Agricultural Chemistry

CHEMISTRY, AGRICULTURAL. Chem isty, " The corner stone," in its broad sense, as now understood, is that science which treats of events and changes in natural bodies not accom panied by sensible motion . According to Ure, it is that science which investigates the compensation of material substances and the permanent changes of constitution which their mutual action produce. Forcroy defines it to be that science which explains the intimate mutual action of all natural bodies. To accomplish the object decomposi tion and combination are the two great forces employed. By the first (analysis) the chemist resolves substances into component parts, and by combination (synthesis) they are brought together again. The older chemists (alchemists) were long employed in the endeavor to find the talisman which would convert the baser metals into gold, and later, in finding a universal solvent (alkaltast). The Arabians first taught chemistry, but in a very crude way. Alchemists flourished up to the sev enteenth century, but in the succeeding and more enlightened age, they were thrown into contempt. The science has since been prosecuted with a view to discover the natural properties and composi tion of matter. Agricultural chemistry seeks to explain all the actions of earth, air and water, upon plants, and their chemical relation to the geology, mineralogy and chemistry of the soil. Chemistry is the great force in nature and has aptly and cor rectly been defined as being the corner stone of agriculture. All soils are composed originally of rock, which has been carried about and ground down through successive epochs and ages in the earth's history. For this reason fertile soils do not necessarily overlie those rocks richest in the inorganic constituents of plants, for plants used as food are cultivated on every variety of rock foundation which the earth presents. The fertile soils of the West, (See article Geology) and those of the whole United States, as a rule, have been transported long distances; have been ground down by glacial action and floods, depos ited as silt by water; have been decomposed by chemical action, and molded over, time and again, by chemical action through the growth of plants upon them ; for the growth of plants is simply phases of that great and wonderful natural force, chemical action. Rocks are divided into two great classes: those formed by fire, ;:nd those formed by water. These divisions relate both to the origin and distribution. Dr. Dana says : In their origin, all rocks are truly igneous, or from fire. In their distribution they are aqueous, or by water. This is the only division necessary to the farmer. It is the division taught and demanded by agricultural geology. The first class includes all the highly crystalline rocks, granite, gneiss, sienite, greenstone, porphyry; it includes, also, basalt and lava. The products of volcanoes, whether ancient or modern, agricultural geology places in the same class, including thus all that portion which forms the largest part of the earth's surface. The second class includes sand, clay, gravel, rounded and rolled stones of all sizes, pudding-stone, conglomerates, sandstones, slates. When these various substances are examined, a large part of sand is found to be composed essen tially of the ingredients of the igneous rocks. This is true, also, of sandstone, slate, of conglom-' crates, of bowlders. There is a large deposit, or formation, in some districts, composed almost wholly of some of the chemical constituents of the igneous rocks, united to air. The constitu ents are lime and magnesia; the air is carbonic acid, forming, by their union, carbonates of lime and magnesia. Marble. limestone, chalk, belong to this formation. These are not to be ranked as original igneous products subsequently distributed by water. The lime, originally a part of igneous rocks, has been separated and combined with air, by animals" or plants, by a living process called secretion. The modern production of carbonate of lime is still going on, under the forms of shells and corals. Though belonging to neither division, the subject will be simplified by referring limestone to the second class of rocks; but it is truly a salt. The chemi cal constitution. of rocks is similar. If rocks are divided into two classes, the first composed of those usually called primary, such as granite, gneiss, mica-slate, porphyry ; and the second class, composed of rocks usually called trappean, as basalt, green-stone, trap, then the great differ ence in their chemical constitution is this: The first or granitic class, contains about twenty per cent. more of silex, and from three to seven per cent. less of lime and magnesia and iron, than the second. or trappean class. If the language of geology is borrowed, and rocks which present the appearance of layers, or a stratified structure, are divided into two