292 
RESEARCH FOR ARSENIC AND ANTIMONY. 
tered in weight, and is not to any perceptible extent dissolved, 
it is obvious that the liquid submitted to analysis cannot 
have received any impregnation of arsenic from the copper 
employed ; and if, under these circumstances, arsenic is de¬ 
posited on the copper, then that poison must have been 
present in the liquid submitted to examination. Cold 
hydrochloric acid, if strong and not too freely exposed to air, 
produces no deposit or change in the appearance of bright 
copper, even after forty-eiuht hours 5 immersion and exposure. 
Whether the copper be pure or arsenicated, there is no per¬ 
ceptible difference. The upper stratum of the liquid has a 
slight-greenish yellow tint, arising from the oxidation and 
solution of a small quantity of copper. If the polished cop¬ 
per is immersed in an acid diluted with eight parts of water, 
it will be found after forty-eight hours that the whole of the 
liquid has a greenish colour, from the formation of chloride ; 
the copper, if arsenicated, is coated with a thick dark-coloured 
deposit; while, if pure, it is of a reddish-brown colour. The 
surface of the metal in either case will be found much cor¬ 
roded, and a number of tetrahedral crystals of subchloride of 
copper are scattered over it. I have not been able to procure 
crystals of arsenious acid by heating impure copper thus 
coated, and I have not detected anv arsenic in the acid 
liquid; the amount of arsenicated copper dissolved is pro¬ 
bably too small to furnish any evidence of arsenic. These 
results confirm Reinsch’s statement that the concentrated 
acid, caberis paribus, exerts a less powerful action on copper 
than the diluted acid; they also prove that arsenicated cop¬ 
per should not be allowed to remain for a long time in the acid 
liquid. The tarnish thus formed might, unless properly test¬ 
ed, be mistaken for arsenic, or conceal an arsenical deposit. 
They prove, however, that the alloy of arsenic and copper 
(arsenide) is not so decomposed by cold diluted hydrochloric 
acid as to set free any arsenious acid in the liquid. In short, 
the danger of any fallacy in the ordinary use of the process 
arises from the presence of arsenic as an impurity in the acid, 
and not from arsenic contained as impurity in the copper. 
But for this fact, no chemist would ever have met with nega¬ 
tive results in employing copper in the state in which it has 
hitherto been used . 1 
1 In the case of Smethurst, out of seventy-six analyses in which the 
process of Reinsch was resorted to, arsenic was detected in only two 
instances. In one of these, the copper was entirely dissolved by reason of 
the unexpected presence of chlorate of potash, and there was no doubt that, 
from subscqueut investigatiou, the arseuic here detected proceeded from the 
