The American Agriculturist 3(2):56-59 (1844)
REVIEW OF LIEBIG. Chemistry in its Applications to Agriculture and Physiology. Third Edition.

It is rather more than three years since this remarkable book was laid before the British Association. In that time two editions have been printed; they have been received on the one hand with most extravagant praise, and on the other with unmeasured censure. The first was attributable to the clearness with which some views that are really new, and others that are thought so, were brought before the public; the second arose from the manner in which Professor Liebig was so ill-advised as to attack vegetable Physiologists, of whose science he knows much less than they of chemistry. The issue of all this has been productive of much good. Had it not been for English trumpets, public attention would never have been so strongly directed to Professor Liebig's excellences; and we have to thank the German catcalls that his own thoughts have been so advantageously turned to the correction of his deficiencies. The two together have produced a book infinitely superior to its predecessors, and to a very considerable extent unlike them. We hear no more of starch consisting of concentric layers of wax and amylin; the exaggerations about grand experiments on woods and meadows are omitted, as is the materialism about the unimportance of a vital principle, (p. 56, ed. 2,) and the offensive observations upon physiologists. In the place of these and other subjects that are cancelled we have a very considerable quantity of new matter. A new chapter is devoted to the consideration of "the Formation of Arable Land," another to "Fallows;" that on the "Rotation of Crops," is almost entirely rewritten, and so is the chapter on manures; while a thirteenth chapter is devoted specially to a general retrospect of the theories included in the previous pages. To these are added supplementary chapters on the sources of ammonia, and on the questions whether nitric acid is food for plants, and whether the nitrogen of the air takes a part in vegetation. In an appendix are given at length the important experiments of Wiegmann and Polstorf on the food of plants.

In the former editions ammonia was the great subject of discussion. As chemists seem agreed in considering it improbable that plants should obtain their nitrogen directly from the air, and as all plants contain that element, ammonia seems to be the only source by which it can be supplied; and in all probability this is a just view of the case. Nevertheless it is by no means proved that larger quantities of ammonia than the atmosphere naturally contains are necessary to the most healthy vegetation; and although it is certain that matter rich in ammoniacal salts is among the most powerful of manures, it has by some been supposed that other substances constantly present along with the ammonia may be of equal or even greater importance. Such is sulphuretted hydrogen; such are phosphates. This opinion is now taken up by Professor Liebig, who devotes a whole chapter to its consideration. After stating that animal matter contains invariably the substances named albumen, fibrin, and casein, all three rich in sulphur, he inquires:—

"From what source does the animal body derive these three fundamental components? Unquestionably they are obtained from the plants upon which the animals subsist; but in what form and in what condition, are they contained in plants?

"Recent investigations of chemists have enabled us to answer these questions with positive certainty. Plants contain, either deposited in their roots or seeds, or dissolved in their juices, variable quantities of compounds containing sulphur. In these nitrogen is au invariable constituent. Two of the compounds containing sulphur exist in the seeds of cereal plants, and in those of leguminous vegetables, such as peas, lentils, and beans. A third is always present in the juices of all plants; and it is found in the greatest abundance in the juices of those which we use for the purposes of the table.

"A very exact inquiry into the properties and composition of these substances has produced a very remarkable result, namely, that the sulphur-compound dissolved in the juice of plants, is, in reality, identical with the ALBUMIN contained in the serum of blood, and in the white of an egg; that the sulphur-compound in the seeds of the cereals possesses the same properties and composition as the FIBRIN of blood: and that the nutritious constituent of peas, beans, and lentils, is actually of the same nature and composition as the CASEIN of milk. Hence it follows that plants, and not animals, generate the constituents of blood containing sulphur. When these are absent from the food given to an animal, its blood can not be formed. From this it also follows, that vegetable food will be proportionally nutritious and fit to sustain the vital processes of the animal body, according to the amount of these ingredients contained within it.

"There also exists certain families of plants, such as the cruciferae, which contain peculiar sulphur-compounds much richer in that element than the vegetable constituents of blood. The seeds of black-mustard, the horse-radish, garlic, onions, and scurvy-grass, are particularly marked in this respect. From all of these plants we obtain, by simple distillation with water, certain volatile oils, differing from all other organic compounds not containing sulphur, by their peculiar, pungent, and disagreeable odor.

