The final reaction is found by filtering, from time to time, a drop on to a glass plate, resting on a blackened surface, and adding the test until no precipitate appears. The results are only accurate when the strength of the solution of the alkaloid is about 1 : 200; so that it is absolutely necessary first to ascertain approximatively the amount present, and then to dilute or concentrate, as the case may be, until the proportion mentioned is obtained.
A convenient method of obtaining the sulphate of an alkaloid for quantitative purposes, and especially from organic fluids, is that recommended by Wagner. The fluid is acidulated with sulphuric acid, and the alkaloid precipitated by a solution of iodine in iodide of potassium. The precipitate is collected and dissolved in an aqueous solution of hyposulphite of soda. The filtered solution is again precipitated with the iodine reagent, and the precipitate dissolved in sulphurous acid, which, on evaporation, leaves behind the pure sulphate of the base.
It is also very useful for quantitative purposes to combine an alkaloid with gold or platinum, by treating the solution with the chlorides of either of those metals—the rule as to selection being to give that metal the preference which yields the most insoluble and the most crystallisable compound.
The following table gives the percentage of gold or platinum left on ignition of the double salt:—
| Gold. | Platinum. | |||||
|---|---|---|---|---|---|---|
| Atropine, | 31 | ·57 | ... | |||
| Aconitine | 20 | ·0 | ... | |||
| Amanitine, | 44 | ·23 | ... | |||
| Berberine, | 29 | ·16 | 18 | ·11 | ||
| Brucine, | ... | 16 | ·52 | |||
| Cinchonine, | ... | 27 | ·36 | |||
| Cinchonidine, | ... | 27 | ·87 | |||
| Codeine, | ... | 19 | ·11 | |||
| Coniine, | ... | 29 | ·38 | |||
| Curarine, | ... | 32 | ·65 | |||
| Delphinine, | 26 | ·7 | ... | |||
| Delphinoidine, | 29 | ·0 | 15 | ·8 | ||
| Emetine, | ... | 29 | ·7 | |||
| Hyoscyamine, | 34 | ·6 | ... | |||
| Morphine, | ... | 19 | ·52 | |||
| Muscarine, | 43 | ·01 | ... | |||
| Narcotine, | 15 | ·7 | 15 | ·9 | ||
| Narceine, | ... | 14 | ·52 | |||
| Nicotine, | ... | 34 | ·25 | |||
| Papaverine, | ... | 17 | ·82 | |||
| Pilocarpine, | 35 | ·5 | 23 | ·6 to 25·2. | ||
| Piperine, | ... | 12 | ·7 | |||
| Quinine, | 40 | ·0 | 26 | ·26 | ||
| Strychnine, | 29 | ·15 | 18 | ·16 | ||
| Thebaine, | ... | 18 | ·71 | |||
| Theine, | 37 | ·02 | 24 | ·58 | ||
| Theobromine, | ... | 25 | ·55 | |||
| Veratrine, | 21 | ·01 | ... | |||
II.—Liquid Volatile Alkaloids.
THE ALKALOIDS OF HEMLOCK—NICOTINE—PITURIE—SPARTEINE.