RESEARCH FOR ARSENIC AND ANTIMONY. 
545 
the arsenic has come over, the acid should be evaporated in 
a light-balanced capsule on a sand-bath, and the weight of 
arsenic may be known by the increase. If converted to 
arseniateof silver, and the quantity is sufficient for collection 
on a filter, this precipitate may be dried and weighed. Every 
100 parts of the arseniate of silver are equivalent to 21*38 
parts of arsenious acid. In reference to imponderable quan¬ 
tities, the only method of estimating the quantity of arsenic 
is the comparing of the amount of metallic deposit obtained 
by heating the current of arseniuretted hydrogen with the 
amount obtained from a weighed quantity of arsenic, dis¬ 
solved in water, and treated in a similar manner. 
For determining the quantity in the tissues, a known 
weight,—one hundred grains of dry liver, maybe distilled:— 
the chloride obtained converted entirely to hydride, and this, 
decomposed by passing the gas into nitric acid until the 
arsenic is exhausted. The residue left by evaporation will 
be arsenic acid, of which 100 parts correspond to 65*2 of 
arsenious acid. 
Objections .—This process appears to be singularly free 
from the objections to which those of Marsh and Reinsch are 
exposed. In the first stage, if properly conducted, arsenic 
is separated from all metals excepting antimony and bismuth, 
and from all metalloids excepting sulphur, phosphorus, and 
that rare substance, selenium. Of all the metals known, 
fourteen produce volatile chlorides; but with the exception 
of arsenic, antimony, and bismuth, these are deposited on 
cooling, in a solid condition. Most of these are chlorides of 
the rarer metals, which are not likely to be met with in any 
analysis of a medico-legal nature. The chloride of arsenic 
is volatile, and is easily distilled with aqueous vapour: the 
chlorides of antimony and bismuth require a much higher 
temperature for volatilization; and unless the material is 
distilled to dryness and subsequently heated, they are not 
likely to be found in the acid distillate.* 
In the second stage, antimony comes over with hydrogen, 
like arsenic. The only other metals which combine with 
hydrogen to form a gas are potassium, tellurium, and zinc; 
and among the metalloids, sulphur, selenium, phosphorus, 
and carbon. When heat is applied to the current of gas, the 
* Ten grains of subnitrate of bismuth were distilled by a sand-bath with 
two drachms of pure hydrochloric acid. A small piece of polished copper 
boiled in the distillate, diluted, was only faintly whitened. Ten grains of 
protochloride of tin were distilled with two drachms of pure hydrochloric 
acid. The acid liquid produced no chauge on metallic copper by Reinsch’s 
process. 
