Qass_ Book- CHEMISTRY IN ITS APPLICATION TO AGEICULTUEE AND PHYSIOLOGY. BY JUSTUS LIEBIG, M.D., Ph.D., F.R.S., M.R.I.A., PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OP GIESSEN, ETC., ETC., ETC. EDITED FROM THE MANUSCRIPT OF THE AUTHOR By LYON PLAYFAIR, Ph. D. WITH VERY NUMEROUS ADDITIONS, AND A NEW CHAPTER ON SOILS. FOURTH AMERICAN, FROM THE SECOND ENGLISH EDITION, WITH NOTES, AND APPENDIX, BY JOHN Wi WEBSTER, M. D., ERVING PROFESSOR OP CHEMISTRY IN HARVARD UNIVERSITY. CAMBRIDGE: PUBLISHED BY JOHN OWEN. BOSTON, JAMES MUNROE AND COMPANY, AND CHARLES C. LITTLE AND JAMES BROWN; NEW YORK, WILEY AND PUTNAM, AND GEORGE C. THORBURN ; PHILADELPHIA, THOMAS, COWPERTHWAIT, AND COMPANY, AND CAEEY AND HART; BALTIMORE, CUSHINO AND BROTHER. 1843. ^ Entered according to Act of Congress, in the year 1842, by John Owen, in the Clerk's office of the District Court of the District of Massachusetts. C A :.I B k I D G E ; STEREOTYPED ^AN"D PRINTED BY MET CALF, KEITH, AND NICHOLS, PRINTEISS TO THE CNIVEESITY. CONTENTS. Preface to the Third American Edition Dedication Preface to the Second English Edition Object of the Work PAG a V Xlll XVII 21 PART FIRST. ON THE CHEMICAL PROCESSES IN THE NUTRITION OF VEGETABLES. CHAPTER PAGE I. — On the Constituent Elements of Plants . . 24 n. — On the Assimilation of Carbon . . .30 III. — On the Origin and Action of Humus . . 63 IV. — On the Assimilation of Hydrogen . . .80 V. — On the Origin and Assimilation of Nitrogen . 85 VI. — On the Inorganic Constituents of Plants . . 105 Vn. — The Art of Culture . . . . 126 Vni. — On the Alternation (Rotation) of Crops . . 161 IX. — On Manure ..... 174 Supplementary Chapter. — On the Chemical Constitu- ents of Soils ..... 208 Appendix to Part I. ..... 249 Action of Charcoal on Vegetation . . 249 Mode of Manuring Vines .... 253 Root Secretions ..... 256 Peat Compost ..... 258 Source of the Carbon of Plants . . . 260 Source of the Hydrogen of Plants . . . 263 Dependence of the Nutritive Qualities of Plants on Nitrogen . . . . .265 iv CONTENTS. Difference in the Power of Plants to decompose Ammonia ..... 266 Practical Inferences .... 268 Use of Phosphate of Soda . . . .286 Daniell's Artificial Manure . . . 287 PART SECOND. ON THE CHEMICAL PROCESSES OF FERMENTATION, DECAY, AND PUTREFACTION. CHAPTER * PAGE I. — Chemical Transformations . . . 289 n. — On the Causes which effect Fermentation, Decay, and Putrefaction .... 292 m. — Fermentation and Putrefaction . . . 300 IV. — On the Transformation of Bodies which do not con- tain Nitrogen as a constituent, and of those in which it is present .... 305 V. — Fermentation of Sugar .... 313 VI. — Eremacausis, or Decay , . . 322 Vn. — Eremacausis of Bodies destitute of Nitrogen : For- mation of Acetic Acid . . . 329 VIII. — Eremacausis of Substances containing Nitrogen: Nitrification . . . .334 IX. — On Vinous Fermentation : Wine and Beer . 338 X. — On the Decay of Woody Fibre . . 357 XL — On Vegetable Mould . . . .363 Xn. — On the Mouldering of Bodies : Paper, Brown Coal, and Mineral Coal . . . .365 Xni. — On Poisons, Contagions, and Miasms . 373 Appendix to Part II. . . . . . 415 Tables, — Showing the Proportion between the Hessian and English Standard of Weights and Measures 416 Index ...... 419 PEEEACE THIRD AMERICAN EDITION. This volume constitutes the First Part of Professor Liebig's Report on Organic Chemistry, drawn up by request of the British Association for the Advancement of Science.* The interest excited in Great Britain on the appear- ance of this work from one of the most eminent chemists in Europe, and the high encomiums be- stowed upon it by individuals, and learned bodies, together with the various notices of it which have been published by Professor Lindley, Professor Dau- beny, and others, all concurring in the opinion, that the information it contains is of great amount, and that from its publication might be dated a new era * The Second Part has just been published, viz., "Animal Chemistry, or Organic Chemistry in its Application to Physiology and Pathology. By Justus Liebig, M. D., F. R. S., M. R. I. A., Professor of Chemistry in the University of Giessen, &c., &-c., &c. Edited from the Author's Manuscript, by William Gregory, M. D., F. R. S., M. R. I. A., Professor of Medicine and Chemistry in the University and King's College, Aberdeen. With Additions, Notes, and Corrections, by Dr. Gregory, and others by John W. Webster, M. D., Erving Professor of Chemistry in Harvard University." Vi PREFACE TO THE in the art of agriculture, induced the editor to suggest its republication in this country. Contrary to the expectations of the author, and of the editor, the work has received the attention not only of scientific readers, for whom it was written, but of practical agriculturists, and those who could hardly have been supposed prepared to derive much advantage from its perusal. The influence of the opinions of Professor Liebig, and the impetus the appearance of the present work gave to the advance- ment of scientific agriculture, have been e,vinced by the many publications which have since appeared, both in Great Britain and in this country. What is valuable in too many of these publications, diluted as it has been and mingled with erroneous statements, was for the first time given in a consistent shape in the present work. Although the fact that nitrogen is essential to the nutrition of plants was known before the publication of Professor Liebig's work, and it had, indeed, been ascertained by Saussure, that germinating seeds absorb nitrogen, it was not supposed that it is derived from the atmosphere exclusively. And this has been deemed the chief discovery of the author, so far as practical questions are concerned. It had indeed been suspected, that very small quantities of ammonia in the atmosphere might furnish the nitrogen, ammonia being a compound of nitrogen and hydrogen. It may be objected, that the quantity of ammonia pres- ent in the atmosphere, and in rain and snow water, is THIRD AMERICAN EDITION. Vll exceedingly small, quite insufficient for the supply of all the nitrogen that enters into the vegetable struc- ture. To this it has been replied by Professor Lind- ley, in an elaborate review of Liebig's work, that " the quantity of ammonia given off from thousands of millions of putrefying animals must furnish an abundant, an everlasting source of that principle." Important as ammonia, or its nitrogen, is conceived to be to plants, it will be seen that Liebig considers carbon not less so. Since the appearance of the former editions of this work, the opinions of American chemists in regard to humus, have become so generally diffused, in the various Agricultural Keports, that it has not been deemed necessary to retain, in this edition, much that was appended to the second. Professor Lindley, in speaking of humus, recogni- ses it as " the dark substance which remains when manure is thoroughly rotted, and which colors the soil black, and without going into any technical ex- amination of this product, we may state," he con- tinues, "that it is a substance formed by the decay of plants, and very rich in carbon." He then quotes the expression of Liebig, that this substance, in the form in which it exists in the soil, does not yield nourish- ment to plants, and expresses surprise, that the author should have thought it worth his while to raise such a phantom for the mere pleasure of subduing it, for no one in Great Britain now entertains the opinion, that humus is in itself the food of plants. '^ Every Viil PREFACE TO THE Student of botany is taught, that humus becomes the food of plants only by combining with the oxygen of the atmosphere and forming carbonic acid gas, and hence the great importance of preserving the roots of plants in communication with the atmosphere, which is the great source of oxygen." In noticing the effect of alkalies, Professor Lindley remarks, that it will lead to the explanation of many things that were inexplicable before. " When it is said, that a plant becomes tired of a soil, and we find that manuring fails to invigorate it, the destruction of alkalies in the soil, and the want of a sufficient supply of those bases in the manure, seem to offer a solution of the enigma. And in like manner the gradual de- cay of trees in public squares and promenades, where the soil is incessantly robbed of alkaline matter for the sake of neatness, may probably be ascribed to the same