Читать книгу Poisons, Their Effects and Detection - Alexander Wynter Blyth - Страница 48

The substances are placed in a porcelain dish and diluted with a sufficient quantity of water to form a thin soup and 20 to 30 c.c. of pure hydrochloric acid added; the dish is placed on the water-bath and 2 grms. of potassic chlorate added. The contents are stirred from time to time, and successive quantities of potassic chlorate are again added, until the contents are coloured yellow. The heating is continued, with, if necessary, the addition of more acid, until all smell of chlorine has ceased. If there is considerable excess of acid, this is to be evaporated away by diluting with a little water and continuing to heat on the water-bath. The dish with its contents is cooled, a little water added, and the fluid is then filtered.

The metals remaining on the filter are:—

 Silver chloride,

 Lead sulphate,

 Barium sulphate;

in the filtrate will be all the other metals.

The filtrate is put in a flask and heated to from 60 to 80 degrees and submitted to a slow stream of hydric sulphide gas; when the fluid is saturated with the gas, the flask is securely corked and allowed to rest for twelve hours; at the end of that time the fluid is filtered and the filter washed with water saturated with hydric sulphide.

The still moist sulphides remaining on the filter are treated with yellow ammonium sulphide containing some free ammonia and washed with sulphide of ammonium water. Now remaining on the filter, if present at all, will be:—

 Mercury sulphide,

 Lead sulphide,

 Copper sulphide,

 Cadmium sulphide;

in the filtrate may be:—

 Arsenic sulphide,

 Antimony sulphide,

 Tin sulphide,

and there may also be a small portion of copper sulphide, because the latter is somewhat soluble in a considerable quantity of ammonium sulphide.

The filtrate from the original hydric sulphide precipitate will contain, if present, the sulphides of zinc and chromium in solution.