Acetic acid, 9·37 per cent.; benzoic acid, 18·85 per cent.; and aconine, 77·52 per cent.
Pure aconitine has a tube melting-point of 188·6°. The behaviour of a sample of Merck’s aconitine in the subliming cell, which had a melting-point of 184°, was as described at [page 259].
Aconitine dissolves in water at 22° in the proportion of 1 in 4431 (Dunstan); it is soluble in 37 of absolute alcohol, 64 of anhydrous ether, 5·5 parts of chloroform and benzene (A. Jurgens); it has basic properties, and a cold watery solution has an alkaline reaction to cochineal, but not to litmus nor to phenol-phthalein. Aconitine is not precipitated by mercuric potassium iodide, but gives a voluminous precipitate with an aqueous solution of iodine in potassium iodide.
It gives a crystalline yellow gold compound with gold chloride, which has a melting-point of 135·5°, and according to its composition, C33H45NO12HAuCl4, should give 19·9 per cent. of gold.
Aconitine is best extracted from the plant, or from organic matters generally, by a 1 per cent. sulphuric acid; this strength is stated not to hydrolyse aconitine if acting in the cold; after purifying the acid liquid by shaking it with amyl alcohol, and then with chloroform, always operating in the cold, the liquid is precipitated by ammonia in very slight excess, and the liquid shaken with ether; the ether is removed, dehydrated by standing over calcium chloride, and then evaporated spontaneously; should the aconitine be mixed with the other alkaloids, advantage can be taken of the method of separating aconitine by converting it into hydrobromide, as described under “Benzoyl-aconine.”
§ 425. Tests for Aconitine.—The most satisfactory and the most delicate is the physiological test; the minutest trace of an aconite-holding liquid, applied to the tongue or lips, causes a peculiar numbing, tingling sensation which, once felt, can readily be remembered.
An alkaloidal substance which, heated in a tube, melts approximately near the melting-point of aconitine, and gives off an acid vapour, would render one suspicious of aconitine, for most alkaloids give off alkaline vapours. Aconitine also may, by heating with dilute acids, be made to readily yield benzoic acid, an acid easy of identification. Aconitine dissolved in nitric acid, evaporated to dryness, and then treated with alcoholic potash, gives off an unmistakable odour of benzoic ester.
Should there be sufficient aconitine recovered to convert it into the gold salt, the properties of the gold salt (that is, its melting-point, and the percentage of gold left after burning) assist materially in the identification.
A minute quantity of aconitine dissolved in water, acidified with acetic acid, and a particle of KI added and the solution allowed to evaporate, gives crystals of aconitine hydriodide, from which water will dissolve out the KI. Iodine water gives a precipitate of a reddish-brown colour in a solution of 1 : 2000.[468]