412 
EESEA11CH FOR ARSENIC AN1) ANTIMONY. 
stances no copper could possibly be derived from the alloy. 
If the substance used to detect copper was a solvent for gold, 
of course this mode of testing would be improper. If in a 
research for poisons we are merely to regard the presence of 
impurity in substances, without reference to the results, no 
analyses could be performed. It is very rare to find sul¬ 
phuric acid, hydrochloric acid, or zinc, absolutely free from 
arsenic. Much depends on the quantity of each article used 
for the purposes of testing purity. Every specimen of zinc, 
if examined in sufficient quantity, would probably yield 
arsenic ; although this metal may be obtained, and is obtained, 
sufficiently pure for use in Marsh’s process. Mr. Bloxam, 
in a paper recently published on the detection of poisons by 
electrolysis,* says, The occasional presence of arsenic in 
the sulphuric acid, and of both arsenic and antimony in the 
zinc, has always been a serious objection to the use of Marsh’s 
process ; and although the hydrogen evolved at the beginning 
of the experiment may be carefully examined before intro¬ 
ducing the suspected liquid, the operator always proceeds 
upon the assumption that the zinc is perfectly homogeneous, 
and that it is impossible for arsenic or antimony which had 
eluded detection in the first portion of hydrogen evolved, to 
become apparent when the mass of zinc has entered into 
solution.” Instances have occurred in which analysts have 
been satisfied with testing their acids in small quantities, 
while they have afterwards employed them for analyses in 
very large quantities. It would be difficult to draw the line 
between a pure and impure article, and insist upon absolute 
purity. There is so much inconsistency in the statements 
of chemists regarding these matters, that the public are 
mystified, and a feeling of distrust is created in all scientific 
processes. One chemist who has himself used arsenical 
copper for sixteen years, condemns its use by others when 
the fact is first made public; another, who professes to use 
electrotype copper, from theoretical notions regarding its 
absolute purity, has adopted, unknowingly, the constant 
practice of using arsenical sulphate of copper as a test for 
arsenic ! While he would probably meet any objection to 
the use of this salt by asserting that the arsenic is in too 
small quantity to affect the results, he would, without refer¬ 
ence to results or quantity, condemn the use of the metal 
itself (containing arsenic) for the detection of this poison. 
The only plan now open to an analyst is, to seek for the 
purest articles which he can obtain, and to test their purity 
bv everv conceivable method before he resorts to their use. 
•/ •/ 
* ‘Quarterly Journal of the Chemical Society,’ 1859-60. 
