specific Gravity, and comparative Wear of Gold. 149 
Experiment 11. 
This experiment was made upon twelve pieces of gold com- 
bined with an equal proportion of copper. The faces which 
were opposed were flat, and without any impression. After 
70640 revolutions, these pieces had lost 103,11 grs. 
Experiment nr. 
Twelve pieces of fine copper, perfectly flat, and not stamped, 
were next placed in the machine, and were taken out after 
22200 revolutions ; they had then lost 174,80 grs. 
From these preliminary experiments it appears, 
1st. That pieces of gold made standard by T J - of copper, 
when rubbed against each other, suffer less than gold much 
debased by copper, or in which the latter metal is in equal pro- 
portion to the gold. And, 
2dly. That pieces of gold alloyed with an equal quantity of 
copper, when rubbed against each other, suffer less than pieces 
of copper which are subjected to a similar process. 
These essential objects being thus ascertained, the following 
experiment was made. 
Experiment 1. 
Forty-eight pieces of gold, variously alloyed, which were 
perfectly flat and smooth, were fixed in the machine No. 1. 
In this experiment, six pieces of each kind of gold were em- 
ployed, and were so arranged, that three of each were made to 
rub against three of a similar quality ; and the loss produced by 
friction, was afterwards estimated upon the whole of the six 
pieces. 
The annexed Table will show the comparative loss sustained 
by the different kinds of gold. 
