IC-NRLF & Mwdlrr. ERKELEY LIBRARY UNIVERSITY Of CALlFORNiA ORGANIC CHEMISTRY IN ITS APPLICATIONS AGRICULTURE AND PHYSIOLOGY, JUSTUS LIEBIG, M.D., PH.D., F.R.S., M.R.I.A., PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF OIESSEN \ KNIGHT OF THE HESSIAN ORDER; MEMBER OF THE ROYAL ACADEMY OF SCIENCES OF STOCKHOLM; CORKESPONDING MEMBER OF THE ROYAL ACADEMIES OF SCIENCES OF BERLIN AND MUNICH ; OF THE IMPERIAL ACADEMY OF ST. PETKRS- BURGH ; OF THE ROYAL INSTITUTION OF AMSTERDAM, ETC. ETC. EDITED FROM THE MANUSCRIPT OF THE AUTHOR BY LYON PLAYFAIR, PH.D. LONDON : PRINTED FOR TAYLOR AND WALTON, BOOKSELLERS AND PUBLISHERS TO UNIVERSITY COLLEGE, UPPER GOWER STREET. MDCCCXL. LONDON : BRADBURY AND EVANS, PRINTERS, WHTTEFRIAKS. LOAN STACK THE BEIT1SH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. ONE of the most remarkable features of modern times is the combination of large numbers of indi- viduals representing the whole intelligence of nations, for the express purpose of advancing science by their united efforts, of learning its pro- gress, and of communicating new discoveries. The formation of such associations is, in itself, an evidence that they were needed. It is not every one who is^called by his situation in life to assist in extending the bounds of science; but all mankind have a claim to the blessings and benefits which accrue from its earnest cultivation. The foundation of scientific institutions is an acknowledgment of these bene- vi PREFACE. fits, and this acknowledgment proceeding from whole nations may be considered as the triumph of mind over empiricism. Innumerable are the aids afforded to the means of life, to manufactures and to commerce, by the truths which assiduous and active inquirers have discovered and rendered capable of practical application. But it is not the mere practical utility of these truths which is of importance. Their influence upon mental culture is most bene- ficial ; and the new views acquired by the know- ledge of them enable the mind to recognise, in the phenomena of nature, proofs of an infinite wisdom, for the unfathomable profundity of which, lan- guage has no expression. At one of the meetings of the chemical section of the " British Association for the Advancement of Science," the honourable task of preparing a report upon the state of organic chemistry was imposed upon me. In the present work I present the Association with a part of this report. I have endeavoured to develop, in a manner correspondent to the present state of science, the fundamental principles of chemistry in general, PREFACE. Vll and the laws of organic chemistry in particular, in their applications to agriculture and physiology ; to the causes of fermentation, decay, and putre- faction ; to the vinous and acetous fermentations, and to nitrification. The conversion of woody fibre into wood- and mineral-coal, the nature of poisons, contagions and miasms, and the causes of their action on the living organism, have been elucidated in their chemical relations. I shall be happy if I succeed in attracting the attention of men of science to subjects which so so well merit to engage their talents and energies, perfect agriculture is the true foundation of all trade and industry it is the foundation of the riches of states. But a rational system of agri- culture cannot be formed without the application of scientific principles; for such a system must be based on an exact acquaintance with the means of nutrition of vegetables, and with the influence of soils and action of manure upon them. This knowledge we must seek from che- mistry, which teaches the mode of investigating the composition and of studying the characters of the different substances from which plants derive their nourishment. Vlll PREFACE. The chemical forces play a part in all the pro- cesses of the living animal organism; and a number of transformations and changes in the living body are exclusively dependent on their influence. The diseases incident to the period of growth of man, contagion and contagious matters, have their analogues in many chemical processes. The investigation of the chemical connexion subsisting between those actions proceeding in the living body, and the transformations presented by chemical compounds, has also been a subject of my inquiries. A perfect exhaustion of this sub- ject, so highly important to medicine, cannot be expected without the co-operation of physiologists. Hence I have merely brought forward the purely chemical part of the inquiry, and hope to attract attention to the subject. Since the time of the immortal author of the " Agricultural Chemistry," no chemist has occu- pied himself in studying the applications of che- mical principles to the growth of vegetables, and to organic processes. I have endeavoured to follow the path marked out by Sir Humphry Davy, who based his conclusions only on that which was capable of inquiry and proof. This is PREFACE. IX the path of true philosophical inquiry, which pro- mises to lead us to truth the proper object of our research. In presenting this'report to the British Associa- tion I feel myself bound to convey my sincere thanks to Dr. Lyon Playfair, of St. Andrews, for the active assistance which has been afforded me in its preparation by that intelligent young chemist during his residence in Giessen. I cannot suppress the wish that he may succeed in being as useful, by his profound and well-grounded knowledge of chemistry, as his talents promise. DR. JUSTUS LIEBIG. Giessen, September 1, 1840. CONTENTS. PART I. THE CHEMICAL PROCESSES IN THE NUTRITION OF VEGETABLES. Page Subject of the Work . . . . . 1 The Constituent Elements of Plants . . .2 The Assimilation of Carbon . . . .4 Composition and Properties of Humus . . 5 Absorption of Humus ..... 9 Fertility of different Soils . . . . . 13 Influence of Manure . . . . .15 Proportion of Carbonic Acid in the Atmosphere . 17 The Atmosphere is the source of Carbon in Plants . 19 Influence of the Shade on Plants . . 27 Exhalation of Oxygen by Plants . . . .33 Neglect of Chemistry by Botanists . . 35 Object of Experiments in Physiology . . .37 Conditions essential to Nutrition . 39 Xll CONTENTS. Page On the Origin and Action of Humus . . .45 Growth of Plants . . . . . . 49 Transformations of Organic Substances . . 51 Nature of Organic Chemical Processes . 53 The use of Humus explained . . 59 Humus is not indispensable for Plants . . 61 Assimilation of Hydrogen . . . .63 Hydrogen is obtained by the Decomposition of Water . 65 Its assimilation is attended with the Evolution of Oxygen . 67 On the Origin and Assimilation of Nitrogen . 69 Source of Nitrogen in Plants . . . - 70 Ammonia is always contained in the Atmosphere . . 73 Use of Gypsum in manuring Meadow Land . . 87 Use of burned Clay as Manure . . 89 The Inorganic Constituents of Plants . . .92 Plants contain an invariable quantity of Alkaline 'Bases . 94 The origin of common Salt in Plants . . .114 The Art of Culture . . . . . 116 Use of Humus . . . . . 1 18 Nutrition and Growth of Plants . . . . 1 23 Necessity of Azotised Substances . . .131 Influence of the Food on the Produce . 133 Composition of Soils . . . . .141 The Fertility of Soils . . . . 145 Fallow Crops . . . . . . J57 The Interchange of Crops and Manure . 159 Manure . .174 CONTENTS. xiii Page Composition of Animal Manures . . . 175 The essential Elements of Manure . . .179 Bone Manure . . . . . . 185 Manure supplies Nitrogen . . . .189 Mode of applying Urine . . . . 193 Value of human Excrements . . . .197 Concluding Remarks . . . . . 201 APPENDIX TO PART I. Growth of Plants without Mould . . 204 On the Action of Charcoal on Vegetation . . -207 On the Rotation of Crops at Bingen, on the Rhine . 211 On a mode of manuring Vines . . 211 PART II. THE CHEMICAL PROCESSES OF FERMENTATION, DECAY, AND PUTREFACTION. Chemical Transformations . . . .217 Their Cause . . . . . . . 220 Chemical Transformations of Organic Compounds . 231 Transformations of Bodies containing Nitrogen . . 240 Fermentation of Sugar ..... 248 Yeast or Ferment, . . . . . . 251 Nature of Fermentation . . . . .257 i8 9 or Decay . . . 260 XIV CONTENTS. Page Nature of the Process . . . . . 263 Nitrification . . . . . . . 276 Vinous Fermentation : Wine and Beer . . 282 Various Properties of Wines . . . . . 293 Fermentation of Beer the Bavarian Process . 295 Decay of Woody Fibre . . . > . 308 Vegetable Mould . . . . .315 On the Mouldering of Bodies . . . . . 317 Paper . ... 318 Brown Coal . . . . ' . . . 321 Mineral Coal . . . . .327 On Poisons, Contagious Matter , and Miasms . . 329 Inorganic Poisons ..... 330 Organic Poisons . . . . . . 343 Putrid Poisons . . . . . .347 % Morbid Poisons , . . . . . 351 Mode of Action of Contagions and Miasms . 355 Addition to Note at Page 17 .... 385 Tables showing the Proportion between the Hessian and English Standard of Weights and Measures . . 386 ERRATA. Page 10 line 18 for essian . . . read Hessian. t/~" 64 6 for 8 cwt. . . read 10 cwt. 9210 from bottom, for are formed, read are found. 103 16 for nitrate of abrontian . read nitrate of strontia. 126 1 and 2, for 476/fo. and 37/fo. read 47 bolls, and 37 bolls. 183 10 for (10 Si Oz+ KO. .) . read (10 Si O3 + KO.) 251 3 for laclate acid . . read lactic acid. 265 8 from bottom, for oxyen . read oxygen. ORGANIC CHEMISTRY APPLIED TO PART I. OF THE CHEMICAL PROCESSES IN THE NUTRITION OF VEGETABLES. THE object of organic chemistry is to discover the chemical conditions which are essential to the life and perfect development of animals and vege- tables, and, generally, to investigate all those pro- cesses of organic nature which are due to the operation of chemical laws. The continued existence of all living beings is dependent on the reception by them of certain substances, which are applied to the nutrition of their frame. An inquiry, therefore, into the condi- tions on which the life and growth of living beings depend, involves the study of those substances which serve them as nutriment, as well as the investigation of the sources whence these sub- stances are derived, and the changes which they undergo in the process of assimilation. The primary source whence man and animals B 2 OF THE CONSTITUENT ELEMENTS derive the means of their growth and support is the vegetable kingdom. Plants, on the other hand, find new nutritive material only in inorganic substances. The purport of this work is to elucidate the chemical processes engaged in the nutrition of vegetables. The first part of it will be devoted to the exami- nation of the matters which supply the nutriment of plants, and of the changes which these matters undergo in the living organism. The chemical compounds which afford to plants their principal constituents, viz., carbon and nitrogen, will here come under consideration, as well as the relations in which the vital functions of vegetables stand to those of the animal economy and to other pheno- mena of nature. The second part of the work will treat of the chemical processes which effect the complete destruction of plants and animals after death, such as the peculiar modes of decomposition, usually described as fermentation, putrefaction, and decay ; and in this part the changes which organic sub- stances undergo in their conversion into inorganic compounds, as well as the causes which determine these changes, will become matter of inquiry. OF THE CONSTITUENT ELEMENTS OF PLANTS. Carbon enters into the composition of all plants, and of all their different parts or organs. OF PLANTS. 3 The substances which constitute the principal mass of every vegetable are compounds of carbon with oxygen and hydrogen in the proper relative proportions for forming water. Woody fibre, starch, sugar, and gum, for example, are such com- pounds of carbon with the elements of water. In another class of substances containing carbon as an element, oxygen and hydrogen are again present ; but the proportion of oxygen is greater than would be required for producing water by union with the hydrogen. The numerous organic acids met with in plants belong, with few exceptions, to this class. A third class of vegetable compounds contain carbon and hydrogen, but no oxygen, or less of that element than would be required to convert all the hydrogen into water. These may be regarded as compounds of carbon with the elements of water and an excess of hydrogen. Such are the volatile and fixed oils, wax, and the resins. Many of them have acid characters. The juices of all vegetables contain organic acids, generally combined with the inorganic bases, or metallic oxides ; for these metallic oxides exist in every plant, and may be detected in its ashes after incineration. Nitrogen is an element of vegetable albumen and gluten ; it is a constituent of the acids, and of what are termed the " indifferent substances," of plants, as well as of those peculiar vegetable compounds OF THE ASSIMILATION OF CARBON. which possess all the properties of metallic oxides, and are known as " organic bases." Estimated by its proportional weight, nitrogen forms only a very small part of plants, but it is never entirely absent from any part of them. Even when it does not absolutely enter into the compo- sition of a particular part or organ, it is always to be found in the fluids which pervade it. It follows from the facts thus far detailed, that the development of a plant requires the presence, first, of substances containing carbon and nitrogen, and capable of yielding these elements to the grow- ing organism ; secondly, of water and its elements ; and lastly, of a soil to furnish the inorganic matters which are likewise essential to vegetable life. OF THE ASSIMILATION OF CARBON. The fertility of every soil is generally supposed by vegetable physiologists to depend on the presence in it of a peculiar substance to which they have given the name of humus. This substance, believed to be the principal nutriment of plants, and to be extracted by them from the soil in which they grow, is itself the product of the decay of other plants. Humus is described by chemists as a brown substance, easily soluble in alkalies, but only slightly soluble in water, and produced during the decomposition of vegetable matters by the action of acids or alkalies. It has, however, COMPOSITION OF HUMUS. 5 received various names according to the different external characters and chemical properties which it presents. Thus, ulmin, humic acid, coal of humus, and humin, are names applied to modifica- tions of humus. They are obtained by treating peat, woody fibre, soot, or brown coal with alkalies ; by decomposing sugar, starch, or sugar-of-milk by means of acids ; or by exposing alkaline solu- tions of tannic and gallic acids to the action of the air. The modifications of humus which are soluble in alkalies, are called humic acid ; while those which are insoluble have received the designations of humin and coal of humus. The names given to these substances might cause it to be supposed that their composition is identical. But a more erroneous notion could not be enter- tained ; since even sugar, acetic acid, and colophan do not differ more widely in the proportions of their constituent elements, than do the various modifications of humus. Humic acid formed by the action of hydrate of potash upon sawdust contains, according to the ac- curate analysis of Peligot, 72 per cent, of carbon, while the humic acid obtained from turf and brown coal contains, according to Sprengel, only 58 per cent.; that produced by the action of dilute sulphuric acid upon sugar, 57 per cent, according to Malaguti ; and that, lastly, which is obtained from sugar or from starch, by means of muriatic acid, according to the 6 OF THE ASSIMILATION OF CARBON. analysis of Stein, 64 per cent. All these analyses have been repeated with care and accuracy, and the proportion of carbon in the respective cases has been found to agree with the estimates of the different chemists above mentioned ; so that there is no rea- son to ascribe the difference in this respect between the varieties of humus to the mere difference in the methods of analysis or degrees of expertness of the operators. Malaguti states, moreover, that humic acid contains an equal number of equivalents of oxygen and hydrogen, that is to say, that these ele- ments exist in it in the proportions for forming water ; while, according to Sprengel, the oxygen is in excess, and Peligot even estimates the quantity of oxygen at 1 4 equivalents, and the hydrogen at only 6 equivalents, making the deficiency of hydro- gen as great as 8 equivalents. It is quite evident, therefore, that chemists have been in the habit of designating all products of the decomposition of organic bodies which had a brown or brownish-black colour by the names of humic acid or humin, according as they were soluble or insoluble in alkalies; although in their composi- tion and mode of origin, the substances thus con- founded might be in no way allied. Not the slightest ground exists for the belief that one or other of these artificial products of the de- composition of vegetable matters exists in nature in the form and endowed with the properties of the vegetable constituents of mould ; there is not the PROPERTIES OF HUMUS. / shadow of a proof that one of them exerts any influ- ence on the growth of plants either in the way of nourishment or otherwise. Vegetable physiologists have, without any appa- rent reason, imputed the known properties of the humus and humic acids of chemists to that consti- tuent of mould which has received the same name, and in this way have been led to their theoretical notions respecting the functions of the latter sub- stance in vegetation. The opinion that the substance called humus is extracted from the soil by the roots of plants, and that the carbon entering into its composition serves in some form or other to nourish their tissues, is so general and so firmly established, that hitherto any new argument in its favour has been considered unnecessary ; the obvious difference in the growth of plants according to the known abundance or scarcity of humus in the soil, seemed to afford in- contestable proof of its correctness. Yet, this position, when submitted to a strict ex- amination, is found to be untenable, and it becomes evident from most conclusive proofs that humus in the form in which it exists in the soil does not yield the smallest nourishment to plants. The adherence to the above incorrect opinion has hitherto rendered it impossible for the true theory of the nutritive process in vegetables to become known, and has thus deprived us of our best guide to a rational practice in agriculture. 8 OF THE ASSIMILATION OF CARBON. Any great improvement in that most important of all arts is inconceivable without a deeper and more perfect acquaintance with the substances which nourish plants, and with the sources whence they are derived ; and no other cause can be discovered to account for the fluctuating and uncertain state of our knowledge on this subject up to the present time, than that modern physiology has not kept pace with the rapid progress of chemistry. In the following inquiry we shall suppose the humus of vegetable physiologists to be really en- dowed with the properties recognised by chemists in the brownish black deposits which they obtain by precipitating an alkaline decoction of mould or peat by means of acids, and which they name humic acid. Humic acid, when first precipitated, is a floccu- lent substance, is soluble in 2500 times its weight of water, and combines with alkalies, lime and mag- nesia, forming compounds of the same degree of solubility. (Sprengel.) Vegetable physiologists agree in the supposition that by the aid of water humus is rendered capable of being absorbed by the roots of plants. But ac- cording to the observation of chemists, humic acid is soluble only when newly precipitated, and be- comes completely insoluble when dried in the ah*, or when exposed in the moist state to the freezing temperature. (Sprengel.) Both the cold of winter and the heat of summer ABSORPTION OF HUMUS. 9 therefore are destructive of the solubility of humic acid, and at the same time of its capability of being assimilated by plants. So that, if it is absorbed by plants, it must be in some altered form. The correctness of these observations is easily demonstrated by treating a portion of good mould with cold water. The fluid remains colourless, and is found to have dissolved less than 100,000 part of its weight of organic matters, and to contain merely the salts which are present in rain- water. Decayed oak-wood, likewise, of which humic acid is the principal constituent, was found by Berzelius to yield to cold water only slight traces of soluble materials; and I have myself verified this observa- tion on the decayed wood of beech and fir. These facts, which show that humic acid in its unaltered condition cannot serve for the nourish- ment of plants, have not escaped the notice of phy- siologists ; and hence they have assumed that the lime or the different alkalies found in the ashes of vegetables render soluble the humic acid and fit it for the process of assimilation. Alkalies and alkaline earths do exist in the dif- ferent kinds of soil in sufficient quantity to form such soluble compounds with the humic acid. Now, let us suppose that humic acid is absorbed by plants in the form of that salt which contains the largest proportion of humic acid, namely, in the form of humate of lime, and then from the known 10 OF THE ASSIMILATION OF CARBON. quantity of the alkaline bases contained in the ashes of plants, let us calculate the amount of hu- mic acid which might be assimilated in this man- ner. Let us admit, likewise, that potash, soda, and the oxides of iron and manganese have the same capacity of saturation as lime with respect to hu- mic acid, and then we may take as the basis of our calculation the analysis of M. Berthier, who found that 1000 Ibs. of dry fir- wood yielded 4 Ibs. of ashes, and that in every 100 Ibs. of these ashes, after the chloride of potassium and sulphate of potash were extracted, 53 Ibs. consisted of the basic metallic oxides, potash, soda, lime, magnesia, iron, and manganese. 40,000 square feet* Hessian measure of wood- land yield annually, according to Dr. Heyer, on an average, 2650 Ibs. Hessian of dry fir- wood, which contain 5*6 Ibs. I \ essian of metallic oxides. Now, according to the estimates of Malaguti and Sprengel, 1 Ib. Hessian of lime combines chemically with 10*9 Ibs. Hessian of humic acid; 5 '6 Ibs. of the metallic oxides would accordingly introduce into the trees 61 Ibs. Hessian of humic acid, which, admitting humic acid to contain 58 per cent, of carbon, would correspond to 91 Ibs. Hessian of dry wood. But we have seen that 2650 Ibs. of fir- wood are really produced. * [The numbers in the text in Hessian feet and pounds will show a proportion to other numbers equally well as if they were reduced to their equivalents in English. For those, however, who prefer knowing the exact English quantities, a table of equivalents is given at the end.] ABSORPTION OF HUMUS. 11 Again, if the quantity of humic acid which might be introduced into wheat in the form of humates is calculated from the known proportion of metallic oxides existing in wheat straw, (the sulphates and chlorides also contained in the ashes of the straw not being included,) it will be found that the wheat growing on 40,000 square feet of land would receive in that way 57i Ibs. Hessian of humic acid, cor- responding to 85 Ibs. Hessian of woody fibre. But the extent of land just mentioned produces, in- dependently of the roots and grain, 1780 Ibs. Hessian of straw, the composition of which is the same as that of woody fibre. It has been taken for granted in these calcula- tions that the basic metallic oxides which have served to introduce humic acid into the plants do not return to the soil, since it is certain that they remain fixed in the parts newly formed during the process of growth. Let us now calculate the quantity of humic acid which plants can receive under the most favour- able circumstances, viz. through the agency of rain-water. The quantity of rain which falls at Erfurt, one of the most fertile districts of Germany, during the months of April, May, June, and July, is stated by Schubler to be \7\ Ibs. Hessian over every square foot of surface ; 40,000 square feet con- sequently receive 700,000 Ibs. Hessian of rain- water. 12 OF THE ASSIMILATION OF CARBON. If, now, we suppose that the whole quantity of this rain is taken up by the roots of a summer plant which ripens four months after it is planted, so that not a pound of this water evaporates except from the leaves of the plant ; and if we further assume that the water thus absorbed is saturated with hu- mate of lime (the most soluble of the humates, and that which contains the largest proportion of humic acid); then the plants thus nourished would not receive more than 300 Ibs. Hessian of humic acid, since one part of humate of lime requires 2500 parts of water for solution. But the extent of land which we have mentioned produces 2580 Ibs. Hessian of corn (in grain and straw, the roots not included), or 20,000 Ibs. Hes- sian of beet-root (without the leaves and small radicle fibres). It is quite evident that the 300 Ibs. of humic acid, supposed to be absorbed, cannot account for the quantity of carbon contained in the roots and leaves alone, even if the supposition were correct, that the whole of the rain-water was absorbed by the plants. But since it is known that only a small portion of the rain-water which falls upon the surface of the earth evaporates through plants, the quantity of carbon which can be conveyed into them in any conceivable manner by means of humic acid must be extremely trifling in comparison with that actually produced in vege- tation. Other considerations, of a higher nature, confute FERTILITY OF DIFFERENT SOILS. 13 the common view respecting the nutritive office of humic acid, in a manner so clear and conclusive that it is difficult to conceive how it could have been so generally adopted. Fertile land produces carbon in the form of wood, hay, grain, and other kinds of growth, the masses of which differ in a remarkable degree. 2650 Ibs. Hessian of firs, pines, beeches, &c. grow as wood upon 40,000 square feet of forest-land with an average soil. The same superficies yields 2500 Ibs. Hessian of hay. A similar surface of corn-land gives from 18,000 to 20,000 Ibs. Hessian of beet-root, or 800 Ibs. Hessian of rye, and 1780 Ibs. Hessian of straw, 160 sheaves of 14 Ibs. Hessian each, in all, 2580 Ibs. Hessian. One hundred parts of dry fir-wood contain 38 parts of carbon ; therefore, 2650 Ibs. contain 1007 Ibs. Hessian of carbon. One hundred parts of hay*, dried in .air, contain 44*31 parts carbon. Accordingly, 2500 Ibs. of hay contain 1008 Ibs. Hessian of carbon. Beet-roots contain from 89 to 89*5 parts water, and from 10*5 to 11 parts solid matter, which consists of from 8 to 9 per cent, sugar, and from 2 * 100 parts of hay, dried at 100 C. (212 F.) and burned with oxide of copper in a stream of oxygen gas, yielded 51-93 water, 165'8 carbonic acid, and 6'82 of ashes. This gives 45-87 carbon, 5-76 hydrogen, 31-55 oxygen, and 6'82 ashes. Hay, dried in the air, loses 1 1-2 p. c. water at 100 C. (212 F.}.Dr. Will. 14 OF THE ASSIMILATION OF CARBON. to 2^ per cent, cellular tissue. Sugar contains 42'4 per cent. ; cellular tissue, 47 per cent, of carbon. 20,000 Ibs. of beet-root, therefore, if they con- tained 9 per cent, of sugar, and 2 per cent, of cellular tissue, would yield 936 Ibs. Hessian of carbon, of which 756 Ibs. Hessian would be due to the sugar, and 180 Ibs. Hessian to the cellular tissue ; the carbon of the leaves and small roots not being included in the calculation. One hundred parts of straw *, dried in air, con- tain 38 per cent, of carbon; therefore 1780 Ibs. of straw contain 676 Ibs. Hessian of carbon. One hundred parts of corn contain 43 parts of carbon ; 800 Ibs. must therefore contain 344 Ibs. Hessian; in all, 1020 Ibs. Hessian of carbon. 40,000 square feet of wood and meadow land produce, consequently, 1007 Ibs. of carbon; while the same extent of arable land yields in beet-root, without leaves, 936 Ibs. ; or in corn, 1020 Ibs. It must be concluded from these incontestable facts, that equal surfaces of cultivated land of an average fertility produce equal quantities of car- bon ; yet, how unlike have been the different conditions of the growth of the plants from which this has been deduced ! Let us now inquire whence the grass in a meadow, * Straw analysed in the same manner, and dried at 100 C., gave 46-37 p. c. of carbon, 5'G8 p. c. of hydrogen, 43*93 p. c. of oxygen, and 4-02 p. c. of ashes. Straw dried in the air at 100 C. lost 18 p. c. of water. Dr. Will. INFLUENCE OF MANURE. 15 or the wood in a forest receives its carbon, since there no manure no carbon has been given to it as nourishment ? and how it happens, that the soil, thus exhausted, instead of becoming poorer, becomes every year richer in this element ? A certain quantity of carbon is taken every year from the forest or meadow, in the form of wood or hay, and, in spite of this, the quantity of carbon in the soil augments ; it becomes richer in humus. It is said, that in fields and orchards all the carbon which may have been taken away as herbs, as straw, as seeds, or as fruit, is replaced by means of manure ; and yet this soil produces no more carbon than that of the forest or meadow where it is never replaced. It cannot be conceived that the laws for the nutrition of plants are changed by culture, that the sources of carbon for fruit or grain, and for grass or trees, are different. It is not denied that manure exercises an influ- ence upon the development of plants ; but it may be affirmed with positive certainty, that it neither serves for the production of the carbon, nor has any influence upon it, because we find that the quantity of carbon produced by manured lands is not greater than that yielded by lands which are not manured. The discussion as to the manner in which manure acts has nothing to do with the present question, which is, the origin of the carbon. The carbon must be derived from other sources ; 16 OF THE ASSIMILATION OF CARBON. and as the soil does not yield it, it can only be extracted from the atmosphere. In attempting to explain the origin of carbon in plants, it has never been considered that the ques- tion is intimately connected with that of the origin of humus. It is universally admitted that humus arises from the decay of plants. No primitive humus, therefore, can have existed ; for plants must have preceded the humus. Now, whence did the first vegetables derive their carbon ? and in what form is the carbon contained in the atmosphere ? These two questions involve the consideration of two most remarkable natural phenomena, which, by their reciprocal and uninterrupted influence, maintain the life of the individual animals and vegetables, and the continued existence of both kingdoms of organic nature. One of these questions is connected with the in- variable condition of the air with respect to oxygen. One hundred volumes of air have been found, at every period and in every climate, to contain 21 volumes of oxygen, with such small deviations, that they must be ascribed to errors of observation. Although the absolute quantity of oxygen con- tained in the atmosphere appears very great when represented by numbers, yet it is not inexhaustible. One man consumes by respiration 45* Hessian cubic * [For the proportions in English weights and measures see the table at the end of the volume ] ITS PROPORTION IN THE ATMOSPHERE. 17 feet of oxygen in 24 hours; 10 centners of charcoal consume 58,112 cubic feet of oxygen during its combustion ; and a small town like Giessen (with about 7000 inhabitants) extracts yearly from the air, by the wood employed as fuel, more than 1000 millions of cubic feet of this gas. When we consider facts such as these, our former statement, that the quantity of oxygen in the atmosphere does not diminish in the course of ages*, that the air at the present day, for example, does not contain less oxygen than that found in jars buried for 1800 years in Pompeii, appears quite incomprehensible, unless some source exists whence the oxygen abstracted is replaced. How does it happen, then, that the proportion of oxygen in the atmosphere is thus invariable ? The answer to this question depends upon an- other ; namely, what becomes of the carbonic acid, which is produced during the respiration of animals, and by the process of combustion ? A cubic foot of oxygen gas, by uniting with carbon so as to form * The air contains, in maxima, TcyBfss carbonic acid gas and oxygen gas. A man consumes, in one year, 166,075 cubic feet of oxygen gas (or 45,000 cubic inches in one day, according to Lavoisier, Seguin, and Dary); a thousand million men must accordingly consume 166 billion cubic feet in one year ; this is equal to y^ of the quantity which is contained in the air in the form of carbonic acid. The carbonic acid in the air would thus be doubled in 1000 years, and man alone would exhaust all the oxygen, and convert it into car- bonic acid in 303 times as many years. The consumption by animals, and by the process of combustion, is not introduced into the calcula- tion. C 18 OF THE ASSIMILATION OF CARBON. carbonic acid, does not change its volume. The billions of cubic feet of oxygen extracted from the atmosphere, produce the same number of billions of cubic feet of carbonic acid, which immediately supply its place. The most exact and most recent experiments of De Saussure, made in every season, for a space of three years, have shown, that the air contains on an average 0.000415 of its own volume of carbonic acid gas ; so that, allowing for the inaccuracies of the experiments, which must diminish the quantity obtained, the proportion of carbonic acid in the atmosphere may be regarded as nearly equal to 1-1000 part of its weight. The quantity varies according to the seasons ; but the yearly average remains continually the same. We have no reason to believe that this propor- tion was less in past ages ; and nevertheless, the immense masses of carbonic acid, which annually flow into the atmosphere from so many causes, ought perceptibly to increase its quantity from year to year. But we find, that all earlier observers describe its volume as from one-half to ten times greater than that which it has at the present time ; so that we can hence at most conclude, that it has diminished. It is quite evident, that the quantities of carbonic acid and oxygen in the atmosphere, which remain unchanged by lapse of time, must stand in some fixed relation to one another ; a cause must exist ITS SOURCE, THE ATMOSPHERE. 19 which prevents the increase of carbonic acid, by removing that which is constantly forming ; and there must be some means of replacing the oxygen, which is removed from the air by the processes of combustion and putrefaction, as well as by the respiration of animals. Both these causes are united in the process of vegetable life. The facts which we have stated in the preceding pages prove, that the carbon of plants must be de- rived exclusively from the atmosphere. Now, car- bon exists in the atmosphere only in the form of carbonic acid ; and, therefore, in a state of com- bination with oxygen. It has been already mentioned likewise, that carbon and the elements of water form the prin- cipal constituents of vegetables ; the quantity of the substances which do not possess this composi- tion being in very small proportion. Now, the relative quantity of oxygen in the whole mass is less than in carbonic acid. It is therefore cer- tain, that plants must possess the power of de- composing carbonic acid, since they appropriate its carbon for their own use. The formation of their principal component substances must ne- cessarily be attended with the separation of the carbon of the carbonic acid from the oxygen, which must be returned to the atmosphere, whilst the carbon enters into combination with water or its elements. The atmosphere must thus receive a c2 20 OF THE ASSIMILATION OF CARBON. volume of oxygen for every volume of carbonic acid which has beeji decomposed. This remarkable property of plants has been demonstrated in the most certain manner, and it is in the power of every person to convince himself of its existence. The leaves and other green parts of a plant absorb carbonic acid, and emit an equal volume of oxygen. They possess this property quite independently of the plant ; for if, after being separated from the stem, they are placed in water containing carbonic acid, and exposed in that con- dition to the sun's light, the carbonic acid is, after a time, found to have disappeared entirely from the water. If the experiment is conducted under a glass receiver filled with water, the oxygen emitted from the plant may be collected and exa- mined. When no more oxygen gas is evolved, it is a sign that all the dissolved carbonic acid is decomposed ; but the operation recommences if a new portion of it is added. Plants do not emit gas when placed in water which either is free from carbonic acid, or contains an alkali that protects it from assimilation. These observations were first made by Priestley and Sennebier. The excellent experiments of De Samsure have further shown, that plants increase in weight during the decomposition of carbonic acid and separation of oxygen. This increase in weight is greater than can be accounted for by the quantity of carbon assimilated ; a fact which con- ITS SOURCE, THE ATMOSPHERE. 21 firms the view, that the elements of water are assi- milated at the same time. The life of plants is closely connected with that of animals, in a most simple manner, and for a wise and sublime purpose. The presence of a rich and luxuriant vegetation may be conceived without the concurrence of animal life, but the existence of animals is un- doubtedly dependent upon the life and develop- ment of plants. Plants not only afford the means of nutrition for the growth and continuance of animal organization, but they likewise furnish that which is essential for the support of the important vital process of respira- tion ; for besides separating all noxious matters from the atmosphere, they are an inexhaustible source of pure oxygen, which supplies the loss which the air is constantly sustaining. Animals on the other hand expire carbon, which plants in- spire ; and thus the composition of the medium in which both exist, namely, the atmosphere, is maintained constantly unchanged. It may be asked, Is the quantity of carbonic acid in the atmosphere, which scarcely amounts to l-10th per cent., sufficient for the wants of the whole vegetation on the surface of the earth, is it possible that the carbon of plants has its origin from the air alone ? This question is very easily answered. It is known, that a column of air of 2216.66 Ibs. weight, Hessian measure, rests upon 22 OF THE ASSIMILATION OF CARBON. every square Hessian foot of the surface of the earth ; the diameter of the earth and its superficies are like- wise known, so that the weight of the atmosphere can be calculated with the greatest exactness. The thousandth part of this is carbonic acid, which contains upwards of 27 per cent, carbon. By this calculation it can be shown, that the atmosphere contains 3000 billion Hessian Ibs. of carbon; a quantity which amounts to more than the weight of all the plants, and of all the- strata of mineral and brown coal, which exist upon the earth. This carbon is, therefore, more than adequate to all the purposes for which it is required. The quantity of carbon contained in sea- water, is proportionally still greater. If, for the sake of argument, we suppose the super- ficies of the leaves and other green parts of plants, by which the absorption of carbonic acid is effected, to be double that of the soil upon which they grow, a supposition which is much under the truth in the case of woods, meadows, and corn fields ; and if we further suppose that carbonic acid equal to 0.00067 of the volume of the air, or 1-1 000th of its weight is abstracted from it during every second of time, for eight hours daily, by a field of 80,000 Hessian square feet; then those leaves would receive 1000 Hessian Ibs. of carbon in 200 days.* * The quantity of carbonic acid which can be extracted from the air in a given time, is shown by the following calculation. During the whitewashing of a small chamber, the superficies of the walls and roof ITS SOURCE, THE ATMOSPHERE. 23 But it is inconceivable, that the functions of the organs of a plant can cease for any one moment during its life. The roots and other parts of it, which possess the same power, absorb constantly water and carbonic acid. This power is indepen- dent of solar light. During the day, when the plants are in the shade, and during the night, car- bonic acid is accumulated in all parts of their structure ; and the assimilation of the carbon and the exhalation of oxygen commence from the instant that the rays of the sun strike them. As soon as a young plant breaks through the surface of the ground, it begins to acquire colour from the top downwards ; and the true formation of woody tissue commences at the same time. The proper, constant, and inexhaustible sources of oxygen gas are the tropics and warm climates, where a sky, seldom clouded, permits the glowing of which we will suppose to be 1 05 square metres, and which receives six coats of lime in fou* days, carbonic acid is abstracted from the air, and the lime is consequently converted, on the surface, into a carbonate. It has been accurately determined that one square decimetre receives in this way, a coating of carbonate of lime which weighs 0.732 grammes. Upon the 105 square metres already mentioned there must accordingly be formed 7686 grains of carbonate of lime, which contain 4325.6 grains of carbonic acid. The weight of one cubic decimetre of carbonic acid being calculated at two grammes, (more accurately 1.97978,) the above mentioned surface must absorb in four days 2.163 cubic metres of carbonic acid. 2500 square metres (one Hessian acre) would absorb, under a similar treatment, 514 cubic metres zz 3296 cubic feet of car- bonic acid in four days. In 200 days it would absorb 2575 cubic metres 164,800 cubic feet, which contain 10,300 Ibs. Hessian of carbonic acid of which 2997 Ibs. are carbon, a quantity three times as great as that which is assimilated by the leaves and roots growing upon the same space. 24 OF THE ASSIMILATION OF CARBON. rays of the sun to shine upon an immeasurably luxuriant vegetation. The temperate and cold zones, where artificial warmth must replace deficient heat of the sun, produce, on the contrary, carbonic acid in superabundance, which is expended in the nutrition of the tropical plants. The same stream of air, which moves by the revolution of the earth from the equator to the poles, brings to us, in its passage from the equator, the oxygen generated there, and carries away the carbonic acid formed during our winter. The experiments of De Saussure have proved, that the upper strata of the air contain more carbonic acid than the lower, which are in contact with plants ; and that the quantity is greater by night than by day, when it undergoes decomposition. Plants thus improve the air, by the removal of carbonic acid, and by the renewal of oxygen, which is immediately applied to the use of man and animals. The horizontal currents of the atmo- sphere bring with them as much as they carry away, and the interchange of air between the upper and lower strata, which their difference of temperature causes, is extremely trifling when compared with the horizontal movements of the winds. Vegetable culture heightens the healthy state of a country, and a previously healthy country would be rendered quite uninhabitable by the ces- sation of all cultivation. The most important function in the life of plants, ITS SOURCE, THE ATMOSPHERE. 25 or, in other words, in their assimilation of carbon, is the separation, we might almost say the genera- tion, of oxygen. No matter can be considered as nutritious, or as necessary to the growth of plants, which possesses a composition either similar to or identical with theirs, and the assimilation of which, therefore, could take place without exercising this function. In the second part of this work, we shall adduce satisfactory proofs that decayed woody fibre (humus) contains carbon and the elements of water, without an excess of oxygen ; its composition differing from that of woody fibre, in its being richer in carbon. Vegetable physiologists consider the formation of woody fibre from humus as very simple ; they say, humus has only to enter into chemical com- bination with water, in order to effect the formation of woody fibre, starch, or sugar *. But the same philosophers have informed us, that aqueous solutions of sugar, starch and gum, are imbibed by the roots of plants, and carried to all parts of their structure, but are not assimilated ; they cannot therefore be employed in their nutrition. We could scarcely conceive a form more convenient for assimilation than that of gum, starch, and sugar, for they all contain the elements of woody fibre, and nearly in the same proportions. All the erroneous opinions concerning the mo- * Mcyen, Pflanzenphysiologie, ii. s. 141. 26 OF THE ASSIMILATION OF CARBON. dus operandi of humus have their origin in the false notions entertained respecting the most im- portant vital functions of plants ; analogy, that fertile source of error, having unfortunately led to the very unapt comparison of the vital functions of plants with those of animals. Substances, such as sugar, starch, &c. which con- tain carbon and the elements of water, are products of the life of plants, which live only whilst they generate them. The same may be said of humus, for it can be formed in plants, like the former sub- stances. Smitkson, Jameson, and Thomson, found, that the black excretions of unhealthy elms, oaks, and horse-chesnuts, consisted of humic acid in com- bination with alkalies. Berzelius detected similar products in the bark of most trees. Now, can it be supposed, that the diseased organs of a plant possess the power of generating the matter, to which its sustenance and vigour are ascribed ? How does it happen, it may be asked, that the absorption of carbon from the atmosphere by plants is doubted by all botanists and vegetable physiologists, and that by the greater number the purification of the air by means of them is wholly denied ? These doubts have arisen from the action of plants on the air in the absence of light, that is, during the night. The experiments of Ingenhouss were in a great measure the cause of this uncertainty of opinion, INFLUENCE OF THE SHADE ON PLANTS. 27 regarding the influence of plants in purifying the air. His observation., that green plants emit car- bonic acid in the dark, led De Saussure and Grischow to new investigations, by which they ascertained that under such conditions plants do really absorb oxygen, and emit carbonic acid ; but that the whole volume of air undergoes diminution at the same time. From the latter fact it follows, that the quantity of oxygen gas absorbed is greater, than the volume of carbonic acid separated ; for if this were not the case, no diminution could occur. These facts cannot be doubted, but the views based on them have been so false, that nothing, except the total want of observation, and the utmost ignorance of the chemical relations of plants to the atmo- sphere, can account for their adoption. It is known, that nitrogen, hydrogen, and a num- ber of other gases, exercise a peculiar, and, in ge- neral, an injurious influence upon living plants. Is it, then, probable, that oxygen, one of the most energetic agents in nature, should remain without influence on plants when one of their peculiar pro- cesses of assimilation has ceased ? It is true, that the decomposition of carbonic acid is arrested by absence of light. But then, namely, at night, a true chemical process com- mences, in consequence of the action of the oxygen in the air, upon the organic substances composing the leaves, blossoms, and fruit. This process is not at all connected with the life of the vegetable or- 28 OF THE ASSIMILATION OF CARBON. ganism, because it goes on in a dead plant exactly as in a living one. The substances composing the leaves of different plants being known, it is a matter of the greatest ease and certainty, to calculate which of them, du- ring life, should absorb most oxygen by chemical action, when the influence of light is withdrawn. The leaves and green parts of all plants, contain- ing volatile oils or volatile constituents in general, which change into resin by the absorption of oxy- gen, should absorb more than other parts which are free from such substances. Those leaves, also, which contain either the constituents of nut-galls, or compounds, in which nitrogen is present, ought to absorb more oxygen than those which do not contain such matters. The correctness of these inferences has been distinctly proved by the obser- vations of De Saussure ; for, whilst the tasteless leaves of the Agave americana absorb only 0.3 of their volume of oxygen, in the dark, during 24 hours, the leaves of the Pinus Abies, which contain volatile and resinous oils, absorb 1 times, those of the Quercus Robur containing tannic acid 1 4 times, and the balmy leaves of the Populus alba 2 1 times that quantity. This chemical action is shown, very plainly, also in the leaves of the Cotyledon calycinwn, the Cacalia ficoides and others ; for they are sour like sorrel in the morning, tasteless at noon, and bitter in the evening. The formation of acids is effected during the night, by a true process of oxi- INFLUENCE OF THE SHADE ON PLANTS. 29 dation : these are deprived of their acid properties during the day and evening, and are changed, by separation of a part of their oxygen, into compounds containing oxygen and hydrogen, either in the same proportions as in water, or even with an ex- cess of hydrogen, which is the composition of all tasteless and bitter substances. Indeed, the quantity of oxygen absorbed could be estimated pretty nearly, by the different periods, which the green leaves of plants require to undergo alteration in colour, by the influence of the atmo- sphere. Those which continue longest green, will abstract less oxygen from the air in an equal space of time, than those, the constituent parts of which suffer a more rapid change. It is found, for ex- ample, that the leaves of the Ilex aquifolium, dis- tinguished by the durability of their colour, absorb only 0.86 of their volume of oxygen gas, in the same time that the leaves of the poplar absorb 8, and those of the beech 9^ times their volume ; both the beech and poplar being remarkable for the rapidity and ease with which the colour of their leaves changes. When the green leaves of the poplar, the beech, the oak, or the holly, are dried under the air pump, with exclusion of light, then moistened with water, and placed under a glass globe filled with oxygen ; they are found to absorb that gas in proportion as they change in colour. The chemical nature of this process is thus completely established. The 30 OF THE ASSIMILATION OF CARBON, diminution of the gas which occurs, can only be owing to the union of a large proportion of oxygen with those substances which are already in the state of oxides, or to the oxidation of the hydrogen, in those vegetable compounds which contain it in ex- cess. The fallen brown or yellow leaves of the oak contain, no longer, tannin, and those of the poplar no balsamic constituents. The property which green leaves possess, of ab- sorbing oxygen, belongs also to fresh wood, whether taken from a twig, or from the interior of the trunk of a tree. When fine chips of such wood are placed in a moist condition, under a jar filled with oxygen, the gas is seen to diminish in volume. But, wood, dried by exposure to the atmosphere and then moistened, converts the oxygen into carbonic acid, without change of volume ; fresh wood, therefore, absorbs most oxygen. MM. Petersen and Schodler have shown, by the careful elementary analyses of 24 different kinds of wood, that they contain carbon and the elements of water, with the addition of a certain quantity of hydrogen. Oak wood, recently taken from the tree, and dried at 100 C. (212 F.), contains 49.432 carbon, 6.069 hydrogen, and 44.499 oxygen. The proportion of hydrogen, which is necessary to combine with 44.498 oxygen in order to form water, is ^ of this quantity, namely 5.56 ; it is evi- dent, therefore, that oak wood contains ^ more hydrogen than corresponds to this proportion. INFLUENCE OF THE SHADE ON PLANTS. 31 In Pinus Larix, P. Abies, and P. picea, the excess of hydrogen amounts to y, and in Tilia europcea to |. The quantity of hydrogen stands in some relation to the specific weight of the wood ; the lighter kinds of wood contain more of it than the heavier. In ebony wood (Diospyros Ebenum) the oxygen and hydrogen are in exactly the same pro- portion as in water. The difference between the composition of the varieties of wood, and that of simple woody fibre, depends, unquestionably, upon the presence of con- stituents, in part soluble, and in part insoluble, such as resin and other matters, which contain a large proportion of hydrogen : the hydrogen of such sub- stances being in the analysis of the various woods superadded to that of the true woody fibre. It has previously been mentioned, that moulder- ing oak wood contains carbon and the elements of water without any excess of hydrogen. But the proportions of its constituents must, necessarily, have been different, if the volume of the air had not changed during its decay, because the propor- tion of hydrogen in those component substances of the wood which contained it in excess is here diminished, and this diminution could only be effected by an absorption of oxygen. Most vegetable physiologists have connected the emission of carbonic acid during the night, with the absorption of oxygen from the atmosphere, and have considered these actions as a true process of 32 OF THE ASSIMILATION OF CARBON. respiration in plants, similar to that of animals, and like it, having for its result the separation of car- bon from some of their constituents. This opinion has a very weak and unstable foundation. The carbonic acid, which has been absorbed by the leaves and by the roots, together with water, ceases to be decomposed on the departure of day- light ; it is dissolved in the juices, which pervade all parts of the plant, and escapes every moment through the leaves, in quantity corresponding to that of the water, which evaporates. A soil, in which plants vegetate vigorously, con- tains a certain quantity of moisture, which is indis- pensably necessary to their existence. Carbonic acid, likewise, is always present in such a soil, whe- ther it has been abstracted from the air, or has been generated by the decay of vegetable matter. Rain and well water, as well as that from other sources, invariably contain carbonic acid. Plants during their life constantly possess the power of absorbing by their roots moisture, and, along with it, air and carbonic acid. Is it, therefore, surprising, that the carbonic acid should be returned, unchanged, to the atmosphere, along with water, when light (the cause of the fixation of its carbon) is absent ? Neither this emission of carbonic acid nor the absorption of oxygen has any connexion with the process of assimilation ; nor have they the slightest relation to one another ; the one is a purely me- chanical, the other a purely chemical process. A EXHALATION OF OXYGEN BY PLANTS. 33 cotton wick, inclosed in a lamp, which contains a liquid saturated with carbonic acid, acts exactly in the same manner as a living plant in the night. Water and carbonic acid are sucked up by capillary attraction, and both evaporate from the exterior part of the wick. Plants, which live in a soil containing humus, exhale much more carbonic acid during the night than those which grow in dry situations ; they also yield more in rainy than in dry weather. These facts point out to us the cause of the numerous contradictory observations, which have been made with respect to the change impressed upon the air by living plants, both in darkness, and in common day-light, but which are unworthy of consideration, as they do not assist in the solution of the main question. There are other facts which prove in a decisive manner that plants yield more oxygen to the at- mosphere than they extract from it ; these proofs, however, are to be drawn with certainty only from plants which live under water. When pools and ditches, the bottoms of which are covered with growing plants, freeze upon their surface in winter, so that the water is completely excluded from the atmosphere, by a clear stratum of ice, small bubbles of gas are observed to escape, continually, during the day, from the points of the leaves and twigs. These bubbles are seen most distinctly when the rays of the sun fall upon the ice ; D 34 OF THE ASSIMILATION OF CARBON. they are very small at first, but collect under the ice and form larger bubbles. They consist of pure oxygen gas. Neither during the night, nor during the day when the sun does not shine, are they ob- served to diminish in quantity. The source of this oxygen is the carbonic acid dissolved in the water, which is absorbed by the plants, but is again sup- plied to the water, by the decay of vegetable sub- stances contained in the soil. If these plants absorb oxygen during the night, it can be in no greater quantity than that which the surrounding water holds in solution, for the gas, which has been ex- haled, is not again absorbed. The action of water- plants cannot be supposed to form .an exception to a great law of nature, and the less so, as the different action of aerial plants upon the atmosphere is very easily explained. The opinion is not new that the carbonic acid of the air serves for the nutriment of plants, and that its carbon is assimilated by them ; it has been admitted, defended, and argued for, by the soundest and most intelligent natural philosophers, namely, by Priestley, Sennebier, De Saussure, and even by Ingenhouss himself. There scarcely exists a theory in natural science, in favour of which there are more clear and decisive arguments. How, then, are we to account for its not being received in its full extent by most other physiologists, for its being even disputed by many, and considered by a few as quite refuted ? NEGLECT OF CHEMISTRY BY BOTANISTS. 35 All this is due to two causes, which we shall now consider. One is, that in botany the talent and labour of inquirers has been wholly spent in the examination of form and structure : chemistry and physics have not been allowed to sit in council upon the expla- nation of the most simple processes ; their expe- rience and their laws have not been employed, though the most powerful means of help in the acquirement of true knowledge. They have not been used, because their study has been neglected. All discoveries in physics and in chemistry, all explanations of chemists, must remain without fruit and useless, because, even to the great leaders in physiology, carbonic acid, ammonia, acids, and bases, are sounds without meaning, words without sense, terms of an unknown language, which awaken no thoughts and no associations. They treat these sciences like the vulgar, who despise a foreign literature in exact proportion to their ignorance of it ; since even when they have had some acquaintance with them, they have not under- stood their spirit and application. Physiologists reject the aid of chemistry in their inquiry into the secrets of vitality, although it alone could guide them in the true path ; they reject chemistry, because in its pursuit of knowledge it destroys the subjects of its investigation ; but they forget that the knife of the anatomist must dis- member the body, and destroy its organs, if an D 2 36 OF THE ASSIMILATION OF CARBON. account is to be given of their form, structure, and functions. When pure potato starch is dissolved in nitric acid, a ring of the finest wax remains. What can be opposed to the conclusion of the chemist, that each grain of starch consists of concentric layers of wax and amylum, which thus mutually protect each other against the action of water and ether ? Can results of this kind, which illustrate so completely both the nature and properties of bodies; be attained by the microscope ? 'Is it possible to make the gluten in a piece of bread visible in all its connexions and ramifications ? It is impossible by means of instru- ments ; but if the piece of bread is placed in a lukewarm decoction of malt, the starch, and the substance called dextrine, are seen to dissolve like sugar in water, and, at last, nothing remains except the gluten, in the form of a spongy mass, the minute pores of which can be seen only by a microscope. Chemistry offers innumerable resources of this kind which are of the greatest use in an inquiry into the nature of the organs of plants, but they are not used, because the need of them is not felt. The most important organs of animals and their func- tions are known, although they may not be visible to the naked eye. But, in vegetable physiology, a leaf is in every case regarded merely as a leaf, notwithstanding that leaves generating oil of tur- pentine or oil of lemons must possess a different OBJECT OF EXPERIMENTS IN PHYSIOLOGY. 37 nature from those in which oxalic acid is formed. Vitality, in its peculiar operations, makes use of a special apparatus for each function of an organ. A rose twig engrafted upon a lemon-tree, does not bring forth lemons but roses. Vegetable physiolo- gists in the study of their science have not directed their attention to that part of it which is most worthy of investigation. The second cause of the incredulity with which physiologists view the theory of the nutrition of plants by the carbonic acid of the atmosphere is, that the art of experimenting is not known in phy- siology, it being an art which can be learned accu- rately only in the chemical laboratory. Nature speaks to us in a peculiar language, in the language of phenomena ; she answers at all times the ques- tions which are put to her ; and such questions are experiments. An experiment is the expression of a thought : we are near the truth when the pheno- menon, elicited by the experiment, corresponds to the thought ; while the opposite result shows that the question was falsely stated, and that the con- ception was erroneous. The critical repetition of another's experiments must be viewed as a criticism of his opinions ; if the result of the criticism be merely negative, if it dcSfnot suggest more correct ideas in the place of those which it is intended to refute, it should be disregarded ; because the worse experimenter the critic is, the greater will be the discrepancy between 38 OF THE ASSIMILATION OF CARBON. the results he obtains and the views proposed by the other. It is too much forgotten by physiologists, that their duty really is not to refute the experiments of others, nor to show that they are erroneous, but to discover truth, and that alone. It is startling, when we reflect that all the time and energy of a multi- tude of persons of genius, talent, and knowledge, are expended in endeavours to demonstrate each other's errors. The question whether carbonic acid is the food of plants or not, has been made the subject of experiments with perfect zeal and good faith ; the results have been opposed to that view. But how was the inquiry instituted ? The seeds of balsamines, beans, cresses, and gourds, were sown in pure Carrara marble, and sprinkled with water containing carbonic acid. The seeds sprang, but the plants did not attain to the development of the third small leaf. In other cases, they allowed the water to penetrate the marble from below, yet, in spite of this, they died. It is worthy of observation, that they lived longer with pure distilled water than with that impregnated with carbonic acid ; but- still, in this case also, they eventually perished. Other experi- menters sowed seeds of plants in flowers of sulphur and sulphate of baryta, and tried to nourish them with carbonic acid, but without success. Such experiments have been considered as posi- CONDITIONS ESSENTIAL TO NUTRITION. 39 tive proofs, that carbonic acid will not nourish plants ; but the manner in which they were insti- tuted is opposed to all rules of philosophical inquiry, and to all the laws of chemistry. Many conditions are necessary for the life of plants ; those of each genus require special condi- tions, and should but one of these be wanting, although all the rest be supplied, the plants will not be brought to maturity. The organs of a plant, as well as those of an animal, contain sub- stances of the most different kinds ; some are formed solely of carbon and the elements of water, others contain nitrogen, and in all plants we find metallic oxides in the state of salts. The food which can serve for the production of all the organs of a plant, must necessarily contain all its elements. These most essential of all the chemical qualities of nutri- ment may be united in one substance, or they may exist separately in several ; in which case, the one contains what is wanting in the other. Dogs die although fed with jelly, a substance which contains nitrogen ; they cannot live upon white bread, sugar, or starch, if these are given as food, to the exclu- sion of all other substances. Can it be concluded from this, that these substances contain no elements suited for assimilation ? Certainly not. Vitality is the power which each organ possesses of constantly reproducing itself ; for this it requires a supply of substances which contain the consti- tuent elements of its own substance, and are capable 40 OF THE ASSIMILATION OF CARBON. of undergoing transformation. All the organs to- gether cannot generate a single element, carbon, nitrogen, or a metallic oxide. When the quantity of the food is too great, or is not capable of undergoing the necessary transfor- mation, or exerts any peculiar chemical action, the organ itself is subjected to a change : all poisons act in this manner. The most nutritious sub- stances may cause death. In experiments such as those described above, every condition of nutrition should be considered. Besides those matters which form their principal constituent parts, both animals and plants require others, the peculiar functions of which are unknown. These are inorganic sub- stances, such as common salt, the total want of which is in animals inevitably productive of death. Plants, for the same reason, cannot live unless supplied with certain metallic compounds. If we knew with certainty that there existed a sub- stance capable, alone, of nourishing a plant and of bringing it to maturity, we might be led to a know- ledge of the conditions necessary to the life of all plants, by studying its characters and composition. If humus were such a substance, it would have precisely the same value as the only single food which nature has produced for animal organisation, namely, milk (Prout). The constituents of milk, are cheese or caseine, a compound containing nitro- gen in large proportion ; butter, in which hydrogen abounds, and sugar of milk, a substance with a CONDITIONS ESSENTIAL TO NUTRITION. 41 large quantity of hydrogen and oxygen in the same proportion^ as in water. It also contains in solution, lactate of soda, phosphate of lime, and common salt ; and a peculiar aromatic product exists in the butter, called butyric acid. The knowledge of the composition of milk is a key to the conditions necessary for the purposes of nutri- tion of all animals. All substances which are adequate to the nourish- ment of animals, contain those materials united, though not always in the same form ; nor can any one be wanting, for a certain space of time, without a marked effect on the health being pro- duced. The employment of a substance as food, presupposes a knowledge of its capacity of assimi- lation, and of the conditions under which this takes place. A carnivorous animal dies in the vacuum of an air-pump, even though supplied with a supera- bundance of food ; it dies in the air, if the demands of its stomach are not satisfied ; and it dies in pure oxygen gas, however lavishly nourishment be given to it. Is it hence to be concluded, that neither flesh, nor air, nor oxygen, is fitted to support life ? Certainly not. From the pedestal of the Trajan column at Rome, we might chisel out each single piece of stone, if, upon the extraction of the second, we re- placed the first. But could we conclude from this, that the column was suspended in the air, and not 42 OF THE ASSIMILATION OF CARBON. supported by a single piece of its foundation ? Assuredly not. Yet the strongest proof would have been given, that each portion of the pedestal could be removed without the downfall of the column. Animal and vegetable physiologists, however, come to such conclusions with respect to the pro- cess of assimilation. They institute experiments without being acquainted with the circumstances necessary for the continuance of life with the qualities and proper nutriment of the animal or plant on which they operate or with the nature and chemical constitution of its organs. These experiments are considered by them as convinc- ing proofs, whilst they are fitted only to awaken pity. Is it possible to bring a plant to maturity by means of carbonic acid and water, without the aid of some substance containing nitrogen, which is an essential constituent of the sap, and indispensable for its production ? Must the plant not die, how- ever abundant the supply of carbonic acid may be, as soon as the first small leaves have exhausted the nitrogen contained in the seeds ? Can a plant be expected to grow in Carrara marble, even when an azotized substance is supplied to it, but when the marble is sprinkled with an aqueous solution of carbonic acid, which dissolves the lime and forms super carbonate of lime ? A plant of the family of the Plumbaginece, upon the leaves of which fine hornlike, or scaly processes of CONDITIONS ESSENTIAL TO NUTRITION. 