cause. So also the injurious action of weeds is explained, by their robbing the soil of that particular kind of food which is necessary to the crops among which they grow. Each will partake of the compo- nent parts of the soil, and in proportion to the vigor of their growth, that of the crop must decrease ; for what one receives the others are deprived of" ''It is impossible for any one acquainted with gar- dening not to perceive the immense importance of these considerations, which show, that by adopting the modern notion, that the action of soil is chiefly mechanical, the science of horticulture has been car- ried backwards, instead of being advanced ; and that THIRD AMERICAN EDITION. IX the most careful examination of the chemical nature both of the soil in which a given plant grows, and of the plant itself, must be the foundation of all exact and economical methods of cultivation." Of the importance of alkalies and salts to plants, there would seem to be no doubt, and although the credit of this discovery is in England given to Liebig, it was not new in the United States, having been an- nounced by Dr. S. L. Dana of Lowell, and urged upon the attention of cultivators in the various Re- ports on the Agriculture of Massachusetts, several years ago. As in this work many chemical and technical terms are necessarily made use of, and it may come into the hands of some persons who are not familiar with them, explanatory notes have been added which it is hoped may render the text more intelligible. The notes that are contained in the original work are distin- guished by initials or abbreviations. A valuable addition has been made in the extracts from the lectures delivered after the appearance of Liebig's work by Professor Daubeny at Oxford, on Agriculture and Rural Economy. The greater part of the third lecture is given in the Appendix, being a summary of the practical applications of the prin- ciples developed and discussed in the body of this work. It has been highly gratifying to the editor, to learn from the gentleman under whose supervision the work first appeared in England, that its republication, and X PREFACE TO THE the manner in which it has been edited in this coun- try, have met with his entire approbation. To Dr. Playfair the editor is also indebted for some valuable suggestions which were followed in preparing the second edition, and for which he would express his thanks. A copious index, in which the original work is de- ficient, has been added, and numerous errors of the English press have been corrected. The estimation in which Professor Liebig's work was viewed by the "British Association for the Ad- vancement of Science," before whom it was brought as a Report, has been expressed by Professor Gregory, of King's College, in the remark, " that the Association had just reason to be proud of such a work, as origi- nating in their recommendation." On the 30th of November, 1840, at the anniversary meeting of the Royal Society, one of the Copley medals was awarded to the author ; and on this occa- sion, in his absence, the President, the Marquis of Northampton, addressed his representative, Professor Daniell, as follows. " Professor Daniell, I hold in my hand, and deliver to you one of the Copley medals, which has been awarded by us to Professor Liebig. My principal difficulty, in the present exercise of this the most agreeable part of my official duty, is to know wheth- er to consider M. Liebig's inquiries as most important in a chemical or in a physiological light. However that may be, he has a double claim on the scientific THIRD AMERICAN EDITION. XI world, enhanced by the practical and useful ends to which he has turned his discoveries." To Dr. S, L. Dana, of Lowell, the editor would ac- knowledge his obligations for valuable suggestions and the communication of some important additions, and also to Mr. Charles E. Buckingham, of the Medical School of this University, for his valuable assistance in correcting the proofs. J. W. W. Cambridge, September, 1842. TO THE BRITISH ASSOCIATION 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 progress, and of commu- nicating new discoveries. The formation of such as- sociations 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 ac- knowledgment of these benefits, and this acknowl- edgment, 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 b XIV DEDICATION. 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 cul- ture is most beneficial ; and the new views acquired by the knowledge of them enable the mind to recog- nise, in the phenomena of nature, proofs of an Infinite Wisdom, for the unfathomable profundity of which, language has no expression. At one of the meetings of the chemical section of the " British Association for the Advancement of Science," the honorable task of preparing a Report upon the state of Organic Chemistry was imposed upon me. In the present work I present to the As- sociation a part of this Report. I have endeavored to develop, in a manner corre- spondent to the present state of science, the fundamen- tal principles of Chemistry in general, and the laws of Organic Chemistry in particular, in their applica- tions to Agriculture and Physiology ; to the causes of fermentation, decay, and putrefaction ; 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 at- tention of men of science to subjects which so well merit to engage their talents and energies. Perfect Agriculture is the true foundation of all trade and in- DEDICATION. XV dustiy, — it is the foundation of the riches of states. But a rational system of Agriculture 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 chemistry, which teaches the mode of investigating the composition and of studying the characters of the different substances from which plants derive their nourishment. The chemical forces play a part in all the processes of the living animal organism ; and a number of trans- formations and changes in the living body are exclu- sively dependent on their influence. The diseases in- cident to the period of growth of man, contagion and contagious matters, have their analogues in many chemical processes. The investigation of the chemi- cal connexion subsisting between those actions pro- ceeding in the living body, and the transformations presented by chemical compounds, has also been a subject of my inquiries. A perfect exhaustion of this subject, so highly important to medicine, cannot be expected without the cooperation of physiologists. Hence I have merely brought forward the purely chemical part of the inquiry, and hope to attract at- tention to the subject. Since the time of the immortal author of the " Ag- ricultural Chemistry," no chemist has occupied him- self in studying the applications of chemical principles to the growth of vegetables, and to organic processes. Xvi DEDICATION. I have endeavored 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 the path of true philosophical inquiry, which promises to lead us to truth, — the proper object of our research. In presenting this Report to the British Association I feel myself bound to convey my sincere thanks to Dr. Lyon Playfair, of St. Andrew's, for the active as- sistance which has been aiforded 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. JUSTUS LIEBIG. Giessen, September 1, 1840. EDITOR'S PHEFACE THE SECOND ENGLISH EDITION, The former edition of this work was prepared in the form of a Report on the present state of Organic Chemistry. The state of a science such as this could not be exhibited by a systematic treatise on organic compounds, but by showing, that the science was so far advanced as to be useful in its practical applications. The work was written by a Chemist, and address- ed to Chemists. The author did not flatter himself, that his opinions would be so eagerly embraced by agriculturists, as circumstances have shown to be the case. Hence his language and style were less adapt- ed for them than for those who are conversant with the abstract details of chemical science. But the eager reception of the work by agriculturists has shown, that they possess an ardent desire to profit by the aids offered to them by Chemistry. It, there- fore, became necessary to adapt the work for those who have not had an opportunity of making that science a peculiar object of study. 