted for 
 absorption, and thus as it were must have anticipated the 
 supplies of future years. This effect has been frequently 
 observed by farmers, and is indeed so common, that it has 
 passed into a proverbial saying, that " lime enriches the 
 fathers and impoverishes the sons." But this is true 
 only when the soil is stinted of other manures, for when 
 it is well manured the exhausting effect of lime is not 
 observed ; and it must be laid down as a piactical rule, 
 that its use necessitates a liberal treatment of the soil in 
 all other respects. But when lime has been once em- 
 ployed it becomes almost necessary to resort to it again ; 
 and generally so soon as its effects are exhausted a new 
 quantity is applied, not so large as that which is used 
 when the soil is first limed, but still considerable. When 
 
COMPOSITION OP MINERAL MANURES. 251 
 
 this is done very frequently, however, bad effects ensue; 
 tlie soil gets into a particular state, in which it is so open 
 that the grain crops become uncertain, and such land is 
 said, in practical language, to be overlimed. The ex- 
 planation of this state of matters commonly assumed by 
 those unacquainted with chemistry is, that the land has 
 become too full of lime; but a moment's consideration of 
 the very small fraction of the soil which even the largest 
 application of lime forms, will serve to shew that this can- 
 not be the cause. Ten tons of lime per acre amounts to only 
 one per cent of the soil, and as a considerable part of the 
 lime is carried off by drainage in the course of years, it 
 is obvious that even very large and frequently repeated 
 doses are not likely to produce any great accumulation of 
 that substance. In point of fact, analyses of overlimed 
 soils have proved that the lime does not exceed the 
 ordinary quantity found in fertile land. The explanation 
 of the phenomenon is probably to be found in the rapid 
 decomposition of organic matter by the lime, and its 
 escape as carbonic acid, by which the soil is left in that 
 curious porous condition so well known in practice. The 
 cure for overliming is found to be the employment of 
 such means as consolidate the soil, such as eating off with 
 sheep, rolling, or laying down to permanent pasture. 
 
 The immediate effect of lime on the vegetation of the 
 land to which it is applied is very striking. It imme- 
 diately destroys all sorts of moss, makes a tender herbage 
 spring up, and eradicates a number of weeds. It im- 
 proves the quantity and quality of most crops, and causes 
 them to arrive more rapidly at maturity. The extent to 
 which it produces these effects is dependent on the form in 
 which it is applied. When the lime is used hot, that is, imme- 
 diately after it has been slaked, they are produced most 
 
252 AGRICULTURAL CHEMISTRY. 
 
 rapidly and effectually; but if it has been so long exposed to 
 the air as to absorb much of the carbonic acid it lost in 
 burning, and has got into what is commonly called the mild 
 state, it operates more slowly ; and when it is applied as 
 chalk, marl, or pounded limestone, its action is still more 
 tardy. Various circumstances, which must depend upon 
 very different considerations, must necessarily influence the 
 farmer in the selection of one or other of these different 
 forms of lime ; but on the whole, it will be found that the 
 greatest advantages are on the side of the well-burned and 
 freshly slaked lime. The consideration of all the mimitise 
 to be attended to, however, would carry us far beyond the 
 limits of this work, and trench to some extent on the 
 subject of practical agriculture. 
 
 Various kinds of refuse matters containing lime have 
 been used in agriculture, but they are generally inferior 
 to good lime, and not generally mor^ economical. The 
 most important of these is gas lime, or lime which has 
 been used for purifying coal gas. In going through this 
 process it absorbs carbonic acid from the gas, and conse- 
 quently passes back, more or less, completely into the form 
 of carbonate of lime. But it also takes up siilphur, which 
 remains in it in the form of sulphuret of calcium. It is 
 well known that all sulphurets are prejudicial to vege- 
 table life, and hence, when fresh gas lime is used, its 
 effects are often injurious rather than beneficial. But if 
 it be exposed for some time to the air, oxygen is absorbed, 
 the sulphur is converted into sulphuric acid, gypsum is 
 produced to the extent of some per cent, and the lime 
 then becomes innocuous. When composted with dry 
 soil, the admission of air into the interior of the lime is 
 facilitated, and this change takes place with greater 
 rapidity. The waste lime from bleach-works, tanneries, 
 
COMPOSITION OF MINERAL MANURES. 253 
 
 and other manufactories, is occasionally used hy farmers ; 
 but unless obtained at a nominal price, it cannot com- 
 pete with good quick lime, owing to the large amount of 
 water it contains, and the consequent increase in the cost 
 of carriage. 
 
 Sulphate of Lime or Gypsum. — Gypsum has been ex- 
 tensively used as a manure, and is found to exert a very 
 remarkable influence upon clover, and leguminous crops 
 generally. It is employed in quantities varying from two 
 cwt. per acre up to a very large quantity, and almost in- 
 variably with good results, in some instances even with the 
 production of double crops. Much speculation has taken 
 place as to the cause of this action which is so specific in 
 its character, and from Sir Humphrey Davy down to the 
 present time, many chemists and agriculturists have con- 
 sidered the matter. Sir Humphrey Davy attributed its 
 action to its supplying sulphur to those plants whith, ac- 
 cording to him, contain an unusually large quantity of 
 that element. That opinion has been since entertained by 
 others, but it can scarcely be considered as well founded, 
 for the more accurate experiments recently made do not 
 point to any conspicuous differences between the quantities 
 of sulphur contained in these and other plants. It is, 
 moreover, to gypsum alone that these effects are due, and 
 if it were merely as a source of sulphur that it was em- 
 ployed, there are other salts which could be equally, per- 
 haps more advantageously, used; such, for instance, as 
 sulphate of soda. Others have attributed its action to its 
 power of fixing ammonia, but this explanation is certainly 
 untenable, for the soil itself possesses this property very 
 powerfully, and it is inconceivable that the addition of a 
 few hundred weights of gypsum should have any effect in 
 promoting this action. The experiments which have been 
 
254: AGRICULTURAL CHEMISTRY. 
 
 made with gypsum leave no doubt as to its effect, more 
 especially on leguminous plants, but they do not afford an 
 explanation of its mode of action, for which further inquiT 
 ries, directed especially to that object, are required. 
 
 The application of gypsum to the soil appears to have 
 diminished of late years, and this is probably due to the 
 large consumption of superphosphates, and other manu- 
 factured manures, which contain it in abundance. In an 
 ordinary application of these substances, there are con- 
 tained from one to two hundredweight of gypsum ; and it 
 is not likely that when they have been extensively used, 
 much benefit will be derived from a further application of 
 it by itself. 
 
CHAPTEE XIT. 
 
 THE VALUATION OF MANUEES. 
 
 The determination of the value of a manure is in many 
 respects a commercial rather than a chemical question, but 
 as it must be founded on the analysis, and presents some 
 peculiarities dependent on the complicated nature of the 
 substances to be valued, it has fallen to some extent into 
 the hands of the chemist. The principle on which the 
 value of any commercial sample is estimated is very simple. 
 It is only necessary to know the price of the pure article, 
 and that of the particular sample to be valued is obtained 
 by making a deduction from this price proportionate to the 
 per centage of impurities shewn by the analysis. Thus, 
 for example, if pure sulphate of ammonia sells at £16 per 
 ton, a sample containing 10 per cent of impurities ought 
 to be purchased for j£l4 : 8s., and so on for any other 
 quantity. This system which answers perfectly with sul- 
 phate of ammonia, nitrate of soda, or any other substance 
 whose value depends on one individual element, is inap- 
 plicable in the case of complex manures, such as guano 
 and the like, in which several factors combine to make up 
 the value. In such cases, manures of very different com- 
 position may have the same value, the deficiency iii one 
 particular element being counterbalanced by the excess of 
 another. Hence it becomes necessary to obtain an esti- 
 
256 AGRICULTDEAL CHBMISTET. 
 
 mate of the value of each factor, from which that not 
 only of one particular substance, but of every possible 
 mixture may be determined. 
 
 When we come to inquire minutely into this question, it 
 appears that the commercial value of any substance is not 
 estimated solely by considerations of composition, but is 
 dependent to a great extent on questions of demand and 
 supply, and applicability to particular purposes. Thus 
 coprolites containing from 55 to 60 per cent of phosphates 
 sell at about £2 : 12s. per ton, while bone-ash containing 
 the same quantity of that ingredient brings about twice 
 as much ; in other words, phosphates are nearly twice as 
 valuable in bone-ash as in coprolites, and as a phosphatic 
 guano their price is generally still higher ; and the reason 
 for this is obvious, in bones and guano the phosphates are 
 in a high state of division, in which they are easily attacked 
 and disintegrated by the carbonic acid of the soil, and 
 rendered available to plants ; while in coprolites they are in 
 a hard and compact form, and are of little use unless they 
 have previously undergone an expensive preparation. In the 
 same way, if the market price of different kinds of guano be 
 inquired into, very great differences are found to exist in 
 the rate at which phosphates are sold, and this is attribut- 
 able in part to the fact that the price at which any article 
 is charged commercially, is such as to cover the prime cost, 
 expense of freight, and other charges, and to leave a profit 
 to the importer ; and partly, also, no doubt, to the careless- 
 ness with which manures are often purchased, and to the 
 want of careful field experiments in which the effects pro-' 
 duced by them are properly compared. It will be readily 
 understood that the state of division of any substance, the 
 readiness with which its constituents can be rendered 
 available to the plants, care of application, and many other 
 
THE VALUATION OF MANURES. 257 
 
 circumstances must influence its price ; but making due 
 allowance for these, differences are met with which appear 
 to some extent to be merely the result of caprice. It is 
 easy to understand why bone-ash should sell at double the 
 price of coprolites, but no good reason can be shewn why 
 the phosphates in one kind of guano should be sold at a 
 much higher price than another, and the difference would 
 probably disappear if greater attention were paid to the 
 results of field experiments. 
 
 However great and inexplicable these differences may 
 be, it is not the business of the valuator of a manure to 
 discuss them. On the contrary, he is bound to accept them 
 as the basis of his calculation, and to endeavour to deduce 
 from them a proper system of estimation for each substance. 
 Strictly speaking, each individual manure ought to be 
 valued according to a plan special to itself, and deduced 
 from its own standard market price ; but it is obvious that 
 this would lead to innumerable complications and defeat its 
 own ends, and hence an attempt has been made to contrive 
 a general system suited to all manures, and which, though 
 not absolutely correct, is a suEScient approximation for all 
 practical purposes, and a tolerably accurate guide to the 
 determination of their relative values. 
 
 The constituents of a manure which are of actual value 
 are ammonia, insoluble phosphates, biphosphate of lime 
 (soluble phosphates), sulphate of lime, nitric acid (as nitrate 
 of soda), potash, soda, and organic matter. These sub- 
 stances differ greatly in value. Ammonia and phosphates, 
 soluble and insoluble, are costly ; and by far the larger 
 part of the value of all guanos, and the common manufac- 
 tured manures, depends on them. Nitric acid and potash 
 are also very valuable substances, but as they are rarely 
 found in manufactured manures, and never in sufficient 
 
 s 
 
258 AGEICULTTJEAL CHBMISTET. 
 
 quantity to exert any material influence in their price, it 
 is not usual to take them into consideration except in par- 
 ticular cases. The alkali which commonly exists in arti- 
 ficial manures is soda, and when alkaline salts appear in 
 any analysis, they must be assumed to consist almost 
 entirely of that substance generally in the form of common 
 salt, and be valued accordingly. Sulphate of lime and 
 organic matter though abundant constituents of most 
 manures, add but little to their value, and it is a moot 
 point whether they ought to be taken into consideration, 
 although most persons allow a small value for them. 
 Carbonate of lime, sand, or siliceous matter, and water, of 
 course, are altogether worthless. 
 
 In order to obtain the value of a manure containing 
 several of these substances, it is necessary to ascertain the 
 average commercial price of each individually. This is 
 easily done when they are met with in commerce separately, 
 or at least mixed only with worthless substances, but some 
 of them are only found in complex mixtures, and in these 
 cases it is necessary to arrive at a result by an indirect 
 process, according to methods which will be immediately 
 explained. The question to be solved is the price actually 
 paid for a ton of each substance in a pure state, and we 
 shall proceed to consider them in succession. 
 