43 crystallised carbonate of lime are formed, might, perhaps, attain maturity under such circumstances ; but these experiments alone are sufficient to prove, that cresses, gourds, and balsamines, cannot be nourished by supercarbonate of lime, in the absence of matter containing nitrogen. We may indeed conclude, that the salt ofc lime acts as a poison, since the development of plants will advance fur- ther in pure water, when lime and carbonic acid are not used. Moist flowers of sulphur attract oxygen from the atmosphere and become acid. Is it possible that a plant can grow and flourish in presence of free sulphuric acid, with no other nourishment than carbonic acid ? It is true, the quantity of sulphuric acid formed thus in hours, or in days, may be small, but the property of each particle of the sulphur to absorb oxygen and retain it, is present every moment. When it is known that plants require moisture, carbonic acid, and air, should we choose, as the soil for experiments on their growth, sulphate of barytes, which, from its nature and specific gravity, completely prevents the access of air ? All these experiments are valueless for the decision of any question. It is absurd to take for them any soil at mere hazard, as long as we are ignorant of the functions performed in plants by those inor- ganic substances which are apparently foreign to them. It is quite impossible to mature a plant of 44 ORIGIN AND ACTION OF HUMUS. the family of the Graminetz, or of the Equisetacece, the solid framework of which contains silicate of potash, without silicic acid and potash, or a plant of the genus Oxalis without potash, or saline plants such as the saltworts (Salsola and Salicornia), without chloride of sodium, or at least some salt of similar properties. All seeds of the Grammes con- tain phosphate of magnesia ; the solid parts of the roots of the altlicea contain more phosphate of lime than woody fibre. Are these -substances merely accidentally present ? A plant should not be chosen for experiment, when the matter which it requires for its assimilation is not well known. What value, now, can be attached to experiments in which all those matters which a plant requires in the process of assimilation, besides its mere nutri- ment, have been excluded with the greatest care ? Can the laws of life be investigated in an organized being which is diseased or dying ? The mere observation of a wood or meadow is infinitely better adapted to decide so simple a ques- tion, than all the trivial experiments under a glass globe ; the only difference is, that instead of one plant there are thousands. When we are acquainted with the nature of a single cubic inch of their soil, and know the composition of the air and rain- water, we are in possession of all the conditions necessary to their life. The source of the different elements entering into the composition of plants cannot possibly escape us, if we know in what form DECAY OF WOODY FIBRE. 45 they take up their nourishment, and compare its composition with that of the vegetable substances which compose their structure. * All these questions will now be examined and discussed. It has been already shown, that the carbon of plants is derived from the atmosphere : it still remains for us to inquire, what power is ex- erted on vegetation by the humus of the soil and the inorganic constituents of plants, and also to trace the sources of their nitrogen. ON THE ORIGIN AND ACTION OF HUMUS. It will be shown in the second part of this work, that all plants and vegetable structures undergo two processes of decomposition after death. One of these is named fermentation, the other decay, putrefaction, or eremacausis* : . It will likewise be shown, that decay is a slow process of combustion, a process, therefore, in which the combustible parts of a plant unite with the oxygen of the atmosphere. The decay of woody fibre (the principal consti- tuent of all plants) is accompanied by a pheno- menon of a peculiar kind. This substance, in contact with air or oxygen gas, converts the latter into an equal volume of carbonic acid, and its decay * The word eremacausis was proposed by the author some time since, in order to explain the true nature of putrefaction ; it is compounded from -/jpe'jua alow and Kav<ns combustion. 46 ORIGIN AND ACTION OF HUMUS. ceases upon the disappearance of the oxygen. If the carbonic acid is removed, and oxygen replaced, its decay recommences, that is, it again converts oxygen into carbonic acid. Woody fibre consists of carbon and the elements of water ; and if we judge only from the products formed during its decom- position, and from those formed by pure charcoal, burned at a high temperature, we might conclude that the causes were the same in both : the decay of woody fibre proceeds, therefore, as if no hydro- gen or oxygen entered into its composition. A very long time is required for the completion of this process of combustion, and the presence of water is necessary for its maintenance : alkalies promote it, but acids retard it ; all antiseptic sub- stances, such as sulphurous acid, the mercurial salts, empyreumatic oils, &c. cause its complete cessation* Woody fibre, in a state of decay, is the substance called humus*. The property of woody fibre to convert surround- ing oxygen gas into carbonic acid diminishes in proportion as its decay advances, and at last a certain quantity of a brown coaly-looking substance remains, in which this property is entirely wanting. This substance is called mould ; it is the product of the complete decay of woody fibre. Mould consti- * The humic acid of chemists is a product of the decomposition of humus by alkalies; it does not exist in the humus of vegetable physio- logists. IT EVOLVES CARBONIC ACID. 47 tutes the principal part of all the strata of brown coal and peat. Humus acts in the same manner in a soil per- meable to air as in the air itself; it is a continued source of carbonic acid, which it emits very slowly. An atmosphere of carbonic acid, formed at the expense of the oxygen of the air, surrounds every particle of decaying humus. The cultivation of land, by tilling and loosening the soil, causes a free and unobstructed access of air. An atmo- sphere of carbonic acid is, therefore, contained in every fertile soil, and is the first and most important food for the young plants which grow in it. In spring, when those organs of plants are absent, which nature has appointed for the assumption of nourishment from the atmosphere, the component substance of the seeds is exclusively employed in the formation of the roots. Each new radicle fibril which a plant acquires may be regarded as consti- tuting at the same time a mouth, a lung, and a stomach. The roots perform the functions of the leaves from the first moment of their formation ; they extract from the soil their proper nutri- ment, namely, the carbonic acid generated by the humus. By loosening the soil which surrounds young plants, we favour the access of air, and the formation of carbonic acid ; and on the other hand the quantity of their food is diminished by every difficulty which 48 ORIGIN AND ACTION OF HUMUS. opposes the renewal of air. A plant itself effects this change of air at a certain period of its growth. The carbonic acid, which protects the undecayed humus from further change, is absorbed and taken away by the fine fibres of the roots, and by the roots themselves ; this is replaced by atmospheric air, by which process the decay is renewed, and a fresh portion of carbonic acid formed. A plant at this time receives its food, both by the roots, and by the organs above ground, and advances rapidly to maturity. When a plant is quite matured, and when the organs, by which it obtains food from the atmo- sphere, are formed, the carbonic acid of the soil is no further required. Deficiency of moisture in the soil, or its com- plete dryness, does not now check the growth of a plant, provided it receives from the dew and the atmosphere as much as is requisite for the process of assimilation. During the heat of summer it derives its carbon exclusively from the atmosphere. We do not know what height and strength nature has allotted to plants ; we are acquainted only with the size which they usually attain. Oaks are shown, both in London and Amsterdam, as remarkable curiosities, which have been reared by Chinese gardeners, and are only one foot and a half in height, although their trunks, barks, leaves, branches, and whole habitus, evince a venerable age. GROWTH OF PLANTS. 49 The small turnip, grown at Tel tow,* when placed in a soil which yields as much nourishment as it can take up, increases to several pounds in weight. The size of a plant is proportional to the surface of the organs which are destined to convey food to it. A plant gains another mouth and stomach with every new fibre of root, and every new leaf. The power which roots possess of taking up nourishment does not cease as long as nutriment is present. When the food of a plant is in greater quantity than its organs require for their own per- fect development, the superfluous nutriment is not returned to the soil, but is employed in the forma- tion of new organs. At the side of a cell, already formed, another cell arises ; at the side of a twig and leaf, a new twig and a new leaf are developed. These new parts could not have been formed had there not been an excess of nourishment. The sugar and mucilage produced in the seeds, form the nutriment of the young plants, and disappear during the development of the buds, green sprouts, and leaves. The power of absorbing nutriment from the atmosphere, with which the leaves of plants are endowed, being proportionate to the extent of their surface, every increase in the size and number of these parts is necessarily attended with an increase * Teltow is a village near Berlin, where small turnips are cultivated in a sandy soil ; they are much esteemed, and weigh rarely above one ounce. E 50 ORIGIN AND ACTION OF HUMUS. of nutritive power, and a consequent further deve- lopment of new leaves and branches. Leaves, twigs, and branches, when completely matured, as they do not become larger, do not need food for their support. For their existence as organs, they require only the means necessary for the performance of the special functions to which they are destined by nature ; they do not exist on their own account. We know that the functions of the leaves and other green parts of plants are ' to absorb carbonic acid, and with the aid of light and moisture, to appropriate its carbon. These processes are con- tinually in operation ; they commence with the first formation of the leaves, and do not cease with their perfect development. But the new products arising from this continued assimilation, are no longer employed by the perfect leaves ^in their own increase : they serve for the formation of woody fibre, and all the solid matters of similar composition. The leaves now produce sugar, amylin or starch, and acids, which were previously formed by the roots when they were necessary for the development of the stem, buds, leaves and branches of the plant. The organs of assimilation, at this period of their life, receive more nourishment from the atmo- sphere than they employ in their own sustenance, and when the formation of the woody substance has advanced to a certain extent, the expenditure of the nutriment, the supply of which still remains the same, takes a new direction, and blossoms are TRANSFORMATIONS OF ORGANIC SUBSTANCES. 51 produced. The functions of the leaves of most plants cease upon the ripening of their fruit, because the products of their action are no longer needed. They now yield to the chemical influence of the oxygen of the ah*, generally suffer therefrom a change in colour, and fall off. A peculiar " transformation" of the matters con- tained in all plants takes place in the period be- tween blossoming and the ripening of the fruit ; new compounds are produced, which furnish con- stituents of the blossoms, fruit, and seed. An organic chemical "transformation" is the separation of the elements of one or several combinations, and their reunion into two or several others, which contain the same number of elements, either grouped in another manner, or in different propor- tions. Of two compounds formed in consequence of such a change, one remains as a component part of the blossom or fruit, while the other is separated by the roots in the form of excrementitious matter. No process of nutrition can be conceived to subsist in animals or vegetables, without a separation of effete matters. We know, indeed, that an organised body cannot generate substances,- but can only change the mode of their combination, and that its sustenance and reproduction depend upon the chemical transformation of the matters which are employed as its nutriment, and which contain its own constituent elements. Whatever we regard as the cause of these trans- E 2 52 ORIGIN AND ACTION OF HUMUS. formations, whether the Vital Principle, Increase of Temperature, Light, Galvanism, or any other in- fluence, the act of transformation is a purely che- mical process. Combination and Decomposition can take place only when the elements are disposed to these changes. That which chemists name affinity indicates only the degree in which they possess this disposition. It will be shown, when considering the processes of fermentation and putrefaction, that every disturbance of the mutual attraction subsist- ing between the elements of a body gives rise to a- transformation. The elements arrange themselves according to the degrees of their reciprocal attrac- tion into new combinations, which are incapable of further change, under the same conditions. The products of these transformations vary with their causes, that is, with the diiferent conditions on which their production depended; and are as innumerable as these conditions themselves. The chemical character of an acid, for example, is its unceasing disposition to saturation by means of a base ; this disposition differs in intensity in different acids ; but when it is satisfied, the acid character entirely disappears. The chemical cha- racter of a base is exactly the reverse of this, but both an acid and a base, notwithstanding the great difference in their properties, effect, in most cases, the same kind of transformations. Hydrocyanic acid and water contain the elements of carbonic acid, ammonia, urea, cyanuric acid, NATURE OF ORGANIC CHEMICAL PROCESSES. 53 cyanilic acid, oxalic acid, formic acid, melam, am- melin, melamin, azulmin, melton, hydromellonic acid, allantoin, fyc. It is well known, that all these very different substances can be obtained from hy- drocyanic acid and the elements of water, by vari- ous chemical transformations. The whole process of nutrition may be understood by the consideration of one of these transformations. Hydrocyanic acid and water, for example, when brought into contact with muriatic acid, are decom- posed into formic acid and ammonia ; both of these products of decomposition contain the elements of hydrocyanic acid and water, although in another form, and arranged in a different order. The change results from the strong disposition or struggle of muriatic acid to undergo saturation, in consequence of which the hydrocyanic acid and water suffer mutual decomposition. The nitrogen of the hydro- cyanic acid and the hydrogen of the water unite together and form a base, ammonia, with which the acid unites ; the chemical characters of the acid being at the same time lost, because its desire for saturation is satisfied by its uniting with am- monia. Ammonia itself was not previously present, but only its elements, and the power to form it. The simultaneous decomposition of hydro- cyanic acid and water in this instance does not take place in consequence of the chemical affinity of muriatic acid for ammonia, since hydrocyanic acid and water contain no ammonia. An affinity S4 ORIGIN AND ACTION OF HUMUS. of one body for a second, which does not exist, is quite inconceivable. The ammonia, in this case, is formed only on account of the existing attractive desire of the acid for saturation. Hence we may perceive how much these modes of decom- position, to which the name of transformations or metamorphoses has been especially applied, differ from the ordinary chemical decompositions. In consequence of the formation of ammonia, the other elements of hydrocyanic acid, namely, carbon and hydrogen, unite with the oxygen of the decomposed water, and form formic acid, the elements of this substance with the power of com- bination being present. Formic acid, here, repre- sents the excrementitious matters ; ammonia, the new substance, assimilated by an organ of a plant or animal. Each organ extracts from the food presented to it, what it requires for its own sustenance ; while the remaining elements, which are not assimilated, combine together and are separated as excrement. The excrementitious matters of one organ come in contact with another during their passage through the organism, and in consequence suffer new trans- formations ; the useless matters rejected by one organ containing the elements for the nutrition of a second and a third organ ; but at last, being ca- pable of no further transformations, they are sepa- rated from the system by the organs destined for that purpose. Each part of an organized being is ORGANIC CHEMICAL PROCESSES. 55 fitted for its peculiar functions. A cubic inch of sulphuretted hydrogen introduced into the lungs, would cause instant death, but it is formed, under a variety of circumstances, in the intestinal canal without any injurious effect. In consequence of such transformations as we have described, excrements are formed of various composition; some of these contain carbon, in excess; others nitrogen, and others again hydrogen and oxygen. The kidneys, liver, and lungs, are organs of excretion; the first separate from the body all those substances in which a large propor- tion of nitrogen is contained; the second, those with an excess of carbon ; and the third, such as are composed principally of oxygen and hydrogen. Alcohol, also, and the volatile oils which are inca- pable of being assimilated, are exhaled through the lungs, and not through the skin. Respiration must be regarded as a slow process of combustion or constant decomposition. If it be subject to the laws which regulate the processes of decomposition generally, the oxygen of the inspired air cannot combine directly with the carbon of com- pounds of that element contained in the blood; the hydrogen only can combine with the oxygen of the air, or undergo a higher degree of oxidation. Oxy- gen is absorbed without uniting with carbon ; and carbonic acid is disengaged, the carbon and oxygen of which must be derived from matters previously existing in the blood. 50 ORIGIN AND ACTION OF HUMUS. All superabundant nitrogen is eliminated from the body, as a liquid excrement, through the uri- nary passages; all solid substances, incapable of further transformation, pass out by the intestinal canal, and all gaseous matters by the lungs. We should not permit ourselves to be withheld, by the idea of a vital principle, from considering, in a chemical point of view, the process of the trans- formation of the food, and its assimilation by the various organs. This is the more necessary, as the views, hitherto held, have produced no results, and are quite incapable of useful application. Is it truly vitality, which generates sugar in the germ for the nutrition of young plants, or which gives to the stomach the power to dissolve, and to prepare for assimilation all the matter introduced into it? A decoction of malt possesses as little power to reproduce itself, as the stomach of a dead calf; both are, unquestionably, destitute of life. But when amylin or starch is introduced into a decoction of malt, it changes, first into a gummy- like matter, and lastly into sugar. Hard-boiled albumen and muscular fibre can be dissolved in a decoction of a calf's stomach, to which a few drops of muriatic acid have been added, precisely as in the stomach itself. * (Schwann, Schulz.) The power, therefore, to effect transformations, * This remarkable action has been completely confirmed in this laboratory (Giessen), by Dr. Vogel, a highly distinguished young phy- siologist. ORGANIC CHEMICAL PROCESSES. 57 does not belong to the vital principle ; each trans- formation is owing to a disturbance in the attrac- tion of the elements of a compound, and is con- sequently a purely chemical process. There is no doubt, that this process takes place in another form, from that of the ordinary decomposition of salts, oxides, or sulphurets. But is it the fault of chemistry that physiology has hitherto taken no notice of this new form of chemical action? Physicians are accustomed to administer whole ounces of borax to patients suffering under urinary calculi, when it is known, that the bases of all alkaline salts, formed by organic acids, are carried through the urinary passages in the form of alkaline carbonates capable of dissolving calculi (Wohler). Is this rational ? The medical reports state, that upon the Rhine, where so much cream of tartar is consumed in wine, the only cases of calculous dis- orders are those which are imported from other districts. We know that the uric acid calculus is transformed into the mulberry calculus, (which con- tains oxalic acid,) when patients suffering under the former exchange the town, for the country, where less animal and more vegetable food is used. Are all these circumstances incapable of explanation ? The volatile oil of the roots of valerian may be obtained from the oil generated during the fer- mentation of potatoes (Dumas), and the oil of the Spircea ulmaria from the crystalline matter of the bark of the willow. (Piria.) We are able to form 58 ORIGIN AND ACTION OF HUMUS. in our laboratories, formic acid, oxalic acid, urea, and the crystalline substances existing in the liquid of the allantois of the cow, all products, it is said, of the vital principle. We see, therefore, that this mysterious principle has many relations in common with chemical forces, and that the latter can indeed replace it. What these relations are, it remains for physiologists to investigate. Truly it would be extraordinary, if this vital principle, which uses everything for its own purposes, had allotted no share to chemical forces, which stand so freely at its disposal. We shall obtain that which is attain- able in a rational inquiry into nature, if we sepa- rate the actions belonging to chemical powers, from those which are subordinate to other influences. But the expression " vital principle " must, in the meantime, be considered as of equal value with the terms specific or dynamic in medicine : everything is specific which we cannot explain, and dynamic is the explanation of all which we do not understand. Transformations of existing compounds are constantly taking place during the whole life of a plant, in consequence of which, and as the results of these transformations, there are produced gaseous matters which are excreted by the leaves and blos- soms, solid excrements deposited in the bark, and fluid soluble substances which are eliminated by the roots. Such secretions are most abundant imme- diately before the formation and during the continu- ance of the blossoms; they diminish after the deve- ITS USE EXPLAINED. 59 lopment of the fruit. Substances, containing a large proportion of carbon, are excreted by the roots and absorbed by the soil. Through the expulsion of these matters unfitted for nutrition, therefore, the soil receives again the greatest part of the carbon, which it had at first yielded to the young plants as food, in the form of carbonic acid. The soluble matter, thus acquired by the soil, is still capable of decay and putrefaction, and by un- dergoing these processes furnishes renewed sources of nutrition to another generation of plants ; it be- comes humus. The leaves of trees, which fall in the forest in autumn, and the old roots of grass in the meadow, are likewise converted into humus by the same influence : a soil receives more carbon in this form than its decaying humus had lost as carbonic acid. Plants do not exhaust the carbon of a soil, in the normal condition of their growth; on the contrary, they add to its quantity. But if it is true that plants give back more carbon to a soil than they take from it, it is evident that their growth must depend upon the reception of nourishment from the atmosphere. The influence of humus upon vegetation is explained by the foregoing facts, in the most clear and satisfactory manner. Humus does not nourish plants, by being taken up and assimilated in its unaltered state, but by presenting a slow and lasting source of carbonic acid which is absorbed by the roots, and is the 60 ORIGIN AND ACTION OF HUMUS. principal nutriment of young plants at a time when, being destitute of leaves, they are unable to extract food from the atmosphere. In former periods of the earth's history, its sur- face was covered with plants, the remains of which are still found in the coal formations. These plants the gigantic monocotyledons, ferns, palms, and reeds, belong to a class, to which nature has given the power, by means of an immense extension of their leaves, to dispense with nourishment from the soil. They resemble, in this respect, the plants which we raise from bulbs and tubers, and which live while young upon the substances contained in their seed, and require no food from the soil, when their exte- rior organs of nutrition are formed. This class of plants is, even at present, ranked amongst those which do not exhaust the soil. The plants of every former period are distin- guished from those of the present, by the inconsi- derable development of their roots. Fruit, leaves, seeds, nearly every part of the plants of a former world, except the roots, are found in the brown coal formation. The vascular bundles, and the perishable cellular tissue, of which then: roots con- sisted, have been the first to suifer decomposition. But when we examine oaks and other trees, which in consequence of revolutions of the same kind oc- curring in later ages have undergone the same changes, we never find their roots absent. The verdant plants of warm climates are very often NOT INDISPENSABLE FOR PLANTS. 61 such as obtain from the soil only a point of attach- ment and are not dependent on it for their growth. How extremely small are the roots of the Cactus, Sedum, and Sempervivum, in proportion to their mass, and to the surface of their leaves ! Again, in the most dry and barren sand, where it is impossible for nourishment to be obtained through the roots, we see the milky-juiced plants attain complete per- fection. The moisture necessary for the nutrition of these plants is derived from the atmosphere, and when assimilated is secured from evaporation by the nature of the juice itself. Caoutchouc and wax, which are formed in these plants, surround the water, as in oily emulsions, with an impenetrable envelope by which the fluid is retained, in the same manner as milk is prevented from evaporating, by the skin which forms upon it. These plants, there- fore, become turgid with their juices. Particular examples might be cited of plants, which have been brought to maturity, upon a small scale, without the assistance of mould ; but fresh proofs of the accuracy of our theory respecting the origin of carbon would be superfluous and useless, and could not render more striking, or more con- vincing, the arguments already adduced. It must not, however, be left unmentioned, that common wood charcoal, by virtue merely of its ordinary well- known properties, can completely replace vegetable mould or humus. The experiments of Lukas, which 62 ORIGIN AND ACTION OF HUMUS. are appended to this work, spare me all further remarks upon its efficacy. Plants thrive in powdered charcoal, and may be brought to blossom and bear fruit if exposed to the influence of the rain and the atmosphere ; the charcoal may be previously heated to redness. Charcoal is the most " indifferent " and most un- changeable substance known ; it may be kept for centuries without change, and is therefore not sub- ject to decomposition. The only substances which it can yield to plants are some salts, which it con- tains, amongst which is silicate of potash. It is known, however, to possess the power of condensing gases within its pores, and particularly carbonic acid. And it is by virtue of this power that the roots of plants are supplied in charcoal exactly as in humus, with an atmosphere of carbonic acid and air, which is renewed as quickly as it is abstracted. In charcoal powder, which had been used for this purpose by Lukas for several years, Buchner found a brown substance soluble in alkalies. This substance was evidently due to the secretions from the roots of the plants which grew in it. A plant placed in a closed vessel in which the air, and therefore the carbonic acid, cannot be renewed, dies exactly as it would do in the vacuum of an air-pump, or in an atmosphere of nitrogen or carbonic acid, even though its roots be fixed in the richest mould. ASSIMILATION OF HYDROGEN. 63 Plants do not, however, attain maturity, under ordinary circumstances, in charcoal powder, when they are moistened with pure distilled water instead of rain or river water. Rain water must, therefore, contain within it one of the essentials of vegetable life ; and it will be shown, that this is the presence of a compound containing nitrogen, the exclusion of which entirely deprives humus and charcoal of their influence upon vegetation. ON THE ASSIMILATION OF HYDROGEN. The atmosphere contains the principal food of plants in the form of carbonic acid, in the state, therefore, of an oxide. The solid part of plants (woody fibre) contains carbon and the constituents of water, or the elements of carbonic acid together with a certain quantity of hydrogen. We can con- ceive the wood to arise from a combination of the carbon of the carbonic acid with the elements of water, under the influence of solar light. In this case, 72*35 parts of oxygen, by weight, must be separated as a gas for every 27*65 parts of carbon, which are assimilated by a plant. Or, what is much more probable, plants, under the same cir- cumstances, may decompose water, the hydrogen of which is assimilated along with carbonic acid, whilst its oxygen is separated. If the latter change takes place, 8*04 parts of hydrogen must unite with 100 parts of carbonic acid, in order to form woody 64 ASSIMILATION OF HYDROGEN. fibre, and the 72'35 parts by weight of oxygen, which was in combination with the hydrogen of the water, and which exactly corresponds in quantity with the oxygen contained in the carbonic acid, must be separated in a gaseous form. Each acre of land, which produces 8 centners or cwts. of carbon, gives annually to the atmosphere 2600 Hessian Ibs. of free oxygen gas. The specific weight of oxygen is expressed by the number 1*1026, hence 1 cubic metre of oxygen weighs 2*864 Hessian Ibs., and^ 2600 Ibs. of oxygen correspond to 908 cubic metres or 58,112 Hessian cubic feet. An acre of meadow, wood, or cultivated land in general, replaces, therefore, in the atmosphere as much oxygen as is exhausted by 8 centners of carbon, either in its ordinary combustion in the air or in the respiratory process of animals. It has been mentioned at a former page that pure woody fibre contains carbon and the component parts of water, but that ordinary wood contains more hydrogen than corresponds to this proportion. This excess is owing to the presence of the green principle of the leaf, wax, resin, and other bodies rich in hydrogen. Water must be decomposed, in order to furnish the excess of this element, and con- sequently one equivalent of oxygen must be given back to the atmosphere for every equivalent of hydrogen appropriated by a plant to the production of those substances. The quantity of oxygen, thus BY THE DECOMPOSITION OF WATER. 65 set at liberty, cannot be insignificant, for the atmosphere must receive 989 cubic feet of oxygen for every pound of hydrogen assimilated. It has already been stated, that a plant, in the formation of woody fibre, must always yield to the at- mosphere the same proportional quantity of oxygen ; that the volume of this gas set free would be the same whether it were due to the decomposition of carbonic acid or of water. It was considered most probable that the latter was the case. From their generating caoutchouc, wax, fats, and volatile oils containing hydrogen in large quantity, and no oxygen, we may be certain that plants possess the property of decomposing water, because from no other body could they obtain the hydro- gen of those matters. It has also been proved by the observations of Humboldt on the fungi, that water may be decomposed without the assimilation of hydrogen. Water is a remarkable combination of two elements, which have the power to separate themselves from one another, in innumerable pro- cesses, in a manner imperceptible to our senses ; while carbonic acid, on the contrary, is only decom- posable by violent chemical action. Most vegetable structures contain hydrogen in the form of water, which can be separated as such, and replaced by other bodies ; but the hydrogen which is essential to their constitution cannot pos- sibly exist in the state of water. All the hydrogen necessary for the formation of F 66 ASSIMILATION OF HYDROGEN. an organic compound is supplied to a plant by the decomposition of water. The process of assimila- tion, in its most simple form, consists in the extraction of hydrogen from water, and carbon from carbonic acid, in consequence of which, either all the oxygen of the water and carbonic acid is sepa- rated, as in the formation of caoutchouc, the volatile oils which contain no oxygen, and other similar substances, or only a part of it is exhaled. The known composition of -the organic com- pounds most generally present in vegetables, enables us to state in definite proportions the quantity of oxygen separated during their formation. 36 eq. carbonic acid and 22 eq. hydrogen derived ) _ ^ , from 22 eq. water . . .3 with the separation of 72 eq. oxygen. 36 eq. carbonic acid and 36 eq. hydrogen derived ? from 36 eq. water . . 3 with the separation of 72 eq. oxygen. 36 eq. carbonic acid and 30 eq. hydrogen derived > Starch from 30 eq. water . . .3 with the separation of 72 eq. oxygen. 36 eq. carbonic acid and 16 eq. hydrogen derived > j, . from 16 eq. water . . 3 ~~ with the separation of 64 eq. oxygen. 36 eq. carbonic acid and ,18 eq. hydrogen derived ) Tartaric Acid from 18 eq. water . . 5 ~~ with the separation of 45 eq. oxygen. 36 eq. carbonic acid and 18 eq. hydrogen derived > Malic Acid from 18 eq. water . . .3 with the separation of 54 eq. oxygen. 36 eq. carbonic acid and 24 eq. hydrogen derived > =O il of Turpentine from 24 eq. water . . .3 with the separation of 84 eq. oxygen. It will readily be perceived that the formation of ATTENDED WITH EVOLUTION OF OXYGEN. 6? the acids is accompanied with the smallest separa- tion of oxygen ; that the amount of oxygen set free increases with the production of the so-named neutral substances, and reaches its maximum in the formation of the oils. Fruits remain acid in cold summers ; while the most numerous trees under the tropics are those which produce oils, caoutchouc, and other substances, containing very little oxygen. The action of sunshine and influence of heat, upon the ripening of fruit, is thus in a certain measure represented by the numbers above cited. The green resinous principle of the leaf dimi- nishes in quantity, while oxygen is absorbed, when fruits are ripened in the dark; red and yellow colouring matters are formed ; tartaric, citric, and tannic acids disappear, and are replaced by sugar, amylin, or gum. 6 eq. Tartaric Add) by absorb- ing 6 eq. oxygen from the air, form Grape Sugar, with the separation of 12 eq. carbonic acid. 1 eq. Tannic Avid, by absorbing 8 eq. oxygen from the air, and 4 eq. water form 1 eq. of Amylin, or starch, with separation of 6 eq. carbonic acid. We can explain, in a similar manner, the forma- tion of all the component substances of plants, which contain no nitrogen, whether they are pro- duced from carbonic acid and water, with separation of oxygen, or by the conversion of one substance into the other, by the assimilation of oxygen and separation of carbonic acid. We do not know in F2 68 ASSIMILATION OF HYDROGEN. what form the production of these constituents takes place ; in this respect, the representation of their formation which we have given must not be received in an absolute sense, it being intended only to render the nature of the process more capable of apprehension ; but it must not be for- gotten, that if the conversion of tartaric acid into sugar, in grapes, be considered as a fact, it must take place under all circumstances in the same proportions. The vital process in plants is, with reference to the point we have been considering, the very reverse of the chemical processes engaged in the formation of salts. Carbonic acid, zinc, and water, when brought into contact, act upon one another, and hydrogen is separated, while a white pulveru- lent compound is formed, which contains carbonic acid, zinc, and the oxygen of the water. A living plant represents the zinc in this process : but the process of assimilation gives rise to compounds, which contain the elements of carbonic acid and the hydrogen of water, whilst oxygen is separated. Decay has been described above as the great operation of nature, by which that oxygen, which was assimilated by plants during life, is again returned to the atmosphere. During the progress of growth, plants appropriate carbon in the form of carbonic acid, and hydrogen from the decomposi- tion of water, the oxygen of which is set free, together with a part or all of that contained in the SOURCE OF THE NITROGEN OF PLANTS. 69 carbonic acid. In the process of putrefaction,, a quantity of water, exactly corresponding to that of the hydrogen, is again formed by extraction of oxygen from the air ; while all the oxygen of the organic matter is returned to the atmosphere in the form of carbonic acid. Vegetable matters can emit carbonic acid, during their decay, only in propor- tion to the quantity of oxygen which they contain ; acids, therefore, yield more carbonic acid than neutral compounds ; while fatty acids, resin, and wax, do not putrify, they remain in the soil without any apparent change. The numerous springs which emit carbonic acid in the neighbourhood of extinct volcanoes, must be regarded as another considerable source of oxygen. Bischof calculated that the springs of carbonic acid in the Eifel (a volcanic district near Coblenz) send into the air every day more than 90,000 Ibs. of car- bonic acid, corresponding to 64,800 Ibs. of pure oxygen. ON THE ORIGIN AND ASSIMILATION OF NITROGEN. We cannot suppose that a plant would attain maturity, even in the richest vegetable mould, with- out the presence of matter containing nitrogen ; since we know that nitrogen exists in every part of the vegetable structure. The first and most important question to be solved, therefore, is : How and in what form does nature furnish 70 SOURCE AND ASSIMILATION nitrogen to vegetable albumen, and gluten., to fruits and seeds ? This question is susceptible of a very simple solution. Plants, as we know, grow perfectly well in pure charcoal, if supplied at the same time with rain- water. Rain-water can contain nitrogen only in two forms, either as dissolved atmospheric air, or as am- monia. Now, the nitrogen of the air cannot be made to enter into combination with any element except oxygen, even by employment of the most powerful chemical means. We have not the slightest reason for believing that the nitrogen of the atmosphere takes part in the processes of assimilation of plants and animals ; on the contrary, we know that many plants emit the nitrogen, which is absorbed by their roots, either in the gaseous form, or in solution in water. But there are on the other hand numerous facts, showing, that the formation in plants of substances containing nitrogen, such as gluten, takes place in proportion to the quantity of this element which is conveyed to their roots in the staje of ammonia, derived from the putrefaction of animal matter. Ammonia, too, is capable of undergoing such a multitude of transformations, when in contact with other bodies, that in this respect it is not inferior to water, which possesses the same property in an emi- nent degree. It possesses properties which we do not find in any other compound of nitrogen ; when OF THE NITROGEN OF PLANTS. 71 pure, it is extremely soluble in water ; it forms soluble compounds with all the acids ; and when in contact with certain other substances, it completely resigns its character as an alkali, and is capable of assuming the most various and opposite forms. Formate of ammonia changes, under the influence of a high temperature, into hydrocyanic acid and water, without the separation of any of its elements. Ammonia forms urea, with cyanic acid, and a series of crystalline compounds, with the volatile oils of mustard and bitter almonds. It changes into splendid blue or red colouring matters, when in contact with the bitter constituent of the bark of the apple-tree (phloridzin), with the sweet prin- ciple of the Variolaria dealbata (ordn), or with the tasteless matter of the Rocella tinctoria (erythrin). All blue colouring matters which are reddened by acids, and all red colouring substances which are rendered blue by alkalies, contain nitrogen, but not in the form of a base. These facts are not sufficient to establish the opinion that it is ammonia, which affords all vege- tables without exception the nitrogen which enters into the composition of their constituent substances. Considerations of another kind, however, give to this opinion a degree of certainty, which completely excludes all other views of the matter. Let us picture to ourselves the condition of a well- cultured farm, so large as to be independent of assistance from other quarters. On this extent of 72 SOURCE AND ASSIMILATION land there is a certain quantity of nitrogen con- tained both in the corn and fruit which it produces, and in the men and animals which feed upon them, and also in their excrements. We shall suppose this quantity to be known. The land is cultivated without the importation of any foreign substance containing nitrogen. Now, the products of this farm must be exchanged every year for money, and other necessaries of life, for bodies therefore which contain no nitrogen. A certain proportion of nitrogen is exported with corn and cattle ; and this exportation takes place every year, without the smallest com- pensation ; yet after a given number of years, the quantity of nitrogen will be found to have increased. Whence, we may ask, comes this increase of nitro- gen ? The nitrogen in the excrements cannot repro- duce itself, and the earth cannot yield it. Plants, and consequently animals, must, therefore, derive their nitrogen from the atmosphere. It will in a subsequent part of this work be shown that the last products of the decay and putrefaction of animal bodies present themselves in two different forms. They are in the form of a combination of hydrogen and nitrogen ammonia, in the temperate and cold climates, and in that of a compound, con- taining oxygen, nitric acid, in the tropics and hot climates. The formation of the latter is preceded by the production of the first. Ammonia is the last product of the putrefaction of animal bodies ; nitric acid is the product of the transformation of OF THE NITROGEN OF PLANTS. 73 ammonia. A generation of a thousand million men is renewed every thirty years : thousands of millions of animals cease to live, and are repro- duced, in a much shorter period. Where is the nitrogen which they contained during life ? There is no question which can be answered with more positive certainty. All animal bodies, during their decay, yield the nitrogen, which they contain, to the atmosphere, in the form of ammonia. Even in the bodies buried sixty feet under ground in the churchyard of the Eglise des Innocens, at Paris, all the nitrogen contained in the adipocire was in the state of ammonia. Ammonia is the simplest of all the compounds of nitrogen ; and hydrogen is the ele- ment for which nitrogen possesses the most powerful affinity. The nitrogen of putrified animals is contained in the atmosphere as ammonia, in the form of a gas which is capable of entering into combination with carbonic acid, and of forming a volatile salt. Am- monia in its gaseous form as well as all its volatile compounds are of extreme solubility in water. Ammonia, therefore, cannot remain long in the atmosphere, as every shower of rain must condense it, and convey it to the surface of the earth. Hence, also, rain-water must, at all times, contain ammonia, though not always in equal quantity. It must be greater in summer than in spring or in winter, because the intervals of time between the showers are in summer greater; and when 74 SOURCE AND ASSIMILATION several wet days occur, the rain of the first must contain more of it than that of the second. The rain of a thunder-storm, after a long protracted drought, ought for this reason to contain the greatest quantity, which is conveyed to the earth at one time. But all the analyses of atmospheric air, hitherto made, have failed to demonstrate the presence of am- monia, although according to our view it can never be absent. Is it possible that it 'could have escaped our most delicate and most exact apparatus ? The quantity of nitrogen contained in a cubic foot of air is certainly extremely small, but notwithstand- ing this, the sum of the quantities of nitrogen from thousands and millions of dead animals is more than sufficient to supply all those living at one time with this element. From the tension of aqueous vapour at 15 C. (59 F.) = 6,98 lines (Paris measure) and from its known specific gravity at C. (32 F.), it follows that when the temperature of the air is 59 F. and the height of the barometer 28", 1 cubic metre or 64 Hessian cubic feet of aqueous vapour are con- tained in 487 cubic metres, or 31,168 cubic feet of air ; 64 cubic feet of aqueous vapour weigh about 1^ Ib. Consequently if we suppose that the air saturated with moisture at 59 F. allows all the water which it contains in the gaseous form to fall as rain ; then 1 Hessian pound of rain- water must be obtained from every 20,800 cubic OF THE NITROGEN OF PLANTS. 75 feet of air. The whole quantity of ammonia contained in the same number of cubic feet will also be returned to the earth in this one pound of rain-water. But if the 20,800 cubic feet of air contain a single grain of ammonia, then ten cubic inches, the quantity usually employed in an analysis, must contain only 0.000000048 of a grain. This extremely small proportion is absolutely inappreciable by the most delicate and best eudiometer ; it might be classed among the errors of observation, even were its quan- tity ten thousand times greater. But the de- tection of ammonia must be much more easy, when a pound of rain-water is examined, for this contains all the gas that was diffused through 20,800 cubic feet of air. If a pound of rain-water contain only ^th of a grain of ammonia, then a field of 40,000 square feet must receive annually upwards of 80 Ibs. of ammo- nia, or 65 Ibs. of nitrogen ; for, by the observations of ScMbler, which were formerly alluded to, about 700,000 Ibs. of rain fall over this surface in four months, and consequently the annual fall must be 2,500.000 Ibs. This is much more nitrogen than is contained in the form of vegetable albumen and gluten, in 2650 Ibs. of wood, 2800 Ibs. of hay, or 200 cwt. of beet-root, which are the yearly produce of such a field, but it is less than the straw, roots, and grain of corn which might grow on the same surface, would contain. 76 SOURCE AND ASSIMILATION Experiments, made in this laboratory (Giessen) with the greatest care and exactness, have placed the presence of ammonia in rain-water beyond all doubt. It has hitherto escaped observation, be- cause no person thought of searching for it. All the rain-water employed in this inquiry was col- lected 600 paces south-west of Giessen, whilst the wind was blowing in the direction of the town. When several hundred pounds of it were distilled in a copper still, and the first two or three pounds evaporated with the addition of a little muriatic acid, a very distinct crystallisation of sal-ammoniac was obtained : the crystals had always a brown or yellow colour. Ammonia may likewise be always detected in snow-water. Crystals of sal-ammoniac were ob- tained by evaporating in a vessel with muriatic acid several pounds of snow, which were gathered from the surface of the ground in March, when the snow had a depth of 10 inches. Ammonia was set free from these crystals by the addition of hydrate of lime. The inferior layers of snow, which rested upon the ground, contained a quantity decidedly greater than those which formed the surface. It is worthy of observation, that the ammonia contained in rain and snow water, possessed an offensive smell of perspiration and animal excre- ments, a fact which leaves no doubt respecting its origin. Hilnefeld has proved, that all the springs in OF THE NITROGEN OF PLANTS. 77 Greifswalde, Wick, Eldena, and Kostenhagen, con- tain carbonate and nitrate of ammonia. Ammo- niacal salts have been discovered in many mineral springs in Kissingen and other places. The am- monia of these salts can only arise from the atmo- sphere. Any one may satisfy himself of the presence of ammonia in rain, by simply adding a little sulphuric or muriatic acid to a quantity of rain-water, and evaporating this nearly to dryness in a clean porce- lain basin. The ammonia remains in the residue, in combination with the acid employed ; and may be detected either by the addition of a little chloride of platinum, or more simply by a little powdered lime, which separates the ammonia, and thus renders its peculiar pungent smell sensible. The sensation which is perceived upon moistening the hand with rain-water, so different from that produced by pure distilled water, and to which the term softness is vulgarly applied, is also due to the carbonate of ammonia contained in the former. The ammonia, which is removed from the atmo- sphere by rain and other causes, is as constantly replaced by the putrefaction of animal and vegeta- ble matters. A certain portion of that which falls with the rain, evaporates again with the water, but another portion is,we suppose, taken up by the roots of plants, and entering into new combinations in the different organs of assimilation, produces albu- men, gluten, quinine, morphia, cyanogen, and a 78 SOURCE AND ASSIMILATION number of other compounds containing nitrogen. The chemical characters of ammonia render it ca- pable of entering into such combinations, and of undergoing numerous transformations. We have now only to consider whether it really is taken up in the form of ammonia by the roots of plants, and in that form applied by their organs to the produc- tion of the azotised matters contained in them. This question is susceptible of easy solution by well- known facts. In the year 1834, I was engaged with Dr. Wil- brand, professor of botany in the university of Giessen, in an investigation respecting the quantity of sugar contained in different varieties of maple- trees, which grew upon soils which were not ma- nured. We obtained crystallised sugars from all, by simply evaporating their juices, without the ad- dition of any foreign substance ; and we unexpect- edly made the observation, that a great quantity of ammonia was emitted from this juice, when mixed with lime, and also from the sugar itself during its refinement. The vessels, which hung upon the trees in order to collect the juice, were watched with greater attention, on account of the suspicion that some evil-disposed persons had introduced urine into them, but still a large quantity of ammonia was again found in the form of neutral salts. The juice had no colour, and had no reaction on that of vegetables. Similar observations were made upon the juice of the birch-tree ; the specimens subjected OF THE NITROGEN OF PLANTS. 79 to experiment were taken from a wood several miles distant from any house, and yet the clarified juice, evaporated with lime, emitted a strong odour of ammonia. In the manufactories of beet-root sugar, many thousand cubic feet of juice are daily purified with lime, in order to free it from vegetable albumen and gluten, and it is afterwards evaporated for crystal- lization. Every person, who has entered such a manufactory, must have been astonished at the great quantity of ammonia which is volatilised along with the steam. This ammonia must be contained in the form of an ammoniacal salt, because the neutral juice possesses the same characters as the solution of such a salt in water ; it acquires, namely, an acid reaction during evaporation, in consequence of the neutral salt being converted by loss of ammonia into an acid salt. The free acid which is thus formed is a source of loss to the manufacturers of sugar from beet-root, by changing a part of the sugar into uncrystallisable grape sugar and syrup. The products of the distillation of flowers, herbs, and roots, with water, and all extracts of plants made for medicinal purposes, contain ammonia. The unripe, transparent and gelatinous pulp of the almond and peach emit much ammonia when treated with alkalies. (RoUquet.) The juice of the fresh tobacco leaf contains ammoniacal salts. The water, which exudes from a cut vine, when evaporated with a few drops of muriatic acid, also yields a gummy 80 SOURCE AND ASSIMILATION deliquescent mass, which evolves much ammonia on the addition of lime. Ammonia exists in every part of plants, in the roots (as in beet-root), in the stem (of the maple-tree), and in all blossoms and fruit in an unripe condition. The juices of the maple and birch contain both sugar and ammonia, and therefore afford all the conditions necessary for the formation of the azo- tised components of the branches, blossoms, and leaves, as well as of those which contain no azote or nitrogen. In proportion as the development of those parts advances, the ammonia diminishes in quantity, and when they are fully formed, the tree yields no more juice. The employment of animal manure in the culti- vation of grain, and the vegetables which serve for fodder to cattle, is the most convincing proof that the nitrogen of vegetables is derived from ammonia. The quantity of gluten in wheat, rye, and barley, is very different ; these kinds of grain also, even when ripe, contain this compound of nitrogen in very different proportions. Proust found French wheat to contain 12.5 per cent.. of gluten; Vogel found that the Bavarian contained 24 per cent. ; Davy obtained 19 per cent, from winter, and 24 from summer wheat ; from Sicilian 21, and from Barbary wheat 19 per cent. The meal of Alsace wheat contains, according to Boussingault, 17.3 per cent, of gluten ; that of wheat grown in the " Jar- din des Plantes" 26.7, and that of winter wheat OF THE NITROGEN OF PLANTS. 81 3*33 per .cent. Such great differences must be owing to some cause, and this we find in the different methods of cultivation. An increase of animal manure gives rise not only to an increase in the number of seeds, but also to a most remarkable difference in the proportion of the gluten which they contain. Animal manure, as we shall afterwards show, acts only by the formation of ammonia. One hundred parts of wheat grown on a soil manured with cow- dung (a manure containing the smallest quantity of nitrogen), afforded only 11*95 parts of gluten, and 64*34 parts of amylin, or starch ; whilst the same quantity, grown on a soil manured with human urine, yielded the maximum of gluten, namely 35*1 per cent. Putrified urine contains nitrogen in the forms of carbonate, phosphate, and lactate of ammonia, and in no other form than that of ammoniacal salts. " Putrid urine is employed in Flanders as a manure with the best results. During the putre- faction of urine, ammoniacal salts are formed in large quantity, it may be said exclusively ; for under the influence of heat and moisture urea, the most pro- minent ingredient of the urine, is converted into carbonate of ammonia. The barren soil on the coast of Peru is rendered fertile by means of a manure called Guano, which is collected from several islands on the South Sea.* It is sufficient to add a small * The guano, which forms a stratum several feet in thickness upon the surface of these islands, consists of the putrid excrements of innumera- ble sea-fowl that remain on them during the breeding season. G 82 SOURCE AND ASSIMILATION quantity of guano to a soil, which consists only of sand and clay, in order to procure the richest crop of maize. The soil itself does not contain the smallest particle of organic matter, and the manure employed is formed only of ur ate, phosphate, oxalate, and carbonate of ammonia, together with a few earthy salts. "* Ammonia, therefore, must have yielded the nitro- gen to these plants. Gluten is obtained not only from corn, but also from grapes -and other plants ; but that extracted from the grapes is called vege- table albumen, although it is identical in composi- tion and properties with the ordinary gluten. It is ammonia which yields nitrogen to the vege- table albumen, the principal constituent of plants ; and it must be ammonia which forms the red and blue colouring matters of flowers. Nitrogen is not presented to wild plants in any other form capable of assimilation. Ammonia, by its transformation, furnishes nitric acid to the tobacco plant, sun- flower, Chenopodium, and Borago qfficinalis, when they grow in a soil completely free from nitre. Nitrates are necessary constituents of these plants, which thrive only when ammonia is present in large quantity, and when they are also subject to the influence of the direct rays of the sun, an influ- ence necessary to effect the disengagement within their stem and leaves of the oxygen, which shall unite with the ammonia to form nitric acid. * Boussingault, Ann. de Ch. et de Phys. Ixv. p. 319. OF THE NITROGEN OF PLANTS. 83 The urine of men and of carnivorous animals contains a large quantity of nitrogen, partly in the form of phosphates, partly as urea. Urea is con- verted during putrefaction into carbonate of am- monia,, that is to say, it takes the form of the very salt which occurs in rain-water. Human urine is the most powerful manure for all vegetables con- taining nitrogen ; that of horses and horned cattle contains less of this element, but infinitely more than the solid excrements of these animals. In addition to urea, the urine of herbivorous animals contains hippuric acid, which is decomposed during putrefaction into benzoic acid and ammonia. The latter enters into the composition of the gluten, but the benzoic acid often remains unchanged : for example, in the Anthoxanthum odoratum. The solid excrements of animals contain compa- ratively very little nitrogen, but this could not be otherwise. The food taken by animals supports them only in so far as it offers elements for assimi- lation to the various organs, which they may require for their increase or renewal. Corn, grass, and all plants, without exception, contain azotised substances. The quantity of food, which animals take for their nourishment, diminishes or increases in the same proportion, as it contains more or less of the substances containing nitrogen. A horse may be kept alive by feeding it with potatoes, which contain a very small quantity of nitrogen ; but life thus supported is a gradual starvation ; the animal G2 84 SOURCE AND ASSIMILATION increases neither in size nor strength, and sinks under every exertion. The quantity of rice which an Indian eats astonishes the European ; but the fact, that rice contains less nitrogen than any other kind of grain at once explains the circumstance. Now, as it is evident that the nitrogen of the plants and seeds used by animals as food must be employed in the process of assimilation, it is natural to expect that the excrements of these animals will be deprived of it, in proportion to the perfect diges- tion of the food, and can only contain it when mixed with secretions from the liver and intestines. Under all circumstances, they must contain less nitrogen than the food. When, therefore, a field is manured with animal excrements, a smaller quan- tity of matter containing nitrogen is added to it than has been taken from it in the form of grass, herbs, or seeds. By means of manure, an addition only is made to the nourishment which the air supplies. In a scientific point of view, it should be the care of the agriculturist so to employ all the substances containing a large proportion of nitrogen which his farm affords in the form of animal excrements, that they shall serve as nutriment to his own plants. This will not be the case unless those substances are properly distributed upon his land. A heap of manure lying unemployed upon his land would serve him no more than his neighbours. The nitrogen in it would escape as carbonate of ammo- nia into the atmosphere, and a mere carbonaceous OP THE NITROGEN OF PLANTS. 85 residue of decayed plants would, after some years, be found in its place. All animal excrements emit carbonic acid and am- monia, as long as nitrogen exists in them. In every stage of their putrefaction an escape of ammonia from them may be induced by moistening them with a potash ley ; the ammonia being apparent to the senses by a peculiar smell, and by the dense white vapour which arises when a solid body moist- ened with an acid is brought near it. This ammo- nia evolved from manure is imbibed by the soil either in solution in water, or in the gaseous form, and plants thus receive a larger supply of nitrogen than is afforded to them by the atmosphere. But it is much less the quantity of ammonia, yielded to a soil by animal excrements, than the form in which it is presented by them, that causes their great influence on its fertility. Wild plants obtain more nitrogen from the atmosphere in the form of ammonia than they require for their growth, for the water which evaporates through their leaves and blossoms, emits, after some time, a putrid smell, a peculiarity possessed only by such bodies as contain nitrogen. Cultivated plants receive the same quantity of nitrogen from the atmosphere as trees, shrubs, and other wild plants ; but this is not sufficient for the purposes of agriculture. Agriculture differs essentially from the cultivation of forests, inasmuch as its principal object consists in the production of nitrogen under any form capa- 86 SOURCE AND ASSIMILATION ble of assimilation ; whilst the object of forest culture is confined principally to the production of carbon. All the various means of culture are sub- servient to these two main purposes. A part only of the carbonate of ammonia, which is conveyed by rain to the soil is received by plants, because a certain quantity of it is volatilised with the vapour of water ; only that portion of it can be assimilated which sinks deeply into the soil, or which is con- veyed directly to the leaves by dew, or is absorbed from the air along with the carbonic acid. Liquid animal excrements, such as the urine with which the solid excrements are impregnated, con- tain the greatest part of their ammonia in the state of salts, in a form, therefore, in which it has com- pletely lost its volatility when presented in this condition ; not the smallest portion of the am- monia is lost to the plants, it is all dissolved by water, and imbibed by their roots. The evident influence of gypsum upon the growth of grasses the striking fertility and luxuriance of a meadow upon which it is strewed depends only upon its fixing in the soil the ammonia of the atmosphere, which would otherwise be volatilised, with the water which evaporates. The carbonate of ammo- nia contained in rain-water is decomposed by gypsum, in precisely the same manner as in the manufacture of sal-ammoniac. Soluble sulphate of ammonia and carbonate of lime are formed ; and this salt of ammonia possessing no volatility is con- OF THE NITROGEN OF PLANTS. 87 sequently retained in the soil. All the gypsum gradually disappears, but its action upon the car- bonate of ammonia continues as long as a trace of it exists. The beneficial influence of gypsum and of many other salts has been compared to that of aromatics, which increase the activity of the human stomach and intestines, and give a tone to the whole system. But plants contain no nerves ; we know of no sub- stance capable of exciting them to intoxication and madness, or of lulling them to sleep and repose. No substance can possibly cause their leaves to appropriate a greater quantity of carbon from the atmosphere, when the other constituents which the seeds, roots, and leaves require for their growth are wanting. The favourable action of small quantities of aromatics upon man, when mixed with his food, is undeniable, but aromatics are given to plants with- out food to be digested, and still they flourish with greater luxuriance. It is quite evident, therefore, that the common view concerning the influence of certain salts upon the growth of plants evinces only ignorance of its cause. The action of gypsum or chloride of calcium really consists in their giving a fixed condition to the nitrogen or ammonia which is brought into the soil, and which is indispensable for the nutrition of plants. In order to form a conception of the effect of 88 SOURCE AND ASSIMILATION gypsum, it may be sufficient to remark that 100 Hess. Ibs. of burned gypsum fixes as much ammo- nia in the soil as 6250 Ibs. of horses' urine * would yield to it, even on the supposition that all the nitrogen of the urea and hippuric acid were absorbed by the plants without the smallest loss, in the form of carbonate of ammonia. If we admit with Bous- singault-f- that the nitrogen in grass amounts to Too of its weight, then every pound of nitrogen which we add increases the produce of the mea- dow 100 Ibs., and this increased produce of 100 Ibs. is effected by the aid of a little more than 4 Ibs. of gypsum. Water is absolutely necessary to effect the de- composition of the gypsum, on account of its diffi- cult solubility, (1 part of gypsum requires 400 parts of water for solution,) and also to assist in the ab- sorption of the sulphate of ammonia by the plants : hence it happens, that the influence of gypsum is not observable on dry fields and meadows. The decomposition of gypsum by carbonate of ammonia does not take place instantaneously ; on the contrary, it proceeds very gradually, and this * The urine of the horse contains, according to Fourcroy and Vau- quelin, in 1 000 parts, Urea 7 parts. Hippurate of soda . . 24 Salts and water . . 979 1000 parts, t Boussingault, Ann. de Ch. et de Phys. t. Ixiii. page 243. OP THE NITROGEN OF PLANTS. 89 explains why the action of the gypsum lasts for several years. The advantage of manuring fields with burned clay and the fertility of ferruginous soils, which have been considered as facts so incomprehensible, may be explained in an equally simple manner. They have been ascribed to the great attraction for water, exerted by dry clay and ferruginous earth ; but common dry arable land possesses this property in as great a degree : and besides, what influence can be ascribed to a hundred pounds of water spread over an acre of land, in a condition in which it can- not be serviceable either by the roots or leaves ? The true cause is this : The oxides of iron and alumina are distinguished from all other metallic oxides by their power of forming solid compounds with ammonia. The pre- cipitates obtained by the addition of ammonia to salts of alumina or iron are true salts, in which the ammonia is contained as a base. Minerals contain- ing alumina or oxide of iron also possess, in an eminent degree, the remarkable property of attract- ing ammonia from the atmosphere and of retaining it. Vauquelin, whilst engaged in the trial of a cri- minal case, discovered that all rust of iron contains a certain quantity of ammonia. Chevalier after- wards found that ammonia is a constituent of all minerals containing iron ; that even hematite, a mineral which is not at all porous, contains one per cent, of it. Bouis showed also, that the peculiar 90 SOURCE AND ASSIMILATION odour observed on moistening minerals containing alumina, is partly owing to their exhaling ammonia. Indeed^ gypsum and some varieties of alumina, pipe-clay for example, emit so much ammonia, when moistened with caustic potash, that even after they have been exposed for two days, litmus paper held over them becomes blue. Soils, therefore, which contain oxides of iron, and burned clay, must ab- sorb ammonia, an action which is favoured by their porous condition ; they further- prevent the escape of the ammonia once absorbed by their chemical properties. Such soils in fact act precisely as a mineral acid would do, if extensively spread over their surface ; with this difference, that the acid would penetrate the ground, enter into combination with lime, alumina, and other bases, and thus lose, in a few hours, its property of absorbing ammonia from the atmosphere. The ammonia absorbed by the clay or ferrugi- nous oxides is separated by every shower of rain, and conveyed in solution to the soil. Powdered charcoal possesses a similar action, but surpasses all other substances in the power which it possesses of condensing ammonia within its pores, particularly when it has been previously heated to redness. Charcoal absorbs 90 times its volume of ammoniacal gas, which may be again separated by simply moistening it with water. (De Saussure.) Decayed wood approaches very nearly to charcoal in this power ; decayed oak wood absorbs 72 times its OF THE NITROGEN OF PLANTS. 91 volume, after having been completely dried under the air-pump. We have here an easy and satisfactory means of explaining still further the properties of humus, or wood in a decaying state. It is not only a slow and constant source of carbonic acid, but it is also a means by which the necessary nitrogen is conveyed to plants. Nitrogen is found in lichens, which grow on basaltic rocks. Our fields produce more of it than we have given them as manure, and it exists in all kinds of soils and minerals which were never in contact with organic substances. The nitrogen in these cases could only have been extracted from the atmosphere. We find this nitrogen in the atmosphere in rain- water and in all kinds of soils, in the form of am- monia, as a product of the decay and putrefaction of preceding generations of animals and vegetables. We find likewise that the proportion of azotised matters in plants is augmented by giving them a larger supply of ammonia conveyed in the form of animal manure. No conclusion can then have a better foundation than this, that it is the ammonia of the atmosphere which furnishes nitrogen to plants. Carbonic acid, water and ammonia, contain the elements necessary for the support of animals and vegetables. The same substances are the ultimate products of the chemical processes of decay and 92 OF THE INORGANIC putrefaction. All the innumerable products of vitality resume, after death, the original form from which they sprung. And thus death the complete dissolution of an existing generation becomes the source of life for a new one. But another question arises, Are the conditions already considered the only ones necessary for the life of vegetables ? It will now be shown that they are not. OF THE INORGANIC CONSTITUENTS OF PLANTS. Carbonic acid, water and ammonia, are necessary for the existence of plants, because they contain the elements from which their organs are formed ; but other substances are likewise requisite for the formation of certain organs destined for special functions peculiar to each family of plants. Plants obtain these substances from inorganic nature. In the ashes left after the incineration of plants, the same substances are formed although in a changed condition. Many of these inorganic constituents vary ac- cording to the soil in which the plants grow, but a certain number of them are indispensable to their development. All substances in solution in a soil are absorbed by the roots of plants, exactly as a sponge imbibes a liquid, and all that it contains, without selection. The substances thus conveyed to plants are retained in greater or less quan- CONSTITUENTS OF PLANTS. 