40 RESEARCH FOR ARSENIC AND ANTIMONY. 
mixture of arsenious acid and metallic arsenic (brown oxide 
of arsenic). Further, that it was decomposed by nitric and 
nitrous acids, by aqua regia, by chlorine, and a great number 
of metallic solutions, the products being water, arsenious 
and arsenic acids. In 1815, the gas was examined by Gehlen, 
and he discovered a new method of preparing it, by applying 
heat to a mixture of arsenic and caustic alkali. Its highly 
poisonous nature was demonstrated by the death of Gehlen 
from the respiration of a small quantity of the gas, during 
the performance of his experiments. An incautious manipu¬ 
lation with this gas has since led to fatal consequences in at 
least three cases. Every cubic inch contains one fourth of a 
cubic inch of arsenic in vapour, and an atmosphere contain¬ 
ing one tenth by volume of the gas is fatal to animal life 
(Berzelius). The gas contains by weight more than 96 per 
cent, of arsenic. It is very heavy, its specific gravity being 
2*69* In 1830 Soubeiran published his researches on this 
compound. This chemist confirmed the results of Gehlen on 
the production of the gas by heating a concentrated alkaline 
solution with arsenic; and he also made the two important 
discoveries : 1st, that when a current of the gas was moder¬ 
ately heated in a tube by a spirit-lamp, it was decomposed; 
and that arsenic of a bright metallic lustre was deposited on 
the interior of the tube ; and 2dly, that a solution of a salt of 
silver was decomposed by it, and that water and arsenious 
acid were the products of the decomposition.* 
To Mr. Marsh alone is the credit due of applying some of 
these facts to a useful and practical purpose in toxicology; 
and the large number of processes which have been put for¬ 
ward since his time by various chemists as new inventions are 
nothing more than the adaptation of some of the above pro¬ 
perties of the gas to Marsh’s original process. The produc¬ 
tion of arseniuretted hydrogen from the action of an alkali on 
arsenic has been, in recent times, assigned to Fleitmann,— 
the decomposition of the gas by a solution of the nitrate of 
silver has been claimed by Lassaigne,—the method of decom¬ 
posing it by heat has been described as the process of Ber¬ 
zelius, Liebig, or Chevallier, while the fixation and decompo¬ 
sition of it by nitric acid has been claimed by M. Meillet. It 
is, however, evident, from the remarks already made, that 
the whole of these properties of the gas were well known at 
the time of Marsh’s discovery ; and if the author himself did 
not make use of them, it was probably because he thought 
* Payen, ‘Traite des Beactifs,’ 1841, Supplement, p. 5; Berzelius 
‘Trahe de Chimie,’ 1829, tom. ii, p.433 ; and ‘Manuel Pratique de l’Ap- 
pariel de Marsh/ par Chevallier et Barse, 1843, p. 60. 