"These compounds containing sulphur are present in the seeds of all plants, as well as in the plants themselves; and as they are particularly abundant in cultivated plants employed for animal nutrition, it is quite obvious that a substance containing sulphur is absolutely essential to the development of such compounds, in order to supply to them their proper proportion of this element."

These are very remarkable statements, and require to be considered with great attention. The opinion, however, that sulphur is beneficial to plants is not originally Liebig's; he, on the contrary, so lately as 1842, adopted the erroneous views of Christison and Turner, and regarded the "hydrosulphate of ammonia (sulphuret of ammonium) as a deadly poison to vegetables, the properties of which we can not change by dilution." (Ed. 2, p. 195.) It was, however, proved experimentally by Mr. Edward Solly, (First Report of the Chemical Committee of the Horticultural Society, p. 9, June, 1842,) that this was a mistake.

"I made use of the hydrosulphuret of ammonia, the very compound described by Liebig as being a 'deadly poison;' but in place of killing plants, I found that in small quantity it produced decidedly beneficial effects: in some cases when it was applied to plants in an unhealthy state from the action of other substances, it had the effect of invigorating them, and of restoring their leaves to a healthy, green, and crisp condition. The plants with which these effects were best observed were the garden-lettuce and the common Windsor-bean. The solution of the hydrosulphuret of ammonia employed was prepared by mixing a saturated solution of the compound with fifty times its bulk of water: such a solution had a most nauseous disgusting smell, and contained of course a large quantity of sulphuretted hydrogen. The plants under experiment were selected from many, and were of the same age and size, and as far as possible in the same healthy state of growth. Some were watered with common water, others with a dilute solution of hydrosulphuret of ammonia. At first only a few drops of the solution were given, hut finding that this produced little or no effect, the dose was increased, and as much as half an ounce a day, and sometimes even more, was given to each plant; it was found that those thus treated became stronger and sturdier, their leaves were of a bright deep-green, the space between the nodes, or the distance from leaf to leaf, was shorter, and the stems were stronger, and the whole plant more flourishing than in those watered in the ordinary way, although all other circumstances were alike, and care was taken to place all under the same condition, by exposing them equally to air and light, and giving them the same quantity of water every day. Plants in a languid state from overdoses of nitrate of potash, or soda, or other saline manures, if not too much injured by their previous treatment, appeared to recover more rapidly when watered with the solution of hydrosulphuret of ammonia, than when merely treated with common water. In some of these latter cases a much stronger solution was employed than that already mentioned, containing two drachms of the saturated solution of hvdrosulphuret of ammonia in fifty of water, and of this eight drachms were given daily. For sometime after thus watering the plants, the earth retained a strong smell of sulphuretted hydrogen, and the water which drained through, when tested by a salt of lead, evidently contained a large quantity of that gas." And then he proceeds to point out the extreme improbability, that a substance so constantly evolved from decaying matter as sulphuretted hydrogen should not be the food of plants. "Its presence in manures is well-known and readily proved, but its presence in the air, in which it exists in exceedingly minute quantity, is less readily shown. We know, however, that it is constantly being formed on the surface of the earth, and we have evidence of its presence in the air by several effects, such as the tarnishing of some metals, and the blackening of white paint these effects, which take place gradually and slowly, are principally occasioned by the presence of sulphuretted hydrogen and its compounds, more particularly the hydrosulphuret of ammonia, in the air. Lastly, if the vegetable kingdom is the great means of purifying the air, and retaining it in a fit state for the respiration of men and animals, the absorption and decomposition of sulphuretted hydrogen by plants must constitute not the least important of their functions."

We believe, too, but can not lay our hands upon the passage, that Dr. Lankester had previously brought forward some evidence to show that sulphuretted hydrogen is not injurious to vegetation.

The source from which sulphur is obtained by plants is not the atmosphere, according to Dr. Liebig, but the soil, Whence it is furnished by the decomposition of sulphates. "The air," he says, (p. 63,) "can not contain any substances in which sulphur is present, unless, indeed, we except minute and scarcely appreciable traces of sulphuretted hydrogen." We confess our inability to understand this. That ammonia is obtained from the air was one of the author's triumphant proofs, Bud yet it exists there in as minute and inappreciable a quantity as sulphuretted hydrogen; and we can not comprehend why the latter should not be thus supplied as well as the former. If not, what, let us ask, becomes of the volumes of this gas continually escaping from the surface of the soil? Are we to suppose that it is all consumed in forming sulphurets? Surely not.