 InsoluWe Phosphates. — These are purchased alone, 
 chiefly in the form of coprolites and bone-ash, or the spent 
 animal charcoal of the sugar refiners. Ground coproHtes, 
 containing about 58 per cent of phosphates, sell at £2 : 12s. 
 per ton, which is at the rate of £4 : 8s. for pure phos- 
 phates. Bone-ash varies considerably in price, but of late 
 samples containing 70 per cent of phosphates have sold as 
 low as £4 : 10s. per ton, and consequently pure phosphates 
 in this form are worth £6 : 8s. per ton. Although these 
 
THE VALUATION OF MANURES. 259 
 
 are the only forms in which phosphates are purchased 
 alone, it is possible to determine the price at which they 
 are sold in bones and phosphatic guanos, by first deducting 
 the value of the ammonia they contain, and assuming the 
 remainder to represent the price paid for the phosphates. 
 In this way we find the following values for insoluble 
 phosphates : — 
 
 InCoprolites . . . £4 10 
 
 Bone-ash . . . 6 8 
 
 Bones .... 750 
 
 Phosphatic guanos . . 10 
 
 It is to be observed that these are actual prices, and they are 
 liable to fluctuate with the state of the market, although 
 they are pretty fair averages. It is important to notice 
 how much they vary in the different forms ; the farmer 
 who buys a phosphatic guano paying for phosphates a 
 much higher price than he could have obtained those for 
 in other substances — a difference which must be attributed 
 to the high state of division in which they exist in the 
 guano. We do not here enter upon the question how far 
 this difference in price is justified ; we are content with 
 the fact that it exists, and we are compelled to estimate 
 the value of phosphates in a phosphatic guano at the 
 price given above, although in Peruvian guano they 
 are sold at a lower rate. For all other manures, of 
 which bones and bone-ash form the basis, £7 may be 
 taken as a fair price, and it is that usually adopted, 
 though £8 and £10 have sometimes been assumed as 
 the average. 
 
 Ammonia is met with in commerce as muriate and 
 
260 A6EICULTURAL CHEMISTRY. 
 
 sulphate of ammonia. The former, owing to its high price, 
 is practically excluded from use as a manure ; the latter 
 sells at present at from £15 to £15 : 10s. per ton, and, 
 making allowance for the usual amount of impurity (5 or 
 6 per cent), the actual ammonia is worth about £63. per 
 ton. Calculating from other substances it appears that 
 ammonia is worth, per ton, in — 
 
 Sulphate of ammonia . . £63 
 
 Bones . . . . 61 
 
 Peruvian guano . . . 57 
 
 the average being £60, which is the price usually 
 adopted. 
 
 Sulphate of Lime and Alkaline Salts (consisting chiefly 
 of soda) are generally estimated at £1 per ton ; and potash 
 in those cases, in which it is necessary to take it into 
 account, is usually valued at from £20 to £30 per ton, 
 the former being its value in kelp, the form in which it 
 can be most cheaply purchased. 
 
 Nitrate of Soda is usually sold at from £15 to £15 : 10s. 
 per ton, and, making allowance for impurities, £16 may 
 be taken as the value of the pure salt. 
 
 Biphosphate of Lime, Soluble Phosplmtes. — Consider- 
 able difficulty is experienced in estimating the value of these 
 substances, because they are not met with in commerce 
 alone, or in any form except that of superphosphate, and 
 the prices at which they are sold in different samples of 
 that manure differ excessively. The only course by which 
 any result can be obtained, is to determine the average 
 price of a good superphosphate, and putting the values 
 already ascertained on all the other constituents to reckon 
 
THE VALUATION OF MANURES. 261 
 
 tbe difference between that sum and the market price as 
 the value of soluble phosphates. Throwing out, as 
 inferior, all samples containing less than 10 per cent of 
 soluble phosphates, and taking the good only, I find that 
 the average composition of the phosphates in the market 
 during the present year has been — 
 
 Water 
 
 10-71 
 
 Organic matter 
 
 9-33 
 
 Biphosphate of lime equivalent to 19'43 
 
 
 "soluble phosphates" 
 
 12-45 
 
 Insoluble phosphates 
 
 14-78 
 
 Sulphate of lime .... 
 
 45-24 
 
 Alkaline salts .... 
 
 2-11 
 
 Sand 
 
 5-38 
 
 
 100-00 
 
 Ammonia ..... 
 
 1-71 
 
 It is more difficult to fix the average price of superphos- 
 phate, as in many cases no information could be obtained on 
 this point ; but among those analyzed were samples at all 
 prices, from £7 up to £10 : 10s. per ton, so that on the whole, 
 £8 may be assumed as an average, and in that case soluble 
 phosphates are worth, £27 : 19s. per ton. Had the inferior 
 samples been included, the price would have been higher, 
 and in fact the rate at which soluble phosphates have 
 been commonly estimated is £30 per ton, or £46 : 16s. for 
 biphosphate of lime, although sometimes the former have 
 been reckoned as low as £25, with a corresponding rate 
 for the latter. It is important that biphosphate of lime 
 and soluble phosphates should not be confounded with one 
 
262 AGRICULTURAL CHEMISTRY. 
 
 another in valuing a manure, the latter having one and a 
 half times the value of the former. 
 
 As manures are liable to considerable fluctuations in 
 price, the value attached to each of their constituents 
 ought to be varied with the state of the market ; but it is 
 obviously impossible for the farmer to watch the changes 
 in price with such minuteness as to enable him to do this, 
 and it is much more convenient, as well as safer, to adopt 
 a fixed average, which can be used with reasonable accu- 
 racy at all times. The fact is, that this system of valua- 
 tion is only an approximation to the truth ; and if absolute 
 accuracy were aimed at, it would be necessary to vary the 
 estimates, not only at different times, but at different loca- 
 lities at the same time, and to some extent also according 
 to the kind of manure. The price of soluble phosphates 
 more especially, fluctuates to a great extent, being practi- 
 cally fixed by each manufacturer according to the facilities 
 which his position or command of raw material offer for 
 producing them at a low rate. We thus find that when 
 made from bones alone, the cost of that substance is not 
 unfrequently as high as £40 per ton, and when bone-ash 
 alone is used it is sometimes as low as £20. Such extreme 
 differences, of course, cannot be taken into account in the 
 system of valuation adopted, where all that can be done is 
 to take average values, which, when applied to average 
 samples, ought to bring out their value. 
 
 The data which have already been given regarding 
 the price of the individual constituents of manures can 
 be applied to the determination of the value of any 
 mixture in two different ways by means of the subjoined 
 table : — 
 
THE VALUATION OF MANURES. 
 
 263 
 
 
 Price per Ton. 
 
 Per cent per Ton. 
 
 Ammonia 
 
 £60 
 
 7 
 
 10 
 
 30 
 
 46 16 
 
 1 
 
 10 
 
 20 
 
 . 16 
 
 10 
 
 £0 12 
 1 5 
 2 
 6 
 9 4J 
 2,% 
 2A 
 4 
 3 2i 
 IJ 
 
 'Insoluble phosphates 
 
 Do. in phosphatic guanos 
 Soluble phosphates 
 
 
 
 Sulphate of lime 
 
 Potash 
 
 
 
 
 Supposing it be desired to calculate the value of a 
 manure by the first column, it is obvious that if we sup- 
 pose 100 tons to be purchased, the per centages of the 
 different constituents shewn in the analysis will give the 
 number of tons of each contained in 100 tons of the mix- 
 ture, and, selecting the analysis of the super-phosphate 
 given in a previous page, we proceed in the calculation as 
 follows : — 
 
 14'11 tons of organic matter at 10s. 
 
 . £7 
 
 
 
 
 
 14-86 „ 
 
 soluble phosphates at £30 
 
 . 446 
 
 
 
 
 
 15-13 „ 
 
 insoluble phosphates at £7 
 
 . 105 
 
 
 
 
 
 39-43 „ 
 
 sulphate of lime at £1 
 
 . 39 
 
 
 
 
 
 3-82 „ 
 
 alkaline salts at £1 . . 
 
 . 4 
 
 
 
 
 
 2-10 „ 
 
 ammonia at £60 . . . 
 
 . 126 
 
 
 
 
 
 Value of ,100 tons 
 or £7 : 5s. per ton. 
 
 £727 
 
 According to the second column, the numbers give the 
 sum by which the per centages of each ingredient must be 
 
264 AGEICDLTUEAL CHEMISTRY. 
 
 multiplied, to give its value in a ton of manure, and it is 
 used for the same manure in the following manner : — 
 
 1 4. 11 organic matter, multiplied by 
 
 lid. 
 
 £0 
 
 1 
 
 5 
 
 14-88 soluble phosphates „ 
 
 6s. 
 
 4 
 
 9 
 
 2 
 
 15-13 insoluble phosphates ,, 
 
 Is. 5d. 
 
 1 
 
 1 
 
 4 
 
 39-43 sulphate of lime „ 
 
 2^. 
 
 
 
 8 
 
 10 
 
 3-82 alkaline salts „ 
 
 2^. 
 
 
 
 
 
 9 
 
 2-10 ammonia „ 
 
 12s. 
 
 1 
 
 5 
 
 3 
 
 Value per ton . 
 
 £7 
 
 6 
 
 9 
 
 The difference is due to the less minute calculation 
 of fractional quantities in the latter case. 
 
 The calculation of the value of any other manure is 
 effected in exactly the same manner, taking care, however, 
 to use the higher value for phosphates in the case of a 
 phosphatic guano. It will be obvious to every one who 
 tries the two methods that the first greatly exceeds the 
 second in convenience and simplicity in the calculations, 
 and it is that most commonly in use, although some per- 
 sons prefer the second. 
 
 Although the data just given must always form the 
 basis of the valuation of any manure, there are a variety 
 of other circumstances which must be taken into account, 
 and which give great scope for the judgment and expe- 
 rience of the valuator. Of these the most important is 
 the proper admixture of the ingredients, and the condition 
 of the manure as regards dryness, complete reduction to 
 the pulverulent state, and the like. A certain allowance 
 ought always to be made for careful manufacture; and, 
 on the other hand, where the manure is damp or ill 
 reduced, a small deduction (the amount of which must be 
 
THE VALUATION OP MANURES. 265 
 
 decided by the experience of the valuator) ought to be 
 made on account of the risk which the farmer runs of loss 
 from unequal distribution, and the extra cost of carriage 
 of an unnecessary quantity of water. 
 
 It is also necessary to take into account the particular 
 element required by the soil. Thus, a farmer who finds 
 his soil wants phosphates, will look to the manure con- 
 taining the largest quantity of that substance, and possibly 
 not requiring ammonia, will not care to estimate at its 
 full value any quantity of that substance which he may be 
 compelled to take along with the former, but will look 
 only to the source from which he can obtain it most 
 cheaply. It may be well, therefore, to point out that 
 ammonia is most cheaply purchased in Peruvian guano ; 
 insoluble phosphates in coprolites ; and soluble phosphates 
 in super-phosphates, made from bone-ash alone. In gene- 
 ral, however, it will be found most advantageous to select 
 manures in which the constituents are properly adjusted to 
 one another, so that neither ammonia, soluble nor insoluble 
 phosphates, preponderate ; but, of course, it must frequently 
 happen that it will prove more economical to buy the sub- 
 stances separately and to make the mixture, than to take 
 the manure in which they are ready mixed. 
 
 In judging of the value of any manure, it is also im- 
 portant to make sure that the analysis which forms the 
 basis of the calculation is that of a fair sample, which 
 correctly represents the bulk actually delivered to the pur- 
 chaser, and not one which has been made to do duty for 
 an unlimited quantity of manure, which is supposed to be 
 all of equal quality, as often happens in the hands of 
 careless manufacturers, and too great attention cannot be 
 devoted to the selection of the sample, which is very often 
 done in an exceedingly slovenly manner. 
 
CHAPTER XIII. 
 
 THE ROTATION OF CROPS. 
 
