specific Gravity , and comparative Wear of Gold. 153 
an equal proportion of copper, so, in this last experiment, the 
copper pieces suffered the most considerable diminution. 
It must however be also remarked, that, contrary to the 
former experiment, gold reduced by copper to 18 carats, lost 
more than gold of 23 car. 3^ grs.; and gold alloyed with tin 
and copper, lost more than that which was alloyed with copper 
and iron ; but, in general, the coincidence of the results of the 
two experiments, appears to be as satisfactory as could with 
reason be expected. 
Lastly, it appears, upon comparing the effects produced, w’ith 
the number of revolutions employed in the two experiments, 
that we have a proof of the increase of wear which attends the 
friction of raised or embossed surfaces. 
Hitherto, the effects produced by the friction of pieces of a 
similar quality only had been examined ; but, in order to ascer- 
tain the comparative wear which would be occasioned by rub- 
bing pieces of a similar and of a different quality against each 
other, by one operation, the following experiment was made. 
Experiment in. 
This experiment was made upon 54 unstamped pieces of 
gold, the different qualities of which are expressed in the an- 
nexed Table; and it is necessary here to observe, that standard 
gold is always to be understood from the terms gold alloyed 
with silver, gold with silver and copper, &c. excepting when 
other proportions are expressly stated. 
1 
MDCCCIII. 
X 
