EXPERIMENTS ON VARIOUS ALLOYS OE GOLD. ] 4(;) 



7th. That the wear of ftandard filver appears to be nearly Standard filver. 

 equal with that of fine gold ; but more than that of gold 

 made ftandard by filver or by copper, and lels than that of 

 gold much debafed by copper. 



8th. That, as gold which is not Inferior to ftandard wears 

 ^ in general lefs than ftandard filver, fo does this latt futfer much 

 lefs than copper. 



The lofs fufiained by copper, when rubbed againft copper. Copper ■ 

 is infinitely more than that of the former metals ; and, when 

 thefe are expofed to the aflion of copper, they, as well as the 

 copper, fufter a very confiderable lofs. This appears from 

 the general refults of thefe experiments, which prove, that 

 pieces of metal which are the moft fubjed to wear, are 

 thofe which produce the greateft lofs upon other pieces of 

 metal, when rubbed againft them ; and it is remarkable, that 

 infucli a cafe, the lofs does not always fall on one in preference 

 to the other ; fo that the wear can only be confidered in the 

 ^Sgi'^'gate, although one of the pieces may be regarded as the 

 principal caufe. 



In order, however, to illuftrate the refults of the preceding 

 experiments, as far as they concern the fofter and harder 

 kinds of ftandard gold, and to afcertain more fully the com- 

 parative wear of flat and fmooth furfaces with that of fuch as 

 were partlj protuberant, an experiment was made, with two 

 kinds of ftandard gold: 1ft. Gold made ftandard by fine Gold made 



Swedifh copper, which was very duftilej and, 2d. Gold f '"'^^'A ^^ *^'/' 



j/ijii • r ^ r. ,. krent kjnds of 



made Itandard by a mixture ot fine Swedilli copper and dollar copper. 



copper. This was as brittle as was compatible with rolling 

 and ftamping ; and was prepared by melting gold made 

 ftandard by fine Swedifii copper, with an equal quantity of 

 gold rendered brittle by the ftandard proportion of Swedifh 

 dollar copper, which was mentioned in the firft fedion of 

 this paper. 



It may here be obferved, that a diftinclion muft be made Dlftioaion be- 

 between hard and brittle metal. If a metal is difpofed to ^^"" ^^'■'' ^"'^ 



1 , 11 1 • 1 • • ,. brittle metal. 



crack when rolled, without requiring any extraordinary force 



to enable it to pafs the rollers, then it may be regarded as 

 brittle; but, if it requires an extraordinary force to make it 

 pafs the rollers, and is not difpofed to crack, then it may be 

 confidered as hard. 



This 



