specific Gravity , and comparative Wear of Gold. 89 
It appears, therefore, that four grains of antimony, or of lead, 
may be present in one ounce, or 480 grains, of copper, without 
producing any very apparent change in colour or ductility, and 
but little in specific gravity ; such copper may, therefore, without 
suspicion, be occasionally employed to alloy gold ; then, how- 
ever, the antimony or lead will produce a powerful effect ; for it 
has been proved, that of either of these will destroy the 
ductility of gold. But, supposing one ounce Troy of copper 
which contains four grains of antimony, or of lead, to be em- 
ployed to alloy eleven ounces of gold, 24 carats fine, there 
would then be four grains of the abovementioned metals in the 
12 ounces or Troy pound; and therefore the quantity of these 
would be considerably more than is required to destroy the 
ductility of gold. For the Troy pound contains 5760 grains; 
and 4 is to 5760 as 1 to 1440 ; consequently, this proportion 
much exceeds the quantity which is capable of producing the 
abovementioned effect.. 
But the copper of commerce often contains a much greater 
proportion of one or other of these metals ; and, although it then 
appears more pale than common, yet it has, without suspicion,, 
been purchased by those who, from their profession, are sup- 
posed to be competent judges, and who especially require copper 
to be as pure as possible. Persons of this description, however, 
are liable to be deceived; for, in 1791, Mr. Roitier, Director 
of the Mint at Paris, purchased a quantity of copper from, 
the mines of Poullaoen in Britany; but he soon discovered, 
from the effects which it produced, when employed as an alloy, 
that it was not pure, and therefore requested Mr. Sage tq 
examine it. By the latter, it was analysed, and was found to, 
contain one forty-eighth of antimony.* 
* Journal de Physique, 1792, Tome XL. p. 273, 
MDCCCIII. N- 
