De Saussure, and even by Ingenhousz himself. | power of different species of vegetable There scarcely exists a theory in natural sci-food is in proportion to the nitrogen they ence in favour of which there are more clear contain. and decisive arguments. How, then, are we to account for its not being received in its full extent by most other physiologists-for its being even disputed by many-and considered by a few as quite refuted ?'—p. 34.

Without entering into minute details, we may state that Professor Liebig has shown that all the nitrogen of plants and animals is derived from ammonia; and This Professor Liebig attributes to two that this ammonia is furnished by the atcauses. First, that most botanists and mosphere, from which it is brought to the physiologists have not availed themselves earth in every shower of rain. Its quanof the assistance of chemistry in their re- tity in the atmosphere is relatively very searches, owing to their slender know- small, but amply sufficient for all the deledge of that science; secondly, that those mands of the animal and vegetable kingwho have experimented, in all good faith, dom. Indeed, as all the nitrogen of past on this very point, have made their re- generations of plants and animals must, searches in a manner totally opposed to in the process of putrefaction, have been all the principles of experimental philo. sent into the atmosphere in the form of sophy. They were utterly unacquainted ammonia, its presence in the air might with the art of experimenting, which, as have been anticipated. It is to Professor he justly says, can only be learned in the Liebig, however, that we owe the experilaboratory. Both accusations are true to mental proof of the fact. He has shown a certain extent; it is certain that if phy- that "the ammonia contained in rain and siologists had availed themselves of che- snow-water always possessed an offensive mistry they would have advanced farther: smell of perspiration and putrid matters as also that if certain experimenters had -a fact which leaves no doubt respecting practically learned the art of research, its origin" (p. 76). From the rain-water they would never have thought of attach- it is absorbed into the plants; and our ing any importance to the results of such author has shown that, previous to its unexperiments as Professor Liebig describes: but we venture to offer a third explanation, namely, that the arguments for the doctrines established by this writer were Although, in the case of land not ma never till now laid down in a clear and nured, all the ammonia is derived from logical manner; and the having done this the atmosphere, it is otherwise in those entitles him to the same honour as if these cases where animal manure is employed. doctrines had originated with him. In One chief use of animal manure is to fact, when the illustrious philosophers yield more ammonia than the air can furwhose names are mentioned above made nish; and for this purpose, those kinds of their researches, chemistry was not suf- manure are obviously the best which conficiently advanced to afford the same tain the largest proportion of ammonia or means of deciding the question as it does of nitrogen. Hence the high value of now. In the opinion held by our author, liquid manure compared with solid, the which indeed it is the chief object of his former being far richer in nitrogen than work to inculcate, that it is to chemistry the latter :we must look for the future improvement of physiology and of agriculture, we cor- Agriculture differs essentially from the culti dially concur. The next generation, both vation of forests, inasmuch as its principal object of physiologists and of eminent agricul- form capable of assimilation by animals; while consists in the production of nitrogen in some turists, we confidently predict, will be the object of forest-culture is confined principalmen accomplished in the art of chemical ly to the production of carbon.'—p. 85. research; and for this we shall be mainly indebted to Professor Liebig.

dergoing those chemical metamorphoses which cause its assimilation, it may be detected in the juices of almost all plants.

Wheat, for example, is composed of Passing over an interesting section on two principles, starch and gluten; of the assimilation of hydrogen by plants, which the latter alone contains nitrogen. we must briefly allude to that on the Now an increased supply of nitrogen in source of the nitrogen in the vegetable the form of ammonia not only increases kingdom. This element is highly im- the number of seeds obtained from one portant, as being an essential part of plant, but also the proportion of gluten those vegetable products which serve as to starch, in other words the nutritive food for man and animals. Indeed Bous- power, of those seeds. Thus 100 parts singault had proved that the nutritive of wheat grown on land manured with

