2S6 
ON THE DETECTION OF ARSENIC. 
pressed solid matters with about ten times their weight of 
boiling water, in a porcelain capsule or glass matrass, and af- 
ter filtering the decoction, you acidulate it with a few drops 
of hydrochloric acid and bring it in contact with hydrosul- 
phuric acid gas. If the solution contains arsenious acid it be- 
comes colored yellow, and a precipitate of sulphuretof arsenic 
is formed. In this case it will be useful to prove that this pre- 
cipitate is occasioned by arsenious acid existing in the solu- 
tion, as the yellow color of the sulphurets of selenium, cad- 
mium, tin and antimony, might be mistaken for it. For 
this purpose, gather the precipitate, dissolve it in water of 
ammonia, afterwards evaporate the ammoniacal solution, and 
calcine the residue in a slender tube with a little black flux or 
potash; the arsenic, separated from its combinations with the 
sulphur, volatilizes, and will be easily distinguished by its 
brilliant metallic aspect, and the alliaceous odor which it gives 
out by contact with incandescent charcoal. 
Berzelius has pointed out another process, different from 
this, and which he considers an excellent method for proving 
the existence of arsenic in medico-legal cases. It is a modi- 
fication of one proposed by Valentine Rose. It is as follows: 
Boil the contents of the stomach, and its membranes cut 
into pieces, with several drachms of caustic potash, to dissolve 
all the arsenic: supersaturate the liquid with hydrochloric 
acid, filter, and pass through it a current of hydrosulphuric 
acid gas. If it contains any arsenic, it becomes, after a short 
time, yellow, and then a precipitate of sulphuret of arsenic 
takes place in the form of a yellow powder. If the quantity 
of arsenic is very feeble, the liquid becomes yellow without 
the formation of a precipitate, but by evaporation the sul- 
phuret of arsenic is deposited in proportion as the acid is con- 
centrated by the evaporation. (The mere yellow color of the 
liquid should not be considered as a proof of the existence of 
arsenic, as this tint is likewise produced by the nitric acid, 
which, being reduced to nitrous acid, colors yellow the dis- 
solved animal matters.) Pass the solution through a small 
filter, and wash the sulphuret of arsenic. If it is in so small a 
