276° On the Art of Hardening Copper. 
opinion. The queftion, however, affumes a different appear- 
ance, when we take into confideration the experiment as re~ 
Jated by Conant Caylus, in his work on the Egyptian, Etruf- 
can, Greek and Roman antiquities *: for it there appears that 
M. Geoffray undertook the above-mentioned experiment by 
the defire of Count Caylus, who defcribes various kinds of 
arrows and javclins of ancient workmanthip, which, though 
they had the appearance of copper, were mixed with iron ;. 
becaufe filings of them were attracted by the magnet; be- 
caufe the fraéture had a different appearance from that of 
other inftruments made of the hardened copper of the an- 
cients mixed with tin, and was at the fame time lefs fufible, 
M. Geoffroy thinks it rather remarkable that mankind fhould 
fo early have fallen on the method of uniting copper with iron 
in an uniform mixture, which even at prefent is confidered 
as a difficult procefs. It is well known that the moft com- 
mion copper ore confifts of copper and iron mineralifed with 
fulphur, and which is called pyrites of copper; not that the 
copper makes the greater part of it, but becaufe the copper 
is of the greateft value, though the iron feems moft generally 
to conftitute the principal component parts. When this ore 
is fmelted, the firft copper obtained, or the fo called black 
or raw copper, is neceffarily rendered impure by a greater or 
lefs quantity of iron, according as more or lefs care has been 
employed to feparate it during the operation. It is therefore 
in our power, it is faid, not only to obtain copper combined 
in this manner with ag much iron as may be neceflary, but 
alfo to caft all kinds of inftruments of it, and afterwards ta 
hammer them cold, or to expofe them to the fame procefs of 
hardening as if they were of pure fteel. Some affert that this 
method has been attended with complete fuccefs; Count 
Caylus‘tried alfo to harden pure copper-by melting 3 but, in- 
ficad of becoming hard, it was fqund fofter and more malle- 
able, which agrees with what has been faid jn the beginning 
of this paper. , 
Without in the leaft leflening the credibility of this affer- 
tion, which feems to have great probability in its favour, we 
% Recueil d’ Antiquités Egyptieunes, Etrufques, Grecques et Romains, 
Vol, 1. p.238e-251. 
may 
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