93 tity, or are entirely separated when not suited for assimilation. Phosphate of magnesia in combination with am- monia is an invariable constituent of the seeds of all kinds of grasses. It is contained in the outer horny husk, and is introduced into bread along with the flour, and also into beer. The bran of flour contains the greatest quantity of it. It is this salt which forms large crystalline concretions, often amounting to several pounds in weight, in the caecum of horses belonging to millers ; and when ammonia is mixed with beer, the same salt sepa- rates as a white precipitate. Most plants, perhaps all of them, contain organic acids of very different composition and properties, all of which are in combination with bases, such as potash, soda, lime or magnesia. These bases evi- dently regulate the formation of the acids, for the diminution of the one is followed by a decrease of the other : thus, in the grape, for example, the quantity of potash contained in its juice is less, when it is ripe, than when unripe ; and the acids, under the same circumstances, are found to vary in a similar manner. Such constituents exist in small quantity in those parts of a plant in which the process of assimilation is most active, as in the mass of woody fibre ; and their quantity is greater in those organs, whose office it is to prepare sub- stances conveyed to them for assimilation by other parts. The leaves contain more inorganic matters 94 OF THE INORGANIC than the branches., and the branches more than the stem. The potato plant contains more potash before blossoming than after it. The acids found in the different families of plants are of various kinds ; it cannot be supposed that their presence and peculiarities are the result of accident. The fumaric and oxalic acids in the liverwort^ the kinovic acid in the China nova, the rocellic acid in the Rocella tinctoria, the tartaric acid in grapes, and the numerous other organic acids, must serve some end in vegetable life. But if these acids constantly exist in vegetables^ and are necessary to their life, which is incontestable, it is equally certain that some alkaline base is also in- dispensable in order to enter into combination with the acids which are always found in the state of salts. All plants yield by incineration ashes con- taining carbonic acid ; all therefore must contain salts of an organic acid. Now, as we know the capacity of saturation of organic acids to be unchanging, it follows that the quantity of the bases united with them cannot vary, and for this reason the latter substances ought to be considered with the strictest attention both by the agriculturist and physiologist. We have no reason to believe that a plant in a condition of free and unimpeded growth produces more of its peculiar acids than it requires for its own existence ; hence, a plant, on whatever soil it grows, must contain an invariable quantity of alka- CONSTITUENTS OF PLANTS. 95 line bases. Culture alone will be able to cause a deviation. In order to understand this subject clearly, it will be necessary to bear in mind, that any one of the alkaline bases may be substituted for another, the action of all being the same. Our conclusion is, therefore, by no means endangered by the exist- ence of a particular alkali in one plant, which may be absent in others of the same species. If this inference be correct, the absent alkali or earth must be supplied by one similar in its mode of action, or in other words, by an equivalent of another base. The number of equivalents of these various bases, which may be combined with a certain portion of acid, must necessarily be the same, and, therefore, the amount of oxygen contained in them must remain unchanged, under all circumstances, and on whatever soil they grow. Of course, this argument refers only to those alkaline bases, which in the form of organic salts form constituents of the plants. Now, these salts are preserved in the ashes of plants, as carbonates, the quantity of which can be easily ascertained. It has been distinctly shown by the analyses of De Saussure and Berthier, that the nature of a soil exer cises a decided influence on the quantity of the dif- ferent metallic oxides contained in the plants, which grow on it ; that magnesia, for example, was con- tained in the ashes of a pine-tree grown at Mont Breven, whilst it was absent from the ashes of a tree 96 OF THE INORGANIC of the same species from Mont La Salle,and that even the proportion of lime and potash was very different. Hence it has been concluded (erroneously, I believe), that the presence of bases exercises no particular influence upon the growth of plants ; but even were this view correct, it must be considered as a most remarkable accident, that these same analyses furnish proof for the very opposite opinion. For although the composition of the ashes of these pine-trees was so very different, they contained, according to the analysis of De Saussure, an equal number of equivalents of metallic oxides ; or what is the same thing, the quantity of oxygen contained in all the bases was in both cases the same. 100 parts of the ashes of the pine-tree from Mont Breven contained*: Carbonate of Potash . 3-60 Quantity of oxygen in the Potash 0-4 1 Lime . 46-34 Lime 7-33 6-77 Magnesia 1'27 Sum of the carbonates 56-71 Sum of the oxygen in the bases 9-01 100 parts of the ashes of the pine from Mont La Salle contained-}-: Carbonate of Potash . 7-36 Quantity of oxygen in the Potash 085 Lime . 51-19 Lime 8-10 Magnesia 00 -00 Sum of the carbonates 58-55 Sum of the oxygen in the bases 8-95 The numbers 9*01 and 8*95 resemble each other as nearly as could be expected even in analyses * 100 parts of this wood gave 1-187 ashes, t 100 parts of this wood gave 1-128 ashes. CONSTITUENTS OF PLANTS. 97 made for the very purpose of ascertaining the fact above demonstrated which the analyst in this case had not in view. Let us now compare Berthier's analyses of the ashes of two fir-trees, one of which grew in Nor- way, the other in Allevard (de'partement de llsere). One contained 50, the other 25 per cent, of solu- ble salts. A greater difference in the proportion of the alkaline bases could scarcely exist between two totally different plants, and yet even here, the quantity of oxygen in the bases of both was the same. 100 parts of the ashes of firwood from Allevard contained according to Berthier, (Ann. de Chim. et de Phys. t. xxxii. p. 248,) Potash and Soda 16-8 in which 3-42 parts must be oxygen. Lime . 29'5 8'20 Magnesia . 3'2 1'20 49-5 12-82 Only part of the potash and soda in these ashes was in combination with organic acids, the remain- der was in the form of sulphates, phosphates, and chlorides. One hundred parts of the ashes con- tained 3*1 sulphuric acid, 4*2 phosphoric acid, and 0*3 hydrochloric acid, which, together, neutralise a quantity of base containing 1.20 oxygen. This number therefore must be subtracted from 12*82. The remainder 11*62 indicates the quantity of oxy- gen in the alkaline bases, combined with organic acids, in the firwood of Allevard. H 98 OF THE INORGANIC The firwood of Norway contained in 100 parts :* Potash . 14-1 of which 2'4 parts would be oxygen. Soda . 20-7 5'3 Lime . 12%3 3'45 Magnesia . 4-35 ,, 1-69 51-45 12-84 And if the quantity of oxygen of the bases in com- bination with sulphuric and phosphoric acid, viz- 1* 3 7) be again subtracted from 12*84, 1T47 parts remain as the amount of oxygen contained in the bases, which were in combination with organic acids. These remarkable approximations cannot be acci- dental ; and if further examinations confirm them in other kinds of plants, no other explanation than that already given can be adopted. It is not known in what form silica, manganese, and oxide of iron, are contained in plants, but we are certain that potash, soda, and magnesia, can be extracted from all parts of their structure in the form of salts of organic acids. The same is the case with lime, when not present as insoluble oxalate of lime. It must here be remembered, that in plants yielding oxalic acid, the acid and potash never exist in the form of a neutral or quadruple salt, but * This calculation is exact only in the case where the quantity of ashes is equal in weight for a given quantity of wood ; the difference cannot, however, be admitted to be so great as to change sensibly the above proportions. Berthier has not mentioned the proportion of ashes contained in the wood. CONSTITUENTS OF PLANTS. 99 always as a double acid salt, on whatever soil they may grow. The potash in grapes, also, is more fre- quently found as an acid salt, viz. cream of tartar, than in the form of a neutral compound. As these acids and bases are never absent from plants, and as even the form in which they present themselves is not subject to change, it may be affirmed, that they exercise an important influence on the deve- lopment of the fruits and seeds, and also on many other functions of the nature of which we are at present ignorant. The quantity of alkaline bases existing in a plant also depends evidently on this circumstance of their existing only in the form of acid salts, for the capa- city of saturation of an acid is constant ; and when we see oxalate of lime in the lichens occupying the place of woody fibre, which is absent, we must regard it as certain, that the soluble organic salts are des- tined to fulfil equally important, though different functions, so much so, that we could not conceive the complete development of a plant without their presence, that is, without the presence of their acids, and consequently of their bases. From these considerations we must perceive that exact and trustworthy examinations of the ashes of plants of the same kind growing upon different soils would be of the greatest importance to vege- table physiology, and would decide whether the facts above-mentioned are the results of an un- changing law for each family of plants, and whether H 2 100 OF THE INORGANIC an invariable number can be found to express the quantity of oxygen which each species of plant con- tains in the bases united with organic acids. In all probability, such inquiries will lead to most im- portant results ; for it is clear, that if the production of a certain unchanging quantity of an organic acid is required by the peculiar nature of the organs of a plant, and is necessary to its existence, then potash or lime must be taken up by it, in order to form salts with this acid ; that if these do not exist in sufficient quantity in the soil, other bases must supply their place ; and that the progress of a plant must be wholly arrested when none are present. Seeds of the Salsola Kali, when sown in common garden soil, produce a plant containing both potash and soda ; while the plants grown from the seeds of this contain only salts of potash, with mere traces @f muriate of soda. (Cadet.) The existence of vegetable alkalies in combina- tion with organic acids gives great weight to the opinion, that alkaline bases in general are connected with the development of plants. If potatoes are grown where they are not supplied with earth, the magazine of inorganic bases, (in cellars for example), a true alkali, called Solanin, of very poisonous nature, is formed in the sprouts which extend towards the light, while not the smallest trace of such a substance can be discovered in the roots, herbs, blossoms, or fruits of potatoes CONSTITUENTS OF PLANTS. 101 grown in fields. (Otto). In all the species of the Cin- chona, kinic acid is found ; but the quantity of qui- nina, cinchonina and liine which they contain is most variable. From the fixed bases in the products of incineration, however, we may estimate pretty accurately the quantity of the peculiar organic bases. A maximum of the first corresponds to a minimum of the latter, as must necessarily be the case if they mutually replace one another according to their equivalents. We know that different kinds of opium contain me conic acid, in combination with very different quantities of narcotina, morphia, eodeia, &c. 3 the quantity of one of these alkaloids diminish- ing on the increase of the others. Thus, the smallest quantity of morphia is accompanied by a maximum of narcotina. Not a trace of meconic acid* can be discovered in many kinds of opium, but there is not on this account an absence of acid, for the meconic is here replaced by sulphuric acid. Here also we have an example of what has been before stated, for in those kinds of opium where both these acids exist, they are always found to bear a certain relative pro- portion to one another. But if it be found, as appears to be the case in the juice of poppies, that an organic acid may be replaced by an inorganic, without impeding the growth of a plant, we must admit the probability * Robiquet did not obtain a trace of meconate of lime from 300 Ibs. of opium, whilst in other kinds the quantity was very considerable Ann. de Chim. liii. p. 425. 102 OF THE INORGANIC of this substitution taking place in a much higher degree in the case of the inorganic bases. When roots find their more appropriate base in sufficient quantity, they will take up less of another. These phenomena do not show themselves so frequently in cultivated plants, because they are subjected to special external conditions for the purpose of the production of particular constituents or particular organs. When the soil, in which a white hyacinth is growing in the state of blossom, is sprinkled with the juice of the Phytolaca decandra, the white blos- soms assume, in one or two hours, a red colour, which again disappears after a few days under the influence of sunshine, and they become white and colourless as before*. The juice in this case evi- dently enters into all parts of the plant, without being at all changed in its chemical nature, or with- out its presence being ^apparently either necessary or injurious. But this condition is not permanent, and when the blossoms have become again colour- less, none of the colouring matter remains ; and if it should occur, that any of its elements were adapted for the purposes of nutrition of the plant, then these alone would be retained, whilst the rest would be excreted in an altered form by the roots. Exactly the same thing must happen when we sprinkle a plant with a solution of chloride of * Biot, in the Comptes rendus des Seances de 1' Academic des Sciences, a Paris, ler Semestre, 1837. p. 12. CONSTITUENTS OF PLANTS. 103 potassium, nitre, or nitrate of strontia ; they will enter into the different parts of the plant, just as the coloured juice mentioned above, and will be found in its ashes if it should be burnt at this period. Their presence is merely accidental ; but no conclusion can be hence deduced against the necessity of the presence of other bases in plants. The experiments of Macaire-Princep have shown that plants made to vegetate with their roots in a weak solution of acetate of lead, and then in rain- water, yield to the latter all the salt of lead which they had previously absorbed. They return, there- fore, to the soil all matters which are unnecessary to their existence. Again, when a plant, freely exposed to the atmosphere, rain, and sunshine, is sprinkled with a solution of nitrate of abrontian, the salt is absorbed, but it is again separated by the roots and removed further from them by every shower of rain, which moistens the soil, so that at last not a trace of it is to be found in the plant. Let us consider the composition of the ashes of two fir-trees as analysed by an acute and most accurate chemist. One of these grew in Norway on a soil, the constituents of which never changed, but to which soluble salts, and particularly common salt, were conveyed in great quantity by rain-water. How did it happen that its ashes contained no appreciable trace of salt, although we are certain that its roots must have absorbed it after every shower ? We can explain the absence of salt in this case 104 OF THE INORGANIC by means of the direct and positive observations referred to, which have shown that plants have the power of returning to the soil all substances unne- cessary to their existence ; and the conclusion to which all the foregoing facts lead us, when their real value and bearing are apprehended, is that the alkaline bases existing in the ashes of plants must be necessary to their growth, since if this were not the case they would not be retained. The perfect development of a plant according to this view is dependent on the presence of alkalies or alkaline earths ; for when these substances are totally wanting, its growth will be arrested, and when they are only deficient, it must be impeded. In order to apply these remarks, let us compare two kinds of tree, the wood of which contain un- equal quantities of alkaline bases, and we shall find that one of these grows luxuriantly in several soils, upon which the others are scarcely able to vegetate. For example, 10,000 parts of oak wood yield 250 parts of ashes, the same quantity of fir-wood only 83, of linden-wood 500, of rye 440, and of the herb of the potato-plant 1500 parts*. Firs and pines find a sufficient quantity of alkalies in granitic and barren sandy soils, in which oaks will not grow ; and wheat thrives in soils favourable for the linden-tree, because the bases, which are necessary to bring it to complete maturity, exist there in sufficient quantity. The accuracy of these conclusions, so highly important to agriculture and * Berthier, Annales de Chimie ct cle Physique, t. xxx. p. 248. CONSTITUENTS OF PLANTS. 105 to the cultivation of forests, can be proved by the most evident facts. All kinds of grasses, the Equisetacece, for example, contain in the outer parts of their leaves and stalk a large quantity of silicic acid and potash, in the form of acid silicate of potash. The proportion of this salt does not vary perceptibly in the soil of corn-fields, because it is again conveyed to them as manure in the form of putrifying straw. But this is not the case in a meadow, and hence we never find a luxuriant crop of grass* on sandy and calcareous soils which contain little potash, evi- dently because one of the constituents indispensable to the growth of the plants is wanting. Soils formed from basalt, grauwacke, and porphyry are, caeteris paribus, the best for meadow land, on account of the quantity of potash which enters into their com- position. The potash abstracted by the plants is re- stored during the annual irrigation-^. That con- * It would be of importance to examine what alkalies are contained in the ashes of the sea-shore plants which grow in the humid hollows of downs, and especially in those of the millet-grass (Hartig). If potash is not found in them it must certainly be replaced by soda as in the salsola, or by lime as in the Plumbacfinece. f A very high value is attached in Germany to the cultivation of grass as winter provision for cattle, and the greatest care is used in order to obtain the greatest possible quantity. In the vicinity of Liegen (a town in Nassau), from three to five perfect crops are obtained from one meadow, and this is effected by covering the fields with river- water, which is conducted over the meadow in spring by numerous small canals. This is found to be of such advantage, that supposing a meadow not so treated to yield 1000 Ibs. of hay, then from one thus watered 4'5000 Ibs. are produced. In respect to the cultivation of meadows, the country around Liegen is considered to be the best in all Germany. 106 OF THE INORGANIC t tained in the soil itself is inexhaustible in comparison with the quantity removed by plants. But when we increase the crop of grass in a meadow by means of gypsum, we remove a greater quantity of potash with the hay than can, under the same circumstances, be restored. Hence it happens, that after the lapse of several years, the crops of grass on the meadows manured with gyp- sum diminish, owing to the deficiency of potash. But if the meadow be strewed from time to time with wood-ashes, even with the lixiviated ashes which have been used by soap-boilers, (in Germany much soap is made from the ashes of wood,) then the grass thrives as luxuriantly as before. The ashes are only a means of restoring the potash. A harvest of grain is obtained every thirty or forty years from the soil of the Luneburg heath, by strewing it with the ashes of the heath-plants (Erica vulgar is) which grow on it. These plants during the long period just mentioned collect the potash and soda, which are conveyed to them by rain-water ; and it is by means of these alkalies, that oats, barley, and rye, to which they are indis- dispensable, are enabled to grow on this sandy heath. The woodcutters in the vicinity of Heidelberg have the privilege of cultivating the soil for their own use, after felling the trees used for making tan. Before sowing the land thus obtained, the branches^ roots and leaves are in every case burned, and CONSTITUENTS OF PLANTS. 10/ < the ashes used as a manure, which is found to be quite indispensable for the growth of the grain. The soil itself, upon which the oats grow in this district, consists of sandstone ; and although the trees find in it a quantity of alkaline earths suffi- cient for their own sustenance, yet in its ordinary condition it is incapable of producing grain. The most decisive proof of the use of strong manure was obtained at Bingen (a town on the Rhine), where the produce and development of vines were highly increased by manuring them with such substances as shavings of horn, &c., but after some years the formation of the wood and leaves decreased to the great loss of the pos- sessor, to such a degree, that he has long had cause to regret his departure from the usual me- thods. By the manure employed by him, the vines had been too much hastened in their growth ; in two or three years they had exhausted the potash in the formation of their fruit, leaves, and wood, so that none remained for the future crops, his manure not having contained any potash. There are vineyards on the Rhine, the plants of which are above a hundred years old, and all of these have been cultivated by manuring them with cow-dung, a manure containing a large pro- portion of potash, although very little nitrogen. All the potash, in fact, which is contained in the food consumed by a cow is again immediately discharged in its excrements. 108 OF THE INORGANIC The experience of a proprietor of land in the vicinity of Gottingen offers a most remarkable example of the incapability of a soil to produce wheat or grasses in general, when it fails in any one of the materials necessary to their growth. In order to obtain potash, he planted his whole land with wormwood, the ashes of which are well known to contain a large proportion of the car- bonate of that alkali. The consequence was,, that he rendered his land quite incapable of bearing grain for many years, in consequence of having entirely deprived the soil of its potash. The leaves and small branches of trees contain the most potash ; and the quantity of them which is annually taken from a wood, for the purpose of being employed as litter*, contain more of that alkali than all the old wood which is cut down. The bark and foliage of oaks, for example, contain from 6 to 9 per cent, of this alkali ; the needles of firs and pines 8 per cent. With every 2650 Ibs. of fir-wood, which are yearly removed from an acre of forest, only from 0*114 to 0*53 Ibs. of alkalies are abstracted from the soil, calculating the ashes at 0.83 per cent. * [This refers to a custom some time since very prevalent in Germany, although now discontinued. The leaves and small twigs of trees were gleaned from the forests by poor people, for the purpose of being used as litter for their cattle. The trees, however, were found to suffer so much in consequence, that a strict prohibition is now placed against their removal. The cause of the injury was that stated in the text. TRANS.] CONSTITUENTS OF PLANTS. 109 The moss, however, which covers the ground, and of which the ashes are known to contain so much alkali, continues uninterrupted in its growth, and retains that potash on the surface, which would otherwise so easily penetrate with the rain through the sandy soil. By its decay, an abundant pro- vision of alkalies is supplied to the roots of the trees, and a fresh supply is rendered unnecessary. The supposition of alkalies, metallic oxides, or in- organic matter in general, being produced by plants, is entirely refuted by these well-authenticated facts. It is thought very remarkable, that those plants of the grass tribe, the seeds of which furnish food for man, follow him like the domestic animals. But saline plants seek the sea-shore or saline springs, and the Chenopodium the dunghill from similar causes. Saline plants require common salt, and the plants, which grow only on dunghills, need ammonia and nitrates, and they are attracted whither these can be found, just as the dung-fly is to animal excrements. So likewise none of our corn plants can bear perfect seeds, that is, seeds yielding flour, without a large supply of phosphate of magnesia and ammonia, substances which they require for their maturity. And hence, these plants grow only in a soil where these three constituents are found combined, and no soil is richer in them, than those where men and animals dwell together ; where the urine and excrements of these are found corn -plants appear, because their 1 10 OF THE INORGANIC seeds cannot attain maturity unless supplied with the constituents of those matters. When we find sea-plants near our salt-works, several hundred miles distant from the sea, we know that their seeds have been carried there in a very natural manner, namely, by wind or birds, which have spread them over the whole surface of the earth, although they grow only in those places in which they find the conditions essential to their life. Numerous small fish, of not more than two inches in length ( ' Gasterosteus aculeatus), are found in the salt-pans of the graduating house at Nidda (a village in Hesse Darmstadt). No living animal is found in the salt-pans of Neuheim, situated about 18 miles from Nidda ; but the water there contains so much carbonic acid and lime, that the walls of the graduating house are covered with stalactites. Hence the eggs conveyed to this place by birds do not find the conditions necessary for their develop- ment, which they found in the former place *. * " The itch-insect (Acarus Scabiei) is considered by Burdach as the production of a morbid condition, so likewise lice in children ; the original generation of the fresh- water muscle (mytiltu) in fish-ponds, of sea-plants in the vicinity of salt-works, of nettles and grasses, of fish in pools of rain, of trout in mountain streams, &c , is according to the same natural philosopher not impossible." A soil consisting of crum- bled rocks, decayed vegetables, rain and salt water, &c., is here supposed to possess the power of generating shell-fish, trout, and saltworts (sali- cornia). All inquiry is arrested by such opinions, when propagated by a teacher who enjoys a merited reputation, obtained by knowledge and hard labour. These subjects, however, have hitherto met with the most superficial observation, although they well merit strict investigation. The dark, the secret, the mysterious, the enigmatic, is, in fact, too CONSTITUENTS OF PLANTS. Ill How much more wonderful and inexplicable does it appear, that bodies which remain fixed in the strong heat of a fire, have under certain conditions the property of volatilizing and, at ordinary tempera- tures, of passing into a state, of which we cannot say whether they have really assumed the form of a gas or are dissolved in one ! Steam or vapours in general have a very singular influence in causing the volatilization of these bodies, that is, of causing them to assume the gaseous form. A liquid during evaporation communicates the power of assuming the same state in a greater or less degree to all sub- stances dissolved in it, although they do not of themselves possess that property. Boracic acid is a substance which is completely fixed in the fire ; it suffers no change of weight appreciable by the most delicate balance, when ex- posed to a white heat, and, therefore, it is not vola- tile. Yet its solution in water cannot be evaporated by the gentlest heat, without the escape of a sensible quantity of the acid with the steam. Hence it is that a loss is always experienced in the analysis of minerals containing this acid, when liquids in which it is dissolved are evaporated. The quantity of boracic acid which escapes with a cubic foot of steam, at the temperature of boiling water, cannot seducing for the youthful and philosophic mind, which would penetrate the deepest depths of nature, without the assistance of the shaft or ladder of the miner. This is poetry, but not sober philosophical inquiry. 112 OF THE INORGANIC be detected by our most sensible re-agents ; and nevertheless the many hundred tons annually brought from Italy as an article of commerce, are procured by the uninterrupted accumulation of this apparently inappreciable quantity. The hot steam which issues from the interior of the earth is allowed to pass through cold water in the lagoons of Castel Nuova and Cherchiago ; in this way is the boracic acid gradually accumulated, till at last it may be obtained in crystals by the evaporation of the water. It is evident, from the temperature of the steam, that it must have come out of depths in which human beings and animals never could have lived, and yet it is very remarkable and highly important that ammonia is never absent from it. In the large works in Liverpool, where natural boracic acid is converted into borax, many hundred pounds of sulphate of ammonia are obtained at the same time. This ammonia has not been produced by the animal organism, it existed before the creation of human beings; it is a part, a primary constituent, of the globe itself. The experiments instituted under Lavoisier's guidance by the Direction des poudres et salpetres, have proved that during the evaporation of the saltpetre ley, the salt volatilizes with the water, and causes a loss which could not before be explained. It is known also, that in sea storms, leaves of plants in the direction of the wind are covered with CONSTITUENTS OF PLANTS. 113 crystals of salt, even at the distance of from 20 to 30 miles from the sea. But it does not require a storm to cause the volatilization of the salt, for the air hanging over the sea always contains enough of this substance to make a solution of nitrate of silver turbid, and every breeze must carry this away. Now, as thousands of tons of sea-water annually evaporate into the atmosphere, a corre- sponding quantity of the salts dissolved in it, viz. of common salt, chloride of potassium, magnesia, and the remaining constituents of the sea-water will be conveyed by wind to the land. This volatilization is a source of considerable loss in salt-works, especially where the proportion of salt in the water is not large. This has been com- pletely proved at the salt-works of Nauheim, by the very intelligent director of that establishment, M. WUhelmi. He hung a plate of glass between two evaporating houses, which were about 1200 paces distant from each other, and found in the morning, after the drying of the dew, that the glass was covered with crystals of salt on one or the other side, according to the direction of the wind. By the continual evaporation of the sea, its salts* * According to Mareet, sea-water contains in 1000 parts, 26'660 Chloride of Sodium. 4-660 Sulphate of Soda. 1 -232 Chloride of Potassium. 5-152 Chloride of Magnesium. 1-5 Sulphate of Lime. J 114 OF THE INORGANIC are spread over the whole surface of the earth ; and being subsequently carried down by the rain, fur- nish to the vegetation those salts necessary to its ex- istence. This is the origin of the salts found in the ashes of plants, in those cases where the soil could not have yielded them . In a comprehensive view of the phenomena of nature, we have no scale for that which we are accustomed to name, small or great ; all our ideas are proportioned to what' we see around us, but how insignificant are they in comparison with the whole mass of the globe ! that which is scarcely observable in a confined district appears incon- ceivably large when regarded in its extension through unlimited space. The atmosphere contains only a thousandth part of its weight of carbonic acid ; and yet small as this proportion appears, it is quite sufficient to supply the whole of the present generation of living beings with carbon for a thou- sand years, even if it were not renewed. Sea- water contains TT^OO" f i ts weight of carbonate of lime ; and this quantity, although scarcely appreciable in a pound, is the source from which myriads of marine mollusca and corals are supplied with mate- rials for their habitations. Whilst the air contains only from 4 to 6 ten -thou- sandth parts of its volume of carbonic acid, sea- water contains 100 times more, (10,000 volumes of sea-water contain 620 volumes of carbonic acid CONSTITUENTS OF PLANTS. 115 Laurent, Bouillon, Lagrange). Ammonia* is also found in this water, so that the same conditions which sustain living beings on the land are com- bined in this medium, in which a whole world of other plants and animals exist. The roots of plants are constantly engaged in collecting from the rain those alkalies which formed part of the sea- water, and also those of the water of springs, which penetrates the soil. Without alka- lies and alkaline bases most plants could not exist, and without plants the alkalies would disappear gradually from the surface of the earth. When it is considered, that sea-water contains less than one-millionth of its own weight of iodine, and that all combinations of iodine with the metallic bases of alkalies are highly soluble in water, some provision must necessarily be supposed to exist in the organization of sea- weed and the different kinds of Fuci, by which they are enabled during their life to extract iodine in the form of a soluble salt from sea-water, and to assimilate it in such a manner, that it is not again restored to the surrounding medium. These plants are collectors of iodine, just as land-plants are of alkalies ; and they yield us this element, in quantities such as we could not otherwise obtain from the water without the evapo- ration of whole seas. * When the solid saline residue obtained by the evaporation of sea- water is heated in a retort to redness, a sublimate of sal-ammoniac is obtained. MARCET. I 2 116 THE ART OF CULTURE. We take it for granted, that the sea plants require metallic iodides for their growth, and that their existence is dependent on the presence of those substances. With equal justice, then, we conclude, that the alkalies and alkaline earths, always found in the ashes of land-plants, are like- wise necessary for their development. THE ART OF CULTURE. THE conditions necessary for the life of all vege- tables have been considered in the preceding part of the work. Carbonic acid, ammonia, and water yield elements for all the organs of plants. Certain inorganic substances salts and metallic oxides serve peculiar functions in their organism, and many of them must be viewed as essential consti- tuents of particular parts. The atmosphere and the soil offer the same kind of nourishment to the leaves and roots. The former contains a comparatively inexhaustible sup- ply of carbonic acid and ammonia ; the latter, by means of its humus, generates constantly fresh carbonic acid, whilst, during the winter, rain and snow introduce into the soil a quantity of am- monia, sufficient for the development of the leaves and blossoms. The complete, or it may be said, the absolute insolubility in cold water of vegetable matter in progress of decay, .(humus,) appears on closer con- sideration to be a most wise arrangement of na- USE OF THE HUMUS. 1 \7 ture. For if humus possessed even a smaller de- gree of solubility, than that ascribed to the sub- stance called humic acid, it must be dissolved by rain-water. Thus, the yearly irrigation of mea- dows (see note at page 105), which lasts for several weeks, would remove a great part of it from the ground, and a heavy and continued rain would impoverish a soil. But it is soluble only when combined with oxygen ; it can be taken up by water, therefore, only as carbonic acid. When kept in a dry place, humus may be pre- served for centuries, but when moistened with water, it converts the surrounding oxygen into carbonic acid. As soon as the action of the air ceases, that is, as soon as it is deprived of oxygen, the humus suffers no further change. Its decay proceeds only when plants grow in the soil con- taining it ; for they absorb by their roots the car- bonic acid as it is formed. The soil receives again from living plants the carbonaceous matter it thus loses, so that the proportion of humus in it does not decrease. The stalactitic caverns in Franconia, and those in the vicinity of Baireuth, and Streitberg, lie beneath a fertile arable soil ; the abundant decaying vege- tables or humus in this soil, being acted on by moisture and air, constantly evolve carbonic acid, which is dissolved by the rain. The rain-water thus impregnated permeates the porous limestone, which forms the walls and roofs of the caverns, and 118 THE ART OF CULTURE. dissolves in its passage as much carbonate of lime as corresponds to the quantity of carbonic acid contained in it. Water and the excess of carbonic acid evaporate from this solution when it has reached the interior of the caverns, and the lime- stone is deposited on the walls and roofs in crystal- line crusts of various forms. There are few spots on the earth where so many circumstances favour- able to the production of humate of lime are com- bined, if the humus actually existed in the soil in the form of humic acid. Decaying vegetable matter, water, and lime in solution, are brought together, but the stalactites formed contain no trace, of vegetable matter, and no humic acid ; they are of a glistening white or yellowish colour, and in part transparent, like calcareous spar, and may be heated to redness without becoming black. The subterranean vaults in the old castles near the Rhine, the " Bergstrasse " and Wetherau, are constructed of sandstone, granite, or basalt, and present appearances similar to the limestone ca- verns. The roofs of these vaults or cellars are covered externally to the thickness of several feet with vegetable mould, which has been formed by the decay of plants. The rain falling upon them sinks through the earth, and dissolves the mortar by means of the carbonic acid derived from the mould ; and this solution evaporating in the inte- rior of the vaults, covers them with small thin sta- lactites, which are quite free from humic acid. USE OF THE HUMUS. 1 19 In such a filtering apparatus, built by the hand of nature, we have placed before us experiments which have been continued for a hundred or a thousand years. Now, if water possessed the power of dissolving a hundred-thousandth part of its own weight of humic acid or humate of lime, and humic acid were present, we should find the inner surface of the roofs of these vaults and ca- verns covered with these substances ; but we can- not detect the smallest trace of them. There could scarcely be found a more clear and con- vincing proof of the absence of the humic acid of chemists in common vegetable mould. The common view, which has been adopted respecting the modus operandi of humic acid, has given occasion to the following inexplicable phe- nomenon : A very small quantity of humic acid dissolved in water gives it a yellow or brown co- lour. Hence it would be supposed, that a soil would be more fruitful in proportion as it was capable of giving this colour to water, that is, of yielding it humic acid. But it is very remarkable that plants do not thrive in such a soil, and that all manure must have lost this property before it can exercise a favourable influence upon their vegetation. Water from barren peat soils and marshy meadows, upon which few plants flourish, contains much of this humic acid ; but all agricul- turists and gardeners agree that the most suitable and best manure for plants is that which has 120 THE ART OF CULTURE. completely lost the property of giving a colour to water. The soluble substance, which gives to water a brown colour, is a product of the putrefaction of all animal and vegetable matters ; its formation is an evidence, that there is not oxygen sufficient to begin or at least to complete the decay. The brown solutions, containing this substance, are decolourized in the air, by absorbing oxygen, and a black coaly matter precipitates the substance named " coal of humus." Now if a soil were im- pregnated with this matter, the effect on the roots of plants would be the same as that of entirely de- priving the soil of oxygen ; plants would as little be able to grow in such ground, as they would if hydrated protoxide of iron were mixed with the soil. All plants die in soils and water which con- tain no oxygen ; absence of air acts exactly in the same manner as an excess of carbonic acid. Stag- nant water 'on a marshy soil excludes air, but a renewal of water has the same effect as a renewal of air, because water contains it in solution. If the water is withdrawn from a marsh, free access is given to the air, and the marsh is changed into a fruitful meadow. In a soil to which the air has no access, or at most but very little, the remains of animals and vegetables do not decay, for they can only do so when freely supplied with oxygen ; but they undergo putrefaction, for which air is present in sufficient USE OF THE HUMUS. 121 quantity. Putrefaction is known to be a most powerful deoxidising process, the influence of which extends to all surrounding bodies, even to the roots and the plants themselves. All sub- stances from which oxygen can be extracted yield it to putrefying bodies ; yellow oxide of iron passes into the state of black oxide, sulphate of iron into sulphuret of iron, &c. The frequent renewal of air by ploughing, and the preparation of the soil, especially its contact with alkaline metallic oxides, the ashes of brown coal, burnt lime or limestone, change the putre- faction of its organic constituents into a pure pro- cess of oxidation ; and from the moment- at which all the organic matter existing in a soil enters into a state of oxidation or decay, its fertility is / -'increased. The oxygen is no longer employed for the conversion of the brown soluble matter into the insoluble coal of humus, but serves for the formation of carbonic acid. This change takes place very slowly, and, in some instances, the oxygen is completely excluded by it. And, when- ever this happens, the soil loses its fertility. Thus, in the vicinity of Salzhausen (a village in Hesse Darmstadt, famed for its mineral springs), upon a meadow called Grimschwalheimer, unfruitful spots are seen here and there covered with a yellow grass. If a hole be bored from 20 to 25 feet deep in one of these spots, carbonic acid is emitted from it with such violence, that the noise 122 THE ART OF CULTURE. made by the escape of the gas may be distinctly heard at the distance of several feet. Here the carbonic acid rising to the surface displaces com- pletely all the air, and consequently all the oxygen, from the soil ; and without oxygen, neither seeds nor roots can be developed ; a plant will not vege- tate in pure nitrogen or carbonic acid gas. Humus supplies young plants with nourishment by the roots, until their leaves are matured suffi- ciently to act as exterior organs of nutrition ; its quantity heightens the fertility of a soil by yielding more nourishment in this first period of growth, and consequently by increasing the number of organs of atmospheric nutrition. Those plants, which receive their first food from the substance of their seeds, such as bulbous plants, could com- pletely dispense with humus ; its presence is use- ful only in so far as it increases and accelerates their development, but it is not necessary, indeed, an excess of it at the commencement of their growth is, in a certain measure, injurious. The amount of food which young plants can take from the atmosphere in the form of carbonic acid and ammonia is limited ; they cannot assimi- late more than the air contains. Now, if the quantity of their stems, leaves, and branches has been increased by the excess of food yielded by the soil at the commencement of their deve- lopment, they will require for the completion of their growth, and for the formation of their bios- NUTRITION AND GROWTH OF PLANTS. soms and fruits, more nourishment from the air than it can afford, and consequently they will not reach maturity. In many cases the nourishment afforded by the air under these circumstances suf- fices only to complete the formation of the leaves, stems, and branches. The same result then ensues as when ornamental plants are transplanted from the pots in which they have grown to larger ones, in which their roots are permitted to increase and multiply. All their nourishment is employed for the increase of their roots and leaves ; they spring, as it is said, into an herb or weed, but do not blossom. When, on the contrary, we take away part of the branches, and of course their leaves with them, from dwarf trees, since we thus prevent the development of new branches, an excess of nutriment is artificially procured for the trees, and is employed by them in the increase of the blossoms and enlargement of the fruit. It is to effect this purpose that vines are pruned. A new and peculiar process of vegetation ensues in all perennial plants, such as shrubs, fruit and forest trees, after the complete maturity of their fruit. The stem of annual plants, at this period of their growth, becomes woody, and their leaves change in colour. The leaves of trees and shrubs on the contrary remain in activity until the com- mencement of the winter. The formation of the layers of wood progresses, the wood becomes harder and more solid, but after August the leaves form no 124 THE ART OF CULTURE. more wood : all the carbonic acid which the plants now absorb is employed for the production of nutri- tive matter for the following year : instead of woody fibre, starch is formed, and is diffused through every part of the plant by the autumnal sap (seve d'Aout) *. According to the observations of M. Heyer, the starch thus deposited in the body of the tree can be recognised in its known form by the aid of a good microscope. The barks of several aspens and pine trees-}- 'contain so much of this substance that it can be extracted from them as from potatoes, by trituration with water. It exists also in the roots and other parts of perennial plants. A very early winter or sudden change of temperature prevents the formation of this provi- sion for the following year ; the wood, as in the case of the vine-stock, for example, does not ripen, and its growth is in the next year very limited. From the starch thus accumulated, sugar and gum are produced in the succeeding spring, while from the gum those constituents of the leaves and young sprouts which contain no nitrogen are, in their turn, formed. After potatoes have germi- nated, the quantity of starch in them is found diminished. The juice of the maple tree ceases to be sweet from the loss of its sugar when its buds, blossoms, and leaves attain their maturity. * Hartig, in Erdmann and Schweigger-S'eidels Journal, V. 217. 1835. t It is well known that bread is made from the barks of pines in Sweden during famines. NUTRITION AND GROWTH OF PLANTS. 125 The branch of a willow, which contains a large quantity of granules of starch in every part of its woody substance, puts forth both roots and leaves in pure distilled rain-water ; but in proportion as it grows, the starch disappears, it being evidently exhausted for the formation of the roots and leaves. In the course of these experiments, M. Heyer made the interesting observation, that such branches when placed in snow-water (which contains ammo- nia) produced roots three or four times longer than those which they formed in pure distilled water, and that this pure water remained clear, while the rain-water gradually acquired a yellow colour. Upon the blossoming of the sugar-cane, like- wise, part of the sugar disappears ; and it has been ascertained, that the sugar does not accumulate in the beet-root until after the leaves are completely formed. Much attention has recently been drawn to the fact that the produce of potatoes may be much increased by plucking off the blossoms from the plants producing them, a result quite consistent with theory. This important observation has been completely confirmed by M. Zeller, the director of the Agricultural Society at Darmstadt. In the year 1839 two fields of the same size, lying side by side and manured in the same manner, were planted with potatoes. When the plants had flowered, the blossoms were removed from those in one field, while those in the other field were left untouched. 126 THE ART OF CULTURE. The former produced 47 /^ --, the latter only Q^7 // (J &v ' 67 f y . These well-authenticated observations remove every doubt as to the part which sugar, starch, and gum play in the development of plants ; and it ceases to be enigmatical, why these three substances exer- cise no influence on the growth or process of nutri- tion of a matured plant, when supplied to them as food. The accumulation of starch in plants during the autumn has been compared, although certainly erroneously, to the fattening of hibernating animals before their winter sleep ; but in these animals every vital function, except the process of respira- tion is suspended, and they only require, like a lamp slowly burning, a substance rich in carbon and hydrogen to support the process of combustion in the lungs. On their awakening from their torpor in the spring, the fat has disappeared, but has not served as nourishment. It has not caused the least increase in any part of their body, neither has it changed the quality of any of their organs. With nutrition, properly so called, the fat in these animals has not the least connexion. The annual plants form and collect their future nourishment in the same way as the perennial ; they store it in their seeds in the form of vegetable albumen, starch, and gum, which are used by the germs for the formation of their leaves and first radicle fibres. The proper nutrition of the plants, NUTRITION AND GROWTH OF PLANTS. 127 their increase in size, begins after these organs are formed. Every germ and every bud of a perennial plant is the engrafted embryo of a new individual, while the nutriment accumulated in the stem and roots, corresponds to the albumen of the seeds. Nutritive matters are, correctly speaking, those substances which, when presented from without, are capable of sustaining the life and all the func- tions of an organism, by furnishing to the different parts of plants the materials for the production of their peculiar constituents. In animals, the blood is the source of the mate- rial of the muscles and nerves ; by one of its com- ponent parts, the blood supports the process of respiration, by others, the peculiar vital functions ; every part of the body is supplied with nourish- ment by it, but its own production is a special function, without which we could not conceive life to continue. If we destroy the activity of the organs which produce it, or if we inject the blood of one animal into the veins of another, at all events, if we carry this beyond certain limits, death is the consequence. If we could introduce into a tree woody fibre in state of solution, it would be the same thing as placing a potato plant to vegetate in a paste of starch. The office of the leaves is to form starch, woody fibre, and sugar ; consequently, if we con- 128 THE ART OP CULTURE. vey these substances through the roots, the vital functions of the leaves must cease, and if the pro- cess of assimilation cannot take another form, the plant must die. Other substances must be present in a plant, be- sides the starch, sugar, and gum, if these are to take part in the development of the germ, leaves, and first radicle fibres. There is no doubt that a grain of wheat contains within itself the component parts of the germ and of the radi'cle fibres, and we must suppose, exactly in the proportion necessary for their formation. These component parts are starch and gluten ; and it is evident that neither of them alone, but that both simultaneously assist in the formation of the root, for they both suffer changes under the action of air, moisture, and a suitable temperature. The starch is con- verted into sugar, and the gluten also assumes a new form, and both acquire the capability of being dissolved in water, and of thus being conveyed to every part of the plant. Both the starch and the gum are completely consumed in the formation of the first part of the roots and leaves ; an excess of either could not be used in the formation of leaves, or in any other way. The conversion of starch into sugar during the germination of grain is ascribed to a vegetable principle called diastase, which is generated during the act of commencing germination. But this NUTRITION AND GROWTH OF PLANTS. 129 mode of transformation can also be effected by gluten, although it requires a longer time. Seeds, which have germinated, always contain much more diastase than is necessary for the conversion of their starch into sugar, for five parts by weight of starch can be converted into sugar by one part of malted barley. This excess of diastase can by no means be regarded as accidental, for, like the starch, it aids in the formation of the first organs of the young plant, and disappears with the sugar ; dia- stase contains nitrogen and furnishes the elements of vegetable albumen. Carbonic acid, water, and ammonia, are the food of fully- developed plants ; starch, sugar, and gum, serve, when accompanied by an azotised substance, to sustain the embryo, until its first organs of nu- trition are unfolded. The nutrition of a foetus and development of an egg proceed in a totally different manner from that of an animal which is separated from its parent ; the exclusion of air does not en^ danger the life of the foetus, but would certainly cause the death of the independent animal. In the same manner, pure water is more advantageous to the growth of a young plant, than that containing car- bonic acid, but after a month the reverse is the case. The formation of sugar in maple-trees does not take place in the roots, but in the woody substance of the stem. The quantity of sugar in the sap augments until it reaches a certain height in the K 130 THE ART OF CULTURE. stem of the plant, above which point it remains stationary. Just as germinating barley produces a substance which, in contact with starch, causes it to lose its insolubility and to become sugar, so in the roots of the maple, at the commencement of vegetation, a substance must be formed, which, being dissolved in water, permeates the wood of the trunk, and converts into sugar the starch, or whatever it may be, which it finds deposited there. It is certain, that when a hole is bored into the trunk of a maple- tree just above its roots, filled with sugar, and then closed again, the sugar is dissolved by the ascend- ing sap. It is further possible, that this sugar may be disposed of in the same manner as that formed in the trunks ; at all events it is certain, that the introduction of it does not prevent the action of the juice upon the starch, and since the quantity of sugar present is now greater than can be ex- hausted by the leaves and buds, it is excreted from the surface of the leaves or bark. Certain diseases of trees, for example that called honey-dew, evi- dently depend on the want of the due proportion between the quantity of the azotised and that of the unazotised substances which are supplied to them as nutriment. In whatever form, therefore, we supply plants with those substances which are the products of their own action, in no instance do they appear to NECESSITY OF NITROGENOUS SUBSTANCES. have any effect upon their growth, or to replace what they have lost. Sugar, gum, and starch, are not food for plants, and the same must be said of humic acid, which is so closely allied to them in composition. If now we direct our attention to the particular organs of a plant, we find every fibre and every particle of wood surrounded by a juice containing an azotised matter ; while the starch granules and sugar are enclosed in cells formed of a substance containing nitrogen. Indeed everywhere, in all the juices of the fruits and blossoms, we find a substance, destitute of nitrogen, accompanied by one which contains that element. The wood of the stem cannot be formed, quasi wood, in the leaves, but another substance must be produced, which is capable of being transformed into wood. This substance must be in a state of solution, and accompanied by a compound contain- ing nitrogen ; it is very probable, that the wood and the vegetable gluten, the starch granules and the cells containing them, are formed simultane- ously, and in this case, a certain fixed proportion between them would be a condition necessary for their production. According to this view the assimilation of the substances generated in the leaves will (cceteris paribus) depend on the quantity of nitrogen con- tained in the food. When a sufficient quantity of nitrogen is not present to aid in the assimilation of K 2 132 THE ART OF CULTURE. the substances which do not contain it, these sub- stances will be separated as excrements from the bark, roots, leaves, and branches. The exudations of mannite, gum, and sugar, in strong and healthy plants cannot be ascribed to any other cause *. Analogous phenomena are presented by the process of digestion in the human organism. In order that the loss which every part of the body sustains by the processes of respiration and perspira- tion may be restored to it, the 'organs of digestion require to be supplied with food, consisting of sub- stance containing nitrogen, and of others destitute of it, in definite proportions. If the substances which do not contain nitrogen preponderate, either they will be expended in the formation of fat, or they will pass unchanged through the organism. This is particularly observed in those people who live almost exclusively upon potatoes ; their excrements contain a large quantity of unchanged granules of starch, of which no trace can be detected when gluten, or flesh, is taken in proper proportions, because, in this case, the starch has been rendered capable of assimilation. Potatoes which, when mixed with hay alone, are scarcely capable of sup- porting the strength of a horse, form with bread and oats a strong and wholesome fodder. * M. Trapp in Giessen possesses a Clerodendron fragram, which grows in the house, and exudes on the surface of its leaves in September large colourless drops of sugar-candy, which form regular crystals upon drying; I am not aware whether the juice of this plant contains sugar. INFLUENCE OF THE FOOD ON THE PRODUCE. 133 It will be evident from the preceding considera- tions, that the products generated by a plant may vary exceedingly, according to the substances given it as food. A superabundance of carbon in the state of carbonic acid conveyed through the roots of plants, without being accompanied by nitrogen, cannot be converted either into gluten, albumen, wood, or any other component part of an organ ; but either it will be separated in the form of excre- ments, such as sugar, starch, oil, wax, resin, man- nite or gum, or these substances will be deposited in greater or less quantity in the wide cells and vessels. The quantity of gluten, vegetable albumen, and mucilage, will augment when plants are supplied with an excess of food containing nitrogen ; and ammoniacal salts will remain in the sap, when, for example, in the culture of the beet, we manure the soil with a highly nitrogenous substance, or when we suppress the functions of the leaves, by removing them from the plant. We know that the ananas is scarcely eatable in its wild state, and that it shoots forth a great quantity of leaves, when treated with rich animal manure, without the fruit on that account acquiring a large amount of sugar ; that the quantity of starch in potatoes increases, when the soil contains much humus, but decreases when the soil is manured with strong animal manure, although then the number of cells increases, the potatoes acquiring 134 THE ART OF CULTURE. in the first case a mealy, in the second a soapy, con- sistence. Beet-roots taken from a barren sandy soil contain a maximum of sugar, and no ammoniacal salts; and the Teltowa turnip loses its mealy state in a manured land, because there, all the circumstances necessary for the formation of cells are united. An abnormal production of certain component parts of plants presupposes a power and capability of assimilation, to which the most powerful chemi- cal action cannot be compared. The best idea of it may be formed, by considering that it surpasses in power the strongest galvanic battery, with which we are not able to separate the oxygen from car- bonic acid. The affinity of chlorine for hydrogen, and its power to decompose water under the influ- ence of light, and set at liberty its oxygen, cannot be considered as at all equalling the power and energy with which a leaf separated from a plant decom- poses the carbonic acid which it absorbs. The common opinion that only the direct solar rays can effect the decomposition of carbonic acid in the leaves of plants, and that reflected or diffused light does not possess this property, is wholly an error, for exactly the same constituents are gene- rated in a number of plants, whether the direct rays of the sun fall upon them, or whether they grow in the shade. They require light, and, indeed, sun-light, but it is not necessary that the direct rays of the sun reach them. Their functions certainly proceed with greater intensity and rapidity INFLUENCE OF LIGHT. 135 in sunshine, than in the diffused light of day ; but there is nothing more in this than the similar action which light exercises on ordinary chemical combinations, it merely accelerates in a greater or less degree the action already subsisting. Chlorine and hydrogen combining form muriatic acid. This combination is effected in a few hours in common daylight, but it ensues instantly with a violent explosion, under exposure to the direct solar rays, whilst not the slightest change in the two gases takes place in perfect darkness. When the liquid hydrocarburet of chlorine, resulting from the union of the olefiant gas of the Dutch chemists with chlorine, is exposed in a vess'el with chlorine gas to the direct solar rays, chloride of carbon is immediately produced ; but the same compound can be obtained with equal facility in the diffused light of day, a longer time only being required. When this experiment is performed in the way first mentioned, two products only are observed (muriatic acid and per chloride of carbon); whilst by the latter method, a class of intermediate bodies are produced, in which the quantity of chlorine constantly augments, until at last the whole liquid hydrocarburet of chlorine is converted into the same two products as in the first case. Here,, also, not the slightest trace of decomposition takes place in the dark. Nitric acid is decomposed in common daylight into oxygen, and peroxide of nitrogen and chloride of silver becomes black in 136 THE ART OF CULTURE. the diffused light of day, as well as in the direct solar rays ; in short, all actions of a similar kind proceed in the same way in diffused light as well as in the solar light, the only difference consisting in the time in which they are effected. It cannot be otherwise in plants, for the mode of their nutri- ment is the same in all, and their component substances afford proof, that their food has suffered absolutely the same change, whether they grow in the sunshine or in the shade. All the carbonic acid therefore which we supply to a plant will undergo a transformation, provided its quantity be not greater than can be decomposed by the leaves. We know that an excess of carbonic acid kills plants, but we know also that nitrogen, to a certain degree, is not essential for the decom- position of carbonic acid. All the experiments hitherto instituted, prove that fresh leaves placed in water, impregnated with carbonic acid, and exposed to the influence of solar light, emit oxygen gas, whilst the carbonic acid disappears. Now, in these experiments no nitrogen is supplied at the same time with the carbonic acid ; hence no other con- clusion can be drawn from them, than that nitrogen is not necessary for the decomposition of carbonic acid, for the exercise, therefore, of one of the functions of plants. And yet the presence of a substance containing this element appears to be indispensable for the assimilation of the products newly formed by the decomposition of the carbonic INFLUENCE OF THE FOOD ON THE PRODUCE. 137 acid; and their consequent adaptation for entering into the composition of the diiferent organs. The carbon abstracted from the carbonic acid acquires in the leaves a new form, in which it is soluble and transferable to all parts of the plant. In this new form the carbon aids in constituting several new products ; these are named sugar when they possess a sweet taste, gum or mucilage when tasteless, and excrementitious matters when ex- pelled by the roots. Hence it is evident, that the quantity and quality of the substances generated by the vital processes of a plant will vary according to the proportion of the diiferent kinds of food with which it is supplied. The development of every part of a plant in a free and uncultivated state depends on the amount and nature of the food aiforded to it, by the spot on which it grows. A plant is developed on the most sterile and unfruitful soil, as well as on the most luxuriant and fertile, the only difference which can be observed being in its height and size, in the number of its twigs, branches, leaves, blos- soms, and fruit. Whilst the individual organs of a plant increase on a fertile soil, they diminish on another, where those substances which are neces- sary for their formation are not so bountifully supplied ; and the proportion of the constituents, which contain nitrogen, and of those which do not, in plants varies with the amount of nitrogenous matters in their food. 138 THE ART OF CULTURE. The development of the stem,, leaves, blossoms,, and fruit of plants is dependent on certain condi- tions,, the knowledge of which enables us to exer- cise some influence on their internal constituents as well as on their size. It is the duty of the natural philosopher to discover what these conditions are; for the fundamental principles of agriculture must be based on a knowledge of them. There is no pro- fession which can be compared in importance with that of agriculture, for to it belongs the production of food for man and animals ; on it depends the wel- fare and development of the whole human species., the riches of states, and all commerce. There is no other profession in which the application of correct principle is productive of more beneficial effects, or is of greater and more decided influence. Hence it appears quite unaccountable, that we may vainly search for one leading principle in the writings of agriculturists and vegetable physiologists. The methods employed in the cultivation of land are different in every country, and in every district ; and when we inquire the causes of these differences we receive the answer, that they depend upon cir- cumstances. (Les circonstances font les assolemens.) No answer could show ignorance more plainly, since no one has ever yet devoted himself to ascer- tain what these circumstances are. Thus also when we inquire in what manner manure acts, we are answered by the most intelligent men, that its action is covered by the veil of Isis ; and when we MANURE. 139 demand further what this means, we discover merely that the excrements of men and animals are sup- posed to contain an incomprehensible something which assists in the nutrition of plants, and increases their size. This opinion is embraced without even an attempt being made to discover the component parts of manure, or to become acquainted with its nature. In addition to the general conditions, such as heat, light, moisture, and the component parts of the atmosphere, which are necessary for the growth of all plants, certain substances are found to exer- cise a peculiar influence on the development of particular families. These substances either are already contained in the soil, or are supplied to it in the form of the matters known under the general name of manure. But what does the soil contain, and what are the components of the substances used as manure ? Until these points are satisfac- torily determined, a rational system of agriculture cannot exist. The power and knowledge of the phy- siologist of the agriculturist and chemist must be united for the complete solution of these questions ; and in order to attain this end, a commencement must be made. The general object of agriculture is to pro- duce in the most advantageous manner certain qualities, or a maximum size, in certain parts or organs of particular plants. Now, this object can be attained only by the application of those sub- HO THE ART OF CULTURE. stances which we know to be indispensable to the development of these parts or organs,, or by supplying the conditions necessary to the produc- Jfon of the qualities desired. The rules of a rational system of agriculture should enable us, therefore, to give to each plant that which it requires for the attainment of the object in view. The special object of agriculture is to obtain an abnormal development and production of certain parts of plants, or of certain vegetable matters, which are employed as food for man and animals, or for the purposes of industry. The means employed for effecting these two purposes are very different. Thus the mode of culture, employed for the purpose of procuring fine pliable straw for Florentine hats, is the very oppo- site to that which must be adopted in order to produce a maximum of corn from the same plant. Peculiar methods must be used for the production of nitrogen in the seeds, others for giving strength and solidity to the straw, and others again must be followed when we wish to give such strength and solidity to the straw as will enable it to bear the weight of the ears. We must proceed in the culture of plants in pre- cisely the same manner as we do in the fattening of animals. The flesh of the stag and roe, or of wild animals in general, is quite devoid of fat, like the muscular flesh of the Arab ; or it contains only COMPOSITION OF FERTILE SOILS. 