classes, fossi]iferous and non-fossiliferous, or those which do, and those which do not contain remains of animals or plants, it will be found, that the fossiliferous are neither granitic nor trappean, yet are they to be classed with the last, agreeing with these, in containing less silica, and more lime, magnesia, and alumina. The stratified, non-fossiliferous rocks agree in chemical composition with the granitic, and the fossiliferous with the trappean and volcanic. The trappean and fossiliferous contain the most lime and magnesia; the gran itic and non•fossiliferous the most silex. The great difference in chemical composition between the two classes, is produced by lime and magne sia, two substances which, more than all others, have been thought to influence the character of the soil. The amount of this difference is about from three to seven per cent. ; yet notwithstand ing this, the general chemical constitution of all rocks approaches so nearly to similarity, that this may be laid down as the first principal in agricultural chemistry, that there is one rock, consequently one soil. A survey of the geo graphical distribution of plants, used for food, will show that the common doctrine of the chem ical influence of rocks on vegetation is not so well supported as to be considered an established principle. It is not intended to deny that rocks do, by their physical condition, affect vegetation. Unless it is shown that their physical state depends upon their chemical constitution, the second principle must be admitted as a general truth. It has been distinctly avowed by Johnston, in his Lectures, that where the soil forms only a surface layer of considerable depth of trans ported materials, it may have no relation what ever, either in mineralogical characters or in chemical constitution, to the immediately subja cent rocks. This is the• genefal disposition of soil. . It is admitted by the author above quoted, that, in Great Britain, in some counties, and in nearly all the coal-fields, the general character and capabilities of the soil have no relation whatever to the rocks on which the loose mate rials immediately rest. A distinguished author ity in our country, Prof. Norton, of Yale, for merly the pupil and assistant of Prof. Johnston, speaking of fertile soils, says that these always contain appreciable quantities of some ten or twelve substances. It makes no difference from whence you bring such a soil, from what part of the world it comes, it will invariably contain these elements in greater or less quantity. Fer tile soils are not confined to particular rock for mations; they are found overlying all formations, —they are so independent of the rock beneath, that they invariably contain similar elements. Though it may seem premature to place before all who may read this work, the results of analy ses, before they have become familiar with chem ical names, yet those, here used, are so common that the proof adduced may not be misunder stood. The analysis of the ashes of plants grown on different geological formations, in soil which is stated to have proceeded from the decomposition of the underlying rock, proves how little depend ent is the plant on the chemical constitution of the soil. The ashes of the grape-vine, grown on four different soils, afford: In No. 4, all the phosphoric acid is included in phosphate of lime, and iron. This analysis is by Crasso, the others by Hruschauer. No. 1 was grown on soil from the debris of quartzose rocks, by the decomposition of gneiss, mica-schist, clay slate, chlorite, hornblende, quartz, and a little lime. No. 2, from soil formed of decomposed limestone, variety called transition. No. 3, from soil formed of decomposed mica-slate. No 4, from soil formed of decomposed porphyry. It is evident, that where the soil has not proceeded from geological drift, as in No. 1, widely differ ent geological formations afford all the mineral elements of plants. Mr. Charles Fox in a work designed for the use of schools and colleges, thus defines the effects of light, and its chemical action: A ray of the sun's light consists of seven rays of different colors, which, uniting, form the ordinary white light. But, besides this, the sun's rays contain three different kinds of rays, as a ray of light, of heat, and a ray of chemical agency. The effect of these on vegetation is essen tially different. Yellow light impedes germina tion, and accelerates that decomposition of carbonic acid, which produces wood and woody tissues. Under its influence, leaves are small and wood short jointed. Red light carries heat, and is favorable to germination if abundance of water is present, increases evaporation, supports the flowering quality, and improves fruit. Under its influence, color is diminished, and leaves are scorched. Blue light, (also called chemical action, or actinism,) accelerates germination, and causes rapid growth. Under its