RESEARCH EOR ARSENIC AND ANTIMONY'. 413 
If he desires to escape the censure of the public, and the un¬ 
charitable criticisms of some fellow-labourers in the same 
branch of research, he must go beyond the ordinary routine 
of testing his materials. He must look for substances, the 
presence of which they have hitherto ignored or disregarded ; 
or, in the end, some of them will be found to claim credit, 
however unjustly, for a degree of caution which they have 
never themselves exercised. Owing to the want of general 
knowledge on such subjects, they may for a time succeed in 
their object, and divert public attention from their own pro¬ 
ceedings. 
Committunt eadem diverso crimina fato, 
Ille crucera pretium sceleris tulit, hie diadema. 
As a rule, the purity of no chemical substance should be 
taken for granted in conducting medico-legal investigations; 
and the operator should, in fairness, always test a quantity 
of the substance equal to that which he is about to employ 
in an analysis. 
Methods of detecting Arsenic in Copper. 
There has hitherto been great difficulty in detecting small 
quantities of arsenic in copper, and this may account for the 
fact, that samples of copper are sold as pure, and are pro¬ 
nounced to be free from arsenic, when a more careful research 
Mould have demonstrated the presence of this substance. 
This difficulty may be appreciated from the fact, that when 
samples of the arsenicated copper-gauze used in the Sme- 
thurst case were forwarded to five experienced analysts in 
England, Scotland, and Ireland, three succeeded and two 
failed in detecting arsenic in it. A sample of Burra Burra 
copper supplied to the Royal Mint as absolutely free from 
arsenic, was found (by a process to be presently explained) 
to contain traces of that substance. Some Swedish copper 
which had been reserved as pure by a distinguished chemist, 
was found, on analysis, to be arsenical. The detection of 
the arsenic depends entirely on the method pursued. 
The first plan which I adopted successfully, consisted in 
oxidizing the copper by nitric acid, evaporating the acid 
liquid to dryness, and then heating the residue to procure 
the black oxide, and, at the same time, to convert the arsenic, 
if present, to arsenic acid. This acid was subsequently de¬ 
tected in the residue by digestion in w’ater, and the addition 
of nitrate of silver. 
Another plan, proposed and employed by Dr. Odling, 
clearly showed the presence of arsenic in a small quantity of 
