ARSENIC. 
§ 768.] 
or potash and a little bit of aluminium added, produces in a short time 
arsine, which will blacken a piece of paper, soaked in nitrate of silver, 
and inserted in the mouth of the flask. This is a convenient test for 
arsenic. No antimoniuretted hydrogen ( stibine) is given off from an 
alkaline solution, and no SH 2 . 
§ 768. The Gutzeit Quantitative Limit Test for Arsenic as laid down 
in the British Pharmacopoeia, 1914. —The apparatus used is a wide¬ 
mouthed flask or bottle holding about 120 c.c., fitted with a rubber 
cork through which passes a glass tube. The tube has a total length 
of 200 mm. and internal diameter of 7 mm. The upper end is widened 
out to a diameter of 8 mm., the lower is drawn out to about 1 mm. 
in diameter, and a hole of about 2 mm. in diameter is blown in the 
side of the tube where it is constricted. 
The wide end of the tube is capped with smooth white filter-paper 
previously wetted with a saturated solution of mercuric chloride and 
dried. To absorb any SH 2 , some pieces of dry lead paper are inserted 
before “ capping,” just beneath the cap. The solution to be examined, 
which should not be more than 50 c.c., is made acid with 10 c.c. of what 
is called stannated hydrochloric acid AsT 1 and 10 grms. of pure arsenic- 
free zinc. The flask is put on a warm plate, and at the end of thirty or 
forty minutes any stain on the paper is examined and compared with 
standard stains. In many cases— e.g. the examination of the sulphates 
of iron, copper, zinc, the carbonates of ammonia, the alkalies, and the 
alkaline earths,-—instead of stannated hydrochloric acid, brominated 
hydrochloric acid AsT 2 is added, excess of bromine being reduced by a 
few drops of the strong solution of stannous chloride. All these solutions 
are tested for traces of arsenic. Standard stains are made by submitting 
to the process known small quantities of a freshly made solution of arsenic 
in dilute HC1, each c.c. of which contains ’01 mgrm. of arsenious acid. 
The stains fade in time. The author, instead of making from time to 
time standard stains, has a series of stains exactly imitated in water¬ 
colours ; such imitations are practically permanent if kept in the dark. 
The B.P. mercuric chloride papers give a disc of 8 mm., but, when 
it is required to detect very minute traces of arsenic, it is better to allow 
the gas to stream through a capillary tube of 2 mm. internal diameter 
on to the mercuric chloride paper. A disc of 8 mm. just shows -01 mm. 
of As 2 0 6 , but when the lumen is reduced to 2 mm., it becomes a brilliant 
1 A strong solution of stannous chloride is prepared by the use of 60 c.c. HC1, 
20 c.c. of water, and 20 grms. of tin. This is heated until gas ceases to be evolved, 
which usually takes much time, and the liquid made up to 100, leaving in the solution 
undissolved tin. 1 c.c. of this solution added to 100 c.c. of pure hydrochloric acid is 
the stannated hydrochloric acid AsT. 
2 Brominated hydrochloric acid AsT is prepared as follows:—First a strong solu¬ 
tion of bromine is made by dissolving 30 grms. Br by means of an equal quantity of 
KBr, and making up to 100 c.c. ; 1 c.c. of this solution is added to 100 c.c. arsenic- 
free HC1. 
