RESEARCH EOR ARSENIC AND ANTIMONY. 
37 
the gaseous compound in the presence of certain metallic and 
non-metallic substances. The presence of copper or mercury 
in a liquid, or of chlorate of potash, either interferes with the 
free production of arseniuretted hydrogen, or leads to its 
decomposition when produced. In addition to the fallacies 
pointed out by others, I may mention that, in the course of 
the analyses made in Smethurst’s case, I found that l-96th 
of a grain of arseniate of potash, mixed with a small quantity 
of solution of chlorate in the tube, did not give the slightest 
indication of the presence of arsenic. It was only when the 
proportion added was about l-l6th of a grain, that deposits 
were readily procured by the combustion of the gas. An ex¬ 
clusive reliance upon Marsh’s process, when applied in the 
manner recommended by the discoverer, might, therefore, 
lead an analyst to the erroneous opinion that arsenic was 
absent, when the presence of the poison might be safely de¬ 
monstrated by other methods of research. 
Deposits or stains resembling those of arsenic, and liable 
to be mistaken for them, may also be met with under circum¬ 
stances of which the conditions are but little understood. It 
was by some accidental result of this kind that Orfila was led 
to affirm that arsenic was a constituent of all flesh, and of 
animal matter generally. This statement was, however, sub¬ 
sequently proved to be unfounded, before a committee of the 
Institute. The cause of the fallacy which had misled so great 
an authority was not, however, satisfactorily explained. Anti¬ 
mony, phosphorus, selenium, sulphur, &c., and even iron and 
zinc, may, it is well known, so combine occasionally with 
hydrogen, as to deceive analysts who rely upon the appear¬ 
ance of the deposits. 
The process of Marsh may be employed either with or 
without the combustion of the arseniuretted hydrogen gas, 
and the examination of the products of its decomposition. 
Assuming that the gas is burnt in the manner recommended 
by the discoverer,—namely, as it issues from a small jet,—l 
believe that the best method at present known for determining 
the arsenical nature of the deposits is the following:—The 
deposits should be collected in small porcelain capsules, i. 
Add strong Nitric acid , which dissolves the deposit, and eva¬ 
porate the acid liquid on a sand-bath to dryness. A white 
deliquescent residue remains, which gives a reddish-coloured 
precipitate, with a solution of nitrate, or of ammonio-nitrate 
of silver (arseniate of silver). 2. A strong and fresh solution 
of Chloride of lime immediately dissolves the arsenical deposit, 
and on evaporating the liquid to dryness, white arseniate of 
lime remains, which gives the red precipitate above men- 
