the oxide of carbon, will give one volume of the oxide, + a volume of oxygen gas.

Thus, in the hypothesis which we now discuss, for each volume of carbonic acid that is modified by the vegetation, there will be half a volume of oxygen gas disengaged. Any oxygen more than this half volume which appears, must be regarded as proceeding from the decomposition of water, the hydrogen of which will have been assimilated by the plant at the same time as the carbonic oxide derived from the carbonic acid; and this view would perhaps enable us to conceive how the volume of oxygen which is disengaged during the process of vegetation, may exceed the volume which ought to be produced, if the carbonic acid decomposed really passed into the state of carbonic oxide.

We may perchance obtain a more convincing proof of the separation of the elements of water, in analyzing plants grown in a soil absolutely without any organic matter capable of affording them hydrogenous elements.

In fact, if a plant, which is grown under such circumstances, contains hydrogen in any larger proportion than that which were necessary to transform its oxygen into water, we might conclude, with some certainty, that the elements of water had been separated; the objection made on the score of the presence of manure would then be got rid of entirely. The analyses which have already been laid before the reader supply data for this investigation; it has only to be ascertained whether, in the elements gained in the course of vegetation, the hydrogen is in excess with reference to the oxygen or not. The following table presents a summary view of our experiments:

Oxygen Hydrogen Hydrogen Hydrogen assimilated. assimilated. forming water. in excess.

In the four first experiments, the hydrogen gained evidently exceeds very sensibly the quantity required by the oxygen to form water. The experiment with the oats, indeed, presents an exception; but it must be remembered that here a loss of azote was ascertained. These analyses, therefore, appear to indicate an assimilation of hydrogen in the course of vegetation, in consequence of a decomposition of water analogous to that of carbonic acid, and very probably effected by the same means.

§ III.-OF THE INORGANIC MATTERS CONTAINED IN PLANTS-THEIR ORIGIN OF THE CHEMICAL NATURE OF SAP.

In a

When a plant is burned, there always remains a residue, which is commonly designated as the ash. Every part of a plant gives a residue of the same essential kind; but it varies in its quantity and somewhat also in its composition. Equal weights of dry herbaceous plants leave more ashes than woody plants.* tree, the trunk gives more ash than the branches, and these give less than the leaves. The residue left by the combustion is commonly composed of salts-alkaline chlorides, with bases of potash and soda, earthy and metallic phosphates, caustic or carbonated lime and magnesia, silica, and oxides of iron and of manganese. Several other substances are also met with there, but in quantities so small that they may be neglected.

The principles usually met with in the ashes of vegetables are always found in the soil which exercises the greatest influence upon the nature and quantity of the saline and earthy matters which remain after the combustion of plants. Those which grow in a soil derived from silicious rocks, yield ashes that are richer in silica than those that are produced in a calcareous soil. But, according to M de Saussure, the quality of the manure has a still more decided influence on the nature of the ash than the geological constitution of the soil; according to this observer, plants of the same species, which have grown upon a calcareous sand, and upon a granitic sand, contain the same kind of ashes, if they have been manured with the same dung; and different species, although growing in the same earth, do not contain the saline and earthy constituents of their ashes in the same proportions.‡

* Kirwan, Memoirs of the Royal Irish Academy, vol. v.
† Pertuis, Annales de Chimie, 1re série, t. xix.

Saussure, Recherches chimiques, p. 283.

QUANTITY OF ASHES CONTAINED IN THE DIFFERENT PARTS OF VEGETABLES, ACCORDING TO M. DE SAUSSURE.*

All these estimates of ashes refer to plants dried during several

weeks in a stove heated to 25° cent. (77° Fahr.) however, vegetable substances are very far from

* Saussure, Recherches chimiques, p. 283.

By such drying, losing the whole

of the water which they contain. The quantities of ashes, therefore, mentioned by M. de Saussure, if they be referred to vegetables absolutely dry, are somewhat too small.

I present a few estimates of ashes from analyses which I have had occasion to make of some of those plants which are the usual subjects of cultivation with us. The drying here was always performed with care in an oil-bath heated to 110° cent. (230° Fahr.)*

We owe to M. Berthier† the following results of the incineration of different kinds of wood burned in the state in which they are gen

erally used.

We possess several analyses of ashes from different parts of the same plants in the researches of MM. de Saussure and Berthier. As the knowledge of these saline substances may prove highly important in our agricultural applications, and as it further completes, in some sort, the facts that bear upon the chemical phenomena of vegetation, I here add a table of the results obtained by the skilful analysts just quoted :

* Ann. de Chimie, t. i. page 234. 3e. série.
† Traité des Essais, t. i, page 259.