141 small quantities of it. The production of flesh and fat may be artificially increased; all domestic animals, for example, contain much fat. We give food to animals, which increases the activity of certain organs, and is itself capable of being trans- formed into fat. We add to the quantity of food, or we lessen the processes of respiration and perspira- tion by preventing motion. The conditions neces- sary to effect this purpose in birds are different from those in quadrupeds ; and it is well known that charcoal powder produces such an excessive growth of the liver of a goose, as at length causes the death of the animal. The increase or diminution of the vital activity of vegetables depends only on heat and solar light, which we have not arbitrarily at our disposal : all that we can do is to supply those substances which are adapted for assimilation by the power already present in the organs of the plant. But what then are these substances ? They may easily be detected by the examination of a soil, which is always fer- tile in given cosmical and atmospheric conditions ; for it is evident, that the knowledge of its state and composition must enable us to discover the circum- stances under which a sterile soil may be rendered fertile. It is the duty of the chemist to explain the composition of a fertile soil, but the discovery of its proper state or condition belongs to the agri- culturist ; our present business lies only with the former. 142 THE ART OF CULTURE. Arable land is originally formed by the crum- bling of rocks, and its properties depend on the nature of their principal component parts. Sand, clay, and lime, are the names given to the principal constituents of the different kinds of soil. Pure sand and pure limestone, in which there are no other inorganic substances except siliceous earth, carbonate or silicate of lime, form absolutely barren soils. But argillaceous earths form always a part of fertile soils. Now from whence come the argillaceous earths in arable land; what are their constituents, and what part do they play in favour- ing vegetation ? They are produced by the disin- tegration of aluminous minerals by the action of the weather ; the common potash and soda fel- spars, Labrador spar, mica, and the zeolites, are the most common aluminous earths, which undergo this change. These minerals are found mixed with other substances in granite, gneiss, mica-slate, porphyry, clay-slate, grauwacke, and the volcanic rocks, basalt, clinkstone, and lava. In the grau- wacke, we have pure quartz, clay-slate, and lime ; in the sandstones, quartz and loam. The transition limestone and the dolomites contain an intermix- ture of clay, felspar, porphyry, and clay-slate ; and the mountain limestone is remarkable for the quantity of argillaceous earths which it contains. Jura limestone contains 3 20, that of the Wur- temberg Alps 4550 per cent, of these earths. COMPOSITION OF SOILS. 143 And in the muschelkalk and the calcaire grassier they exist in greater or less quantity. It is known, that the aluminous minerals are the most widely diffused on the surface of the earth, and as we have already mentioned, all fertile soils, or soils capable of culture, contain alumina as an invariable constituent. There must, therefore, be something in aluminous earth which enables it to exercise an influence on the life of plants, and to assist in their development. The property on which this depends is that of its invariably con- taining potash and soda. Alumina exercises only an indirect influence on vegetation, by its power of attracting and retaining water and ammonia ; it is itself very rarely found in the ashes of plants, but silica is always present, having in most places entered the plants by means of alkalies. In order to form a distinct conception of the quantities of alkalies in aluminous minerals it must be remembered that felspar contains I7f per cent, of potash, albite 11*43 per cent, of soda, and mica 3 5 per cent. ; and that zeolite con- tains 13 16 per cent, of both alkalies taken together. The late analyses of Ch. Gmelin, Lowe, Fricke, Meyer, and Redtenbacher, have also shown, that basalt contains from f to 3 per cent, of potash, and from 5 7 per cent, of soda, that clay-slate contains from 2*75 3*31 per cent, of potash, and loam from 1^ 4 per cent, of potash. 144 THE ART OF CULTURE. If, now, we calculate from these data, and from the specific weights of the different substances, how much potash must be contained in a layer of soil, which has been formed by the disintegration of 40,000 square feet (1 Hessian acre) of one of these rocks to the depth of 20 inches, we find that a soil of Felspar contains 1,152,000 Ibs. Clink-stone , from 200,000 to 400,000 ,, Basalt Clay-slate Loam 47,500 75,000 100,000',, 200,000 87,000 300,000 Potash is present in all clays ; according to Fuchs, it is contained even in marl ; it has been found in all the argillaceous earths in which it has been sought. The fact that they contain potash may be proved in the clays of the transition and strati- fied mountains, as well as in the recent formations surrounding Berlin, by simply digesting them with sulphuric acid, by which process alum is formed. (Mitscherlich.) It is well known also to all manu- facturers of alum, that the leys contain a certain quantity of this salt ready formed, the potash of which has its origin from the ashes of the stone and brown coal, which contain much argillaceous earth. When we consider this extraordinary distribu- tion of potash over the surface of the earth, is it reasonable to have recourse to the idea, that the presence of this alkali in plants is due to the gene- ration of a metallic oxide by a peculiar organic OF THE FERTILITY OF SOILS. 145 process from the component parts of the atmo- sphere. This opinion found adherents even after the method of detecting potash in soils was known, and suppositions of the same kind may be found even in the writings of some physiologists of the present day. Such opinions belong properly to the time when flint was conceived to be a product of chalk, and when everything, which appeared in- comprehensible ,on account of not having been in- vestigated, was explained by assumptions far more i n comprehensible. A thousandth part of loam mixed with the quartz in new red sandstone, or with the lime in the dif- ferent limestone formations, affords as much potash to a soil only 20 inches in depth as is sufficient to supply a forest of pines growing upon it for a cen- tury. A single cubic foot of felspar is sufficient to supply a wood, covering a surface of 40,000 square feet, with the potash required for five years. Land of the greatest fertility contains argilla- ceous earths and other disintegrated minerals with chalk and sand, in such a proportion as to give free access to air and moisture. The land in the vicinity of Vesuvius may be considered as the type of a fertile soil, and its fertility is greater or less in dif- ferent parts, according to the proportion of clay or sand which it contains. The soil which is formed by the disintegration of lava cannot possibly, on account of its origin, contain the smallest trace of vegetable matter, and L 146 THE ART OF CULTURE. yet it is well known, that when the volcanic ashes have been exposed for some time to the influence of air and moisture, a soil is gradually formed in which all kinds of plants grow with the greatest luxuriance. This fertility is owing to the alkalies which are contained in the lava, and which, by exposure to the weather, are rendered capable of being absorbed by plants. Thousands of years have been necessary to convert stones and rocks into the soil of arable land, and thousands of years more will be requisite for their perfect reduction^ that is for the complete exhaustion of their alkalies. We see from the composition of the water in rivers, streamlets, and springs, how little rain-water is able to extract alkali from a soil, even after a term of years ; this water is generally soft, and the common salt, which even the softest invariably contains, proves that those alkaline salts, which are carried to the sea by rivers and streams, are returned again to the land by wind and rain. Nature itself shows us what plants require at the commencement of the development of their germs and first radicle fibres. Bequerel has shown that the graminece, leguminostz, crucifertz, cichoracece, unibellifercz, coniferce, and cmurbitacece emit acetic acid during germination. A plant which has just broken through the soil, and a leaf just burst open from the bud, furnish ashes by incineration, which contain as much, and 'generally more, of OF THE FERTILITY OF SOILS. 147 alkaline salts than at any period of their life. (De Saussure). Now we know also from the experi- ments of Bequerel in what manner these alkaline salts enter young plants ; the acetic acid formed during germination is diffused through the wet or moist soil, becomes saturated with lime, magnesia, and alkalies, and is again absorbed by the radicle fibres in the form of neutral salts. After the ces- sation of life, when plants are subjected to decom- position by means of decay and putrefaction, the soil receives again that which had been extracted from it. Let us suppose that a soil has been formed by the action of the weather on the component parts of granite, grauwacke, mountain limestone, or por- phyry, and that nothing has vegetated for thousands of years. Now this soil would have become a magazine of alkalies, in a condition favourable for their assimilation by the roots of plants. The interesting experiments of Struve have proved that water impregnated with carbonic acid decomposes rocks which contain alkalies, and then dissolves a part of the alkaline carbonates. It is evident that plants, also, by producing carbonic acid during their decay, and by means of the acids which exude from their roots in the living state, contribute no less powerfully to destroy the cohe- rence of rocks. Next to the action of air, water, and change of temperature, plants themselves are L 2 148 THE ART OF CULTURE. the most powerful agents in effecting the disinte- gration of rocks. Air, water, and the change of temperature prepare the different species of rocks for yielding to plants the alkalies which they contain. A soil which has been exposed for centuries to all the influences which effect the disintegration of rocks, but from which the alkalies have not been removed, will be able to afford the means of nourishment to those vegetables which require alkalies for its growth during many years ; but it must gradually become exhausted, unless those alkalies which have been removed are again replaced ; a period, there- fore, will arrive, when it will be necessary to expose it, from time to time, to a further disintegration, in order to obtain a new supply of soluble alkalies. For small as is the quantity of alkali which plants require, it is nevertheless quite indispensable for their perfect development. But when one or more years have elapsed without any alkalies having been extracted from the soil, a new harvest may be expected. The first colonists of Virginia found a country, the soil of which was similar to that mentioned above ; harvests of wheat and tobacco were obtained for a century from one and the same field without the aid of manure, but now whole districts are converted into unfruitful pasture land, which with- out manure produces neither wheat nor tobacco. OF THE FERTILITY OF SOILS. 149 From every acre of this land, there were removed in the space of one hundred years 1200 Ibs. of alkalies in leaves, grain, and straw ; it became unfruitful therefore, because it was deprived of every particle of alkali, which had been reduced to a soluble state, and because that which was rendered soluble again in the space of one year, was not sufficient to satisfy the demands of the plants. Almost all the cultivated land in Europe is in this condition ; fallow is the term applied to land left at rest for further disintegration. It is the greatest possible mistake to suppose that the temporary diminution of fertility in a soil is owing to the loss of humus ; it is the mere consequence of the exhaustion of the alkalies. Let us consider the condition of the country around Naples, which is famed for its fruitful corn- land ; the farms and villages are situated from 1 8 to 24 miles distant from one another, and between them there are no roads, and consequently no transportation of manure. Now corn has been cultivated on this land for thousands of years, without any part of that which is annually removed from the soil being artificially restored to it. How can any influence be ascribed to humus under such circumstances, when it is not even known whether .humus was ever contained in the soil ? The method of culture in that district completely explains the permanent fertility. It appears very bad in the eyes of our agriculturists, but there it is 150 THE ART OF CULTURE. the best plan which could be adopted. A field is cultivated once every three years, and is in the inter- vals allowed to serve as a sparing pasture for cattle. The soil experiences no change in the two years during which it there lies fallow, further than that it is exposed to the influence of the weather, by which a fresh portion of the alkalies contained in it are again set free or rendered soluble. The animals fed on these fields yield nothing to these soils which they did not formerly possess. The weeds upon which they live spring from the soil, and that which they return to it as excrement, must always be less than that which they extract. The field, therefore, can have gained nothing from the mere feeding of cattle upon them ; on the contrary, the soil must have lost some of its constituents. Experience has shown in agriculture, that wheat should not be cultivated after wheat on the same soil, for it belongs with tobacco to the plants which exhaust a soil. But if the humus of a soil gives it the power of producing corn, how happens it that wheat does not thrive in many parts of Brazil, where the soils are particularly rich in this sub- stance, or in our own climate, in soils formed of mouldered wood ; that its stalk under these cir- cumstances attains no strength, and droops prema- turely? The cause is this, that the strength of the stalk is due to silicate of potash, and that the corn requires phosphate of magnesia, neither of which substances a soil of humus can afford, since OF THE FERTILITY OF SOILS. 151 it does not contain them ; the plant may indeed, under such circumstances, become an herb, but will not bear fruit. Again, how does it happen that wheat does not flourish on a sandy soil, and that a calcareous soil is also unsuitable for its growth, unless it be not mixed with a considerable quantity of clay ? It is because these soils do not contain alkalies in suffi- cient quantity, the growth of wheat being arrested by this circumstance, even should all other sub- stances be presented in abundance. It is not mere accident that only trees of the fir tribe grow on the sandstone and limestone of the Carpathian mountains and the Jura, whilst we find on soils of gneiss, mica-slate, and granite in Bavaria, of clinkstone on the Rhone, of basalt in Vogelsberge, and of clay-slate on the Rhine and Eifel, the finest forests of other trees which cannot be produced on the sandy or calcareous soils upon which pines thrive. It is explained by the fact, that trees, the leaves of which are renewed annually, require for their leaves six to ten times more alkalies than the fir-tree or pine, and hence, when they are placed in soils in which alkalies are contained in very small quantity, do not attain maturity.* When we see such trees growing on a sandy or calcareous * One thousand parts of the dry leaves of oaks yielded 55 parts of ashes, of which 24 parts consisted of alkalies soluble in water ; the same quantity of pine leaves gave only 29 parts of ashes, which contained 4-6 parts of soluble salts. (De Saussure.) 152 THE ART OF CULTURE. soil the red-beech, the service-tree, and the wild- cherry, for example, thriving luxuriantly on lime- stone, we may be assured that alkalies are present in the soil, for they are necessary to their existence. Can we, then, regard it as remarkable, that such trees should thrive in America, on those spots on which forests of pines which have grown and col- lected alkalies for centuries, have been burnt, and to which the alkalies are thus at once restored ; or that the Spartiwn scoparium, Erysimum latifolium, Blitum capitatum, Senecio viscosus, plants remark- able for the quantity of alkalies contained in their ashes, should grow with the greatest luxuriance on the localities of conflagrations.* Wheat will not grow on a soil which has produced wormwood, and, vice versa, wormwood does not thrive where wheat has grown, because they are mutually prejudicial by appropriating the alkalies of the soil. One hundred parts of the stalks of wheat yield 15*5 parts of ashes (H. Davy] ; the same quantity of the dry stalks of barley, 8' 54 parts (Schroder) ; and one hundred parts of the stalks of oats, only 4*42 ; the ashes of all these are of the same composition. We have in these facts a clear proof of what * After the great fire in London, large quantities of the En/simum latifolium were observed growing on the spots where a fire had taken place. On a similar occasion, the BHtum capitatnm was seen at Copen- hagen, the Senecio viacosus in Nassau, and the Spartium scoparium in Languedoc. After the burnings of forests of pines in North America poplars grew on the same soil. (Franklin.} OF THE FERTILITY OF SOILS. 153 plants require for their growth. Upon the same field, which will yield only one harvest of wheat, two crops of barley and three of oats may be raised. All plants of the grass kind require silicate of potash. Now this is conveyed to the soil, or ren- dered soluble in it by the irrigation of meadows. The equisetacece, the reeds and species of cane, for example, which contain such large quantities of siliceous earth, or silicate of potash, thrive luxuri- antly in marshes, in argillaceous soils, and in ditches, streamlets, and other places, where the change of water renews constantly the supply of dissolved si- lica. The amount of silicate of potash removed from a meadow, in the form of hay, is very considerable. We need only call to mind the melted vitreous mass found on a meadow between Manheim and Heidel- berg after a thunder-storm. This mass was at first supposed to be a meteor, but was found on exami- nation (by Gmeliri) to consist of silicate of potash ; a flash of lightning had struck a stack of hay, and nothing was found in its place except 'the melted ashes of the hay. Potash is not the only substance necessary for the existence of most plants, indeed it has been already shown that the potash may be replaced, in many cases, by soda, magnesia, or lime ; but other substances, besides alkalies, are required to sustain the life of plants. Phosphoric acid has been found in the ashes of 154 THE ART OF CULTURE. all plants hitherto examined, and always in combi- nation with alkalies or alkaline earths. Most seeds contain certain quantities of phosphates. In the seeds of different kinds of corn, particularly, there is abundance of phosphate of magnesia. Plants obtain their phosphoric acid from the soil. It is a constituent of all land capable of cultiva- tion, and even the heath at Liineburg contains it in appreciable quantity. Phosphoric acid has been detected, also, in all mineral waters in which its presence has been tested ; and in those in which it has not been found, it has not been sought for. The most superficial strata of the deposits of sul- phuret of lead (galena) contain crystallized phos- phate of lead (greenlead ore)-, clay-slate, which forms extensive strata, is covered in many places with crystals of phosphate of alumina ( Wavellite) ; all its fractured surfaces are overlaid with it. Phosphate of lime (Apatite) is found even in the volcanic bowl- ders on the Laacher See in the Eifel, near Ander- nach. The soil in which plants grow furnishes them with phosphoric acid, and they in turn yield it to animals, to be used in the formation of their bones, and of those constituents of the brain which con- tain phosphorus. Much more phosphorus is thus afforded to the body than it requires, when flesh, bread, fruit, and husks of grain are used for food, and this excess in them is eliminated in the urine and the solid excrements. We may form an idea OF THE FERTILITY OF SOILS. 155 of the quantity of phosphate of magnesia contained in grain, when we consider that the concretions in the coscum of horses consist of phosphate of mag- nesia and ammonia, which must have been obtained from the hay and oats consumed as food. Twenty- nine of these stones were taken after death from the rectum of a horse belonging to a miller in Eber- stadt, the total weight of which amounted to 3lbs. ; and Dr. F. Simon has lately described a similar concretion found in the horse of a carrier, which weighed l^lb. It is evident that the seeds of corn could not be formed without phosphate of magnesia, which is one of their invariable constituents ; the plant could not under such circumstances reach maturity. Some plants, however, extract other matters from the soil besides silica, potash, and phosphoric acid, which are essential constituents of the plants ordinarily cultivated. These other matters, we must suppose, supply, in part at least, the place and perform the function of the substances just named. We may thus regard common salt, sul- phate of potash, nitre, chloride of potassium, and other matters, as necessary constituents of several plants. Clay-slate contains generally small quantities of oxide of copper ; and soils formed from micaceous schist contain some metallic fluorides. Now, small quantities of these substances also are absorbed 156 THE ART OF CULTURE. into plants, although we cannot affirm that they are necessary to them. It appears that, in certain cases, fluoride of cal- cium may take the place of the phosphate of lime in the bones and teeth ; at least, it is impossible otherwise to explain its constant presence in the bones of antediluvian animals, by which they are distinguished from those of a later period. The bones of human skulls found at Pompeii contain as much fluoric acid as those of animals of a former world, for if they be placed in a state of powder in glass vessels, and digested with sulphuric acid, the interior of the vessel will, after twenty -four hours, be found powerfully corroded, (Liebig) ; whilst the bones and teeth of animals of the present day contain only traces of it, (Berzelius). De Saussure remarked, that plants require unequal quantities of the component parts of soils in different stages of their development ; an obser- vation of much importance in considering the growth of plants. Thus, wheat yielded y^fo of ashes a month before blossoming, TtHhr while in blos- som, and TO oo~ after the ripening of the seeds. It is therefore, evident, that wheat from the time of its flowering restores a part of its organic constituents to the soil, although the phosphate of magnesia remains in the seeds. The fallow-time, as we have already shown, is that period of culture, during which land is exposed FALLOW-CROPS. 15/ to a progressive disintegration by means of the influence of the atmosphere, for the purpose of rendering a certain quantity of alkalies capable of being appropriated by plants. Now, it is evident, that the careful tilling of fallow land must increase and accelerate this disintegra- tion. For the purpose of agriculture, it is quite indifferent, whether the land is covered with weeds, or with a plant which does not abstract the potash inclosed in it. Now many plants in the family of the leguminosce, are remarkable on account of the small quantity of alkalies or salts in general, which they contain; the Vicia faba, for example, contains no free alkalies, and not one per cent, of the phos- phates of lime and magnesia (Eirikof). The bean of the Phaseolus Vulgaris contains only traces of salts (Braconnot). The stem of the Medicago sativa contains only 0*83 per cent., that of the Ervum lens only 0*57 of phosphate of lime with albumen (Crome). Buck-wheat dried in the sun yields only 0*681 per cent, of ashes, of which 0*09 parts are soluble salts (Zenneck)* These plants belong to those which are termed fallow-crops, and the cause wherefore they do not exercise any injurious influ- ence on corn which is cultivated immediately after * The small quantity of phosphates which the seeds of the lentils, beans and peas contain, must be the cause of their small value as articles of nourishment, since they surpass all other vegetable food in the quantity of nitrogen which enters into their composition. But as the component parts of the bones (phosphate of lime and magnesia) are absent, they satisfy the appetite without increasing the strength. 158 THE ART OF CULTURE. them is, that they do not extract the alkalies of the soil, and only a very small quantity of phosphates. It is evident that two plants growing beside each other will mutually injure one another, if they withdraw the same food from the soil. Hence it is not surprising that the Matricaria chamomilla, and Spartium scoparium, impede the growth of corn, when it is considered that both yield from 7 to 7*43 per cent, of ashes, which contain $ of carbonate of potash. The darnel, and the Erigeron acre, blossom and bear fruit at the same time as the corn, so that when growing mingled with it, they will partake of the component parts of the soil, and in proportion to the vigour of their growth, that of the corn must decrease ; for what one receives, the others are deprived of. Plants will, on the contrary, thrive beside each other, either when the substances necessary for their growth which they extract from the soil are of different kinds, or when they themselves are not both in the same stages of development at the same time. On a soil, for example, which contains potash, both wheat and tobacco may be reared in succes- sion, because the latter plant does not require phosphates, salts which are invariably present in wheat, but requires only alkalies, and food con- taining nitrogen. According to the analysis of Posselt and jReimann, 10,000 parts of the leaves of the tobacco-plant INTERCHANGE OF CROPS. 159 contain 16 parts of phosphate of lime, 8*8 parts of silica, and no magnesia ; whilst an equal quantity of wheat-straw contains 47*3 parts, and the same quantity of the grain of wheat 99'45 parts of phos- phates (De Saussure). Now, if we suppose that the grain of wheat is equal to half the weight of its straw, then the quan- tity of phosphates extracted from a soil by the same weights of wheat and tobacco must be as 97*7 : 16. This difference is very considerable. The roots of tobacco, as well as those of wheat, extract the phos- phates contained in the soil, but they restore them again, because they are not essentially necessary to the development of the plant. OF THE INTERCHANGE OF CROPS, AND OF MANURE. It has long since been found by experience, that the growth of annual plants is rendered imperfect, and their crops of fruit or herbs less abundant, by cultivating them in successive years on the same soil, and that, in spite of the loss of time, a greater quantity of grain is obtained, when afield is allowed to be uncultivated for a year. During this interval of rest, the soil, in a great measure, regains its original fertility. It has been further observed, that certain plants, such as peas, clover, and flax, thrive on the same soil only after a lapse of years ; whilst others, such as hemp, tobacco, helianthus tuberosus, rye, and 160 INTERCHANGE OF CROPS. oats, may be cultivated in close succession when proper manure is used. It has also been found, that several of these plants improve the soil, whilst others, and these are the most numerous, impove- rish or exhaust it. Fallow turnips, cabbage, beet, spelt, summer and winter barley, rye, and oats, are considered to belong to the class which impoverish a soil ; whilst by wheat, hops, madder, late turnips, hemp, poppies, teasel, flax, weld, and licorice, it is supposed to be entirely exhausted. The excrements of man and animals have been employed from the earliest times for the purpose of increasing the fertility of soils ; and it is com- pletely established by all experience, that they restore certain constituents to the soil, which are removed with the roots, fruit, or grain, or entire plants grown upon it. But it has been observed that the crops are not always abundant in proportion to the quantity of manure employed, even although it may have been of the most powerful kind ; that the produce of many plants, for example, diminishes, in spite of the apparent replacement of the substances re- moved from the soil by manure, when they are cultivated on the same field for several years in succession. On the other hand it has been remarked, that a field which has become unfitted for a certain kind of plants was not on that account unsuited for another; and upon this observation, a system of THEORIES OF ITS JUSE. 161 agriculture has been gradually founded, the prin- cipal object of which is to obtain the greatest possible produce with the least expense of manure. Now it was deduced from all the foregoing facts that plants require for their growth different con- stituents of soil, and it was very soon perceived, that an alternation of the plants cultivated main- tained the fertility of a soil quite as well as leaving it at rest or fallow. It was evident that all plants must give back to the soil in which they grow different proportions of certain substances, which are capable of being used as food by a succeeding generation. But agriculture has hitherto never sought aid from chemical principles, based on the knowledge of those substances which plants extract from the soil on which they grow, and of those restored to the soil by means of manure. The discovery of such principles will be the task of a future genera- tion, for what can be expected from the present, which recoils with seeming distrust and aversion from all the means of assistance offered it by chemistry, and which does not understand the art of making a rational application of chemical discoveries ? A future generation, however, will derive incalculable advantage from these means of help. Of all the views which have been adopted regard- ing the cause of the favourable effects of the alter- nations of crops, that proposed by M. Decandolle M 162 THE INTERCHANGE OF CROPS. alone deserves to be mentioned as resting on a firm basis. Decandolle supposes that the roots of plants imbibe soluble matter of every kind from the soil, and thus necessarily absorb a number of substances which are not adapted to the purposes of nutrition, and must subsequently be expelled by the roots, and returned to the soil as excrements. Now as excrements cannot be assimilated by the plant which ejected them, the more of these matters which the soil contains, the more unfertile must it be for plants of the same species. These excre- mentitious matters may, however, still be capable of assimilation by another kind of plants, which would thus remove them from the soil, and render it again fertile for the first. And if the plants last grown also expel substances from their roots, which can be appropriated as food by the former, they will improve the soil in two ways. Now a great number of facts appear at first sight to give a high degree of probability to this view. Every gardener knows that a fruit-tree cannot be made to grow on the same spot where another of the same species has stood ; at least not until after a lapse of several years. Before new vine-stocks are planted in a vineyard from which the old have been rooted out, other plants are cultivated on the soil for several years. In connexion with this it has been observed, that several plants thrive best when growing beside one another ; and on the contrary, THEORIES OF ITS USE. 163 that others mutually prevent each other's develop- ment. Whence it was concluded, that the bene- ficial influence in the former case depended on a mutual interchange of nutriment between the plants, and the injurious one in the latter on a poisonous action of the excrements of each on the other respectively. A series of experiments by Macaire-Princep gave great weight to this theory. He proved beyond all doubt that many plants are capable of emitting extractive matter from their roots. He found that the excretions were greater during the night than by day (?), and that the water in which plants of the family of the Leguminosce grew, acquired a brown colour. Plants of the same species, placed in water impregnated with these excrements, were impeded in their growth, and faded prematurely, whilst, on the contrary, corn-plants grew vigor- ously in it, and the colour of the water diminished sensibly ; so that it appeared, as if a certain quan- tity of the excrements of the Leguminosce had really been absorbed by the corn-plants. These experiments afforded as their main result, that the characters and properties of the excrements of dif- ferent species of plants are different from one another, and that some plants expel excrementitious matter of an acrid and resinous character ; others mild (douce) substances resembling gum. The former of these, according to Macaire- Princep, may be regarded as poisonous, the latter as nutritious. M 2 164 THE INTERCHANGE OF CROPS. The experiments ofMacaire-Princep are positive proof that the roots, probably of all plants, expel matters, which cannot be converted in their organism either into woody fibre, starch, vegetable albumen, or gluten, since their expulsion indicates that they are quite unfitted for this purpose. But they cannot be considered as a confirmation of the theory of Decandolle, for they leave it quite unde- cided whether the substances were extracted from the soil, or formed by the plant itself from food received from another source. It is certain that the gummy and resinous excrements observed by Macaire-Princep could not have been contained in the soil ; arid as we know that the carbon of a soil is not diminished by culture, but, on the contrary, increased, we must conclude, that all excrements which contain carbon must be formed from the food obtained by plants from the atmosphere. Now, these excrements are compounds, produced in consequence of the transformations of the food, and of the new forms which it assumes by entering into the composition of the various organs. M. Decandolle' s theory is properly a modifica- tion of an earlier hypothesis, which supposed that the roots of different plants extracted different nutritive substances from the soil, each plant selecting that which was exactly suited for its assimilation. According to this hypothesis, the matters incapable of assimilation are not extracted from the soil, whilst M. Decandolle considers that THEORIES OF ITS USE. 165 they are returned to it in the form of excrements. Both views explain how it happens that after corn, corn cannot be raised with advantage, nor after peas, peas ; but they do not explain how a field is improved by lying fallow, and this in proportion to the care with which it is tilled and kept free from weeds ; nor do they show how a soil gains carbon- aceous matter by the cultivation of certain plants such as lucern and esparsette. Theoretical considerations on the process of nu- trition, as well as the experience of all agricultur- ists, so beautifully illustrated by the experiments of Macaire-Princep, leave no doubt that substances are excreted from the roots of plants, and that these matters form the means by which the carbon received from humus in the early period of their growth, is restored to the soil. But we may now inquire whether these excrements in the state in which they are expelled, are capable of being em- ployed as food by other plants. The excrements of a carnivorous animal contain no constituents fitted for the nourishment of another of the same species ; but it is possible that an herbi- vorous animal, a fish, or a fowl, might find in them undigested matters, capable of being digested in their organism, from the very circumstance of their organs of digestion having a different structure. This is the only sense in which we can conceive that the excrements of one animal could yield matter adapted for the nutrition of another. 166 THE INTERCHANGE OF CROPS. A number of substances contained in the food of animals pass through their alimentary organs with- out change, and are expelled from the system ; these are excrements but not excretions. Now a part of such excrementitious matter might be as- similated in passing through the digestive apparatus of another animal. The organs of secretion form combinations of which only the elements were con- tained in the food. The production of these new compounds is a consequence of the changes which the food undergoes in becoming chyle and chyme, and of the further transformations to which these are subjected by entering into the composition of the organism. These matters, likewise, are elimi- nated in the excrements, which must therefore con- sist of two different kinds of substances, namely, of the indigestible constituents of the food, and of the new compounds formed by the vital process. The latter substances have been produced in con- sequence of the formation of fat, muscular fibre, cerebral and nervous substance, and are quite inca- pable of being converted into the same substances in any other animal organism. Exactly similar conditions must subsist in the vital processes of plants. When substances, which are incapable of being employed in the nutrition of a plant, exist in the matter absorbed by its roots, they must be again returned to the soil. Such ex- crements might be serviceable and even indispens- able to the existence of several other plants. But CAUSES OF ITS BENEFICIAL INFLUENCE. 167 substances that are formed in a vegetable organism during the process of nutrition, which are produced, therefore, in consequence of the formation of woody fibre, starch, albumen, gum, acids, &c., cannot again serve in any other plants to form the same constituents of vegetables. The consideration of these facts enables us to distinguish the difference between the views of Decandolle and those of Macaire-Princep. The substances which the former physiologist viewed as excrements, belonged to the soil ; they were undi- gested matters, which although not adapted for the nutrition of one plant, might yet be indispensable to another. Those matters, on the contrary, de- signated as excrements by Macaire-Princep, could only in one form serve for the nutrition of vegeta- bles. It is scarcely necessary to remark, that this excrementitious matter must undergo a change be- fore another season. During autumn and winter it begins to suffer a change from the influence of air and water ; its putrefaction, and at length, by continued contact with the air, which tillage is the means of procuring, its decay are effected ; and at the commencement of spring it has become converted, either in whole or in part, into a sub- stance which supplies the place of humus, by being a constant source of carbonic acid. The quickness with which this decay of the excre- ments of plants proceeds, depends on the composi- tion of the soil, and on its greater or less porosity. 168 THE INTERCHANGE OF CROPS. It will take place very quickly in a calcareous soil ; for the power of organic excrements to attract oxy- gen and to putrify, is increased by contact with the alkaline constituents, and by the general porous nature of such kinds of soil, which freely permit the access of air. But it requires a longer time in heavy soils consisting of loam or clay. The same plants can be cultivated with advan- tage on one soil after the second year., but in others not until the fifth or ninth, merely on account of the change and destruction of the excrements which have an injurious influence on the plants being completed in the one, in the second year ; in the others not until the ninth. In some neighbourhoods, clover will not thrive till the sixth year ; in others not till the twelfth ; flax in the second or third year. All this depends on the chemical nature of the soil ; for it has been found by experience, that in those districts where the intervals at which the same plants can be cultivated with advantage, are very long, the time cannot be shortened even by the use of the most powerful manures. The destruction of the peculiar excrements of one crop must have taken place before a new crop can be pro- duced. Flax, peas, clover, and even potatoes, are plants the excrements of which, in argillaceous soils, require the longest time for their conversion into humus ; but it is evident, that the use of alkalies CAUSES OF ITS BENEFICIAL INFLUENCE. 169 and burnt lime, or even small quantities of ashes which have not been lixiviated, must enable a soil to permit the cultivation of the same plants in a much shorter time. A soil lying fallow owes its earlier fertility, in part, to the destruction or conversion into humus of the excrements contained in it, which is effected during the fallow season, at the same time that the land is exposed to a further disintegration. In the soils in the neighbourhood of the Rhine and Nile, which contain much potash, and where crops can be obtained in close succession from the same field, the fallowing of the land is superseded by the inundation ; the irrigation of meadows effects the same purpose. It is because the water of rivers and streams contains oxygen in solution, that it effects the most complete and rapid putre- faction of the excrements contained in the soil which it penetrates, and in which it is continually renewed. If it was the water alone which produced this effect, marshy meadows should be the most fertile. It follows from what has preceded, that the advantage of the alternation of crops is owing to two causes. A fertile, soil ought to afford to a plant all the inorganic bodies indispensable for its existence in sufficient quantity and in such condition as allows their absorption. All plants require alkalies, which are contained 170 THE INTERCHANGE OF CROPS. in some, in the graminece for example, in the form of silicates, in others, in that of tartrates, citrates, acetates, or oxalates. When these alkalies are in combination with silicic acid, the ashes obtained by the incineration of the plant contain no carbonic acid ; but when they are united with organic acids, the addition of a mineral acid to their ashes causes an effervescence. A third species of plants requires phosphate of lime, another, phosphate of magnesia, and several do not thrive without carbonate of lime. Silicic acid is the first solid substance taken up by plants ; it appears to be the material from which the formation of the wood takes its origin, acting like a grain of sand around which the first crystals form in a solution of a salt which is in the act of crystallizing. Silicic acid appears to perform the function of woody fibre in the Equisetacece and bam- boos, just as the crystalline salt, oxalate of lime, does in many of the lichens. When we grow in the same soil for several years in succession different plants, the first of which leaves behind that which the second, and the second that which the third may require, the soil will be a fruitful one for all the three kinds of pro- duce. If the first plant, for example, be wheat, which consumes the greatest part of the silicate of potash in a soil, whilst the plants which succeed it are of such a kind as require only small quantities of potash, as is the case with the Leguminosce, CAUSES OF ITS BENEFICIAL INFLUENCE. \7 \ turnips, potatoes, &c. ; the wheat may be again sowed with advantage after the fourth year ; for, during the interval of three years, the soil will, by the action of the atmosphere, be rendered capable of again yielding silicate of potash in sufficient quantity for the young plants. The same precautions must be observed with regard to the other inorganic constituents, when it is desired to grow different plants in succession on the same soil ; for a successive growth of plants which extract the same component parts, must gradually render it incapable of producing them. Each of these plants, during its growth, returns to the soil a certain quantity of substances containing carbon, which are gradually converted into humus, and are for the most part equivalent to as much carbon as the plants had formerly extracted from the soil in the state of carbonic acid. But although this is sufficient to bring many plants to maturity, it is not enough to furnish their different organs with the greatest possible supply of nourishment. Now the object of agriculture is to produce either articles of commerce, or food for man and animals, but a maximum of produce in plants is always in proportion to the quantity of nutriment supplied to them in the first stage of their development. The nutriment of young plants consists of car- bonic acid, contained in the soil in the form of humus, and of nitrogen in the form of ammonia, both of which must be supplied to the plants if the 1/2 THE INTERCHANGE OF CROPS. desired purpose is to be accomplished. The forma- tion of ammonia cannot be effected on cultivated land, but humus may be artificially produced ; and this must be considered as an important object in the alternation of crops, and as the second reason of its peculiar advantages. The sowing of a field with fallow plants, such as clover, rye, buck- wheat, &c. and the incorporation of the plants, when nearly at blossom, with the soil, affect this supply of humus in so far, that young plants subsequently growing in it find, at a certain period of their growth, a maximum of nu- triment, that is, matter in the process of decay. The same end is obtained, but with much greater certainty, when the field is planted with esparsette or lucern. These plants are remarkable on account of the great ramification of their roots, and strong development of their leaves, and for requiring only a small quantity of inorganic matter. Until they reach a certain period of their growth, they retain all the carbonic acid and ammonia which may have been conveyed to them by rain and the air, for that which is not absorbed by the soil is appropriated by the leaves : they also possess an extensive four or six fold surface capable of assimilating these bodies, and of preventing the volatilization of the ammonia from the soil, by completely covering it in. An immediate consequence of the production of the green principle of the leaves, and of their remaining component parts, as well as of those of CAUSES OF ITS BENEFICIAL INFLUENCE. 173 the stem, is the equally abundant excretion of organic matters into the soil from the roots. The favourable influence which this exercises on the land, by furnishing it with matter capable of being converted into humus lasts for several years, but barren spots gradually appear after the lapse of some time. Now, it is evident, that after from six to seven years the ground must become so impreg- nated with excrements that every fibre of the root will be surrounded with them. As they remain for some time in a soluble condition, the plants must absorb part of them and suffer injurious effects in consequence, because they are not capable of assi- milation. When such a field is observed for several years, it is seen, that the barren spots are again covered with vegetation, (the same plants being always supposed to be grown,) whilst new spots become bare and apparently unfruitful, and so on alternately. The causes which produce this alter- nate barrenness and fertility in the different parts of the land are evident. The excrements upon the barren spots receiving no new addition, and being subjected to the influence of air and moisture, they pass into putrefaction, and their injurious influence ceases. ' The plants now find those substances, which formerly prevented their growth, removed, and in their place meet with humus, that is, vegetable matter in the act of decay. We can scarcely suppose a better means of pro- ducing humus than by the growth of plants, the 174 OF MANURE. leaves of which are food for animals ; for they pre- pare the soil for plants of every other kind, but par- ticularly for those to which, as to rape and flax, the presence of humus is the most essential condition of growth. The reasons why this interchange of crops is so advantageous, the principles which regulate this part of agriculture, are, therefore, the artificial pro- duction of humus, and the cultivation of different kinds of plants upon the same field, in such an order of succession, that each shall extract only certain components of the soil, whilst it leaves behind or restores those which a second or third species of plant may require for its growth and perfect deve- lopment. Now, although the quantity of humus in a soil may be increased to a certain degree by an artifi- cial cultivation, still, in spite of this, there cannot be the smallest doubt that a soil must gradually lose those of its constituents which are removed in the seeds, roots, and leaves of the plants raised upon it. The fertility of a soil cannot remain un- impaired, unless we replace in it all those substances of which it has been thus deprived. Now this is effected by manure. When it is considered that every constituent of the body of man and animals is derived from plants, and that not a single element is generated by the vital principle, it is evident that all the inorganic constituents of the animal organism must be re- COMPOSITION OF ANIMAL MANURES. 175 garded, in some respect or other, as manure. During their life, the inorganic components of plants which are not required by the animal system, are disengaged from the organism, in the form of excrements. After their death, their nitrogen and carbon pass into the atmosphere as ammonia and carbonic acid, the products of their putrefaction* and at last nothing remains except the phosphate of lime and other salts in their bones. Now this earthy residue of the putrefaction of animals must be considered, in a rational system of agriculture, as a powerful manure for plants, because that which has been abstracted from a soil for a series of years must be restored to it, if the land is to be kept in a permanent condition of fertility. We may now inquire whether the excrements of animals, which are employed as manure, are all of a like nature and power, and whether they, in every case, administer to the necessities of a plant by an identical mode of action. These points may easily be determined by ascertaining the composition of the animal excrements, because we shall thus learn what substances a soil really receives by their means. According to the common view, the action of solid animal excrements depends on the decaying organic matters which replace the humus, and on the presence of certain compounds of nitrogen, which are supposed to be assimilated by plants, and employed in the production of gluten and other azotised substances. But this view requires further 176 OF MANURE. confirmation with respect to the solid excrements of animals, for they contain so small a proportion of nitrogen, that they cannot possibly by means of it exercise any influence upon vegetation. We may form a tolerably correct idea of the chemical nature of animal excrement without further examination, by comparing the excrements of a dog with its food. When a dog is fed with flesh and bones, both of which consist in great part of organic substances containing ^nitrogen, a moist white excrement is produced which crumbles gradually to a dry powder in the air. This excre- ment consists of the phosphate of lime of the bones, and contains scarcely y^o P ar ^ of its weight of foreign organic substances. The whole process of nutrition in an animal consists in the progressive extraction of all the nitrogen from the food, so that the quantity of this element found in the excre- ments must always be less than that contained in the nutriment. The analysis of the excrements of a horse by Macaire and Marcet proves this fact completely. The portion of excrements subjected to analysis was collected whilst fresh, and dried in vacuo over sulphuric acid ; 1 00 parts of it (cor- responding to from 350 to 400 parts of the dung before being dried) contained 0*8 of nitrogen. Now every one who has had experience in this kind of analysis is aware that a quantity under one per cent, cannot be determined with accuracy. We should, therefore, be estimating its proportion at a COMPOSITION OF ANIMAL MANURES. 177 maximum., were we to consider it as equal to one- half per cent. It is certain, however, that these excrements are not entirely free from nitrogen, for they emit ammonia when digested with caustic potash. The excrements of a cow, on combustion with oxide of copper, yielded a gas which contained one vol. of nitrogen gas, and 26*30 vol. of carbonic acid. 100 parts of fresh excrements contained Nitrogen . . . 0'506 Carbon . . . 6-204 Hydrogen . . . 0'824 Oxygen . . .4-818 Ashes . . . 1-748 Water . . . 85-900 100-000 Now, according to the analysis of Boussingault, which merits the greatest confidence, hay contains one per cent, of nitrogen ; consequently in the 25 Ibs. of hay which a cow consumes daily, \ of a Ib. of nitrogen must have been assimilated. This quantity of nitrogen entering into the composition of muscular fibre would yield 8*3 Ibs. of flesh in its natural condition*. The daily increase in size of a cow is, however, much less than this quantity. We find that the nitrogen, apparently deficient, is actually contained in the milk and urine of the * 100 Ibs of flesh contain on an average 15-86 of muscular fibre : 18 parts of nitrogen are contained in 100 parts of the latter. N 178 OF MANURE. animal. The urine of a milch-cow contains less nitrogen than that of one which does not yield milk ; and as long as a cow yields a plentiful supply of milk, it cannot be fattened. We must search for the nitrogen of the food assimilated not in the solid, but in the liquid excrements. The influence which the former exercise on the growth of vege- tables does not depend upon the quantity of nitro- gen which they contain. For if this were the case, hay should possess the same influence ; that is, from 20 to 25 Ibs. ought to have the same power as 100 Ibs. of fresh cow-dung. But this is quite opposed to all experience. Which then are the substances in the excrements of the cow and horse which exert an influence on vegetation ? When horse's-dung is treated with water, a por- tion of it to the amount of 3 or 3^ per cent, is dissolved, and the water is coloured yellow. The solution is found to contain phosphate of magnesia, and salts of soda, besides small quantities of organic matters. The portion of the dung undissolved by the water yields to alcohol a resinous substance pos- sessing all the characters of gall which has under- gone some change ; while the residue possesses the properties of sawdust, from which all soluble matter has been extracted by water, and burns without any smell. 100 parts of the fresh dung of a horse being dried at 100 C. (212 F.) leave from 25 to 30 or 31 parts of solid substances, and contained, ac- ITS ESSENTIAL ELEMENTS. 179 eordingly,from 69 to 75 parts of water. From the dried excrements, we obtain, by incineration, varia- ble quantities of salts and earthy matters according to the nature of the food which has been taken by the animal. Macaire and Marcet found 27 per cent, in the dung analysed by them ; I obtained only 10 per cent, from that of a horse fed with chopped straw, oats, and hay. It results then that with from 3600 to 4000 Ibs of fresh horse's-dung, cor- responding to 1000 Ibs of dry dung, we place on the land from 2484 to 3000 Ibs. of water, and from 730 to 900 Ibs. of vegetable and altered gall, and also from 100 to 270 Ibs of salts and other inor- ganic substances. The latter are evidently the substances to which our attention should be directed, for they are the same which formed the component parts of the hay 5 straw, and oats, with which the horse was fed. Their principal constituents are the phosphates of lime and magnesia, carbonate of lime and silicate of potash ; the first three of these preponderated in the corn, the latter in the hay. Thus in 1000 Ibs. of horse's-dung, we present to a field the inorganic substances contained in 6000 Ibs. of hay, or 8300 Ibs. of oats, (oats containing 3*1 per cent, ashes according to De Saussure). This is sufficient to supply 1^ crop of wheat with potash and phosphates. The excrements of cows, black cattle and sheep, contain phosphate of lime, common salt, and silicate N 2 180 OF MANURE. of lime, the weight of which varies from 9 to 28 per cent., according to the fodder which the animal receives ; the fresh excrements of the cow contain from 86 to 90 per cent, of water. Human faeces have been subjected to an exact ana- lysis by Berzelius. When fresh they contain, besides f of their weight of water, nitrogen in very variable quantity, namely, in the minimum 1^, in the maxi- mum 5 per cent. In all cases, however, they were richer in this element than were .the excrements of other animals. Berzelius obtained by the incinera- tion of 100 parts of dried excrements, 15 parts of ashes, which were principally composed of the phosphates of lime and magnesia. It is quite certain that the vegetable constituents of the excrements with which we manure our fields cannot be entirely without influence upon the growth of the crops on them, for they will decay, and thus furnish carbonic acid to the young plants. But it cannot be imagined that their influence is very great, when it is considered that a good soil is manured only once every six or seven years, or once every eleven or twelve years, when esparsette or lucern have been raised on it, that the quantity of carbon thus given to the land corresponds to only 5*8 per cent, of what is removed in the form of herbs, straw, and grain, and further that the rain- water received by a soil contains much more carbon in the form of carbonic acid than these vegetable constituents of the manure. ITS ESSENTIAL ELEMENTS. 181 The peculiar action, then, of the solid excrements is limited to their inorganic constituents, which thus restore to a soil that which is removed in the form of corn, roots, or grain. When we manure land with the dung of the cow or sheep, we supply it with silicate of potash and some salts of phos- phoric acid. In human faeces we give it the phos- phates of lime and magnesia ; and in those of the horse, phosphate of magnesia, and silicate of potash. In the straw which has served as litter, we add a further quantity of silicate of potash and phos- phates ; which, if the straw be putrified, are in exactly the same condition in which they were before being assimilated. It is evident, therefore, that the soil of a field will alter but little, if we collect and distribute the dung carefully ; a certain portion of the phosphates, however, must be lost every year, being removed from the land with the corn and cattle, and this portion will accumulate in the neighbourhood of large towns. The loss thus suffered must be compensated for in a well managed farm, and this is partly done by allowing the fields to lie in grass. In Germany, it is considered that for every 100 acres of corn-land, there must, in order to effect a profitable cultivation, be 20 acres of pasture-land, which produce annually, on an average, 500 Ibs. of hay. Now, assuming that the ashes of the excrements of the animals fed with this hay amount to 6*82 per cent,, then 341 Ibs. of the 182 OF MANURE. silicate of lime and phosphates of magnesia and lime must be yielded by these excrements, and will in a certain measure compensate for the loss which the corn-land had sustained. The absolute loss in the salts of phosphoric acid, which are not again replaced, is spread over so great an extent of surface, that it scarcely deserves to be taken account of. But the loss of phosphates is again replaced in the pastures by the ashes of the wood used in our houses for fuel. We could keep our fields in* a constant state of fertility by replacing every year as much as we remove from them in the form of produce ; but an increase of fertility, and consequent in- crease of crop, can only be obtained when we add more to them than we take away. It will be found, that of two fields placed under conditions otherwise similar, the one will be most fruitful upon which the plants are enabled to appropriate more easily and in greater abundance those contents of the soil which are essential to their growth and de- velopment. From the foregoing remarks it will readily be inferred, that for animal excrements, other sub- stances containing their essential constituents may be substituted. In Flanders, the yearly loss of the necessary matters in the soil is completely restored by covering the fields with ashes of wood or bones, which may or may not have been lixiviated, and of which the greatest part consists of phosphates of lime and magnesia. The great THE USE OF WOOD ASHES. 183 importance of manuring with ashes has been long recognised by agriculturists as the result of experi- ence. So great a value, indeed, is attached to this material in the vicinity of Marburg and in the Wetterau,* that it is transported as a manure from the distance of 18 or 24 miles. Its use will be at once perceived, when it is considered that the ashes, after having been washed with water, con- tain silicate of potash exactly in the same propor- tions as in straw (10 Si 03 + K O.), and that their only other constituents are salts of phosphoric acid. But ashes obtained from various kinds of trees are of very unequal value for this purpose ; those from oak-wood are the least, and those from beech the most serviceable. The ashes of oak-wood contain only traces of phosphates, those of beech the fifth part of their weight, and those of the pine and fir from 9 to 15 per cent. The ashes of pines from Norway contain an exceedingly small quantity of phosphates, namely, only 1*8 per cent, of phosphoric acid. (Berthier.) With every 100 Ibs. of the lixiviated ashes of the beech which we spread over a soil, we furnish as much phosphates as 460 Ibs. of fresh human" ex- crements could yield. Again, according to the analy- sis of De Samsure, \ 00 parts of the ashes of the grain of wheat contain 32 parts of soluble, and 4 4 '5 of insoluble phosphates, in all 76*5 parts. Now the * Two well-known agricultural districts ; the first in Hesse-Cassel, the second in Hesse-Darmstadt. TBANS. 184 OF MANURE. ashes of wheat straw contain 11*5 per cent, of the same salts; hence with every 100 Ibs. of the ashes of the beech, we supply a field with phosphoric acid suf- ficient for the production of 3820 Ibs. of straw (its ashes being calculated at 4*3 per cent. De Saussure), or for 15-18000 Ibs. of corn, the ashes of which amount, according to De Saussure, to 1*3 per cent. Bone manure possesses a still greater importance in this respect. The primary sources from which the bones of animals are derived are the hay, straw, or other substances which they take as food. Now if we admit that bones contain 55 per cent, of the phosphates of lime and magnesia (Berzelius), and that hay contains as much of them as wheat- straw, it will follow that 8 Ibs. of bones contain as much phosphate of lime as 1000 Ibs. of hay or wheat-straw, and 2 Ibs. of it as much as 1000 Ibs. of the grain of wheat or oats. These numbers ex- press pretty exactly the quantity of phosphates which a soil yields annually on the growth of hay and corn. Now the manure of an acre of land with 40 Ibs. of bone dust is sufficient to supply three crops of wheat, clover, potatoes, turnips, &c., with phosphates. But the form in which they are restored to a soil does not appear to be a matter of indifference. For the more finely the bones are reduced to powder, and the more intimately they are mixed with the soil, the more easily are they assimilated. The most easy and practical mode of effecting their division is to pour over the bones, in a state of fine powder, half of their weight of BONE MANURE. 185 sulphuric acid diluted with three or four parts of water, and after they have been digested for some time, to add one hundred parts of water, and sprinkle this mixture over the field before the plough. In a few seconds, the free acids unite with the bases contained in the earth, and a neutral salt is formed in a very fine state of division. Ex- periments instituted on a soil formed from grau- wacke, for the purpose of ascertaining the action of manure thus prepared, have distinctly shown that neither corn, nor kitchen-garden plants, suffer injurious effects in consequence, but that on the contrary they thrive with much more vigour. In the manufactories of glue, many hundred tons of a solution of phosphates in muriatic acid are yearly thrown away as being useless. It would be important to examine whether this solution might not be substituted for the bones. The free acid would combine with the alkalies in the soil, espe- cially with the lime, and a soluble salt would thus be produced, which is known to possess a favour- able action upon the growth of plants. This salt, muriate of lime (or chloride of calcium), is one of those compounds which attracts water from the atmosphere with great avidity, and might supply the place of gypsum in decomposing carbonate of ammonia, with the formation of sal-ammoniac and carbonate of lime. A solution of bones in muriatic acid placed on land in autumn or in winter would, therefore, not only restore a necessary constituent 186 OF MANURE. of the soil, and attract moisture to it, but would also give it the power to retain all the ammonia which fell upon it dissolved in the rain during the period of six months. The ashes of brown coal and peat often contain silicate of potash, so that it is evident that these might completely replace one of the principal con- stituents of the dung of the cow and horse, and they contain alsp some phosphates. Indeed, they are much esteemed in the Wetterau as manure for meadows and moist land. It is of much importance to the agriculturist, that he should not deceive himself respecting the causes which give the peculiar action to the sub- stances just mentioned. It is known, that they possess a very favourable influence on vegetation ; and it is likewise certain, that the cause of this is their containing a body, which, independently of the influence which it exerts by virtue of its form, porosity, and capability of attracting and retaining moisture, also assists in maintaining the vital processes in plants. If it be treated as an un- fathomable mystery, the nature of this aid will never be known. In medicine, for many centuries, the mode of actions of all remedies was supposed to be concealed by the mystic veil of Isis, but now these secrets have been explained in a very simple manner. An unpo- etical hand has pointed out the cause of the wonderful and apparently inexplicable healing virtues of the PRINCIPLES OF ITS USE. 187 springs in Savoy., by which the inhabitants cured their goitre ; it was shown, that they contain small quantities of iodine. In burnt sponges used for the same purpose, the same element was also detected. The extraordinary efficacy of Peruvian bark was found to depend on a small quantity of a crystalline body existing in it, viz. quinine ; and the causes of the various effects of opium were detected in as many different ingredients of that drug. Calico-printers used for a long time the solid excrements of the cow, in order to brighten and fasten colours on cotton goods ; this material appeared quite indispensable, and its action was ascribed to a latent principle which it had obtained from the living organism. But since its action was known to depend on the phosphates contained in it, it has been completely replaced by a mixture of salts, in which the principal constituent is phosphate of soda. Now all such actions depend on a definite cause, by ascertaining which, we place the actions them- selves at our command. It must be admitted as a principle of agriculture, that those substances which have been removed from a soil must be completely restored to it, and whether this restoration be effected by means of excrements, ashes, or bones, is in a great measure a matter of indifference. A time will come when fields will be manured with a solution of glass (silicate of potash), with the ashes of burnt straw, 188 OF MANURE. and with salts of phosphoric acid, prepared in chemical manufactories, exactly as at present medi- cines are given for fever and goitre. There are some plants which require humus and do not restore it to the soil by their excrements ; whilst others can do without it altogether, and add humus to a soil which contains it in small quantity. Hence, a rational system of agricul- ture would employ all the humus at command for the supply of the former, and not expend any of it for the latter ; and would in fact make use of them for supplying the others with humus. We have now considered all that is requisite in a soil, in order to furnish its plants with the materials necessary for the formation of the woody fibre, the grain, the roots, and the stem, and now proceed to the consideration of the most important object of agri- culture, viz. the production of nitrogen in a form capable of assimilation the production, therefore, of substances containing this element. The leaves, which nourish the woody matter, the roots, from which the leaves are formed, and which prepare the substances for entering into the composition of the fruit, and, in short, every part of the organism of a plant, contain azotised matter in very varying pro- portions, but the seeds and roots are always particularly rich in them. Let us now examine in what manner the greatest possible production of substances containing nitro- gen can be effected. Nature, by means of the IT SUPPLIES NITROGEN. 