SEPARATION OF ARSENIC. 
307 
The manufacturer of chlorate of potassa should, therefore, 
vary his process with the state of his solutions of chloride of 
potassa; if these are without excess of chlorine, as when ob- 
tained from chloride of lime, they may be evaporated at their 
boiling point; but if, as is usually the case, they are saturated 
with the gas, they should be concentrated at a temperature not 
exceeding 50° or 60° Cen. 
ART. — XLIX. — SEPARATION OF ARSENIC. By Mr. James 
Marsh, of the Royal Arsenal, Woolwich. 
Notwithstanding the improved methods that have of 
late been invented of detecting the presence of small quantities 
of arsenic in the food, in the contents of the stomach, and 
mixed with various other animal and vegetable matters, a pro- 
cess was still wanting for separating it expeditiously and com- 
modiously, and presenting it in a pure unequivocal form for 
examination by the appropriate tests. Such a process should 
be capable of detecting arsenic not only in its usual state of 
white arsenic or arsenious acid, but likewise in that of arse- 
nic acid and of all the compound salts formed by the union of 
either of these acids with alkaline substances. It ought, also, 
to exhibit the arsenic in its reguline or metallic state, free 
from the ambiguity which is sometimes caused by the use of 
carbonaceous reducing fluxes. It appeared to me, that these 
objects might be attained by presenting to the arsenic hydro- 
gen gas in its nascent state: the first action of which would be 
to deoxygenate the arsenic; and the next, to combine with 
the arsenic, thus deoxygenated, into the well-known gas called 
arsenuretted hydrogen. Being thus brought to the gaseous 
state, the arsenic would spontaneously (so to speak) separate 
itself from the liquor in which it was before dissolved, and 
might be collected for examination by means of any common 
gas apparatus; thus avoiding the trouble, difficulty, and ambi- 