influence, plants become weak and long jointed. These three agencies exist in different proportions in the sunbeam in the spring, summer, and autumn, The blue is greater in spring; the yellow, in summer. The blue, (chemical ray) is less in the fall; and then the heating ray, red, predominates. Thus the sun's rays differ in their properties at different seasons of the year; and are adapted to the peculiar needs of the plant at the time. Still further, the proportions of these agencies vary in different latitudes and climates. Daguerreotypes, depend ing on these principles, are poor in England, better in France, superior in New York, but best in the Northwestern States. Probably the chemical rays are more abounding in the above proportion, but there is yet much to learn on this subject; and it is not unlikely that the many differences known to exist in animal and vege table life in these countries will be found to be more or less controlled by these peculiarities of the sun's rays. Gardeners have attempted to make practical use of these facts by means of •colored glasses, but, apparently, without much success. Agricultural Chemistry teaches of the -composition of the soil and of manures, showing the relative quantities of soluble and insoluble pabulum contained. Thus a soil may contain the inherent principles of fertility, and yet it may be locked up, because insoluble. The air is the great reservoir of fertility, for into the air all organic matter ultimately escapes, and from thence it is again returned to the soil. Decay and decomposition convert organic matter into gases. As such they are held by the air until washed down by the rain, or set free by electrical action. Of these nitrogen is the most important. James F. W. Johnston, in his Lectures on Agricul tural Chemistry, treats of the chemical changes by which the substances of which plants chiefly consist are formed from those on which they live. A digest of his remarks must suffice: Before a seed will begin to sprout, it must he placed for a time in a sufficiently moist situation. In the seed no circulation can take place—no motion among the particles of matter—until water has been largely imbibed; nor can the food be con veyed through the growing vessels, unless a con stant supply of fluid be afforded to the seed and and its infant roots. A certain degree of warmth —a slight elevation of temperature—is also favor able, and in most cases necessary, to germination. The degree of warmth which is required in order that seeds may begin to grow, varies with the nature of the seed itself. In Northern Siberia

and other icy countries, plants are observed to spring up at a temperature but slightly raised above the freezing point (32° F.,) but it is fami liar to every practical agriculturist, that the seeds he yearly consigns to the soil require to be pro tected from the inclemency of the weather, and sprout most quickly when they are stimulated by the warmth of approaching spring, or by the heat of a summer's sun. The same fact is fami liarly shown in the malting of barley, where large heaps of grain are moistened in a warm atmosphere. When germination commences, the grain heats spontaneously, and the growth in creases in rapidity as the heap of corn attains a higher temperature. It thus appears that some portion of that heat which the growth of the germ and radicles requires, is provided by natural processes in the grain itself ; in some such way as, in the bodies of animals, a constant supply of heat is kept up by the vital processes—by which supply the cooling effect of the surrounding air is continually counteracted. It has been observed that seeds refuse to germinate if they are entirely excluded from the air. Hence seeds which are buried beneath such a depth of soil that the atmospheric air cannot reach them, will remain long unchanged, evincing no signs of life—and yet, when turned up or brought near the surface, will speedily begin to sprout. Thus in trench ing the land, or in digging deep ditches and drains, the farmer is often surprised to find the earth, thrown up from a depth of many feet, become covered with young plants, of species long extirpated from or but rarely seen in his cultivated fields. Yet light is, generally speaking, prejudical to germination. Hence the necessity of covering the seed, when sown in our gardens and corn fields, and yet not so far burying it that the air shall he excluded. When seeds are made to germinate in a limited portion of atmospheric air, the bulk of the air undergoes no material alteration, but on examination its oxygen is found to have diminished, and carbonic acid to have taken its place. Therefore, during germination, seeds absorb oxygen gas and give off carbonic acid. Hence it is easy to understand why the presence of air is necessary to germination, and why seeds refuse to sprout in hydrogen, nitrogen, or carbonic acid gases. They cannot sprout