189 atmosphere, furnishes nitrogen to a plant in quan- tity sufficient for its normal growth. Now its growth must be considered as normal, when it pro- duces a single seed, capable of reproducing the same plant in the following year. Such a normal condi- tion would suffice for the existence of plants, and prevent their extinction, but they do not exist for themselves alone ; the greater number of animals depend on the vegetable world for food, and by a wise adjustment of nature, plants have the remarkable power of converting, to a certain degree, all the nitrogen offered to them into nutri- ment for animals. We may furnish a plant with carbonic acid, and all the materials which it may require, we may supply it with humus in the most abundant quan- tity, but it will not attain complete development unless nitrogen is also afforded to it ; an herb will be formed, but no grain, even sugar and starch may be produced, but no gluten. But when we give a plant nitrogen in con- siderable quantity, we enable it to attract with greater energy, from the atmosphere, the carbon which is necessary for its nutrition, when that in the soil is not sufficient ; we afford to it a means of fixing the carbon of the atmosphere in its organism. We cannot ascribe much of the power of the excrements of black cattle, sheep, and horses, to the nitrogen which they contain, for its quantity is 190 OF MANURE. too minute. But that contained in the faeces of man is proportionably much greater, although by no means constant. In the faeces of the inhabitants of towns, for example, who feed on animal matter, there is much more of this constituent than in those of peasants, or of such people as reside in the country. The faeces of those who live principally on bread and potatoes are similar in composition and properties to those of animals. All excrements have in this respect a very variable and relative value. Thus, those of black cattle and horses, are of great use on soils consisting of lime and sand, which contain no silicate of potash and phosphates, whilst their value is much less when applied to soils formed of argillaceous earth, basalt, granite, porphyry, clinkstone, and even mountain- limestone, because all these contain potash in con- siderable quantity. In such soils human excrements are extremely beneficial, and increase their fertility in a remarkable degree ; they are, of course, as advantageous for other soils also ; but for the manure of those first mentioned, the excrements of other animals are quite indispensable. We possess only one other source of manure which acts by its nitrogen, besides the faeces of animals, namely, the urine of man and animals. Urine is employed as manure either in the liquid state, or with the faeces which are impregnated with it. It is the urine contained in them which gives to the solid faeces the property of emitting ammonia, COMPOSITION OF URINE. 191 a property which they themselves possess only in a very slight degree. When we examine what substances we add to a soil by supplying it with urine, we find that this liquid contains in solution ammoniacal salts, uric acid, (a substance containing a large quantity of nitrogen), and salts of phosphoric acid. According to Berzelius 1000 parts of human urine contain : Urea . . . . . 30-10 Free Lactic acid, Lactate of Ammonia, and animal matter not separable from them 17*14 Uric acid .... 1-00 Mucus of the bladder . . . 0-32 Sulphate of Potash . . . 3- 71 Sulphate of Soda . . . .3-16 Phosphate of Soda . . . 2'94 Phosphate of Ammonia . . 1 65 Chloride of Sodium . . . 4-46 Muriate of Ammonia . . .1-50 Phosphates of Magnesia and Lime . . 1*00 Siliceous earth .... 0*03 Water .... 933-00 1000.00 If we subtract from the above the urea, lactate of ammonia, free lactic acid, uric acid, the phosphate and muriate of ammonia, 1 per cent, of solid mat- ter remains, consisting of inorganic salts, which must possess the same action when brought on a field, whether they are dissolved in water or in urine. Hence the powerful influence of urine must depend upon its other ingredients, namely, the urea and ammoniacal salts. The urea in human urine exists 192 OF MANURE. partly as lactate of urea, and partly in a free state. (Henry.) Now when urine is allowed to putrify spontaneously, that is, to pass into that state in which it is used as manure, all the urea in com- bination with lactic acid is converted into lactate of ammonia, and that which was free, into volatile carbonate of ammonia. In dung-reservoirs well constructed and protected from evaporation, this carbonate of ammonia is retained in the state of solution, and when the putrified urine is spread over the land, a part of the ammonia will escape with the water which eva- porates, but another portion will be absorbed by the soil, if it contains either alumina or iron ; but in general, only the muriate, phosphate, and lactate of ammonia remain in the ground. It is these alone, therefore, which enable the soil to exercise a direct influence on plants during the progress of their growth, and not a particle of them escapes being absorbed by the roots. On account of the formation of this carbonate of ammonia, the urine becomes alkaline, although it is acid in ite natural state. When it is lost by being volatilized in the air, which happens in most cases, the loss suffered is nearly equal to one half of the weight of the urine employed, so that if we fix it, that is, if we deprive it of its volatility, we increase its action twofold. The existence of car- bonate of ammonia in putrified urine long since suggested the manufacture of sal-ammoniac from MODE OF APPLYING URINE. 193 this material. When the latter salt possessed a high price, this manufacture was even carried on by the farmer. For this purpose the liquid ob- tained from dunghills was placed in vessels of iron, and subjected to distillation ; the product of this distillation was converted into muriate of ammonia by the common method. (Demachy.) But it is evident that such a thoughtless proceeding must be wholly relinquished, since the nitrogen of 100 Ibs. of sal-ammoniac (which contains 26 parts of nitrogen) is equal to the quantity of nitrogen con- tained in 1200 Ibs. of the grain of wheat, 1480 Ibs. of that of barley, or 2755 Ibs. of hay. (Bous- singault.) The carbonate of ammonia formed by the putre - faction of urine, can be fixed or deprived of its volatility in many ways. If a field be strewed with gypsum, and then with putrified urine or the drainings of dunghills, all the carbonate of ammonia will be converted into the sulphate which will remain in the soil. But there are still simpler means of effecting this purpose ; gypsum, chloride of calcium, sulphuric or muriatic acid, and super-phosphate of lime, are all substances of a very low price, and completely neutralize the urine, converting its ammonia into salts which possess no volatility. If a basin filled with concentrated muriatic acid is placed in a common necessary, so that its surface is in free communication with the vapours which rise o 194 OF MANURE. from below, it becomes filled after a few days with crystals of muriate of ammonia. The ammonia, the presence of which the organs of smell amply testify, combines with the muriatic acid and loses entirely its volatility, and thick clouds or fumes of the salt newly formed hang over the basin. In stables the same may be seen. The ammonia that escapes in this manner, is not only entirely lost as far as our vegetation is concerned, but it works also a slow, though not less certain destruction of the walls of the building. For when in contact with the lime of the mortar, it is converted into nitric acid, which gradually dissolves the lime. The injury thus done to a building by the formation of the soluble nitrates, has received (in Germany) a special name sal- peterfrass. The ammonia emitted from stables and neces- saries is always in combination with carbonic acid. Carbonate of ammonia and sulphate of lime (gypsum) cannot be brought together at common temperatures, without mutual decomposition. The ammonia enters into combination with the sul- phuric acid, and the carbonic acid with the lime, forming compounds which are not volatile, and, consequently, destitute of all smell. Now if we strew the floors of our stables, from time to time, with common gypsum, they will lose all their of- fensive smell, and none of the ammonia which forms can be lost, but will be retained in a condi- tion serviceable as manure. TETE USE OF URINE. 195 With the exception of urea, uric acid contains more nitrogen than any other substance generated by the living organism ; it is soluble in water, and can be thus absorbed by the roots of plants, and its nitrogen assimilated in the form of ammonia, and of the oxalate, hydrocyanate, or carbonate of am- monia. It would be extremely interesting to study the transformations which uric acid suffers in a living plant. For the purpose of experiment, the plant should be made to grow in charcoal powder pre- viously heated to redness, and then mixed with pure uric acid. The examination of the juice of the plant, or of the component parts of the seed or fruit, would be a means of easily detecting the differences. In respect to the quantity of nitrogen contained in excrements, 100 parts of the urine of a healthy man are equal to 1300 parts of the fresh dung of a horse, according to the analyses of Macaire and Marcet. and to 600 parts of those of a cow. Hence it is evident that it would be of much importance to agriculture if none of the human urine were lost. The powerful effects of urine as a manure are well known in Flanders, but they are considered invalu- able by the Chinese, who are the oldest agricultural people we know. Indeed so much value is attached to the influence of human excrements by these peo- ple, that laws of the state forbid that any of them should be thrown away, and reservoirs are placed o 2 196 OF MANURE. in every house, in which they are collected with the greatest care. No other kind of manure is used for their corn-fields. China is the birth-place of the experimental art ; the incessant striving after experiments has con- ducted the Chinese a thousand years since to dis- coveries, which hare been the envy and admiration of Europeans for centuries, especially in regard to dyeing and painting, and to the manufactures of porcelain, silk, and colours for painters. These we were long unable to imitate, and yet they were dis- covered by them without the assistance of scientific principles ; for in the books of the Chinese we find recipes and directions for use, but never explana- tions of processes. Half a century sufficed to Europeans, not only to equal but to surpass the Chinese in the arts and manufactures, and this was owing merely to the application of correct principles deduced from the study of chemistry. But how infinitely inferior is the agriculture of Europe to that of China! The Chinese are the most admirable gardeners and trainers of plants, for each of which they under- stand how to prepare and apply the best adapted manure. The agriculture of their country is the most perfect in the world ; and there, where the cli- mate in the most fertile districts differs little from the European, very little value is attached to the excrements of animals. With us, thick books are written, but no experiments instituted ; the quan- VALUE OF HUMAN EXCREMENTS. 19/ tity of manure consumed by this and that plant, is expressed in hundredth parts, and yet we know not what manure is ! If we admit that the liquid and solid excrements of man amount on an average to 1^ Ibs. daily (fib. urine and % Ib. faeces), and that both taken together contain 3 per cent, of nitrogen, then hi one year they will amount to 547 Ibs., which contain 16*41 Ibs. of nitrogen, a quantity sufficient to yield the nitrogen of 800 Ibs. of wheat, rye, oats, or of 900 Ibs. of barley. (Boussingault.) This is much more than it is necessary to add to an acre of land, hi order to obtain, with the assist- ance of the nitrogen absorbed from the atmo- sphere, the richest possible crop every year. Every town and farm might thus supply itself with the manure, which besides containing the most nitro- gen,, contains also the most phosphates ; and if an alternation of the crops were adopted, they would be most abundant. By using, at the same time, bones and the lixiviated ashes of wood, the excre- ments of animals might be completely dispensed with. When human excrements are treated in a proper manner, so as to remove the moisture which they contain without permitting the escape of ammonia, they may be put into such a form as will allow them to be transported, even to great distances. This is already attempted in many towns, and the preparation of human excrements for trans- 198 OF MANURE. portation constitutes not an unimportant branch of industry. But the manner in which this is done is the most injudicious which could be conceived. In Paris, for example, the excrements are preserved in the houses in open casks, from which they are collected and placed in deep pits at Montfaucon, but are not sold until they have attained a certain degree of dryness by evaporation in the air. But whilst lying in the receptacles appropriated for them in the houses, the greatest part of their urea is converted into carbonate of ammonia; lactate and phosphate of ammonia are also formed, and the vegetable matters contained in them putrefy ; all their sulphates are decomposed, whilst their sulphur forms sulphuretted hydrogen and hydro- sulphate of ammonia. The mass when dried by exposure to the air has lost more than half of the nitrogen which the excrements originally contained; for the ammonia escapes into the atmosphere along with the water which evaporates ; and the residue now consists principally of phosphate of lime, with phosphate and lactate of ammonia, and small quantities of urate of magnesia and fatty matter. Nevertheless it is still a very powerful manure, but its value as such would be twice or four times as great, if the excrements before being dried were neutralised with a cheap mineral acid. In other manufactories of manure, the excre- ments whilst still soft are mixed with the ashes of URINE OF ANIMALS. 199 wood, or with earth, both of which substances contain a large quantity of caustic lime, by means of which a complete expulsion of all their ammonia is effected, and they are completely deprived of smell. But such a residue applied as manure can act only by the phosphates which it still contains, for all the ammoniacal salts have been decomposed, and their ammonia expelled. The sterile soils of the South American coast are manured with a substance called guano, consisting of urate of ammonia, and other ammoniacal salts, by the use of which a luxuriant vegetation and the richest crops are obtained. The corn-fields in China receive no other manure than human excre- ments. But we cover our fields every year with the seeds of weeds, which from their nature and form pass undigested along with the excrements through animals, without being deprived of their power of germination, and yet it is considered sur- prising that where they have once flourished, they cannot again be expelled by all our endeavours : we think it very astonishing, while we really sow them ourselves every year. A famous botanist, attached to the Dutch embassy to China, could scarcely' find a single plant on the corn-fields of the Chinese, except the corn itself*. The urine of horses contains less nitrogen and phosphates than that of man. According to Fourcroy and Vauquelin it contains only five per * Ingenhouss on the Nutrition of Plants, page 129 (German edition). 200 OF MANURE. cent, of solid matter, and in that quantity only 0.7 of urea; whilst 100 parts of the urine of man contain more than four times as much. The urine of a cow is particularly rich in salts of potash ; but according to Rouelle and Brande, it is almost destitute of salts of soda. The urine of swine contains a large quantity of the phosphate of magnesia and ammonia; and hence it is that concretions of this salt are so frequently found in the urinary bladders of these animals. It is evident that if we place the solid or liquid excrements of man, or the liquid excre- ments of animals, on our land, in equal propor- tion to the quantity of nitrogen removed from it in the form of plants, the sum of this element in the soil must increase every year ; for the quantity which we thus supply, another portion is added from the atmosphere. The nitrogen whichjwe export as corn and cattle, and which is thus absorbed by large towns, serves only to benefit other farms, if we do not replace it. A farm which possesses no pastures, and not fields suffi- cient for the cultivation of fodder, requires manure containing nitrogen to be imported from else- where, if it is desired to produce a full crop. In large farms, the annual expenditure of nitrogen is completely replaced by means of the pastures. The only absolute loss of nitrogen, therefore, is limited to the quantity which man carries with him to his grave ; but this at the utmost cannot amount CONCLUDING REMARKS. 201 to more than 3 Ibs. for every individual, and is being collected during his whole life. Nor is this quan- tity lost to plants, for it escapes into the atmosphere as ammonia during the putrefaction and decay of the body. A high degree of culture requires an increased supply of manure. With the abundance of the manure the produce in corn and cattle will augment, but must diminish with its deficiency. From the preceding remarks it must be evident, that the greatest value should be attached to the liquid excrements of man and animals when a manure is desired which shall supply nitrogen to the soil. The greatest part of a superabundant crop, or in other words, the increase of growth which is in our power, can be obtained exclusively by their means. When it is considered that With every pound of ammonia which evaporates, a loss of 60 Ibs. of corn is sustained, and that with every pound of urine a pound of wheat might be produced, the indifference with which these liquid excrements are regarded is quite incomprehensible. In most places, only the solid excrements impregnated with the liquid are used, and the dunghills containing them are protected neither from evaporation nor from rain. The solid excrements contain the insoluble, the liquid all the soluble phosphates, and the latter contain likewise all the potash which 202 OF MANURE. existed as organic salts in the plants consumed by the animals. Fresh bones, wool, hair, hoofs, and horn, are manures containing nitrogen as well as phos- phates, and are consequently fit to aid the process of vegetable life. One hundred parts of dry bones contain from 32 to 33 per cent, of dry gelatine ; now, supposing this to contain the same quantity of nitrogen as animal glue, viz. 5*28 per cent., then 100 parts of bones must be considered as equivalent to 250 parts of human urine. Bones may be preserved unchanged for thousands of years, in dry or even in moist soils, provided the access of rain is prevented, as is exemplified by the bones of antediluvian animals found in loam or gyp- sum, the interior parts being protected by the exte- rior from the action of water. But they become warm when reduced to a fine powder, and moistened bones generate heat and enter into putrefaction ; the gelatine which they contain is decomposed, and its nitrogen converted into carbonate of ammonia and other ammoniacal salts, which are retained in a great measure by the powder itself. (Bones burnt till quite white, and recently heated to redness, absorb 7*5 times their volume of pure ammoniacal gas.) Charcoal in a state of powder must be considered as a very powerful means of promoting the growth CONCLUDING REMARKS. 203 of plants on heavy soils, and particularly on such as consist of argillaceous earth. Ingenhouss proposed dilute sulphuric acid as a means of increasing the fertility of a soil. Now, when this acid is sprinkled on calcareous soils, gypsum (sulphate of lime) is immediately formed, which of course prevents the necessity of manuring the soils with this material. 100 parts of concen- trated sulphuric acid diluted with from 800 to 1000 parts of water, are equivalent to 176 parts of gypsum. APPENDIX TO PART I. GROWTH OF PLANTS WITHOUT MOULD. ' (See Page 61.) " SOME account of a suspended plant of Ficus Australis, which was grown for eight months without earth in the stove of the Botanic Garden at Edinburgh. By Mr. William Macnab, superintendant of the Garden." (From the 3rd vol. of the ' Edinburgh Philosophical Journal,' p. 77. Slightly abridged.) 44 Ficus Australis is a native of New South Wales, and was introduced into the British gardens in 1789, by the Right Honourable Sir Joseph Banks. The plant is not uncommon now in collections in this country, where it has been usually treated as a greenhouse plant ; and in a good greenhouse it thrives tolerably well, although it seems rather more impatient of cold than many of the plants from the same country. *' When I came to superintend this garden in 1810, I found a specimen of it among the greenhouse plants, where it remained for some time afterwards ; but owing to the bad construction of the greenhouse here, and the very hardy way in which J was obliged to treat the plants in that depart- ment, I did not find the Ficus thrive so well as I had been accustomed to see it do. I concluded that it required more heat, and in the spring of 1811 I placed it in the stove, when it soon began to grow as vigorously as I had ever seen it do. APPENDIX. 205 " The stem of the plant was about a foot in height before any branches set out; on one of the branches, above two feet from the junction with the stem, a root was put out. As soon as this had grown about a foot long, I placed a pot under it. As soon as I found this pot filled with roots, I determined to try whether if supplied plentifully with water it would support the whole plant. " In August 1816, 1 left off watering the original large pot, and supplied the smaller one very freely with water ; I kept it in this state for about eight months, till the earth in the large pot was so completely dry, that I was satisfied the plant could receive no nourishment from it. The shrub continued quite as healthy and vigorous as when supplied with water at the original root. In the spring of 1817, I took off the large pot in which the original roots were, and exposed the roots to the full rays of the sun, by gradually shaking off the dry earth from among them ; this had no ill effect on the plant, as it still remained perfectly healthy ; it, however, had the effect of making roots be put out freely all over the plant, much more so than had hitherto been the case. " In the latter end of the summer of 1817, I placed a root in a third pot, which was put out from a branch about three feet from the junction with the stem, and on the opposite side of the plant from that which had supported it for some time past. As soon as I found this pot filled with fibres, I sup- plied it freely with water, and kept the other small pot dry, as I had done before with the original root. I found the plant still continue equally vigorous as before. In the spring of 1818, I took away the second pot, which I had for some time kept dry, and exposed the roots gradually, as I had formerly done with those in the original pot. " The third pot, which now alone supported the plant, was four feet from the lower end of the stem, and very near to the extremity of the branch, the original roots, and the second set of roots, both hanging loose in the air. The plant, how- ever, remained in this state for nearly a year in perfect 206 APPENDIX. health. In May 1819, I took a very small pot, about two inches in diameter, and filled it with earth as I had done the others, and set it on the surface of the earth in the third pot which now supported the plant. Into this small pot I introduced a root which came from the same branch, a little below the one which was in the larger (third) pot. As soon as the small pot was filled with roots, I supplied it freely with water, and gave the larger pot none but what might hap- pen to run through the small one. After remaining in this state for near two months, I cut the branch off between the two pots ; I still supplied the small pot only with water, but occasionally at this time threw a little water over the whole plant. It continued to look as well as it had done before. " In July last 1819, 1 examined the small pot (the fourth used), arid found it completely filled with roots, very little earth remaining in the pot. By this time the plant appeared to me to be very tenacious of life, and I determined to try whether it would live wholly without earth. I accordingly took the small (fourth) pot off, and gradually worked off what little earth remained among the roots. I at this time, however, threw plenty of water over the leaves, generally twice in the day: this was done about the latter end of July, when the weather was very warm, but it seemed to have no bad effects on the Ficus. " What may appear rather remarkable, is, that though this Ficus is a plant by no means free in producing fruit in the usual way of cultivating it, this specimen, quite suspended without a particle of earth, was loaded with figs during the months of September, October, and part of November. Two fruit were produced at the axilla of almost every leaf, and these were quite as large as I had ever seen on the plant in the hot-houses of Kew garden. The plant is beginning to grow or extend, although it has now been suspended for eight months without a particle of earth, and during that time we have had very hot weather, and also very coid weather. Roots have been put out very freely all over the stem and branches during that time. The plant now APPENDIX. 207 (February 1819) measures 7-J- feet between the extremity of the root and the top of the branches, and the stem at the thickest part is 5|- inches in circumference." EXPERIMENTS AND OBSERVATIONS ON THE ACTION OF CHARCOAL FROM WOOD ON VEGETATION. BY EDWARD LUCAS. (See page 61.) " IN a division of a low hothouse in the botanical garden at Munich, a bed was set apart for young tropical plants, but instead of being filled with tan, as is usually the case, it was filled with the powder of charcoal, (a material which could be easily procured,) the large pieces of charcoal hav- ing been previously separated by means of a sieve. The heat was conducted by means of a tube of white iron into a hollow space in this bed, and distributed a gentle warmth, sufficient to have caused tan to enter into a state of fermen- tation. The plants placed in this bed of charcoal quickly vegetated, and acquired a healthy appearance. Now, as always is the case in such beds, the roots of many of the plants penetrated through the holes in the bottom of the pots, and then spread themselves out ; but these plants evidently surpassed in vigour and general luxuriance plants grown in the common way, for example, in tan. Several of them, of which I shall only specify the beautiful Thun- bergia alata, and the genus Peireskia, throve quite astonish- ingly; the blossoms of the former were so rich, that all who saw it affirmed, they had never before seen such a specimen. It produced also a number of seeds without any artificial aid, while in most cases it is necessary to apply the pollen by the hand. The Peireskia grew so vigorously, that the P. aculeata produced shoots several ells in length, and the P. grundifolia acquired leaves of a foot in length. These facts, as well as the quick germination of the seeds which had been scattered spontaneously, and the abundant appearance of young Filices 9 naturally attracted my 208 APPENDIX. attention, and I was gradually led to a series of experi- ments, the results of which may not be uninteresting ; for, besides being of practical use in the cultivation of most plants, they demonstrate also several facts of importance to physiology. " The first experiment which naturally sug- gested itself, was to mix a certain proportion of charcoal with the earth in which different plants grew, and to increase its quantity according as the advantage of the method was per- ceived. An addition off of charcoal, for example, to vegeta- ble mould, appeared to answer excellently for the Gesneria, and Gloxyma, and also for the tropical Aroidecs with tuberous roots. The two first soon excited the attention of connois- seurs, by the great beauty of all their parts and their general appearance. They surpassed very quickly those cultivated in the common way, both in the thickness of their stems and dark colour of their leaves ; their blossoms were beautiful, and their vegetation lasted much longer than usual, so much so, that in the middle of November, when other plants of the same kinds were dead, these were quite fresh and partly in bloom. Aroideae took root very rapidly, and their leaves surpassed much in size the leaves of those not so treated ; the species, which are reared as ornamental plants on account of the beautiful colouring of their leaves, (I mean, such as the Caladium bicolor, Pictum, Pcecile, &.C.), were particularly remarked for the liveliness of their tints; and it happened here also, that the period of their vegetation was unusually long. A cactus planted in a mixture of equal parts of charcoal and earth throve progressively, and attained double its former size in the space of a few weeks. The use of the charcoal was very advantageous with several of the Bromeliacea, and Liliacece, with the Citrus and Begonia also, and even with the Palmce. The same advantage was found in the case of almost all those plants for which sand is used, in order to keep the earth porous, when charcoal was mixed with the soil instead of sand ; the vegetation was always rendered stronger and more vigorous. " At the same time that these experiments were performed APPENDIX. 209 with mixtures of charcoal with different soils, the charcoal was also used free from any addition, and in this case the best results were obtained. Cuts of plants from different genera took root in it well and quickly ; I mention here only the Euphorbia fastuosa andfulgens which took root in ten days, Pandanus utilis in three months, P. amaryllifolius, Chamce- dorea elatior in four weeks, Pipernigrum, Begonia, Ficus, Cecropia, Chiococca, Buddleja, Hakea, PhyUanthus, Capparis, Laurus, Stifftia, Jacquinia, Mimosa, Cactus, in from eight to ten days, and several others amounting to forty species, in- cluding Ilex, and many others. Leaves, and pieces of leaves, and even pedunculi, or petioles, took root and in part budded in pure charcoal. Amongst others we may mention the foliola of several of the Cycadece as having taken root, as also did parts of the leaves of the Begonia Telsairice, andJacaranda brasiliensis ; leaves of the Euphorbia fastuosa, Oxalis Barri- lieri, Ficus, Cyclamen, Polyanihes, Mesembrianthemum ; also, the delicate leaves of the Lophospermum and Martynia, pieces of a leaf of the Agave Americana ; tufts of Pinus, &c. ; and all without the aid of a previously formed bud. " Pure charcoal acts excellently as a means of curing unhealthy plants. A Dorianthes excelsa, for example, which had been drooping for three years, was rendered completely healthy in a very short time by this means. An orange-tree which had the very common disease in which the leaves become yellow, acquired within four weeks its healthy green colour, when the upper surface of the earth was removed from the pot in which it was contained, and a ring of charcoal of an inch in thickness strewed in its place around the peri- phery of the pot. The same was the case with the Gardenia. " I should be led too far were I to state all the results of the experiments which I have made with charcoal. The object of this paper is merely to show the general effect exercised by this substance on vegetation, but the reader who takes particular interest in the subject, will find more extensive observations in the ' Allgemeine deutsche Gartenzeitung ' of Otto and Dietrich in Berlin. 210 APPENDIX. " The charcoal employed in these experiments was the dust-like powder of charcoal from firs and pines, such as is used in the forges of blacksmiths, and may be easily pro- cured in any quantity. It was found to have most effect when allowed to lie during the winter exposed to the action of the air. In order to ascertain the effects of different kinds of charcoal, experiments were also made upon that obtained from the hard woods and peat, and also upon animal charcoal, although I foresaw the probability that none of them would answer so well as that of pinewood, both on account of its porosity and the ease with which it is decomposed. '* It is superfluous to remark, that in treating plants in the manner here described, they must be plentifully supplied with water, since the air having such free access penetrates and dries the roots, so that unless this precaution is taken, the failure of all such experiments is unavoidable. " The action of charcoal consists primarily in its preserving the parts of the plants with which it is in contact ; whether they be roots, branches, leaves, or pieces of leaves, un- changed in their vital power for a long space of time, so that the plant obtains time to develop the organs which are necessary for its further support and propagation. There can scarcely be a doubt also that the charcoal under- goes decomposition ; for after being used five to six years it becomes a coaly earth ; and if this is the case, it must yield carbon, or carbonic oxide, abundantly to the plants growing in it, and thus afford the principal substance ne- cessary for the nutrition of vegetables. In what other manner indeed can we explain the deep green colour and great luxu- riance of the leaves and every part of the plants, which can be obtained in no other kind of soil, according to the opinion of men well qualified to judge? It exercises likewise a favourable influence by decomposing and absorbing the matters absorbed [query, excreted] by the roots, so as to keep the soil free from the putrefying substances which are often the cause of the death of the spongiolce. Its porosity as well as APPENDIX. 211 the power which it possesses, of absorbing water with rapidity, and, after its saturation, of allowing all other water to sink through it, are causes also of its favourable effects. These experiments show what a close affinity the component parts of charcoal have to all plants, for every experiment was crowned with success, although plants belonging to a great many different families were subjected to trial/' (Buchner's Repertorium,\\. Reihe, xix. Ed. S. 38.) ON THE ROTATION OF CROPS AT BINGEN ON THE RHINE. (See Page 172.) The alternation of crops with esparsette and lucern is now universally adopted in Bingen and its vicinity as well as in the Palatinate ; the fields in these districts receive manure only once every nine years. In the first year after the land has been manured, turnips are sown upon it, in the next following years barley, with esparsette or lucern ; in the seventh year potatoes, in the eighth wheat, in the ninth barley ; on the tenth year it is manured, and then the same rotation again takes place. ON A MODE OF MANURING VINES. The observations contained in the following pages should be extensively known, because they furnish a remarkable proof of the principles which have been stated in the preced- ing part of the work, both as to the manner in which manure acts, and on the origin of the carbon and nitrogen of plants. They prove that a vineyard may be retained in fertility without the application of animal matters, when the leaves and branches pruned from the vines are cut into small pieces and used as manure. According to the first of the following statements, both of which merit complete con- fidence, the perfect fruitfulness of a vineyard has been P 2 212 APPENDIX. maintained in this manner for eight years, and 'according to the second statement for ten years. Now, during this long period, no carbon was conveyed to the soil, for that contained in the pruned branches was the produce of the plant itself, so that the vines were placed exactly in the same condition as trees in a forest which received no manure. Under ordinary circumstances a manure containing potash must be used, otherwise the fertility of the soil will decrease. This is done in all wine- countries, so that alkalies to a very considerable amount must be extracted from the soil. When, however, the method of manuring now to be described is adopted, the quantity of alkalies exported in the wine does not exceed that which the progressive disinte- gration of the soil every year renders capable of being absorbed by the plants. On the Rhine 1 litre of wine is cal- culated as the yearly produce of a square metre of land (10'8 square feet English). Now if we suppose that the wine is three-fourths saturated with cream of tartar, a proportion much above the truth, then we remove from every square metre of land with the wine only 1*8 gramme of potash. 1000 grammes (1 litre) of champagne yield only 1'54, and the same quantity of Wachenheimer 1*72 of a residue which after being heated to redness is found to consist of car- bonates. One vine-stock, on an average, grows on every square metre of land, and 1000 parts of the pruned branches contain 56 to 60 parts of carbonate, or 38 to 40 parts of pure potash. Hence it is evident that 45 grammes, or 1 ounce, of these branches contain as much potash as 1000 grammes (1 litre) of wine. But from ten to twenty times this quantity of branches are yearly taken from the above extent of surface. In the vicinity of Johannisberg, Rudesheim, and Budes- heim, new vines are not planted after the rooting out of the old stocks, until the land has lain for five or six years in barley and esparsette or lucern ; in the sixth year the young stocks planted, but not manured till the ninth. APPENDIX. 213 ON THE MANURING OF THE SOIL IN VINEYARDS.* " In reference to an article in your paper, No. 7, 1838, and No. 29, 1839, 1 cannot omit the opportunity of again calling the public attention to the fact that nothing more is neces- sary for the manure of a vineyard, than the branches which are cut from the vines themselves. " My vineyard has been manured in this way for eight years, without receiving any other kind of manure, and yet more beautiful and richly laden vines could scarcely be pointed out. I formerly followed the method usually prac- tised in this district, and was obliged in consequence to purchase manure to a large amount. This is now entirely saved, and my land is in excellent condition. 66 When I see the fatiguing labour used in the manuring of vineyards horses and men toiling up the mountains with unnecessary materials I feel inclined to say to all, come to my vineyard and see how a bountiful Creator has provided that vines shall manure themselves, like the trees in a forest, and even better than they ! The foliage falls from trees in a forest, only when they are withered, and they lie for years before they decay ; but the branches are pruned from the vine in the end of July or beginning of August whilst still fresh and moist. If they are then cut into small pieces and mixed with the earth, they undergo putrefaction so com- pletely, that, as 1 have learned by experience, at the end of four weeks not the smallest trace of them can be found." * Slightly abridged from an article by M. Krebs of Seeheim in the " Zeitschrift fur die landwirthschaftlichen Vereine des Grosherzogthums Hessen." No. 28, July 9, 1840. 214 APPENDIX. " Remarks of the editor. We find the following notices of the same fact in Henderson's c History of Wines of the old and new time f " ' The best manure for vines is the branches pruned from the vines themselves, cut into small pieces, and immediately mixed with the soil.'' " These branches were used as manure long since in the Bergstrasse. M. Frauenfelder says : * " * I remember that twenty years ago, a man called Peter Mliller had a vineyard here which he manured with the branches pruned from the vines, and- continued this practice for thirty years. His way of applying them was to hoe them into the soil after having cut them into small pieces. 46 ' His vineyard was always in a thriving condition; so much so indeed, that the peasants here speak of it to this day wondering that old Miiller had so good a vineyard, and yet used no manure/ " Lastly, Wilhelm Ruf of Schriesheim writes : " < For the last ten years I have been unable to place dung on my vineyard, because I am poor and can buy none. But I was very unwilling to allow my vines to decay, as they are my only source of support in my old age ; and I often walked very anxiously amongst them, without knowing what I should do. At last my necessities became greater, which made me more attentive, so that I remarked that the grass was longer on some spots where the branches of the vine fell than on those on which there were none. So I thought upon the matter, and then said to myself: If these branches can make the grass large, strong, and green, they must also be able to make my plants grow better, and become strong and green. I dug therefore my vineyard as deep as if I would put dung into it, and cut the branches into pieces, placing * Badisches landwirthschaftliches Wochenblatt, v.. 1834. S. 52 and 79. APPENDIX. 215 them in the holes and covering them with earth. In a year I had the very great satisfaction to see my barren vineyard become quite beautiful. This plan I continued every year, and now my vines grow splendidly, and remain the whole summer green, even in the greatest heat. " All my neighbours wonder very much how my vineyard is so rich, and that I obtain so many grapes from it, and yet they all know that I have put no dung upon it for ten years." PART II. OF THE CHEMICAL PROCESSES OF FERMENTATION, DECAY' AND PUTREFACTION. CHEMICAL TRANSFORMATIONS. WOODY fibre, sugar, gum, and all such organic compounds, suffer certain changes when in contact with other bodies, that is, they suffer decomposition. There are two distinct modes in which these decompositions take place in organic chemistry. When a substance composed of two compound bodies, crystallised oxalic acid for example, is brought in contact with concentrated sulphuric acid, a complete decomposition is effected upon the application of a gentle heat. Now crystallised oxalic acid is a combination of water with the anhy- drous acid ; but concentrated sulphuric acid pos- sesses a much greater affinity for water than oxalic acid, so that it attracts all the water of crystallization from that substance. In consequence of this abstrac- tion of the water, anhydrous oxalic acid is set free ; but as this acid cannot exist in a free state, a divi- sion of its constituents necessarily ensues, by which carbonic acid and carbonic oxide are produced, and evolved in the gaseous form in equal volumes. In this example, the decomposition is the con- sequence of the removal of two constituents (the 218 CHEMICAL TRANSFORMATIONS. elements of water), which unite with the sulphuric acid,, and its cause is the superior affinity of the acting body (the sulphuric acid) for water. In consequence of the removal of the component parts of water, the remaining elements enter into a new form ; in place of oxalic acid, we have its elements in the form of carbonic acid and carbonic oxide. This form of decomposition, in which the change is effected by the agency of a body which unites with one or more of the constituents of a com- pound, is quite analogous to the decomposition of inorganic substances. When we bring sulphuric acid and nitrate of potash together, nitric acid is separated in consequence of the affinity of sulphuric acid for potash ; in consequence, therefore, of the formation of a new compound (sulphate of potash). In the second form of these decompositions, the chemical affinity of the acting body causes the component parts of the body which is decom- posed to combine so as to form new compounds, of which either both, or only one, combine with the acting body. Let us take dry wood, for example, and moisten it with sulphuric acid ; after a short time the wood is carbonised, while the sulphuric acid remains unchanged, with the exception of its being united with more water than it possessed before. Now this water did not exist as such in the wood, although its elements, oxygen and hydrogen, were present ; but by the chemical attraction of sul- EXAMPLES. 219 phuric acid for water, they were in a certain measure compelled to unite in this form ; and in consequence of this, the carbon of wood was separated as charcoal. Hydrocyanic acid, and mater., in contact with hydrochloric acid, are mutually decomposed. The nitrogen of the hydrocyanic acid, and a certain quantity of the hydrogen of the water, unite to- gether and form ammonia ; whilst the carbon and hydrogen of the hydrocyanic acid combine with the oxygen of the water, and form formic acid. The ammonia combines with the muriatic acid. Here the contact of muriatic acid with water and hydro- cyanic acid causes a disturbance in the attraction of the elements of both compounds, in consequence of which they arrange themselves into new com- binations, one of which ammonia possesses the power of uniting with the acting body. Inorganic chemistry can present instances analo- gous to this class of decomposition also ; but there are forms of organic chemical decomposition of a very different kind, in which none of the compo- nent parts of the matter which suffers decomposition enters into combination with the body which de- termines the decomposition. In cases of this kind a disturbance is produced in the mutual attraction of the elements of a compound, and they in conse- quence arrange themselves into one or several new combinations, which are incapable of suffering further change under the same conditions. 220 CHEMICAL TRANSFORMATIONS. When, by means of the chemical affinity of a second body, by the influence of heat, or through any other causes, the composition of an organic compound is made to undergo such a change, that its elements form two or more new compounds, this manner of decomposition is called a chemical transformation or metamorphosis. It is an essen- tial character of chemical transformations, that none of the elements of the body decomposed are singly set at liberty. The changes, which are designated by the terms fermentation, decay, and putrefaction, are chemical transformations effected by an agency which has hitherto escaped attention, but the existence of which will be proved in the following pages. ON THE CAUSES WHICH EFFECT FERMENTATION, DECAY,* AND PUTREFACTION. ATTENTION has been recently directed to the fact, that a body in the act of combination or de- composition exercises an influence upon any other body with which it may be in contact. Platinum, for example, does not decompose nitric acid ; it may be boiled with this acid without being oxidised * An essential distinction is drawn in the following part of the work, between decay and putrefaction (Verwesung und F'dulniss\ and they are shown to depend on different causes ; but as the word decay is not gene- rally applied to a distinct species of decomposition, and does not indi- cate its true nature, I shall in future, at the suggestion of the author, employ the term eremacausis, the meaning of which has been already ex- plained. TRANS. THEIR CAUSE. 221 by it, even when in a state of such fine division, that it no longer reflects light (black spongy platinum). But an alloy of silver and platinum dissolves with great ease in nitric acid ; the oxida- tion which the silver suffers, causes the platinum to submit to the same change ; or, in other words, the latter body from its contact with the oxidizing silver, acquires the property of decomposing nitric acid. Copper does not decompose water, even when boiled in dilute sulphuric acid, but an alloy of copper, zinc, and nickel, dissolves easily in this acid with evolution of hydrogen gas. Tin decomposes nitric acid with great facility, but water with difficulty ; and yet, when tin is dis- solved in nitric acid, hydrogen is evolved at the same time, from a decomposition of the water con- tained in the acid, and ammonia is formed in addition to oxide of tin. In the examples here given, the only combina- tion or decomposition which can be explained by chemical affinity is the last. In the other cases, electrical action ought to have retarded or prevented the oxidation of the platinum or copper while they were in contact with silver or zinc, but, as experience shows, the influence of the opposite electrical con- ditions is more than counterbalanced by chemical actions. The same phenomena are seen in a less dubious form in compounds, the elements of which are held 222 CHEMICAL TRANSFORMATIONS. together only by a weak affinity. It is well known that there are chemical compounds of so unstable a nature, that changes in temperature and electrical condition, or even simple mechanical friction, or contact with bodies of apparently totally indifferent natures, cause such a disturbance in the attraction of their constituents, that the latter enter into new forms, without any one of them combining with the acting body. These compounds appear to stand but just within the limits of chemical combination, and agents exercise a powerful influence on them, which are completely devoid of action on com- pounds of a stronger affinity. Thus, by a slight increase of temperature, the elements of hypochlo- rous acid separate from one another with evolution of heat and light ; chloride of nitrogen explodes by contact with many bodies, which combine neither with chlorine nor nitrogen at common tempera- tures; and the contact of any solid substance is sufficient to cause the explosion of iodide of nitro- gen, or fulminating silver. It has never been supposed that the causes of the decomposition of these bodies should be ascribed to a peculiar power, different from that which regulates chemical affinity, a power which mere contact with the down of a feather is sufficient to set in activity, and which, once in action, gives rise to the decomposition. These substances have always been viewed as chemical combinations of a very unstable nature, in which THEIR CAUSE. 223 the component parts are in a state of such ten- sion, that the least disturbance overcomes their chemical affinity. They exist only by the vis inertia, and any shock or movement is sufficient to destroy the attraction of their component parts, and consequently their existence in their definite form. Peroxide of hydrogen belongs to this class of bodies ; it is decomposed by all substances capable of attracting oxygen from it, and even by contact with many bodies, such as platinum or silver, which do not enter into combination with any of its con- stituents. In this respect, its decomposition depends evidently upon the same causes which effect that of iodide of nitrogen, or fulminating silver. Yet it is singular that the cause of the sudden separation of the component parts of peroxide of hydrogen has been viewed as different from those of common decomposition, and has been ascribed to a new power termed the catalytic force. Now, it has not been considered, that the presence of the platinum and silver serves here only to accelerate the decom- position ; for without the contact of these metals, the peroxide of hydrogen decomposes spontane- ously, although very slowly. The sudden separa- tion of the constituents of peroxide of hydrogen differs from the decomposition of gaseous hypochlo- rous acid, or solid iodide of nitrogen, only in so far as the decomposition takes place in a liquid. A remarkable action of peroxide of hydrogen has 224 CHEMICAL TRANSFORMATIONS. attracted much attention, because it differs from ordinary chemical phenomena. This is the reduc- tion which certain oxides suffer by contact with this substance, on the instant at which the oxygen sepa- rates from the water. The oxides thus easily re- duced, are those of which the whole, or part at least, of their oxygen is retained merely by a feeble affinity, such as the oxides of silver and of gold, and peroxide of lead. Now, other oxides which are very stable in com- position, effect the decomposition of peroxide of hydrogen, without experiencing the smallest change ; but when oxide of silver is employed to effect the decomposition, all the oxygen of the silver is carried away with that evolved from the peroxide of hydro- gen, and as a result of the decomposition, water and metallic silver remain. When peroxide of lead is used for the same purpose, half its oxygen escapes as a gas. Peroxide of manganese may in the same manner be reduced to the protoxide, and oxygen set at liberty, if an acid is at the same time present, which will exercise an affinity for the protoxide and convert it into a soluble salt. If, for example, we add to peroxide of hydro- gen sulphuric acid, and then peroxide of man- ganese in the state of fine powder, much more oxygen is evolved than the compound of oxygen and hydrogen could yield; and if we examine the solution which remains, we find a salt of the protoxide of manganese, so that half of the THEIR CAUSE. oxygen has been evolved from the peroxide of that metal. A similar phenomenon occurs, when carbonate of silver is treated with several organic acids. Pyr- uvic acid, for example, combines readily with pure oxide of silver, and forms a salt of sparing solubility in water. But when this acid is brought in contact with carbonate of silver, the oxygen of part of the oxide escapes with the carbonic acid, and metallic silver remains in the state of a black powder. (Berzelius.) Now no other explanation of these phenomena can be given, than that a body in the act of combina- tion or decomposition enables another body, with which it is in contact, to enter into the same state. It is evident that the active state of the atoms of one body has an influence upon the atoms of a body in contact with it; and if these atoms are capable of the same change as the former, they likewise undergo that change ; and combinations and decompositions are the consequence. But when the atoms of the second body are not capable of such an action, any further disposition to change ceases from the moment at which the atoms of the first body assume the state of rest, that is, when the changes or transformations of this body are quite completed. This influence exerted by one compound upon the other, is exactly similar to that which a body in the act of combustion exercises upon a combus- Q 226 CHEMICAL TRANSFORMATIONS. tible body in its vicinity ; with this difference only, that the causes which determine the participation and duration of these conditions are different. For the cause, in the case of the combustible body, is heat, which is generated every moment anew ; whilst in the phenomena of decomposition and combination, which we are considering at present, the cause is a body in the state of chemical action, which exerts the decomposing influence only so long as this action continues. Numerous facts show that motion alone exercises a considerable influence on chemical forces. Thus, the power of cohesion does not act in many saline solutions, even when they are fully saturated with salts, if they are permitted to cool whilst at rest. In such a case, the salt dissolved in a liquid does not crystallise, but when a grain of sand is thrown into the solution, or when it receives the slightest movement, the whole liquid becomes suddenly solid while heat is evolved. The same phenomenon happens with water, for this liquid may be cooled much under 32 (0 C.), if kept completely undis- turbed, but solidifies in a moment when put in motion. The atoms of a body must in fact be set in mo- tion before they can overcome the vi$ inertice so as to arrange themselves into certain forms. A dilute solution of a salt of potash mixed with tar- taric acid yields no precipitate whilst at rest ; but if motion is communicated to the solution by agi- THEIR CAUSE. 227 tating it briskly, solid crystals of cream of tartar are immediately deposited. A solution of a salt of magnesia also, which is not rendered turbid by the addition of phosphate of ammonia, deposits the phosphate of magnesia and ammonia on those parts of the vessel touched with the rod employed in stirring. In the processes of combination and decomposition under consideration, motion, by overcoming the vis inertia, gives rise immediately to another arrange- ment of the atoms of a body, that is, to the produc- tion of a compound which did not before exist in it. Of course these atoms must previously possess the power of arranging themselves in a certain order, otherwise both friction and motion would be without the smallest influence. The simple permanence in position of the atoms of a body, is the reason that so many compounds appear to present themselves, in conditions, and with properties, different from those which they possess, when they obey the natural attractions of their atoms. Thus sugar and glass, when melted and cooled rapidly, are transparent, of a conchoidal fracture, and elastic and flexible to a certain degree. But the former becomes dull and opaque on keep- ing, and exhibits crystalline faces by cleavage, which belong to crystallised sugar. Glass assumes also the same condition, when kept soft by heat for a long period ; it becomes white, opaque, and so hard as to strike fire with steel. Now, in both Q2 228 CHEMICAL TRANSFORMATIONS. these bodies, the compound molecules evidently have different positions in the two forms. In the first form their attraction did not act in the direc- tion in which their power of cohesion was strongest. It is known also, that when sulphur is melted and cooled rapidly by throwing it into cold water, it remains transparent, elastic, and so soft that it may be drawn out into long threads ; but that after a few hours or days, it becomes again hard and crystalline. The remarkable fact here is, that the amorphous sugar or sulphur returns again into the crystalline condition, without any assistance from an exterior cause ; a fact which shows that their molecules have assumed another position, and that they possess, therefore, a certain degree of mobility, even in the condition of a solid. A very rapid transposition or transformation of this kind is seen in arragonite, a mineral which possesses exactly the same composition as calcareous spar, but of which the hardness and different crystalline form prove that its molecules are arranged in a different manner. When a crystal of arragonite is heated, an interior motion of its molecules is caused by the expansion ; the permanence of their arrangement is destroyed; and the crystal splinters with much violence, and falls into a heap of small crystals of calcareous spar. It is impossible for us to be deceived regarding the causes of these changes. They are owing to a disturbance of the state of equilibrium, in conse- FERMENTATION AND DECAY. 229 quence of which, the particles of the body put in motion obey other affinities or their own natural attractions. But if it is true, as we have just shown it to be, that mechanical motion is sufficient to cause a change of condition in many bodies, it cannot be doubted that a body in the act of combination or decomposition is capable of imparting the same condition of motion or activity in which its atoms are to certain other bodies : or in other words, to enable other bodies with which it is in contact to enter into combinations, or suifer decompositions. The reality of this influence has been already sufficiently proved by the facts derived from in- organic chemistry, but it is of much more frequent occurrence in the relations of organic matters, and causes very striking and wonderful phenomena. By the terms fermentation, putrefaction, and eremacausis, are meant those changes in form and properties which compound organic substances undergo when separated from the organism, and exposed to the influence of water and a certain temperature. Fermentation and putrefaction are examples of that kind of decomposition which we have named transformations ; the elements of the bodies capable of undergoing these changes arrange themselves into new combinations, in which the constituents of water generally take a part. Eremacausis (or decay) differs from fermentation and putrefaction, inasmuch as it cannot take place 230 CHEMICAL TRANSFORMATIONS without the access of air, the oxygen of which is absorbed by the decaying bodies. Hence it is a process of slow combustion, in which heat is uniformly evolved, and occasionally even light. In the processes of decomposition, termed fermenta- tion and putrefaction, gaseous products are very frequently formed, which are either inodorous, or possess a very offensive smell. The transformations of those matters which evolve gaseous products without odour, are now, by pretty general consent, designated by the term fermentation ; whilst to the spontaneous decompo- sition of bodies which emit gases of a disagreeable smell, the term putrefaction is applied. But the smell is of course no distinctive character of the nature of the decomposition, for both fermentation and putrefaction are processes of decomposition of a similar kind, the one of substances destitute of nitrogen, the other of substances which contain it. It has also been customary to distinguish from fermentation and putrefaction a particular class of transformations, viz., those in which conversions and transpositions are effected without the evolution of gaseous products. But the conditions under which the products of the decomposition present them- selves are purely accidental ; there is therefore no reason for the distinction just mentioned. OF ORGANIC COMPOUNDS. 231 -X FERMENTATION AND PUTREFACTION. Several bodies appear to enter spontaneously into the states of fermentation and putrefaction,, parti- cularly such as contain nitrogen or azotised sub- stances. Now, it is very remarkable, that very small quantities of these substances, in a state of fermentation or putrefaction, possess the power of causing unlimited quantities of similar matters to pass into the same state. Thus, a small quantity of the juice of grapes in the act of fermentation, added to a large quantity of the same fluid, which does not ferment, induces the state of fermentation in the whole mass. So likewise the most minute portion of milk, paste, juice of the beet-root, flesh, or blood, in the state of putrefaction, causes fresh milk, paste, juice of the beet-root, flesh, or blood, to pass into the same condition when in contact with them. These changes evidently differ from the class of common decompositions which are effected by chemical affinity ; they are chemical actions, con- versions, or decompositions, excited by contact with bodies already in the same condition. In order to form a clear idea of these processes, analogous and less complicated phenomena must previously be studied. The compound nature of the molecules of an organic body, and the phenomena presented by them when in relation with other matters, point out the true cause of these transformations. Evidence 232 CHEMICAL TRANSFORMATIONS is afforded even by simple bodies, that in the forma- tion of combinations, the force with which the combining elements adhere to one another is inversely proportional to the number of simple atoms in the compound molecule. Thus, protoxide af manganese by absorption of oxygen is converted into the sesquioxide, the peroxide, and manganic and hypermanganic acids, the number of atoms of oxygen being augmented by 1, by 1, by 2, and by 5* But all the oxygen contained in these com- pounds, beyond that which belongs to the protoxide, is bound to the manganese by a much more feeble affinity ; a red heat causes an evolution of oxygen from the peroxide, and the manganic and hyper- manganic acids cannot be separated from their bases without undergoing immediate decomposition. There are many facts which prove, that the most simple inorganic compounds are also the most stable, and undergo decomposition with the greatest difficulty, whilst those which are of a complex com- position yield easily to changes and decompositions. The cause of this evidently is, that in proportion to the number of atoms which enter into a com- pound, the directions in which their attractions act will be more numerous. Whatever ideas we may entertain regarding mat- ter in general, the existence of chemical proportions removes every doubt respecting the presence of certain limited groups or masses of matter which we have not the power of dividing. The particles of matter called equivalents in chemistry are not OF ORGANIC COMPOUNDS. 233 infinitely small,, for they possess a weight, and are capable of arranging themselves in the most various ways, and of thus forming innumerable compound atoms. The properties of these compound atoms differ in organic nature, not only according to the form, but also in many instances according to the direction and place, which the simple atoms take in the compound molecules. When we compare the composition of organic compounds with inorganic, we are quite amazed at the existence of combinations, in one single mole- cule of which, ninety or several hundred atoms or equivalents are united. Thus, the compound atom of an organic acid of very simple composition, acetic acid for example, contains twelve equivalents of simple elements ; one atom of kinovic acid con- tains 33, 1 of sugar 36, 1 of amygdalin 90, and 1 of stearic acid 138 equivalents. The component parts of animal bodies are infinitely more complex even than these. Inorganic compounds differ from organic in as great a degree in their other characters as in their simplicity of constitution. Thus, the decomposition of a compound atom of sulphate of potash is aided by numerous causes, such as the power of cohesion, or the capability of its constituents to form solid, insoluble, or at certain temperatures volatile compounds with the body brought into con- tact with it, and nevertheless a vast number of other substances produce in it not the slightest change- 234 CHEMICAL TRANSFORMATIONS Now, in the decomposition of a complex organic atom, there is nothing similar to this. The empirical formula of sulphate of potash is SKO 4 . It contains only 1 eq. of sulphur, and 1 eq. of potassium. We may suppose the oxygen to be differently distributed in the compound, and by a decomposition we may remove a part or all of it, or replace one of the constituents of the compound by another substance. But we cannot produce a different arrangement of the atoms, because they are already disposed in the simplest form in which it is possible for them to combine. Now, let us compare the composition of sugar of grapes with the above: here 12eq. of carbon, 12 eq. of hydrogen, and 12 eq. of oxygen, are united together, and we know that they are capable of combining with each other in the most various ways. From the formula of sugar, we might consider it either as a hydrate of carbon, wood, starch, or sugar of milk, or further, as a compound of ether with alcohol or of formic acid with sachul- min.* Indeed we may calculate almost all the known organic compounds containing no nitrogen from sugar, by simply adding the elements of water, or by replacing any one of its elementary consti- tuents by a different substance. The elements necessary to form these compounds are therefore contained in the sugar, and they must also possess * The black precipitate obtained by the action of hydrochloric acid on sugar. OF ORGANIC COMPOUNDS. 235 the power of forming numerous combinations amongst themselves by their mutual attractions. Now, when we examine what changes sugar undergoes when brought into contact with other bodies which exercise a marked influence upon it, we find, that these changes are not confined to any narrow limits, like those of inorganic bodies, but are in fact unlimited. The elements of sugar yield to every attraction, and to each in a peculiar manner. In inorganic compounds, an acid acts upon a particular consti- tuent of the body, which it decomposes, by virtue of its affinity for that constituent, and never resigns its proper chemical character, in whatever form it may be applied. But when it acts upon sugar, and induces great changes in it, it does this, not by its superior affinity for a base existing in the sugar, but by disturbing the equilibrium in the mutual attraction of the elements of the sugar amongst themselves. Muriatic and sulphuric acids, which differ so much from one another both in characters and composition, act in the same manner upon sugar. But the action of both varies according to the state in which they are ; thus they act in one way when dilute, in another when concentrated, and even differences in their temperature cause a change in their action. Thus sulphuric acid of a moderate degree of concentration converts sugar into a black carbonaceous matter, forming at the same time acetic and formic acids. But when the acid is more 236 CHEMICAL TRANSFORMATIONS diluted, the sugar is converted into two brown sub- stances, both of them containing carbon and the elements of water. Again, when sugar is subjected to the action of alkalies, a whole series of different new products are obtained, while oxidizing agents, such as nitric acid, produce from it carbonic acid, acetic acid, oxalic acid, formic acid, and many other products which have not yet been examined. If from the facts here stated we estimate the power with which the elements of sugar are united together, and judge of the force of their attraction by the resistance which they offer to the action of bodies brought into contact with them, we must regard the atom of sugar as belonging to that class of compound atoms, which exist only by the vis inertice of their elements. Its elements seem merely to retain passively the position and condi- tion in which they had been placed, for we do not observe that they resist a change of this condition by their own mutual attraction, as is the case with sulphate of potash. Now it is only such combinations as sugar, com- binations therefore which possess a very complex molecule, which are capable of undergoing the decompositions named fermentation and putrefac- tion. We have seen that metals acquire a power which they do not of themselves possess, namely, that of decomposing water and nitric acid, by simple contact with other metals in the act of chemical combination. OF ORGANIC COMPOUNDS. 