of it, a lupin feed, and a grain of maize, he proceeded to make an accurate analysis of its component parts. In order to feparate the vegetable mould falts, he ufed repeated agitation with diftilled water, and found that no fenfible quantity of falt was prefent, but that the foil contained above a third part of its weight of vegetable mould. The calcareous matter, or carbonate of lime, was then feparated by means of acetous acid, and was found to compofe about a tenth part of the mafs. Sulphuric acid feparated the argil, which amounted to fomewhat more than the vegetable mould in weight; and the filicious matter being above one fixth, there were loft in the whole operation, not more than a two hundredth part.

The two veffels in which the plants were to grow, contained each twenty pounds of this foil, completely covered from the external air and moisture, except in a fmall hole for the stalk of the vegetable, and another for watering it. The water which exuded from this operation, was carefully collected. The veffels were fcrupuloufly kept at a distance from all fources of carbonic acid, as fires, animals, fermentations, effervefcences, &c.; were placed at a confiderable height from the ground for the fame reason; and were moistened only with water, which the teft of aqua calcis proved to be quite free from any admixture of carbonic acid. The rain which fell during the four months that the experiment continued, was eight inches and four lines, but it was found to contain no carbonic acid: it feldom was allowed to touch the leaves, and never the foil. The water from time to time poured on the foil, was firft carefully filtrated, and found to be of the exact weight of diftilled water.

It only remained, when the plants had grown fufficiently large, to examine the changes produced, by the progrefs of their growth, upon the foil in the veffels. For this purpofe, they were carefully drawn out, without taking away a particle of the mould, or leaving a fingle tendril of their roots in it. The mould of the lupin being weighed, was found to have loft 2910 grains in 116,400; that of the maize had loft 3395. The quality of this refiduum was then examined, by a repetition of the analyfis formerly defcribed; and it was found, that the argillaceous and filicious parts had not been at all affected; that the vegetable mould was moft diminilhed, having loft in the lupin pot 2546 grains, and in the maize pot 2971; while the calcareous earth had loft, in the former, 364, in the latter 424 grains. From this interefting refult, our author concludes, that the carbonaceous matter alone furnishes the vegetable food, and that the mould and carbonate of lime are only useful as furnishing that carbon; a conclufion which we think by no means warranted by the preceding experiments.

Much

Much of the evidence on which it refts must no doubt depend on the fubfequent portion of the inquiry, in which the conftituent parts of the plants themfelves are examined. But, in the prefent itage of the inveftigation, it is obvious to remark, that nothing can with confidence be laid down beyond this one pofition,-that vegetable mould and calcareous earth contribute to the nutriment of vegetables, and that argillaceous and filicious earths do not contribute thereto, at leaft by immediate abforption, into the vegetable mafs. It remains to prove, both the fpecific manner in which plants feed upon the two former bodies, and the negative pofition, that the two other fubftances are incapable of fupplying indirectly fome of the requifite aliment. The vegetable mould is not a fimple carbon; the calcareous earth contains lime as well as carbonic acid. Therefore our author, by fhewing that the plants diminifh the quantity of mould and of calcareous earth, has not proved that the diminution falls upon carbon and carbonic acid alone. He ought obviously to have repeated his procefs upon foil impregnated with lime, and containing no carbonate, and to have examined what he vaguely calls vegetable mould, the oleaginous matter of which no doubt contains carbon, as well as the more stubborn parts, but carbon united with hydrogen and oxygen, and in every refpect different from the fimple element itfelf. It was evidently neceffary to undertake this previous investigation, inftead of being fatisfied with reducing the foil to four elements, argil, filex, carbonate of lime, and vegetable mould; which laft is not a fimple fubftance. It was neceflary to confider that a body is not compofed of all the fimple fubftances which it contains, in binary and ternary compounds; and that plants, like animals, may be nourished by thofe compounds, when they could, poffibly, find no food in the fimple elements. It was, therefore, incumbent on our author to vary his experiments in a fecond particular, and to feed his plants upon vegetable mould, whofe component parts were determined; to that he might examine the change produced on it by the procefs of vegetation. Laftly, in order to thew the inutility of argil and filex to this procefs, it was neceffary to vary the experiment ftill farther-to make the plants grow in a foil where no fuch bodies exifted. He has only proved, that those fubftances are not actually abforbed by plants. They may, nevertheless, be as neceflary to vegetation as the others. From all these plain confiderations refuits a different, but compendious and accurate method of bringing the points at iffue to a decifion. Various proceffes of vegetation fhould at once have been begun, in the fame circumftances, as to the nature of the feed, of the air, and of the water employed; but differing in the nature of the foil. One feed fhould have been fown in filex,

and

and argil; another in vegetable mould; another in calcareous earth; another in mixtures of the two; another in various mixtures of thofe, with one or both of the former two fubftances. From the whole would have refulted, by examination of the foils after the different proceffes, a clear folution of the question.

We have only one other remark to offer upon this first branch of the inquiry. It appears to be a confiderable overlight in the author, not to have reflected, that the lofs of weight fustained by the foil might poffibly be occafioned by the extrication of fome of its volatile compounds, without any equal addition of weight to the plant. The foil was covered up, but a space was left for the plant to shoot forth its ftem; and through this fpace, the gafes, &c. may eafily have made their escape. Nay, the respiration and tranfpiration of the leaves and buds of the vegetable itself, may have carried off part of the foil in a volatile form after fecretion. The analogy of the animal economy would lead us to expect fuch an event; and there is little reafon to fuppofe, that plants only. refpire and tranfpire the moisture which they imbibe, or its component parts. On the contrary, we know that they give out azotic gas in the night; and it remains to fhow, that this does not come from the foil as well as from the atmosphere. Indeed, it is not easy to conceive that it should come from the atmosphere alone; for, in the day, they give out oxygenous gas, evidently from the decompofition of fomething contained in them, effected by the fun's rays attracting the oxygen: And if the oxygen is thus feparated from azote, fuppofing them to have abforbed atmospheric air, how fhould the darkness of the night affift the evolution of that azote? In other words, how fhould the light prevent the azote from flying off? The coincidence of the weight of the plant with the lofs of the foil, admitting it to be much more com→ plete than it is found to be, proves nothing in this question; for the plant has abforbed water and air.