cow-dung, a manure containing the small- the inorganic or mineral constituents of est proportion of nitrogen, afforded only plants. And here we have another admi11.97 parts of gluten; while the same rable specimen of the manner in which he quantity grown on a soil manured with handles an obscure and difficult subject. human urine, which is very rich in nitro- He first points out that all plants contain, gen, yielded the largest proportion of although in small quantity, certain minegluten yet found, namely, 35.1 per cent. ral substances, often different in different Professor Liebig, after bringing for- plants, but generally the same in the ward numerous proofs that it is ammo- same species. Thus for example, the nia which yields to plants all their nitro- stems and leaves of all the gramineæ ingen, then proceeds to explain the princi- variably contain silicate of potash, while ple on which gypsum, burnt clay, and phosphate of magnesia and ammonia are ferruginous earth acts in promoting ferti- found in their seeds. He then shows that lity. All these substances possess the pro- those alkaline or earthy bases which are perty of absorbing and fixing the ammo- found in the ashes of plants in the form nia, whether derived from the air or from of carbonates, existed originally in the manure. Many other substances have plants in the form of salts, that is, comthe same effect; such as powdered char- bined with vegetable acids which have coal, diluted acids, &c., and some of these been destroyed by the combustion. As will no doubt be employed hereafter. It certain of these vegetable acids are peis easy to see why gypsum, for example, culiar to certain species, and constantly does not equally improve all soils. In occur in them, he concludes that they are some there is already a sufficient quantity essential to the development of the species either of gypsum, or of some analogous in which they occur; and as they occur substance, to fix all the ammonia that they in combination with alkaline bases, it is receive. If sterile, their sterility must obvious that these bases also are essendepend on some other cause: forno tial to the plants. conclusion,' says the author, can have a better foundation than this, that it is the ammonia of the atmosphere (where manure is not used) that furnishes nitrogen to plants.'

We have already seen that the carbon is furnished by carbonic acid, while water yields the oxygen and hydrogen:

"Carbonic acid, water, and ammonia contain the (organic) elements necessary for the support of animals and vegetables. The same substances are the ultimate products of the chemical processes of decay and putrefaction. All the innumerable products, therefore, of vitality resume, after death, the original form from which they sprung. And thus death-the complete dissolution of an existing generation-becomes the source of life for a new one.'—pp. 91, 92.

In many cases-for example, in wheat the acids as well as the bases are of mineral origin; and in others, such as opium and cinchona bark, the bases are organic, while the acids are partly mineral and partly vegetable. Further, it appears that one base or acid may, within certain limits, supply the place of another, without injury to the plant; while, in most cases, the absence of the proper mineral base or acid arrests entirely the development of the plant. Thus, opium contains variable proportions of sulphuric and meconic acids; and when there is much of the latter there is always a deficiency of the former. In cinchona bark, quinine and lime are found; and the more lime is present, the less quinine does the bark contain. Again, pine-wood in one soil has been found to contain much lime, little potash, no magnesia; in a different soil, less lime, more potash, and a certain quantity of magnesia; but in both, the power of the bases taken together to neutralize acids was almost exactly equal. Nay, a third specimen, containing potash, soda, lime, and magnesia, was still found to have the same neutralizing power. These curious facts, all taken from the researches of the most accurate observers, but observed without special reference to this point, and consequently beyond all suspicion, lead to the conclusion that each vegetable requires a

definite amount of mineral bases to com-geously cultivated in that soil, which of bine with its proper acid or acids; and them cannot be so cultivated, and how consequently that these bases have an the soil may be rendered capable of proimportant function to perform in the ducing the latter as well as the former. economy of the plant. In many cases Lastly, we learn on what the exhaustion this function can only be performed by of soils depends; on the removal, nameone base and one acid. Thus, in wheat-ly, in the crop, of the mineral elements straw silica is the acid and potash the contained in the plant; for if these be base; and without these materials, happi-not restored the soil retains too little for ly present in most soils, wheat cannot another crop. Hence the use of allowing thrive. It may be, indeed, that the silica land to lie fallow; for during fallow the and potash are not combined; the potash action of air and moisture extracts a might be, and probably is, in part combin- fresh supply of bases from the subjacent ed in wheat with an organic acid; but rock, and prepares the soil for a new the fact is not the less certain, that silica crop. and potash are as essential to the growth of wheat as carbonic acid, water, and

ammonia.