unless oxygen be within their reach. The leaves of plants in the sunshine give off oxygen gas and absorb carbonic acid,—while in the dark the reverse takes place. So it is with seeds which have begun to germinate. When exposed to the light they give off oxygen instead of carbonic acid, and thus the natural process is reversed. But it is necessary to the growth of the young germ, that oxygen should be absorbed, and car bonic acid given off—and as this can take place to the required extent only in the dark, the cause of the prejudical action of light is sufficiently apparent as well as the propriety of covering the seed with a thin layer of soil. During germina tion, vinegar (acetic acid) and diastase are pro duced. That acetic acid is formed is shown by causing seeds to germinate in powdered chalk or carbonate of lime, when after a time acetate of lime may be washed out from the chalk (Brawn not) in which they have been made to grow. The acid contained in this acetate must have been formed in the seed, and afterwards excreted or thrown out into the soil. When the germ has shot out from the seed and attained to a sensible length, it is found to be possessed of a sweet taste. This taste is owing to the presence of grape sugar in the sap which has already begun to circulate through its vessels. It has not been clearly ascertained whether the vinegar or the diastase is first produced when germination com mences, but there seems little doubt that the grape sugar is formed subsequently to the appearance of both. The young shoot which rises upwards from the seed consists of a mass of vessels, which gradually increase in length, and after a short time expand into the first true leaves. The ves sels of this first shoot do not consist of unmixed woody fibre. The vessels of the young sprout, therefore, and of the early radicles, probably consist of the cellular fibre of Payen. They are unquestionably formed of a substance which is in a state of transition between starch or sugar and woody fibre, and which has a constitution analogous to that of both. Having thus glanced at the phenomena which attend upon germina tion, let us now consider the chemical changes by which these phenomena are accompanied. The seed absorbs oxygen and gives off carbonic acid. Now it appears that in contact with the oxy gen of the atmosphere, a portion of the starch is actually separated into carbon and water, the carbon at the moment of separation uniting with the oxygen, and forming carbonic acid, This acid is given off into the soil in the form of gas, and thence partially escapes into the air. The action of dilute acids gradually changes starch into cane sugar, and the latter into grape sugar. While it remains in the sap of the sprouting seed, the vinegar may aid the diastase in transforming the insoluble starch into soluble food for the plant, and may be an instrument in securing the conversion of the cane sugar, which is the first formed, into grape sugar,—since cane sugar can not long exist in the presence of an acid. The early sap of the young shoot is sweet; it contains grape sugar. This sugar is also derived from the starch of the seed. Being rendered soluble by the diastase formed at the base of the germ, the starch is gradually converted into grape sugar as it ascends. The water which is im bibed by the seed from the soil, forms an abun dant source from which the whole of the starch, rendered soluble by the diastase, can be supplied with the elements of the two atoms of water which are necessary to its subsequent conversion into grape sugar. The diastase is formed when the seed begins to sprout, at the expense of the gluten or vegetable albumen of the seed. When the true leaf becomes expanded, true wood first appears in sensible quantity. When the true leaf is formed the plant has entered upon a new stage of its existance. Up to this time it is nourished almost solely by the food contained in the seed—it henceforth derives its sustenance from the air and from the soil. The apparent mode of growth is the same, the stem shoots upwards, the roots descend, and they consist essentially of the same chemical substances, but they are no longer formed at the expense of the starch of the seed, and the chemical changes of which they are the result are entirely different The leaf absorbs carbonic acid in the sunshine. and gives off oxygen in equal hulk. It is in the light of the sun that plants.. increase in size— their growth, therefore, is intimately connected with this absorption of carbonic acid. If car bonic acid be absorbed by the leaf and the whole of its oxygen given off again, carbon alone is added to the plant by this function of the leaf. But it is added in the presence of the .water of the sap, and thus is enabled by uniting with it to form, as it may be directed, or as may be necessary, any one of these numerous compounds which may be represented by carbon and water, and