237 We have also seen, that peroxide of hydrogen and the persulphuret of the same element, in the act of decomposition, cause other compounds of a similar kind, but of which the elements are much more strongly combined, to undergo the same decompo- sition, although they exert no chemical affinity or attraction for them or their constituents. The cause which produces these phenomena will be also recognised, by attentive observation, in those matters which excite fermentation or putrefaction. All bodies in the act of combination or decomposi- tion have the property of inducing those processes ; or, in other words, of causing a disturbance of the statical equilibrium in the attractions of the elements of complex organic molecules, in consequence of which those elements group themselves anew, ac- cording to their special affinities. The proofs of the existence of this cause of action can be easily produced ; they are found in the characters of the bodies which effect fermenta- tion and putrefaction, and in the regularity with which the distribution of the elements takes place in the subsequent transformations. This regularity depends exclusively on the unequal affinity which they possess for each other in an isolated condition. The action of water on wood, charcoal, and cyano- gen, the simplest of the compounds of nitrogen, suffices to illustrate the whole of the transforma- tions of organic bodies ; of those in which nitrogen is a constituent, and of those in which it is absent. 238 CHEMICAL TRANSFORMATIONS ON THE TRANSFORMATION OF BODIES WHICH DO NOT CONTAIN NITROGEN AS A CONSTI- TUENT. WHEN oxygen and hydrogen combined in equal equivalents, as in steam, are conducted over char- coal, heated to the temperature at which it pos- sesses the power to enter into combination with one of these elements, a decomposition of the steam ensues. An oxide of carbon (either carbonic oxide or carbonic acid) is under all circumstances formed, while the hydrogen of the water is liberated, or, if the temperature be sufficient, unites with the carbon forming carburetted hydrogen. Accord- ingly, the carbon is shared between the elements of the water, the oxygen and hydrogen. Now a participation of this kind, but even more complete, is observed in every transformation, whatever be the nature of the causes by which it is effected. Acetic and meconic acids suffer a true transfor- mation under the influence of heat, that is, their component elements are disunited, and form new compounds without any of them being singly dis- engaged. Acetic acid is converted into acetone and carbonic acid (04 H3 O3 = C3 H3 O + CO2), and meconic acid into carbonic acid and komenic acid ; whilst by the influence of a higher tempera- ture, the latter is further decomposed into pyro- meconic acid and carbonic acid. Now in these cases the carbon of the bodies de- OF BODIES DESTITUTE OF NITROGEN. 239 composed is shared between the oxygen and hydro- gen ; part of it unites with the oxygen and forms carbonic acid, whilst the other portion enters into combination with the hydrogen, and an oxide of a carbohydrogen is formed,, in which all the hydrogen is contained. In a similar manner, when alcohol is exposed to a gentle red heat, its carbon is shared between the elements of the water an oxide of a carbo- hydrogen which contains all the oxygen, and some gaseous compounds of carbon and hydrogen being produced. It is evident that during transformations caused by heat, no foreign affinities can be in play, so that the new compounds must result merely from the elements arranging themselves, according to the degree of their mutual affinities, into new combina- tions which are constant and unchangeable in the conditions under which they were originally formed, but undergo changes when these conditions become different. If we compare the products of two bodies, similar in composition but different in pro- perties, which are subjected to transformations by two different causes, we find that the manner in which the atoms are transposed, is absolutely the same in both. In the transformation of wood in marshy soils, by what we call putrefaction, its carbon is shared between the oxygen and hydrogen of its own substance, and of the water carburetted hydro- 240 CHEMICAL TRANSFORMATIONS gen is consequently evolved, as well as carbonic acid, both of which compounds have an analogous composition (CH2, CO2). Thus also in that transformation of sugar, which is called fermentation, its elements are divided into two portions ; the one, carbonic acid, which contains f of the oxygen of sugar ; and the other, alcohol, which contains all its hydrogen. In the transformation of acetic acid produced by a red heat, carbonic acid which contains f of the oxygen of the acetic acid is formed, and acetone which contains all its hydrogen. It is evident from these facts, that the elements of a complex compound are left to their special attractions whenever their equilibrium is disturbed, from whatever cause this disturbance may proceed. It appears also, that the subsequent distribution of the elements, so as to form new combinations, al- ways takes place in the same way, with this differ- ence only, that the nature of the products formed is dependent upon the number of atoms of the ele- ments which enter into action ; or in other words, that the products differ ad infinitum, according to the composition of the original substance. ON THE TRANSFORMATION OF BODIES CONTAINING NITROGEN. When those substances are examined which are most prone to fermentation and putrefaction, it is found that they are all, without exception, bodies OF BODIES CONTAINING NITROGEN. 241 which contain nitrogen. In many of these com- pounds, a transposition of their elements occurs spontaneously as soon as they cease to form part of a living organism ; that is, when they are drawn out of the sphere of attraction in which alone they are able to exist. There are, indeed, bodies destitute of nitrogen, which possess a certain degree of stability only when in combination, but which are unknown in an isolated condition, because their elements, freed from the power by which they were held together, arrange themselves according to their own natural attractions. Hypermanganic acid, manganic acid, and hyposulphurous acid, belong to this class of substances, which however are rare. The case is very different with azotised bodies. It would appear that there is some peculiarity in the nature of nitrogen, which gives its com- pounds the power to decompose spontaneously with so much facility. Now, nitrogen is known to be the most indifferent of all the elements ; it evinces no particular attraction to any one of the simple bodies, and this character it preserves in all its combinations, a character which explains the cause of its easy separation from the matters with which it is united. It is only when the quantity of nitrogen exceeds a certain limit, that azotised compounds have some degree of permanence, as is the case with melamin, ammelin, &c. Their liability to change is also R 242 CHEMICAL TRANSFORMATIONS diminished, when the quantity of nitrogen is very small in proportion to that of the other elements with which it is united, so that their mutual attractions preponderate. This easy transposition of atoms is best seen in the fulminating silvers, in fulminating mercury, in the iodide or chloride of nitrogen, and in all fulmi- nating compounds. All other azotised substances acquire the same power of decomposition, when the elements of water are brought into play, and indeed, the greater part of them are not capable of trans- formation, while this necessary condition to the transposition of their atoms is absent. Even the compounds of nitrogen, which are most liable to change, such as those which are found in animal bodies, do not enter into a state of putrefaction when dry. The result of the known transformations of azotised substances proves, that the water does not merely act as a medium in which motion is per- mitted to the elements in the act of transposition, but that its influence depends on chemical affinity. When the decomposition of such substances is effected with the assistance of water, their nitrogen is invariably liberated in the form of ammonia. This is a fixed rule without any exceptions, what- ever may be the cause which produces the decom- positions. All organic compounds containing nitrogen, evolve the whole of that element in OF BODIES CONTAINING NITROGEN. 243 the form of ammonia when acted on by alkalies. Acids, and increase of temperature, produce the same effect. It is only when there is a deficiency of water or its elements, that cyanogen or other azotised compounds are produced. From these facts it may be concluded, that ammonia is the most stable compound of nitrogen ; and that hydrogen and nitrogen possess a degree of affinity for each other, which surpasses the attraction of the latter body for any other element. Already in considering the transformations of substances containing no nitrogen, we have seen that a powerful cause effecting the disunion of the elements of a complex organic atom in a definite manner, is the great affinity which carbon possesses for oxygen. But carbon is also invariably contained in azotised compounds, while the great affinity of nitrogen for hydrogen furnishes a new and power- ful cause, facilitating the transposition of their com- ponent parts. Thus, in the bodies which do not contain nitrogen we have one element, and in those in which that substance is present, two elements, which mutually share the elements of water. Hence there are two opposite affinities at play, which strengthen mutually each other's action. Now we know, that the most powerful attractions may be overcome by the influence of two affinities. Thus, a decomposition of alumina may be effected with the greatest facility, when the affinity of R 2 244 CHEMICAL TRANSFORMATIONS charcoal for oxygen, and of chlorine for alu- minium, are both put in action, although neither of these alone has any influence upon it. There is in the nature and constitution of the com- pounds of nitrogen a kind of tension of their com- ponent parts, and a strong disposition to yield to transformations, which effect spontaneously the trans- position of their atoms on the instant that water or its elements are brought in contact with them. The characters of the hydrated cyanic acid, one of the simplest of all the compounds of nitrogen, are perhaps the best adapted to convey a distinct idea of the manner in which the atoms are disposed of in transformations. This acid con- tains nitrogen, hydrogen, and oxygen, in such pro- portions, that the addition of a certain quantity of the elements of water is exactly sufficient to cause the oxygen contained in the water and acid to unite with the carbon and form carbonic acid, and the hydrogen of the water to combine with the nitrogen and form ammonia. The most favourable conditions for a complete transformation are, therefore, associated in these bodies, and it is well known, that the disunion takes place on the instant that the cyanic acid ,and water are brought into contact, the mixture being converted into carbonic acid and ammonia, with brisk effer- vescence. This decomposition may be considered as the type of the transformations of all azotised com- OF BODIES CONTAINING NITROGEN. 245 pounds ; it is putrefaction in its simplest and most perfect form, because the new products, the car- bonic acid and ammonia, are incapable of further transformations. Putrefaction assumes a totally different and much more complicated form, when the products, which are first formed, undergo a further change. In these cases the process consists of several stages, of which it is impossible to determine when one ceases and the other begins. The transformations of cyanogen, a body com- posed of carbon and nitrogen, and the simplest of all the compounds of nitrogen, will convey a clear idea of the great variety of products which are produced in such a case : it is the only example of the putrefaction of an azotised body which has been at all accurately studied. A solution of cyanogen in water becomes turbid after a short time, and deposits a black, or brownish Hack matter, which is a combination of ammonia with another body, produced by the simple union of cyanogen with water. This substance is insoluble in water, and is thus enabled to resist further change. A second transformation is effected by the cya- nogen being shared between the elements of the water, in consequence of which cyanic acid is formed by a certain quantity of the cyanogen combining with the oxygen of the water, while hydrocyanic acid is also formed by another portion 246 CHEMICAL TRANSFORMATIONS of the cyanogen uniting with the hydrogen which was liberated. Cyanogen experiences a third transformation, by which a complete disunion of its elements takes place, these being divided between the constituents of the water. Oxalic acid is the one product of this disunion, and ammonia the other. Cyanic acid, the formation of which has been mentioned above, cannot exist in contact with water, being decomposed immediately into carbonic acid and ammonia. The cyanic acid, however, newly formed in the decomposition of cyanogen, escapes this decomposition by entering into combination with the free ammonia, by which urea is produced. The hydrocyanic acid is also decomposed into a brown matter which contains hydrogen and cyano- gen, the latter in greater proportion than it does in the gaseous state. Oxalic acid, urea, and carbonic acid, are also formed by its decomposition, and formic acid and ammonia are produced by the decomposition of its radical. Thus, a substance into the composition of which only two elements (carbon and nitrogen) enter, yields eight totally different products. Several of these products are formed by the transformation of the original body, its elements being shared between the constituents of water; others are produced in consequence of a further disunion of those first formed. The urea and carbonate of ammonia are generated by the combination of two OF BODIES CONTAINING NITROGEN. 247 of the products, and in their formation the whole of the elements have assisted. These examples show, that the results of decom- position by fermentation or putrefaction compre- hend very different phenomena. The first kind of transformation is, the transposition of the elements of one complex compound, by which new compounds are produced with or without the assistance of the elements of water. In the pro- ducts newly formed in this manner, either the same proportions of those component parts which were contained in the matter before transformation, are found, or with them, an excess, consisting of the constituents of water which had assisted in pro- moting the disunion of the elements. The second kind of transformations consists of the transpositions of the atoms of two or more com- plex compounds, by which the elements of both arrange themselves mutually into new products, with or without the co-operation of the elements of water. In this kind of transformations, the new products contain the sum of the constituents of all the compounds which had taken a part in the decomposition. The first of these two modes of decomposition is, that designated fermentation, the second putrefac- tion ; and when these terms are used in the follow- ing pages, it will always be to distinguish the two processes above described^ which are so different in their results. 248 FERMENTATION FERMENTATION OF SUGAK. The peculiar decomposition which sugar suffers may be viewed as a type of all the transformations designated fermentation. When yeast is made into a thin paste with water, and 1 cubic centimeter of this mixture introduced into a graduated glass receiver filled with mercury, in which are already 10 grammes of a solution of cane-sugar, containing 1 gramme of pure solid sugar; it is found, after the mixture has been exposed for 24 hours to a temperature of from 20 to 25 C. (6877 F.), that a volume of car- bonic acid has been formed, which, at C. (32 F.) and an atmospheric pressure indicated by 0*76 metre Bar. would be from 245 to 250 cubic centi- meters. But to this quantity we must add 11 cubic centimeters of carbonic acid, with which the 1 1 grammes of liquid would be saturated, so that in all 255 259 cubic centimeters of carbonic acid are obtained. This volume of car- bonic acid corresponds to from 0*503 to 0'5127 grammes by weight. Now Thenard obtained from 100 grammes of cane-sugar 0*5262 of absolute al- cohol. 100 parts of sugar from the cane yield, therefore, 103*89 parts of carbonic acid and alco- hol. The entire carbon in these products is equal to 42 parts, which is exactly the quantity originally contained in the sugar. The analysis of sugar from the cane, proves that OF SUGAR. 249 it contains the elements of carbonic acid and alcohol, minus 1 atom of water. The alcohol and carbonic acid produced by the fermentation of a certain quan- tity of sugar, contain together one equivalent of oxy- gen, and one equivalent of hydrogen, the elements, therefore, of one equivalent of water, more than the sugar contained. The excess of weight in the products is thus explained most satisfactorily ; it is owing, namely, to the elements of water having taken part in the metamorphosis of the sugar. It is known that 1 atom of sugar contains 12 equivalents of carbon, both from the propor- tions in which it unites with bases, and from the composition of saccharic acid the product of its oxidation. Now none of these atoms of car- bon are contained in the sugar as carbonic acid, because the whole quantity is obtained as oxalic acid, when sugar is treated with hypermanganate of potash (Gregory); and as oxalic acid is a lower degree of the oxidation of carbon than carbonic acid, it is impossible to conceive that the lower degree should be produced from the higher, by means of one of the most powerful agents of oxida- tion which we possess. " It can be also proved, that the hydrogen of the sugar does not exist in it in the form of alcohol, for it is converted into water and a kind of carbon- aceous matter, when treated with acids, particularly with such as contain no oxygen ; and this manner of decomposition is never suffered by a compound of alcohol. 250 FERMENTATION OF SUGAR. Sugar contains, therefore, neither alcohol nor carbonic acid, so that these bodies must be pro- duced by a different arrangement of its atoms, and by theirninion with the elements of water. In this metamorphosis of the sugar, the elements of the yeast, by contact with which its fermentation was effected, take no appreciable part in the trans- position of the elements of the sugar ; for in the products resulting from the action, we find no component part of this substance. We may now study the fermentation of a vege- table juice, which contains not only saccharine matter, but also such substances as albumen and gluten. The juices of parsnips, beet-roots, and onions, are well adapted for this purpose. When such a juice is mixed with yeast at common tem- peratures, it ferments like a solution of sugar. Car- bonic acid gas escapes from it with effervescence, and in the liquid, alcohol is found in quantity ex- actly corresponding to that of the sugar originally contained in the juice. But such a juice under- goes spontaneous decomposition at a temperature of from 95 to 104 (35 40 C.). Gases possessing an offensive smell are evolved in considerable quan- tity, and when the liquor is examined after the de- composition is completed, no alcohol can be de- tected. The sugar has also disappeared, and with it all the azotised compounds which existed in the juice previously to its fermentation. Both were decomposed at the same time ; the nitrogen of the azotised compounds remains in the liquid as am- YEAST OR FERMENT. 251 monia, and, in addition to it, there are tnree new products, formed from the component parts of the juice. One of these is lactate acid, the slightly volatile compound found in the animal organism ; the other is the crystalline body which forms the principal constituent of manna ; and the third is a mass resembling gum-arabic, which forms a thick viscous solution with water. These three products weigh more than the sugar contained in the juice, even without calculating the weight of the gaseous products. Hence they are not produced from the elements of the sugar alone. None of these three substances could be detected in the juice before fermentation. They must, therefore, have been formed by the interchange of the elements of the sugar with those of the foreign substances also present. It is this mixed transformation of two or more compounds which receives the special name of putrefaction. ON YEAST OR FERMENT. When attention is directed to the condition of those substances which possess the power of induc- ing fermentation and putrefaction in other bodies, evidences are found in their general characters, and in the manner in which they combine, that they all are bodies, the atoms of which are in the act of transposition. The characters of the remarkable matter which is deposited in an insoluble state during the fer- 252 YEAST OR FERMENT, mentation of beer, wine, and vegetable juices, may be first studied. This substance, which has been called yeast or ferment, from the power which it possesses of causing fermentation in sugar, or saccharine vege- table juices, possesses all the characters of a com- pound of nitrogen in the state of putrefaction and eremacausis. Like wood in the state of eremacausis, yeast con- verts the oxygen of the surrounding air into carbo- nic acid, but it also evolves this gas from its own mass, like bodies in the state of putrefaction. (Colin.) When kept under water, it emits carbonic acid, accompanied by gases of an offensive smell (Thenard), and is at last converted into a sub- stance resembling old cheese. (Proust.) But when its own putrefaction is completed, it has no longer the power of inducing fermentation in other bodies. The presence of water is quite necessary for sus- taining the properties of ferment, for by simple pressure its power to excite fermentation is much diminished, and is completely destroyed by drying. Its action is arrested also by the temperature of boiling water, by alcohol, common salt, an excess of sugar, oxide of mercury, corrosive sublimate, pyroligneous acid, sulphurous acid, nitrate of silver, volatile oils, and in short by all antiseptic sub- stances. The insoluble part of the substance called ferment does not cause fermentation. For when the yeast ITS PROPERTIES. 253 from wine or beer is carefully washed with water, care being taken that it is always covered with this fluid, the residue does not produce fermen- tation. The soluble part of ferment likewise does not excite fermentation. An aqueous infusion of yeast may be mixed with a solution of sugar, and preserved in vessels from which the air is excluded, without either experiencing the slightest change. What then, we may ask, is the matter in ferment which excites fermentation, if neither the soluble nor in- soluble parts possess the power ? This question has been answered by Colin in the most satisfactory manner. He has shown that in reality it is the soluble part. But before it obtains this power, the decanted infusion must be allowed to cool in contact with the air, and to remain some time exposed to its action. When introduced into a solution of sugar in this state, it produces a brisk fermentation ; but without previous exposure to the air, it manifests no such property. The infusion absorbs oxygen during its exposure to the air, and carbonic acid may be found in it after a short time. Yeast produces fermentation in consequence of the progressive decomposition which it suffers from the action of air and water. Now when yeast is made to act on sugar, it is found, that after the transformation of the latter 254 YEAST OR FERMENT, substance into carbonic acid and alcohol is com- pleted, part of the yeast itself has disappeared. From 20 parts of fresh yeast from beer, and 100 parts of sugar, Thenard obtained, after the fer- mentation was completed, 13*7 parts of an insolu- ble residue, which diminished to 10 parts when employed in the same way with a fresh portion of sugar. These ten parts were white, possessed of the properties of woody fibre, and had no further action on sugar. It is evident, therefore, that during the fermenta- tion of sugar by yeast, both of these substances suffer decomposition at the same time, and disappear in consequence. But if yeast be a body which excites fermentation by being itself in a state of decomposition, all other matters in the same condi- tion should have a similar action upon sugar ; and this is in reality the case. Muscle, urine, isin- glass, osmazome, albumen, cheese, gliadine, gluten, legumin, and blood, when in a state of putrefaction, have all the power of producing the putrefaction, or fermentation of a solution of sugar. Yeast, which by continued washing has entirely lost the property of inducing fermentation, regains it when its putrefaction has recommenced, in consequence of its being kept in a warm situation for some time. Yeast and putrifying animal and vegetable matters act as peroxide of hydrogen does on oxide of silver, ITS MODE OF ACTION. 255 when they induce bodies with which they are in contact to enter into the same state of decompo- sition. The disturbance in the attraction of .the constituents of the peroxide of hydrogen effects a disturbance in the attractions of the elements of the oxide of silver, the one being decomposed, on account of the decomposition of the other. Now if we consider the process of the fermenta- tion of pure sugar, in a practical point of view, we meet with two facts of constant occurrence. When the quantity of ferment is too small in proportion to that of the sugar, its putrefaction will be com- pleted before the transformation of all the sugar is effected. Some sugar here remains undecomposed, because the cause of its transformation is absent, viz. contact with a body in a state of decompo- sition. But when the quantity of ferment predominates, a certain quantity of it remains after all the sugar has fermented, its decomposition proceeding very slowly, on account of its insolubility in water. This residue of ferment is still able to induce fer- mentation, when introduced into a fresh solution of sugar, and retains the same power until it has passed through all the stages of its own transfor- mation. Hence a certain quantity of yeast is necessary in order to effect the transformation of a certain portion of sugar, not because it acts by its quantity increasing any affinity, but because its influence 256 YEAST OR FERMENT. depends solely on its presence, and its presence is necessary, until the last atom of sugar is decom- posed. These facts and observations point out the exist- ence of a new cause, which effects combinations and decompositions. This cause is the action which bodies in a state of combination or decomposition exercise upon substances, the component parts of which are united together by a feeble affinity. In its action it resembles a peculiar power, attached to a body in the state of combination or decomposition, but exerting its influence beyond the sphere of its own attractions. We are now able to account satisfactorily for many known phenomena. A large quantity of hippuric acid may be obtained from the fresh urine of a horse, by the addition of muriatic acid ; but when the urine has undergone putrefaction, no trace of it can be discovered. The urine of man contains a considerable quantity of urea, but when the urine putrifies, the urea entirely disappears. When urea is added to a solution of sugar in the state of fermentation, it is decomposed into carbonic acid and ammonia. No asparagin can be detected in a putrified infusion of asparagin, liquorice-root, or the root of alihcpa officinalis. It has already been mentioned, that the strong affinity of nitrogen for hydrogen, and that of car- bon for oxygen, are the cause of the facility with which the elements of azotised compounds are dis- NATURE OF FERMENTATION. 257 united ; those affinities aiding each other, inasmuch as by virtue of them different elements of the com- pound strive to take possession of the different elements of water. Now since it is found that no body destitute of nitrogen possesses, when pure, the property of decomposing spontaneously whilst in contact with water, we must ascribe this property which azotised bodies possess in so eminent a de- gree, to something peculiar in the nature of the compounds of nitrogen, and to their constituting, in a certain measure, more highly organised atoms. Every azotised constituent of the animal or vegetable organism enters spontaneously into pu- trefaction, when exposed to moisture and a high temperature. Azotised matters are accordingly the only causes of fermentation and putrefaction in vegetable sub- stances. Putrefaction, on account of its effects, as a mixed transformation of many different substances, may be classed with the most powerful processes of deoxida- tion, by which the strongest affinities are overcome. When a solution of gypsum in water is mixed with a decoction of sawdust, or any other organic matter capable of putrefaction, and preserved in well-closed vessels, it is found, after some time, that the solution contains no more sulphuric acid, but in its place carbonic and free hydrosulphuric acid, between which the lime of the gypsum is shared. In stagnant water containing sulphates in solution, 258 YEAST OR FERMENT. crystallised pyrites is observed to form on the de- caying roots. Now we know that in the putrefaction of wood under water, when air therefore is excluded, a part of its carbon combines with the oxygen of the water, as well as with the oxygen which the wood itself contains ; whilst its hydrogen and that of the decomposed water are liberated either in a pure state, or as carburetted hydrogen. The products of this decomposition are therefore of the same kind as those generated when steam is conducted over red-hot charcoal. It is evident, that if with the water a substance containing a large quantity of oxygen, such as sul- phuric acid, be also present, the matters in the state of putrefaction will make use of the oxygen of that substance as well as that of the water, in order to form carbonic acid ; and the sulphur and hydro- gen being set free will combine whilst in the nas- cent state, producing hydrosulphuric acid, which will be again decomposed if metallic oxides be pre- sent ; and the results of this second decomposition will be water and metallic sulphurets. The putrefied leaves of woad (Isatis tinctoria), in contact with indigo-blue, water, and alkalies, suffer further decomposition, and the indigo is deoxidised and dissolved. The mannite formed by the putrefaction of beet- roots and other plants which contain sugar, con- tains the same number of equivalents of carbon and NATURE OF FERMENTATION. 259 hydrogen as the sugar of grapes, but two atoms less of oxygen ; and it is highly probable that it is produced from sugar of grapes, contained in those plants, in precisely the same manner as indigo-blue is converted into deoxidised white indigo. During the putrefaction of gluten, carbonic acid and pure hydrogen gas are evolved; phosphate, acetate, caseate, and lactate of ammonia being at the same time produced in such quantity, that the further decomposition of the gluten ceases. But when the supply of water is renewed, the decom- position begins again, and in addition to the salts just mentioned, carbonate of ammonia and a white crystalline matter resembling mica (caseous oxide) are formed, together with hydrosulphate of am- monia, and a mucilaginous substance coagulable by chlorine. Lactic acid is almost always pro- duced by the putrefaction of organic bodies. We may now compare fermentation and pu- trefaction with the decomposition which organic compounds suffer under the influence of a high temperature. Dry distillation would appear to be a process of combustion or oxidation going on in the interior of a substance, in which a part of the carbon unites with all or part of the oxygen of the com- pound, while other new compounds containing a large proportion of hydrogen are necessarily pro- duced. Fermentation may be considered as a process of combustion or oxidation of a similar kind, taking place in a liquid between the elements of s2 260 EREMACAUSIS OR DECAY. the same matter, at a very slightly elevated temper- ature ; and putrefaction as a process of oxidation, in which the oxygen of all the substances present comes into play. EREMACAUSIS OR DECAY. v In organic nature, besides the processes of de- composition named fermentation and putrefaction, another and not less striking class of changes oc- cur, which bodies suffer from the influence of the air. This is the act of gradual combination of the combustible elements of a body with the oxygen of the air ; a slow combustion or oxidation, to which we shall apply the term of eremacausis. The conversion of wood into humus, the forma- tion of acetic acid out of alcohol, nitrification, and numerous other processes, are of this nature. Vege- table juices of every kind, parts of animal and vege- table substances, moist sawdust, blood, &c., cannot be exposed to the air, without suffering immediately a progressive change of colour and properties, during which oxygen is absorbed These changes do not take place when water is excluded, or when the substances are exposed to the temperature of 32, and it has been observed that different bodies require different degrees of heat, in order to effect the absorption of oxygen, and, consequently, their eremacausis. The property of suffering this change is possessed in the highest degree by substances which contain nitrogen. CONDITIONS FOR ITS OCCURRENCE. 261 When vegetable juices are evaporated by a gentle heat in the air, a brown or brownish-black sub- stance is precipitated as a product of the action of oxygen upon them. This substance, which appears to possess similar properties from whatever juice it is obtained, has received the name of extractive matter; it is insoluble or very sparingly soluble in water, but is dissolved with facility by alkalies. By the action of air on solid animal or vegetable mat- ters, a similar pulverulent brown substance is formed, and is known by the name of humus. (Terreau.) The conditions which determine the commence- ment of eremacausis are of various kinds. Many organic substances, particularly such as are mix- tures of several more simple matters, oxidise in the air when simply moistened with water ; others not until they are subjected to the action of alkalies ; but the greatest part of them undergo this state of slow combustion or oxidation, when brought in contact with other decaying matters. The eremacausis of an organic matter is retarded or completely arrested by all those substances which prevent fermentation or putrefaction. Min- eral acids, salts of mercury, aromatic substances, empyreumatic oils, and oil of turpentine, possess a similar action in this respect. The latter sub- stances have the same effect on decaying bodies as on phosphuretted hydrogen, the spontaneous inflammability of which they destroy. 262 EREMACAUSIS OR DECAY. Many bodies which do not decay when moistened with water, enter into eremacausis when in contact with an alkali. Gallic acid, haematin, and many other compounds, may be dissolved in water and yet remain unaltered, but if the smallest quantity of a free alkali is present, they acquire the property of attracting oxygen, and are converted into a brown substance like humus, evolving very frequently at the same time carbonic acid. (Chevreul.) A very remarkable kind of eremacausis takes place in many vegetable substances, when they are exposed to the influence of air, water, and ammonia. They absorb oxygen very rapidly, and form splendid violet or red-coloured liquids, as in the case of orcin and erythrin. They now contain an azotised sub- stance, not in the form of ammonia. All these facts show that the action of oxygen seldom affects the carbon of decaying substances, and this corresponds exactly to what happens in combustion at high temperatures. It is well known, for example, that when no more oxygen is admitted to a compound of carbon and hydrogen than is suf- ficient to combine with its hydrogen, the carbon is not burned, but is separated as lamp-black ; while, if the quantity of oxygen is not sufficient even to consume all the hydrogen, new compounds are formed, such as naphthalin and similar matters, which contain a smaller proportion of hydrogen than those compounds of carbon and hydrogen which previously existed in the combustible substance. NATURE OF THE PROCESS. 263 There is no example of carbon combining di- rectly with oxygen at common temperatures, but numerous facts show that hydrogen, in certain states of condensation, possesses that property. Lamp- black which has been heated to redness may be kept in contact with oxygen gas, without forming carbonic acid ; but lamp-black, impregnated with oils which contain a large proportion of hydrogen, gradually becomes warm, and inflames sponta- neously. The spontaneous inflammability of the charcoal used in the fabrication of gunpowder has been correctly ascribed to the hydrogen which it contains in considerable quantity ; for during its reduction to powder, no trace of carbonic acid can be detected in the air surrounding it; it is not formed until the temperature of the mass has reached the red heat. The heat which produces the inflammation is therefore not caused by the oxidation of the carbon. The substances which undergo eremacausis may be divided into two classes. The first class com- prehends those substances which unite with the oxygen of the air, without evolving carbonic acid ; and the second, such as emit carbonic acid by ab- sorbing oxygen. When the oil of bitter almonds is exposed to the air, it absorbs two equivalents of oxygen, and is converted into benzoic acid ; but half of the oxygen absorbed combines with the hydrogen of the oil, 264 EREMACAUSIS OR DECAY. and forms water, which remains in union with the anhydrous benzoic acid. According to the experiments of Dobereiner, 160 parts of pyrogallic acid absorb 38*09 parts of oxygen when in contact with ammonia and water ; the acid being changed in consequence of this absorp- tion into a mouldy substance, which contains less oxygen than the acid itself. It is evident that the substance which is formed is not a higher oxide ; and it is found, on comparing the quantity of the oxygen absorbed with that of 'the hydrogen con- tained in the acid, that they are exactly in the pro- portions for forming water. When colourless orcin is exposed together with ammonia to the contact of oxygen gas, the beauti- ful red- coloured orcein is produced. Now, the only changes which take place here are, that the absorption of oxygen by the elements of orcin and ammonia causes the formation of water ; 1 equiva- lent of orcin CIS H12 O8, and I equivalent of ammonia, NH3 absorb 5 equivalents of oxygen, and 5 equivalents of water are produced, the composition of orcein being CIS H 10 O8 N. (Dumas.) In this case it is evident, that the oxygen absorbed has united merely with the hydrogen. But, although it appears very probable that the oxygen acts primarily and principally upon hydro- gen, the most combustible constituent of organic matter in the state of decay ; still it cannot thence NATURE OF THE PROCESS. 265 be concluded that the carbon is quite devoid of the power to unite with oxygen, when every particle of it is surrounded with hydrogen, an element with which the oxygen combines with greater facility. We know, on the contrary, that nitrogen, which cannot be made to combine with oxygen directly, is oxidised and forms nitric acid, when mixed with a large quantity of hydrogen, and burned in oxygen gas. In this case its affinity is evidently increased by the combustion of the hydrogen, which is in fact communicated to it. It is conceivable, that, in a similar manner, the carbon may be directly oxidised in several cases, obtaining from its contact with hydrogen in eremacausis a property which it does not itself possess at common temperatures. But the formation of carbonic acid during the eremacausis of bodies which contain hydrogen, must in most cases be ascribed to another cause. It appears to be formed in a manner similar to the formation of acetic acid, by the eremacausis of saiiculite of potash. This salt, when exposed to a moist atmosphere, absorbs 3 atoms of oxyen ; melanic acid is produced, a body resembling humus, in consequence of the formation of which, the elements of 1 atom of acetic acid are separated from the saliculous acid. An alkaline solution of hsematin being exposed to an atmosphere of oxygen, 0*2 Grm. absorb 28*6 cubic centimeters of oxygen gas in twenty-four 266 EREMACAUSIS OR DECAY. hours, the alkali acquiring at the same time 6 cubic centimeters of carbonic acid. (Chevreul.) But these 6 cubic 4 centimeters of carbonic acid contain only an equal volume of oxygen, so that it is certain from this experiment that f of the oxygen absorbed have not united with the carbon. It is highly probable, that during the oxidation of the hydrogen, a portion of the carbon had united with the oxygen contained in the haematin, and had separated from the other elements as carbonic acid. The experiments of De Saussure upon the decay of woody fibre show that such a sepa- ration is quite possible. Moist woody fibre evolved one volume of carbonic acid for every volume of oxygen which it absorbed. It has just been mentioned that carbonic acid contains its own volume of oxygen. Now, woody fibre con- tains carbon and the elements of water, so that the result of the action of oxygen upon it is exactly the same as if pure charcoal had combined directly with oxygen. But the characters of woody fibre show, that the elements of water are not contained in it in the form of water ; for, were this the case, starch, sugar, and gum, must also be considered as hydrates of carbon. But if the hydrogen does not exist in woody fibre in the form of water, the direct oxidation of the carbon cannot be considered as at all probable, without rejecting all the facts established NATURE OF THE PROCESS. 267 by experiment regarding the process of combus- tion at low temperatures. If we examine the action of oxygen upon such a substance as alcohol which contains a large quantity of hydrogen, we find most distinctly, that the direct formation of carbonic acid is the last stage of its oxidation, and that it is preceded by a series of changes, the last of which is a complete com- bustion of the hydrogen. Aldehyde, acetic acid, formic acid, oxalic acid, and carbonic acid, form a connected chain of products arising from the oxidation of alcohol; and the successive changes which this fluid experiences from the action of oxy- gen may be readily traced in them. Aldehyde is alcohol minus hydrogen ; acetic acid is formed by the direct union of aldehyde with oxygen. Formic acid and water are formed by the union of acetic acid with oxygen. When all the hydrogen is removed from this formic acid, oxalic acid is pro- duced ; and the latter acid is converted into carbonic acid by uniting with an additional portion of oxygen. All these products appear to be formed simultaneously, by the action of oxidising agents on alcohol ; but it can scarcely be doubted, that the formation of the last product, the carbonic acid, does not take place until all the hydrogen has been abstracted. The absorption of oxygen by drying oils certainly does not depend upon the oxidation of their carbon ; for in raw nut-oil, for example, which was not free 268 EREMACAUSIS OR DECAY. from mucilage and other substances,, only twenty- one volumes of carbonic acid were formed for every 146 volumes of oxygen gas absorbed. It must be remembered, that combustion or oxi- dation at low temperatures produces results quite similar to combustion at high temperatures with limited access of air. The most combustible element of a compound, which is exposed to the action of oxygen, must become oxidized first, for its superior combustibility is caused by its being enabled to unite with oxygen at a temperature at which the other elements cannot enter into that combination ; this property having the same effect as a greater affinity. The combustibility of potassium is no measure of its affinity for oxygen ; we have reason to believe that the attraction of magnesium and aluminium for oxygen is greater than that of potas- sium for the same element ; but neither of those metals oxidises either in air or water at common temperatures, whilst potassium decomposes water with great violence, and appropriates its oxygen. Phosphorus and hydrogen combine with oxygen at ordinary temperatures, the first in moist air, the second, when in contact with finely-divided plati- num ; while charcoal requires a red heat before it can enter into combination with oxygen. It is evident that phosphorus and hydrogen are more combustible than charcoal, that is, that their affi- nity for oxygen at common temperatures is greater ; and this is not the less certain, because it is found, NATURE OF THE PROCESS. 269 that carbon in certain other conditions shows a much greater affinity for oxygen than either of those substances. In putrefaction, the conditions are evidently present, under which the affinity of carbon for oxygen comes into play ; neither expansion, cohe- sion, nor the gaseous state, opposes it, whilst in ere- macausis all these restraints have to be overcome. The evolution of carbonic acid during the decay or eremacausis of animal or vegetable bodies, which are rich in hydrogen, must accordingly be ascribed to a transposition of the elements or dis- turbance in their attractions, similar to that which gives rise to the formation of carbonic acid in the processes of fermentation and putrefaction. The eremacausis of such substances is, therefore, a decomposition analogous to the putrefaction of azotised bodies. For in these there are two affini- ties at play ; the affinity of nitrogen for hydrogen, and that of carbon for oxygen, which facilitate the disunion of the elements. Now there are two affinities also in action in those bodies which decay with the evolution of carbonic acid. One of these affinities is the attraction of the oxygen of the air for the hydrogen of the substance, which corre- sponds to the attraction of nitrogen for the same element ; and the other is the affinity of the carbon of the substance for its oxygen, which is constant under all circumstances. When wood putrefies in marshes, carbon and 270 EREMACAUSIS OR DECAY. oxygen are separated from its elements in the form of carbonic acid, and hydrogen in the form of carbu- retted hydrogen. But when wood decays or putre- fies in the air, its hydrogen does not combine with carbon, but with oxygen, for which it has a much greater affinity at common temperatures. Now it is evident from the complete similarity of these processes, that decaying and putrefying bodies can mutually replace one another in their reciprocal actions. All putrefying bodies pass into the state of decay when exposed freely to the air ; and all decaying matters into that of putrefaction, when air is excluded. All bodies, likewise, in a state of decay are capable of inducing putrefaction in other bodies in the same manner as putrefying bodies them- selves do. EREMACAUSIS OR DECAY OF BODIES WHICH DO NOT CONTAIN NITROGEN I FORMATION OF ACETIC ACID. ALL those substances which appear to possess the property of entering spontaneously into fermenta- tion and putrefaction, do not in reality suifer those changes without some previous disturbance in the attraction of their elements. Eremacausis always precedes fermentation and putrefaction, and it is not until after the absorption of a certain quantity of oxygen that the signs of a transformation in the interior of the substances show themselves. OF BODIES DESTITUTE OF NITROGEN. 271 It is a very general error to suppose that organic substances have the power of undergoing change spontaneously, without the aid of an external cause. When they are not in a state of change, it is neces- sary, before they can assume that state, that the existing equilibrium of their elements should be disturbed; and the most common cause of this disturbance is undoubtedly the atmosphere which surrounds all bodies. The juices of the fruit or other part of a plant which very readily undergo decomposition, retain their properties unchanged as long as they are pro- tected from immediate contact with the air, that is as long as the cells or organs in which they are contained resist the influence of the air. It is not until after the juices have been exposed to the air, and have absorbed a certain quantity of oxygen, that the substances dissolved in them begin to be decomposed. The beautiful experiments of Gay-Lussac upon the fermentation of the juice of grapes, as well as the important practical improvements to which they have led, are the best proofs of the atmosphere having an influence upon the changes of organic substances. The juice of grapes which were expressed under a receiver filled with mercury, so that air was completely excluded, did not ferment. But when the smallest portion of air was introduced, a certain quantity of oxygen became absorbed, and fermentation immediately began. When the juice 272 EREMACAUSIS OR DECAY. was expressed from the grapes in contact with air, under the conditions therefore necessary to cause its fermentation, still this change did not ensue when the juice was heated in close vessels to the temperature of boiling water. When thus treated, it could be preserved for years without losing its property of fermenting. A fresh exposure to the air at any period caused it to ferment. Animal food of every kind, and even the most delicate vegetables, may be preserved unchanged if heated to the temperature of boiling water in vessels from which the air is completely excluded. Food thus prepared has been kept for fifteen years, and upon opening the vessels after this long time, has been found as fresh and well flavoured as when originally placed in them. The action of the oxygen in these processes of decomposition is very simple ; it excites changes in the composition of the azotised matters dissolved in the juices ; the mode of combination of the elements of those matters undergoes a disturbance and change in consequence of their contact with oxygen. The oxygen acts here in a similar manner to the friction or motion which effects the mutual decomposition of two salts, the crystallisation of salts from their solution, or the explosion of fulmi- nating mercury. It causes the state of rest to be converted into a state of motion. When this condition of intestine motion is once excited, the presence of oxygen is no longer OF BODIES DESTITUTE OF NITROGEN. 273 necessary. The smallest particle of an azotised body in this act of decomposition exercises an influence upon the particles in contact with it, and the state of motion is thus propagated through the substance. The air may now be completely excluded, but the fermentation or putrefaction proceeds unin- terruptedly to its completion. It has been remarked that the mere contact of carbonic acid is sufficient to produce fermentation in the juices of several fruits. The contact of ammonia and alkalies in general may be mentioned amongst the chemical condi- tions which determine the commencement of eremacausis ; for their presence causes many substances to absorb oxygen and to decay, in which neither oxygen nor alkalies alone produce that change. Thus alcohol does not combine with the oxygen of the air at common temperatures. But a solution of potash in alcohol absorbs oxygen with much rapidity, and acquires a brown colour. The alcohol is found after a short time to contain acetic acid, formic acid, and the products of the decomposition of aldehyde by alkalies, including aldehyde resin, which gives the liquid a brown colour. The most general condition for the production of eremacausis in organic matter is contact with a body already in the state of eremacausis or putre- faction. We have here an instance of true conta- 274 EREMACAUSIS OR DECAY gion ; for the communication of the state of com- bustion is in reality the effect of the contact. It is decaying wood which causes fresh wood around it to assume the same condition, and it is the very finely divided woody fibre in the act of decay, which in moistened gall-nuts converts the tannic acid with such rapidity into gallic acid. A most remarkable and decided example of this induction of combustion has been observed by De Samsure. It has already been mentioned, that moist woody fibre, cotton, silk, or vegetable mould, in the act of fermentation or putrefaction, converts oxygen gas which may surround it into carbonic acid, without change of volume. Now, De Sam- sure added a certain quantity of hydrogen gas to the oxygen, and observed a diminution in volume immediately after the addition. A part of the hydrogen gas had disappeared, and along with it a portion of the oxygen, but a corresponding quantity of carbonic acid gas had not been formed. The hydrogen and oxygen had disappeared in exactly the same proportion as that in which they combine to form water ; a true combustion of the hydrogen, therefore, had been induced by mere contact with matter in the state of eremacausis. The action of the decaying substance here produced results exactly similar to those effected by spongy platinum ; but that they proceeded from a different cause was shown by the fact,that the presence of carbonic oxide,which OF BODIES DESTITUTE OF NITROGEN. arrests completely the action of platinum on carburetted hydrogen, did not retard in the slightest degree the combustion of the hydrogen in contact with the decaying bodies. But the same bodies were found by De Saussure not to possess the property just described, before they were in a state of fermentation or decay ; and he has shown that even when they are in this state, the presence of antiseptic matter destroys com- pletely all their influence. Let us suppose a volatile substance containing a large quantity of hydrogen, to be substituted for the hydrogen gas in De Saussure's experiments. Now, the hydrogen in such compounds being con- tained in a state of greater condensation would suffer a more rapid oxidation, that is, its combus- tion would be sooner completed. This principle is in reality attended to in the manufactories in which acetic acid is prepared according to the new plan. In the process there adopted all the conditions are afforded for the eremacausis of alcohol, and for its consequent conversion into acetic acid. The alcohol is exposed to a moderate heat, and spread over a very extended surface, but these conditions are not sufficient to effect its oxidation. The alcohol must be mixed with a substance which is with facility changed by the oxygen of the air, and either enters into eremacausis by mere contact with oxygen, or by its fermentation or putrefac- tion yields products possessed of this property. T 2 276 EREMACAUSIS OR DECAY A small quantity of beer, acescent wine, a decoc- tion of malt, honey, and numerous other substances of this kind, possess the action desired. The difference in the nature of the substances which possess this property shows, that none of them can contain a peculiar matter which has the property of exciting eremacausis ; they are only the bearers of an action, the influence of which extends beyond the sphere of its own attractions. Their power consists in a condition of decomposition or eremacausis, which impresses the same condition upon the atoms of alcohol in its vicinity ; exactly as in the case of an alloy of platinum and silver dissolving in nitric acid, in which the platinum be- comes oxidised, by virtue of an inductive action which the silver in the act of its oxidation exercises upon it. The hydrogen of the alcohol is oxidised at the expense of the oxygen in contact with it, and forms water, evolving heat at the same time ; the re- sidue is aldehyde, a substance which has as great an affinity for oxygen as sulphurous acid, and combines, therefore, directly with it, producing acetic acid. EREMACAUSIS OF SUBSTANCES CONTAINING NITROGEN. NITRIFICATION. WHEN azotised substances are burned at high temperatures, their nitrogen does not enter into direct combination with oxygen. The knowledge of this fact is of assistance in considering the process of the eremacausis of such substances. Azotised OF BODIES CONTAINING NITROGEN. 277 organic matter always contains carbon and hydro- gen, both of which elements have a very strong affinity for oxygen. Now nitrogen possesses a very feeble affinity for that element, so that its compounds during their combustion present analogous phenomena to those which are observed in the combustion of substances containing a large proportion of hydrogen and car- bon ; a separation of the carbon of the latter sub- stances in an uncombined state takes place, and in the same way the substances containing nitrogen give out that element in its gaseous form. When a moist azotised animal matter is exposed to the action of the air, ammonia is always liberated, and nitric acid is never formed. But when alkalies or alkaline bases are present, a union of oxygen with the nitrogen takes place under the same circumstances, and nitrates are formed together with the other products of oxi- dation. Although we see the most simple means and direct methods employed in the great processes of decomposition which proceed in nature, still we find that the final result depends on a succession of actions, which are essentially influenced by the chemical nature of the bodies submitted to decom- position. When it is observed that the character of a sub- stance remains unaltered in a whole series of phe- nomena, there is no reason to ascribe a new cha- 278 EREMACAUSIS OR DECAY racter to it, for the purpose of explaining a single phenomenon, especially where the explanation of that according to known facts offers no difficulty. The most distinguished philosophers suppose that the nitrogen in an animal substance, when ex- posed to the action of air, water, and alkaline bases, obtains the power to unite directly with oxygen, and form nitric acid, but we are not acquainted with a single fact which justifies this opinion. It is only by the interposition of a large quantity of hydrogen in the state of combustion or oxidation, that nitrogen can be converted into an oxide. When a compound of nitrogen and carbon, such as cyanogen, is burned in oxygen gas, its carbon alone is oxidised ; and when it is conducted over a metallic oxide heated to redness^ an oxide of nitro- gen is very rarely produced, and never when the carbon is in excess. 'Kuhlmann found in his ex- periments, that it was only when cyanogen was mixed with an excess of oxygen gas, and conducted over spongy platinum, that nitric acid was gene- rated. Kuhlmann could not succeed in causing pure nitrogen to combine directly with oxygen, even under the most favourable circumstances ; thus, with the aid of spongy platinum at different tempera- tures, 'no union took place. The carbon in the cyanogen gas must, there- fore, have given rise to the combustion of the ni- trogen by induction. OF BODIES CONTAINING NITROGEN. 279 On the other hand we find that ammonia, which is a compound of hydrogen and nitrogen, cannot be exposed to the action of oxygen, without the formation of an oxide of nitrogen, and in conse- quence the production of nitric acid. It is owing to the great facility with which am- monia is converted into nitric acid, that it is so difficult to obtain a correct determination of the quantity of nitrogen in a compound subjected to analysis, in which it is either contained in the form of ammonia, or from which ammonia is formed by an elevation of temperature. For when ammonia is passed over red-hot oxide of copper, it is converted, either completely or partially, into binoxide of nitrogen. When ammoniacal gas is conducted over per- oxide of manganese or iron heated to redness, a large quantity of nitrate of ammonia is obtained, if the ammonia be in excess ; and the same decom- position happens, when ammonia and oxygen are together passed over red-hot spongy platinum. It appears, therefore, that the combination of oxygen with nitrogen occurs rarely during the com- bustion of compounds of the latter element with carbon, but that nitric acid is always a product when ammonia is present in the substance exposed to oxidation. The cause wherefore the nitrogen in ammonia ex- hibits such a strong disposition to become converted into nitric acid is undoubtedly, that the two products, which are the result of the oxidation of the consti- 280 EREMACAUSIS OR DECAY tuents of ammonia, possess the power of uniting with one another. Now this is not the case in the combustion of compounds of carbon and nitrogen ; here one of the products is carbonic acid, which, on account of its gaseous form, must oppose the combination of the oxygen and nitrogen, by pre- venting their mutual contact, while the superior affinity of its carbon for the oxygen during the act of its formation will aid in this effect. When sufficient access of air is admitted during the combustion of ammonia, water is formed as well as nitric acid, and both of these bodies com- bine together. The presence of water may, indeed, be considered as one of the conditions of nitrifica- tion, since nitric acid cannot exist without it. Eremacausis is a kind of putrefaction, differing from the common process of putrefaction, only in the part which the oxygen of the air plays in the transformations of the body in decay. When this is remembered, and when it is considered, that in the transposition of the elements of azotised bodies their nitrogen assumes the form of ammonia, and that in this form, nitrogen possesses a much greater disposition to unite with oxygen than it has in any of its other compounds ; we can with difficulty resist the conclusion, that ammonia is the general cause of nitrification on the surface of the earth. Azotised animal matter is not, therefore, the immediate cause of nitrification, it contributes to OF BODIES CONTAINING NITROGEN. 281 the production of nitric acid only in so far as it is a slow and continued source of ammonia. Now it has been shown in the former part of this work, that ammonia is always present in the atmo- sphere, so that nitrates might thence be formed in substances which themselves contained no azotised matter. It is known also, that porous substances possess generally the power of condensing ammonia ; there are few ferruginous earths which do not evolve ammoniacal products when heated to redness, and ammonia is the cause of the peculiar smell per- ceived upon moistening aluminous minerals. Thus, ammonia, by being a constituent of the atmosphere, is a very widely diffused cause of nitrification, which will come into play whenever the different conditions necessary for the oxidation of ammonia are com- bined. It is probable that other organic bodies in the state of eremacausis are the means of causing the combustion of ammonia ; at all events, the cases are very rare, in which nitric acid is generated from ammonia, in the absence of all matter capable of eremacausis. From the preceding observations on the causes of fermentation, putrefaction, and decay, we may now draw several conclusions calculated to correct the views generally entertained respecting the fermen- tation of wine and beer, and several other impor- tant processes of decomposition which occur in nature. 282 VINOUS FERMENTATION. ON VINOUS FERMENTATION : WINE AND BEER. It has already been mentioned, that fermenta- tion is excited in the juice of grapes by the access of air ; alcohol and carbonic acid being formed by the decomposition of the sugar contained in the fluid. But it was also stated, that the process once commenced, continues until all the sugar is com- pletely decomposed, quite independently of any further influence of the air. In addition to the alcohol and carbonic acid formed by the fermentation of the juice, there is also produced a yellow or grey insoluble substance, which contains a large quantity of nitrogen. It is this body which possesses the power of inducing fermentation in a new solution of sugar, and which has in consequence received the name si ferment. The alcohol and carbonic acid are produced from the elements of the sugar, and the ferment from those azotised constituents of the grape juice, which have been termed gluten, or vegetable albumen. According to the experiments of De Saussure, fresh impure gluten evolved, in five weeks, twenty- eight times its volume of a gas of which f consisted of carbonic acid, and of pure hydrogen gas ; ammoniacal salts of several organic acids were formed at the same time. Water must, therefore, be decomposed during the putrefaction of gluten ; the oxygen of this water must enter into combina- tion with some of its constituents, whilst hydrogen REPRODUCTION OF YEAST. 283 is liberated, a circumstance which happens only in decompositions of the most energetic kind. Neither ferment nor any substance similar to it is formed in this case ; and we have seen that in the fermenta- tion of saccharine vegetable juices, no escape of hydrogen gas takes place. It is evident that the decomposition which gluten suffers in an isolated state,, and that which it under- goes when dissolved in a vegetable juice, belong to two different kinds of transformations. There is reason to believe that its change to the insoluble state depends upon an absorption of oxygen, for its separation in this state may be effected under cer- tain conditions, by free exposure to the air, without the presence of fermenting sugar. It is known also that the juice of grapes, or vegetable juices in gene- ral, become turbid when in contact with air, before fermentation commences; and this turbidity is owing to the formation of an insoluble precipitate of the same nature as ferment. From the phenomena which have been observed during the fermentation of wort *, it is known with perfect certainty that ferment is formed from gluten at the same time that the transformation of the sugar is effected ; for the wort contains the azotised matter of the corn, namely, gluten in the same condition as it exists in the juice of grapes. The wort ferments by the addition of yeast, but after * Wort is an infusion of malt ; it consists of insoluble parts of this substance dissolved in water. TRANS. 284 VINOUS FERMENTATION. its decomposition is completed, the quantity of fer- ment or yeast is found to be thirty times greater than it was originally. Yeast from beer and that from wine, examined under the microscope, present the same form and general appearance. They are both acted on in the same manner by alkalies and acids, and possess the power of inducing fermentation anew in a solution of sugar ; in short, they must be considered as identical. The fact that water is decomposed during the putrefaction of gluten has been completely proved. The tendency of the carbon of the gluten to appro- priate the oxygen of water must also always be in action, whether the gluten is decomposed in a soluble or insoluble state. These considerations, therefore, as well as the circumstance which all the experiments made on this subject appear to point out, that the conversion of gluten to the insoluble state is the result of oxidation, lead us to conclude that the oxygen consumed in this process is derived from the elements of water, or from the sugar which contains oxygen and hydrogen in the same propor- tion as water. At all events, the oxygen thus con- sumed in the fermentation of wine and beer is not taken from the atmosphere. The fermentation of pure sugar in contact with yeast must evidently be a very different process from the fermentation of wort or must *. * The liquid expressed from grapes when fully ripe is called must. OILY AND ETHEREAL PRODUCTS. 285 In the former case, the yeast disappears during the decomposition of the sugar; but in the latter, a transformation of gluten is effected at the same time, by which ferment is generated. Thus yeast is destroyed in the one case, but is formed in the other. Now since no free hydrogen gas can be detected during the fermentation of beer and wine, it is evi- dent that the oxidation of the gluten, that is, its conversion into ferment, must take place at the cost either of the oxygen of the water, or of that of the sugar ; whilst the hydrogen which is set free must enter into new combinations, or by the deoxi- dation of the sugar, new compounds containing a large proportion of hydrogen, and small quantity of oxygen, together with the carbon of the sugar, must be formed. It is well known that wine and fermented liquors generally contain, in addition to the alcohol, other substances which could not be detected before their fermentation, and which must have been formed, therefore, during that process in a manner similar to the production of mannite. The smell and taste which distinguish wine from all other fermented liquids are known to depend upon an ether of a vola- tile and highly combustible acid, which is of an oily nature, and to which the name of (Enanthic ether has been given. It is also ascertained that the smell and taste of brandy from corn and potatoes is owing to a peculiar oil, the oil of potatoes. This oil is 286 VINOUS FERMENTATION. more closely allied to alcohol in its properties, than to any other organic substance. These bodies are products of the deoxidation of the substances dissolved in the fermenting liquids ; they contain less oxygen than sugar or gluten, but are remarkable for the large quantity of hydrogen which enters into their composition. (Enanthic acid contains an equal number of equivalents of carbon and hydrogen, exactly the same proportions of these elements, therefore, as sugar, but by no means the same proportion of oxygen. The oil of potatoes contains much more hydrogen. Although it cannot be doubted that these volatile liquids are formed by a mutual interchange of the elements of gluten and sugar, in consequence, therefore, of a true process of putrefaction, still it is certain, that other causes exercise an influence upon their production and peculiarities. The substances in wine to which its taste and smell are owing are generated during the fermen- tation of the juice of such grapes as contain a certain quantity of tartaric acid ; they are not found in wines which are free from all acid, or which con- tain a different organic acid, such as acetic acid. The wines of warm climates possess no odour ; wines grown in France have it in a marked degree, but in the wines from the Rhine the perfume is most intense. The kinds of grapes on the Rhine, which ripen very late, and scarcely ever completely, OILY AND ETHEREAL PRODUCTS. 