"The perfect development of a plant, according to this view, is dependent on the presence of alkalies or alkaline earths; when these substances are totally wanting its growth will be arrested; and when they are deficient it must be impeded.

facts.

We have already said that Professor Liebig deserves the highest praise for his manner of treating this subject, and for the clearness with which he has demon'Let us compare two kinds of tree, the wood strated the absolute necessity of the min- of which contains unequal quantities of alkaline eral constituents of plants, which have bases, and we shall find that one of these grows been generally viewed as accidentally luxuriantly in several soils on which the others present. But he has gone further, and 10,000 parts of oak wood yield 250 parts of are scarcely able to vegetate. For example, has shown that on this principle are to be ashes, the same quantity of fir wood only 83, of explained the good effects of many prac-lime wood 500, of rye 440, and of the herb of tices empirically pursued. Nay, he has the potato-plant 1500. proved that cow-dung, the most common Firs and pines find a sufficient quantity of animal manure, which, as already men- alkalies in granitic and barren sandy soils, in tioned, is very poor in nitrogen, is valua- which oaks will not grow; and wheat thrives ble, not on account of its organic, but its bases which are necessary to bring it to complete in soils favourable to the lime tree, because the inorganic contents, namely, potash and maturity are present in sufficient quantity. The phosphates. It is not easy to imagine a accuracy of these conclusions, so highly import more unexpected result, one more satis-ant to agriculture and to the cultivation of factorily demonstrated, or one more ca- forests, may be proved by the most evident pable of immediate practical application. From the section on the inorganic ele- of their leaves and stalk a large quantity of silicic All kinds of grasses contain in the outer parts ments of plants we gather the following acid and potash, in the form of acid silicate of highly important conclusions. First, that potash. The proportion of this salt does not since the carbon and nitrogen of plants vary perceptibly in the soil of corn-fields, because are derived from the atmosphere, the it is restored to them as manure in the form of causes of fertility must be sought for in putrefying straw. But this is not the case with the mineral or inorganic elements of the a meadow, and hence we never find a luxuriant soil. Secondly, that since one plant re- contain little potash, evidently because one of crop of grass on sandy and calcareous soils, which quires different mineral elements from the constituents indispensable to the growth of another, a soil may be fertile for one the plants is wanting. Soils formed from basalt, plant and sterile for another, or vice grauwacke, and porphyry are, ceteris paribus, versâ; or, finally, fertile for both. Third- the best for meadow land, on account of the ly, that an exact analysis of the ashes of quantity of potash which enters into their comevery part of a plant will give us a corposition. The potash abstracted by the plants rect knowledge of those mineral substan-tained in the soil itself is inexhaustible in com is restored by the annual irrigation. That conces which are essential to its develop parison with the quantity removed by plants. ment, and which therefore must be pre- But when we increase the crop of grass in a sent in the soil in which we wish to grow meadow by means of gypsum, we remove a the plant. Fourthly, that a careful analy-greater quantity of potash with the hay than sis of any soil, the composition of the can, under the same circumstances, be restored. ashes of a certain number of plants being previously known, will teach us at once which of these plants may be advanta

Hence it happens that after the lapse of several with gypsum diminish, owing to the deficiency years the crops of grass on the meadows manured of potash. But if the meadow be strewed

occasionally with wood-ashes, even with the lixiviated ashes which have been used by soapboilers, then the grass thrives as luxuriantly as before. The ashes are only a means of restoring the potash.

'A harvest of grain is obtained every thirty or forty years from the soil of the Luneburg-heath, by strewing it with the ashes of the heathplants which grow on it. These plants during the long period just mentioned collect the potash and soda which are conveyed to them by rain water; and it is by means of these alkalies that oats, barley, and rye, to which they are indispensable, are enabled to grow on this sandy heath.'-p. 104–106.