 Reference has already been more than once made to the 
 fact that a crop growing in any soil must necessarily 
 exhaust it to a greater or less extent by withdrawing from 
 it a certain quantity of the elements to which its fertility 
 is due. That this is the case has been long admitted in 
 practice, and it has also been established that the exhaust- 
 ing effects of different species of plants are very different ; 
 that while some rapidly impoverish the soil, others may 
 be cultivated for a number of years without material injury, 
 and some even apparently improve it Thus, it is a noto- 
 rious fact that white crops exhaust, while grass improves 
 the soil j but the improvement in the latter case is really 
 dependent on the fact, that when the land is laid down in 
 pasture, nothing is removed from it, the cattle which feed 
 on its produce restoring all but a minute fraction of the 
 mineral matters contained in their food ; and as the plants 
 derive a part, and in some instances a very large part, of 
 their organic constituents from the air, the fertility of the 
 soil must manifestly be increased, or at all events main- 
 tained in its previous state. When, however, the plant, 
 or any portion of it, is removed from the soil, there must be 
 a reduction of fertility dependent on the quantity of valuable 
 matters withdrawn by it ; and thus it happens that when a 
 plant has grown on any soil, and has removed from it a 
 
THE ROTATION OP CROPS. 267 
 
 large quantity of nutritive matters, it becomes incapable 
 of producing an equally large crop of the same species ; 
 and if the attempt be made to grow it in successive years, 
 the land becomes incapable of producing it at all, and is 
 then said to be thoroughly exhausted. But if the exhausted 
 land be allowed to lie for some time without a crop, it 
 regains its fertility more or less rapidly according to cir- 
 cumstances, and again produces the same plant in remune- 
 rative quantity. The observation of this fact led to the 
 introduction of naked fallows, which, up to a comparatively 
 recent period, were an essential feature in agriculture. 
 But after a time it was observed that the land which had 
 been exhausted by successive crops of one species was not 
 absolutely barren, but was still capable of producing a 
 luxuriant growth of other plants. Thus peas, beans, 
 clover, or potatoes, could be cultivated with success on 
 land which would no longer sustain a crop of grain, and 
 these plants came into use in place of the naked fallow 
 under the name of fallow crops. On this was founded the 
 rotation of crops ; for it was clear that a judicious inter- 
 change of the plants grown might enable the soil to regain 
 its fertility for one crop at the time when it was produc- 
 ing another ; and when exhausted for the second, it might 
 be again ready to bear crops of the first. 
 
 The necessity for a rotation of crops has been explained 
 in several ways. The oldest view is that of DecandoUe, 
 who founded his theory on the fact that the plants excrete 
 certain substances from their roots. He found that when 
 plants are grown in water, a peculiar matter is thrown off 
 by the roots ; and he believed that this extrementitious 
 substance is eliminated because it is injurious to the plant, 
 and that, remaining in the soil, it acts as a poison to those 
 of the same species, and so prevents the growth of another 
 
268 AGRICULTURAL CHEMISTRY. 
 
 crop. But this excretion, though poisonous to the plants 
 from which it is excreted, he believed to be nutritive to 
 those of another species which is thus enabled to grow 
 luxuriantly where the others failed. Nothing can be 
 more simple than this explanation, and it was readily 
 embraced at the time it was propounded and considered 
 fully satisfactory. But when more minutely examined, it 
 becomes apparent that the facts on which it is founded 
 are of a very uncertain character. Decandolle's observa- 
 tions regarding the radical excretions of plants have not 
 been confirmed by subsequent observers. On the contrary, 
 it has been shewn that though some plants, when growing 
 in water, do excrete a particular substance in small 
 quantity, nothing of the sort appears when they are grown 
 in a siliceous sand. And hence the inference is, that the 
 peculiar excretion of plants growing in water is to be 
 viewed as the result of the abnormal method of their 
 growth rather than as a natural product of vegetation. 
 But even admitting the existence of these matters, it would 
 be impossible to accept the explanation founded upon them, 
 because it is a familiar fact that, on some soils, the repeated 
 growth of particular crops is perfectly possible, as, for 
 instance, on the virgin soils of America, from which many 
 successive crops of wheat have been taken ; and in these 
 cases the alleged excretion must have taken place without 
 producing any deleterious effect on the crop. Besides, it 
 is in the last degree improbable that these excretions, con- 
 sisting of soluble organic matters, should remain in the 
 soil without undergoing decomposition, as all similar sub- 
 stances do ; and even if they did, we cannot, with our 
 present knowledge of the food of plants, admit the possi- 
 bility of the direct absorption of any organic substance 
 whatever. Indeed, the idea of radical excretions, as an 
 
THE ROTATION OF CROPS. 269 
 
 explanation of the rotation of crops, must be considered as 
 being entirely abandoned. 
 
 The necessity for a rotation of crops is now generally 
 attributed to the different quantities of valuable matters 
 which different plants remove from the soil, and more 
 especially to their mineral constituents. It has been 
 already observed that great differences exist in the com- 
 position of the ash of different plants in the section on 
 that subject ; and it was stated that a distinction has been 
 made between lime, potash, and silica plants, according 
 as one or other of these elements preponderate in their 
 ashes. The remarkable difference in the proportion of 
 these elements has been supposed to afford an explanation 
 of rotation. It is supposed that if a plant requiring a 
 large quantity of any one element, potash, for example, be 
 grown during a succession of years on the same soil, it 
 will sooner or later exhaust all, or nearly all, the potash 
 that soil contains in an available form, and it will conse- 
 quently cease to produce a luxuriant crop. But if this 
 plant be replaced by another which requires only a small 
 quantity of potash and a large quantity of lime, it will 
 flourish, because it finds what is necessary to its growth. 
 In the meantime, the changes which are proceeding in the 
 soil, are liberating new quantities of the inorganic matters 
 from those forms of combination in which they are not 
 immediately available, and when after a time the plant 
 which requires potash is again sown on the soU, it finds a 
 sufficient quantity to serve its purpose. "We have already, 
 in treating of the ashes of plants, pointed out the extent of 
 the differences which exist ; but these will be made more 
 obvious by the annexed table, giving the quantity of the 
 different mineral matters contained in the produce of an 
 imperial acre of the different crops. 
 
270 
 
 AGRICULTURAL CHEMISTRY. 
 
 Q 
 
 03 
 
 ^ 
 
 c8 g 
 
 -2 fe 
 
 S 
 
 S 
 
 
 
 O 
 OS 
 
 16-13 
 45-33 
 34-98 
 
 CO i-H -"^ 
 
 OOip 
 
 CD A t^ 
 ^ (M 
 
 14-10 
 41-64 
 46-10 
 
 00 00 cx) w 
 
 Q0C33 Ticcp CM 
 CO CM CO CO CO 
 (M t^COCN m 
 
 
 CO 
 
 6 
 
 t~005 
 •^ Oi T^H 
 
 CO COCO 
 
 1> I> T-H 
 
 00 t- t^ 
 
 CO 00 
 
 iCSCM ■* 
 
 oowsq 
 
 (M>00 
 
 ■<r GO Oi t» 
 OOOOCM CO 
 
 CO ■* cbi^ m 
 
 111 
 
 CM 
 
 CO 
 
 CO OC(M 
 ^ COiO 
 
 1— 1 y-\ 
 
 t> (M CO 
 <M (N 
 
 »o CM vrt 
 CO-* CO 
 
 CO T-< 
 
 •>ll OS t>- CO 01 
 
 c6 b-cM>bi^ 
 
 T-c CM CM 
 
 -1^ 
 
 CO 
 
 6 
 
 »0 00 00 
 CO CO o 
 
 OlO 
 
 00 00 CO 
 
 t- CO CM ■* Ir- 
 
 CO cp CM 10 
 
 CMcn ciio CO 
 
 CO T-l 1-H 
 
 sl 
 
 
 (M 
 
 • * 1-H 
 
 0!N O 
 CO-* IN 
 rt (MO 
 
 »o ■> : 
 
 »d-l ^H 
 cp CM CO 
 
 tr- 1^- CO CO cJ3 
 
 T-l CO 
 
 S a 
 
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 QO 
 
 COCO o 
 
 "?" ? 7* 
 <fa l^- CO 
 
 l> 00 o 
 (N lO •* 
 
 o^ o 
 
 lOlOcp 
 
 >o cii ■* 
 
 ■* -*>I0^CM 
 t> t^ CO ^ CO 
 
 «3 t~ -^ ^ 03 
 
 2 
 
 3 
 
 P 
 
 CO [~CO 
 
 u3 lO b- 
 
 oo c^ o 
 
 1-H t- T-H 
 
 coioco 
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 CjO— 1 
 qq CO o 
 
 ci>>bcb 
 
 [-00 OOCO 
 CO cp CO CM ■* 
 0^ (M CX> T— c iO 
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 OOO CO 
 
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 CO CO to 
 
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 1-^ •* t- CX) 00 
 
 en CO-* CM-* 
 ^ I-l ^ 
 
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 Ot-h O 
 1^00 ■* 
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 !M CO 
 
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 CM CO O 
 
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 t~. t>o 
 
 Ot^ CO 
 
 CO-* CO 
 
 ^ 1-H kO CM C53 
 COCO CO C33 [. 
 C3D ci) b- ci) C33 
 ■Tjc t> IC CM CM 
 
 
 IM 
 
 CO 
 
 00 0-* 
 ^ tOCN 
 
 ■* OOOJ 
 T-H CO 00 
 
 oit en CO 
 
 03^ ^ 
 
 COCMt- 
 lO ■* C33 
 
 CO CM O 
 
 -* 05 10 
 
 T-t T-t 
 
 *-t QCIO OO^H 
 iO ■* ir-lp CO 
 
 c» ^ cbib 1^ 
 
 CO ^ 10 CJ3 
 
 i-ii-l CM CO 
 
 3 II 
 
 o 
 
 QO 
 
 CD 
 
 tH 
 
 O OS 
 
 t- : -* 
 
 CO o 
 
 i-H • CO 
 
 O^ • CO 
 (M~ rt" 
 
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 -* : lo 
 
 CM_ ■ CO 
 
 c>r T-T 
 
 000 
 -* ; -^ CM 
 
 CM^ -CM^C-CO 
 
 cm" cocoo" 
 
 53 
 
 =••3 
 
 00 -►j 
 
 m : §co 
 a ■ j= »fi 
 
 3 co-S 
 ^ CO •* 
 
 QJ M "73 CO t" „^ 
 
 li|iliJS|:lil 
 
 CO =S (M CS -.-1 '-'• 
 
 
 
 mHcS 
 
 
 1 
 
 • ■ m 
 
 : :£ 
 
 « 2 ■§ 
 
 6 
 
 ■> 
 
THE ROTATION OF CROPS. 271 
 
 The minor constituents, such as oxide of iron, manga- 
 nese, etc., have been omitted as being of little importance ; 
 and the quantity of nitrogen, which is of great moment in 
 estimating the exhaustive effects of various crops, has been 
 added. 
 
 In examining this table, it becomes apparent that while 
 in regard to some of the elements, the quantities removed 
 by different crops do not differ to any marked extent, in 
 others the variation is very great. The cereals and grasses 
 are especially distinguished by the larger quantity of silica 
 they contain, and the exhaustive effect consequent upon the 
 removal of both grain and straw from soils which contain but 
 a limited supply of that substance in an available condition 
 is obvious. It is clear that under such circumstances the 
 frequent repetition of a cereal crop may so far diminish the 
 amount of available silica as to render its cultivation im- 
 possible, although the other substances may be present in 
 sufficient quantity to produce a plentiful crop of any plant 
 which does not require that element. Beans and peas, 
 turnips and hay, on the other hand, require a very large 
 quantity of alkalies, and especially of potash. 
 
 Looking more minutely, however, into this matter, 
 certain points attract attention which appear to be at vari- 
 ance with commonly received opinions. With the excep- 
 tion of silica, for example, the cereals do not withdraw 
 from the soil so large a quantity of mineral matters as some 
 of the so-called fallow crops, and if their straw be returned 
 to the soil they are by far the least exhaustive of all cul- 
 tivated plants ; and we thus recognise the justice of that 
 practical rule, which lays it down as an essential point of 
 good husbandry that the straw ought, as far as possible, to 
 be consumed on the farm on which it is produced. As 
 regards the general constituents of the ash, it is also to be 
 
272 AGRICULTURAL CHEMISTRY. 
 
 remarked that though differences in their proportions exist, 
 they are by no means so marked as might be expected ; 
 thus there are no plants for which a large quantity of 
 potash, nitrogen, and phosphoric acid is not required ; 
 and it is not very easy to see how the substitution of the 
 one for the other should be of much importance in this 
 respect. Indeed, the more minutely the subject is exa- 
 mined, the more do we become convinced of the insufS- 
 ciency of that view which attributes the necessity for a 
 rotation of crops to differences in chemical composition 
 alone. There can be no doubt that the nature of the 
 plant and the particular mode in which it gathers its 
 nutriment, have a most important influence. Certain 
 plants are almost entirely dependent on the soil for their 
 organic constituents, while othere derive a large proportion 
 of them from the air, and a plant of the latter class will 
 flourish in a soil in which one of the former is incapable of 
 growing. In other cases, the structure and distribution 
 of the roots is the cause of the difference. Some plants 
 have roots distributed near the surface and exhaust the 
 superficial layer of the soil, others penetrate into the 
 deeper layers, and not only derive an abundant supply of 
 food from them, but actually promote the fertility of the 
 surface soil by the refuse portions of them which are left 
 upon it. Experience has in this respect arrived at results 
 which tally with theory, and it is for this reason that the 
 broad-leafed turnip, which obtains a considerable quantity 
 of its nutriment from the air, alternates with grain crops 
 which are chiefly dependent on the soU. It is undoubtedly 
 to some such cause that several remarkable instances of 
 what may be called natural rotations are to be attributed. 
 It is well known in Sweden that when a pine forest is 
 felled, a growth, not of pine but of birch, immediately 
 
THE ROTATION OP CROPS. 273 
 
 springs up. Now the difference in composition of the ash 
 of these trees is not sufficient to explain this fact, and it 
 must clearly be due to some difference in the distribution 
 of their roots, or the mode in which they obtain their 
 food. 
 
