6j6 POISONS : THEIR EFFECTS AND DETECTION. [§ 863 , 
§ 863. Detection and Estimation of Silver.— The examination of 
the solid salts of silver usually met with (viz. the nitrate, bromide, 
iodide, cyanide, and chloride) is most speedy by the dry method on 
charcoal; in this way in less than 120 seconds any practical chemist 
could identify each compound. The nitrate, bromide, iodide, and 
cyanide, all, if ignited on charcoal, yield buttons of metallic silver 
deflagration, bromine vapours, iodine vapours, and cyanogen vapours 
being the respective phenomena observed. Chloride of silver fuses to a 
pearl-grey, brown, or black globule on charcoal, according to its purity , 
but is only in the reducing flame gradually reduced to metal. With soda, 
or fused in hydrogen or coal gas, the reduction is rapid enough. 
Nitrate of Silver in solution might be identified by a very large 
number of tests, since it forms so many insoluble salts. In practice one 
is, however, satisfied with three tests, viz. :—(1) A curdy precipitate of 
chloride, on the addition of hydrochloric acid or alkaline chlorides, soluble 
only in ammonia, cyanide of potassium, or hyposulphite of soda , (2) a 
yellow precipitate, but little soluble in ammonia, on the addition of 
iodide of potassium ; and (3) a blood-red precipitate on the addition of 
chromate of potash. 
The separation of silver from the contents of the stomach is best 
ensured by treating it with cyanide of potassium ; for, unless a very 
large quantity of silver nitrate has been taken, it is tolerably certain 
that the whole of it has passed into chloride, and will, therefore, not be 
attacked easily by acids. The contents of the stomach, then, or the 
tissues themselves, are placed in a flask and warmed for some time with 
cyanide of potassium, first, if necessary, adding ammonia. The fluid is 
separated from the solid matters by subsidence (for an alkaline fluid of 
this kind will scarcely filter), and then decomposed by hydrochloric acid 
in excess. The flask containing this fluid is put on one side in a warm 
place, and the clear fluid decanted from the insoluble chloride. The 
latter is now collected on a filter, well washed with hot water, and then 
dried and reduced on charcoal ; or it may be put in a little porcelain 
crucible with a rod of zinc and a few drops of hydrochloric acid. The 
silver is soon deposited, and must be washed with water, then with 
sulphuric acid. By the aid of a wash-bottle the particles of silver are 
now collected on a small filter, again washed, and on the moist mass a 
crystal of nitrate of potash and a little carbonate of soda laid. The 
whole is then dried, and all the filter cut away, save the small portion 
containing the silver. This small portion is now heated on charcoal 
until a little button of pure silver is obtained, which may first be 
weighed, then dissolved in nitric acid, and tested by the methods 
detailed. 
In a similar way hair, suspected of being dyed with silver, can be 
treated with chlorine gas, and the chloride dissolved in potassic cyanide. 