In like manner the author explains that during life that portion of the inorganic constituents of the food which is not assimilated by the animal must be found in its excrements. We have thus two sources of animal manure-the excrements, and the residue left after putrefaction; in other words, the earth of bones.

Pro

It is commonly supposed that cow and horse-dung act by virtue of their organic constituents, which on the one hand in decaying yield humus, or a carbonaceous residue, and on the other ammonia. fessor Liebig has shown that, admit. In reference to this interesting subject ting the value of humus (which he has we would mention the following anec- proved elsewhere to consist in its yielddote, for the truth of which we can ing a slow and constant supply of carbonvouch, having heard it attested by the ic acid, partly to the air, partly to the parties themselves. A distinguished pro- roots of plants), the quantity of humus fessor of chemistry in Germany, in dis- yielded by these manures is quite trifling cussing with the author the question of compared to the amount of carbon colthe use of alkalies to plants, and in par- lected in the crop; and we have already ticular the necessity of potash for the seen that horse and cow-dung contain growth of wheat, mentioned, as unfavour- very little nitrogen. But on analyzing able to that view, the fact that fine crops these manures they are found to contain of wheat were obtained from a purely another element, namely, mineral and calcareous soil, lying over limestone, in saline substances. Hanover. Then,' answered Professor Liebig, you may rely upon it that the limestone contains potash.' His friend dry dung, yield from 100 to 270 lbs. of salts and other inorganic substances. These are evidently took an early opportunity to investigate the substances to which our attention should be the matter, and found, to his surprise, directed; for they are the same which formed that the limestone in question did con- the component parts of the hay, straw, and oats, tain a very notable proportion of potash, with which the horse was fed. Their principal a fact previously unknown. He found constituents are-the phosphates of lime and potash also in other fertile limestones, magnesia, carbonate of lime and silicate of and in every specimen of clay he exa-potash: the first three preponderated in the corn, the latter in the hay. Thus in 1000 lbs. of dried mined, even in the purest pipe-clay. We horse-dung we present to a field the inorganic doubt not, therefore, that potash in some substances contained in 6000 lbs. of hay, or 8300 form will be found in every soil in which lbs. of oats. This is sufficient to supply one wheat thrives. crop and a half of wheat with potash and phosphates. . . . The peculiar action, then, of the solid excrements of animals is limited to their inorganic constituents, which restore to a soil that which is removed in the form of hay or straw, roots or grain.'-pp. 179, 181.

6

Intimately connected with this subject are those of the art of culture, the rotation of crops, and manures. We cannot refrain from giving our readers a few il

lustrations of the results at which Professor Liebig has arrived in regard to the last of these:

'4000 lbs. of fresh horse-dung, or 1000 lbs. of

It is plain that, even when the dung of a farm is carefully applied with the straw as manure, a certain loss is sustained in When it is considered that every constituent the potash and phosphates which are carof the body of man and animals is derived from ried away in the corn and cattle annually plants, and that not a single element is generated by the vital principle, it is evident that all the sold. This loss is partly compensated by inorganic constituents of the animal organism the annual disintegration of the subjacent must be regarded, in one respect or other, as strata by the weather; partly, in a large manures. The earthy residue of the putrefaction farm, by the dung of animals fed on of animals must be considered, in a rational meadow-hay grown without manure : in system of agriculture, as a powerful manure for Germany it is also partly made up by the plants, because that which has been abstracted from a soil for a series of years (in the food of use of wood-ashes, containing potash and the animals living on it) must be restored to it, phosphates, as manure; and the ultimate if the land is to be kept in a permanent condition loss is spread over so large a surface as of fertility.'-p. 174. to become nearly inappreciable.

