314 
SELECTED ARTICLES. 
Fowler's solution of arsenic, which only contains part of 
a grain. 
The presence of arsenic in artificial orpiment and realgar, 
in Scheele's green, and in the sulphuret of antimony, may be 
readily shewn by this process, when not more than half a 
grain of any of those compounds is employed. 
In conclusion, I beg to remark, that although the instru- 
ments I have now finished describing, are the form I prefer, 
to all that I have employed, yet it must be perfectly evident 
to any one, that many very simple arrangements might be 
contrived. Indeed, I may say unequivocally, that there is no 
town or village in which sulphuric acid and zinc can be ob- 
tained, but every house w r ould furnish to the ingenious experi- 
mentalist ample means for his purpose; for, a two-ounce phial, 
with a cork and piece of tobacco-pipe, or a bladder, with the 
same arrangement fixed to its mouth, might, in cases of ex- 
treme necessity, be employed with success, as I have repeat- 
edly done for this purpose. 
The only ambiguity that can possibly arise in the mode of 
operating above described, arises from the circumstance, that 
some samples of the zinc of commerce themselves contain 
arsenic; and such, when acted on by dilute sulphuric acid 
give out arsenuretted hydrogen. It is, therefore, necessary 
for the operator to be certain of the purity of the zinc which 
he employs, and this is easily done by putting a bit of it into 
the apparatus, with only some dilute sulphuric acid; the gas 
thus obtained is to be"set fire to as it issues from the jet; and 
if no metallic film is deposited on the bit of flat glass, and no 
white sublimate within the open tube, the zinc may be regard- 
ed as in a fit state for use. 
Transactions of the Society of Arts. 