 Whatever weight may be given to these different 
 explanations of rotation, there is no doubt about the im- 
 portance of attending to it, and there are various practical 
 deductions of much importance to be drawn from the facts 
 with which we are acquainted. Thus it is to be observed 
 that the quantities of mineral matters withdrawn by plants 
 of the same class are generally similar, and hence it may 
 be inferred that crops of the most opposite class ought as 
 much as possible to alternate with one another, and each 
 plant should be repeated as seldom as possible, so that, 
 even when it is necessary to return to the same class, a 
 different member of it should be employed. Thus, for 
 instance, in place of immediately repeating wheat, when 
 another grain crop is necessary, it would theoretically 
 be preferable to employ oats or barley, and to replace 
 the turnip by mangold-wurzel or some other root. It is 
 obvious, however, that this system caijnot be carried out 
 in practice to its full extent; for the superior value of 
 individual crops causes the more frequent repetition of 
 those which make the largest return. But experience 
 has so far concurred with theory that it has taught 
 the farmer the advantage of long rotations ; and we 
 have seen the successive introduction of the three, four, 
 five, and six-course shift, and even, in some instances, of 
 longer periods. 
 
 Such is the theory of rotation, and while it will always 
 be most advantageous to adhere to it, it is by no means 
 necessary that this should be done in an absolutely 
 
274 AGEICULTCKAL CHEMISTET. 
 
 rigid manner. In the practice of agriculture, plants are 
 placed in artificial circumstances, and instead of allowing 
 them to depend entirely on the soil, they are supplied 
 with a quantity of manure containing all the elements they 
 require, and if it be used in sufficiently large quantity, 
 the same crop may be grown year after year. And 
 accordingly the order of rotation, which is theoretically 
 the best, may be, and every day is, violated in practice, 
 although this must necessarily be done at the expense of 
 a certain quantity of the valuable matters of the manure 
 added, and is so far a practice which ought theoretically 
 to be avoided. In actual practice, however, the matter is 
 to be decided on other grounds. The object then is, not 
 to produce the largest crops, but those which make the 
 largest money return, and thus it may be practically econo- 
 mical to grow a crop of high commercial value more fre- 
 quently than is theoretically advantageous. In such cases 
 the farmer must seek to do away as far as possible with 
 the disadvantages which such a course entails, and this he 
 will endeavour to accomplish by careful management and a 
 liberal treatment of the soil. 
 
 But while this system may be adopted to some ex- 
 tent, it must also be borne in mind that the frequent repe- 
 tition of some crops cannot be practised with impunity, for 
 plants are liable to certain diseases which manifest them- 
 selves to the greatest extent when they have been too often 
 cultivated in the same soil. Clover sickness, which afifects 
 the plant when frequently repeated on light soils, and the 
 potatoe disease and fihger and toe have been attributed to 
 the same cause. Whether this is the sole origin of these 
 diseases is questionable, but there is no doubt that they 
 are aggravated by frequent repetition, and hence a strong 
 argument in favour of rotation. It has been asserted by 
 
THE ROTATION OP CROPS. 275 
 
 great authorities in high farming, that with our present 
 command of manures, rotations may be done away with ; 
 but this is an opinion to which science gives no counte- 
 nance, and he would be a rash man who attempted to carry 
 it out in practice. 
 
CHAPTEE XIV. 
 
 THE FEEDING OF FARM STOCK. 
 
 The feeding of cattle, once a subordinate part of the 
 operations of the farm, has now become one of its most 
 important departments, and a large number of minute and 
 elaborate experiments have been made by chemists and 
 physiologists with the view of determining the principles 
 on which its successful and economical practice depends. 
 These investigations, while they have thrown much light 
 on the matter, have by no means exhausted it, and it will 
 be readily understood that the complete elucidation of a 
 subject of such complexity, touching on so many of the 
 most abstruse and difficult problems of chemistry and 
 physiology, and in which the experiments are liable to 
 be affected by disturbing causes, dependent on peculiarities 
 of constitution of different animals, cannot be otherwise 
 than a slow process. 
 
 In considering the principles of feeding, it is necessary 
 to point out, in the first instance, that the plant and 
 animal are composed of the same chemical elements, 
 hence the food supplied to the latter invariably con- 
 tains all the substance's it requires for the maintenance of 
 its functions. And not only is this the case, but these 
 elements are to a great extent combined together in a 
 similar manner, — the fibrine, caseine, albumen, and fatty 
 matters contained in animals corresponding in all respects 
 
THE FEEDING OP FARM STOCK. 277 
 
 with the compounds extractefi from plants under the 
 same name ; and though the starchy and saccharine sub- 
 stances do not form any part of the animal body, they 
 are represented in the milk, the food which nature has 
 provided for the young animal. It has been frequently 
 assumed that the nitrogenous and fatty matters are simply 
 absorbed into the animal system, and deposited imchanged 
 in its tissues ; but it is probable that the course of events 
 is not quite so simple, although, doubtless, the decompo- 
 sition which occurs is comparatively trifling. The starchy 
 matters, on the other hand, are completely changed, and 
 devoted to purposes which will be immediately explained. 
 It is a matter of familiar experience, that if the food 
 be properly proportioned to the requirements of the ani- 
 mal, its weight remains unchanged ; and the . inference to 
 be drawn from this fact obviously is, that the food does 
 not remain permanently in the system, but must be again 
 got rid of. It escapes partly through the lungs, and 
 partly by the excretions, which do not consist merely of the 
 part which has not been digested, but also of that portion 
 which has been absorbed, and after performing its allotted 
 flinctions within the system, has become effete and useless. 
 When the weights of the excretions, the carbon contained 
 in the carbonic acid expired by the lungs and the small 
 quantity of matter which escapes in the form of perspira- 
 tion, are added together, they are found in such a case to 
 be exactly equal to the food. If the animal be deprived 
 of nutriment, it immediately begins to lose weight, because 
 its functions must continue— carbon' must still be converted 
 into carbonic acid to maintain respiration — and the excre- 
 tions be eliminated, although diminished in quantity, be- 
 cause they no longer contain the nudigested portion of 
 the daily food, and the substances already stored up in 
 
278 AGRICULTURAL CHEMISTRY. 
 
 the body are consumed to maintain the functions of life. 
 Universal experience has shewn that, under such circum- 
 stances, the fat which has accumulated in various parts of 
 the body disappears, and the animal becomes lean ; but it 
 is less generally recognised that the muscular flesh, that 
 is the lean part of the body, also diminishes, although it 
 is sufficiently indicated by the fact that nitrogen still con- 
 tinues to be found in the urine, and that the animal be- 
 comes feeble and incapable of muscular exertion. Kespi- 
 ration and secretion, in fact, proceed quite irrespective of 
 the food, which is only required to repair the loss they 
 occasion. When the course of events within the animal 
 body is traced, it is found to be somewhat as follows : 
 The food consumed is digested and absorbed into the 
 blood, where it undergoes a series of complicated 
 changes, as a consequence of which part of it is con- 
 verted into carbonic acid, and eliminated by the lungs, 
 and part is deposited in the tissues as fat and flesh. After 
 the lapse of a certain period, longer or shorter according 
 to circumstances, a new set of actions comes into play, by 
 which the complex constituents of the tissues are resolved 
 into simpler substances, and excreted chiefly by the lungs 
 and kidneys. The changes thus produced are, to a great 
 extent, identical with those which wOuld take place if the 
 fat and flesh were consumed in a fire ; and the animal 
 frame may, in a certain sense, be compared to a fnmace, 
 in which, by the daily consumption of a certain quantity 
 of fuel and air inhaled in the process of respiration, its 
 temperature is maintained above that of the surround- 
 ing atmosphere. If the daily supply of fuel, that is of 
 ftwd, be properly adjusted to the loss by combustion, 
 the weight of the animal remains constant ; if it be re- 
 duced below this quantity, it diminishes ; but if it be in- 
 
THE FEEDING OF FAEM STOCK. 279 
 
 creased, the stomach either refuses to digest and assimilate 
 the excess, or it is absorbed and stored up in the body, 
 increasing both the fat and flesh. 
 
 When an animal is fed in such a manner that its 
 weight remains constant, a balance is produced between 
 the supply of nutriment contained in the food and the , 
 waste of the tissues, the gain from the former exactly 
 counterpoising the loss occasioned by the latter. If in 
 this state of matters an additional supply of food be 
 given, this balance is deranged, and the nutriment being 
 in excess of the loss, the animal gains weight, and it con- 
 tinues to do this for some time, until it reaches a point at 
 which a new balance is established, and its weight again 
 becomes constant ; and this is due to the fact that the 
 animal becomes subject to an additional waste, consequent 
 on the increased weight of matter accumulated in its 
 tissues. If, after the aniibal has attained its new constant 
 weight, the food be a second time increased, a further gain 
 is obtained, and so on, with every addition to the supply 
 of nutriment, until at length a certain point is reached, 
 beyond which its weight cannot be forced. In fact, 
 each successive increase of , weight is obtained at a 
 greater expenditure of food. If, for example, a lean ani- 
 mal is taken, and its food increased by a given quantity, 
 it will rapidly attain a certain additional weight, but if 
 another extra supply of food be given, the increase due to 
 it will be much more slowly attained, and so on until at 
 length an additional increase can only be secured by the 
 long-continued consumption of a very large quantity of 
 food. The great object of the feeder is to obtain the 
 greatest possible increase with the smallest expenditure of 
 food, and to know the point beyond which it is no longer 
 economical to attempt to force the process of fattening. 
 
280 AGEICtJLTOSAL CHEMISTRT. 
 
 To do this it is necessary first to consider the composition of 
 the animal itself, then that of its food, and lastly, the 
 mode in which it may be most economically used. 
 
 It has been already observed that the animal tissues 
 are composed of albuminous or nitrogenous compounds, 
 fat, mineral matters, and water; but the proportions of 
 these substances have, until lately, been very imperfectly 
 known. Water is well known to be by far the largest con- 
 stituent, and amounts in general to about two-thirds of the 
 entire weight, and it has been generally supposed that the 
 nitrogenous matters stood next in point of abundance, 
 but a most important and elaborate series of experiments 
 by Messrs. Lawes and Gilbert have shewn that they are 
 greatly exceeded by the fatty matters. The following 
 table contains a summary of the composition of ten dif- 
 ferent animals in different stages of fattening. The first 
 division gives the composition of the carcass, that is, the 
 portion of the animal usually consumed as human food; 
 the second that of the offal, consisting of the parts not 
 usually employed as food ; and the third that of the entire 
 animals, including the contents of the stomach and intes- 
 tines : — 
 
THE FEEDING OF FARM STOCK. 
 
 281 
 
 H S 
 
 _ n 
 
 (M Eh 
 
 "is 
 
 
 25 
 
 5b 
 •3*-' 
 
 B(« 
 
 BTJ 
 ^§ 
 
 a i 
 
 IS 
 
 5g 
 "Sb 
 
 .g°-S 
 
 •J8JK^ 
 
 o»OH90oe3(N-*cfl^cp 
 
 piic sqDBUlu^S 
 JO s^us^uoo 
 
 ■iiQ TOO! 
 
 t*oaoo-*oiO<Noo«i^ 
 rt .^ 01 >p o o o 1^ (N OS 
 
 CO 
 
 CD 
 
 
 « 
 
 eo 
 
 CO 
 
 ODcoint«t>>^-cocot«i^ 
 
 'V^S. 
 
