ART. IV. Chemistry in its application to Agriculture and Physiology. By Justus Liebig, M. D., &c. James M. Campbell & Co. 1843.

We do not know that we can fill a few of our pages more profitably to some of our readers, than by directing their attention to the great subject of scientific agriculture. Every statesman knows that agriculture is the chief of the great pecuniary interests of society; and that it must be made the foundation of every enlightened system of political economy. It becomes then, the duty not only of the man of science, but of the statesman, to enquire into the means which the progress of knowledge has furnishd for fostering this cardinal interest. And it is the duty not of the statesman only, but also of all that great class who constitute the foundation of the political edifice, the agriculturalists, to enquire, what science has done, in its rapid onward march, to improve the great interest, which in the social organization, has been entrusted to their care. Indeed, every class, and individual, in the society of every civilized man, has a deep interest in this great subject. For there is no such thing, in the circle of human employments, as an isolated and antagonist interest. All are dependent on each other. And agriculture is the foundation of them all.

The same practical philosophy, which has torn off the veil from so many other mysteries of the universe, and discovered to man a knowledge by which he can promote his physical comforts, is fast disclosing those secrets of vegetable organism, which together with the truths of inorganic chemistry will enable us to build up a system of scientific agriculture that will effect as great a revolution in the culture of the earth, as steam and the mechanic arts have produced in the manufacture of the substances derived from it. Since the property which oxygen has of converting hydrogen into water, and carbon or charcoal, into carbonic acid gas, while with nitrogen it does not unite except under peculiar circumstances, has been made use of by Liebig and other colaborators, to analyze organic substances by heating them with a compound capable of imparting oxygen sufficient to saturate their hydrogen and carbon, the organic branch of chemistry has been extended until it occupies a very large space in the circle of the sciences. The process is performed in a tube of refractory glass, the aeriform pro

ducts being made to pass successively through other tubes and bulbs containing solids and liquids, of which the one absorbs the carbonic acid, the other, the water; and the respective quantities of the products taken up are subsequently ascertained by being weighed. This process has been greatly improved by Liebig, though it was originally suggested by Gay Lussac and Thenard. By this simple process is chemistry unveiling the hitherto unapproachable mysteries of vegetation. All vegetables, are now known to be composed of four simple bodies, carbon, hydrogen, nitrogen and oxygen, together with a comparatively minute quantity of inorganic matter.. The question then very readily suggests itself to the vegetable physiologist, from whence does the plant derive the elements which constitute it ?

They must be derived from the atmosphere or the earth; or from both. It had long been known, that marine plants. reaching the enormous height of three hundred and sixty feet, and which nourish thousands of marine animals, grow upon naked rocks. It was obvious that they could not draw their nourishment through their roots, from the rock, as its surface underwent no change. They must therefore derive it through their leaves from the sea-water, in which they float, spread out in their enormous ramifications, so that every part of the plant is presented to the surface of the water. And sea-water is found to contain all the constituents of plants, carbonic acid, ammonia, and the alkaline and earthy phosphates and carbonates, required by these plants for their growth, and which are always found to be the constituents of their ashes. It is therefore seen that plants may derive all their nourishment through their leaves. But do terrestrial plants also derive all their nourishment through their leaves? This cannot be so; because the only medium from which these plants can derive nourishment through their leaves, is the atmosphere, and it does not contain all the elements of plants. The atmosphere is composed of oxygen, and nitrogen, together with watery vapour and carbonic acid gas, to which Liebig adds ammonia, which are not all the constituents of plants, the inorganic matter being wanting. Terrestrial plants must therefore derive some nourishment at least from the soil. But do they derive all their nourishment from the soil? It is evident that they do not. Because, though the earth is a magazine of organic as well as inorganic matter, yet as plants are found

to flourish upon soils where the quantity of carbon and nitrogen contained in them cannot have been in the soil, as well as from many other facts, the conclusion is irresistible, that terrestrial plants derive their nourishment from both the atmosphere and the soil. And what, to the uninformed, must appear extraordinary, Liebig has proved, by one of the most beautiful specimens of inductive research to be found in the whole history of philosophy, that nearly all the carbon which forms the woody tissue of plants is derived from the carbonic acid of the atmosphere, and not from decayed vegetable matter in the earth, as had been supposed. He shows by calculation, that agreeably to analysis, there are three thousand millions of millions of pounds of carbon in the air in the state of carbonic acid, and infers that the carbon in all the mineral coal known, bears but a small proportion to that thus existing in the aeriform state; and in this way he indicates that there is carbonic acid in the air sufficient to supply the woody tissue to all the vegetation upon the face of the earth. He maintains also that the nitrogen of plants is derived indirectly from the ammonia of the atmosphere, and supports this opinion with great acumen and dialectical ingenuity, urging considerations in favour of it, which he thinks, "give to this opinion a degree of certainty which completely excludes all other views of the matter." We see then that plants derive some of their nourishment from the soil and some from the atmosphere.