Next to sulphur stand phosphates in their importance to vegetation. This, indeed is not a new doctrine; on the contrary, their value was pointed out in the former editions; not, however, we think, so strongly as now. We are rejoiced to find Prof. Liebig ranged on this side of the question, for it seems to us that if practical agriculture points out one thing more strongly than another, it is the great importance of phosphates. Nothing is more remarkable than the action of the superphosphate of lime on plants in gardens; no single agent that we have yet seen employed can be compared to it. This probably arises from garden-soil being rich in all other substances except phosphoric acid, which is always largely carried off, and but sparingly returned in the processes of garden-culture. The remarks of Prof. Liebig on this subject are too striking to be omitted:—

"In a former letter I showed you how great a waste of phosphates is unavoidable in England, and referred to the well-known fact that the importation of bones restored in a most admirable manner the fertility of the fields exhausted from this cause. In the year 1827 the importation of bones for manure amounted to 40,000 tons, and Huskisson estimated their value to be from 100,000l to 200,000l sterling. The importation is still greater at present, but it is far from being sufficient to supply the waste.

"Another proof of the efficacy of the phosphates in restoring fertility to exhausted land is afforded by the use of the guano—a manure which, although of recent introduction into England, has found such general and extensive application.

"We believe that the importation, of one hundred-weight of guano, is equivalent to the importation of eight hundred-weight of wheat—the hundred-weight of guano assumes in a time which can be accurately estimated the form of a quantity of food corresponding to eight hundred-weight of wheat. The same estimate is applicable in the valuation of bones.

"If it were possible to restore to the soil of England and Scotland the phosphates which during the last fifty years have been carried to the sea by the Thames and the Clyde, it would be equivalent to manuring with millions of hundred-weights of bones, and the produce of the land would increase one third, or perhaps double itself in five or ten years.

"We can not doubt that the same result would follow if the price of the guano admitted the application of a quantity to the surface of the fields, containing as much of the phosphates as have been withdrawn from them in the same period.

"If a rich and cheap source of phosphate of lime and the alkaline phosphates were open to England, there can be no question that the importation of foreign grain might be altogether dispensed with after a short time. For these materials England is at present dependant upon foreign countries, and the high price of guano and of bones prevents their general application, and in sufficient quantity. Every year the trade in these substances must decrease, or their price will rise as the demand for them increases.

"According to these premises, it can not be disputed, that the annual expense of Great Britain for the importation of bones and guano is equivalent to a duty on grain: with this difference only, that the amount is paid to foreigners in money.

"To restore the disturbed equilibrium of constitution of the soil,—to fertilize her fields,—England requires an enormous supply of animal excrements, and it must therefore excite considerable interest to learn that she possesses beneath her soil beds of fossil guano, strata of animal excrements, in a state which will probably allow of their being employed as a manure at a very small expense. The coprolithes discovered by Dr. Buckland, (a discovery of the highest interest to Geology,) are these excrements; and it seems extremely probable that in these strata England possesses the means of supplying the place of recent bones, and therefore the principal conditions of improving agriculture— of restoring and exalting the fertility of her fields.

"In the autumn of 1842, Dr. Buckland pointed out to me a bed of coprolithes in the neighborhood of Clifton, from half to one foot thick, enclosed in a limestone formation, extending as a brown stripe in the rocks, for miles along the banks of the Severn. The limestone marl of Lyme Regis consists, for the most part, of one fourth part of fossil excrements and bones. The same are abundant in the lias of Bath, Eastern and Broadway Hill, near Eversham. Dr. Buckland mentions beds, several miles in extent, the substance of which consists in many places, of a fourth part of coprolithes.

"Pieces of the limestone-rock of Clifton, near Bristol, which is rich in coprolithes and organic remains, fragments of bones, teeth, &c., were subjected to analysis, and were found to contain above 18 per cent, of phosphate of lime. If this limestone is burned and brought in that state to the fields, it must be a perfect substitute for bones, the efficacy of which as a manure does not depend, as has been generally but erroneously supposed, upon the nitrogenized matter which they contain, but on their phosphate of lime. The osseous breccia found in many parts of England deserves especial attention, as it is highly probable that in a short time it will become an important article of commerce. What a curious and interesting subject for contemplation! In the remains of an extinct animal world, England is to find the means of increasing her wealth in agricultural produce, as she has already found the great support of her manufacturing industry in fossil fuel,—the preserved matter of primeval forests,—the remains of a vegetable world."