 OC — «i-iiot;»«iCOCOCO<M 
 
 •gpunodmoo 
 BnoaaSoa^i^ 
 
 c4cauDcoooo(NC3t>o:i 
 
 
 C0'*03(NC0C0(N(NIN'-I 
 
 •J9^B^ 
 
 
 •9on:K).sqng 
 
 THTt<<N»C>C0CSQ0^T-ICO 
 
 cpl>.cpi;^fH>CtTt(»OOop 
 i-li-itN(Mi^i-f(MCOi-((M 
 
 •sponodmoo 
 saonaSoji)!^ 
 
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 -* 
 
 <N 
 
 C4 
 
 (N 
 
 '«f* 
 
 
 
 *» 
 
 
 
 la^Bii. 
 
 epoQooepi>t*ococo 
 
 «D«3^-*»O-*C0C0»OCO 
 
 ■aou'B^sqng 
 
 t*p^rJtb-cpcpOt>-Tr< 
 
 Cft-^iO'O-^iOtDCD-i^CD 
 
 pep00O300ep^iHr-i»p 
 i-toqeooSfflCO'^iOiM"* 
 
 ■Bpanoduioo 
 
 cogooo)tocn^iHO>c 
 
 rH r-lTH 1-1 iH t-^ rH »-H i-4 
 
 Tuiaaipn 
 
 ■^lO-^COTjt-^CONNf-i 
 
 >4 
 o 
 
 So 
 
 •CO 
 
 bo 
 
 I I^SPl, 
 
 V 
 
 .a Si's g.^ M, . 
 
 ■ i^l^^a^ 
 
 ^ CO S III (i) CO |si 
 
 5 "2 
 
 sas 
 
 
 
282 AGRICULTURAL CHEMISTRY. 
 
 From this table it appears that, in the carcass, the 
 proportion of fat is, in general, even in lean animals, much 
 greater than that of nitrogenous compounds. In one cas? 
 only, that of the fat calf, are they equal. But in the lean 
 sheep there is more than one and a half times as much fat 
 as nitrogenous matters, in the half fat sheep twice, in 
 the fat sheep four times, and in the very fat sheep about 
 six times as much. As a general result of the analyses 
 it may be stated, that in the carcass of an ox in good con- 
 dition, the quantity of fat will be from two to nearly three 
 times as great as that of the so called albuminous com- 
 pounds ; in a sheep three or four times, and in the pig 
 four or five times as great. In the offal, including the 
 hide, intestines, and other parts not usually consumed as 
 food, the proportion is very dififerent, — the quantity of fat 
 being much smaller, and that of nitrogenous compounds 
 considerably larger. 
 
 Taking a general average of the whole, the following 
 may be assumed as representing approximately the general 
 composition of a lean and a fat animal : — 
 
 Lean. Fat. 
 
 Mineral matters 6 3 
 
 Nitrogenous compoimds 15 12"5 
 
 Fat 24 33 
 
 Water 56 485 
 
 100 100-0 
 
 The data given in the preceding table, coupled with a 
 knowledge of the relative weights of the lean and fat ani- 
 mals, enable us to ascertain the composition of the in- 
 crease during the fattening process. It is obvious, from 
 the material diminution of the per centage of water, that 
 the matters deposited in the tissues must contain a much 
 larger proportion of dry matters than the whole body ; and 
 the reduced per centage of nitrogenous matters shews that 
 
THE FEEDING OF FAEM STOCK. 
 
 283 
 
 the fat must also greatly preponderate. This is still more 
 distinctly illustrated by the following table, giving the per 
 centage composition of the increase in fattening oxen, 
 sheep, and pigs : — 
 
 
 Mineral 
 Matters. 
 
 Nitrogenous 
 Compounds. 
 
 Fat. 
 
 Water. 
 
 Oxen 
 
 Sheep 
 
 Pigs 
 
 1-47 
 2-34 
 0-06 
 
 7-69 
 7-13 
 6-44 
 
 66-2 
 70-4 
 71-5 
 
 24-6 
 20-1 
 22-0 
 
 Hence it may be stated in round numbers, that for 
 every pound of nitrogenous matters added to the weight of 
 a fattening animal, it will gain ten pounds of fat, and 
 three of water. These are the proportions over the whole 
 period of fattening, but it is probable that during the 
 last few weeks of the process the ratio of fat to nitro- 
 genous matters is still higher. 
 
 In considering the composition of the food of animals, 
 it will be readily admitted that the milk, the nutriment 
 supplied by nature for the maintenance of the young 
 animal, must afford special instruction as to its require- 
 ments during the early stages of existence, and indicate, 
 at least, some of the points to be attended to under the 
 altered conditions of mature life. The following table 
 gives the average composition of the milk of the most 
 important farm animals : — 
 
 Cow. Ewe. Goat. 
 
 Caseine 3-4 4-50 4-02 
 
 Butter 3-6 420 3-32 
 
 Sugar of milk.. 6-0 5-00 5-28 
 
 Ash 0-2 ....'. 0-68 0-58 
 
 Water 86-8 85-62 86-80 
 
 100-00 
 
 100-00 
 
 100-00 
 
284 AGEICULTUEAIi CHEMISTRY. 
 
 In examining these, and all other analyses of food, it' 
 is necessary to draw a distinction between the flesh-form- 
 ing and the respiratory elements; the former including 
 the nitrogenous compounds which are used in the pro- 
 duction of flesh, the latter, the non-nitrogenous substances 
 which produce fat and support the process of respiration. 
 The former, however much they may differ in name, are 
 nearly or altogether identical in chemical composition, the 
 latter embracing two great classes — ^the fats which exist in 
 the body and the saccharine compounds, including the 
 different kinds of sugar and starch which are not found in 
 the animal tissues. It was at one time supposed that 
 these substances were entirely consumed in the respiratory 
 process, and eliminated by the lungs in the form of car- 
 bonic acid and water, but it has been clearly shewn that 
 they may be and often are converted into fat, and accu- 
 mulated in the system. Careful experiments on bees have 
 demonstrated that when fed on sugar they continue to 
 produce wax, which is a species of fat, and animals re- 
 tain their health and become fat, even when their food 
 contains scarcely any oil. There is, however, an impor- 
 tant difference between these two classes of substances as 
 regards their fat-producing effect. A pound of fat con- 
 tained in the food is capable of producing the same quan- 
 tity within the animal ; but the case is different with 
 starch and sugar, the most trustworthy experiments shew- 
 ing that two and a half pounds of these substances are 
 necessary for that purpose. Hence we talk of the fat 
 equivalent of sugar, by which is meant the amount of fat 
 it is capable of producing, and which is obtained by 
 dividing its quantity by 2'5. Applying this principle to 
 the analyses of the milk, it appears that the relative pro- 
 portions of the two great classes of nutritive substances 
 stand thus : — 
 
THE FEEDING OP FARM STOCK. 285 
 
 Mesh Eespiratory, expressed in 
 
 fotming their fat equivalent, 
 
 Cow 3-4 6-0 
 
 Ewe 4-5 6-2 
 
 Goat 4-0 5-4 
 
 Taking the general average, it may be stated, that 
 for every pound of flesh-forming elements contained in the 
 food of the sucking animal, it consumes respiratory com- 
 pounds capable of producing one and a half pounds of fat, 
 and this does not differ materially from the ratio subsisting 
 between these substances in the lean animal. When the 
 young animal is weaned, it obtains a food in which the 
 ratio of nitrogenous to respiratory elements is maintained 
 nearly unchanged ; but the latter, in place of containing 
 a large amount of fatty matters, is in many cases nearly 
 devoid of these substances, and consists almost exclusively 
 of starch and sugar, mixed most commonly with a consi- 
 derable quantity of woody fibre. 
 
 A very large number of analyses of difierent kinds of 
 cattle food have been made by chemists, but our informa- 
 tion regarding them is still in some respects imperfect. 
 The quantity of nitrogenous compounds and of oil has 
 been accurately ascertained in almost all, but the amount 
 of starch, sugar, and woody fibre is still imperfectly deter- 
 mined in many substances. This is due partly to the fact 
 that the nitrogenous and fatty matters were formerly 
 believed to be of the highest importance, and might be 
 used as the measure of the nutritive value of food to the 
 exclusion of its other constituents, and partly also to the 
 imperfect nature of the processes in use for obtaining the 
 amounts of woody fibre, starch, and sugar. These diffi. 
 cullies have now, to a certain extent, been overcome, 
 and the quantity of fibre and of respiratory elements has 
 been ascertained, and is .introduced, so far as is known, 
 in the subjoined table : — 
 
286 
 
 AGRICULTURAL CHEMISTRY. 
 
 Table giving the Composition of the Principal Varieties of Cattle FoocL 
 
 Note. — ^Where a blank occurs in the oil colonm, the quantity of that substance is 
 so small as to be unimportant. When the respiratory elements and fibre 
 have not been separated, the sum of the two is given. 
 
 
 » 
 
 
 ts 
 
 
 
 
 
 9 
 
 Oil. 
 
 } 
 
 Fibre. 
 
 Aih. 
 
 Water. 
 
 
 4400 
 
 8-86 
 
 » e 
 ecu 
 
 19-34 
 
 6-13 
 
 14-05 
 
 8-62 
 
 Decorticated earth-nnt cake 
 
 Decorticated cotton cake . 
 
 41-25 
 
 16-05 
 
 16-45 
 
 8-92 
 
 8-05 
 
 9-28 
 
 Poppy cake .... 
 
 3403 
 
 11-04 
 
 23-25 
 
 11-33 
 
 13-79 
 
 6-66 
 
 Teel or sesamum cake 
 
 31-93 
 
 12-86 
 
 21-92 
 
 9-06 
 
 13-85 
 
 10-38 
 
 Rape cake 
 
 29-76 
 
 8-63 
 
 38-72 
 
 7-30 
 
 8-65 
 
 6-96 
 
 Dotter cake .... 
 
 29-00 
 
 7-99 
 
 27-04 
 
 16-12 
 
 12-59 
 
 7-26 
 
 Tares, home-grown 
 
 28-57 
 
 1-30 
 
 58-64 
 
 2-60 
 
 8-99 
 
 Linseed cake . 
 
 28-53 
 
 12-47 
 
 35781 6-32 
 
 6-11 
 
 10-79 
 
 Eiibsen cake 
 
 26-87 
 
 11-00 
 
 31-471 16-96 
 
 8-00 
 
 6-71 
 
 Tares, foreign .... 
 
 26-73 
 
 1-59 
 
 53-04 
 
 2-84 
 
 16-80 
 
 Earth-nut cake (entire seed) . 
 
 26-71 
 
 12-76 
 
 45-69 
 
 3-29 
 
 11-56 
 
 Niger cake .... 
 
 25-74 
 
 6-58 
 
 42.18111-15 
 
 8-12 
 
 6-23 
 
 Beans (65 lbs. per bushel) 
 
 24-70 
 
 1-59 
 
 54-61 
 
 3-36 
 
 15-84 
 
 Lentils 
 
 24-57 
 
 1-51 
 
 58-82 
 
 2-79 
 
 12-31 
 
 Linseed 
 
 24-44 
 
 34-00 
 
 30-73 
 
 3-33 
 
 7-50 
 
 Grey peas . 
 
 24-25 
 
 3-30 
 
 57-99 
 
 2-52 
 
 11-94 
 
 Foreign beans .... 
 
 23-49 
 
 1-51 
 
 59-67 
 
 3-14 
 
 1221 
 
 Cotton cake (with husk) 
 
 22-94 
 
 6-07 
 
 36-52 
 
 16-99 
 
 6-02 
 
 11-46 
 
 Pea-nut cake . 
 
 22 25 
 
 7-62 
 
 30-25 
 
 26-97 
 
 3-71 
 
 9-20 
 
 Sunflower cake .... 
 
 21-68 
 
 8-94 
 
 19-05 
 
 33-00 
 
 9-33 
 
 8-00 
 
 Hempseed cake. 
 
 21-47 
 
 7-90 
 
 22-48 
 
 25-16 
 
 15-79 
 
 7-21 
 
 Kidney beans .... 
 
 2006 
 
 1-22 
 
 62-16 
 
 3-66 
 
 13-00 
 
 Maple peas .... 
 
 19-43 
 
 1-72 
 
 6318 
 
 2-04 
 
 13-63 
 
 Madia satiya (seed) . 
 
 18-41 
 
 36-56 
 
 34-59 
 
 4-13 
 
 6-32 
 
 Clover hay (mean of different 
 
 
 
 
 
 
 species of clover) . 
 
