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its food from the air. Its inorganic constituents must be found in the soil or in the manure in the form of silicates, carbonates, or phosphates, and may be supplied in a crude form as in potash, ashes, lime, bones, &c. Its nitrogen is to be supplied, in the form of ammonia, from decayed animal or vegetable substances in one way or another. The excrements of some animals are in this respect much richer than those of others. The excrements of inan are much richer in nitrogen, than those of any other animals, and those of men living upon animal more so than those of inen living upon vegetable diet. In the urine of animals nitrogen is found in much greater abundance than in the solid excrements. In respect to nitrogen, 100 parts of the urine of a healthy man are equal to 1300 parts of the fresh dung of a horse. This ammonia is supplied in the soil ; or floating in the air, it is taken up by rain water or by snow, and supplied to the vegetation in that form. The manures of different animals likewise return to the soil the inorganic constituents of plants, the various salts which have formed a part of the vegetable products, which have been taken from the fields and been consumed by the cattle; and thus every thing goes on in an eternal round of reciprocity.
We have thus given a general and imperfect sketch of the main principles of the work of Liebig. We have confined ourselves to the part, which is principally agricultural. The second part, on chemical transformations, fermentation, putrefaction, decay, and various kindred subjects, is equally interesting ; but we cannot now examine it. We regard the work of Liebig as a work of extraordinary philosophical acumen, and conferring upon him the highest honor. The more it is examined, the deeper will be the interest which it will create, and the stronger the admiration of the ability with which it is written. It is not a work to be read, but studied ; and if further inquiries and experiments should demonstrate, as seems to us from many facts within our own knowledge in the highest degree probable, the soundness of his views, his work, not merely as a matter of the most interesting philosophical inquiry, but of the highest practical utility, will be invaluable.
We are much indebted to Dr. Webster for giving this handsome edition to the public, enriched with several valuable notes. We could have wished that the introduction, intended as explanatory of the general principles of chemistry,
compiled from another work of Liebig, and designed to assist the unlearned reader, had been appended instead of prefixed; for either from an inherent fault of expression, or from badness of translation, some portions of it are so intensely obscure (witness for example the 129th and 195th paragraphs among many others), that it must operate as a great discouragement to the perusal of the main work with many persons, serving as it now does, instead of an explanation, in some cases only to render darkness visible.
There are various notes, appended to the volume, of great interest. It is mentioned that Mr. Hayes, who stands in the foremost rank among our practical chemists, had discovered the
presence of ammonia in the rain waters in Vermont; but it does not appear that he had given the fact to the public. A long and highly interesting note is appended, containing some letters from Dr. S. L. Dana, of Lowell, to Dr. Hitchcock, of Amherst College, and taken from the forthcoming third edition of Dr. Hitchcock's “Geology of Massachusetts, on geine or humus, and some views of Dr. C. T. Jackson, of Boston, on the same subject.
The views of these gentlemen in some measure conflict with each other, and with those of Liebig. We do not propose to arbitrate between them, but only to remark on them, in a very few words, with a perfect respect for all the parties concerned. The eminent Swedish chemist, Berzelius, bad discovered in several vegetable substances, a residuum, which he regarded as the proper food or pabulum of vegetables, and which he denominated humus or geine. Dr. Dana, by his independent researches, had arrived at the same result. This geine or apotheme was found to be the uniform result of decayed vegetation ; and soils are in general found productive or otherwise, as this vegetable substance or residuum is more or less abundant in them. The opinion of Dr. Dana has been that geine in a dissolved state is taken up as the food of plants. If obliged to relinquish this ground, and with Liebig, regard geine as only a source of carbonic acid to plants, he would regard its value to vegetation in the same light. But he obviates in a most ingenious manner one of the difficulties of Liebig, in respect to the solubility, or, we may more properly say, the solution of geine, by showing that it contains within itself the instrument, to a considerable degree, of its own resolution, in the water formed by the union of the hydrogen of the geine with the oxygen of the atmosphere.
6. The amount of water produced in this case," he remarks, " is truly astonishing. It has been found equal per hour, from an acre of fresh ploughed sward, to 950 lbs. This is equal to the evaporation per hour from an acre, after most copious rains. To show that this depends upon the decomposition of the geine, the quantity of water evaporated per hour in the day time, from a well-manured acre, was found equal to 5000 lbs.”
That humus or geine does not constitute the actual food of plants would seem to be established by various considerations. Liebig has shown by several calculations, as exact as the nature of the case would seem to admit of, that the amount of humic acid contained in any soil is insufficient to supply the carbon in the average product of that soil, in the proportion of 91 to 2650. Secondly, volcanic salts, containing not the slightest trace of vegetable matter, as is evident from their origin, with a due mixture of earths are among the most fertile in the world. The ashes being exposed to air and moisture, a soil is gradually formed, and the decomposed lavas furnish alkalies in abundance, which, by being exposed to air and moisture, become the source of rich nourishment to plants. A third reason, and certainly a strong fact in the case, is, that the bumus in a forest, so far from being diminished by the growth of wood, is continually increasing. It is so, likewise, in a cultivated field, where the produce of that field is returned in the form of manure.