We quote this passage for the sake of showing the vivid style of the author, and not because we quite concur in Prof. Liebig's anticipations concerning coprolites, whose value is probably exaggerated.

From these we turn to other considerations. It will be remembered that in former editions the author adopted, as a proved fact, the theory of excrementitious deposites by plants, and even went so far as to assert that it was a necessary consequence of their secreting power, that excrementitious matters should be formed. We and others have pointed out the objections that must be taken to these views; and upon turning over the pages of this new edition we at first believed that they had been quietly abandoned. We find, however, at p. 75, that the accuracy of Macaire Prinsep's views is still unquestioned, at least in part. In this instance Dr. Liebig relies upon the following case :—

"Let us," he says, "consider the composition of the ashes of two fir-trees, as analysed by an acute and most accurate chemist. One of these grew in Norway, on a soil of invariable composition, but to which soluble salts, and particularly common salt, were conveyed in great quantity by rain-water. How did it happen that its ashes contained no appreciable trace of salt, although we are certain that its roots must have absorbed it after every shower?

"We can explain the absence of salt in this case by means of the direct and positive observations referred to, which have shown that plants have the power of returning to the soil all substances unnecessary to their existence."

But to our apprehension, there must either be some error in these analyses, or the trees never could have absorbed any salt. For if they had ever taken it up, there must have been some portion remaining at the time when they were felled. It strikes us that this case proves too much.

But if the old theory of vegetable excrements be virtually abandoned, or limited to the extrication of oxygen, (p. 170,) we have a new one, which is not a little curious. Professor Liebig considers bark a kind of excrement. To avoid the suspicion of misrepresentation we quote his words:—

"These barks are in so far true excrements, that they arise from living plants, and play no further part in their vital functions; they may even be removed from them, without thereby endangering their existence. It is known that certain trees throw off annually their barks: this circumstance viewed in its proper light, shows that, during the formation of certain products formed by the vital processes, materials arise which ate incapable of experiencing a further change.

"There is every reason to believe that this separation takes place over the whole surface; it is observed not only on the stem, but also on the smallest twigs; and hence we must conclude that the same excretory process goes on in the roots."

We will not set about seriously refuting this strange hallucination, but content ourselves with asking whether scurf-skin, the points of our hairs, the ends of our nails, or the slough of a snake, are excrements?

We had hoped that Professor Mohl had put an end to the folly of asserting that dryness of the soil is of no consequence to plants when matured; that is, we suppose, when the fruit is ripened. We are, however, mistaken. Professor Liebig maintains this opinion with as much pertinacity as if there was not a tree or bush within a hundred miles of Giessen:—

"When a plant is quite matured, and when the organs by which it obtains food from the atmosphere are formed, the carbonic acid of the soil is no further required.

"Deficiency of moisture in the soil, or its complete dryness, does not now check the growth of a plant, provided it receives from the dew and from the atmosphere as much as is requisite for the process of assimilation. During the heat of summer it derives its carbon exclusively from the atmosphere."

It seems useless to put him right upon such points, for he does not appear to be acquainted with some of the commonest facts connected with vegetable life. We shall therefore dismiss the subject for the present without further comment, in the hope that with time this learned chemist may become sensible of such errors as this, and his speculations about lactescent plants, which he still maintains have their moisture secured from evaporation by a coating of caoutchouc and wax, which surrounds them by a waterproof envelope ! ! Gardeners' Chronicle.


American Agriculurist 4:226 (1847)

New Manure.—It is said that Professor Liebig has discovered a mineral substance, which, when combined with guano, will produce one of the most fertilizing manures known. A joint-stock company, with a capital of £120,000 sterling, composed for the most part of leading English capitalists, has been formed for the purpose of carrying on upon a large scale the manufacture of the new compound. Among the subscribers are several eminent professors of agriculture, who, according to the Impartial du Rhin, give out that the application of this substance to the culture of lands will produce an entire revolution in the agricultural system.