6* Xviii EDITOR'S PREFACE TO THE The Editor has endeavored to effect this change. In doing so, it was necessary to retain the original character of the work ; hence those alterations only have been made which are calculated to render the work more generally useful. It must be remember- ed, that the object of the author was not to write a " System of Agricultural Chemistry," but to furnish a '' Treatise on the Chemistry of Agriculture." It is to be hoped, that those who are acquainted with the general doctrines of Chemistry will find no diffi- culty in comprehending any of the principles here developed. The author has enriched the present edition with many valuable additions ; allusion may be particular- ly made to the practical illustration of his principles furnished in the supplementary Chapter on Soils. The analyses of soils contained in that chapter will serve to point out the culpable negligence exhibited in the examination of English soils. Even in the analyses of professional chemists, published in detail, and with every affectation of accuracy, the estima- tion of the most important ingredients is neglected. How rarely do we find phosphoric acid amongst the products of their analyses ? potash and soda would appear to be absent from all soils in the British ter- ritories ! Yet these are invariable constituents of fertile soils, and are conditions indispensable to their fertility. It is necessary to state, that all additions and alter- ations, with a few unimportant exceptions, have been SECOND ENGUSH EDITION. XIX submitted to the revision of the author. The Index at the end of the volume has been principally com- piled from one furnished by Professor Webster, of Harvard University, in his American edition of this work. The editor gladly avails himself of this op- portunity to thank this gentleman for the care and attention which he has displayed in superintending its republication. Primrose, November 22, 1841. OEGANIC CHEMISTEY IN ITS APPLICATION TO VEGETABLE PHYSIOLOGY AND AGKICULTURE. The object of Chemistry is to examine into the composition of the numerous modifications of mat- ter, which occur in the organic and inorganic king- doms of nature, and to investigate the laws by which the combination and decomposition of their parts is effected. Although material substances assume a vast vari- ety of forms, yet chemists have not been able to de- tect more than fifty-five bodies which are simple, or contain only one kind of matter, and from these all other substances are produced. They are considered simple only because it has not been proved that they consist of two or more parts. The greater number of the elements occur in the inorganic kingdom. Four only are found in organic matter. But it is evident that this limit to their number must render it more difficult to ascertain the precise circumstances, under which their union is effected, and the laws which regulate their combinations. Hence chemists have only lately turned their atten- tion to the study of the nature of bodies generated by organized beings. A few years have, however, sufficed to throw much light upon this interesting department of science, and numerous facts have been discovered which cannot fail to be of importance in their practical applications. 22 CONDITIONS ESSENTIAL TO NUTRITION. The peculiar object of organic chemistry * is to discover the chemical conditions essential to the life and perfect development of animals and vegetables, and generally to investigate all those processes of organic nature which are due to the operation of chemical laws. Now, the continued existence of all living beings is dependent on the reception by them of certain substances, which are applied to the nu- trition of their frame. An inquiry, therefore, into the conditions on which the life and growth of living beings depend, involves the study of those substan- ces which serve them as nutriment, as well as the investigation of the sources whence these substances are derived, and the changes which they undergo in the process of assimilation. A beautiful connexion subsists between the or- ganic and inorganic kingdoms of nature. Inorganic matter affords food to plants, and they, on the other hand, yield the means of subsistence to animals. The conditions necessary for animal and vegetable nutrition are essentially different. An animal re- quires for its development, and for the sustenance of its vital functions, a certain class of substances which can only be generated by organic beings pos- sessed of life. Although many animals are entirely carnivorous, yet their primary nutriment must be derived from plants ; for the animals upon which they subsist receive their nourishment from vegeta- ble matter. But plants find new nutritive material only in inorganic substances. Hence one great end of vegetable life is to generate matter adapted for the nutrition of animals out of inorganic substances, which are not fitted for this purpose. Now the pur- * Every vegetable and animal constitutes a machine of greater or less complexity, composed of a variety of parts dependent on each other, and acting all of them to produce a certain end. Vegetables and anim&,ls, on this account, are called organized beings ; and the chemi- cal history of those compounds which are of animal or vegetable origin, or of organic substances, is called organic cliemistrij. See Thomson's Chemistry of Organic Bodies, and Webster's Manual of Chemistry, 3d edit., p. 3G2. SUBJECT OF THE WORK. 23 port of this work is, to elucidate the chemical pro- cesses engaged in the nutrition of vegetables. The first part of it will be devoted to the exam- ination of the matters which supply the nutriment of plants, and of the changes which these matters undergo in the living organism. The chemical com- pounds which afford to plants their principal con- stituents, 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 phenomena of nature. The second part of the work will treat of the chemical processes which effect the complete de- struction of plants and animals after death, such as the peculiar modes of decomposition, usually de- scribed diS fei'inentation, putrefaction, and decay ; and in this part the changes which organic substances undergo in their conversion into inorganic com- pounds, as well as the causes which determine these changes, will become matter of inquiry. PART I. OF THE CHEMICAL PROCESSES IN THE NUTRITION OF VEGETABLES. CHAPTER I. OF THE CONSTITUENT ELEMENTS OF PLANTS. The ultimate constituents of plants are those which form organic matter in general, namely, Carbon, Hy- drogen, Nitrogen, and Oxygen. These elements are always present in plants, and produce by their union the various proximate principles of which they con- sist. It is, therefore, necessary, to be acquainted with their individual characters, for it is only by a correct appreciation of these that we are enabled to explain the functions which they perform in the veg- etable organization. Carbon is an elementary substance, endowed with a considerable range of affinity. With oxygen it unites in two proportions, forming the gaseous com- pounds known under the names of carbonic acid and carbonic oxide. The former of these is emitted in immense quantities from many volcanoes and mineral springs, and is a product of the combustion and de- cay of organic matter. It is subject to be decom- posed by various agencies, and its elements then ar- range themselves into new combinations. Carbon is familiarly known as chaj^coal, but in this state it is mixed with several earthy bodies ; in a state of ab- solute purity it constitutes the diamond.* * Wood charcoal contains about l-50th of its weigiit of alkaline and earthy salts, which constitute the ashes when it is burned. OF THE CONSTITUENT ELEMENTS OF PLANTS. 