287 such as the Riessling and Orleans, have the strongest perfume or bouquet, and contain, proportionally, a larger quantity of tartaric acid. The earlier grapes, such as the Rulander, and others, contain a large proportion of alcohol, and are similar to Spanish wines in their flavour, but they possess no bouquet. The grapes grown at the Cape from Riesslings transplanted from the Rhine, produce an excellent wine, which does not however possess the aroma which distinguishes Rhenish wine. It is evident from these facts, that the acid of wines, and their characteristic perfumes, have some connexion, for they are always found together, and it can scarcely be doubted that the presence of the former exercises a certain influence on the forma- tion of the latter. This influence is very plainly observed in the fermentation of liquids, which are quite free from tartaric acid, and particularly of those which are nearly neutral or alkaline, such as the mash* of potatoes or corn. The brandy obtained from corn and potatoes contains an ethereal oil of a similar composition in both, to which these liquors owe their peculiar smell. This oil is generated during the fermenta- tion of the mash ; it exists ready formed in the fer- mented liquids, and distils over with alcohol, when a gentle heat is applied. It is observed that a greater quantity of alcohol * Mash is the mixture of malt, potatoes, and water, in the mash tun, a large vessel in which it is infused. TRANS. 288 VINOUS FERMENTATION. is obtained when the mash is made quite neutral by means of ashes or carbonate of lime, but that the proportion of oil in the brandy is also increased. Now it is known that brandy made from potato starch, which has been converted into sugar by dilute sulphuric acid, is completely free from the potato oil, so that this substance must be gene- rated in consequence of a change suffered by the cellular tissue of the potatoes during their fermen- tation. Experience has shown that the simultaneous fermentation or putrefaction of the cellular tissue, by which this oil is generated, may be completely prevented in the fabrication of brandy from corn.* The same malt, which in the preparation of brandy yields a fluid containing the oil of which we are speaking, affords in the formation of beer a spirituous liquor, in which no trace of that oil can be detected. The principal difference in the preparation of the two liquids is, that in the fermen- tation of wort, an aromatic substance (hops) is added, and it is certain that its presence modifies the transformations which take place. Now it is known, that the volatile oil of mustard, and the empyreumatic oils, arrest completely the action of yeast ; and although the oil of hops does not possess * In the manufactory of M. Dubrunfaut, so considerable a quantity of this oil is obtained under certain circumstances from brandy made from potatoes, that it might be employed for the purpose of illumina- ting his whole manufactory. OILY AND ETHEREAL PRODUCTS. 289 this property, still it diminishes, in a great de- gree, the influence of decomposing azotised bodies upon the conversion of alcohol into acetic acid. There is, therefore, reason to believe that some aro- matic substances, when added to fermenting mix- tures, are capable of producing very various modi- fications in the nature of the products generated. Whatever opinion, however, may be held regard- ing the origin of the volatile odoriferous substances obtained in the fermentation of wine, it is quite certain that the characteristic smell of wine is owing to an ether of an organic acid, resembling one of the fatty acids. It is only in liquids which contain other very soluble acids, that the fatty acids and cenanthic acid are capable of entering into combination with the ether of alcohol, and of thus producing com- pounds of a peculiar smell. This ether is found in all wines which contain free acid, and is absent from those in which no acids are present. This acid, therefore, is the means by which the smell is produced ; since without its presence cenanthic ether could not be formed. The greatest part of the oil of brandy made from corn consists of a fatty acid not converted into ether; it dissolves oxide of copper and metallic oxides in general, and combines with the alkalies. The principal constituent of this oil is an acid identical in composition with cenanthic acid, but different in properties. (Mulder.) It is formed in u 290 VINOUS FERMENTATION. fermenting liquids, which, if they be acid, contain only acetic acid, a body which has no influence in causing other acids to form ethers. The oil of brandy made from potatoes is the hydrate of an organic base analogous to ether, and capable, therefore, of entering into combination with acids. It is formed in considerable quantity in fermenting liquids which are slightly alkaline, under circumstances, consequently, in which it is incapable of combining with an acid. The products of the fermentation and putrefac- tion of neutral vegetable and animal matters, are generally accompanied by substances of an offensive odour ; but the most remarkable example of the generation of a true ethereal oil is seen in the fer- mentation of the Herba centaurium minorius, a plant which possesses no smell. When it is ex- posed in water to a slightly elevated temperature it ferments, and emits an agreeable penetrating odour. By the distillation of the liquid, an ethereal oily substance of great volatility is obtained, which excites a pricking sensation in the eyes, and a flow of tears. (Biichner.) The leaves of the tobacco plant present the same phenomena ; when fresh they possess very little or no smell. When they are subjected to distillation with water, a weak ammoniacal liquid is obtained^ upon which a white fatty crystallizable substance swims, which does not contain nitrogen, and is quite destitute of smell. But when the same plant, after OILY AND ETHEREAL PRODUCTS. 291 being dried, is moistened with water, tied together in small bundles, and placed in heaps, a peculiar process of decomposition takes place. Fermentation commences, and is accompanied by the absorption of oxygen ; the leaves now become warm and emit the characteristic smell of prepared tobacco and snuff. When the fermentation is carefully promoted and too high a heat avoided, this smell increases and becomes more delicate ; and after the fermentation is completed, an oily azotised volatile matter called nicotine is found in the leaves. This substance nicotine, which possesses all the properties of a base, was not present before the fermentation. The different kinds of tobacco are distinguished from one another, like wines, by having very different odoriferous substances, which are generated along with the nicotine. We know that most of the blossoms and vegeta- ble substances which possess a smell, owe this pro- perty to a volatile oil existing in them ; but it is not less certain, that others emit a smell only when they undergo change or decomposition. Arsenic and arsenious acid are both quite in- odorous. It is only during their oxidation that they emit their characteristic odour of garlic. The oil of the berries of the elder-tree, many kinds of oil of turpentine, and oil of lemons, possess a smell only during their oxidation or decay. The same is the case with many blossoms ; and Geiger has u 2 292 VINOUS FERMENTATION. shown, that the smell of musk is owing to its gra- dual putrefaction and decay. It is also probable, that the peculiar odorous principle of many vegetable substances is newly formed during the fermentation of the saccharine juices of the plants. At all events, it is a fact, that very small quantities of the blossoms of the violet, elder, linden, or cowslip, added to a fer- menting liquid, are sufficient to communicate a very strong taste and smell, which the addition of the water distilled from a quantity a hundred times greater would not effect. The various kinds of beer manufactured in Bavaria are distinguished by dif- ferent flavours, which are given by allowing small quantities of the herbs and blossoms of particular plants to ferment along with the wort. On the Rhine, also, an artificial bouquet is often given to wine for fraudulent purposes, by the addition of several species of the sage and rue to the ferment- ing liquor ; but the perfume thus obtained differs from the genuine aroma, by its inferior durability, it being gradually dissipated. The juice of grapes grown in different cli- mates differs not only in the proportion of free acid which it contains, but also in respect of the quantity of sugar dissolved in it. The quantity of azotised matter in the juice seems to be the same in whatever part the grapes may grow; at least no difference has been observed in the amount of VARIOUS PROPERTIES OF WINES. 293 yeast formed during fermentation in the south of France, and on the Rhine. The grapes grown in hot climates, as well as the boiled juice obtained from them, are proportionally rich in sugar. Hence, during the fermentation of the juice, the complete decomposition of its azo- tised matters, and their separation in the insoluble state, are effected before all the sugar has been converted into alcohol and carbonic acid. A cer- tain quantity of the sugar consequently remains mixed with the wine in an m undecomposed state, the condition necessary for its further decomposi- tion being absent. The azotised matters in the juice of grapes of the temperate zones, on the contrary, are not com- pletely separated in the insoluble state, when the entire transformation of the sugar is effected. The wine of these grapes, therefore, does not contain sugar, but variable quantities of undecomposed gluten in solution. This gluten gives the wine the property of becoming spontaneously converted into vinegar, when the access of air is not prevented. For it absorbs oxygen and becomes insoluble ; and its oxidation is communicated to the alcohol, which is converted into acetic acid. By allowing the wine to remain at rest in casks with a very limited access of air, and at the lowest possible temperature, the oxidation of this azotised 294 FERMENTATION OF BEER. matter is effected without the alcohol undergoing the same change, a higher temperature being necessary to enable alcohol to combine with oxygen. As long as the wine in the stilling-casks deposits yeast, it can still be caused to ferment by the addi- tion of sugar, but old well-layed wine has lost this property, because the condition necessary for fer- mentation, namely, a substance in the act of decom- position or putrefaction, is no longer present in it. In hotels and other places .where the wine is drawn gradually from, a cask, and a proportional quantity of air necessarily introduced, its erema- causis, that is, its conversion into acetic acid, is prevented by the addition of a small quantity of sul- phurous acid. This acid, by uniting itself with the oxgyen of the air contained in the cask, or dis- solved in the wine, prevents the oxidation of the organic matter. The various kinds of beer differ from one another in the same way as the wines. English, French, and most of the German beers, are converted into vinegar when exposed to the action of air. But this property is not possessed by Bavarian beer, which may be kept in vessels only half-filled without acidifying or experiencing any change. This valuable quality is obtained for it by a peculiar management of the fermentation of the wort. The perfection of experimental know- ledge has here led to the solution of one of the THE BAVARIAN PROCESS. 295 most beautiful problems of the theory of fermen- tation. Wort is proportionally richer in gluten than in sugar, so that during its fermentation in the com- mon way, a great quantity of yeast is formed as a thick scum. The carbonic acid evolved during the process attaches itself to the particles of the yeast, by which they become specifically lighter than the liquid in which they are formed, and rise to its sur- face. Gluten in the act of oxidation comes in con- tact with the particles -of the decomposing sugar in the interior of the liquid. The carbonic acid from the sugar and insoluble ferment from the gluten are disengaged simultaneously, and cohere together. A great quantity of gluten remains dissolved in the fermented liquid, even after the transformation of the sugar is completed, and this gluten causes the conversion of the alcohol into acetic acid, on account of its strong disposition to attract oxygen, and to undergo decay. Now, it is plain, that with its separation, and that of all substances capable of attracting oxygen, the beer would lose the property of becoming acid. This end is completely attained in the process of fermentation adopted in Bavaria. The wort, after having been treated with hops in the usual manner, is thrown into very wide flat vessels, in which a large surface of the liquid is ex- posed to the air. The fermentation is then allowed to proceed while the temperature of the chambers 296 FERMENTATION OF BEER. in which the vessels are placed,, is never allowed to rise above from 45 to 50 F. The fermentation lasts from three to six weeks, and the carbonic acid evolved during its continuance is not in large bubbles which burst upon the surface of the liquid, but in small bubbles like those which escape from a liquid saturated by high pressure. The surface of the wort is scarcely covered with a scum, and all the yeast is deposited on the bottom of the vessel in the form of a viscous sediment. In order to obtain a clear conception of the great difference between the two kinds of fermentation, it may perhaps be sufficient to recall to mind the fact, that the transformation of gluten or other azo- tised matters is a process consisting of several stages. The first stage is the conversion of the gluten into insoluble ferment in the interior of the liquid, and as the transformation of the sugar goes on at the same time, carbonic acid and yeast are simulta- neously disengaged. It is known with certainty, that this formation of yeast depends upon oxygen being appropriated by the gluten in the act of decomposition ; but it has "not been sufficiently shown, whether this oxygen is derived from the water, sugar, or from the gluten itself ; whether it combines directly with the gluten, or merely with its hydrogen, so as to form water. For the purpose of obtaining a definite idea of the process, we may designate the first change as the stage of oxidation. THE BAVARIAN PROCESS. 29/ This oxidation of the gluten then, and the transpo- sition of the atoms of the sugar into alcohol and carbonic acid, are necessarily attendant on each other, so that if the one is arrested the other must also cease. Now, the yeast which rises to the surface of the liquid is not the product of a complete decomposi- tion, but is oxidised gluten still capable of under- going a new transformation by the transposition of its constituent elements. By virtue of this condition it has the power to excite fermentation in a solu- tion of sugar ; and if gluten be also present, the de- composing sugar induces its conversion into fresh yeast, so that, in a certain sense, the yeast appears to reproduce itself. Yeast of this kind is oxidised gluten in a state of putrefaction, and by virtue of this state it induces a similar transformation in the elements of the sugar. The yeast formed during the fermentation of Bavarian beer is oxidised gluten in a state of decay. The process of decomposition which its constituents are suffering, gives rise to a very protracted putrefac- tion (fermentation) in the sugar. The intensity of the action is diminished in so great a degree, that the gluten which the fluid still holds in solution takes no part in it ; the sugar in fermentation does not excite a similar state in the gluten. But the contact of the already decaying and pre- cipitated gluten or yeast, causes the eremacausis of 298 FERMENTATION OF BEER. the gluten dissolved in the wort ; oxygen gas is absorbed from the air, and all the gluten in solution is deposited as yeast. The ordinary frothy yeast may be removed from fermenting beer by filtration, without the fermen- tation being thereby arrested; but precipitated yeast of Bavarian beer cannot be removed without the whole process of its fermentation being inter- rupted. The beer ceases to ferment altogether, or, if the temperature is raised, undergoes the ordinary fermentation. The precipitated yeast does not excite ordinary fermentation, and consequently is quite unfitted for the purpose of baking, but the common frothy yeast can cause the kind of fermentation by which the former kind of yeast is produced. When common yeast is added to wort at a tempera- ture of between 40 and 45 F., a slow tranquil fer- mentation takes place, and a matter is deposited on the bottom of the vessel, which may be employed to excite new fermentation ; and when the same oper- ation is repeated several times in succession, the ordinary fermentation changes into that process by which only precipitated yeast is formed. The yeast now deposited has lost the property of exciting ordinary fermentation, but it produces the other process even at a temperature of 50 F. In wort subjected to fermentation, at a low tem- perature, with this kind of yeast, the condition THE BAVARIAN PROCESS. 299 necessary for the transformation of the sugar is the presence of that yeast; but for the conver- sion of gluten into ferment by a process of oxida- tion, something more is required. When the power of gluten to attract oxygen is increased by contact with precipitated yeast in a state of decay, the unrestrained access of air is the only other condition necessary for its own conversion into the same state of decay, that is for its oxida- tion. We have already seen that the presence of free oxygen and gluten are conditions which deter- mine the eremacausis of alcohol and its conversion into acetic acid, but they are incapable of exerting this influence at low temperatures. A low temper- ature retards the slow combustion of alcohol, while the gluten combines spontaneously with the oxygen of the air, just as sulphurous acid does when dis- solved in water. Alcohol undergoes no such change at low temperatures, but during the oxidation of the gluten in contact with it, is in the same condition as the gluten itself is placed in when sulphurous acid is added to the wine in which it is contained. The oxygen of the air unites both with the gluten and alcohol of wine not treated with sulphurous acid, but when this acid is present it combines with neither of them, being altogether absorbed by the acid. The same thing happens in the peculiar process of fermentation adopted in Bavaria. The oxygen of the air unites only with the gluten and not with the alcohol, although it would have com- 300 FERMENTATION OF BEER. bined with both at higher temperatures, so as to form acetic acid. Thus, then, this remarkable process of fermenta- tion with the precipitation of a mucous-like ferment consists of a simultaneous putrefaction and decay in the same liquid. The sugar is in the state of putrefaction, and the gluten in that of decay. Apperfs method of preserving food, and this kind of fermentation of beer, depend on the same principle. In the fermentation of beer after this manner, all the substances capable of decay are separated from it by means of an unrestrained access of air, while the temperature is kept sufficiently low to prevent the alcohol from combining with oxygen. The removal of these substances diminishes the tendency of the beer to become acescent, or in other words, to suffer a further transformation. In Apperfs mode of preserving food, oxygen is allowed to enter into combination with the sub- stance of the food, at a temperature at which decay, but neither putrefaction nor fermentation, can take place. With the subsequent exclusion of the oxygen and the completion of the decay, every cause which could effect further decomposi- tion of the food is removed. The conditions for putrefaction are rendered insufficient in both cases ; in the one by the removal of the substances sus- ceptible of decay, in the other by the exclusion of the oxygen which would effect it. THE BAVARIAN PROCESS. 301 It has been stated (page 296) to be uncertain, whether gluten during its conversion into common yeast, that is, into the insoluble state in which it separates from fermenting liquids, really combines directly with oxygen. If it does combine with oxygen, then the difference between gluten and ferment would be, that the latter would contain a larger proportion of oxygen. Now it is very diffi- cult to ascertain this, and even their analyses cannot decide the question. Let us consider, for example, the relations of alloxan and alloxantin to one another. Both of these bodies contain the same elements as gluten, although in different pro- portions. Now they are known to be convertible into each other, by oxygen being absorbed in the one case, and in the other extracted. Both are composed of absolutely the same elements, in equal proportions ; with the single exception, that al- loxantin contains 1 equivalent of hydrogen more than alloxan. When alloxantin is treated with chlorine and nitric acid, it is converted into alloxan, into a body, there- fore, which is alloxantin minus 1 equivalent of hydro- gen. If on the other hand a stream of sulphuretted hydrogen is conducted through alloxan, sulphur is precipitated, and alloxantin produced. It may be said, that in the first case hydrogen is abstracted, in the other added. But it would be quite as simple an explanation, if we considered them as oxides of the same radical ; the 1 alloxan being re- 302 FERMENTATION OF BEER. garded as a combination of a body composed of C8 N2 H2 O8 with 2 equivalents of water, and alloxantin as a combination of 3 atoms of water, with a compound consisting of C8 N2 H2 O7. The conversion of alloxan into alloxantin would in this case result from its eight atoms of oxygen being reduced to seven, while alloxan would be formed out of alloxantin, by its combining with an addi- tional atom of oxygen. Now, oxides are known which combine with water, and present the same phenomena as alloxan and alloxantin. But no compounds of hydrogen are known which form hydrates ; and custom, which rejects all dissimilarity until the claim to peculiarity is quite proved, leads us to prefer an opinion, for which there is no further foundation than that of analogy. The woad (Isatis tinctoria) and several species of the Nerium contain a substance similar in many respects to gluten, which is deposited as indigo blue, when an aqueous infusion of the dried leaves is exposed to the action of the air. Now it is very doubtful whether the blue insoluble indigo is an oxide of the colourless soluble indigo, or the latter a combination of hydrogen with the indigo blue. Dumas has found the same elements in both, except that the soluble compound contained 1 equi- valent of hydrogen more than the blue. In the same manner the soluble gluten may be considered a compound of hydrogen, which becomes ferment by losing a certain quantity of this ele- THE BAVARIAN PROCESS. 303 ment when exposed to the action of the oxygen of the air under favourable circumstances. At all events, it is certain that oxygen is the cause of the insoluble condition of gluten ; for yeast is not de- posited on keeping wine, or during the fermen- tation of Bavarian beer, unless oxygen has access to the fluid. Now whatever be the form in which the oxygen unites with the gluten whether it combines di- rectly with it or extracts a portion of its hydrogen, forming water the products formed in the interior of the liquid, in consequence of the conversion of the gluten into ferment, will still be the same. Let us suppose that gluten is a compound of another substance with hydrogen, then this hydrogen must be removed during the ordinary fermentation of must and wort, by combining with oxygen, exactly as in the conversion of alcohol into aldehyd by eremacausis. In both cases the atmosphere is excluded ; the oxygen cannot, then, be derived from the air, nei- ther can it be supplied by the elements of water, for it is impossible to suppose that the oxygen will separate from the hydrogen of water, for the pur- pose of uniting with the hydrogen of gluten, in order again to form water. The oxygen must, therefore, be obtained from the elements of sugar, a portion of which substance must, in order to the formation of ferment, undergo a different de- composition from that which produces alcohol. 304 FERMENTATION OF BEER. Hence a certain part of the sugar will not be converted into carbonic acid and alcohol, but will yield other products containing less oxygen than sugar itself contains. These products, as has already been mentioned, are the cause of the great difference in the qualities of fermented liquids, and particularly in the quantity of alcohol which they contain. Must and wort do not, therefore, in ordinary fer- mentation, yield alcohol in proportion to the quan- tity of sugar which they hold in solution, a part of the sugar being employed in the conversion of gluten into ferment, and not in the formation of alcohol. But in the fermentation of Bavarian beer all the sugar is expended in the production of alcohol ; and this is especially the case whenever the trans- formation of the sugar is not accompanied by the formation of yeast. It is quite certain that in the distilleries of brandy from potatoes, where no yeast is formed, or only a quantity corresponding to the malt which has been added, the proportion of alcohol and car- bonic acid obtained during the fermentation of the mash corresponds exactly to that of the carbon contained in the starch. It is also known that the volume of carbonic acid evolved during the fermen- tation of beet-roots gives no exact indication of the proportion of sugar contained in them, for less carbonic acid is obtained than the same quantity of pure sugar would yield. THE BAVARIAN PROCESS. 305 Beer obtained by the mode of fermentation adopted in Bavaria contains more alcohol, and pos- sesses more intoxicating properties, than that made by the ordinary method of fermentation, when the quantities of malt used are the same. The strong taste of the former beer is generally ascribed to its containing carbonic acid in larger quantity, and in a state of more intimate combination ; but this opinion is erroneous. Both kinds of beer are, at the conclusion of the fermentation, completely satu- rated with carbonic acid, the one as much as the other. Like all other liquids, they must both retain such a portion of the carbonic acid evolved as corresponds to their power of solution, that is, to their volumes. The temperature of the fluid during fermenta- tion has a very important influence on the quantity of alcohol generated. It has been mentioned, that the juice of beet-roots allowed to ferment at from 86 to 95 (30 to 35 C.) yield no alcohol ; and that afterwards, in the place of the sugar, mannite, a substance incapable of fermentation, and contain- ing very little oxygen, is found, together with lactic acid and mucilage. The formation of these pro- ducts diminishes in proportion as the temperature is lower. But in vegetable juices, containing nitro- gen, it is impossible to fix a limit, where the trans- formation of the sugar is undisturbed by any other process of decomposition. It is known that in the fermentation of Bavarian 306 FERMENTATION OF BEER. beer the action of the oxygen of the air, and the low temperature, cause complete transformation of the sugar into alcohol ; the cause which would pre- vent that result, namely, the extraction of the oxygen of part of the sugar by the gluten, in its conversion into ferment, being avoided by the in- troduction of oxygen from without. The quantity of matters in the act of transfor- mation is naturally greatest at the beginning of the fermentation of must and wort ; and all the phe- nomena which accompany the process, such as evo- lution of gas, and heat, are best observed at that time. These signs of the changes proceeding in the fluid dimmish when the greater part of the sugar has undergone decomposition ; but they must cease entirely before the process can be regarded as completed. The less rapid process of decomposition which succeds the violent evolution of gas, continues in wine and beer until the sugar has completely dis- appeared ; and hence it is observed, that the spe- cific gravity of the liquid diminishes during many months. This slow fermentation, in most cases, resembles the fermentation of Bavarian beer, the transformation of the dissolved sugar being in part the result of a slow and continued decomposition of the precipitated yeast ; but a complete separation of the azotised substances dissolved in it cannot take place when air is excluded. The great influence which a rational manage- THE BAVARIAN PROCESS. 307 ment of fermentation exercises upon the quality of beer is well known in several of the German states. In the grand-duchy of Hesse, for example, a con- siderable premium is offered for the preparation of beer, according to the Bavarian method ; and the premium is to be adjudged to any one who can prove that the beer brewed by him has lain for six months in the store-vats without becoming acid. Hundreds of casks of beer became changed to vinegar before an empirical knowledge of those conditions was obtained, the influence of which is rendered intelligible by the theory. Neither alcohol alone, nor hops, nor indeed both together, preserve beer from becoming acid. The better kinds of ale and porter in England are pro- tected from acidity, but at the loss of the interest of an immense capital. They are placed in large closed wooden vessels, the surfaces of which are covered with sand. In these they are allowed to lie for several years, so that they are treated in a manner exactly similar to wine during its ripening. A gentle diffusion of air takes place through the pores of the wood, but the quantity of azotised substances being very great in proportion to the oxygen which enters, they consume it, and prevent its union with the alcohol. But the beer treated in this way does not keep for two months without acidifying, if it be placed in smaller vessels, to which free access of the air is permitted. x2 308 DECAY DECAY OF WOODY FIBRE. The conversion of woody fibre into the sub- stances termed humus and mould is, on account of its influence on vegetation, one of the most re- markable processes of decomposition which occur in nature. Decay is not less important in another point of view ; for, by means of its influence on dead vege- table matter, the oxygen which plants retained during life is again restored to the atmosphere. The decomposition of woody fibre is effected in three forms, the results of which are different, so that it is necessary to consider each separately. The first takes place when it is in the moist con- dition, and subject to free uninterrupted access of air ; the second occurs when air is excluded ; and the third when the wood is covered with water, and in contact with putrefying organic matter. It is known that woody fibre may be kept under water, or in dry air, for thousands of years without suffering any appreciable change ; but that when brought into contact with air, in the moist condi- tion it converts the oxygen surrounding it into the same volume of carbonic acid, and is itself gradually changed into a yellowish brown, or black matter, of a loose texture. According to the experiments of De Saussure, 240 parts of dry sawdust of oak wood convert 10 cubic inches of oxygen into the same quantity of OF WOODY FIBRE. 309 carbonic acid, which contains 3 parts, by weight, of carbon; while the weight of the sawdust is di- minished by 15 parts. Hence 12 parts, by weight, of water, are at the same time separated from the elements of the wood. It has already been mentioned, that pure woody fibre contains carbon and the elements of water. Humus, however, is not produced by the decay of pure woody fibre, but by that of wood which con- tains foreign soluble and insoluble organic sub- stances, besides its essential constituent. The relative proportion of the component ele- ments are, on this account, different in oak wood and in beech, and the composition of both of these differs very much from woody fibre, which is the same in all vegetables. The difference, however, is so trivial, that it may be altogether neglected in the consideration of the questions which will now be brought under discussion ; besides, the quantity of the foreign substances is not constant, but varies according to the season of the year. According to the careful analysis of Gay-Lussac and Thenard, 100 parts of oak wood, dried at 212 (100 C.), from which all soluble substances had been extracted by means of water and alcohol, con- tained 52*53 parts of carbon, and *47'47 parts of hydrogen and oxygen, in the same proportion as they are contained in water. Now it has been mentioned that moist wood acts in oxygen gas exactly as if its carbon combined 310 DECAY directly with oxygen, and that the products of this action are carbonic acid and humus. If the action of the oxygen were confined to the carbon of the wood, and if nothing but carbon were removed from it, the remaining elements would ne- cessarily be found in the humus, unchanged except in the particular of being combined with less car- bon. The final result of the action would therefore be a complete disappearance of the carbon, whilst nothing but the elements of water would remain. But when decaying wood is subjected to exami- nation in different stages of its decay, the remark- able result is obtained, that the proportion of carbon in the different products augments. Consequently, if we did not take into consideration the evolution of carbonic acid under the influence of the air, the conversion of wood into humus might be viewed as a removal of the elements of water from the carbon. The analysis of mouldered oak wood, which was taken from the interior of the trunk of an oak, and possessed a chocolate brown colour and the struc- ture of wood, showed that 100 parts of it contained 53*36 parts of carbon and 46*44 parts of hydrogen and oxygen in the same relative proportions as in water. From an examination of mouldered wood of a light brown colour, easily reducible to a fine powder, and taken from another oak, it appeared that it contained 56*21 1 carbon and 43*789 water. These indisputable facts point out the similarity OF WOODY FIBRE. 311 of the decay of wood, with the slow combustion or oxidation of bodies which contain a large quantity of hydrogen. Viewed as a kind of combustion, it would indeed be a very extraordinary process, if the carbon combined directly with the oxygen ; for it would be a combustion in which the carbon of the burning body augmented constantly, instead of di- minishing. Hence it is evident that it is the hy- drogen which is oxidised at the expense of the oxygen of the air; while the carbonic acid is formed from the elements of the wood. Carbon never combines at common temperatures with oxy- gen, so as to form carbonic acid. In whatever stage of decay wood may be, its ele- ments must always be capable of being represented by their equivalent numbers. The following formula illustrates this fact with great clearness : C36 H22'O22 oak wood, according to Gay-Lussac and Thenard.* C35 H20 O20 humus from oak wood ( Meyer) .f C34 HIS O18 (Dr. JVilT).% It is evident from these numbers that for every two equivalents of hydrogen which is oxidised, two atoms of oxygen and one of carbon are set free. Under ordinary circumstances, woody fibre re- quires a very long time for its decay ; but this pro- cess is of course much accelerated by an elevated * The calculation gives 52'5 carbon, and 47-5 water. -}- The calculation gives 54 carbon and 46 water. The calculation gives 56 carbon and 44 water. 312 DECAY temperature and free unrestrained access of air. The decay, on the contrary, is much retarded by absence of moisture, and by the wood being sur- rounded with an atmosphere of carbonic acid, which prevents the access of air to the decaying matters. Sulphurous acid, and all antiseptic substances, arrest the decay of woody fibre. It is well known that corrosive sublimate is employed for the purpose of protecting the timber of ships from decay ; it is a substance which completely deprives vegeta- ble or animal matters, the most prone to decom- position, of their property of entering into fermen- tation, putrefaction, or decay. But the decay of woody fibre is very much ac- celerated by contact with alkalies or alkaline earths ; for these enable substances to absorb oxygen, which do not possess this power themselves ; alcohol (page 273), gallic acid, tannin, the vegetable colouring matters (page 261), and several other substances, are thus effected by them. Acids produce quite an opposite effect ; they greatly retard decay. Heavy soils, consisting of loam, retain longest the most important condition for the decay of the vegetable matter contained in it, viz., water ; but their impermeable nature prevents contact with the air. In moist sandy soils, particularly such as are composed of a mixture of sand and carbonate of lime, decay proceeds very quickly, it being aided by the presence of the slightly alkaline lime. OF WOODY FIBRE. 313 Now let us consider the decay of woody fibre during a very long period of time, and suppose that its cause is the gradual removal of the hydro- gen in the form of water, and the separation of its oxygen in that of carbonic acid. It is evident that if we subtract from the formula C36, H22, O22, the 22 equivalents of oxygen, with 11 equivalents of carbon, and 22 equivalents of hydrogen, which are supposed to be oxidised by the oxygen of the air, and separated in the form of water ; then from 1 atom of oak wood, 25 atoms of pure carbon will remain as the final product of the decay. In other words, 100 parts of oak, which contain 52*5 parts of carbon, will leave as a residue 37 parts of car- bon, which must remain unchanged, since carbon does not combine with oxygen at common tempera- tures. But this final result is never attained in the de- cay of wood under common circumstances ; and for this reason, that with the increase of the proportion of carbon in the residual humus, as in all decomposi- tions of this kind, its attraction for the hydrogen, which still remains in combination, also increases, until at length the affinity of oxygen for the hydro- gen is equalled, by that of the carbon for the same element. In proportion as the decay of woody fibre ad- vances, its property of burning with flame, or in other words, of developing carburetted hydrogen on the application of heat, diminishes. Decayed wood 314 DECAY OF WOODY FIBRE. burns without flame ; whence no other conclusion can be drawn, than that the hydrogen, which an- alysis shows to be present, is not contained in it in the same form as in wood. Decayed oak contains more carbon than fresh wood, but its hydrogen and oxygen are in the same proportion. We would naturally expect that the flame given out by decayed wood should be more brilliant, in proportion to the increase of its carbon, but we find, on the contrary, that it burns like tinder, ex- actly as if no hydrogen were present. For the purposes of fuel, decayed or diseased wood is of little value, for it does not possess the property of burning with flame, a property upon which the ad- vantages of common wood depend. The hydro- gen of decayed wood must consequently be sup- posed to be in the state of water ; for had it any other form, the characters we have described would not be possessed by the decayed wood. If we suppose decay to proceed in a liquid, which contains both carbon and hydrogen, then a com- pound containing still more carbon must be formed, in a manner similar to the production of the crys- talline colourless napthalin from a gaseous com- pound of carbon and ^hydrogen. And if the com- pound thus formed were itself to undergo further decay, the final result must be the separation of carbon in a crystalline form. Science can point to no process capable of ac- VEGETABLE MOULD. 315 counting for the origin and formation of diamonds, except the process of decay. Diamonds cannot be produced by the action of fire, for a high tempera- ture, and the presence of oxygen gas, would call into play their combustibility. But there is the greatest reason to believe that they are formed in the humid way, that is, in a liquid, and the process of decay is the only cause to which then* formation can with probability be ascribed. Amber, fossil resin, and the acids in mellite, are the products of vegetable matter which has suffered decomposition. They are found in wood or brown coal, and have evidently proceeded from the de- composition of substances which were contained in quite a different form in the living plants. They are all distinguished by the proportionally small quantity of hydrogen which they contain. The acid from the mellite (mellitic acid) contains pre- cisely the same proportions of carbon and oxygen as that from amber (succinic acid) ; they differ only in the proportion of their hydrogen. M. Bromeis* found that succinic acid might be artificially formed by the action of nitric acid on stearic acid, a true process of eremacausis ; the experiment was made in this laboratory (Giesseri). VEGETABLE MOULD. The term vegetable mould, in its general sig- nification, is applied to a mixture of disintegrated * Liebig's Annalen, Band xxxiv., heft 3. 316 VEGETABLE MOULD. minerals, with the remains of animal and vegetable substances. It may be considered as earth in which humus is contained in a state of decomposi- tion. Its action upon the air has been fully inves- tigated by Ingenhouss and De Saussure. When moist vegetable mould is placed in a ves- sel full of air, it extracts the oxygen therefrom with greater rapidity than decayed wood, and replaces it by an equal volume of carbonic acid. When this carbonic acid is removed and fresh air admitted, the same action is repeated. Cold water dissolves only To^rooth of its own weight of vegetable mould ; and the residue left on its evaporation consists of common salt with traces of sulphate of potash and lime, and a minute quan- tity of organic matter, for it is blackened when heated to redness. Boiling water extracts several substances from vegetable mould, and acquires a yellow or yellowish brown colour, which is dissipated by absorption of oxygen from the air, a black floc- culent deposit being formed. When the coloured solution is evaporated, a residue is left which be- comes black on being heated to redness, and after- wards yields carbonate of potash when treated with water. A solution of caustic potash becomes black when placed in contact with vegetable mould, and the addition of acetic acid to the coloured solution causes no precipitate or turbidity. But dilute sul- phuric acid throws down a light flocculent precipi- MOULDERING OF VEGETABLE SUBSTANCES. 317 tate of a brown or black colour, from which the acid can be removed with difficulty by means of water. When this precipitate,, after having been washed with water, is brought whilst still moist under a receiver filled with oxygen, the gas is absorbed with great rapidity ; and the same thing takes place when the precipitate is dried in the air. In the perfectly dry state it has entirely lost its solubility in water, and even alkalies dissolve only traces of it. It is evident, therefore, that boiling water extracts a matter from vegetable mould, which owes its solu- bility to the presence of the alkaline salts contained in the remains of plants. This substance is a product of the incomplete decay of woody fibre. Its composition is intermediate between woody fibre and humus into which it is converted, by being exposed in a moist condition to the action of the air. ON THE MOULDERING OF BODIES. PAPER, BROWN COAL, AND MINERAL COAL. The decomposition of wood, woody fibre, and all vegetable bodies when subjected to the action of water, and excluded from the air, is termed moul- dering. Wood- or brown-coal and mineral coal, are the remains of vegetables of a former world ; their appearance and characters show, that they are pro- 318 DECOMPOSITION OF WOOD, COAL, ETC. ducts of the processes of decomposition termed decay and putrefaction. We can easily ascertain by analysis the manner in which their constituents have been changed, if we suppose the greater part of their bulk to have been formed from woody fibre. But it is necessary before we can obtain a distinct idea of the manner in which coal is formed, to con- sider a peculiar change which woody fibre suffers by means of moisture, when partially or entirely excluded from the air. It is known, that when pure woody fibre, as linen, for example, is placed in contact with water, con- siderable heat is evolved, and the substance is con- verted into a soft friable mass which has lost all coherence. This substance was employed in the fabrication of paper before the use of chlorine, as an agent for bleaching. The rags employed for this purpose were placed in heaps, and it was observed, that on their becoming warm a gas was disengaged, and their weight diminished from 18 to 25 per cent. When sawdust moistened with water is placed in a closed vessel, carbonic acid gas is evolved in the same manner as when air is admitted. A true putrefaction takes place, the wood assumes a white colour, loses its peculiar texture, and is converted into a rotten friable matter. The white decayed wood found in the interior of trunks of dead trees which have been in IN CONTACT WITH WATER. 319 contact with water, is produced in the way just mentioned. An analysis of wood of this kind, obtained from the interior of the trunk of an oak, yielded, after having been dried at 212, Carbon 47-11 . . 48'14 Hydrogen 6*31 . . 6'06 Oxygen 45-31 . . 44'43 Ashes 1-27 . . 137 100-00 100-00 Now, on comparing the proportions obtained from these numbers with the composition of oak wood, according to the analysis of Gay-Lussac and Thenard, it is immediately perceived, that a certain quantity of carbon has been separated from the constituents of wood, whilst the hydrogen is, on the contrary, increased. The numbers obtained by the analysis correspond very nearly to the formula C33 H27 O24. (The calculation from this formula gives in 100 parts 47*9 carbon, 6'1 hydrogen, and 46 oxygen.) The elements of water have, therefore, become united with the wood, whilst carbonic acid is dis- engaged by the absorption of a certain quantity of oxygen. If the elements of 5 atoms of water and ,3 atoms of oxygen be added to the composition of the woody fibre of the oak, and 3 'atoms of carbonic acid deducted, the exact formula for white mouldered wood is obtained. 320 DECOMPOSITION OF WOOD, COAL, ETC. Wood C36 H22 O22 To this add 5 atoms of water , . . H 5 O 5 3 atoms of oxygen .... O 3 C36 H27 O30 Subtract from this 3 atoms Carbonic acid C 3 O 6 C33 H27 O24 The process of mouldering is, therefore, one of putrefaction and decay, proceeding simultaneously, in which the oxygen of the air and the component parts of water take part. But the composition of mouldered wood must change according as the access of oxygen is more or less prevented. White mouldered beech-wood yielded on analysis 47'67 carbon, 5*67 hydrogen, and 46*68 oxygen ; this corresponds to the formula C33 H25 O24. The decomposition of wood assumes, therefore, two different forms, according as the access of the air is free or restrained. In both cases carbonic acid is generated; and in the latter case, a certain quantity of water enters into chemical combination. It is highly probable that in this putrefactive process, as well as in all others, the oxygen of the water assists in the formation of the carbonic acid. Wood coal (brown coal of Werner) must have been produced by a process of decomposition similar to that of mouldering. But it is not easy to obtain wood coal suited for analysis, for it is gene- rally impregnated with resinous or earthy sub- stances, by which the composition of those parts which have been formed from woody fibre is essen- tially changed. PRODUCTION OF WOOD-COAL. 321 The wood coal which forms extensive layers in the Wetterau (a district in Hesse Darmstadt.) is distinguished from that found in other places, by possessing the structure of wood unchanged, and by containing no bituminous matter. This coal was subjected to analysis, a piece being selected upon which the annual circle could be counted. It was obtained from the vicinity of Laubach ; 100 parts contained Carbon . -. 57-28 Hydrogen . . 6*03 Oxygen . . 36'10 Ashes . . 0-59 10000 The large amount of carbon, and small quan- tity of oxygen, constitute the most obvious differ- ence between this analysis and that of wood. It is evident that the w^od which has undergone the change into coal must have parted with a certain portion of its oxygen. The proportion of these numbers are expressed by the formula C33 H21 016. (The calculation gives 57*5 carbon and 5'98 hydrogen.) When these numbers are compared with those obtained by the analysis of oak, it would appear that the brown coal was produced from woody fibre by the separation of one equivalent of hydro- gen, and the elements of three equivalents of car- bonic acid. 322 CONVERTION OF WOOD 1 atom wood . . . C36 H22 O22 Minus 1 atom hydrogen and 3 atoms > r, TJ, ~- arbonicacid > C3 Hl 6 WOOD COAL. C33 H2t O16 ; All varieties of wood coal, from whatever strata they may be taken, contain more hydrogen than wood does, and less oxygen than is necessary to form water with this hydrogen ; consequently they must all be produced by the same process of decom- position. The excess of hydrogen is either hydro- gen of the wood which has remained in it unchanged, or it is derived from some exterior source. The analysis of wood coal from Ringkuhl, near Cassel, where it is seldom found in pieces with the structure of wood, gave, when dried at 2 1 2, Carbon 62'60 . . 63*83 Hydrogen 5 "02 . 4*80 Oxygen 26*52 . . 25-51 Ashes 5-86 . 5.86 100-00 100-00 The proportions derived from these numbers cor- respond very closely to the formula, C32 H 1 5 O9, or they represent the constituents of wood, from which the elements of carbonic acid, water, and 2 equivalents hydrogen have been separated. C36 H22 O22 = Wood. Subtract C4 H7 O13 zz: 4 atoms carbonic acid + 5 atoms of water + 2 atoms of hydrogen. C82 HI5 O9 = Wood Coal from Ringkuhl. INTO BROWN OR WOOD-COAL. 323 The formation of both these specimens of wood coal appears from these formulae to have taken place under circumstances which did not entirely exclude the action of the air, and consequent oxi- dation and removal of a certain quantity of hydro- gen. Now the Laubacher coal is covered with a layer of basalt, and the coal of Ringkuhl was taken from the lowest seam of layers, which possess a thickness of from 90 to 120 feet ; so that both may be considered as well protected from the air. During the formation of brown coal, the ele- ments of carbonic acid have been separated from the wood either alone, or at the same time with a certain quantity of water. It is quite possible that the difference in the process of decomposition may depend upon the high temperature and pressure under which the decomposition took place. At least, a piece of wood assumed the character and appearance of Laubacher coal, after being kept for several weeks in the boiler of a steam engine, and had then precisely the same composition. The change in this case was effected in water, at a tem- perature of from 334 to 352 F. ( 1 50 160 C.), and under a corresponding pressure. The ashes of the wood amounted to 0*5 1 per cent. ; a little less, there- fore, than those of the Laubacher coal; but this must be ascribed to the peculiar circumstances under which it was formed. The ashes of plants exa- mined by Berthier amounted always to much more than this. Y 2 324 CONVERSION OF WOOD The peculiar process by which the decomposi- tion of these extinct vegetables has been effected, namely, a disengagement of carbonic acid from their substance, appears still to go on at great depths in all the layers of wood coal. At all events it is remarkable that springs impregnated with carbonic acid occur in many places, in the country between Meissner, in the electorate of Hesse, and the Eifel, which are known to possess large layers of wood coal. These springs of, mineral water are produced on the spot at which they are found ; the springs of common water meeting with carbonic acid during their ascent, and becoming impreg- nated with it. In the vicinity of the layers of wood coal at Salz- hausen (Hesse Darmstadt) an excellent acidulous spring of this kind existed a few years ago, and sup- plied all the inhabitants of that district ; but it was considered advantageous to surround the sides of the spring with sandstone, and the consequence was, that all the outlets to the carbonic acid were closed, for this gas generally gains access to the water from the sides of the spring. From that time to the present this valuable mineral water has disappeared, and in its place is found a spring of common water. Springs of water impregnated with carbonic acid occur at Schwalheim, at a very short distance from the layers of wood coal at Dorheim. M. Wil- helmi observed some time since, that they are INTO BROWN OR WOOD-COAL. 325 formed of common spring water which ascends from below, and of carbonic acid which issues from the sides of the spring. The same fact has been shown to be the case in the famed Fachinger spring, by M. Schapper. The carbonic acid gas from the springs in the Eifel is, according to Bischof, seldom mixed with nitrogen or oxygen, and is probably produced in a manner similar to that just described. At any rate the air does not appear to take any part in the formation of these acidulous springs. Their carbonic acid has evidently not been formed either by a combustion at high or low temperatures ; for if it were so, the gas resulting from the com- bustion would necessarily be mixed with f of nitrogen, but it does not contain a trace of this element. The bubbles of gas which escape from these springs are absorbed by caustic potash, with the exception of a residuum too small to be appre- ciated. The wood coal of Dorheim and Salzhausen must have been formed in the same way as that of the neighbouring village of Laubach ; and since the latter contains the exact elements of woody fibre, minus a certain quantity of carbonic acid, its com- position indicates very plainly the manner in which it has been produced. The coal of the upper bed is subjected to an in- cessant decay by the action of the air, by means 326 CONVERSION OF WOOD of which its hydrogen is removed in the same manner as in the decay of wood. This is recognised by the way in which it burns, and by the formation of carbonic acid in the mines. The gases which are formed in mines of wood- coal, and cause danger in their working, are not combustible or inflammable as in mines of mineral coal ; but they consist generally of carbonic acid gas, and are very seldom intermixed with combus- tible gases. Wood-coal from the middle bed of the strata at Ringkuhl gave on analysis 65*40 - 64'01 carbon and 4*75 4*76 * hydrogen ; the proportion of carbon here is the same as in specimens procured from greater depths, but that of the hydrogen is much less. Wood and mineral coal are always accompanied by iron pyrites (sulphuret of iron) or zinc blende (sulphuret of zinc); which minerals are still formed from salts of sulphuric acid, with iron or zinc, during the putrefaction of all vegetable matter. It is possible that the oxygen of the sulphates in the layers of wood-coal is the means by which the removal of the hydrogen is effected, since wood- coal contains less of this element than wood. According to the analysis of Richardson and * The analysis of brown coal from Ringkuhl, as well as all those of the same substance given in this work, have been executed in this laboratory by M. Kuhnert of Cassel. INTO MINERAL COAL. 327 Regnault, the composition of the combustible materials in splint coal from Newcastle, and cannel coal from Lancashire, is expressed by the formula C24 H13 O. When this is com pared with the com- position of woody fibre, it appears that these coals are formed from its elements, by the removal of a certain quantity of carburetted hydrogen and carbonic acid in the form of combustible oils. The composition of both of these coals is obtained by the subtraction of 3 atoms of carbu- retted hydrogen, 3 atoms of water, and 9 atoms of carbonic acid from the formula of wood. C36 H22 O22=: wood 3 atoms of carburetted hydrogen C3 H6 3 atoms of water . . H3 O3 9 atoms of carbonic acid C9 O18 Mineral coal C12 H9 O21 O24 H13 O Carburetted hydrogen generally accompanies all mineral coal ; other varieties of coal contain volatile oils which may be separated by distillation with water. (Reichenbach.) The origin of naphtha is owing to a similar process of decomposition. Cak- ing coal from Caresfield, near Newcastle, contains the elements of cannel coal, minus the consti- tuents of olefiant gas C4 H4. The inflammable gases which stream out of clefts in the strata of mineral coal, or in rocks of the coal formations, always contain carbonic acid, according to a recent examination by Bischojf, and also car- buretted hydrogen, nitrogen, and olefiant gas ; the 328 FORMATION OF COAL. last of which had not been observed, until its exist- ence in these gases was pointed out tyBischoff. The analysis of fire-damp after it had been treated with caustic potash showed its constituents to be, Gas from an abandoned Gerhard spas- Gas from a mine near Sa 8 e near Lu ~ mhie near Wallesweiler. "enthal. Liekwege. Vol. Vol. Vol. Light carburetted hydrogen &/-S6 83-08 89-10 Olefiantgas 6-32 1-98 16-11 Nitrogen gas 2*32 14-1)4 4-79 100-00 ' 100-00 100-00 The evolution of these gases proves that changes are constantly proceeding in the coal. It is obvious from this, that a continual removal of oxygen in the form of carbonic acid is effected from layers of wood-coal, in consequence of which the wood must approach gradually to the composi- tion of mineral coal. Hydrogen, on the contrary, is disengaged from the constituents of mineral coal in the form of a compound of carbo -hydrogen ; a complete removal of all the hydrogen would convert coal into anthracite. The formula C36 H22 O22, which is given for wood, has been chosen as the empirical expression of the analysis, for the purpose of bringing all the transformations which woody fibre is capable of undergoing under one common point of view. Now, although the correctness of this formula must be doubted, until we know with certainty the true constitution of woody fibre, this cannot have POISONS, CONTAGIONS, MIASMS. 329 the smallest influence on the account given of the. changes to which woody fibre must necessarily be subjected in order to be converted into wood or mineral coal. The theoretical expression refers to the quantity, the empirical merely to the relative proportion in which the elements of a body are united. Whatever form the first may assume, the empirical expression must always remain un- changed. ON POISONS, CONTAGIONS, AND MIASMS. A great many chemical compounds, some derived from inorganic nature, and others formed in animals and plants, produce peculiar changes or diseases in the living animal organism. They destroy the vital functions of individual organs ; and when their action attains a certain degree of intensity, death is the consequence. The action of inorganic compounds, such as acids, alkalies, metallic oxides, and salts, can in most cases be easily explained. They either destroy the con- tinuity of particular organs, or they enter into com- bination with their substance. The action of sul- phuric, muriatic, and oxalic acids, hydrate of potash, and all those substances which produce the direct destruction of the organs with which they come into contact, may be compared to a piece of iron, which can cause death by inflicting an injury on particular organs, either when heated to redness, or when in the form of a sharp knife. 330 POISONS, CONTAGIONS. MIASMS. Such substances are not poisons in the limited sense of the word, for their injurious action depends merely upon their condition. The action of the proper inorganic poisons is owing, in most cases, to the formation of a chemical compound by the union of the poison with the constituents of the organ upon which it acts ; it is owing to an exercise of a chemical affinity more powerful than the vitality of the organ. It is well to consider the action of inorganic substances in general, in order to obtain a clear conception of the mode of action of those which are poisonous. We find that certain soluble com- pounds, when presented to different parts of the body, are absorbed by the blood, whence they are again eliminated by the organs of secretion, either in a changed or in an unchanged state. Iodide of potassium, sulpho-cyanuret of potas- sium, ferro-cyanuret of potassium, chlorate of pot- ash, silicate of potash, and all salts with alkaline bases, when administered internally to man and animals in dilute solutions, or applied externally, may be again detected in the blood, sweat, chyle, gall, and splenic veins ; but all of them are finally excreted from the body through the urinary pas- sages. Each of these substances, in its transit, produces a peculiar disturbance in the organism in other words, they exercise a medicinal action upon it, but they themselves suffer no decomposition. If any EFFECTS OF SALTS ON THE ORGANISM. 331 of these substances enter into combination with any part of the body, the union cannot be of a permanent kind; for their re-appearance in the urine shows that any compounds thus formed must have been again decomposed by the vital processes. Neutral citrates, acetates, and tartrates of the alkalies, suffer change in their passage through the organism. Their bases can indeed be detected in the urine, but the acids have entirely disappeared, and are replaced by carbonic acid which has united with the bases. (Gilbert Blane and Wohler.) The conversion of these salts of organic acids into carbonates, indicates that a considerable quan- tity of oxygen must have united with their ele- ments. In order to convert 1 equivalent of acetate of potash into the carbonate of the same base, 8 equivalents of oxygen must combine with it, of which either 2 or 4 equivalents (according as an acid or neutral salt is produced) remain in com- bination with the alkali ; whilst the remaining 6 or 4 equivalents are disengaged as free carbonic acid. There is no evidence presented by the organism itself, to which these salts have been administered, that any of its proper constituents have yielded so great a quantity of oxygen as is necessary for their conversion into carbonates. Their oxidation can, therefore, only be ascribed to the oxygen of the air. During the passage of these salts through the lungs, their acids take part in the peculiar process 332 POISONS, CONTAGIONS, MIASMS. of eremacausis which proceeds in that organ ; a certain quantity of the oxygen gas inspired unites with their constituents, and converts their hydro- gen into water, and their carbon into carbonic acid. Part of this latter product (1 or 2 equiva- lents) remains in combination with the alkaline base, forming a salt which suffers no further change by the process of oxidation ; and it is this salt which is separated by the kidneys or liver. It is manifest that the presence of these organic salts in the blood must produce a change in the process of respiration. A part of the oxygen in- spired, which usually combines with the constitu- ents of the blood, must, when they are present, combine with their acids, and thus be prevented from performing its usual office. The immediate consequence of this must be the formation of ar- terial blood in less quantity, or in other words, the process of respiration must be retarded. Neutral acetates, tartrates, and citrates placed in contact with the air, and at the same time with animal or vegetable bodies in a state of eremacausis, produce exactly the same effects as we have de- scribed them to produce in the lungs. They par- ticipate in the process of decay, and are converted into carbonates just as in the living body. If im- pure solutions of these salts in water are left exposed to the air for any length of time, their acids are gradually decomposed, and at length entirely dis appear. EFFECTS OF SALTS ON THE ORGANISM. 333 Free mineral acids, or organic acids which are not volatile, and salts of mineral acids with alka- line bases, completely arrest decay when added to decaying matter in sufficient quantity ; and when their quantity is small, the process of decay is pro- tracted and retarded. They produce in living bodies the same phenomena as the neutral organic salts, but their action depends upon a different cause. The absorption by the blood of a quantity of an inorganic salt sufficient to arrest the process of eremacausis in the lungs, is prevented by a very remarkable property of all animal membranes, skin, cellular tissue, muscular fibre, &c. ; namely, by their incapability of being permeated by con- centrated saline solutions. It is only when these solutions are diluted to a certain degree with water that they are absorbed by animal tissues. A dry bladder remains more or less dry in satu- rated solutions of common salt, nitre, ferro-cyanuret of potassium, sulpho-cyanuret of potassium, sul- phate of magnesia, chloride of potassium, and sul- phate of soda. These solutions run off its surface in the same manner as water runs from a plate of glass besmeared with tallow. Fresh flesh, over which salt has been strewed, is found after 24 hours' swimming in brine, although not a drop of water has been added. The water has been yielded by muscular fibre itself, and having 334 POISONS, CONTAGIONS, MIASMS. dissolved the salt in immediate contact with it, and thereby lost the power of penetrating animal sub- stances, it has on this account separated from the flesh. The water still retained by the flesh con- tains a proportionally small quantity of salt, having that degree of dilution at which a saline fluid is capable of penetrating animal substances. This property of animal tissues is taken advan- tage of in domestic economy for the purpose of re- moving so much water from meat that a sufficient quantity is not left to enable it to enter into pu- trefaction. In respect of this physical property of animal tissues, alcohol resembles the inorganic salts. It is incapable of moistening, that is, of penetrating animal substances, and possesses such an affinity for water as to extract it from moist substances. When a solution of a salt, in a certain degree of dilution, is introduced into the stomach, it is ab- sorbed ; but a concentrated saline solution, in place of being itself absorbed, extracts water from the organ, and a violent thirst ensues. Some inter- change of water and salt takes place in the stomach ; the coats of this viscus yield water to the solution, a part of which having previously become sufficiently diluted, is, on the other hand, absorbed. But the greater part of the concentrated solution of salt remains unabsorbed, and is not removed by the urinary passages ; it consequently enters the intes- INORGANIC POISONS. 335 tines and intestinal canal, where it causes a dilution of the solid substance deposited there, and thus acts as a purgative. Each of the salts just mentioned possess this purgative action, which depends on a physical pro- perty shared by all of them ; but besides this they exercise a medicinal action, because every part of the organism with which they come in contact absorbs a certain quantity of them. The composition of the salts has nothing to do with their purgative action ; it is quite a matter of indifference as far as the mere production of this action is concerned (not as to its intensity), whether the base be potash or soda, or in many cases lime and magnesia; and whether the acid be phos- phoric, sulphuric, nitric, or hydrochloric. Besides these salts, the action of which does not depend upon their power of entering into combi- nation with the component parts of the organism ; there is a large class of others which, when intro- duced into the living body, effect changes of a very different kind, and produce diseases or death, ac- cording to the nature of these changes, without effecting a visible lesion of any organs. These are the true inorganic poisons, the action of which depends upon their power of forming permanent compounds with the substance of the membranes, and muscular fibre. Salts of lead, iron, bismuth, copper, and mer- cury, belong to this class. 336 POISONS, CONTAGIONS, MIASMS. When solutions of these salts are treated with a sufficient quantity of albumen, milk, muscular fibre, and animal membranes, they enter into com- bination with those substances, and lose their own solubility ; while the water in which they were dis- solved loses all the salt which it contained. The salts of alkaline bases extract water from animal substances ; whilst the salts of the heavy metallic oxides are, on the contrary, extracted from the water, for they enter into combination with the animal matters. Now, when these substances are administered to an animal, they lose their solubility by entering into combination with the membranes, cellular tissue, and muscular fibre ; but in very few r cases can they reach the blood. All experiments instituted for the purpose of determining whether they pass into the urine have failed to detect them in that secretion. In fact, during their pas- sage through the organism, they come into contact with many substances by which they are retained. The action of corrosive sublimate and arsenious acid is very remarkable in this respect. It is known that these substances possess, in an eminent degree, the property of entering into combination with all parts of animal and vegetable bodies, ren- dering them at the same time insusceptible of decay or putrefaction. Wood and cerebral sub- stance are both bodies which undergo change with great rapidity and facility when subject to the INORGANIC POISONS. 