696 POISONS : THEIR EFFECTS AND DETECTION. [§ 889 . 
warm, and kept there for about forty-eight hours. It acquired a slight 
silvery lustre, and globules of mercury were obtained from it by 
sublimation.” 
To detect the cyanide of mercury may require special treatment, 
and Yitali 1 recommends the following process :—The fluid is acidified 
with tartaric acid and neutralised by freshly precipitated CaC0 3 ; a 
slight excess of hydric sulphide is added, and the flask allowed fco rest 
for twenty-four hours in the cold. Then a further quantity of SH 2 
is added, and a current of hydrogen passed through the liquid ; the 
effluent gas is first made to bubble through a solution of bismuth 
nitrate in dilute nitric acid (for the purpose of absorbing SH 2 ), and 
then through aqueous potash (to absorb HC1) ; in the first flask 
the analyst will separate and identify mercury sulphide, while in the 
last flask there will be potassic cyanide, which will respond to the 
usual tests. 
In those cases where no special search is made for mercury, but an 
• V ' 
acid (hydrochloric) solution is treated with sulphuretted hydrogen, 
mercury is indicated by the presence of a black precipitate, which does 
not dissolve in warm nitric acid, but is soluble in aqua regia. It is also 
soluble in hydriodic acid, as prepared by dissolving 5 grms. of potassium 
iodide in 12 c.c. of 10 per cent, sulphuric acid and diluting to 25 c.c. 
(S. Gutman, Biochem. Zeitschr ., 1918). 
The further treatment of the black sulphide may be undertaken in 
two ways :— 
1. It is collected on a porcelain dish, with the addition of a little 
nitric acid, and evaporated to dryness in order to destroy organic 
matter. Hydrochloric and a few drops of nitric acid are next added ; 
the action is aided by a gentle heat, the solution finally evaporated to 
dryness on the water-bath, and the residue taken up by warm distilled 
water. The solution is that of a persalt of mercury, and the mercury 
can be separated by electrolysis, or indicated by the tests already 
detailed. 
2. The other method, and the most satisfactory, is to mix the sul¬ 
phide while moist with dry carbonate of soda, make it into a pellet 
which will easily enter a reducing or subliming tube, dry it carefully, 
and obtain a sublimate of metallic mercury. 
A neat method of recognising mercury when deposited as a film on 
c opper has been proposed by E. Brugnatelli : 2 the copper, after being 
washed, is transferred to a glass vessel, and a porcelain lid, on which a 
drop of gold chloride solution has been placed, adjusted over the dish. 
The whole is heated by a water-bath. The mercury vapour reduces the 
gold chloride, and gold is deposited as a bluish-violet stain ; mgrm. 
mercury may by this test be identified. 
1 L'Orosi, xii. 181-196. 
2 Gazze.Ua , xix. 418-422. 
