specific Gravity , and comparative Wear of Gold. 185 
3dly. That earthy powders and metallic filings produce 
similar effects, and tend to wear the different kinds of gold in 
proportion to their respective degrees of ductility. 
Fine gold, being extremely soft and ductile, sustains a consi- 
derable loss, under many of the general circumstances of friction ; 
and as at all times it appears certain, that the impressions which 
have been stamped upon it are most easily obliterated, even 
when actual abrasion does not take place, there is much reason ■ 
to conclude, that gold of such extreme ductility is not that 
which is the most proper to be formed into coin. 
But gold of the opposite quality, or at least so hard as to be 
** augmente-t’elle ou diminue-t’elle la perte qu’elles essuient par le frottement ? C’est 
*« une question qui n’a jamais ete resolue par des experiences directes ; et l’Academie 
“ se propose d’en faire, pour eclairer un fait dont la connoissance peut etre utile, non 
“ seulement pour l’art de fabriquer les monnoies, mais pour un grand nombre d’autres. 
“ Les premieres experiences ont prouve, que les monnoies d’ argent pur perdoient moins 
“ que les monnoies alliees, lorsque le frottement avoit lieu entre des pieces semblables, 
“ mais qu'elles perdoient davantage, lorsque le frottement avoit lieu entre les pieces 
“ pures et les pieces alliees .” 
Rapport fait a l’Academie des Sciences, le 27 Octobre, 1790/sur les titres des Metaux 
monnoies, &c. par MM. Borda, Lagrange, Lavoisier, Tillet, et Condor- 
cet. Annales de Cbimie, 1793, Tome XVL p. 230, et 231. 
The effects thus stated to have been produced upon pure and upon alloyed silver, 
most probably in like manner prevail in respect to gold ; but this cannot be stated as a 
certain fact ; for, although there is much reason to supple, that under a small or very 
moderate pressure, the wear of gold against gold of an equal quality is uniformly in 
an inverse ratio to the degree of ductility, and allowing that under such circum- 
stances fine gold would suffer a less diminution than gold which is alloyed, yet the 
present experiments prove, that under a considerable pressure, the order of wear is 
in some measure different ; for, extremely soft or fine gold is then found to suffer as 
great, or indeed a greater diminution, than gold which is but moderately ductile : 
and the whole of the experiments which have been made for the purpose of the present 
investigation, concur to show, that gold which is neither extremely soft nor extremely 
hard, is best adapted to resist friction in general. 
.MDCCCIII. B b 
