PRESENCE OF ARSENIC. 595 
With one drop of Fowler’s solution of arsenic, 
which only contains about the one 120th part ofa 
grain, he is able to obtain distinct metallic films. 
When arsenic is present in large quantity in the 
matter suspected to contain it, he can separate 
sufficient in the form of arsenious acid to enable 
him to form a pure solution from it, the identity 
of which he can then verify by the several tests 
usually employed, and which I have before 
alluded to: but, though his plan of operating is 
generally applicable, yet it is only indispensable 
to adopt it, when the poison is present in very 
minute quantity. Great as is the value at which 
we are compelled to estimate it in reference to its 
application where the quantity of poison present 
is but minute, and entangled with organic matter, 
there is still reason why it may have been consi- 
dered incomplete, and viewed as dangerous to 
have been resorted to by the inexperienced 
operator, or even by one accustomed to general 
chemical practice but hasty in arriving at conclu- 
sions from mere superficial resemblances. 
Had it been the fact that arsenic is the only 
metal which enters into combination with hydro- 
gen, and which is capable of being deposited upon 
cold surfaces, when the gas is allowed to undergo 
