Note 700 — PART IX.—INORGANIC POISONS.

Fresenius has pointed out that sulphur may mask small quantities of arsenic, antimony, tin, &c., and he recommends that the turbid liquid in which apparently nothing but sulphur has separated should be treated as follows:—A test-tube is half filled with the liquid, and then a couple of c.c. of petroleum ether or of benzene added, the tube closed by the thumb, and the contents well shaken. The sulphur dissolves, and is held in solution by the solvent, which latter forms a clear upper layer. If traces of a metallic sulphide were mixed with the sulphur, thin coloured films are seen at the junction of the two layers, and the sulphides may also coat the tube above the level of the liquid with a slight faintly-coloured pellicle (Chem. News, Jan. 4, 1895).