25 Hydrogen (htflamniable Air) is a very important constituent of vegetable matter. It possesses a special affinity for oxygen, with which it unites and forms water. The whole of the phenomena of decay depend upon the exercise of this affinity, and many of the processes engaged in the nutrition of plants originate in the attempt to gratify it. Hydrogen, when in the state of a gas, is very combustible, and the lightest body known ; but it is never found in nature in an isolated condition. Water is the most common combination in which it is presented ; and it may be removed by various processes from the oxygen, with which it is united in this body. Nitrogen * is quite opposed in its chemical char- acters to the two bodies now described. Its princi- pal characteristic is an indifference to all other sub- stances, and an apparent reluctance to enter into combination with them. When forced by peculiar circumstances to do so, it seems to remain in the combination by a vis inei^tice ; and very slight forces effect the disunion of these feeble compounds. Yet nitrogen is an invariable constituent of plants, and during their life is subject to the control of the vital powers. But when the mysterious principle of * This gas was discovered in 1772, and is called also aiote or azotic gas, from the Greek, expressive of its being incapable of supporting life. The name JYitrogen was given to it from its entering into the composition of nitric acid (aqua fortis). It has been suspected to be a compound, but this has not been verified. The atmosphere is compos- ed of four fifths nitrogen and one fifth oxygen, not, however, chemical- ly united ; it also contains a ten thousandth part of carbonic acid and watery vapor. A mixture of oxygen and nitrogen in the proportions named, exhibits the general properties of the atmosphere. Nitrogen may be obtained from common air by removing its oxygen, and from the lean part of flesh meat by boiling it in diluted nitric acid. It unites with different proportions of oxygen, and forms as many distinct com- pounds, viz. form 5 P^o^^o^i'^^ of Nitrogen, nitrous ^ oxide, or exhilarating gas. Binoxide of Nitrogen or Nitric oxide. Hyponitrous acid. Nitrous acid. Nitric acid. For other details, see Webster's Cliemistnj,dd edit., p. 134, &c. 3 JVitrog. 100 + Oxyg. 50 lOO + 100 100 100 ino + + + 150 200 250 26 OF THE CONSTITUENT ELEMENTS OF PLANTS. life has ceased to exercise its influence, this element resumes its chemical character, and materially assists in promoting the decay of vegetable matter, by es- caping from the compounds of which it formed a constituent. Oxygen, the only remaining constituent of organic matter, is a gaseous element, which plays a most important part in the economy of nature. It is the agent employed in effecting the union and disunion of a vas-t number of compounds. It is superior to all other elements in the extensive range of its af- finities. The phenomena of combustion and decay are examples of the exercise of its power. Oxygen is the most generally diffused element on the surface of the earth; for, besides constituting the principal part of the atmosphere which surrounds it, it is a component of almost all the earths and minerals found on its surface. In an isolated state it is a gaseous body, possessed of neither taste nor smell. It is slightly soluble in water, and hence is usually found dissolved in rain and snow, as well as in the water of running streams. Such are the principal characters of the elements which constitute organic matter ; but it remains for us to consider in what form they are united in plants. The substances which constitute the principal mass of every vegetable are compounds of carbon with ox- ygen and hydrogen, in the proper relative propor- tions for forming water. Woody fibre, starch, sugar, and gum, for example, are such compounds of carbon with the elements of water. In another class of sub- stances containing carbon as an element, oxygen and hydrogen are again present ; but the proportion of oxygen is greater than would be required for produc- ing water by union with the hydrogen. The numer- ous organic acids met with in plants belong, with few exceptions, to this class. A third class of vegetable compounds contains car- bon and hydrogen, but no oxygen, or less of that element than would be required to convert all the OF THE COMPOSITION OF THE ATMOSPHERE. 27 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 me- tallic 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 acid, and of what are termed the " indifferent substances " of plants, as well as of those peculiar vegetable compounds 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 composi- tion of a particular part or organ, it is always to be found in the fluids which pervade it. It follows from the facts th\is 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 COMPOSITION OF THE ATMOSPHERE. In the normal state of growth, plants can only derive their nourishment from the atmosphere and the soil. Hence it is of importance to be acquainted with the composition of these, in order that we may be enabled to judge from which of their constituents the nourishment is afforded. The composition of the atmosphere has been exam- 28 OF THE COMPOSITION OF THE ATMOSPHERE. iiied by many chemists with great care, and the results of their researches have shown, that its principal constituents are always present in the same propor- tion. These are the two gases, oxygen and nitro- gen, the general properties of which have been already described. One hundred parts, by weight, of atmospheric air contain 23-1 parts of oxygen, and 76-9 parts of nitrogen ; or 100 volumes of air contain nearly 21 volumes of oxygen gas. From the extensive range of affinity which this gas pos- sesses, it is obvious, that were it alone to constitute our atmosphere, and left unchecked to exert its powerful effects, all nature would be one scene of universal destruction. It is on this account that nitrogen is present in the air in so large proportion. It is peculiarly adapted for this purpose, as it does not possess any disposition to unite with oxygen, and exerts no action upon the processes proceeding on the earth. These two gases are intimately mixed, by virtue of a property which .all gases possess in common, of diffusing themselves equally through every part of another gas, with which they are placed in contact. Although oxygen and nitrogen form the principal constituents of the atmosphere, yet they are not the only substances found in it. Watery vapor and carbonic acid gas materially modify its properties. The former of these falls upon the earth as rain, and brings with it any soluble matter which it meets in its passage through the air. Carbonic acid gas is discharged in immense quan- tities from the active volcanoes of America, and from many of the mineral springs which abound in various parts of Europe; it is also generated during the combustion and decay of organic matter. It is not, therefore, surprising that it should have been detected in every part of the atmosphere in which its presence has been looked for. Saussui*e found it even in the air on the summit of Mont Blanc, which is covered with perpetual snow, and where it could OF SOILS. 29 not have been produced by the immediate agency of vegetable matter. Carbonic acid gas performs a most important part in the process of vegetable nutrition, the consideration of which belongs to another part of the work. Carbonic acid, water, and ammonia (a compound of hydrogen and nitrogen) are the final products of the decay of animal and vegetable matter. In an isolated condition, they usually exist in the gaseous form. Hence, on their formation, they must escape into the atmosphere. But ammonia has not hitherto been enumerated amongst the constituents of the air, although, according to our view, it can never be absent. The reason of this is, that it exists in extremely minute quantity in the amount of air usu- ally subjected to experiment in chemical analysis ; it has consequently escaped detection. But rain which falls through a large extent of air, carries down in solution all that remains in suspension in it. Now ammonia always exists in rain-water, and from this fact we must conclude that it is invariably pres- ent in the atmosphere. Nor can we be surprised at its presence when we consider that many volcanoes now in activity emit large quantities of it.* This subject will, however, be discussed more fully in another part of the work. Such are the principal constituents of the atmo- sphere from which plants derive their nourishment; for although other matters are supposed to exist in it in minute quantity, yet they do not exercise any influence on vegetation, nor has even their presence been satisfactorily demonstrated. OF SOILS. A soil may be considered a magazine of inorganic matters, which are prepared by the plant to suit the * The annual evolution of carbonic acid from springs and fissures in the ancient volcanic district of the EilLi, on the Rhine, has been estimated by Bischof, at not less than 100,000 tons, containing 27,000 tons of carbon. 