PRESENCE OF ARSENIC. 597 
stances; and although a practised eye may discern 
some difference between the crusts, that from 
antimony being more silvery and metallic; yet the 
line of demarcation is not easily drawn ; for a thin 
film of antimony looks like arsenic, and a thick 
crust of arsenic has the metallic appearance of 
antimony: and, after showing the similarity of 
appearances produced by sulphuretted hydrogen 
upon the oxides of the two metals, and the falla- 
cious results likely to be arrived at in endea- 
vouring to determine which of the two is present 
by the ammoniacal sulphate of copper, he states 
that they may be distinguished by adding a drop 
of nitric acid to the crusts, which will dissolve 
them, and on evaporation to dryness a white 
powder be left in each instance : a little of a dilute 
solution of nitrate of silver being added, and the 
whole then exposed to the fumes arising from a 
stopper moistened with ammonia, the antimonial 
solution will deposit a dense white precipitate, 
whereas that from arsenic will give the well known 
canary yellow flocculi: he prefers this mode of 
using silver to the ammoniacal nitrate of that 
metal, because the slightest excess of ammonia 
destroys the colour, but by watching the effect of 
the vapour, the exact quantity requisite is easily 