Berzelius is reported to have altered his opinions of the nature of geine, by a more exact analysis of its composition, and now denies its existence as a proximate principle ; and Dr. C. T. Jackson, who has distinguished himself as a chemist by his analytical researches, appears to have made, without knowing what had been done by Berzelius, the same discoveries, in ascertaining that the substance called geine is only a combination of crenic and apocrenic acids, with some other substances, all of which are not yet determined. How many of these may have been, as suggested by Dr. Dana, the mere product of chemical manipulation, or whether any of them, are questions, which, in the present state of the inquiry, cannot be determined. Upon the supposition that these are original and fixed elements in the composition of geine, we consider Dr. Jackson entitled to much honor for his investigations. All truth is valuable; but, in the present condition of our knowledge, in a practical view, these points are not of great importance, or rather not of immediate utility. According to the principles of Liebig, Raspail, Dana, Jackson, Hitchcock, and others, the presence of hunius in a soil is, quoad hoc, an indication of fertility. Now, whether it be a proximate element, or a mere combination of crenic and apocrenic acids with other substances, though exceedingly interesting to the philosophical inquirer, is, without some further light on the subject, of little moment to the farmer. Dr. Jackson has not, as we understand, discovered either of these acids in the plants themselves ; he has not shown us how they are to be used, or what part they perform in vegetation. He is not able by any artificial process, which he can adopt, separate from the vegetable organism, to produce an atom of geine; and, however nearly he may have approached it, and we commend hiin for every step in his progress, he has by no means reached the ultima Thule ; for crenic, and apocrenic, and ulmic acids, are themselves resolvable into certain proportions of carbon, hydrogen, nitrogen, and oxygen. The question, however, whether geine constitutes in itself the food of plants, in its solution by water or by some alkaline substance, or whether it merely acts as an instrument of the supply of carbonic acid to the plant in the first stages of its progress, is another question, which is certainly not without its difficulties. not able to understand by what process it is ascertained, that, after the leaves of the plant are formed, it ceases to draw any nourishment from the earth. This is a fact in vegetable physiology, of which at present we are without the proof. Dr. Dana has never denied that plants receive much of their nourishment from the air. His inquiries were limited wholly to what they gather from the earth.
Nor do we see any difficulty in the supposition that geine may serve, in its decomposition, as the food of plants. For, if geine, according to Dr. Jackson, is a mixture of crenic or apocrenic acids, and if crenic and apocrenic acids are resolvable into carbon, hydrogen, nitrogen, and oxygen, these are the very elements of vegetable substance; and we may leave it to the subtile operations of that vital action, wonderful and mysterious as it is in ils operations, to accomplish what human skill and sagacity have as yet in vain essayed, the separation and appropriation to itself, by the living plant or animal, of the proper materials of its own growth.
It is exceedingly gratifying to see men of science engaging in these, we will not say humble, for scarcely any are more important, but useful subjects of investigation. Every department of nature abounds in matters of interesting inquiry ; and none more than that of organic life. Nature in her various changes, transformations, and productions, is everywhere full of the miracles of wisdom, power, and goodness. The perfections of the Creator are written all over ber in letters of living light. The highest duty of rational beings is “ 10 read, mark, learn, and inwardly digest them.”
In looking at the infinitely multiplied productions of the vegetable world, in observing a small seed rising into a towering plant, an acorn changed into an oak, and what seems a minute pellicle, driven about by the wind, growing up into a mighty and wide-spreading eln, we must be lower than the beasts, which repose under its grateful shade, if we do not ask, How can these things be? When we see the earth in a measure obedient to our commands, and in return for our labor pouring into our laps the means of subsistence and luxury with an unstinted liberality ; when we see the dependence everywhere existing between what we do and what we receive, what we sow and the harvest we gather ; when we observe the changes of the seasons, and the obvious effects of light and heat, and moisture and manure, we can hardly claim the character of rational beings, if we do not seek to understand how these things are. It is idle to pretend that the mysteries of nature are 100 sacred for inquiry. The gist of understanding and the power of its use imply the duty of inquiry. It is as idle to pretend, that they are mysteries which never can be understood. The human understanding has its limits, doubtless, beyond which it cannot pass; but how far is it at present from having reached them ? Every day is disclosing to us some new truth. Many things, once enveloped in all the terrors of mystery, are now familiar to the understanding of a child. The works of God and the courses of his providence are not so many isolated facts, but they are facts compacted together, and under the control of general laws; so that beyond all question, inany of the most extraordinary phenomena, which present themselves in nature, are explicable upon the simplest principles. In many cases a single key will open the most complicated lock, and is at the same time applicable to a thousand others. The discussions of Liebig furnish some beautiful illustrations of these principles.