of which the solid parts of plants are chiefly made up. There are two ways in which we may suppose the oxygen given off by the leaf to be set free, and the starch, sugar, and gum, to be subsequently formed. The action of light on the leaf of the plant may directly decompose the carbonic acid after it has been absorbed, and cause the oxygen to separate from the carbon, and escape into the air; while at the same . instant the carbon thus set free, may unite with the water of the sap in different proportions, so as to produce either sugar, gum, or starch. Or the action of the sun's rays may be directed, in the leaf, to the decomposition, not of carbonic acid, but of the water of the sap. The oxygen of the water may be separated from the hydro gen, while at the same instant the latter element (hydrogen) may unite with the carbonic acid to produce the sugar or starch. The result here is the same as before, but the mode in which it is brought about is very differently represented, and appears much more complicated. Water is first decomposed and its oxygen evolved, then its hydrogen again combines with the carbon and oxygen of the carbonic acid, and forming two products—water and sugar or starch. This view is not only more complicated, but it supposes the same action of light to be—continually, at the same time, and in the same circumstances— both decomposing water and re-forming_ it from its elements. While, therefore, there can be no doubt, for other reasons not necessary to be stated in this place, that the light of the sun really does decompose water in the leaves of plants, and more in some than in others—yet.it appears probable that the oxygen evolved by the leaf is derived in a great measure from the car bonic acid which is absorbed; and that the principal part of the solid substance of living vegetables, in so far at least as it is derived from the air, is produced by the union of the carbon. of this acid with the elements of water in the sap. Prof. R. C. Kedzie, in an address before the Michigan Legislature, on The Application of Chemistry to Practical Agriculture and the Laws of Health, thus describes the duties of an agri cultural chemist: One duty often assigned to the agricultural chemist by those who know little either of chemistry or agriculture, is to analyze the soil, as if the chemical analysis of the soil would determine every question of its. agricultural capabilities, the kind, amount, and quality of the crops it would raise. In the early history of the science, analysis of certain barren soils revealed the cause of the barrenness in the sulphate of iron present. When this was re moved or decomposed by lime, the soil was fruit ful. A few instances of this kind gave great hopes of benefit from But such instances of barrenness from purely chemical causes are extremely rare and exceptional. But it is often found that the most careful chemical analysis will not distinguish between a. barren and a fertile soil. One reason is that the barren ness may be due to physical causes—for instance, want of drainage. Chemical analysis can only determine the chemical conditions of the soil, and will not always reveal physical evils. Agri cultural chemists now regard the analysis of the soil as of only secondary importance. One duty, of the chemist is to explain the facts which are already known in agriculture. By knowing the reason why we do a thing we may discover bet ter ways Of doing it, or that some other or easier process may accomplish the same result. We thus sift our processes and eliminate needless. elements or introduce better ones. The chem ist may benefit the farmer by making analyses of manures and determining their nature and value. Artificial manures are being largely in troduced into this country, and farmers may want to know whether it will pay to buy and use them. The Sheffield Scientific School, of Connecticut, has done the farmers of the East good service by analyzing these manures—the superphosphates, • guanos, etc —showing their composition and real cash value. The chemist may aid the farmer by showing the value of manurial matters within his reach, enabling him to secure at home what is now imported at such great expense from abroad. Deherain, of France, made the important discovery that when veget able matter undergoes decomposition in presence of some alkaline substance, it combines with free nitrogen and retains it in a fixed form. Thia has been confirmed at the Sheffield Scientific. School, and science may yet point out the means by which the farmer may make at home all the combined nitrogen he may need for his farm. Some late researches have shown many important and interesting facts in the relations of chemistry to agriculture. Thus the experiments of Prof. Goessman, of the Massachusetts Agricultural Col lege, upon the culture of the beet, have shown that it is better that the organic matter in the soil should.