[537] M. Duquesnel, Pharm. J. Trans. (3), v. 847.
It gives a precipitate with gold chloride, reducing the gold; also one with mercuric chloride easily soluble in hydrochloric acid. It gives no precipitate with platinum chloride.
§ 488. Tests.—Da Silva’s[538] test for eserine is as follows:—A minute fragment of eserine or one of its salts is dissolved in a few drops of fuming nitric acid; this makes a yellow solution, but evaporated to complete dryness it is pure green. The green substance, called by others chloreserine, dissolves to a non-fluorescent green solution; in water and also in strong alcohol it shows a band in the red between λ670 and λ688, a broader but more nebulous band in the blue and violet between λ400 and λ418, and a very feeble band in the orange.
[538] S. J. Ferreira da Silva, Compt. Rend., cxvii. 330, 331.
J. B. Nagelvoort[539] has recommended the following tests:—(a) An amorphous residue of a permanent blue colour is obtained if a trace of the alkaloid, or one of its salts, is evaporated in the presence of an excess of ammonia; this blue alkaloid dissolves in dilute acids with a red colour; sensitiveness 0·00001 gm. (1 : 100000). The solution has beautiful red fluorescence in reflected light; when evaporated, it leaves a residue that is green at first, changing to blue afterwards, the blue residue being soluble in water, alcohol, and chloroform, but not in ether. Chloroform extracts the blue colour from the watery ammoniacal solution only partially. The blue solutions are reddened at first by H2S, and discoloured afterwards. The blue colour is restored by expelling the H2S on the water-bath. (b) A red fluid is obtained when 0·010 gm. eserine or its salicylate, 0·050 gm. of slacked lime, and 1 c.c. of water are added together. Warmed in a water-bath, it turns green, and a piece of red litmus-paper suspended in the test-tube turns blue; a glass rod moistened with HCl gives off the well-known white clouds characteristic of an ammonia reaction. The green solution does not lose its colour by evaporation. Baryta water, added to an eserine solution, gives a white precipitate that turns red when strongly agitated, sensitive to 0·01 mgrm. (1 : 100000).