DETECTING THE PRESENCE OF ARSENIC. 591 
however, that so much of the powder can be col- 
lected separately from the rest of the contents of 
the stomach as is required for its reduction by — 
carbonaceous matter to the metallic state, or for 
the distinct exhibition by that agent of the charac- 
teristic alliaceous smell of the heated metal ; 
owing to the oxide having been administered in 
the state of solution, or, if administered in powder, 
to its having become dissolved by the liquid con- 
tained in the stomach, or to its having got inti- 
mately diffused and mixed among the other undis- 
solved matter in the stomach. In such instances, 
without applying a mode of testing published in 
the year 1836, we cannot so readily conclude as 
to its presence ; but then have to operate upon 
a fluid by the application of certain tests capable 
of effecting known chemical changes with arse- 
nious acid, by the power which they possess of 
acting upon it when in solution. Some of these 
tests are incapable of giving satisfactory results 
when the solution of arsenious acid is accompanied 
by one or more of many ingredients which often 
form a part of the contents of the stomach ; and 
however strong our suspicions may be, it is not 
safe to conclude decidedly that arsenic is present 
when only one of the tests alluded to produces 
that apparent action which it ought to produce 
