XI. DRYING THE WATERY FLUID WITH THE ADDITION OF POWDERED GLASS, AND EXTRACTION OF THE FINELY-DIVIDED RESIDUE BY CHLOROFORM.
The residue of the first chloroform extract lessens the number of respirations of a frog; the residue of the second and third chloroform extract becomes, by sulphuric acid and bichromate of potash, blue, passing into a permanent red.
| Another portion of this residue becomes red on warming with diluted sulphuric acid. |
| Curarine. |
Shorter Process for Separating some of the Alkaloids.
§ 310. A shorter process, recommended conditionally by Dragendorff, for brucine, strychnine, quinine, cinchonine, and emetine, is as follows:—
The substance, if necessary, is finely divided, and treated with sulphuric acid (dilute) until it has a marked acid reaction. To every 100 c.c. of the pulp (which has been diluted with distilled water to admit of its being filtered later), at least 5 to 10 c.c. of diluted sulphuric acid (1 : 5) are added. It is digested at 50° for a few hours, filtered, and the residue treated again with 100 c.c. of water at 50°. This extract is, after a few hours, again filtered; both the filtrates are mixed and evaporated in the water-bath to almost the consistency of a thin syrup. The fluid, however, must not be concentrated too much, or fully evaporated to dryness. The residue is now placed in a flask, and treated with three to four times its volume of alcohol of 90 to 95 per cent.; the mixture is macerated for twenty-four hours, and then filtered. The filtrate is distilled alcohol-free, or nearly so, but a small amount of alcohol remaining is not objectionable. The watery fluid is diluted to about 50 c.c., and treated with pure benzene; the mixture is shaken, and after a little time the benzene removed—an operation which is repeated. After the removal the second time of the benzene, the watery fluid is made alkaline with ammonia, warmed to 40° or 50°, and the free alkaloid extracted by twice shaking it up with two different applications of benzene. On evaporation of the latter, if the alkaloid is not left pure, it can be dissolved in acid, precipitated by ammonia, and again extracted by benzene.
§ 311. Scheibler’s Process.—A method very different from those just described is one practised by Scheibler. This is to precipitate the phosphotungstate of the alkaloid, and then to liberate the latter by digesting the precipitate with either hydrate of barium or hydrate of calcium, dissolving it out by chloroform, or, if volatile, by simple distillation. The convenience of Scheibler’s process is great, and it admits of very general application. In complex mixtures, it will usually be found best to precede the addition of phosphotungstic acid[337] by that of acetate of lead, in order to remove colouring matter, &c.; the excess of lead must in its turn be thrown out by SH2, and the excess of SH2 be got rid of by evaporation. Phosphotungstic acid is a very delicate test for the alkaloids, giving a distinct precipitate with the most minute quantities (1⁄200000 of strychnine and 1⁄100000 of quinine). A very similar method is practised by Sonnenschein and others with the aid of phospho-molybdic acid. The details of Scheibler’s process are as follows:—
[337] The method of preparing this reagent is as follows:—Ordinary commercial sodium tungstate is treated with half its weight of phosphoric acid, specific gravity, 1·13, and then allowed to stand for some days. Phosphotungstic acid separates in crystals.