RESEARCH FOR ARSENIC AND ANTIMONY. 
235 
be somewhat brittle. Nothing can be more unsafe than a 
reliance upon these alleged physical effects of arsenic on 
copper, as evidence of the presence or absence of that sub¬ 
stance. The facts now ascertained are simply the reverse. 
Copper may contain sufficient arsenic to lead to fallacious 
results in analysis, without any change of colour, and with¬ 
out losing any of its malleability or ductility ; while, when 
entirely deprived of arsenic and other metals, it has been 
found so brittle that, even after several meltings and anneal¬ 
ings, it was impossible to roll it into thin foil.* From 
some experiments recently made by Dr. Hofmann and Dr. 
Matthiessen on the conductility of copper, it would appear 
that the electric conductive power of ductile copper is mate¬ 
rially affected by the presence of small quantities of arsenic, 
as well as of other metals and metalloids. An analysis of 
the black precipitate formed during the electrolytic decompo¬ 
sition of sulphate of copper by the galvanic current, has led 
to the discovery of twelve metals, which must have been 
contained in the original copper. One hundred parts of this 
black sediment yielded 7*40 parts of arsenic. The other 
metals found in variable proportions were antimony (9"22 
per cent.), platinum, gold, silver, lead, iron, nickel, cobalt, 
vanadium, and tin.*)* It now becomes, indeed, a serious 
question whether purity, in regard to this and other metals, 
is not merely a relative term ; and whether the discovery of 
these metallic impurities does not depend on the quantity of 
copper or zinc submitted to analysis at any one time. 
I am indebted to Dr. Matthiessen, of Torrington Street, 
London, a skilled metallurgical chemist, for some useful facts 
regarding the effects of arsenic on copper. He informs me 
that there is no test so delicate or certain for the detection of 
this impurity in copper, as its power of conducting the 
electric current. While pure copper has a maximum power 
of conduction, the presence in it of the smallest traces of 
arsenic, &c., scarcely discoverable by chemical processes, 
reduces the conducting power to a measurable extent. He 
has given to me,— 1 . A sample of copper containing 5*4 per 
cent, of arsenic. Its colour is pale red, it has evidently 
undergone a change; but its ductility has been so little 
affected that it has been drawn into a wire onlv l-80th of an 
t / 
* I sent a sample of copper without arsenic to my friend Mr. Brande, for 
the purpose of having it rolled under the Mint presses. He writes to me, 
that “there is an inherent hardness and brittleness about it which we have in 
vain attempted by repeated fusions, &c., to get rid of, so that it has ultimately 
produced a riband full of flaws and fissures.” 
j ‘Proceedings of the Loyal Society,’ tome x, No. 38, I860 1 p, 302. 
