608 ON DETECTING THE 
Mr. Marsh’s original. discovery, per se, is in- 
valuable in enabling us with ease and certainty to 
bring out from among organic materials arsenic, 
when present in very minute quantity, and in - 
giving us the power of submitting it to ocular 
demonstration ; but it is wanting in the capability 
of convincing us that what we separate, from sus- 
pected matter, having the superficial appearance 
of arsenic, is most decidedly in every instance 
that metal; it leaves us to find out by other 
means whether the metallic looking substance is 
arsenic, or antimony, or something else. Though 
there may be other substances besides arsenic and 
antimony capable of combining with hydrogen, 
and of giving the flame of that gas the property 
of depositing upon cold surfaces dark coloured 
films or crusts having more or less of a metallic 
lustre, yet, I think it is not probable that any 
substance besides antimony will cause a film or 
crust, so nearly resembling one of arsenic in ap- 
pearance and chemical properties, as to settle 
strong doubt upon the mind of an experimentalist 
accustomed to investigations, such as the one 
under consideration. Orfila states, that he has 
observed stains to result even from organic mat- 
ter only ; but these differed from arsenic in being 
less volatile, and in having none of the chemical 
