ON THE PROCESS FOR THE DETECTION OF ARSENIC. 109 
open at both extremities, in which metallic arsenic and arse- 
nious acid are deposited." 
" Marsh has in this neglected a property of the gas, which 
may with great certainty be turned to good account, viz.: that 
of depositing the arsenic by heat; it is only necessary to pass 
the gas through a tube heated to redness in one part; the arse- 
niuretted hydrogen is then decomposed into arsenic, which is 
deposited further on in a cool part of the tube, and into hy- 
drogen which is disengaged in a pure state. For this pur- 
pose, there is need of no other apparatus than a flask for the 
disengagement of the gas, a pipe to conduct the gas, as soon 
as disengaged, through a glass tube heated to redness in one 
part by the flame of a spirit lamp. If we wish, for greater cer- 
tainty, to place in the red part of the tube a small quantity of 
a known weight of copper reduced by hydrogen, a white ar- 
seniuret of copper will be obtained, and we may thence ascer- 
tain with great exactness the weight of the arsenic which 
accompanies the hydrogen. 
" I dissolved a millegramme of white arsenic in a little di- 
luted sulphuric acid; I then added to the solution six ounces 
of water and some zinc; I passed the hydrogen thus obtained, 
upon a known weight of copper previously reduced by hy- 
drogen, heated to redness in a narrow glass tube. 
" The presence of arsenic was very evident; the anterior part 
of the copper became silver white, and heated in a lamp gave 
out a,strong odor of arsenic. 
" Having operated with one centigramme of arsenic, I ob- 
tained two-thirds of the arsenic which it contained, combined 
with the copper. It results that this process, although not 
applicable to a quantitive analysis, deserves all our attention 
as an analysis well suited to all cases of legal medicine." 
This testimony of Berzelius tends to increase our confi- 
dence in the process under consideration, while at the same 
time it points out an improvement in the mode of manipula- 
tion. On the other hand, a late discovery of Mr. L. Thomp- 
son, shows that this method might lead to very erroneous 