3* 30 OF THE ASSIMILATION OF CARBON. purposes for which they are destined in its nutrition. The composition and uses of such substances cannot, however, be studied with advantage, until we have considered the manner in which the organic matter is obtained by plants. Some virgin soils, such as those of America, con- tain vegetable matter in large proportion ; and as these have been found eminently adapted for the cultivation of most plants, the organic matter con- tained in them has naturally been recognised as the cause of their fertility. T.o this matter, the term " vegetable mould " or humus has been applied. Indeed, this peculiar substance appears to play such an important part in the phenomena of vegetation, that vegetable physiologists have been induced to ascribe the fertility of every soil to its presence. It is believed by many to be the principal nutriment of plants, and is supposed to be extracted by them from the soil in which they grow. It is itself the product of the decay of vegetable matter, and must therefore contain many of the constituents which are found in plants during life. Its action will therefore be examined in considering whence these constituents are derived. CHAPTER II. OF THE ASSIMILATION OF CARBON. COMPOSITION OF HUMUS. The humus, to which allusion has been made, is described by chemists as a brow^n substance easily soluble in alkalies, but only slightly so in water, and produced during the decomposition of vegetable matters by the action of acids or alkalies. It has, however, received various names according. to the different external characters and chemical properties which it presents. Thus, ulmin, humic acid, coal of COMPOSITION OF HUMUS. 31 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 solutions of tannic and gallic acids to the action of the air. The modifications of /minus which are soluble in alkalies, are called humic acid; while those which are insoluble have received the designations oi 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 resin do not differ more widely in the proportions of their constituent elements, than do the various modifica- tions of humus. Humic acid formed by the action of hydrate f of * The soluble matters were formerly called by the eminent Swedish chemist Berzelius, extract of humus, and the insoluble geine (from the Greek yij, the earth), also apoiheme and carlonaceous hvmvs. This substance is now known to be composed of various ingredients, and of these the two acids, which have received the names of Crenic and Jipocrcnic, are particularly interesting. See Professor Hitchcock's Report, and American Joxirnal of Science, Vol. XXXVI., Art. XII. Dr. S. L. Dana considers geine as forming the basis of all the nour- ishing part of all vegetable manures, and, in the three states of " vegeta- ble extract, geine, and carbonaceous mould," to be the principle which gives fertilit}' to soils long after the action of common manures has ceased. See Report on the reexaminntion of the Economical Geology of Massachusetts. In the Third Report on the Agriculture of the Slate of Massachusetts, 1840, Dr. Dana remarks, that geine "is the decom- posed organic matter of the soil. It is the product of putrefaction; continually subjected to air and moisture, it is finally wholly dissipated in air, leaving only the inorganic bases of the plant, with which it was once combined. Now, whether we consider this as a simple substance, or composed of several others, called crenic, apocrenic, puteanic, ulmic acids, glairin, apotheme, extract, humus, or mould, agriculture ever has and probably ever will consider it one and the same thing, requir- ing always similar treatment to produce it; similar treatment to render it soluble when produced; similar treatment to render it an effectual manure. It is the end of all compost heaps to produce soluble geine, no matter how compound our chemistry may teach this substance to be." Page 191. t Hydrates are compounds of oxides, salts, &c., with definite quan- tities of water, — a substance from which all the water has been re- moved is anhydrous. Even after exposure to a red heat, caustic potash retains water. 32 OF THE ASSIMILATION OF CARBON. potash upon sawdust contains, according to the accurate 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 sul- phuric 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 analysis of Stein, 64 per cent. All these analyses have been repeated with care and accuracy, and the proportion of carbon in the re- spective cases has been found to agree with the estimates of the different chemists above mentioned; so that there is no reason 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 elements exist in it in the pro- portions for forming water ; while, according to Sprengel, the oxygen is in excess, and Peligot even estimates the quantity of oxygen at 14 equivalents, and the hydrogen at only 6 equivalents, making the deficiency of hydrogen as great as 8 equivalents. And although Mulder* has very recently explained many of these conflicting results, by showing that there are several kinds of humus and humic acids essentially distinct in their characters, and fixed in their composition, yet he has afforded no proof that the definite compounds obtained by him really exist, as such, in the soil. On the contrary, they appear to have been formed by the action of the potash and ammonia, which he employed in their preparation. 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 color by the names of humic * Bulletin des Scienc. Phys. et Natur. de Neerl.1840, p. 1-102. PROPERTIES OF HUMUS. 33 acid or humin, according as they were soluble or insoluble in alkalies ; although in their composition and mode of origin, the substances thus confounded 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 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 appar- ent reason, imputed the known properties of the humus and huniic acids of chemists to that constitu- ent 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 substance 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 considered by many as so firmly established, that any new argument in its favor has been deemed unneces- sary; the obvious difference in the growth of plants, according to the known abundance or scarcity of himms in the soil, seemed to afford incontestable 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 * This remark applies more to German than to English botanists and physiologists. In England, the idea that humus, as such, affords nour- ishment to plants is by no means general ; but on the Continent, the views of Berzelius on this subject have been almost universally adopt- ed.— Ed. 34 OF THE ASSIMILATION OF CARBON. 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. Any great im- provement in that most important of all arts is in- conceivable, without a deeper and more perfect ac- quaintance 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 hu- mus of vegetable physiologists to be really endowed with the properties recognised by chemists in the brownish black deposits, which they obtain by pre- cipitating an alkaline decoction of mould or peat by means of acids, and which they name fuimic acid.* Humic acid, when first precipitated, is a flocculent substance, is soluble in 2500 times its weight of wa- ter, and combines with alkalies, lime and magnesia, forming compounds of the same degree of solubility. (Sprengel.) Vegetable physiologists agree in the supposition that by the aid of water hiimvs is rendered capable * The extract obtained by Berzelins from black, brownish soils has been designated as humic extract, in some cases with a substance called glair in. The glairin is described by Thomson as a peculiar substance which has been observed in certain sulphureous mineral waters, and was first noticed by Vauquelin {Jinn, de Chim. XXXIX. 171-!), who de- scribed several of its properties and considered it analogous to gelatin. An account of it was drawn up by M. Anglada, of Montpellier, and communicated to the Royal Academy of Medicine of Paris, in 1827. It gelatinizes with water when sufficiently concentrated. Sometimes it is white, and at others of a red color ; when dried it shrinks to j'^th of its bulk when moist. It saturates ammonia, and decomposes several me- tallic salts. It is destitute of smell and taste. It does not glue sub- stances together like gelatin and albumen. It yields ammonia by de- composition, and is capable of putrefaction like animal bodies. The general opinion is, that it is of vegetable origin, and allied to the genus tremella, though its existence in mineral waters has not been account- ed for. Thomson's Organic Chemistry., 694. I found it very abun- dant about the hot sulphureous waters of the island of St. Michael, Azores. — W. ABSORPTION OF HUMUS. 