 15-81 
 
 3-18 
 
 34-42:22-47 
 
 7-59 
 
 16-63 
 
 Kye 
 
 14-20 
 
 
 81-611 2-47 
 
 1-82 
 
 14-66 
 
 Bran. 
 
 13-80 
 
 6"56 
 
 61-67 
 
 6-11 
 
 12-86 
 
 Oats ... . . 
 
 11-85 
 
 5-89 
 
 67-461 900 
 
 2-72 
 
 13-09 
 
 Fine barley dust 
 
 11-49 
 
 2-92 
 
 71-41 
 
 2-67 
 
 11-51 
 
 Wheat 
 
 11-48 
 
 ... 
 
 73-52 
 
 0-68 
 
 0-82 
 
 13-50 
 
 Bere 
 
 10-25 
 
 
 62-85 
 
 1008 
 
 2-60 
 
 14-22 
 
 Hay (mean of different grasses) 
 
 9-40 
 
 2-56 
 
 38-54 
 
 29-14 
 
 6-84 
 
 14-30 
 
 Barley 
 
 8-69 
 
 
 64-52 
 
 9-67 
 
 2-82 
 
 14-30 
 
 Coarse barley dust . 
 
 8-46 
 
 3-'47 
 
 69-73 
 
 7-31 
 
 11-03 
 
 Rice dust ... 
 
 808 
 
 2-95 
 
 69-22 
 
 8-12 
 
 11-63 
 
 Oat dust . . . . 
 
 6-92 
 
 3-21 
 
 72-86 
 
 7-70 
 
 931 
 
 Winter bean straw . 
 
 5-71 
 
 
 67-50 
 
 6-39 
 
 20-40 
 
 Carob bean .... 
 
 3-11 
 
 0-41 
 
 62-51 
 
 18-60 
 
 2-80 
 
 12-57 
 
 Potato 
 
 2-81 
 
 
 17-30 
 
 1-07 
 
 1-13 
 
 77-69 
 
 Carrot 
 
 1-87 
 
 
 7-91 
 
 3-07 
 
 1-11 
 
 86-04 
 
 Wheat straw . 
 
 1-79 
 
 ... 
 
 31-06 
 
 45-45 
 
 7-47 
 
 14-23 
 
 Barley straw .... 
 
 1-68 
 
 ... 
 
 39-98 
 
 39-80 
 
 4-24 
 
 14-30 
 
 Oat straw 
 
 1-63 
 
 
 37-86 
 
 43-60 
 
 4-95 
 
 12-06 
 
 Mangold-wnrzel 
 
 1-64 
 
 
 8-60 
 
 1-12 
 
 0-96 
 
 87-78 
 
 Cabbage 
 
 1-31 
 
 
 4-53 
 
 1-05 
 
 93-11 
 
 Turnips 
 
 1-27 
 
 0-20 
 
 4-07 1 1-08 
 
 1-7) 
 
 91-47 
 
THE FEEDING OF FAKM STOCK. 287 
 
 It is at once obvious that in many of these descrip- 
 tions of food the ratio of the flesh to the fatrforming con- 
 stituents differ very widely from that existing in the milk, 
 and this becomes still more apparent when the latter 
 are represented in their fat equivalent, as is done for a 
 few of them in the following table : — 
 
 Flesh Eespiratoiy, expressed 
 forming, in their fat eqmvalent, 
 
 Decorticated earth-nut cake .... 44'0 16'6 
 
 Linseed cake 28-5 26-7 
 
 Tares 26-73 18-8 
 
 Clover hay 15-81 16-8 
 
 Oats 11-85 28-8 
 
 Hay (mean of grasses) 9-40 17-9 
 
 Potato 2-81 6-9 
 
 Wheat straw 1-79 12-4 
 
 Turnip 1-27 1-8 
 
 It is especially note-worthy that those varieties of 
 food, which common experience has shewn to promote the 
 fattening of stock to the greatest extent, contain in many 
 instances the smallest quantity of respiratory or fat-form- 
 ing elements relatively to their nitrogenous compounds. 
 This is especially the case with the different kinds of oil 
 cake, the leguminous seeds, clover, hay, and turnips. On 
 the other hand, in the grains the ratio is nearly that of 
 one to three, or similar to that found in fat cattle ; while 
 in the straw, the excess of the respiratory elements is 
 extremely great. 
 
 These facts appear at first sight to be completely at 
 variance with the composition of the increase of fattening 
 animals, as ascertained by Messrs. Lawes and Gilbert 
 already referred to, and which have shewn that for every 
 pound of nitrogenous compounds, nearly ten pounds of fat 
 
288 AGRICULTtJEAL CHEMISTET. 
 
 are stored within the animal ; and it might be supposed 
 that those kinds of food wliich contain the largest relative 
 amount of respiratory elements ought to fatten most rapidly, 
 and should be selected by the farmer in preference to oil- 
 cakes and similar substances. But there are other matters 
 to be considered, dependent on the complex nature of the 
 changes attending the absorption and assimilation of the 
 food. It must be particularly borne in mind that only a 
 small proportion of the food consumed is stored up within 
 the body, and goes to increase the weight of the animal. 
 Even in the case of the milk, ia which economy in the 
 supply of nutritive matters has been most clearly attended 
 to by nature, a considerable proportion escapes assimilation, 
 and in the adult animal a large amount of the food passes 
 off with the excretions. The justice of this position is 
 apparent when it is remembered that an ox will go on 
 day after day consuming from a hundred weight to a 
 hundred weight and a half of turnips, three or four pounds 
 of bean-meal or oil-cake, and a considerable quantity of 
 straw, although its daily increase in live weight may not 
 exceed a couple of pounds. And in this direction a very 
 fertile field of inquiry lies open to the agricultural experi- 
 menter; for it would be most important to determine 
 whether there are not some substances from which the 
 nutritive matters may not be more easily assimilated than 
 from others, and what proportion of each is absorbable 
 under ordinary circumstances. On this point no informa- 
 tion has yet been obtained applicable to individual feeding 
 substances, but the experiments of Messrs. Lawes and 
 Gilbert have shewn the quantity of the total food, and of 
 each of its constituents, stored up in the fattening animal, 
 and a summary of their results is contained in the following 
 Table :— 
 
THE FEEDING OF FABM STOCK. 
 
 289 
 
 TABLE shewing the Amount of each Class of Consti- 
 tuents, stored in the increase, for 100 consumed in the 
 Food. 
 
 
 Mineral 
 Matters 
 
 Nitrogenons 
 Compounds. 
 
 J,, i Total Dry 
 "''• ^ Substance. 
 
 Sheep 
 
 Pigs 
 
 3-27 
 
 0-58 
 
 4-41 
 7-34 
 
 9-4 
 21-2 
 
 8-06 
 17-3 1 
 
 Hence it appears that the pig makes a better use of its 
 food than the sheep, retaining twice as much of its solid 
 constituents within the body, from which may be deduced 
 the important practical conclusion, that the former must 
 be fattened at a much smaller cost than the latter. Look- 
 ing at the individual constituents, it appears that, in the 
 sheep, less than one-twentieth of the nitrogenous com- 
 pounds, and one-tenth of the non-nitrogenous substances 
 contained in the food, remain in the body ; and a knowledge 
 of these facts tends to modify the conclusions which might 
 be drawn from the composition of the increase in the 
 fattening animal. Its influence may be best illustrated 
 by a particular example. If, for instance, the increase in 
 a sheep contained its nitrogenous and respiratory elements 
 in the ratio of 1 to 10, it would be totally incorrect to 
 supply these substances in the food in the same propor- 
 tions. On the contrary, it would be necessary at the very 
 least to double the proportion of the former, because one- 
 tenth of the fat-forming elements are absorbed, and only 
 one-twentieth of the nitrogenous. 
 
 On farther consideration, also, it seems unquestionable 
 that the quantity of the nutritive elements stored up must 
 depend to a large extent on the nature of the food and the 
 
290 AGEICULTUEAL CHEMISTRT. 
 
 particular state in which they exist in it. It is probable, 
 or at least possible, that some kinds of food may contain 
 their nitrogenous constituents in an easily assimilable 
 state, and their respiratory elements in a nearly indigestible 
 condition, or vice versa, and under these circumstances 
 their nutritive value would be below that indicated by 
 analysis ; but these points can only be determined by 
 elaborate and long continued feeding experiments. It 
 is well known, however, that the mechanical state of the 
 food has a most important influence on its nutritive value. 
 Thus, for example, the presence of a large quantity of 
 woody fibre protects the nutritive substances from assi- 
 milation, and seeds witb hard husks pass unchapged 
 through the animal, although, so far as their composi- 
 tion alone is concerned, they may be highly nutritive ; and- 
 the loss of a certain quantity of many varieties of food in 
 this way is familiar to every one. 
 
 The proper adjustment of the relative quantities of the 
 great groups of nutritive elements in the food is a matter 
 the importance of which cannot be over-rated, for it is in 
 fact the foundation of successful and economical feeding ; 
 and this will be readily understood if we consider what 
 would be the result of giving to an animal a supply of 
 food containing a large quantity of nitrogenous and a 
 deficiency of fat-forming compounds. In such circum- 
 stances, the animal must either languish for want of the 
 latter, or it is forced to supply the defect by an increased 
 consumption of food, in doing which it must take into the 
 system a larger quantity of nitrogenous compounds than 
 would otherwise have been requisite, and in this way the 
 other elements, which are present in abundance, are wasted, 
 and the theoretical and practical value of a food so con- 
 stituted may be very different, and it is only when the 
 
THE FEEDING OP FARM STOCK. 29 1 
 
 proportions of the different groups are properly attended 
 to that the most economical resalt can be obtained. It 
 can scarcely be said that the experiments yet made by 
 feeders enable us to fix the most suitable proportion in 
 which those substances can. be employed, although expe- 
 rience has led them to the use of mixtures which are in 
 most cases theoretically correct ; thus they combine oil- 
 cakes or turnips with straw, which is poor nitroge- 
 nous, and rich in fat-forming elements ; and in general 
 it will be found that where different kinds of food are 
 mixed, the deficiencies of the one are counterbalanced by 
 the other, and though this has hitherto been done empi- 
 rically, it cannot be doubted that as our knowledge 
 advances it will more and more be determined by refer- 
 ence to the composition of the food. 
 
 Although the presence of a sufficient quantity of 
 nutritive compounds in the food is necessarily the funda- 
 mental matter for consideration, its bulk is scarcely less 
 important. The function of digestion requires that the 
 food shall properly fill the stomach, and however large 
 the supply of nutritive matters may be, their effect is im- 
 perfectly brought out if the food is too small in bulk, and 
 it actually may become more valuable if diluted with woody 
 fibre, or some other inert substance. At first sight this 
 may appear at variance with the observations already 
 made as to the effects of woody fibre in protecting the 
 nutritive matters from absorption ; but practically there 
 are two opposite evils to be contended against, a food 
 having too small a bulk, or one containing so large a 
 proportion of inert substances as to become disadvan- 
 tageously voluminous. The most favourable condition 
 lies between the two extremes, and the natural food of all 
 herbivorous animals is diluted with a certain amount of 
 
292 AGKICULT0BAL CHEMISTRY. 
 
 woody fibre. When these are replaced by substances 
 containing a large quantity of nutritive matters in a smaU 
 bulk, the result is that the natural instinct of the animal 
 causes it to continue feeding until the stomach is properly 
 distended, and it consequently consumes a much larger 
 quantity of food than it is capable of digesting, and a 
 more or less considerable quantity passes unchanged 
 through the intestines, and is lost. On the other hand, 
 if the food be too bulky, the sense of repletion causes the 
 animal to cease eating long before it has obtained a suffi- 
 cient supply of nutritive matter. It is most necessary, 
 therefore, to study the mixture of different kinds of food, 
 so as to obtain a proper relation between the bulk and 
 the nutritive matters contained in the mixture ; and on 
 examining the nature of the mixed foods most in vogue 
 among feeders, it will be found that a very bulky food is 
 usually conjoined with another of opposite qualities. Hence 
 it is that turnips, the most voluminous of all foods, are 
 used along with oil-cake and bean-meal, and if from any 
 circumstances it becomes necessary to replace a large 
 amount of the former by either of the latter substances, the 
 deficient bulk must be replaced by hay or straw. 
 
