112 
ORIGINAL COMMUNICATIONS. 
antimoniuretted hydrogen, does not set free the metallic 
antimony, it only forms a small quantity of chloride of anti- 
mony, which may be recognised by means of sulphuretted 
hydrogen. Arseniuretted hydrogen, on the contrary, into 
which a few bubbles of chlorine has been passed, deposits 
much metallic arsenic, which attaches itself to the sides of the 
vessel; and the appearance of a black film is very sensible, 
even when arseniuretted hydrogen is mixed with forty or 
fifty times its bulk of pure hydrogen gas. Chlorine offers, 
therefore, much greater security in detecting traces of arse- 
niuretted hydrogen, when mixed with a large quantity of pure 
hydrogen, than the combustion of this mixture in the air, 
although it then deposits a small quantity of metallic arsenic. 
When arseniuretted hydrogen is mixed with so much air as 
to be no longer inflammable, we may even then separate the 
arsenic in a metallic state by a bubble of chlorine. In all 
these cases it is necessary that the chlorine should be added 
to these gaseous mixtures in very small quantities, for without 
this precaution the metallic film will either not appear, or will 
disappear immediately after." 
M. Vogel then proceeds to prove that the hydrogen ob- 
tained, when a salt or oxide of antimony has been used, 
contains more of the metal than that from the alloy. He 
likewise differs from Mr. Thompson with regard to the diffi- 
culty of discriminating the results produced by the combustion 
of these different gases; for after stating the assertion of Mr. 
Thompson, he remarks : 
" I do not see the necessity of taking these pains, neither 
do I partake in the fears of Mr. Thompson, that sulphuretted 
hydrogen will give rise to error, and cause antimony to be con- 
founded with arsenic. It appears to me more simple to arrive 
at the same end in the following manner: add to the two films 
of arsenic and of antimony a single drop of aqua regia, composed 
of two parts of concentrated hydrochloric and one of nitric 
acid; this acid will dissolve these films without heat; moisten 
these spots with several drops of water well charged with 
