The organic mixture is repeatedly extracted by water strongly acidified with sulphuric acid; the extract is evaporated at 30° to the consistence of a thin syrup; then diluted with water, and, after several hours’ standing, filtered in a cool place. To the filtered fluid phosphotungstic acid is added in excess, the precipitate filtered, washed with water to which some phosphotungstic acid solution has been added, and, whilst still moist, rinsed into a flask. Caustic baryta or carbonate of potash is added to alkaline reaction, and after the flask has been connected with bulbs containing HCl, it is heated at first slowly, then more strongly. Ammonia and any volatile alkaloids are driven over into the acid, and are there fixed, and can be examined later by suitable methods. The residue in the flask is carefully evaporated to dryness (the excess of baryta having been precipitated by CO2), and then extracted by strong alcohol. On evaporation of the alcohol, the alkaloid is generally sufficiently pure to be examined, or, if not so, it may be obtained pure by re-solution, &c.
The author has had considerable experience of Scheibler’s process, and has used it in precipitating various animal fluids, but has generally found the precipitate bulky and difficult to manage.
§ 312. Grandval and Lajoux’s Method.[338]—The alkaloids are precipitated from a solution slightly acidified by hydrochloric or sulphuric acid by a solution of hydrarg-potassium iodide. The precipitate is collected on a filter, washed and then transferred to a flask; drop by drop, a solution of sodium sulphide is added; after each addition the suspended precipitate is shaken and allowed to stand for a few minutes, and a drop of the liquid taken out and tested with lead acetate; directly a slight brown colour appears, sufficient sodic sulphide has been added. The liquid is now left for half-an-hour, with occasional shaking. Then sulphuric acid is added until it is just acid, and the liquid is filtered and the mercury sulphide well washed. In the filtrate will be the sulphate of any alkaloid in solution; this liquid is now made alkaline with soda carbonate and shaken up, as in Dragendorff’s process, with appropriate solvents; such, for example, as ether, or chloroform, or acetone, or amylic alcohol, according to the particular alkaloid the analyst is searching for, and the solvent finally separated and allowed to evaporate, when the alkaloid is found in the residue.
[338] “Dosage des alcaloides à l’aide de l’iodure double de mercure et de potassium,” par MM. A. Grandval et Henri Lajoux, Journ. de Pharmacie, 5 sér. t. xxviii. 152-156.
§ 313. Identification of the Alkaloids.—Having obtained, in one way or other, a crystalline or amorphous substance, supposed to be an alkaloid, or, at all events, an active vegetable principle, the next step is to identify it. If the tests given in Dragendorff’s process have been applied, the observer will have already gone a good way towards the identification of the substance; but it is, of course, dangerous to trust to one reaction.
In medico-legal researches there is seldom any considerable quantity of the material to work upon. Hence the greatest care must be taken from the commencement not to waste the substance in useless tests, but to study well at the outset what—by the method of extraction used, the microscopic appearance, the reaction to litmus paper, and the solubility in different menstrua—it is likely to be. However minute the quantity may be, it is essential to divide it into different parts, in order to apply a variety of tests; but as any attempt to do this on the solid substance will probably entail loss, the best way is to dissolve it in a watch-glass in half a c.c. of alcohol, ether, or other suitable solvent. Droplets of this solution are then placed on watch-glasses or slips of microscopic glass, and to these drops, by the aid of a glass rod, different reagents can be applied, and the changes watched under the microscope as the drops slowly evaporate.
§ 314. Sublimation of the Alkaloids.—A very beautiful and elegant aid to the identification of alkaloids, and vegetable principles generally, is their behaviour towards heat.
Alkaloids, glucosides, the organic acids, &c., when carefully heated, either—(1) sublime wholly without decomposition (like theine, cytisin, and others); or (2) partially sublime with decomposition; or (3) are changed into new bodies (as, for example, gallic acid); or (4) melt and then char; or (5) simply char and burn away.