35 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 becomes completely insoluble when dried in the air, or when exposed in the moist state to the freezing tempera- ture. (Sprengel.) Both the cold of winter and the heat of summer 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 colorless, 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 nourishment of plants, have not escaped the notice of physiolo- gists ; and hence they have assumed that the lime or the different alkalies, found in the ashes of vegeta- bles, render soluble the humic acid and fit it for the process of assimilation. Alkalies and alkaline earths do exist in the differ- ent 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 quantity of the alkaline bases contained in the ashes of plants, let us calculate the amount of humic acid which might be assimilated in this manner. Let us admit, likewise, that potash, soda, and the oxides of iron 36 OF THE ASSIMILATION OF CAKBOM. and manganese have the same capacity of saturation as lime with respect to humic acid, and then we may take as the basis of our calculation the analysis of M. Berthier, who found that 1000 lbs. of dry fir-wood yielded 4 lbs. of ashes, and that in every 100 lbs. of these ashes, after the chloride of potassium and sul- phate of potash were extracted, 53 lbs. consisted of the basic metallic oxides, potash, soda, lime, magne- sia, iron, and manganese. One Hessian acre* of woodland yields annually, according to Dr. Heyer, on an average, 2920 lbs. of dry fir-wood, which contain 6.17 lbs. of metallic oxides. Now, according to the estimates of Malaguti and Sprengel, 1 lb. of lime combines chemically with 12 lbs. of humic acid; 6.17 lbs. of the metallic oxides would accordingly introduce into the trees 74.04 of humic acid, which, admitting humic acid to contain 58 per cent, of carbon, would correspond to 100 lbs. of dry wood. But we have seen that 2920 lbs. of fir-wood are really produced. 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 w^heat growing on 1 Hessian acre would receive in that way 63 lbs. of humic acid, corresponding to 93,6 lbs. of woody fibre. But the extent of land just men- tioned produces, independently of the roots and grain, 1961 lbs. of straw, the composition of which is the same as that of woody fibre. It has been taken for granted in these calculations 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 * One Hessian acre is equal to 40,000 square feet, Hessian, or 26,910 square feet, English measure P. ABSORPTION OF HUMUS. 37 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 favorable 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 19.3 lbs. over every square foot of surface; 1 Hessian acre, or 26,910 square feet, con- sequently receive 519,363 lbs. of rain-water. 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 humate of lime (the most soluble of the huraates, and that which contains the largest proportion of humic acid) ; then the plants thus nourished would not receive more than 330 lbs. 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 2843 lbs. of corn (in grain and straw, the roots not included), or 22,000 lbs. of beet-root (without the leaves and small radical fibres). It is quite evident that the 330 lbs. of humic acid, sup- posed to be absorbed, cannot account for the quan- tity 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 vegetation. 4 38 OF THE ASSIMILATION OF CARBON. Other considei'ations of a higher nature confute 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. 2920 lbs. of firs, pines, beeches, &c. grow as wood upon one Hessian acre of forest-land with an average soil. The same superficies yields 2755 lbs. of hay. A similar surface of corn-land gives from 19,000 to 22,004 lbs. of beet-root, or 881 lbs. of rye, and 1961 lbs. of straw, 160 sheaves of 15.4 lbs. each, — in all, 2843 lbs. One hundred parts of dry fir-wood contain 38 parts of carbon ; therefore, 2920 lbs. contain 1109 lbs. of carbon. One hundred parts of hay,* dried in air, contain 44.31 parts carbon. Accordingly, 2755 lbs. of hay contain 1110 lbs. of carbon. Beet-roots contain from 89 to 89.5 parts water, and from 10.5 to 11 parts solid matter, which con- sists of from 8 to 9 per cent, sugar, and from 2 to 2| per cent, cellular tissue. Sugar contains 42.4 per cent.; cellular tissue, 47 per cent, of carbon. 22,004 lbs. of beet-root, therefore, if they contain 9 per cent, of sugar, and 2 per cent, of cellular tis- sue, would yield 1031 lbs. of carbon, of which 833 lbs. would be due to the sugar, and 198 lbs. to the cellular tissue ; the carbon of the leaves and small roots not being included in the calculation. One hundred parts of straw ,f dried in air, contain * 1(30 parts of hay, dried at 100° C. (212° F.) and burned with oxide of copper in a stream of oxygen gas, yielded 5193 water, 165-8 car- bonic acid, and G-82 of ashes. This gives 45 87 carbon, 5 76 hydrogen, 31"55 oxygen, and 6 82 ashes. Hay, dried in the air, loses 11-2 p. c. water at 100° C. (212 F. ) — {Dr. UlU.) t Straw analyzed in the same manner, and dried at 100° C, gave 46 37 p. c. of carbon, 5 08 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 IS p. c. of water. — (Dr. Will.) FERTILITY OF DIFFERENT SOILS. 39 38 per cent, of carbon; therefore 1961 lbs. of straw contain 745 lbs. of carbon. One hundred parts of corn contain 43 parts of carbon; 882 lbs. must therefore contain 379 lbs., — in all, 1124 lbs. of car- bon. 26,910 square feet of wood and meadow land pro- duce, consequently, 1109 lbs. of carbon; while the same extent of arable land yields in beet-root, without leaves, 1032 lbs., or in corn, 1124 lbs. It must be concluded from these incontestable facts, that equal surfaces of cultivated land of an average fertility produce equal quantities of carbon; 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, or the wood in a forest, receives its carbon, since there no manure — no carbon — has been given to it as nourishment 1 and how it happens, that the soil, thus exhausted, instead of becoming poorer, becomes every year richer in this element 1 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 nutri- tion 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 influence 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 influ- ence upon it, because we find that the quantity of carbon produced by manured lands is not greater 40 OF THE ASSIMILATION OF CARBON. 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 orio-in of the carbon. The carbon must be derived from other sources ; and as the soil does not yield it, it can only be extracted from the atmo- sphere. 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 inva- riable 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 25 cubic feet of oxygen in 24 hours ; 10 cwt. of charcoal consume 32,066 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 551 millions of cubic feet of this gas. When we consider facts such as these, our former QUANTITY OF OXYGEN IN THE ATMOSPHERE. 41 statement, that the quantity of oxygen in the atmo- sphere 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 another j 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 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 * 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 vapor of water, so that we may as- sume its height to be one geographical mile = 22,843 Parisian feet. Now the radius of the earth is equal to 8G0 geographical miles ; hence the Volume of the atmosphere = 9,:507,500 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. (L.) The weight of carbon which presses upon each square inch of the earth's surface being 17'39 grains, on an acre of land will be 7 tons. — (Johnston.) A man daily consumes 45,000 cubic inches (Parisian). A man yearly consumes 9505-2 cubic feet. 100 million men yearly consume 9,505,200,000,000 cubic feet. Hence a thousand million men yearly consume 0-79745 cubic miles of oxj^gen. But the air is rendered incapable of supporting the pro- cess of respiration, when the quantity of its oxygen is decreased 12 percent.; 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. When the air returns from the lungs, the carbonic acid gas amounts, on an average, to jjth of the whole ; or its quantity is increased one hundred times. — (Johnston.) A full grown man gives off from his lungs, in the course of a year, upwards of lllO lbs. of carbon. It is estimated by Johnston, that at least one third of the carbon of the food of men is daily returned to the air. 4* 42 OF THE ASSIMILATION OF CARBON. 