Our author proceeds, in the fecond place, to lay down certain practical inferences, of much importance to agricultural science, but furely not diftinguished by any great degree of originality;that foil compofed of fand and clay is unfit for vegetation; that fuch foil may be fertilized by manure, or by calcareous matter, or by mixture with other foils; that different plants require different degrees of fertility in the foil, in proportion as they confift of more or lefs carbon. Of thefe pofitions, however, our author's experiments may be admitted to furnish a theory or arrangement according to principle.

Our author next examined the constitution of the plants whofe procefs of vegetation had been thus feduloufly watched. The apparatus employed for this purpofe was fimple and well contrived:

VOL. VI. NO. II.

M

is

it confifted of an air-tight furnace with a bellows; a separate place for the plant to burn upon, and a feries of hydropneumatic veffels, the firft filled with cold water, and deftined to contain a phial through which the vapours of the burning plant fhould pass, in order that their aqueous parts might be collected; the reft containing pure folutions of cauftic alkali, whofe weight was previoufly afcertained, and destined to abforb the carbonic acid produced in the combustion. The procefs being now commenced,. the combuftion of the lupin furnished 8842 grains of carbonic acid; whence our author computes, that it contained 2475 grains of carbon; and he found the caput mortuum to confift of 168 grains. The maize furnished 10289 grains of carbonic acid, and confequently 2881 of carbon, and 200 of refiduum. By an eafy computation, but founded upon the fuppofition that the vegetable mould only furnishes carbon, and the calcareous matter only carbonic acid to the plant, our author reckons the total difference, on comparing the analyfis of the plants with that of their foil, to be 5 grains in the cafe of the lupin, and 9 grains in the cafe of the maize.

From all these investigations, our author concludes, that the growth of plants, in fo far as the eflential element of carbon is concerned, depends entirely on the foil, that is, the vegetable mould and calcareous parts of the earth in which they grow; and that nothing can be lefs juft than the hypothefs which afcribes to water the powers of nourishing vegetables: that the carbon which forms, according to his theory, the chief food of plants, is prefented to them either uncombined, or in the form of acid, and that in both thefe forms, the plants can receive it: that, unlike animals, they have no choice in their food, but muft receive and fecrete it as circumftances prefent it to them. He concludes his paper with a corollary, relating to the importance of analyzing different fpecies of vegetables, by the apparatus and procefs above defcribed. To afcertain their relative quantities of carbonaceous matter, is, according to him, the fame thing with afcertaining their adaptation to various foils, and appreciating the changes which each foil must undergo, to render it a fit nurfery of particular given vegetables. He gives an example in the analyfis of a piece of wood 3000 grains in weight, which was found to contain 420 grains of hydrogen, 156 of oxygen, 2262 of carbon, and 162 of afhes. It is proper to remark, that none of these substances was obtained per se; the hydrogen was in the form of water; the carbon, in carbonic acid gas; and the oxygen, in both the one and the other. So that its prefence is only deduced, and its quantity estimated, from comparing the original weight of the wood, with that of

the

the products of combuftion, calculating how much of thefe products (carbonic acid and water) confifts of oxygen, deducting this as furnished by the atmosphere, and concluding that the difference between the remainder and the original 3000 grains, is oxygen contained in the plant. The paper clofes with a tirade on the profpect which is opened, partly, if we well underftand our author, by his researches, of ftudying nature in her moft mysterious procefs, and a fervent prayer that the refult may have un influenza diretta full' fcienze incremento delle fcienze è fui vantaggi dell' uomo.' p. 20.

This paper, more efpecially the general inferences which it contains, will afford matter for fome farther reflections, in addition to those formerly offered.

The apparatus employed by our author for afcertaining the conftituent parts of the two plants, differs only in one respect from that ufed in the procefs known by the name of the chemical analyfis. In that procefs, vegetables (or animal matter) are placed in a strong earthen retort, and the heat of a fand-bath is applied gradually, and at laft pufhed to a great degree of intensity. The condenfible vapours which fly off are received in refrigerating recipients; the uncondenfable vapours, or permanently elaftic fluids, are received in a pneumatic apparatus; and the body fubmitted to this rude fpecies of trial, is vaguely and falfely faid to be compofed of the different products thus obtained, together with the caput mortuum or fixed refiduum which remains in the retort. The extreme incorrectnefs of this inference is obvious; for the procefs, inftead of fimply feparating the elements of the body, mixes them in new proportions and combinations, fo as to form a variety of compounds, not before exifting in the fubftance fubmitted to examination. The procefs of Signor S. Martino differs from this only in fubftituting combuftion for dif tillation; and the difference is only an augmentation of inaccuracy and error. Had he analyfed the vegetables in the old way, by diftillation, he would have driven off all their volatile parts, and obtained a refiduum which must have included the carbonaceous matter required. This matter could never have been united with the oxygen of the plant during a flow diftillation, or with the oxygen contained in the water of the plant; for both the oxygen and the water would have been driven off before any heat had been applied fufficient to oxygenate the carbon; the oil would have been driven off, in like manner, without decompofition whereas, our author's procefs lofes fight of this component part altogether, by decompofing it; and the quantity of carbon exifting as fuch in the plant would immediately have been obtained, by an eafy procefs, for analyfing the fixed refiduum. Inflead