 It has been already remarked that there are three great 
 purposes to which the food consumed is appropriated ; the 
 increase of weight of the animal — the object the feeder has 
 in view and desires to promote — the supplying the waste 
 of the tissues, and the process of respiration, both of which 
 are sources of loss of food, and which it must necessarily 
 be his aim to diminish as much as possible. The circum- 
 stances which must be attended to in order to do this are 
 sufficiently well understood. It has been clearly estab- 
 lished that the natural heat of the animal is sustained by 
 the consumption of a certain quantity of its food in the 
 
THE FEEDING OF PAEM STOCK. 293 
 
 respiratory process, during which it undergoes exactly the 
 same changes as those which occur during combustion. It 
 has further been observed, that the temperature of the body 
 remains unchanged, whatever be that of the surrounding 
 air ; and it is obvious that if it is to continue the same in 
 winter as in summer, a larger quantity of fuel {i. e. food) 
 must be consumed for this purpose, just as a room requires 
 more fire to keep it warm in winter than in summer, and 
 hence it naturally follows, that if the animal be kept in a 
 warm locality the food is economized. It may also be 
 inferred that, if it were possible, consistently with the 
 health of the animal, to keep it in a room artificially 
 heated to the temperature of its own body, this source of 
 waste of food would be entirely removed. It is not pos- 
 sible, however, to do this, because a limit is set to it by 
 physiological laws, which cannot be infringed with im- 
 punity ; but the housing of cattle, so as to diminish this 
 waste as far as possible, is a point in regard to the pro- 
 priety of which theory and practice are at one. 
 
 The old feeders kept their cattle in large open courts, 
 where they were exposed to every vicissitude of the 
 weather, but as intelligence advanced, we find them sub- 
 stituting, first hammels, and then stalls, in which the 
 animals are kept during the whole time of fattening at 
 an equable temperature. The effect of this is necessarily 
 to introduce a considerable economy of the food required 
 to sustain the animal heat ; but it also produces a saving 
 in another way, for it diminishes the waste of the tissues. 
 
 It has been ascertained by accurate experiments made 
 chiefly on man, that muscular exertion is one of the most 
 important causes of the waste of the tissues, and of in- 
 creased respiratory activity. We cannot move a limb 
 without producing a corresponding consumption of matters 
 
294 AGRICULTDKAL CHEMISTRY. 
 
 already laid np within the body ; and it has also been 
 found, that the difference in the quantity of carbonic acid 
 expired during rest and active exertion, is very large. 
 The inference to be drawn from this is, that when it is 
 sought to fatten an animal rapidly, every effort must be 
 made to restrain muscular motion so far as compatible 
 with health. Hence, the peculiar advantage of stall- 
 feeding, in which the animal is confined to one spot, and 
 the more thoroughly it can be kept still, the greater will 
 be the economy of food. This is gained by darkening the 
 house, and excluding all persons, except when their pre- 
 sence is indispensable. 
 
 An extension of the same principle has led to the 
 use of food artificially heated, but it is doubtful whether 
 the advantages derived from it are commensurate to the 
 increased expense of the process ; at least opinions differ 
 among the best informed practical men on this subject. 
 
 Many other matters, besides these mentioned, exercise 
 an important influence on the feeding of stock, such as 
 the general health of the animal, the breed, etc. These 
 are subjects, however, which bear more directly on practical 
 agriculture, and need not be discussed here. 
 
 The judicious feeder will not only give due weight 
 to the principles already discussed in all he does, but he 
 must take into consideration the extent to which they are 
 liable to be modified in particular cases. He must 
 also attend to the cost of different kinds of food, and 
 the value of the manure produced by them, subjects of 
 much importance in a practical point of view, and which 
 must influence him greatly in choice of the particular 
 substances he supplies to his cattle. 
 
INDEX. 
 
 Acin, apocrenio, 21. 
 
 Carbonic, 10, 15, 20, 37, 57, 
 
 115. 
 Cerotic, 48. 
 Crenic, 21. 
 Geic, 21. 
 Hippnric, 168. 
 Uumic, 21. 
 Lactic, 168. 
 Margaric, 47. 
 Nitric, 11, 17, 30, 33, 38, 62, 
 
 112. 
 Oleic, 47. 
 Pectic, 46. 
 Phosplioric, 73, 90. 
 Stearic, 47. 
 Sulphuric, 182, 237. 
 Ulmio, 21. 
 Uric, 168. 
 Adulteration of guano, 211. 
 Agricultural Chemistry Association 
 
 of Scotland, 6. 
 Air, influence of, on germination, 
 55. 
 In the pores of soils, 115. 
 Albite, 86. 
 Albumen, 48. 
 Albuminous constituents of plants 
 
 and animals, 48. 
 Algoa Bar guano, 208. 
 Alkaline salts, value of, 260. 
 Alumina, 73, 86, 103. 
 Ammonia, absorption of, by plants, 
 29,38. 
 Absorption of, by soils, 123. 
 Carbonate of^ 29. 
 Composition of, 12. 
 Decomposition of, by plants, CI. 
 Presence in dew, 17. I 
 
 „ rain, 17. 
 
 Production of, 12. ! 
 
 Properties of, 12. ' 
 
 Ammonia, proportion of, in air, 16, 
 20. 
 
 Proportion of, in drain water, 
 112. 
 
 Proportion of, in soils, 107. 
 
 Sulphate of, 29, 227. 
 
 Sulphomuriate of, 227. 
 
 Urate of, 205. 
 
 Valuation of, 259. 
 Ammoniacal liquor, 229. 
 Amylaceous constituents of plants, 
 
 40. 
 Angamos guano, 207, 210. 
 Animal charcoal, 224. 
 
 Manures, 204. 
 Animals, composition of, 281. 
 
 Nitrogenous constituents of, 48, 
 281. 
 Apatite, 235. 
 
 Ascension Island guano, 208. 
 Augite, 89. 
 
 Australian guano, 207. 
 Avenine, 60. 
 
 Bases, amount of ash in, 66. 
 
 Barley, 286. 
 
 Barrenness of soils, 109. 
 
 iiasalt, 92. 
 
 Beans, 286. 
 
 Bere, 286. 
 
 Biphosphate of lime, 237, 260. 
 
 Bird Island guano, 208, 
 
 Blood as a manure, 220. 
 
 Bone ash, 234. 
 
 Bone oil, 229. 
 
 Bones as a manure, 223. 
 
 Dissolved, 237. 
 Box-feeding, 183. 
 Bolivian guano, 207, 210. 
 Bran, 197, 286. 
 
 Burning, improvement of soils by, 
 146. 
 
296 
 
 INDEX. 
 
 Cabbaob, 286. 
 Cane sugar, 43. 
 Carbon, properties of, 10. 
 
 Proportion of, in plants, 10. 
 Carbonate of ammonia, 29. 
 
 Lime, 96, 247. 
 
 Magnesia, 96. 
 
 Potash, 232. 
 
 Soda, 232. 
 Carbonic acid, absorption of, by 
 plants, 37. 
 
 Decomposition of, by plants,67. 
 
 Evolntion of, by plants, 58. 
 
 How obtained, 10, 
 
 Properties, 10. 
 
 Proportion o£ in air, 15, 20. 
 Carbnretted hydrogen, 19. 
 Calcinm, snlphnret of. 252. 
 Caramel, 44. 
 Carrot, 286. 
 Caseine, 50, 283. 
 Castor cake, 195. 
 Cattle food, composition of, 286. 
 Cellnlose, 40. 
 Cerine, 48. 
 Cerotic acid, 48. 
 Chaff, 197. 
 Challi, 96, 245. 
 Charcoal, animal, 224. 
 Chilian guano, 207. 
 China-clay, 87. 
 Chloride of potassium, 73, 102. 
 
 .Sodium, 73, 232. 
 
 Manganese, 182. 
 Clay, 87. 
 
 Absorbent action of, 121. 
 
 Composition of, 95, 
 
 Source of, 88, 94. 
 Clay-slate, 95. 
 Classification of plants, 81. 
 Coprolites, 98, 235. 
 Coral sand, 246. 
 Cotton cake, 196, 286. 
 Crenic acid, 21. 
 Crops, Mineral matters in, 270. 
 
 Nitrogen in-different, 270. 
 
 Sotation of, 81, 266. 
 
 Deep Ploughiko, effects of, 144. 
 Dew, ammonia in, 17. 
 Nitric acid in, 19. 
 Dextrine, 43. 
 Diastase, 43, 53, 55. 
 Diorite, 92. 
 Dissolved bones, 237. 
 
 Dolerite, 92. 
 
 Dotter cake, 286. 
 
 Drainage water, analyses of, 112. 
 
 Draining, 138. 
 
 Dung, composition of, 170. 
 
 Dung heaps, management of, 179. 
 
 Earth-nut cake, 286. 
 Emulsine, 50. 
 Exhaustion of soils, 81 . 
 
 Fakm stock, feeding of, 276. 
 Farm-yard manure, 166, 172. 
 
 Application of, 186. 
 Fat, amount of, in' animals, 281. 
 Fattv acids, 47. 
 
 Matters, 46. 
 Feeding cakes, 286. 
 Feeding of farm stock, 276. 
 Felspar, 86. 
 
 Decomposition of, 88. 
 Fermentation of manure, 184. 
 Fire-clay, 95, 
 Fish manure, 221. 
 Flesh as a manure, 220. 
 Fog, ammonia in, 17. 
 
 Nitric acid in, 19. 
 Food, cattle, 286. 
 Fruits, amount of ash in, 66. 
 
 Gas Lime, 252. 
 Geic acid, 21. 
 Germination, 64. 
 Gluten, 49, 
 Glntin, 49, 
 Glycerine, 47. 
 Gneiss, 91. 
 Granite, 91. 
 Grape sugar, 44. 
 Greenstone, 92. 
 Green manuring, 1 98. 
 Guano, 204. 
 
 Adulteration of, 211. 
 
 Application of, 214. 
 
 Averape composition o^ 207. 
 
 Fish, 222. 
 
 Peruvian, characters o^ 209. 
 
 Phospho-Peruvian, 243. 
 
 Sombrero Island, 236. 
 
 Hair, 218. 
 
 Hay, 286. 
 
 Heat, evolution of, by plants, 60, 
 
 Hempseed cake, 286. 
 
 Hippuric acid, 168. 
 
INDEX. 
 
 297 
 
 Horn, 218. 
 Hornblende, 89. 
 Hnmic acid, 21. 
 Homin, 22. 
 Hamus, 21, 98, 133. 
 Hydrogen, 10. 
 
 ICHABOU GnAKo, 207. 
 
 Indian guano, 208. 
 
 Inorganic constitnents of plants, 
 
 9,34. 
 Inorganic constituents ; 
 
 Absorption by plants, 38. 
 
 Proportion in plants, 64. 
 Inorganic constitnents of soils, 85. 
 Innline, 43. 
 Iodine in plants, 76. 
 Iron, protoxide of, in soils, 107. 
 
 Sulphate of, 182. 
 
 Snlphuret of, in snbsoils, 135. 
 
 Kaolin, 87. 
 
 Kooria Mooria guano, 207. 
 
 Labradokite, 86. 
 Lactic acid, 1G8. 
 Latham Island guano, 207. 
 Leares, amount of ash in, 65. 
 
 As a manure, 202. 
 Legumine, 50. 
 Lichen starch, 42. 
 Light, influence of, on plants, 57. 
 Lime, action of, on soils, 248. 
 As a manure, 245. 
 Bicarbonate of, 122. 
 Carbonate of, 96. 
 Biphosphate of, 237, 260. 
 Hiimate of, 125 
 Phosphate of, 96, 233, 258. 
 Sulphate of, 96, 253, 260. 
 Lime-plants, 82. 
 Limestone, 96. 
 Linseed cake, 195. 
 Liquid manure, 166, 187. 
 
 Madia Satita, 286. 
 Magnesia, carbonate of, 96. 
 
 Snlphate of, 182, 233. 
 Magnesian limestone, 96. 
 Malt-dust, 197. 
 Manganese in plants, 73. 
 
 Oxide of, 73, 87. 
 
 Chloride of, 182. 
 Mangold-wnrzel, 286. 
 Manures, animal, 204. 
 
 Manures, application o^ 165, 186. 
 
 Fermentation of, 184. 
 
 Farmvard, 166, 172. 
 
 Liquid, 166, 187. 
 
 Mineral, 226. 
 
 Theory of, 166. 
 
 Setrage, 191. 
 
 Vegetable, 195. 
 
 Valuation of, 255. 
 Manuring, Green, 198. 
 
