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SELECTED ARTICLES. 
and hydrochloric acids, together with the zinc used, were 
perfectly free from arsenic. 
The method of Mr. Marsh constitutes an epoch in the 
history of examinations for arsenic, and renders all other 
means superfluous. We possess a sufficient number of pro- 
ceedings to extract arsenic in a metallic state from its com- 
binations, a proof that we have isolated it, but it is precisely 
here that the difficulty lies. The boiling of the stomach and 
intestines, frequently half putrid, a long filtration of the 
liquors, the separation of the precipitated sulphuret of arsenic, 
rendered often impossible by the viscosity of the liquid, and 
then the final treatment of the precipitate mixed with animal 
substances ; all these inconveniences disappear. We place 
the suspected matters in a common glass flask, add hydro- 
chloric acid, and heat for some time to dissolve the solid 
combinations of the arsenic, add some pieces of zinc, inflame 
the gas, and thus obtain, in a short time, a result equally as 
positive as we can obtain by any other method in trials of a 
week. Is it necessary to state that, to prevent explosion, we 
should not loose sight of the well known precautions? But 
as it is important to be able to inflame the gas promptly, the 
vessel should be filled as full as convenient with the liquid 
when the disengagement takes place. 
The two most certain indications of arsenic, the presence 
of a volatile metal of a particular aspect, and peculiar smell, 
are exhibited and bring the most perfect conviction. 
We must not confound the film of arsenic with the little 
black points and spots which are deposited on the porcelain, 
during the rapid solution of iron and other metals in the 
acids. 
This method is likewise applicable to the discovery, of 
arsenic in solid substances. We then endeavor to bring 
them to the state of solution, avoiding, however, any disen- 
gagement of hydrogen. 
Antimony and its sulphuret are, in the first place, oxidized 
by nitric acid, the liquid decanted, and heated with hydro- 
chloric acid, until all the nitric acid is destroyed; and then 