We could keep our fields in a constant state It is here that chemistry offers so of fertility by replacing every year as much as many resources to the agriculturist. 'In we remove from them in the form of produce the manufactories of glue from bones,' but an increase of fertility can only be obtained when we add more to them than we take away. says our author, many hundred tons of a It will readily be inferred that for animal solution of bone-earth in muriatic acid manures other substances, containing their essen- are yearly thrown away as useless.' As tial ingredients, may be substituted. In Flanders this solution much resembles that above the yearly loss of the necessary matters in the mentioned, he recommends that it should soil is completely restored by covering the fields be preserved, and tried as a substitute for with ashes of wood or bones, which may or may the bones. The muriatic acid would not have been lixiviated, and of which the

greater part consists of the phosphates of lime unite with the lime of the soil and form a and magnesia. The great importance of manur-salt, which is already known to act faing with ashes has long been recognised by vourably on soils, most probably by the agriculturists as the result of experience. So fixation of ammonia, as gypsum does. great a value, indeed, is attached to this material There is here, therefore, a double prosin the vicinity of Marburg and in the Wetterau, pect of usefulness. that it is transported as a manure from a distance of eighteen to twenty-four miles.'-p. 182.

"It is of the utmost importance to the agricul turist, that he should not deceive himself respecting the causes which produce the effects just mentioned as the peculiar action of certain substances. It is known that they possess a favourable influence on vegetation; and it is likewise certain that the cause of this must be that they contain a body or bodies, which, independently form, porosity, and capability of attracting and of the influence they exert by virtue of their retaining moisture, also assist in maintaining the vital processes in plants. If it be treated as an unfathomable mystery, if the veil of Isis be thrown over it, the nature of the aid they afford will never be known '-p. 186.

Bone-manure, the effects of which have excited so much astonishment, acts on the very same principle. Every particle of the bones of cattle, like all the other parts of their bodies, has been derived from the grass on which they fed, and consequently from the soil on which the grass grew; and hence, in manuring a field with bone earth, we are merely restoring what had been removed from it during a much longer period in the form of grass, hay, corn, or turnips. Had the true principle of manures been known, 'It must be admitted as a principle of agricul the introduction of bone-earth had not removed from a soil must be completely restored ture, that those substances which have been been left for the nineteenth century. to it; and whether this restoration be effected Even now, of those who use it how few by means of dung, ashes, or bones, is in a great have the slightest conception of the rea- measure a matter of indifference. A time will son why it is a manure at all? 8 lbs. of come when fields will be manured with a solubones contain as much phosphate of lime tion of silicate of potash, with the ashes of burnt as 1000 lbs. of hay or wheat-straw; and straw, and with salts of phosphoric acid, pre2 lbs. contain as much as 1000 lbs. of the pared in chemical manufactories, exactly as at present medicines are prepared for the cure of grain of wheat or oats: 40 lbs. of boneague and goître.'-p. 187. dust, added to an acre of land, is sufficient to supply with phosphates three crops of wheat, clover, potatoes, turnips,

&c.

We have great satisfaction in mentioning, as a note to the preceding paragraph, that the Professor has been inM. Liebig recommends (p. 184) to formed, since the publication of his book, powder the bones, to mix them with half that the ashes of straw have long been their weight of oil of vitriol, previously used in certain districts of Germany as dilated with three or four parts of water; the best manure for wheat. But those and after maceration for some time, to who used them had no idea of the cause add 100 parts of water, and sprinkle this of their superior excellence as a manure. mixture over the field before the plough. They acted empirically; and we could By this means the phosphates are brought not desire a better proof of the great into a soluble state, and the free acids truth, that every discovery, legitimately are instantly neutralized by the alkaline inferred from observed facts, will sooner bases of the soil, producing neutral salts or later be found to coincide with the in a state of fine division, eminently fa- best practice and to explain it. We may vourable to absorption. He has ascer-add that we have seen letters from Gertained by experiment on a soil formed of man agriculturists, cordially appreciating grauwacke, that this treatment is perfect-the principles developed in Liebig's work, ly safe and highly successful, both for as supplying them with that which they corn and for garden vegetables. Thad earnestly sought for during their