EXPERIMENTS ON VARIOUS ALLOYS OF GOLD. X57 " 



fion; but the real lofs would probably be greater, they being, 

 in the cafe of the friflion of coin againft coin of firailar quality, 

 more fufceptible of abrafion. 



Upon the whole, there is every reafon to believe, that our 

 gold coin fuffers but little by fridion againft itfelf ; and the 

 chief caufe of natural and fair wear probably arifes from extra- 

 neous and gritty particles, to the adion of which the pieces njay 

 occationally be expofed in the courfe of circulation. But ftill it 

 muft be repeated, that the united effeds of every fpecies of 

 friction to which they may be fubjedled, fairlif and una-eoidablij ^ 

 during circulation, cannot produce any other wear than that 

 which is extremely gradual and flow, and fuch as will by no 

 means account for the great and rapid diminution which has 

 been obferved in the gold coin of this country. 



SECTION 11. 



ON THE SPECIFIC GRAVITY OF GOLD WHEN ALLOYED 

 BY VARIOUS MKTALS. 



Difficulties in afcertaining the fpecilic gravities of bodies, Theproblemof 

 particularly from the inaccaracies of balances, the application ^"'^'."g fpecjfic 

 and temperature of water, and the poroiity of the objed itfelf_ tended with nu- 

 Metals vary in their denfity by cafting in a mould, by fpeedy merous diffi- 

 or ilow coohng, and by hammermg. 



Hammering and rolling is an imperfect remedy, and not ap- Hammering, 

 plicable to the brittle metals. 



The effeds of alloys on the fpecific gravity of gold are very Alloys afteft 

 intricate, and only capable of being determined by a dired ^^^ ^^*^' 1^^^^^' 

 trial: for a numerous feries of experiments clearly proved, not Angularly. 

 only that the fpecific gravity of the compound may differ from 

 the mean of the component parts, but that the effcd of the 

 fame alloy, inflead of being proportionate to the quantity em- 

 ployed, may differ confiderabiy from this. To the peculiar Compound 

 effeds produced by certain proportions of fome of the metals *"°y^* 

 muft be added the efteds peculiar to certain compound alloys, 

 whence arifes an immenfe complicated feries of alterations in 

 fpecific gravity, never yet inveftigated by philofophers. 



With regard to the espanfion or contradion of the compound, Expanfion prs- 

 liUie alteration appears to be produced by alloying gold with Jj^"^,'" ^°*'* ^^ 

 ^\ of pure filver," as it produced only an expanfion of 0,10. 

 Wilh copper it was 0,66 : with equal parts of filver and cop- copper ; 



per 



