334 
ON POISONING BY ARSENIOUS ACID. 
salt, although somewhat poisonous, because as soon as these 
salts are decomposed by the acid of the stomach, the arseni- 
cal acid set free is seized and neutralized by another portion 
of the peroxide, which, as is constantly recommended, should 
be administered in large amount. 
Let me add a few words upon the complications in medico- 
legal research, which may arise from the presence of hydrat- 
ed peroxide of iron in the digestive organs. I announced last 
September, that certain colcothars and certain hyelrated pe- 
roxides of iron of pharmacy, contained arsenic, and that it is 
sometimes sufficient to introduce only a few grammes into 
Marsh's apparatus, to obtain numerous arsenical spots. Sup- 
pose that, in a case of poisoning by an arsenical acid, the hy- 
drated peroxide of iron had been administered, and being sub- 
sequently extracted from the stomach or intestines, was recog- 
nized as arsenical; how shall we determine whether the 
arsenic furnished, is derived from the peroxide of iron, natu- 
rally containing arsenic, or from the sub-salt of iron, resulting 
from the combination of the peroxide with an arsenical acid 
taken as a poison? This question, of incontestable importance, 
is easily resolved. 
1. Every fact leads to the belief that, when poisoning re- 
sults, the arsenical acid has not been entirely neutralized by 
the peroxide, with which it is perhaps mixed ; if so, it will 
suffice to boil, for 25 or 30 minutes, the peroxide with distill- 
ed water, which will dissolve the free arsenical acid, while it 
will not exercise any action upon the arsenic naturally con- 
tained in the peroxide of iron, or upon the arsenite, or arseni- 
ate of iron which it may have formed. 
2. Admitting that boiling water has not dissolved traces of 
arsenious or arsenic acid, then shake up 15 or 16 grammes of 
the peroxide of iron well washed, with as much alcoholic 
potassa in the cold; this alkali, which will not separate a sin- 
gle atom of the arsenic naturally contained in the peroxide, 
will combine with the arsenical acid which may have been 
neutralized by the peroxide, in however small an amount 
the notable quantity of this acid may be in the sub-salt of 
