125 
specific Gravity, and comparative Wear of Gold. 
1 . Gold of 23 car. 3 \ grs. fine - - 6 pieces. 
2. Gold alloyed with silver - 6 pieces. 
3. Gold alloyed with silver and copper - 6 pieces. 
4. Gold alloyed with copper - 6 pieces. 
3. Gold alloyed with copper and iron - 6 pieces. 
6 . Gold alloyed with ~ of copper and f of tin - 6 pieces. 
7. Gold alloyed with an equal part of copper - 6 pieces. 
The specific gravity of each of the foregoing series of six 
pieces was then taken, with every possible precaution : and after- 
wards the pieces were fixed in a machine, so that three of each 
series were opposed to the other three which were of a similar 
quality. The machine was then put in motion ; and these pieces 
were made to rub against each other for a considerable time, 
or till 200300 revolutions had been performed; after which, the 
pieces were removed, and the specific gravity of each series was 
again ascertained. 
The following comparative statement will show, that a very 
evident diminution of the original specific gravity had taken 
place, in consequence of this long continued friction. 
