The commercial Sulphate (C21H22N2O2H2SO4 + 2H2O) is an acid salt crystallising in needles which lose water at 150°, the neutral sulphate (2C21H22N2O2,H2SO4 + 7H2O) crystallises in four-sided, orthorhombic prisms, and is soluble in about 50 parts of cold water.
The Nitrate (C21H22N2O2,HNO3) crystallises on evaporation from a warm solution of the alkaloid in dilute nitric acid, in silky needles, mostly collected in groups. The solubility of this salt is considerable, one part dissolving in 50 of cold, in 2 of boiling water; its solubility in boiling and cold alcohol is almost the same, taking 60 of the former and 2 of the latter.
The Acetate crystallises in tufts of needles; as stated, it is not officinal in any of the European pharmacopœias.
The chief precipitates or sparingly soluble crystalline compounds of strychnine are—
(1.) The Chromate of Strychnine (C21H22N2O2CrHO2), formed by adding a neutral solution of chromate of potash to a solution of a strychnine salt, crystallises out of hot water in beautiful, very insoluble, orange-yellow needles, mixed with plates of various size and thickness. The salt is of great practical use to the analyst; for by its aid strychnine may be separated from a variety of substances, and in part from brucine—the colour tests being either applied direct to the strychnine chromate, or the chromate decomposed by ammonia, and the strychnine recovered from the alkaline liquid by chloroform.
(2.) Sulphocyanide of Strychnine (C21H22N2O2CNHS) is a thick, white precipitate, produced by the addition of a solution of potassic sulphocyanide to that of a strychnine salt; on warming it dissolves, but on cooling reappears in the form of long silky needles.
(3.) Double Salts.—The platinum compound obtained by adding a solution of platinic chloride to one of strychnine chloride has the composition C21H22N2O2HClPtCl2, and crystallises out of weak boiling alcohol (in which it is somewhat soluble) in gold-like scales. The similar palladium compound (C21H22N2O2HCl,PdCl) is in dark brown needles, and the gold compound (C21H22N2O2HClAuCl3) in orange-coloured needles.
(4.) Strychnine Trichloride.—The action of chlorine on strychnine—by which chlorine is substituted for a portion of the hydrogen—has been proposed as a test. The alkaloid is dissolved in very dilute HCl, so as to be only just acid; on now passing through chlorine gas, a white insoluble precipitate is formed, which may be recrystallised from ether; it has probably the composition C21H19Cl3N2O2, and is extremely insoluble in water.
(5.) The Iodide of Strychnine (C21H22N2O2HI3) is obtained by the action of iodine solution on strychnine sulphate; on solution of the precipitate in alcohol, and evaporation, it forms violet-coloured crystals, very similar to those of potassic permanganate.
§ 388. Pharmaceutical and other Preparations of Nux Vomica and Strychnine, with Suggestions for their Valuation.