284 Means of detecting Arsenic in the Animal Body, &e. 
one should see them. It is volatile by heat, and is dissolved by 
cold nitric acid, which solution gives to the nitrate of silver a 
brick-red precipitate, the arsenate of silver. sal 
The antimonial tache is less metallic than the former in its ap- 
pearance, also blacker, and when very Seuse even smutty. It 
can be volatilized, but with great difficulty, and not before it has 
been as it were chased about the surface of the porcelain. Itis — 
soluble in cold nitric acid, which solution gives no red precipitate 
with nitric acid. ‘ | 
The next tache to be spoken of, is the compound one, of arse- 
nic and antimony; at the same time mention.will be made of 
the method adopted by M. Orfila for detecting the one or the other 
of these metals in it. It partakes, as might be expected, of the 
characters of both the metals that enter into its composition, being 
partially volatile, soluble in nitric acid, from which the brick-red 
precipitate of arsenate of silver can be obtained.  M. Orfila pro- 
poses a plan of separating the constituents of this tache, and of. 
testing each by itself, He proceeds as follows: having @ollected 
_anumber of the compound taches upon a porcelain plate, he dis- 
solves them in nitric acid, which solution being poured into.a 
capsule, is evaporated to dryness, and a residue remains com 
of antimonious acid and a mixture of arsenic and arsenious acids. 
Upon this residue a little water is poured, and the capsule slightly 
heated, which enables the water to disdilive more readily the two 
last mentioned acids. The antimonious acid being allowed to 
settle, the clear liquid is decanted, and a few drops of nitrate of 
silver being thrown upon it, the brick-red arsenate of silver is 
formed, which is sometimes mixed with a considerable quantity 
of a yellow precipitate, the arsenite of silver. This will, how- 
ever, rarely happen, if a large quantity of nitric acid has been 
used ; for by so doing, only an extremely small quantity can Te 
main in the state of arsenious acid, the oxidation being carried & 
degree higher. Nevertheless, if the entire precipitate produced 
by the nitrate of silver be yellow, it can have no effect i0 de- 
stroying the fact concerning the presence of arsenic, as it only indi- 
cates that it has met with arsenious and not arsenic acid: But 
to return to the substance left in the capsule :—A small quantity 
of muriatie acid, slightly diluted, is poured upon it, which imme- 
diately dissolves it. A current of sulphuretted hydrogeD is now 
made to pass through this solution, when the orange-colored sul- 
