36 
RESEARCH FOR ARSENIC AND ANTIMONY. 
limb of the apparatus, before introducing the substance to 
be examined. Having been a member of the committee that 
awarded to the late Mr. Marsh, in the year 1836, the large 
Gold Medal of the Society of Arts, for his ingenious dis¬ 
covery, and having seen him operate, I can confirm the cor¬ 
rectness of the above extracts from his paper. Although, as 
he left it, his invention was a useful addition to the ordinary 
processes for detecting arsenic in clear liquids, it was quite 
unfitted for the detection of the poison when associated with 
much organic matter. 
The first improvement on Marsh’s method of analysis was 
made by Orfila, in 1839. This toxicologist deflagrated the 
organic matter in a dry state with nitrate of potash, according 
to a plan suggested by Rapp. He subsequently employed 
nitric acid, to destroy the organic matter; he then brought 
the mass, by evaporation, to a dry, carbonaceous state, and 
acted on the residue by nitro-hydrochloric acid. The arsenic 
was dissolved in water as arsenic acid, and in this state it 
was placed in the hydrogen apparatus. By means of these 
processes, Orfila was enabled to concentrate the arsenic, and 
to remove it from the organic matter; and thus, by the aid 
of Marsh’s tube, he succeeded in detecting the poison in 
nearly all the organs and fluids of the body. MM. Danger 
and Flandin advised the carbonization of the organic matter 
by concentrated sulphuric acid and heat. Fresenius and 
Babo destroyed the organic matter by boiling the substance 
in a mixture of hydrochloric acid and chlorate of potash ; 
and others, with a similar object, have employed chlorine and 
potash. In all these cases, the arsenic is more or less com¬ 
pletely converted to arsenic acid, and in this state the pre¬ 
sence of the poison is easily demonstrated. Analysts who 
have had occasion to employ these various methods of de¬ 
stroying organic matter must have observed that, in some 
instances, they are liable to occasion a loss of arsenic; in 
others, they overload the liquid with chemical compounds, or 
in default of entire carbonization, they yield a dark, syrupy- 
residue, which is liable to produce so much froth in the tube, 
as to render it difficult to procure arseniuretted hydrogen 
gas in a state fitted for testing. The use of nitric acid in 
large proportion, as advised by Orfila, is objectionable ; for 
unless great care is subsequently taken to expel the whole 
of this acid, the arsenic is not in a proper state for separation, 
either by the process of Marsh or by that of Reinsch. 
Apart from the great trouble and difficulty of procuring 
the organic liquid in a state fitted for evolving arseniuretted 
hyd rogen, there are other obstacles to the reproduction of 
