combine the necessary degree of preciseness with a certain degree of rapidity of execution.

The general process of analysing the ashes of plants, is properly divided into four parts; viz.

1. The incineration of the plant.

2. The estimation of the total amount of ashes yielded by a vegetable substance.

3. The actual analysis of the ashes.

4. The statement and arrangement of the results.

1. INCINERATION.
$174.

The first condition requisite for the proper incineration of plants is, that the plant, or the part of it which it is intended to reduce to ashes, be perfectly free from extraneous impurities; the second condition is, that the ashes contain as little as possible of unconsumed organic ingredients.

To satisfy the first condition, it is necessary to select and clean with great care, the plant, or part of the plant, intended for incineration, without, however, having recourse to washing, since this would cause a loss of part of the soluble salts. To satisfy the second condition, the kind and nature of the plant, or part of the plant intended for incineration, must be had regard to.

Woods, stalks, and matter of similar descriptions are incinerated best after having previously been most thoroughly dried at a brisk fire, either upon a clean iron plate, or in a perfectly clean small iron stove. Dry seeds are incinerated in hessian crucibles, which latter, are to be placed obliquely amidst red-hot charcoal. In some cases, perfect incineration is readily accomplished, when the ashes will speedily acquire a white appearance. On the other hand, there are many seeds that require long-protracted ignition, even to the extent of several days, to effect the consumption of the whole, or at least of the greatest part of the carbon which they contain. The temperature ought to be kept within

certain limits, to prevent the fusion, or agglutination of the ashes, since this would protect the still admixed carbon from the access of air, and would consequently prevent its combustion. The whitest and purest ashes are obtained, if the operator refrains altogether from stirring, or shaking the carbonized matter in the crucible, since this will leave the whole mass bulky and porous, and thus facilitate the free access of air to all parts. Succulent roots and fruits are to be cut in slices, which latter are thoroughly dried on glass plates, and subsequently incinerated in hessian crucibles in the same manner as seeds.

The ashes thus prepared, in either manner, are, if necessary, kept for some time longer, in a state of feeble ignition, for which purpose they are to be transferred to a flat platinum dish, which is then to be exposed to the heat of a spirit- lamp, the ashes being stirred all the time. The ashes are then, while still warm, reduced to a very fine powder, which is uniformly intermixed and kept in well-stoppered bottles.

2. ESTIMATION OF THE TOTAL AMOUNT OF ASHES YIELDED BY A VEGETABLE SUBSTANCE.

$ 175.

To determine the total amount of ashes which a given vegetable substance yields upon incineration; it is necessary, in the first place, to dry the substance in question, in the water-bath, or should it contain volatile ingredients under a bell-glass over sulphuric acid, (§ 14.) without applying heat; the process of exsiccation is in either case continued until the weight of the substance ceases to vary. The quantity to be used for incineration depends upon the proportion of fixed constituents present; in the case of herbs or seeds containing abundance of fixed constituents, from 2 to 3 grammes will yield sufficiently accurate results, whilst in the case of woods, which yield sometimes as little as 0.2 per cent. of ashes, 10 times the amount and more

K K

will be required. The process of incineration is conducted best in a covered platinum crucible with thin sides. At the commencement of the process, a gentle heat only should be applied, which is to be increased afterwards, the crucible being opened and placed in an oblique position, with the removed lid leaning against it. (Compare § 32. Plate XXIX.)

