600 ON DETECTING THE 
undermost. The gas as it issues from the jet is 
to be inflamed in the usual manner, but the piece 
of glass with its drop of water is to be held about 
an inch above the jet, or just above the apex of . 
the cone of flame: the arsenic by this arrange- 
ment is oxidised at the same time that hydrogen 
is undergoing combustion, and coming in contact 
with the drop of water held above, forms a solu- 
tion of arsenious acid, should arsenic have been 
in the mixture submitted to examination: a 
minute drop of ammoniacal nitrate of silver being 
dropped on the solution so obtained, if arsenic be 
present, the well known characteristic lemon 
yellow colour produced by this test, when used 
for testing for that substance, is immediately pro- 
duced, viz., the insoluble arsenite of silver ; anti- 
mony under the same circumstances produces no 
change. He hopes that the process will be found 
to possess all the delicacy and precision necessary 
for distinguishing the two metals from each other, 
and that it will be the means of removing every 
doubt from the minds of experimentalists in fu- 
ture. I should have been glad to have been able 
to say Mr. Marsh’s hopes are realized ; it happens 
on the contrary, however, that I must give my 
decided opinion, that the results obtained by his 
mode of testing ought not to be considered 
