Fig. 44.—Photo-micrograph of
sulphocyanate of strychnine, × 50.
(R. J. M. Buchanan.)
Chemical Analysis.—The poison may fail to be detected, and this link in the scientific evidence may be wanting, as was the case in Palmer‘s trial. In that case the strychnine had been administered in pills; and when after death the stomach had been cut open, and the contents lost, there was little hope of discovering the poison. The non-discovery of the poison was made a strong point on the part of the defence, ignoring at the same time the fact that the stomach had been tampered with and the contents spilt. The alkaloid abstracted from the tissues or contents of the stomach by the process generally used for extraction of alkaloids, may have the following tests applied to it:
1. Scarcely soluble in water, but readily soluble in acidulated water.
2. Intensely bitter taste.
3. Not affected by sulphuric acid; but when a little peroxide of lead, or peroxide of manganese, or bichromate of potash, or ferricyanide or permanganate of potassium is added, a magnificent purple-blue colour, changing to crimson, and finally to a light red tint, is the result. The ¹/₂₀₀₀₀ part of a grain of strychnine has been stated to give this reaction.
4. The physiological test consists in introducing a small quantity of the suspected substance under the skin of a frog, and noting whether or not the animal suffers from tetanic spasms.
5. The Galvanic Test.—Place a solution of strychnine, say one part of strychnine in 15,000 of water, in a slight depression in a piece of platinum foil, and allow the mixture to evaporate. When dry, moisten the spot with sulphuric acid, connect the foil with a positive pole of a single-cell Grove‘s battery, and then touch the acid solution with the negative pole. A violet colour will be at once produced, remaining permanent.
6. Bloxam‘s Test.—To the solid alkaloid in a porcelain dish a drop or two of strong nitric acid is added and gently heated; on adding a small quantity of potassium chlorate a scarlet colour is produced. Ammonia changes this colour to brown and a brown precipitate falls. If the mixture he evaporated to dryness it leaves a dark green residue forming a green solution in water, changed to orange-brown with caustic potash and green again with nitric acid. This test distinguishes strychnine from any of the alkaloids which commonly occur in cases of poisoning.
7. Potassium bichromate when added to a solution of a salt of strychnine, produces a yellow crystalline precipitate of chromate of strychnine: the reaction can be done on a microscope slide and the crystals examined. On drying the crystals and then touching them with a drop of strong sulphuric acid, the purple colour changing through red to green is produced.