544 
RESEARCH FOlt ARSENIC AND ANTIMONY. 
tube into nitric acid until the acid liquid in the apparatus is 
exhausted, a sufficient quantity of arsenic acid may be 
obtained, on evaporation, to admit of the application of the 
silver test, and the production thereby of the red arseniate of 
silver. 
Whether the arseniuretted hydrogen is coming over, or has 
ceased to come over, is a fact which can always be determined 
by the application of filtering-paper, wetted with the nitrate 
of silver, to the open end of the tube from which the gas is 
issuing. 
Various experiments were tried in order to determine 
whether other reagents might be used for oxidizing arseniu¬ 
retted hydrogen and producing arsenic acid, in a form for 
testing. Solutions of chlorine and of chloride of lime in 
water were found to stop it only partially. Nearly one half 
of the gas escaped decomposition. On evaporating the 
liquids to dryness, some time after arseniuretted hydrogen 
had been passed into them, arsenic acid was readily proved 
to be present in the residues, by the addition of nitrate of 
silver. Bromine acts in a similar manner. Iodine has no 
effect. Solutions of the chlorides of gold, platina, and 
mercury, of permanganate of potash, of sulphate of copper, 
and iodic acid, were successively used for receiving the 
arseniuretted hydrogen. The gas underwent decomposition 
in all of these solutions, but only to a partial extent. Among 
those above enumerated, the solution of chloride of mercury, 
as stated by Berzelius more than thirty years ago,* appeared 
to have the greatest power in arresting and fixing the arsenic. 
The results of these experiments were, that no liquids so 
completely oxidized arseniuretted hydrogen, without loss, as 
nitric acid and a strong solution of nitrate of silver. When 
the current was properly managed, not a trace of the gas 
sclaped. 
Quantitative analysis .—If the quantity of arsenic present is 
moderately large, it may be determined in the first stage, 
viz., by adding to the distillate containing chloride of arsenic 
a sufficient quantity of a solution of chloride of gold, and 
wanning the mixture. After some time the gold is entirely 
reduced and precipitated. Its weight will enable the operator 
to calculate the proportion of arsenic present.*!* If there is 
a ponderable quantity of arsenic present, the distillate, or an 
aliquot part of it, should be diluted, placed, with metallic 
zinc, in the apparatus described, and the gas produced, en¬ 
tirely transmitted into strong-nitrico-nitrous acid. When all 
* ‘ Traite de Chimie/ 1829, tome ii, p. 437. 
f See Will’s ‘Guide de l’Analvse Chimique/ 1858, p. 66. 
