EXPERIMENTS ON VARIOUS ALLOYS OF GOLD. QQf 



SECTION III.* 



ON THE COMPARATIVE WEAR OF GOLD, WHEN ALLOYED 

 BY VARIOUS METALS. 



Gold, when in the form of coin, appears to be generally ex- Nature of the 

 pofed to three varieties of friflion, viz. Sffipi is 



I ft. Fri&ion between pieces of gold coin of a fimilar or of e*pofed 

 a different quality. 



2d. Friclion of gold coin againft coin of other metals, fuch 

 as filver and copper. 



3d. The friction which gold coins of various qualities fuffer, 

 when expofed to the action of certain fubftances, fuch as the * 

 particles or filings of metals, gritty powders, &c. 



The confideration of thefe. different modes of wear, points 

 out the bed method to be purfued in an experimental invefti- 

 gation. 



The whole of the experiments which compofe this feclion 

 may therefore be divided into three fubordinate feries ; the two 

 firft of which have been directed to the confideration of that 

 part of the diminution of the coin which arifes from the rub- 

 bing of one piece of metal againft another ; while, 



The third of thefe fubordinate feries was intended to (how 

 the comparative power of gold, differently alloyed, to refift 

 abrafion from fand or other gritty powders. 



In the firft fet of experiments, 28 pieces of coin were fixed Defcrtptlon of 

 to a frame, and over each of them was placed another piece of ^f ex P e . r, ™ ents t 

 coin, which was preffed againft it by a weight. 'Thefe upper coin, fingly 

 pieces were all attached to a fecond frame, fo that, by means 

 of the motion communicated thereto by cranks, each upper 

 piece was made to move about -J of* an inch backwards and for- 

 wards on the lower one. This mode of experiment afforded 

 an opportunity of trying the comparative diminution of gold 

 differently alloyed; both when rubbed againft pieces of (he fame 

 and* of a different alloy ; and alfo of examining the difference 

 of wear between pieces with plain and with ftamped faces. 



* The fails detailed in this important memoir having extended 

 my abridgement beyond my full eftimate, I find myfeif under the 

 nectffity either of tranlpofing the 2d and 3d fe&ions on the Specific 

 Gravity and the comparative Wear of Cold, or elfe of iepai ating 

 Plate XIV. from its defcriptioij. 



In 