 Principles of, 152. 
 Maple peas, 286. 
 Maracaybo guano, 236. 
 Margaric acid, 47. 
 Margarine, 46. 
 IVfarl, 245. 
 
 Mexican guano, 207. 
 Mica, 88. 
 Mica slate, 91. 
 Milk, composition of, 283. 
 
 Curding of, 51 
 Mineral constituents of plants, 9, 
 
 63. 
 Mineral manures, 226. 
 Mineral matters in different crops, 
 270. 
 In animals, 281. 
 Moisture, influence o^ on germi- 
 nation, 55. 
 Mucilage, 44. 
 
 Natrolite, 90. 
 New Island guano, 208. 
 Niger cake, 286. 
 Night-soil, 217. 
 Nitrate of potash, 229. 
 Nitrate of soda, 229, 260. 
 Nitric acid, absorbtion of, by plants, 
 30, 38. 
 
 Decomposition of, by plants, C2. 
 
 In drainage water, 112. 
 
 In dew, 19. 
 
 In air, 17. 
 
 In fog, 19. 
 
 Production of, 11, 33.1 
 Nitrification, 11. 
 
 Nitrogen, amount in a six-course 
 rotation, 160. 
 
 Amount of, in different crops, 
 270. 
 
 Presence in the atmosphere, 11. 
 
 Properties of, 11. 
 
 Proportion of, in plants, 1 1. 
 Nitrogenous constituents of plants, 
 48, 286. 
 
298 
 
 INDEX 
 
 Nitrogenons constituents of animals, 
 48, 281. 
 
 Oats, 286. 
 
 Proportion of ash in, 68, 70. 
 Oil-cakes, 195, 286. 
 Oils, sweet principle of, 47. 
 Oily matters, 46. 
 Oleic acid, 47. 
 Oleine, 46. 
 Oligoclase, 86. 
 Oolitic limestone, 96. 
 Organic constituents of plants, 8. 
 
 Sources of the, 13, 20. 
 Organic constituents of soils, 103. 
 Orthoclase, 86. 
 
 Oxide of iron in rocks and soils, 87, 
 107. 
 
 Of manganese, 87- 
 Oxygen, evolution of, by plants, 
 68. 
 
 Influence of, on germination, 55. 
 
 Presence in atmosphere, 12. 
 
 Properties of, 12. 
 
 Proportion of, in plants, 12. 
 
 Pacquico Gdano, 207. 
 
 Paring, improvement of soils by, 146. 
 
 Patagonian guano, 207. 
 
 Pea-nut cake, 2s6. 
 
 Peas, 286. 
 
 Peat, as a manure, 203. 
 
 Peat, use o^ in dung-heaps, 184. 
 
 Pectic acirf, 46. 
 
 Pectine, 46. 
 
 Peruvian Guano, 205, 207, 209. 
 
 Upper, 207, 213. 
 Phosphate of lime, 96, 233. 
 
 . Value of, 258. 
 Phosphates, insoluble, 258. 
 
 Soluble, 237, 260. 
 Phospho-Pemvian guano, 243. 
 Phosphuretted hydrogen in air, 19, 
 Pigeons' dung, 216. 
 Plants, Albuminous constituents of, 
 48. 
 
 Amylaceiius constituents of, 40. 
 
 Ash of, 64, 73. 
 
 Classification of, 81. 
 
 Inorganic constituents of, 9, 34, 
 38,63. 
 
 Oily constituents of, 46. 
 , Organic constituents of, 8. 
 
 Proximate constituents of, 40. 
 
 Saccharine constituents of, 40, 
 
 Poppy cake, 196, 286. 
 Potash, carbonate of, 232, 
 
 Muriate of, 231, 
 
 Nitrate of, 229. 
 
 Plants, 82, 
 
 Salts, 231. 
 Potato, 280. 
 Poudrette, 217, 
 
 Proximate constituents of plants, 40, 
 Pyroguanite, 236, 
 
 Quartz, 86, 
 
 Rainwater, 17, 18. 
 Kape Cake, 196, 286, 
 
 Dust, 195. 
 Rocks, crystalline, 85, 
 
 Composition of, 91, 
 
 Disintegration of, 85, 
 
 Sedimentary, 86, 
 Roots of plants, amount of ash in, 
 
 65, 
 Rotation of crops, 81, 266, 
 Kubsen cake, 286, 
 Eye, 286, 
 
 Saccharine Constitdents of 
 
 plants, 40, 
 Saldanha Bay guano, 207, 
 Salt, common, 232, 
 Sandstones, 95, 
 Schubler's experiments, 127, 
 Sea Bear Bay guano, 208, 
 Sea weed, 200, 201, 
 Seeds, amount of ash in, 64, 
 Sesamum cake, 286, 
 Sewage manure, 191, 
 Shell sand, 246, 
 Silica plants, 82, 
 Silicate of potash, 23-3, 
 
 Soda, 233, 
 Skin, 218, 
 Soda, carbonate of, 232, 
 
 Nitrate of, 229, 260, 
 
 Salts, 231, 
 
 Silicate of, 233, 
 Sodium, chloride of, 232, 
 Soil, the, 20, 83. 
 
 Influence on the composition of 
 the ash of plants, 71. 
 
 Chemical composition of, 98. 
 
 Chemical and physical charac- 
 ters of, 83. 
 
 Improvement of, by mechanical 
 means, 137. 
 
INDEX. 
 
 299 
 
 Soi], relation of, to heat and mois- 
 ture, 127. 
 Soila, absorbent action of. 122. 
 
 Air in the pores of, 114. 
 
 Analysis, 101, 118. 
 
 Barrenness of, 109. 
 
 Classification of, 135. 
 
 Exhaustion of, 81. 
 
 Inorganic constituents of, 85. 
 
 Mixing of, 160. 
 
 Origin of, 84. 
 
 Organic matters in, 103. 
 
 Physical characters of, 118, 127. 
 Sombrero Island guano, 236. 
 Starch, 41. 
 
 Lichen, 42. 
 Stearic acid, 47. 
 Stearine, 46. 
 
 Stems of plants, ash in, 64. 
 Straw, amount of ash in, 64. 
 
 As a manure, 197. 
 Sulphiite of iron, 182. 
 
 Lime, 96, 253, 260. 
 
 Magnesia, 182. 
 
 Ammonia, 29, 227. 
 
 I'otash, 231. 
 Sulphomuriate of ammonia, 227. 
 Sulphur in plants, 78. 
 Sulphuret of iron, 135. 
 
 Calcium, 252. 
 Sulphuretted hydrogen, 19. 
 Sugar, 43. 
 
 Of milk, 283. 
 Subsoil, the, 134. 
 
 Ploughing, 143. 
 Sunflower cake, 286. 
 Svenite, 91. 
 
 Tares, 286. 
 Teelcake, 286. 
 
 Temperature, influence of, on ger- 
 mination, 54. 
 Thomsonite, 90. 
 Trap rock, 92. 
 Tubers, amount of ash in, 65. 
 
 Ulmic acid, 21. 
 
 Ulmin, 22. 
 
 Upper Peruvian guano, 207, 213. 
 
 Urate, 216 
 
 Of ammonia, 205. 
 Urea, 168. 
 Uric acid, 168, 205. 
 Urine, composition of, 167. 
 
 Human, 168. 
 
 Sulphated, 216. 
 
 Valuation of manures, 255. 
 Vegetable manures, 195. 
 Vegetation, influence of lipht on, 57. 
 Voelcker's analyses of dung, 174. 
 
 Wakpihg, 148. 
 
 Water, absorption of, by plants, 35. 
 
 Decomposition of, bv plants, 60. 
 
 Exhalation of, by plants, 35. 
 
 Rain, 17, 18. 
 Wax, 48. 
 Wheat, 286. 
 
 Woods, amount of ash in, 65. 
 Woody fibre, 41. 
 Wool, 219. 
 
 Zeolites, 90. 
 
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 Hivemick, Heinrich August Christ., late 
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 Jamieson, Robert, D.D., Minister of St. 
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 Jennings, Isaac. 
 
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 Morren, Nathanael, M.A. 
 
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 Poole, Reg. Stuart, British Museum. 
 
 Porter, J. Leshe, M.A., Professor of Sacred 
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 Boyle, J. F., M.D., F.B.S.,F.L.S., F.G.S. 
 
 Eyland, J. E. 
 
 Smith, C. Hamilton, Lieut. -Colonel, K.H. 
 and K.W., F.R.S., F.R.L.S., etc. 
 
 Smith, John Pye, D.D., P.RS, F.G.S. 
 
 Stebbine, Heniy, D.D. of St. John's Col- 
 lege, Cambridge. 
 
 Tholuck, August, D.D., Professor of Theo- 
 logy in the University of Halle. 
 
 Wace, Henry, M.A. 
 
 Wright, William, M.A andLL.D. of Trinity 
 College, Dublin. • 
 
 EDINBTJEGH : ADAM AND CHARLES BLACK. 
 
16 
 
 ADAM AND CHARLES BLACK S PUBLICATIONS. 
 
 NEW EDITION, 1862. 
 
 In folio, half hound morocco, gilt edges, price £3, 
 A new edition of 
 
 BLACK'S GENERAL ATLAS OF THE WORLD, 
 
 Series of Fifty-six Maps, containing all the Latest Discoveries, 
 beautifully coloured, and accompanied by an Alphabetical Index 
 of 65,000 Names, forming a ready Key to the places mentioned 
 in the Maps. 
 
 List of Maps in the order in which they occur. 
 PHYSICAL GEOGRAPHY, Etc. 
 
 1. The World in Hemispheres, with Com- 
 
 parative View of Mountains and 
 Rivers. 
 
 2. The World on Mercator's Projection. 
 
 3. Physical and Ethnographical Charts 
 
 of the World. 
 
 4. Zoological and Botanical Charts of the 
 
 World. 
 
 5. Isothermal Chart shewing the Tem- 
 
 perature of the Earth's Surface. 
 
 6. Northern and Southern Celestial He- 
 
 misphere. 
 
 7. Solar System, Theory of the Seasons, 
 
 etc. 
 
 EUROPE. 
 
 8. Europe. 
 
 9. England (North Part). 
 
 10 (Soutli Part). 
 
 11. Scotland (North Part). 
 12 (South Part). 
 
 13. Ireland. 
 
 14. France. 
 
 15. Switzerland. 
 
 16. Holland and Belgium. 
 
 17. Railway Map of Central Europe. 
 
 18. Germany. 
 
 19. Austria. 
 
 20. Prussia. 
 
 21. Denmark. 
 
 22. Sweden and Norway, with Baltic Sea. 
 
 23. Russia in Europe. 
 
 24. Spain and PortugaL 
 
 25. Italy (North). 
 26 (South). 
 
 27. Turkey in Europe. 
 
 28. Greece and Ionian Islands. 
 
 ■^^^■^ 55. The World as known to the Ancientg. 
 
 29. Asia. 56, The Principal Countries of the Ancient 
 
 30. Turkey in Asia. World, with the Roman and Persian 
 
 31. Palestine. Empires. 
 
 Accompanied hy Sketch Maps of the Federal and Confederate States^ 
 and of a portion of Mexico; 
 
 EDINBUEGH : ADAM A:^!) CHAELES BLACK. 
 
 32. Persia, Afghanistan, and Beloochistan- 
 
 33. India. 
 
 34. China, 
 
 35. Indian Archipelago, and Further India, 
 including Burmah, Siam, etc. 
 
 AFRICA. 
 
 36. Africa, with Earth's, Livingstone's, and 
 Burton's Routes. 
 
 37. Egypt. 
 
 38. South Africa. 
 AMERICA. 
 
 39. North America, with Enlargement of 
 British Columbia. 
 
 40. British America and Arctic Regions.' 
 
 41. Canada East, New Brunswick, Nova 
 Scotia, etc. 
 
 42. Canada West. 
 
 43. United States of America (General 
 Map). 
 
 44. The Eastern or Principal States. 
 
 45. The Western States (California, Ore- 
 gon, Utah, etc.) 
 
 Mexico, Central America, etc. . 
 
 West India Islands. 
 
 South America. 
 
 Venezuela, New Granada, Equador, 
 and Peru. 
 
 Chili — Argentine Republic, and Bo- 
 livia. 
 
 Brazil, Uruguay, and Guayana. 
 
 AUSTRALIA AND ISLANDS OF THE 
 PACIFIC. 
 
 52. Australia. 
 
 53. New Zealand, Tasmania, and Western 
 Australia. 
 
 64. Polynesia and Pacific Ocean.