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 averajie 0-000415 of its own volume of carbonic acid gas ; so that, allowing for the inaccuracies of the experiments, which must diminish the quantity ob- tained, the proportion of carbonic acid in the atmo- sphere may be regarded as nearly equal to jgosth 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 proportion was less in past ages; and nevertheless, the im- mense masses of carbonic acid which annually flow into the atmosphere from so many sources, ought per- ceptibly 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 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 re- moved 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, carbon exists in the atmosphere only in the form of carbonic acid, and therefore in a state of combination with oxygen. LIBERATION OF OXYGEN. 43 It has been already mentioned likewise, that car- bon and the elements of water form the principal constituents of vegetables; the quantity of the sub- stances which do not possess this composition being in a very small proportion. Now, the relative quan- tity of oxygen in the whole mass is less than in car- bonic acid; for the latter contains two equivalents of oxygen, whilst one only is required to unite with hydrogen in the proportion to form water. The veg- etable products which contain oxygen in larger pro- portion than this, are, comparatively, few in number; indeed in many the hydrogen is in great excess. It is obvious, that when the hydrogen of water is as- similated by a plant, the oxygen in combination with it must be liberated, and will afford a quantity of this element sufficient for the wants of the plants. If this be the case, the oxygen contained in the car- bonic acid is quite unnecessary in the process of vegetable nutrition, and it will consequently escape into the atmosphere in a gaseous form. It is there- fore certain, that plants must possess the power of decomposing carbonic acid, since they appropriate its carbon for their own use. The formation of their principal component substances must necessarily be attended with the separation of the carbon of the carbonic acid fram the oxygen, which must be re- turned to the atmosphere, whilst the carbon enters into combination with water or its elements. The atmosphere must thus receive a volume of oxygen for every volume of carbonic acid which has been decomposed. This remarkable property of plants has been de- monstrated 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 inde- pendently of the plant ; for if, after being separated from the stem, they are placed in water containing carbonic acid, and exposed in that condition to the 44 OF THE ASSIMILATION OF CARBON. 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 examined. When no more oxygen gas is evolved, it is a sign that all the dissolved car- bonic acid is decomposed ; but the operation recom- mences 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 al- kali that protects it from assimilation. These observations were first made by Priestley and Sennebier. The excellent experiments of De Saussure 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 confirms the view, that the elements of water are assimilated 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 undoubtedly de- pendent upon the life and development 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 inspire ; and thus the composition of the medium in which both exist, name- ly, the atmosphere, is maintained constantly un- changed. It may be asked, — Is the quantity of carbonic acid ITS SOURCE THE ATMOSPHERE. 45 in the atmosphere, which scarcely amounts to i^th. per cent., sufficient for the wants of the whole vege- tation 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 2441 lbs. weight rests upon every square Hessian foot (=0-567 square foot English) of the surface of the earth; the diame- ter of the earth and its superficies are likewise known, so that the weight of the atmosphere can be calcu- lated 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 3306 billion lbs. 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 ade- quate 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 su perficies 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 i^o^^^ of its weight, is abstracted from it during every second of time, for eight hours daily, by a field of 53,820 square feet { = 2 Hessian acres) ; then those leaves would re- ceive 1102 lbs. of carbon in 200 days.* * The qu^«''''«. with the separation of 72 eq oxygen. 36 eq. carbonic acid and 16 eq. hydrogen derived ) „, . - . , from 16 eq. water .... ^— tannic Mad, with the separation of 64 eq. oxygen. 36 eq. carbonic acid and 18 eq. hydrogen derived ) ™ ■ a -j ti-om 18 eq. water .... ^ — lartanc Jlcia, with the separation of 4.5 eq. oxygen. 36 eq. carbonic acid and 18 eq. liydrogen derived \ ,, ,. a -j from 18 eq. water .... ^ — MaucJicia, with the separation of 54 eq. oxygen. 36 eq. carbonic acid and 24 eq. hydrogen derived ) ni fT from 24 eq. water .... ^ — uuojiurpentme, with the separation of 84 eq. oxygen. It will readily be perceived, that the formation of the acids is accompanied with the smallest separation 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 diminishes in quantity, while oxygen is absorbed, when fruits are ripened in the dark ; red and yellow coloring matters are formed ; tartaric, citric, and tannic acids disappear, and are replaced by sugar, ainylin, or gum. 6 eq. Tartaric Acid, by absorbing 6 eq. oxy- gen from the air, form Grape Sugar, with the separa- tion of 12 eq. carbonic acid. 1 eq. Tannic Acid, by absorbing 8 eq. oxygen from the air, and 4 eq. 84 ASSIMILATIO OF HYDROGEN. water, form 1 eq. of Amylin, or starch, with separa- tion 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 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 ren- der the nature of the process more capable of ap- prehension; but it must not be forgotten, 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 re- verse of the chemical processes engaged in the for- mation of salts. Carbonic acid, zinc, and water, when brought into contact, act upon one another, and hydrogen is separated, while a white pulverulent 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 con- tain 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 re- turned to the atmosphere. During the progress of growth, plants appropriate carbon in the form of carbonic acid, and hydrogen from the decomposition of water, the oxygen of which is set free, together with a part of all of that contained in the carbonic acid. In the process of putrefaction, a quantity of water, exactly corresponding to that of the hydro- SOURCE AND ASSIMILATION OF NITROGEN. 85 gen, 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 proportion to the quan- tity of oxygen which they contain ; acids, therefore, yield more carbonic acid than neutral compounds ; while fatty acids, resin, and wax, do not putrefy ; they remain in the soil without any apparent change. The numerous springs which emit carbonic acid in the neighborhood of extinct volcanoes, must be regarded as another means of compensating for the carbonic acid absorbed and retained by plants dur- ing life, and consequently as a source by which oxygen is supplied to the atmosphere. Bischof calculated that the springs of carbonic acid in the Eifel (a volcanic district near Coblenz) send into the air every day more than 99,000 lbs. of carbonic acid, corresponding to 71,000 lbs. of pure oxygen. CHAPTER V. ON THE ORIGIN AND ASSIMILATION OF NITROGEN. We cannot suppose that a plant could 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 impor- tant question to be solved, therefore, is : How and in what form does nature furnish nitrogen to vege- table albumen, and gluten, to fruits and seeds 1 This question is susceptible of a very simple solu- tion. 