This method of estimating the quantity of the ashes which a plant yields, is not free from defects, whence it happens that the results of repeated incinerations of one and the same substance do not perfectly correspond. Thus the amount of carbonate of lime undergoing calcination, and also that of the sulphates passing to the state of sulphurets, depend upon the degree of heat applied, and upon the application of an intense heat whilst a considerable portion of charcoal remains; carbonate of soda and chloride of sodium undergo decomposition when intensely ignited with silicic acid, and even simply with charcoal. Upon the degree of heat applied, the duration of the process of ignition, the presence of alkaline carbonates, &c., depends the form in which the phosphoric acid is obtained, and likewise the more or less complete combustion of the charcoal, &c. As the quantity of ashes, however, which a plant yields is not constant, since two specimens of the same plant never produce exactly the same amount of ashes, we rest usually satisfied with the results obtained in the manner described, although some of the indicated defects admit of a remedy. Thus, ashes which do not effervesce with acids may be readily freed from charcoal by moistening them with nitric acid, and igniting them again; the same end may be attained in the case of ashes containing carbonates and sulphurets, by mixing them with peroxide of mercury, and exposing the mixture subsequently to an intense and protracted ignition, which will moreover serve to effect the reconversion into sulphuric acid of the whole of the sulphur present; thus, carbonic acid which has escaped may be replaced by moistening the ashes with solution of carbonate of ammonia, drying, and subsequent gentle ignition, &c.

3. ACTUAL ANALYSIS OF THE ASHES.

§ 176.

The ashes of plants may be classed under the following heads, according to their respective principal constituents.

a. Ashes in which carbonates of the alkalies and alkaline earths predominate; e. g. the ashes of woods, of herbaceous plants, &c.

b. Ashes in which phosphates of the alkalies and alkaline earths predominate; to this class belong the ashes of nearly all kinds of seeds.

c. Ashes in which silicic acid predominates; e. g. those of the stalks of the graminacea, of the equisetaceæ, &c.

This classification, although it is quite obvious that the limits between the different classes cannot be drawn very strictly, must be maintained, in order to impart a certain degree of clearness and simplicity to the analytical methods which I am now going to describe; for the general process requires of course certain modifications according to the respective class to which the ashes under examination belong.

a. QUALITATIVE ANALYSIS.

The general constituents of the ashes of plants being already known, a perfect qualitative analysis of every kind of ashes which may happen to come under our notice would be superfluous. A few preliminary experiments suffice to ascertain the presence or absence of the more rarely occurring constituents, and more particularly the class to which the ashes under examination belong. This preliminary investigation proceeds as follows:

1. The operator has to ascertain whether the ashes under examination decompose completely when heated with concentrated hydrochloric acid. Ashes which effervesce strongly when concentrated hydrochloric acid is poured over them, may be at once considered decomposed by this menstruum. The ashes of the stalks of the graminaceæ, &c., which contain a large proportion of

silicic acid, are usually the only kind of ashes that resist complete decomposition.

2. Upon mixing the hydrochloric solution of any kind of ashes whatsoever, (after separation of the silicic acid,) with an alkaline acetate, or neutralizing it with ammonia, and adding subsequently free acetic acid, a gelatinous yellowish white precipitate of perphosphate of iron will almost invariably separate. Now it becomes necessary to ascertain whether, besides the phosphoric acid in this precipitate, the ashes contain still a further portion of this acid or not. For this purpose, the fluid is filtered off from the precipitated perphosphate of iron, and ammonia in excess is added to the filtrate; should this fail to produce a precipitate, or should the precipitate produced be red, and consequently consist of hydrated peroxide of iron, this is a proof that the ashes contain no more phosphoric acid; but if, on the contrary, a white precipitate is formed, (phosphate of lime, and phosphate of magnesia and ammonia), this is a positive proof that the ashes contain more phosphoric acid than the peroxide of iron present is able to combine with, and the ashes are consequently to be classed under the second head.

3. The ashes are tested for manganese, by mixing a small portion of them with carbonate of soda, and (exposing the mixture on a platinum plate, to the external flame of the blow pipe. (Compare “Elementary instruction in Qualitative Analysis.")

4. The ashes are tested for iodine, bromine, and fluorine, (compare "Elementary instruction in Qualitative Analysis,") for the two former elements if the analyst has reason to suspect their presence, and for fluorine in cases when it is intended to ascertain whether traces of this element are present or not.

b. QUANTITATIVE ANALYSIS.

I. Ashes in which the carbonate of the alkalies or alkaline earths predominate, and in which the whole of the phosphoric acid present is combined with peroxide of iron.