626 POISONS : THEIR EFFECTS AND DETECTION. [§ 794. 
indicates arsenic; a white coating slowly volatilising, antimony ; and 
ultimately tin, if present, may be obtained as small globules. 
The dry process is, however, more applicable for the quantities met 
with in mineral analysis than for toxicological research. 
(b) Wet Processes. —The sulphides are treated with concentrated 
hydrochloric acid and heated to about 70°. Antimony and tin sulphides 
pass into solution ; arsenic sulphide, if present, remains, and may be 
dissolved by ammonia and ammonium carbonate. 
The solution of possible antimony and tin sulphides is placed in 
a platinum dish, and a small strip of zinc foil immersed therein. 
Antimony immediately causes a dark stain ; on removing the zinc 
thus stained, and well washing, the zinc is treated with hot nitric acid. 
The nitric acid solution will respond to the special tests for antimony 
(■ e.g . it may be tested with the caesium compound salt). The strip of 
zinc freed from the antimony deposit may be replaced in the original 
liquid ; if tin is present, tin in a metallic form will be deposited. 
Hyposulphite Method of Separation. —This excellent method of 
obtaining a separation of the three sulphides has been already described 
(see p. 56). 
Tartaric Acid Method. —The sulphide or sulphides are treated 
with 15 c.c. of nitric acid, and the mixture evaporated to dryness. 
The residue is dissolved in 100 c.c. of warm water. The arsenic acid 
dissolves, and may be precipitated by magnesia mixture ; antimony 
and tin, if present, remain as insoluble oxides; on treatment with 
tartaric acid solution for an hour—antimony oxide dissolves, tin oxide 
is left. The tartrate of antimony solution may be now feebly saturated 
with hydric sulphide, adding a little HC1 ; the sulphide collected is 
converted into oxide by nitric acid and weighed as tetroxide. 1 
It will, however, be advisable to reserve a small portion of the 
tartaric acid solution for a confirmatory test, such as the formation 
of antimony caesium iodide. 
Sodium Peroxide Method. —The sulphides are diluted and heated 
with a little water in a porcelain basin, and caustic soda, in not too 
great excess, added until no more of the precipitate seems to dissolve. 
Three or four drops of ammonium sulphide solution are then added, and 
the liquid boiled until free from odour of ammonia. The solution is 
now diluted with warm water and filtered. 
The filtrate contains the arsenic group, and, possibly, mercury. After 
further dilution the filtrate is boiled, and sodium peroxide gradually 
added until there is a permanent effervescence of oxygen ; any mercury 
will go down as sulphide and can be filtered off—the filtrate contains 
only sodium arsenate, antimoniate, and stannate. 
Should tin be present, this is separated by adding ammonium chloride 
1 \\ m. R. Lang, C. M. Carson, and J. C. Mackintosh, Soc. Chem. Ind., 1902. 
