One of the distinctive properties of the three alkaloids in question, _viz._, their behavior with ether—places in our hands a ready means of detecting the mixture of cinchonine and { 144} quinidine, with quinine. Schweitzer (_Lond. Med. Gazette_, vol. xxi., p. 175) has already employed ether for the detection of cinchonine with complete success, and his process has, with justice, been subsequently quoted in most manuals, as it answers its purpose completely; cinchonine is known to be entirely insoluble in ether, whatever may be the quantity of ether employed. The solubility of quinidine in ether, as compared with that of quinine, is but slight; ten grains of pure sulphate of quinine dissolve in sixty drops of ether, and twenty drops of spirit of ammonia, while only one grain of sulphate of quinidine is soluble in the same quantity of the fluid; and in proportion quinine containing quinidine will always be less soluble than pure sulphate of quinine.
Guided by this fact I can recommend the following simple and very convenient process for the detection of quinidine and quinine:―
Ten grains of the salt to be examined is to put into a strong test tube, furnished with a tight-fitting cork, to this are to be added ten drops of diluted sulphuric acid, (one acid and five water) with fifteen drops of water, and a gentle heat applied to accelerate the solution. This having been affected, and the solution entirely cooled, sixty drops of officinal sulphuric ether with twenty drops of spirits of ammonia, must be added, and the whole well shaken while the top is closed by the thumb. The tube is then to be closely stopped and shaken gently from time to time, so that the bubbles of air may more readily enter the layer of ether.
If the salt examined be free from cinchonine and quinidine, or contain the latter in no greater proportion than ten per cent., it will be completely dissolved; while on the surface, where contact of the two layers of clear fluid takes place, the mechanical impurities only will be separated (in which respect the various sorts of commercial quinine differ.) After sometime longer the layer of ether becomes hard and gelatinous, after which no further observation is possible.