It has been found that plants which are peculiar to a certain locality contain elements peculiar to the soil of that locality. Inland plants for example, yield by incineration, potash; and plants on the borders of the ocean, yield soda, an analogous substance; and in various species of grain certain salts are found to exist, always in a certain ratio. Liebig very justly infers from this, supported by other considerations, that however minute are the proportions of these substances, unless they are in the soil, the plant can not be successfully cultivated; as these substances can not be furnished by the atmosphere. And it is now well settled, that unless there are in the soil, certain alkaline and other mineral substances, plants can not assimilate the carbonic acid and ammonia of the atmosphere, from which their woody tissue and their nitrogen are formed. The presence in the soil of these substances is an indispensable condition to enable the plants to derive advantage from the elements. furnished to them by the atmosphere.

These considerations open before us the whole field of agricultural chemistry.

In order then to show the influence which the progress of knowledge has exercised upon agriculture, let us look back a little into its history, and in the course of the survey, apply the scientific principles, which we have developed, in elucidation of the subject!

When our forefathers landed upon these shores, the agriculture of the country was nothing but a few patches of stunted corn and unwholesome herbs cultivated by the Indians here and there amidst the millions of acres of forests. All the agricultural product from the St. Lawrence to the Red river, and from the Atlantic ocean to the Pacific did not then amount to that which is now the product of some one county in every State in the Union. And the agriculture of all Europe was at one time in as low a state as that of the Indians. But by the diffusion of knowledge, it has attained its present comparatively flourishing condition. And as wide as is the difference between the agriculture of the Indians when this country was discovered, and that which now enriches and beautifies our fields, we believe that chemistry and the mechanic arts are destined to effect quite as wide a difference between our present agriculture, and that which, in some future generation of our race, is destined to bless the world with its abundance.

We must not infer from the fact that improvements in agriculture have heretofore been so slow, that they will continue to be so for the future. The chief cause why these improvements have been so slow, is that agriculture has always been an empirical art, in which improvements must be made only after repeated trials of various means, through many ages, and after many failures, and even then succeeding in most instances, more from accident, than intelligent design. For it has been only a few years since any thing was known either of the organic structure or the elementary constituents of plants; or of the nature of the soil or of the atmosphere from which, as we have shown, are derived all the elements concerned in vegetation, or of the nature of water which is an all-important agent in vegetation. Je thro Tull as late as 1733, published a treatise, in which he maintained the opinion, that minute earthy particles supplied the whole nourishment to vegetables, and that air and water were merely useful in disintegrating these particles from the earth; and that the whole agency of manures is

mechanical, as they merely render the soil more mellow. This ingenious author was led to this theory, from the fact, that a minute division of the soil by pulverization of it by exposure to dew and air, acts so favourably upon vegetation. In 1754 Duhamel a celebrated horticulturalist adopted the opinion of Tull, and maintained that by dividing the soil, any number of crops might be raised in immediate succession from the same land; and that manures are useless, if the earth is kept sufficiently pulverized by other means. And in ancient times, many philosophers, from observing in southern countries the luxuriancy of vegetation near water, thought that water was the element of which all vegetables are composed, and that all plants are finally resolved into water again. And as late as 1610 Van Helmont, thought that he had actually proved by experiment that all the products of vegetables are capable of being produced from water. These are the philosophical principles relative to agriculture which prevailed amongst the learned until very late times. With such notions on the part of those whose office it is in the organization of society to enlighten such as are engaged in the practical pursuits of agriculture, how can we wonder, that they, who have tilled the earth, should have been so ignorant of the true principles upon which their noble art depends, and that improvements in agriculture should have been so slow. It is true that Lord Bacon, with mavellous sagacity conjectured some very important agricultural principles relative to the succession of crops, and improving vegetables by grafting and contiguous planting, yet as his inferences were founded entirely upon an induction of facts observed in the growth of vegetables, and not upon any knowledge of vegetable physiology or of the chemical elements of plants or soils, they could at most lead merely to empirical agriculture, with all the inaptitude and hindrances of a mere empirical art.

But agriculture is now fast being extricated from its shackles, and is acquiring all the freedom which every science gives to its kindred art. The true agency of the soil the atmosphere and water in vegetation, have now been discovered. The soil is known to furnish to plants certain inorganic matters which are essential to their growth; the atmosphere to furnish to them certain constituents which form their organic matter; and the water is known to act as a solvent and vehicle of all soluble matter in the