33/ influence of air and water ; but if they are digested for some time with arsenious acid or corrosive sub- limate, they may subsequently be exposed to all the influence of the atmosphere without altering in colour or appearance. It is further known that those parts of a body, which come in contact with these substances during poisoning, and which therefore enter into combi- nation with them, do not afterwards putrefy ; so that there can be no doubt regarding the cause of their poisonous qualities. It is obvious that if arsenious acid and corrosive sublimate are not prevented by the vital principle from entering into combination with the component parts of the body, and consequently from rendering them incapable of decay and putrefaction, they must deprive the organs of the principal property which appertains to their vital condition, viz. that of suf- fering and effecting transformations ; or, in other words, organic life must be destroyed. If the poisoning is merely superficial, and the quantity of the poison so small, that only individual parts of the body which are capable of being regenerated have entered into combination with it, then eschars are produced a phenomenon of a secondary kind the compounds of the dead tissues with the poison being thrown off by the healthy parts. From these considerations it may readily be inferred that all internal signs of poisoning are variable and un- certain ; for cases may happen, in which no apparent z 338 POISONS, CONTAGIONS, MIASMS. indication of change can be detected by simple observations of the parts, because, as has been already remarked, death may occur without the destruction of any organs. When arsenious acid is administered in solution, it may enter into the blood. If a vein is exposed and surrounded with a solution of this acid, every blood-globule will combine with it, that is, will become poisoned. The compounds of arsenic, which have not the property of entering into combination with the tissues of the organism, are without influence on life, even in large doses. Many insoluble basic salts of arsenious acid are known not to be poison- ous. The substance called alkargen, discovered by Bunsen, which contains a very large quantity of arsenic, and approaches very closely in composition to the organic arsenious compounds found in the body, has not the slightest injurious action upon the organism. These considerations enable us to fix with toler- able certainty the limit at which the above sub- stances cease to act as poisons. For since their combination with organic matters must be regu- lated by chemical laws, death will inevitably result, when the organ in contact with the poison finds sufficient of it to unite with atom for atom ; whilst if the poison is present in smaller quantity, a part of the organ will retain its vital functions. INORGANIC POISONS. 339 According to the experiments of Mulder* the equivalent in which fibrin combines with muriatic acid, and with the oxides of lead and copper, is ex- pressed by the number 6361. It may be assumed therefore approximatively, that a quantity of fibrin corresponding to the number 6361 combines with 1 equivalent of arsenious acid, or 1 equivalent of corrosive sublimate. When 6361 parts of anhydrous fibrin are com- bined with 30,000 parts of water, it is in the state in which it is contained in muscular fibre or blood in the human body. 100 grains of fibrin in this condition would form a neutral compound of equal equivalents with 3^ - grains of arsenious acid, and 5 grains of corrosive sublimate. The atomic weight of the albumen of eggs and of the blood deduced from the analysis of the com- pound which it forms with oxide of silver is 7447, and that of animal gelatin 5652. 100 grains of albumen containing all the water with which it is combined in the living body, should consequently combine with 1 \ grain of arsenious acid. These proportions, which may be considered as the highest which can be adopted, indicate the remarkably high atomic weights of animal sub- stances, and at the same time teach us what very small quantities of arsenious acid or corrosive subli- mate are requisite to produce deadly effects. * PoggendorfF's Annalen, Band xl. S. 259. z 2 340 POISONS, CONTAGIONS, MIASMS. All substances administered as antidotes in cases of poisoning, act by destroying the power which arsenious acid and corrosive sublimate possess, of entering into combination with animal matters, and of thus acting as poisons. Unfortunately no other body surpasses them in that power, and the compounds which they form can only be broken up by affinities so energetic, that their action is as injurious as that of the above-named poisons them- selves. The duty of the physician consists, there- fore, in his causing those parts of the poison which may be free and still uncombined, to enter into combination with some other body, so as to pro- duce a compound incapable of being decomposed or digested in the same conditions. Hydrated peroxide of iron is an invaluable substance for this purpose. When the action of arsenious acid or corrosive sublimate is confined to the surface of an organ, those parts only are destroyed which enter into combination with it ; an eschar is formed which is gradually thrown off. Soluble salts of silver would be quite as deadly a poison as corrosive sublimate, did not a cause exist in the human body by which their action is prevented, unless their quantity is very great. This cause is the presence of common salt in all animal liquids. Nitrate of silver, it is well known, com- bines with animal substances, in the same manner as corrosive sublimate, and the compounds formed INORGANIC POISONS. 341 by both; are exactly similar in the character of being incapable of decay or putrefaction. When nitrate of silver in a state of solution is ap- plied to skin or muscular fibre, it combines with them instantaneously ; animal substances dissolved in any liquid are precipitated by it, and rendered insolu- ble, or as it is usually termed they are coagulated. The compounds thus formed are colourless, and so stable that they cannot be decomposed by other powerful chemical agents. They are blackened by exposure to light, like all other compounds of silver, in consequence of a part of the oxide of silver which they contain being reduced to the metallic state. Parts of the body which have united with salts of silver, no longer belong to the living organism, for their vital functions have been ar- rested by combination with oxide of silver ; and if they are capable of being reproduced, the neigh- bouring living structures throw them off in the form of an eschar. When nitrate of silver is introduced into the stomach, it meets with common salt and free mu- riatic acid ; and if its quantity is not too great, it is immediately converted into chloride of silver a substance which is absolutely insoluble in pure water. In a solution of salt or muriatic acid, how- ever, chloride of silver does dissolve in extremely minute quantity; and it is this small part which exercises a medicinal influence when nitrate of sil- ver is administered ; the remaining chloride of silver 342 POISONS, CONTAGIONS, MIASMS. is eliminated from the body in the ordinary way. Solubility is necessary to give efficacy to any sub- stance in the human body. The soluble salts of lead possess many properties in common with the salts of silver and mercury ; but all compounds of lead with organic matters are capable of decomposition by dilute sulphuric acid. The disease called painter's colic is unknown in all manufactories of white lead in which the workmen are accustomed to take as a preservative sulphuric acid-lemonade (a solution of sugar rendered acid by sulphuric acid). The organic substances which have combined in the living body with metallic oxides or metallic salts, lose their property of imbibing water and re- taining it, without at the same time being rendered incapable of permitting liquids to penetrate through their pores. A strong contraction and shrinking of a surface is the general effect of contact with these metallic bodies. But corrosive sublimate, and seve- ral of the salts of lead, possess a peculiar property, in addition to those already mentioned. When they are present in excess, they dissolve the first formed insoluble compounds, and thus produce an effect quite the reverse of contraction, namely, a softening of the part of the body on which they have acted. Salts of oxide of copper, even when in combina- tion with the most powerful acids, are reduced by many vegetable substances, particularly such as ORGANIC POISONS. 343 sugar and honey, either into metallic copper, or into the red suboxide, neither of which enters into combination with animal matter. It is well known that sugar has been long employed as the most convenient antidote for poisoning by copper. With respect to some other poisons, namely, hydrocyanic acid and the organic bases strychnia and brucia, we are acquainted with no facts calcu- lated to elucidate the nature of their action. It may, however, be presumed with much certainty, that experiments upon their mode of action on different animal substances, would very quickly lead to the most satisfactory conclusions regarding the cause of their poisonous effects. There is a peculiar class of substances, which are generated during certain processes of decomposi- tion, and which act upon the animal economy as deadly poisons, not on account of their power of entering into combination with it, or by reason of their containing a poisonous material, but solely by virtue of their peculiar condition. In order to attain to a clear conception of the mode of action of these bodies, it is necessary to call to mind the cause on which we have shown the phenomena of fermentation, decay, and putrefaction, to depend. This cause may be expressed by the following law, long since proposed by La Place and Berthollet, although its truth with respect to chemical phe- nomena has only lately been proved. " A molecule set 344 POISONS, CONTAGIONS^ MIASMS. in motion by any power can impart its onm motion to another molecule with which it may be in contact." This is a law of dynamics, the operation of which is manifest in all cases, in which the resistance (force, affinity, or cohesion) opposed to the motion is not sufficient to overcome it. We have seen that ferment or yeast is a body in the state of decomposition, the atoms of which, consequently, are in a state of motion or transposi- tion. Yeast placed in contact with sugar, com- municates to the elements of that compound the same state, in consequence of which, the consti- tuents of the sugar arrange themselves into new and simpler forms, namely, into alcohol and carbonic acid. In these new compounds the elements are united together by stronger affinities than they were in the sugar, and therefore under the con- ditions in which they were produced further de- composition is arrested. We know, also, that the elements of sugar assume totally different arrangements, when the substances which excite their transposition are in a different state of decomposition from the yeast just men- tioned. Thus, when sugar is acted on by rennet or putrefying vegetable juices, it is not converted into alcohol and carbonic acid, but into lactic acid, mannite, and gum. Again, it has been shown, that yeast added to a solution of pure sugar gradually disappears, but that when added to vegetable juices which contain gluten ORGANIC POISONS. 345 as well as sugar, it is reproduced by the decompo- sition of the former substance. The yeast with which these liquids are made to ferment, has itself been originally produced from gluten. The conversion of gluten into yeast in these vegetable juices is dependent on the decomposition (fermentation) of sugar ; for, when the sugar has completely disappeared, any gluten which may still remain in the liquid, does not suffer change from contact with the newly-deposited yeast, but retains all the characters of gluten. Yeast is a product of the decomposition of gluten ; but it passes into a second stage of decomposition when in contact with water. On account of its being in this state of further change, yeast excites fermentation in a fresh solution of sugar, and if this second saccharine fluid should contain gluten, (should it be wort, for example,) yeast is again generated in consequence of the transposition of the elements of the sugar exciting a similar change in this gluten. After this explanation, the idea that yeast repro- duces itself as seeds reproduce seeds, cannot for a moment be entertained. From the foregoing facts it follows, that a body in the act of decomposition (it may be named the exciter), added to a mixed fluid in which its consti- tuents are contained, can reproduce itself in that fluid, exactly in the same manner as new yeast is 346 POISONS, CONTAGIONS, MIASMS. produced when yeast is added to liquids containing gluten. This must be more certainly effected when the liquid acted upon contains the body by the metamorphosis of which the exciter has been originally formed. It is also obvious, that if the exciter be able to impart its own state of transformation to one only of the component parts of the mixed liquid acted upon, its own reproduction may be the consequence of the decomposition of this one body. This law may be applied to organic substances forming part of the animal organism. We know that all the constituents of these substances are formed from the blood, and that the blood by its nature and constitution is one of the most complex of all existing matters. Nature has adapted the blood for the reproduc- tion of every individual part of the organism ; its principal character consists in its component parts being subordinate to every attraction. These are in a perpetual state of change or transformation, which is effected in the most various ways through the influence of the different organs. The individual organs, such as the stomach, cause all the organic substances conveyed to them which are capable of transformation to assume new forms. The stomach compels the elements of these substances to unite into a compound fitted for the formation of the blood. But the blood possesses no power of causing transformations ; on the con- PUTRID POISONS. 347 trary, its principal character consists in its readily suffering transformations ; and no other matter can be compared in this respect with it. Now it is a well-known fact, that when blood, cerebral substance, gall, pus, and other substances in a state of putrefaction, are laid upon fresh wounds ; vomiting, debility, and at length death, are occasioned. It is also well known that bodies in anatomical rooms frequently pass into a state of decomposition which is capable of imparting itself to the living body, the smallest cut with a knife which has been used in their dissection producing in these cases dangerous consequences. The poison of bad sausages belongs to this class of noxious substances. Several hundred cases are known in which death has occurred from the use of this kind of food. In Wiirtemberg especially these cases are very frequent, for there the sausages are prepared from very various materials. Blood, liver, bacon, brains, milk, meal and bread, are mixed together with salt and spices ; the mix- ture is then put into bladders or intestines, and after being boiled is smoked. When these sausages are well prepared they may be preserved for months, and furnish a nourishing savoury food ; but when the spices and salt are deficient, and particularly when they are smoked too late or not sufficiently, they undergo a peculiar kind of putrefaction which begins at the centre of 348 POISONS, CONTAGIONS, MIASMS. the sausage. Without any appreciable escape of gas taking place they become paler in colour, and more soft and greasy in those parts which have undergone putrefaction, and they are found to contain free lactic acid or lactate of ammonia ; products which are universally formed during the putrefaction of animal and vegetable matters. The cause of the poisonous nature of these sausages was ascribed at first to hydrocyanic acid, and afterwards to sebacic acid, although neither of these substances had been detected in them. But sebacic acid is no more poisonous than ben zoic acid, with which it has so many properties in com- mon ; and the symptoms produced are sufficient to show that hydrocyanic acid is not the poison. The death which is the consequence of poisoning by putrefied sausages succeeds very lingering and remarkable symptoms. There is a gradual wasting of muscular fibre, and of all the constituents of the body similarly composed ; the patient becomes much emaciated, dries to a complete mummy, and finally dies. The carcase is stiff as if frozen, and is not subject to putrefaction. During the progress of the disease the saliva becomes viscous and ac- quires an offensive smell. Experiments have been made for the purpose of ascertaining the presence of some matter in the sausages to which their poisonous action could be ascribed ; but no such matter has been detected. Boiling water and alcohol completely destroy the PUTRID POISONS. 349 poisonous properties of the sausages, without them- selves acquiring similar properties. Now this is the peculiar character of all sub- stances which exert an action by virtue of their existing condition of those bodies the elements of which are in the state of decomposition or trans- position ; a state which is destroyed by boiling water and alcohol without the cause of the influ- ence being imparted to those liquids ; for a state of action or power cannot be preserved in a liquid. Sausages, in the state here described, exercise an action upon the organism, in consequence of the stomach and other parts with which they come in contact not having the power to arrest their de- composition ; and entering the blood in some way or other, while still possessing their whole power, they impart their peculiar action to the constituents of that fluid. The poisonous properties of decayed sausages are not destroyed by the stomach as those of the small-pox virus are. All the substances in the body capable of putrefaction are gradually decom- posed during the course of the disease, and after death nothing remains except fat, tendons, bones, and a few other substances which are incapable of putrefying in the conditions afforded by the body. It is impossible to mistake the modus operandi of this poison, for Colin has clearly proved that muscle, urine, cheese, cerebral substance, and other matters, in a state of putrefaction, communicate 350 POISONS, CONTAGIONS, MIASMS. their own state of decomposition to substances much less prone to change of composition than the blood. When placed in contact with a solution of sugar, they cause its putrefaction, or the trans- position of its elements into carbonic acid and alcohol. When putrefying muscle or pus is placed upon a fresh wound, it occasions disease and death. It is obvious that these substances communicate their own state of putrefaction to the sound blood from which they mere produced, exactly in the same manner as gluten in a state of decay or putrefac- tion causes a similar transformation in a solution of sugar. Poisons of this kind are even generated by the body itself in particular diseases. In small-pox, plague, and syphilis, substances of a peculiar nature are formed from the constituents of the blood. These matters are capable of inducing in the blood of a healthy individual a decomposition similar to that of which they themselves are the subjects ; in other Words, they produce the same disease. The morbid virus appears to reproduce itself just as seeds appear to reproduce seeds. The mode of action of a morbid virus exhibits such a strong similarity to the action of yeast upon liquids containing sugar and gluten, that the two processes have been long since compared to one another, although merely for the purpose of illus- tration. But when the phenomena attending the MORBID POISONS. 351 action of each respectively are considered more closely, it will in reality be seen that their influence- depends upon the same cause. In dry air, and in the absence of moisture, all these poisons remain for a long time unchanged ; but when exposed to the air in the moist condition, they lose very rapidly their peculiar properties. In the former case, those conditions are afforded which arrest their decomposition without destroying it ; in the latter, all the circumstances necessary for the completion of their decomposition are pre- sented. The temperature at which water boils, and contact with alcohol, render such poisons inert. Acids, salts of mercury, sulphurous acid, chlorine, iodine, bromine, aromatic substances, volatile oils, and par- ticularly empyreumatic oils, smoke, and a decoction of coffee, completely destroy their contagious pro- perties, in some cases combining with them or otherwise effecting their decomposition. Now all these agents, without exception, retard fermenta- tion, putrefaction, and decay, and when present in sufficient quantity, completely arrest these pro- cesses of decomposition. A peculiar matter to which the poisonous action is due, cannot, we have seen, be extracted from decayed sausages ; and it is equally impossible to obtain such a principle from the virus of small-pox or plague, and for this reason, that their peculiar power is due to an active condition recognisable 352 POISONS, CONTAGIONS, MIASMS. by our senses, only through the phenomena which it produces. In order to explain the effects of contagious mat- ters, a peculiar principle of life has been ascribed to them a life similar to that possessed by the germ of a seed, which enables it under favourable conditions to develop and multiply itself. It would be impossible to find a more correct figurative re- presentation of these phenomena ; it is one which is applicable to contagions, as well as to ferment? to animal and vegetable substances in a state of fermentation, putrefaction, or decay, and even to a piece of decaying wood, which by mere contact with fresh wood, causes the latter to undergo gra- dually the same change and become decayed and mouldered. If the property possessed by a body of producing such a change in any other substance as causes the reproduction of itself, with all its properties, be regarded as life, then, indeed, all the above pheno- mena may be ascribed to life. But in that case they must not be considered as the only processes due to vitality, for the above interpretation of the expression embraces the majority of the pheno- mena which occur in organic chemistry. Life would, according to that view, be admitted to exist in every body in which chemical forces act. If a body A, for example, oxamide (a substance scarcely soluble in water, and without the slightest taste), be brought into contact with another com- MORBID POISONS. 353 pound B, which is to be reproduced ; and if this second body be oxalic acid dissolved in water, then the following changes are observed to take place : The oxamide is decomposed by the oxalic acid, provided the conditions necessary for their exercis- ing an action upon one another are present. The elements of water unite with the constituents of oxamide, and ammonia is one product formed, and oxalic acid the other, both in exactly the proper proportions to combine and form a neutral salt. Here the contact of oxamide and oxalic acid in- duces a transformation of the oxamide, which is de- composed into oxalic acid and ammonia. The oxalic acid thus formed, as well as that originally added, are shared by the ammonia or in other words, as much free oxalic acid exists after the decomposi- tion as before it, and is of course still possessed of its original power. It matters not whether the free oxalic acid is that originally added, or that newly produced ; it is certain that it has been reproduced in an equal quantity by the decomposition. If we now add to the same mixture a fresh por- tion of oxamide, exactly equal in quantity to that first used, and treat it in the same manner, the same decomposition is repeated ; the free oxalic acid enters into combination, whilst another portion is liberated. In this manner a very minute quan- tity of oxalic acid may be made to effect the de- composition of several hundred pounds of oxamide ; A A 354 POISONS, CONTAGIONS, MIASMS. and one grain of the acid to reproduce itself in unlimited quantity. We know that the contact of the virus of small- pox causes such a change in the blood, as gives rise to the reproduction of the poison from the constituents of the fluid. This transformation is not arrested until all the particles of the blood which are susceptible of the decomposition have undergone the metamorphosis. We have just seen that the contact of oxalic acid with oxamide caused the production of fresh oxalic acid, which in its turn exercised the same action on a new portion of oxamide. The transformation was only arrested in consequence of the quantity of oxamide present being limited. In their form both these transfor- mations belong to the same class. But no one but a person quite unaccustomed to view such changes will ascribe them to a vital power, although we admit they correspond remarkably to our common conceptions of life ; they are really chemical pro- cesses dependent upon the common chemical forces. Our notion of life involves something more than mere reproduction, namely, the idea of an active power exercised ~by virtue of a definite form, and production and generation in a definite form. By chemical agency we can produce the constituents of muscular fibre, skin, and hair ; but we can form by their means no organised tissue, no organic cell. The production of organs, the co-operation of a THEIR MODE OF ACTION. 355 system of organs, and their power not only to produce their component parts from the food pre- sented to them, but to generate themselves in their original form and with all their properties,, are cha- racters belonging exclusively to organic life ; and constitute a form of reproduction independent of chemical powers. The chemical forces are subject to the invisible cause by which this form is produced. Of the existence of this cause itself we are made aware only by the phenomena which it produces. Its laws must be investigated just as we investigate those of the other powers which effect motion and changes in matter. The chemical forces are subordinate to this cause of life, just as they are to electricity, heat, mecha- nical motion and friction. By the influence of the latter forces, they suffer changes in their direction, an increase or diminution of their intensity, or a complete cessation or reversal of their action. Such an influence and no other is exercised by the vital principle over the chemical forces ; but in every case where combination or decomposition takes place, chemical affinity and cohesion are in action. The vital principle is only known to us through the peculiar form of its instruments, that is, through the organs in which it resides. Hence, whatever kind of energy a substance may possess, if it is amorphous and destitute of organs from which the A A2 356 POISONS, CONTAGIONS, MIASMS. impulse, motion or change proceeds, it does not live. Its energy depends in this case on a chemical action. Light, heat, electricity, or other influences may increase, diminish, or arrest this action, but they are not its efficient cause. In the same way the vital principle governs the chemical powers in the living body. All those substances to which we apply the general name of food, and all the bodies formed from them in the organism, are chemical compounds. The vital principle has, therefore, no other resistance to over- come, in order to convert these substances into component parts of the organism, than the chemical powers by which their constituents are held toge- ther. If the food possessed life, not merely the chemical forces, but this vitality, would offer resist- ance to the vital force of the organism it nourished. All substances adapted for assimilation are bodies of a very complex constitution ; their atoms are highly complex, and are held together only by a weak chemical action. They are formed by the union of two or more simpler compounds ; and in proportion as the number of their atoms augments, their disposition to enter into new combination is diminished ; that is, they lose the power of acting chemically upon other bodies. Their complex nature, however, renders them more liable to be changed, by the agency of exter- nal causes, and thus to suffer decomposition. Any external agency, in many cases even mechanical THEIR MODE OF ACTION. 357 friction, is sufficient to cause a disturbance in the equilibrium of the attraction of their constituents; they arrange themselves either into new, more sim- ple, and permanent combinations, or if a foreign attraction exercise its influence upon it, they arrange themselves in accordance with that attraction. The special characters of food, that is of sub- stances fitted for assimilation, are absence of active chemical properties, and the capability of yielding to transformations. The equilibrium in the chemical attractions of the constituents of the food is disturbed by the vital principle, as we know it may be by many other causes. But the union of its elements, so as to produce new combinations and forms, indicates the presence of a peculiar mode of attraction, and the existence of a power distinct from all other powers of nature, namely, the vital principle. All bodies of simple composition possess a greater or less disposition to form combinations. Thus oxalic acid is one of the simplest of the organic acids, while stearic acid is one of the most complex ; and the former is the strongest, the latter one of the weakest in respect to active chemical character. By virtue of this disposition, simple compounds produce changes in very body which offers no resistance to their action ; they enter into combi- nation and cause decomposition. The vital principle opposes to the continual action of the atmosphere, moisture and tempera- 358 POISONS, CONTAGIONS, MIASMS. ture upon the organism, a resistance which is, in a certain degree, invincible. It is by the constant neutralisation and renewal of these external influ- ences that life and motion are maintained. The greatest wonder in the living organism is the fact that an unfathomable wisdom has made the cause of a continual decomposition or destruction, namely, the support of the process of respiration, to be the means of renewing the organism, and of resisting all the other atmospheric influences, such as those of moisture and changes of temperature. When a chemical compound of simple constitu- tion is introduced into the stomach, or any other part of the organism, it must exercise a chemical action upon all substances with which it comes in contact; for we know the peculiar character of such a body to be an aptitude and power to enter into combinations and effect decompositions. The chemical action of such a compound is of course opposed by the vital principle. The results produced depend upon the strength of their respective actions ; either an equilibrium of both powers is attained, a change being effected without the destruction of the vital principle, in which case a medicinal effect is occasioned ; or the acting body yields to the superior force of vitality, that is, it is digested ; or lastly, the chemical action obtains the ascendancy and acts as a poison. Every substance may be considered as nutriment, which loses its former properties when acted on by THEIR MODE OF ACTION.. 359 the vital principle, and does not exercise a chemical action upon the living organ. Another class of bodies change the direction, the strength, and intensity of the resisting force (the vital principle), and thus exert a modifying influ- ence upon the functions of its organs. They^. produce a disturbance in the system, either by their presence, and by themselves undergoing a change ; these are medicaments. A third class of compounds are called poisons, when they possess the property of uniting with organs or with their component parts, and when their power of effecting this is stronger than the resistance offered by the vital principle. The quantity of a substance and its condition must, obviously, completely change the mode of its chemical action. Increase of quantity is known to be equivalent to superior affinity. Hence a medicine administered in excessive quantity may act as a poison, and a poison in small doses as a medicine. Food will act as a poison, that is, it will produce disease, when it is able to exercise a chemical action by virtue of its quantity ; or, when either its con- dition or its presence retards, prevents, or arrests the motion of any organ. A compound acts as a poison when all the parts of an organ with which it is brought into contact enter into chemical combination with it, while it 360 POISONS, CONTAGIONS, MIASMS. may operate as a medicine, when it produces only a partial change. No other component part of the organism can be compared to the blood, in respect of the feeble resistance which it offers to exterior influences. The blood is not an organ which is formed, but an organ in the act of formation ; indeed, it is the sum of all the organs which are being formed. The chemical force and the vital principle hold each other in such perfect equilibrium, that every dis- turbance, however trifling, or from whatever cause it may proceed, effects a change in the blood. This liquid possesses so little of permanence, that it can- not be removed from the body without immediately suffering a change, and cannot come in contact with any organ in the body, without yielding to its attraction. The slightest action of a chemical agent upon the blood exercises an injurious influence ; even the momentary contact with the air in the lungs, although effected through the medium of cells and membranes, alters the colour and other qualities of the blood. Every chemical action propagates itself through the mass of the blood ; for example, the active chemical condition of the constituents of a body undergoing decomposition, fermentation, pu- trefaction, or decay, disturbs the equilibrium between the chemical force and the vital principle in the circulating fluid. The former obtains the THEIR MODE OF ACTION. 361 preponderance. Numerous modifications in the composition and condition of the compounds pro- duced from the elements of the blood, result from the conflict of the vital force with the chemical affinity, in their incessant endeavour to overcome one another. All the characters of the phenomena of contagion tend to disprove the existence of life in the conta- gious matters. They without doubt exercise an influence very similar to some processes in the living organism ; but the cause of this influence is chemical action, which is capable of being subdued by other chemical actions, by opposed agencies. Several of the poisons generated in the body by disease lose all their power when introduced into the stomach, but others are not thus destroyed. It is a fact very decisive of their chemical nature and mode of action, that those poisons which are neutral or alkaline, such as the poisonous matter of the contagious fever in cattle, (typhus contagiosus ruminantium,) or that of the small-pox, lose their whole power of contagion in the stomach ; whilst that of sausages, which has an acid reaction, retains all its frightful properties under the same circum- stances. In the former of these cases, the free acid present in the stomach destroys the action of the poison, the chemical properties of which are opposed to it ; whilst in the latter it strengthens, or at all events does not offer any impediment to poisonous action. 362 POISONS, CONTAGIONS, MIASMS. Microscopical examination has detected peculiar bodies resembling the globules of the blood in malig- nant putrefying pus, in the matter of vaccine, &c. The presence of these bodies has given weight to the opinion, that contagion proceeds from the development of a diseased organic life ; and these formations have been regarded as the living seeds of disease. This view, which is not capable of discussion, has led those philosophers who are accustomed to search for explanations of phenomena in forms, to con- sider the yeast produced by the fermentation of beer as possessed of life. They have imagined it to be composed of animals or plants, which nourish themselves from the sugar in which they are placed, and at the same time yield alcohol and carbonic acid as excrementitious matters*. It would perhaps appear wonderful if bodies, possessing a crystalline structure and geometrical figure, were formed during the processes of fermen- tation and putrefaction from the organic substances and tissues of organs. We know, on the contrary, that the complete dissolution into inorganic com- pounds is preceded by a series of transformations, in which the organic structures gradually resign their forms. Blood, in a state of decomposition, may appear to the eye unchanged ; and, when we recognise the globules of blood in a liquid contagious matter, the * Annalen der Pharmacie, Band xxix. S. 93 und 100. THEIR MODE OF ACTION. 363 utmost that we can thence infer is, that those glo- bules have taken no part in the process of decom- position. All the phosphate of lime may be removed from bones, leaving them transparent and flexible like leather, without the form of the bones being in the smallest degree lost. Again, bones may be burned until they be quite white, and consist merely of a skeleton of phosphate of lime, but they will still possess their original form. In the same way processes of decomposition in the blood may affect individual constituents only of that fluid, which will become destroyed and disap- pear, whilst its other parts will maintain the original form. Several kinds of contagion are propagated through the air : so that, according to the view already men- tioned, we must ascribe life to a gas, that is, to an aeriform body. All the supposed proofs of the vitality of conta- gions are merely ideas and figurative representa- tions, fitted to render the phenomena more easy of apprehension by our senses, with out explaining them. These figurative expressions, with which we are so willingly and easily satisfied in all sciences, are the foes of all inquiries into the mysteries of nature ; they are like the fata morgana, which show us deceitful views of seas, fertile fields, and luscious fruits, but leave us languishing when we have most need of what they promise. It is certain that the action of contagions is the 364 POISONS, CONTAGIONS, MIASMS, result of a peculiar influence dependent on chemi- cal forces, and in no way connected with the vital principle. This influence is destroyed by chemical actions, and manifests itself wherever it is not sub- dued by some antagonist power. Its existence is recognised in a connected series of changes and transformations, in which it causes all substances capable of undergoing similar changes to parti- cipate. An animal substance in the act of decomposition, or a substance generated from the component parts of a living body by disease, communicates its own condition to all parts of the system capable of enter- ing into the same state, if no cause exist in these parts by which the change is counteracted or destroyed. Disease is excited by contagion. The transformations produced by the disease assumes a series of forms. In order to obtain a clear conception of these transformations, we may consider the changes which substances, more simply composed than the living body, suffer from the influence of similar causes. When putrefying blood or yeast in the act of trans- formation is placed in contact with a solution of sugar, the elements of the latter substance are transposed, so as to form alcohol and carbonic acid. A piece of the rennet-stomach of a calf in a state of decomposition occasions the elements of sugar to THEIR MODE OF ACTION. 365 assume a different arrangement. The sugar is con- verted into lactic acid without the addition or loss of any element. (1 atom of sugar of grapes C12 H12 O12 yields two atoms of lactic acid =2(C6 H6 O6.) When the juice of onions or of beet-root is made to ferment at high temperatures, lactic acid, man- nite, and gum are formed. Thus, according to the different states of the transposition of the elements of the exciting body, the elements of the sugar arrange themselves in different manners, that is, different products are formed. The immediate contact of the decomposing sub- stance with the sugar, is the cause by which its particles are made to assume new forms and natures. The removal of that substance occasions the cessation of the decomposition of the sugar, so that should its transformation be completed before the sugar, the latter can suffer no further change. In none of these processes of decomposition is the exciting body reproduced ; for the conditions neces- sary to its reproduction do not exist in the elements of the sugar. Just as yeast, putrefying flesh, and the stomach of a calf, in a state of decomposition, when intro- duced into solutions of sugar, effect the transforma- tion of this substance, without being themselves regenerated ; in the same manner, miasms and certain contagious matters produce diseases in the human organism, by communicating the state of. decomposition, of which they themselves are the 366 POISONS, CONTAGIONS, MIASMS. subject, to certain parts of the organism, without themselves being reproduced in their peculiar form and nature during the progress of the decompo- sition. The disease in this case is not contagious. Now when yeast is introduced into a mixed liquid containing both sugar and gluten, such as wort, the act of decomposition of the sugar effects a change in the form and nature of the gluten, which is, in consequence, also subjected to trans- formation. As long as some of the fermenting sugar remains, gluten continues to be separated as yeast, and this new matter in its turn excites fermenta- tion in a fresh solution of sugar or wort. If the sugar, however, should be first decomposed, the gluten which remains in solution is not converted into yeast. We see, therefore, that the reproduc- tion of the exciting body here depends 1. Upon the presence of that substance from which it was originally formed. 2. Upon the presence of a compound which is capable of being decomposed by contact with the exciting body. If we express in the same terms the reproduction of contagious matter in contagious diseases, since it is quite certain that they must have their origin in the blood, we must admit that the blood of a healthy individual contains substances, by the de- composition of which the exciting body or conta- gion can be produced. It must further be admitted, THEIR MODE OF ACTION. 367 when contagion results, that the blood contains a second constituent capable of being decomposed by the exciting body. It is only in consequence of the conversion of the second constituent, that the original exciting body can be reproduced. A susceptibility of contagion indicates the pre- sence of a certain quantity of this second body in the blood of a healthy individual. The susceptibility for the disease and its intensity, must augment ac- cording to the quantity of that body present in the blood; and in proportion to its diminution or disap- pearance, the course of the disease will change. When a quantity, however small, of contagious matter, that is of the exciting body, is introduced into the blood of a healthy individual, it will be again generated in the blood, just as yeast is re- produced from wort. Its condition of transformation will be communicated to a constituent of the blood ; and in consequence of the transformation suffered by this substance, a body identical with or similar to the exciting or contagious matter will be pro- duced from another constituent substance of the blood. The quantity of the exciting body newly produced must constantly augment, if its further transformation or decomposition proceeds more slowly than that of the compound in the blood, the decomposition of which it effects. If the transformation of the yeast generated in the fermentation of wort proceeded with the same rapidity as that of the particles of the sugar con- 368 POISONS, CONTAGIONS, MIASMS. tained in it, both would simultaneously disappear when the fermentation was completed. But yeast requires a much longer time for decomposition than sugar, so that after the latter has completely disap- peared, there remains a much larger quantity of yeast than existed in the fluid at the commcement of the fermentation, yeast which is still in a state of incessant progressive transformation, and there- fore possessed of its peculiar property. The state of change or decomposition which affects one particle of blood, is imparted to a second, a third, and at last to all the particles of blood in the whole body. It is communicated in like man- ner to the blood of another individual, to that of a third person, and so on or in other words, the disease is excited in them also. It is quite certain that a number of peculiar sub- stances exist in the blood of some men and animals, which are absent from the blood of others. The blood of the same individual contains, in childhood and youth, variable quantities of sub- stances, which are absent from it in other stages of growth. The susceptibility of contagion by peculiar exciting bodies in childhood, indicates a propaga- tion and regeneration of the exciting bodies, in consequence of the transformation of certain sub- stances which are present in the blood, and in the absence of which no contagion could ensue. The form of a disease is termed benignant, when the transformations are perfected on constituents of the THEIR MODE OF ACTION. 369 body which are not essential to life, without the other, parts taking a share in the decomposition ; it is termed malignant when they affect essential organs. It cannot be supposed that the different changes in the blood, by which its constituents are con- verted into fat, muscular fibre, substance of the brain and nerves, bones, hair, &c., and the trans- formation of food into blood, can take place without the simultaneous formation of new compounds, which require to be removed from the body by the organs of excretion. In an adult these excretions do not vary much either in their nature or quantity. The food taken is not employed in increasing the size of the body, but merely for the purpose of replacing any sub- stances which may be consumed by the various actions in the organism ; every motion, every mani- festation of organic properties, and every organic action being attended by a change in the material of the body, and by the assumption of a new form by its constituents.* But in a child this normal condition of suste- nance is accompanied by an abnormal condition of growth and increase in the size of the body, and of * The experiments of Barruel upon the different odours emitted from blood on the addition of sulphuric acid, prove that peculiar sub- stances are contained in the blood of different individuals; the blood of a man of a fair complexion and that of a man of dark complexion were found to yield different odours ; the blood of animals also differed in this respect very perceptibly from that of man. B B 370 POISONS, CONTAGIONS, MIASMS. each individual part of it. Hence there must be a much larger quantity of foreign substances, not belonging to the organism, diffused through every part of the blood in the body of a young individual. When the organs of secretion are in proper action, these substances will be removed from the system ; but when the functions of those organs are impeded, they will remain in the blood or become accumu- lated in particular parts of the body. The skin, lungs, and other organs, assume the functions of the diseased secreting organs, and the accumulated substances are eliminated by them. If, when thus exhaled, they happen to be in the state of progres- sive transformation, these substances are conta- gious, that is, they are able to produce the same state of disease in another healthy organism, pro- vided the latter organism is susceptible of their action or in other words, contains a matter cap- able of suffering the same process of decomposi- tion.* The production of matters of this kind, which render the body susceptible of contagion, may be occasioned by the manner of living, or by the nu- triment taken by an individual. A superabundance of strong and otherwise wholesome food may pro- duce them, as well as a deficiency of nutriment, * Cold meat is always in a state of decomposition, that is, in a state of eremacausis ; it is possible that this state may be communicated to the system of a feeble individual, and may be one of the sources of consumption. THEIR MODE OF ACTION. 371 uncleanliness, or even the use of decayed substances as food. All these conditions for contagion must be con- sidered as accidental. Their formation and accu- mulation in the body may be prevented, and they may even be removed from it without disturbing its most important functions or health. Their presence is not necessary to life. The action, as well as the generation of the matter of contagion is, according to this view, a chemical process participated in by all substances in the living body, and by all the constituents of those organs in which the vital principle does not overcome the chemical action. The contagion, ac- cordingly, either spreads itself over every part of the body, or is confined particularly to certain or- gans, that is, the disease attacks all the organs or only a few of them, according to the feebleness or intensity of their resistance. In the abstract chemical sense, reproduction of a contagion depends upon the presence of two substances, one of which becomes completely de- composed, but communicates its own state of trans- formation to the second. The second substance thus thrown into a state of decomposition is the newly formed contagion. The second substance must have been originally a constituent of the blood : the first may be a body accidentally present ; but it may also may be a matter necessary to life. If both be constituents B B 2 372 POISONS, CONTAGIONS, MIASMS. indispensable for the support of the vital functions of certain principal organs, death is the consequence of their transformation. But if the absence of the one substance which was a constituent of the blood do not cause an immediate cessation of the func- tions of the most important organs, if they continue in their action, although in an abnormal condition, convalescence ensues. In this case the products of the transformations still existing in the blood are used for assimilation, and at this period secretions of a peculiar nature are produced. When the constituent removed from the blood is a product of an unnatural manner of living, or when its formation takes place only at a certain age, the susceptibility of contagion ceases upon its disappearance. The effects of vaccine matter indicate that an accidental constituent of the blood is destroyed by a peculiar process of decomposition, which does not affect the other constituents of the circulating fluid. If the manner in which the precipitated yeast of Bavarian beer acts (page 266) be called to mind, the modus operandi of vaccine lymph can scarcely be matter of doubt. Both the kind of yeast here referred to and the ordinary ferment are formed from gluten, just as the vaccine virus and the matter of small-pox are produced from the blood. Ordinary yeast and the virus of human small-pox, however, effect a violent THEIR MODE OF ACTION. 373 tumultuous transformation, the former in vegetable juices, the latter in blood, in both of which fluids respectively their constituents are contained, and they are reproduced from these fluids with all their characteristic properties. The precipitated yeast of Bavarian beer on the other hand acts entirely upon the sugar of the fermenting liquid and occa- sions a very protracted decomposition of it, in which the gluten which is also present takes no part. But the air exercises an influence upon the latter substance, and causes it to assume a new form and nature, in consequence of which this kind of yeast also is reproduced. The action of the virus of cow-pox is analogous to that of the low yeast ; it communicates its own state of decomposition to a matter in the blood, and from a second matter is itself regenerated, but by a totally different mode of decomposition ; the pro- duct possesses the mild form, and all the properties of the lymph of cow-pox. The susceptibility of infection by the virus of human small-pox must cease after vaccination, for the substance to the presence of which this sus- ceptibility is owing has been removed from the body by a peculiar process of decomposition artifi- cially excited. But this substance may be again generated in the same individual so that he may again become liable to contagion, and a second or a third vaccination will again remove the peculiar substance from the system. Chemical actions are propagated in no organs so 374 POISONS, CONTAGIONS, MIASMS. easily as in the lungs, and it is well known that diseases of the lungs are above all others frequent and dangerous. If it is assumed that chemical action and the vital principle mutually balance each other in the blood, it must further be supposed that the chemi- cal powers will have a certain degree of preponde- rance in the lungs, where the air and blood are in immediate contact ; for these organs are fitted by nature to favour chemical action ; they offer no resistance to the changes experienced by the venous blood. The contact of air with venous blood is limited to a very short period of time by the motion of the heart, and any change beyond a determinate point is, in a certain degree, prevented by the rapid removal of the blood which has become arterialised. Any disturbance in the functions of the heart, and any chemical action from without, even though weak, occasions a change in the process of respi- ration. Solid substances also, such as dust from vegetable, (meal,) animal, (wool,) and inorganic bodies, act in the same way as they do in a satu- rated solution of a salt in the act of crystallisation, that is, they occasion a deposition of solid matters from the blood, by which the action of the air upon the latter is altered or prevented. When gaseous and decomposing substances, or those which exercise a chemical action, such as sul- phuretted hydrogen and carbonic acid, obtain access to the lungs, they meet with less resistance in this THEIR MODE OF ACTION. 375 organ tnan in any other. The chemical process of slow combustion in the lungs is accelerated by all substances in a state of decay or putrefaction, by ammonia and alkalies ; but it is retarded by empy- reumatic substances, volatile oils, and acids. Sulphuretted hydrogen produces immediate decom- position of the blood, and sulphurous acid combines with the substance of the tissues, the cells, and membranes. When the process of respiration is modified by contact with a matter in the progress of decay, when this matter communicates the state of decom- position, of which it is the subject, to the blood, disease is produced. If the matter undergoing decomposition is the product of a disease, it is called contagion ; but if it is a product of the decay or putrefaction of animal and vegetable substances, or if it acts by its chemi- cal properties, (not by the state in which it is,) and therefore enters into combination with parts of the body, or causes their decomposition, it is termed miasm. Gaseous contagious matter is a miasm emitted from blood, and capable of generating itself again in blood. But miasm properly so called, causes disease without being itself reproduced. All the observations hitherto made upon gaseous contagious matters prove, that they also are sub- stances in a state of decomposition. When vessels filled with ice are placed in air impregnated with gaseous contagious matter, their outer surfaces 376 POISONS, CONTAGIONS, MIASMS. become covered with water containing a certain quantity of this matter in solution. This water soon becomes turbid, and in common language putrefies, or, to describe the change more correctly, the state of decomposition of the dissolved conta- gious matter is completed in the water. All gases emitted from putrefying animal and vegetable substances in processes of disease, gene- rally possess a peculiar nauseous offensive smell, a circumstance which, in most cases, proves the presence of a body in a state of decomposition. Smell itself may in many cases be considered as a reaction of the nerves of smell, or as a resistance offered by the vital powers to chemical action. Many metals emit a peculiar odour when rubbed, but this is the case with none of the precious metals, those which suffer no change when exposed to air and moisture. Arsenic, phosphorus, musk, the oils of linseed, lemons, turpentine, rue, and peppermint, possess an odour only when they are in the act of eremacausis (oxidation at common temperatures). The odour of gaseous contagious matters is owing to the same cause ; but it is also generally accom- panied by ammonia, which may be considered in many cases as the means through which the con- tagious matter receives a gaseous form, just as it is the means of causing the smell of innumerable substances of little volatility, and of many which have no odour. (Robiquet.)* * Ann. de Chim. et de Phys. XV. 27. THEIR MODE OF ACTION. 377 Ammonia is very generally produced in cases of disease ; it is always emitted in those in which con- tagion is generated, and is an invariable product of the decomposition of animal matter. The presence of ammonia in the air of chambers in which diseased patients lie, particularly of those afflicted with a contagious disease, may be readily detected ; for the moisture condensed by ice in the manner just described, produces a white precipitate in a solution of corrosive sublimate, just as a solution of am- monia does. The ammoniacal salts also, which are obtained by the evaporation of rain water after an acid has been added, when treated with lime so as to set free their ammonia, emit an odour most closely resembling that of corpses, or the peculiar smell of dunghills. By evaporating acids in air containing gaseous contagions, the ammonia is neutralised, and we thus prevent further decomposition, and destroy the power of the contagion, that is, its state of chemical change. Muriatic and acetic acids, and in several cases nitric acid, are to be preferred for this purpose before all others. Chlorine also is a substance which destroys ammonia and organic bodies with much facility ; but it exerts such an injurious and prejudicial influence upon the lungs, that it may be classed amongst the most poisonous bodies known, and should never be employed in places in which men breathe. Carbonic acid and sulphuretted hydrogen, which 378 POISONS, CONTAGIONS, MIASMS. are frequently evolved from the earth in cellars, mines, wells, sewers, and other places, are amongst the most pernicious miasms. The former may he removed from the air by alkalies ; the latter, by burning sulphur (sulphurous acid), or by the evaporation of nitric acid. The characters of many organic compounds are well worthy of the attention and study both of phy- siologists and pathologists, more especially in rela- tion to the mode of action of medicines and poisons. Several of such compounds are known, which to all appearance are quite indifferent substances, and yet cannot be brought into contact with one another in water without suffering a complete transformation. All substances which thus suffer a mutual decomposition, possess complex atoms ; they belong to the highest order of chemical com- pounds. For example, amygdalin, a constituent of bitter almonds, is a perfectly neutral body, of a slightly bitter taste, and very easily soluble in water. But when it is introduced into a watery solution of synaptas, (a constituent of sweet almonds,) it disappears completely without the disengagement of any gas, and the water is found to contain free hydrocyanic acid, hydruret of benzule (oil of bitter almonds), a peculiar acid and sugar, all substances of which merely the elements existed in the amygdalin. The same decomposition is ef- fected when bitter almonds, which contain the same white matter as the sweet, are rubbed into a THEIR MODE OF ACTION. 379 powder and moistened with water. Hence it hap- pens that bitter almonds pounded and digested in alcohol, yield no oil of bitter almonds, containing hydrocyanic acid, by distillation with water; for the substance which occasions the formation of those volatile substances, is dissolved by alcohol without change, and is therefore extracted from the pounded almonds. Pounded bitter almonds contain no amygdalin, also, after having been moistened with water, for that substance is completely decom- posed when they are thus treated. No volatile compounds can be detected by their smell in the seeds of the Sinapis alba and S. nigra. A fixed oil of a mild taste is obtained from them by pressure, but no trace of a volatile substance. If, however, the seeds are rubbed to a fine powder, and subjected to distillation with water, a volatile oil of a very pungent taste and smell passes over along with the steam. But if, on the contrary, the seeds are treated with alcohol previously to their distillation with water, the residue does not yield a volatile oil. The alcohol contains a crystalline body called sinapin, and several other bodies. These do not possess the characteristic pungency of the oil, but it is by the contact of them with water, and with the albuminous constituents of the seeds, that the volatile oil is formed. Thus bodies regarded as absolutely indifferent in inorganic chemistry, on account of their pos- sessing no prominent chemical characters, when 380 POISONS, CONTAGIONS, MIASMS. placed in contact with one another, mutually de- compose each other. Their constituents arrange themselves in a peculiar manner, so as to form new combinations ; a complex atom dividing into two or more atoms of less complex constitution, in conse- quence of a mere disturbance in the attraction of their elements. The white constituents of the almonds and mus- tard which resemble coagulated albumen, must be in a peculiar state in order to exert their action upon amygdalin, and upon those constituents of mustard from which the volatile pungent oil is produced. If almonds, after being blanched and pounded, are thrown into boiling water, or treated with hot alcohol, with mineral acids, or with salts of. mercury, their power to effect a decomposition in amygdalin is completely des- troyed. Synaptas is an azotised body which cannot be preserved when dissolved in water. Its solu- tion becomes rapidly turbid, deposits a white pre- cipitate, and acquires the offensive smell of putre- fying bodies. It is exceedingly probable that the peculiar state of transposition into which the elements of syna- ptas are thrown when dissolved in water, may be the cause of the decomposition of amygdalin, and formation of the new products arising from it. The action of synaptas in this respect is very similar to that of rennet upon sugar. Malt, and the germinating seeds of corn in THEIR MODE OF ACTION. 381 general, contain a substance called diastase, which is formed from the gluten contained in them, and cannot be brought in contact with starch and water, without effecting a change in the starch. When bruised malt is strewed upon warm starch made into a paste with water, the paste, after a few minutes becomes quite liquid, and the water is found to contain, in place of starch, a substance in many respects similar to gum. But when more malt is added and the heat longer continued, the liquid acquires a sweet taste, and all the starch is found to be converted into sugar of grapes. The elements of diastase have at the same time arranged themselves into new combinations. The conversion of the starch contained in food into sugar of grapes in diabetes indicates that amongst the constituents of some one organ of the body a substance or substances exist in a state of chemical action, to which the vital principle of the diseased organ opposes no resistance. The com- ponent parts of the organ must suffer changes simultaneously with the starch, so that the more starch is furnished to it, the more energetic and intense the disease must become ; while if only food which is incapable of suffering such transformations from the same cause is supplied, and the vital energy is strengthened by stimulant remedies and strong nourishment, the chemical action may finally be subdued, or in other words, the disease cured. The conversion of starch into sugar may also be 382 POISONS, CONTAGIONS, MIASMS. effected by pure gluten, and by dilute mineral acids. From all the preceding facts, we see that very various transpositions, and changes of composition and properties, may be produced in complex organic molecules, by every cause which occasions a dis- turbance in the attraction of their elements. When moist copper is exposed to air containing carbonic acid, the contact of this acid increases the affinity of the metal for the oxygen of the air in so great a degree that they combine, and the surface of the copper becomes covered with green car- bonate of copper. Two bodies, which possess the power of combining together, assume, however, opposite electric conditions at the moment at which they come in contact. When copper is placed in contact with iron, a peculiar electric condition is excited, in consequence of which the property of the copper to unite with oxy- gen is destroyed, and the metal remains quite bright. When formate of ammonia is exposed to a tem- perature of 388 F. (180 C.) the intensity and direction of the chemical force undergo a change, and the conditions under which the elements of this compound are enabled to remain in the same form cease to be present. The elements, therefore, arrange themselves in a new form ; hydrocyanic acid and water being the results of the change. Mechanical motion, friction, or agitation, is suffi- cient to cause a new disposition of the constituents THEIR MODE OF ACTION. 383 of fulminating silver and mercury, that is, to effect another arrangement of their elements, in conse- quence of which, new compounds are formed. We know that electricity and heat possess a de- cided influence upon the exercise of chemical affi- nity ; and that the attractions of substances for one another are subordinate to numerous causes which change the condition of these substances, by alter- ing the direction of their attractions. In the same manner, therefore, the exercise of chemical powers in the living organism is dependent upon the vital principle. The power of elements to unite together, and to form peculiar compounds, which are generated in animals and vegetables, is chemical affinity; but the cause by which they are prevented from arrang- ing themselves according to the degrees of their natural attractions the cause, therefore, by which they are made to assume their peculiar order and form in the body, is the vital principle. After the removal of the cause which forced their union that is, after the extinction of life most organic atoms retain their condition, form, and nature, only by a vis inertitz ; for a great law of nature proves that matter does not possess the power of spontaneous action. A body in motion loses its motion only when a resistance is opposed to it ; and a body at rest cannot be put in motion or into any action whatever, without the operation of some exterior cause. 384 POISONS,, CONTAGIONS, MIASMS. The same numerous causes which are opposed to the formation of complex organic molecules, under ordinary circumstances, occasion their de- composition and transformations when the only antagonist power, the vital principle, no longer counteracts the influence of those causes. Contact with air and the most feeble chemical action now effect changes in the complex molecules ; even the presence of any body the particles of which are undergoing motion or transposition is often sufficient to destroy their state of rest, and to disturb the statical equilibrium in the attractions of their con- stituent elements. An immediate consequence of this is that they arrange themselves according to the different degrees of their mutual attractions, and that new compounds are formed in which che- mical affinity has the ascendancy, and opposes any further change, while the conditions under which these compounds were formed remain unaltered. 385 ADDITION TO NOTE AT PAGE 17. IF the atmosphere possessed, in its whole extent, the same density as it does on the surface of the sea, it would have a height of 24,555 Parisian feet; but it contains the vapour of water, so that we may assume its height to be one geographical mile = 22,843 Parisian feet. Now the radius of the earth is equal to 860 geographical miles ; hence the Volume of the Atmosphere =9,307,500 cubic miles = cube of 210-4 miles. Volume of Oxygen . . =1,954,578 cubic miles = cube of 125' miles. Volume of Carbonic Acid = 3,862-7 cubic miles = cube of 15*7 miles. The maximum of the carbonic acid contained in the atmosphere has not here been adopted, but the mean, which is equal to 0-000415. A man daily consumes 45,000 cubic inches (Parisian). A man yearly consumes 9505-2 cubic feet. 1000 million men yearly consume 9,505,200,000,000 cubic feet. 1 cubic mile is equal to 11,919,500,000,000 cubic feet. Hence a thousand million men yearly consume 79745 cubic miles of oxygen. But the air is rendered incapable of supporting the process of respiration, when the quantity of its oxygen is decreased 12 per cent.; so that a thousand million men would make the air unfit for respiration in a million years. The consumption of oxygen by animals, and by the process of combustion, is not introduced into the calculation. C C 386 TABLES SHOWING THE PROPORTION BETWEEN THE HESSIAN AND ENGLISH STANDARD OF WEIGHTS AND MEASURES. As the numbers throughout the Work have been stated in reference to some common measure, it has been thought advisable not to state the English equivalents to the Hessian numbers in the text, lest they should distract the attention of the reader by being placed in decimals. The numbers do not represent absolute quantities, but are merely intended to denote a proportion to other numbers ; so that it is quite indifferent in what standard of weights or measures they are stated. In almost every case where the term " Hessian pounds " are employed, the word " parts " may be substi- tuted. For those, however, who wish to be acquainted with the exact English quantities, a table is given below. lib. English is equal to 0-9071 9 Ibs. Hessian; hence, about one-tenth less than the latter. 2 Ibs. Hessian are equal to 2-20 Ibs. English. 3 ... 3-306 4 - - - 4-409 5 - 5-51 6 - - - - 6-61 7 - 7-716 8 - - - 8-818 9 - - 9-92 10 - - - 11-02 20 - - 22-04 30 - - - - 33-06 40 - - 44-09 50 - - - 55-11 60 - 66-12 70 - - 77-16 80 - - 88-18 90 - - 99-29 100 - 110-2 200 - - - 220-4 300 - - 230-6 400 - - 440-9 500 551-1 600 - - - 661-2 700 771-6 800 - - - - 881-8 900 992-9 1000 - - - - 1102-0 387 SQUARE FEET. The Hessian acre is equal to 40,000 Hessian square feet, or 26,917 English square feet ; 1 English square foot being equal to 1*4864 Hessian. The following is a Table to save the trouble of calculation. The Table is only stated to the figure 10, but by removing the decimal point one or two figures, the whole series given in the case of the pounds will also be obtained. 2 Square Feet Hessian are equal to 1-345 Square Feet English. 3 4 - 5 6 - 7 8 - 9 10 - 2-011 2-691 3-363 4-036 4-709 5-382 6-054 - 6-727 CUBIC FEET. One English cubic foot contains 1 '81218 of a Hessian cubic foot; the Hessian and English cubic inch may be considered as equal, one English cubic inch containing 1-048715 Hessian cubic inch. 1 cubic foot Hessian is equal to 0-551 cubic foot English. 2 feet 3 4 5 6 7 8 9 10 1-103 1-655 2-207 2-759 3-311 3-863 4.415 4-966 5-518 feet THE END. LONDON : BRAWIURY AND EVANS, PRINTKKS, \\HITBFRIARS. 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