Pur. See Quinine, Sulphates of, and Quinometry (below).
Tests. Quinine is recognised by—1. Its appearance under the microscope.—2. Its solubility in ether, and in pure ammonia water.—3. Its solubility in concentrated nitric acid, forming a colourless liquid, which does not become yellowish until it is heated.—4. The solubility of itself and salts, when pure, in concentrated sulphuric acid, forming colourless fluids, “which do not acquire any coloration upon being heated to the point of incipient evaporation of the sulphuric acid, but which afterwards become yellow, and finally brown.” (Fresenius.)—5. Its solubility in concentrated sulphuric acid to which some nitric acid has been added, forming a colourless, or, at the most, only a faintly yellowish liquid.—6. It is wholly destroyed by heat.
A solution of quinine in acidulated water, and solutions of its salts, exhibit the following reactions:—1. Ammonia, potassa, and the alkaline carbonates, give white, pulverulent precipitates, becoming crystalline after some time (see above), and which are soluble in ammonia in excess, and which, when ether is added after the ammonia, and the whole is agitated, redissolve in the ether, whilst the clear liquid, on repose, presents two distinct layers.—2. Bicarbonate of soda (avoiding excess) gives a similar precipitate, both in acid and neutral solutions of quinine, either at once or after a short time. The precipitate is soluble in excess of the precipitant, and is again precipitated from the new solution upon protracted ebullition. “Vigorous stirring of the liquid promotes the separation of this precipitate.” (Fresenius.)—3. If recently prepared chlorine be added to it, and then ammonia, a beautiful emerald-green colour is developed. (Ph. L.)—4. A concentrated solution of ferrocyanide of potassium being added, in excess, after the chlorine, instead of the ammonia, a dark red colour is instantly produced, which after some time passes into green, especially when freely exposed to the light. This reaction is not characteristic of quinine, for with quinidine one gets the same reaction.—5. If caustic potassa be used instead of ammonia (see above), the solution acquires a sulphur-yellow colour. “These reactions are restricted to this alkaloid.” (Dr Garrod.)
Flückiger[126] says;—“The most characteristic test for ascertaining the presence of quinine is the formation of the splendid green compound called thalleiochine, which is produced if solutions of the alkaloid or its salts are mixed with chlorine water, and then a drop of ammonia added.”
[126] In ‘Jahrb. f. Pharm.,’ April, 1872, 136 (‘Ph. Journ,’, 3rd series, ii, 901).
If one part of quinine is dissolved in 4000 parts of acidulated water, and then about 1⁄10 of the volume of the liquid, of chlorine water, and a drop of ammonia added, a green zone will be readily formed if the liquids are cautiously placed in a flask without shaking.
If the solution of quinine contain no more
than 1⁄5000, the green of one may still be obtained, but in more diluted solutions the success becomes more and more uncertain.
From a practical point of view we may state that 1⁄5000 of the alkaloid is the smallest quantity whose presence can thus be discovered with certainty; Kerner (1870) has succeeded with 1⁄20000 but I was not able to corroborate this statement.
The author was also induced to try the action of bromine in place of chlorine. The thalleiochine is then, indeed, produced in solution which contain only 1⁄20000 of quinine.