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 86 SOURCE AND ASSIIMILATION OF NITROGEN. ammonia, which consists of this element and hydro- gen. Now, the nitrogen of the air cannot be made to enter into combination with any element except oxygen, even by the employment of the most power- ful chemical means. We have not the slightest reason for believing that the nitrogen of the atmo- sphere 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 sub- stances containing nitrogen, such as gluten, takes place in proportion to the quantity of this element which is conveyed to their roots in the state 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 eminent degree. It possesses properties which we do not find in any other compound of nitrogen : when 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 f changes, under the influence of a high temperature, into hydrocyanic acid and water, without the separation of any of its elements. * Ammonia is a compound gas, consisting of one volume of nitrogen and three volumes of hydrogen. It is produced during the decompo- sition of many animal substances. It is given off" when sal-ammoniac and lime are rubbed together. It was formerly called volatile alkali. t Formic acid (p 70. n ) is also obtained from sugar and many other vegetable substances ; a pound of sugar yields a quantity capable of saturating five or six ounces of carbonate of lime. A process for obtaining it has been given by Emmet in the Jlmcriam Journal, Vol. XXXII. p. 140. See details in Webster's Manual of Chemistry, 2d edition, p. 374. Its composition is carbon 2, water 3. With ammonia and other bases it yields the salts called formates. SOURCE AND ASSIJIILATION OF NITROGEN. 87 Ammonia forms urea,* with cyanic acid,t and a series of crystalline compounds, with the volatile oils of mustard and bitter almonds. It changes into splendid blue or red coloring matters, when in contact with the bitter constituent of the bark of the apple-tree (^phloridzi7i), with the sweet principle of the Variolaria dealbata (orciii), or with the taste- less matter of the Rocella tifictoria (^erythrin). All blue coloring matters which are reddened by acids, and all red coloring 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 vegeta- bles, 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 land there is a certain quantity of nitrogen contained both in 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 necessa- ries of life — for bodies, therefore, which contain no nitrogen. A certain proportion of nitrogen is ex- ported 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. * Urea was discovered in urine, being a constituent of uric acid. It contains the elements of cyanate of ammonia (NH4 O -f- C4 NO). t This acid consists of 1 cyanogen and 1 oxygen. See Webster's Chemistry, p. 398. 88 SOURCE AND ASSIMILATION OF NITROGEN. 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, — a7nnionia, — in the tem- perate and cold climates, and in that of a compound containing oxygen, — nitric acid, — in the tropics and hot climates. The formation of the latter is pre- ceded 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 ammonia. A generation of a thousand million men is renewed every thirty years : thousands of millions of animals cease to live, and are reproduced, 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 nitro- gen 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.* Ammo- nia is the simplest of all compounds of nitrogen; and hydrogen is the element for which nitrogen pos- sesses the most powerful affinity. The nitrogen of putrefied animals is contained in the atmosphere as ammonia, in the form of a gas * In 1786 - 7, when this churchyard was cleared out, it was discov- ered that many of the bodies had been converted into a soapy white substance. Fourcroy attempted to prove that tJie fatty body was an ammoniacal soap, containing phosphate of lime, that the fat was simi- lar to spermaceti and to wax, hence he called it adipocire. Its naelting point was 120..")° F. For notice of the analysis and opinions of other chemists, see Uke's Dictionary of Arts and Manufactures, p. 14. PRODUCTS OF PUTREFACTION. 89 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, is of extreme solubility in water.* Am- monia, therefore, cannot remain long in the atmo- sphere, 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 in- tervals of time between the showers are in summer greater ; and when 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 we have formerly stated, that all the analyses of atmospheric air hitherto made have failed to de- monstrate the presence of ammonia, although, ac- cording 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 nitro- gen contained in a cubic foot of air is certainly ex- tremely small, but, notwithstanding this, the sum of the quantities of nitrogen from thousands and mil- lions of dead animals is more than sufficient to sup- ply all those living at one time with this element. From the tension of aqueous vapor at 15° C. (59° F.) = 6,98 lines (Paris measure), and from its known specific gravity at 0° 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 35*3 cubic feet of aqueous vapor are contained in 487 cubic metres, or 17,198 cubic feet of air; 35*3 cubic feet of aqueous vapor weigh about 1.65 lb. Conse- quently, if we suppose that the air saturated with moisture at 59° F. allows all the water which it con^ * According to Dr. Thomson, water absorbs 780 times its bulk of ammonia. 90 SOURCE AND ASSIMILATION OF NITROGEN. tains in the gaseous form to fall as rain, then l-l pound of rain water must be obtained from every 11,477 cubic feet of air. The whole quantity of am- monia 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 11,477 cubic feet of air contain a single grain of ammonia, then ten cubic inches, — the quantity usually employed in an analy- sis, — must contain only 0.000000050 of a grain. This extremely small proportion is absolutely inap- preciable by the most delicate and best eudiometer ; * it might be classed among the errors of observation, even were its quantity ten thousand times greater. But the detection 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 11,477 cubic feet of air." If a pound of rain-water contain only ,^th of a grain of ammonia, then a field of 26,910 square feet must receive annually upwards of 88 lbs. of ammonia, or 71 lbs. of nitrogen ; for by the observations of Schu- bler, which were formerly alluded to, about 770,000 lbs. of rain fall over this surface in four months, and consequently the annual fall must be 2,310,000 lbs. This is much more nitrogen than is contained in the form of vegetable albumen and gluten, in 2920 lbs. of wood, 3085 lbs. 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. f * A eudiometer is an instrument used in the analyses of the atmo- sphere. It means a measure of purity. It is also used in the analysis of mixtures of gases. Several varieties are described in Webster's Mannal, p. 137. t The advocates of the importance of humus as a nourishment for plants, being driven from their position by the facts brought forward in the preceding chapters, have found in the ammonia of the atmosphere an explanation of the manner in which humus acquires its solubility, and therefore its capability of being assimilated by plants. Now, it is very true that humic acid is soluble in ammonia ; but the humic acid of chemists is nnt contained in soils. Were it so, on treating mould with water we should obtain a dark-colored solution of humate of ammonia. But we obtain a solution whicii is entirely devoid of this acid. It can- EXISTENCE OF AMBIONIA IN RAIN. 91 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, because no per- son thouofht of searchinjj for it.* All the rain-water employed in this inquiry was collected 600 paces southwest 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 addi- tion of a little muriatic acid, a very distinct crystal- lization of sal-ammoniac was obtained : the crystals had always a brown or yellow color. Ammonia may likewise be always detected in snow- water. Crystals of sal-ammoniac were obtained by evaporating in a vessel with muriatic acid several pounds of snow, which were gathered from the sur- face 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. f It is worthy of observation, that the ammonia con- tained in rain and snow water possesses an offensive smell of perspiration and animal excrements, — a fact which leaves no doubt respecting its origin. not be too distinctly kept in mind that humic acid is the product of the decomposition of //7