§ 318. The Conium maculatum, or spotted hemlock, is a rather common umbelliferous plant, growing in waste places, and flowering from about the beginning of June to August. The stem is from three to five feet high, smooth, branched, and spotted with purple; the leaflets of the partial involucres are unilateral, ovate, lanceolate, with an attenuate point shorter than the umbels; the seeds are destitute of vittæ, and have five prominent crenate wavy ridges. The whole plant is fœtid and poisonous. Conium owes its active properties to a volatile liquid alkaloid, Coniine, united with a crystalline alkaloid, Conhydrine.
§ 319. Coniine (conia, conicine), (C8H17N)—specific gravity 0·862 at 0°; melting-point, -2·5°; boiling-point, 166·6°. Pure coniine has been prepared synthetically by Ladenburg, and found to be propyl-piperidine C5H10NC3H7, but the synthetically-prepared piperidine has no action on polarised light. By uniting it with dextro-tartaric acid, and evaporating, it is possible to separate the substance into dextro-propyl-piperidine and lævo-propyl-piperidine. The former is in every respect identical with coniine from hemlock; it is a clear, oily fluid, possessing a peculiarly unpleasant, mousey odour. One part is soluble in 150 parts of water,[341] in 6 parts of ether, and in almost all proportions of amyl alcohol, chloroform, and benzene. It readily volatilises, and, provided air is excluded, may be distilled unchanged. It ignites easily, and burns with a smoky flame. It acts as a strong base, precipitating the oxides of metals and alkaline earths from their solutions, and it coagulates albumen. Coniine forms salts with hydrochloric acid (C8H15N.HCl), phosphoric acid, iodic acid, and oxalic acid, which are in well-marked crystals. The sulphate, nitrate, acetate, and tartrate are, on the other hand, non-crystalline.
[341] The saturated watery solution of coniine at 15°, becomes cloudy if gently warmed, and clears again on cooling.
If coniine is oxidised with nitric acid, or bichromate of potash, and diluted sulphuric acid, butyric acid is formed; and since the latter has an unmistakable odour, and other characteristic properties, it has been proposed as a test for coniine. This may be conveniently performed thus:—A crystal of potassic bichromate is put at the bottom of a test-tube, and some diluted sulphuric acid with a drop of the supposed coniine added. On heating, the butyric acid reveals itself by its odour, and can be distilled into baryta water, the butyrate of baryta being subsequently separated in the usual way, and decomposed by sulphuric acid, &c.
Another test for coniine is the following:—If dropped into a solution of alloxan, the latter is coloured after a few minutes an intense purple-red, and white needle-shaped crystals are separated, which dissolve in cold potash-lye into a beautiful purple-blue, and emit an odour of the base.[342] Dry hydrochloric acid gives a purple-red, then an indigo-blue colour, with coniine; but if the acid is not dry, there is formed a bluish-green crystalline mass. This test, however, is of little value to the toxicologist, the pure substance alone responding with any definite result.
[342] Schwarzenbach, Vierteljahrsschr. f. prakt. Pharm., viij. 170.