RESEARCH FOR ARSENIC AND ANTIMONY. 233 
arsenic, or even liquids of which hydrochloric acid was a large 
constituent. He pointed out the fact, that in most researches 
for arsenic, the volatile chloride may be produced ; and if in 
small quantity, the poison may be entirely lost, and a negative 
result obtained, when with greater care, the presence of the 
poison would have been detected. 1 
Having given to this method a fair trial, I find it far 
inferior to that which I have above recommended. In mixing 
the salt and acid there is great frothing, with a large escape of 
vapour. In some cases in which pure hydrochloric acid operates 
effectually, this process will not detect arsenic. This occurs 
in reference to arsenic in metallic copper, and in certain 
metallic salts. Schneider states, that the sulphide of arsenic 
is readily converted to the chloride by this process, provided a 
larger quantity of salt and acid is used, and the distillation 
maintained for a longer time. The further steps of the 
process, as described by Schneider, are as follows :—The dis¬ 
tillate containing chloride of arsenic is placed in a Marsh’s 
tube; the resulting gas is decomposed by heat, so as to produce 
an arsenical mirror, and another portion is allowed to pass 
into a solution of nitrate of silver, in order to procure a solu¬ 
tion of arsenious acid, to which the usual tests may be applied. 
As a result of some recent investigations, it has been 
found that an excess of sulphuric acid prevents the formation 
of chloride of arsenic. In fact, the chloride, when treated 
with concentrated sulphuric acid, is decomposed into hy¬ 
drochloric and arsenious acids, the latter of which remains 
behind in the retort. 2 Hence, unless care be taken respecting 
the proportions used, the object of the process will be entirely 
defeated. On one point the results of my experiments are 
quite in accordance with those of Schneider. If the distilla¬ 
tion is carefully and properly conducted, and carried on for a 
sufficient time, the whole of the arsenic contained in the 
organic matter will be transferred to the distillate. 3 
Schneider’s process has been largely employed in Germany, 
but it has been little used in this country. A description of it 
was published in the Pharmaceutical Journal for July, 1853, 
p. 38. About this date Dr. Clark, of Aberdeen, took up the 
subject, and, as I am informed, employed the process success¬ 
fully in some medico-legal investigations for arsenic. In the 
fifth edition of my ( Medical Jurisprudence,’ 1854, I briefly 
referred to it, stating that the arsenic contained in organic 
liquids or solids might be procured as chloride, in a receiver, 
1 Op. cit., p. 194. 
2 ‘ Archiv. der Pharm.,’ and ‘Chemical News,’ June 23rd, 18G0, p. 24. 
3 Op. cit., p. 207. 
