Legal Chemistry / A Guide to the Detection of Poisons, Examination of Tea, Stains, Etc., as Applied to Chemical Jurisprudence

by Alfred Naquet

GRAHAM AND HOFMAN'S METHOD.

This method, which is applied to the detection of strychnine in beer, is founded upon the fact that an aqueous solution of a strychnine salt yields the alkaloid to animal charcoal, from which it can be subsequently extracted by boiling with alcohol. The beer to be examined is shaken with 30 grammes of animal charcoal, and the mixture then allowed to stand twenty-four hours, with occasional shaking. The solution is next filtered, the animal charcoal washed with water, and boiled for half-an-hour with four times its weight of 90 per cent. alcohol. The apparatus represented in Fig. 12 is employed, in order to avoid a loss of substance in this operation.

Fig. 12.

The alcohol is filtered hot, evaporated, and the residue obtained treated with a small quantity of solution of potassa, and then agitated with ether. Upon spontaneous evaporation, the ethereal solution leaves the strychnine present in a comparatively pure state.

Macadam proposes to use this process for the detection of strychnine in animal bodies. For this purpose, the suspected materials are heated with a solution of oxalic acid, as in Stas's method, and the strychnine detected in the filtered solution in the manner just described. This method is scarcely to be recommended: the use of animal charcoal is doubtless serviceable in the examination of beer, as it effects the separation of a small amount of strychnine from a large quantity of fluid, but its application to other researches is much less to be advised.

APPLICATION OF DIALYSIS IN THE DETECTION OF ALKALOIDS.

In order to apply the dialytic method to the separation of alkaloids, the suspected substances are heated with hydrochloric acid, and the solution introduced into the dialyzer. The hydrochlorates of the alkaloids, being crystalline bodies, transverse the membrane, and are contained, for the greater part, after twenty-four hours, in the outer solution. The fluid is then concentrated, and the alkaloids either directly precipitated, or purified by one of the preceding methods.

IDENTIFICATION OF THE ALKALOID.

The alkaloid having been isolated by one of the preceding methods, it remains to establish its identity. Owing to the small number of reactions characteristic of organic compounds, this is a matter of considerable difficulty. There are two cases possible: the alkaloid may either be volatile or fixed.