Pure potass or soda ley is poured over about four grammes of the ashes, and the mixture is then evaporated to dryness in a platinum or silver basin. This process serves to decompose the whole of the silicates contained in the ashes, without affecting the sand that may happen to be present, or, at all events, affecting the latter substance only to an exceedingly trifling extent. The heat should not be raised sufficiently high, towards the end of the process, to fuse the mass. Dilute hydrochloric acid is now poured over the residue, the mixture is evaporated, and the residue again acted upon with hydrochloric acid; the hydrochloric solution is filtered off from the insoluble residue, (silicic acid, charcoal, and sand,) and the latter subsequently treated as directed at I. A. 1. (§ 177.) The filtrate is treated as directed at I. A. 2. (with the exception, of course, of that part of the process which relates to the estimation of the alkalies, since these must of necessity be determined in a separate portion of the ashes, as already stated.)

b. ESTIMATION OF THE ALKALIES.

A second portion of the ashes (about three grammes) are decomposed with four times the amount of hydrated barytes, in a platinum-or silver-crucible, (compare § 20. b. ß.) The residue is treated with hydrochloric acid, the mixture is evaporated, the residue again acted upon with hydrochloric acid, and the solution filtered off from the silica, the filtrate being finally treated, strictly according to the directions of I. A. 2. b. (§ 177).

4. METHOD OF STATING AND ARRANGING THE RESULTS.

§ 180.

It is only very recently that chemists have begun to turn their attention seriously to the analysis of the ashes of plants, for the benefit of vegetable physiology and agriculture. The questions which it is intended to solve by the analysis of the ashes of plants, are in the main the following:

1. Do plants absolutely require certain constituents in certain definite proportions? and if they do, what are those constituents?

2. May some of the inorganic constituents of plants be replaced by others?

3. Has every plant a definite saturation capacity, that is, in other terms, is the amount of oxygen contained in the bases present, invariably the same?

It is quite obvious that a proper and satisfactory solution of these questions can be expected only from the results of an exceedingly large number of analyses, and that consequently a great many chemists must contribute towards the final solution.

Under these circumstances, it is of the utmost importance that the respective results of the various analyses should be stated and arranged in a uniform and corresponding manner, so that they may readily and without previous calculation admit of mutual comparison.

Since the manner in which the bases and acids found were originally combined in the plants cannot be inferred from the ashes with any degree of positive certainty, and since, moreover, as I have already had occasion to state, the form in which the phosphoric acid is obtained, &c. differs according to the degree of heat employed, &c., it is unquestionably the most judicious way to enumerate the percentage weights of the bases and acids separately. Chlorine, however, is to be arranged as chloride of sodium; (and, should the quantity of soda present be insufficient for this purpose, chloride of potassium); the proportion of sodium contained in the chloride is to be calculated upon soda, and the calculated weight of the latter finally subtracted from the total amount of soda formed; since, otherwise, a surplus would be invariably obtained in the analysis, the chloride of sodium originally present in the ashes being reckoned as chlorine and soda, instead of chlorine and sodium, as it ought to be. Should any manganese have been found, this is to be given as manganosomanganic oxide, since it exists as such in the ashes.

The following analysis of the ashes of beech seeds, by SOUCHAY

It is evident, however, that this kind of statement is not sufficiently precise for an accurate comparison of the results given with those of another analysis, since we find here near twenty per cent. of substances enumerated which are altogether immaterial, viz., carbonic acid, charcoal, and sand. For the proportion in which these substances are present in the ashes of plants, nay, their very presence, depends altogether upon accidental circumstances, such as the degree of care with which the vegetable substances are cleaned previously to incineration, the degree of heat used, and the extent of time that the process of ignition lasts.

To render the mutual comparison of the results obtained in several analyses practicable, it is necessary to strike out the numbers for the inessential ingredients, viz., carbonic acid, sand, and charcoal, and to calculate the weight of the remaining essential constituents upon one hundred parts.

This calculation will give the following results for the above quoted analysis:

Potass

Soda.

22.82

9.50

To satisfy all demands, it is therefore necessary to state the results of every analysis of vegetable ashes, both ways. The first statement will enable chemists to pronounce upon the accuracy of the results, whilst the second statement will render mutual comparisons between the results of several analyses practicable. Should the analyst feel desirous to render his statement still more complete, he may also calculate the proportional amount of oxygen contained in the several bases, and communicate the resulting sum total of this element.

III. ANALYSIS OF SOILS.*

$181.

The proposition being established that every plant requires for its growth and development certain inorganic matters which are provided by the soil in which it grows, it is self-evident that the knowledge of the composition of the soil must be a subject of paramount importance to the practical farmer, whether he wishes to know to which kind of plants a given soil will afford the re

* I cannot begin this chapter without expressing my warmest thanks to Professor OTTO for the great benefit which I have derived from his excellent paper on the analysis of soils, (vide SPRENGELL'S BODENKUNDE.)

quisite sustenance—or whether he wishes to adapt a soil for the cultivation of a certain definite plant by a proper supply of ma

nure.

But as plants can absorb with their roots substances in a state of solution only, it is not sufficient for their growth and proper development that the necessary ingredients should be present in the soil; but it is necessary, moreover, that these ingredients should be present in a form admitting of their absorption by the roots of the plants. If, therefore, the analysis of a soil is intended to enable the agriculturist to judge of the appropriateness of the analysed soil for the cultivation of a certain plant, it is necessary not only to know what are its constituents, but the form or state in which these constituents are present in the examined soil.

In this point of view, the inorganic constituents of the soil may be ranged under three heads:

1. Constituents which dissolve in water.

2. Constituents which, though not dissolving in water, dissolve in dilute acids.

3. Constituents which dissolve neither in water nor in dilute acids.

The ingredients belonging to the first class are supplied directly to the plants with the water which they imbibe from the soil. The absorption of the ingredients of the second class is somewhat more difficult, since these ingredients are rendered soluble only by the agency of carbonic acid, and of the acid decomposition products of decaying organic substances, (humic acid). The constituents belonging to the third class require a thorough modification, before they can exercise any influence upon the development of plants; and this modification they suffer slowly and gradually by the progressive disintegration and decomposition of their particles.

The ingredients which are soluble in water serve therefore for immediate use, whilst those soluble in acids exercise a more permanent action, and those, finally, which are alto