PRESENCE OF ARSENIC. 609 
less volatile, and in having none of the chemical 
characters of that metal. Then, since the ques- 
tion is only likely to be whether or not a given 
metallic deposit is arsenic or antimony, I trust 
that my mode of applying heat, particularly in 
addition to the method of testing recommended 
by Mr. Thompson, will tend to make Mr. Marsh’s 
discovery as perfect as it probably ever will be; 
and, Idoubt not, that ‘“Marsh’s test”’ will continue 
to be regarded as a valuable assistant in a che- 
mical laboratory. I have myself often applied 
it successfully in determining the presence of 
arsenic, in small quantity, in minerals I have had 
under examination ; in such instances, I venture 
to suppose no one will dispute its utility ; but, in 
cases of poisoning, unless a large quantity of the 
suspected arsenical ingredient can, by direct 
means, be produced, it ought not to be regarded 
in a stronger light than capable of furnishing good 
collateral evidence ; it must, indeed, be lament- 
able to consider that so much confidence should 
be placed upon appearances produced by its ope- 
ration, as to cause a positive conclusion to be 
arrived at that death was caused by arsenic, when 
it had been needful to resort to intricate manipu- 
lation in order todetect therequisite characteristics, 
and when, at length, only a slight crust or film 
could be obtained. In cases of poisoning, no man, 
4u 
