EXPERIMENTS ON VARIOUS AtLOYS OF GOLD. l55 



This fort of ftandard gold, as well as that which is alloyed 

 with filver and copper, appears commonly, after a certain de- 

 gree of wear, of a coppery colour, more or lefs deep, in thofe 

 parts which are the moft prominent ; and, when coin thus 

 ailoyed exhibits fuch an appearance, it is frequently and vul- 

 garly faid to have been in contact with copper money ; and 

 fometimes guineas having this appearance iiave been refufed, 

 upon the fuppofilion that they were debafed. But the real 

 fad is, that when copper conftituies part or the whole of the 

 alloy, it becomes oxidized or calcined upon the furface of the 

 blanks, by the procefs of annealing ; and the blackifl) cruft of 

 copper, in this ftate, muft then be removed by (he folution 

 of alum, called the blanching liquor. Now it is evident, 

 that after this operation, the furfaces of the blanks or un- 

 unftamped pieces, can no longer be regarded as fiandard gold. 

 For, if copper alone forms the alloy, it raufl: be diffolved and 

 leparated from the furface of each piece of coin ; and the 

 fame effe<5t muft alfo take place, with refpefl to the copper, 

 in the alloy formed of copper and filver. So that, in the 

 firft cafe, each piece, when blanched, will coniift of gold 

 made flandard by copper, covered with a thin coat of fine 

 gold; and, in the fecond cafe, each piece will be compofed 

 of gold made fiandard by filver and copper, coated with gold 

 alloyed with ~ of filver, or with half of the flandard pro- 

 portion of alloy, fuppofing the filver and copper to have been 

 in equal quantities. 7\s, therefore, the ftandard gold of 

 which the pieces confift is always, more or lefs, of a 

 deeper colour than the coating or film of the finer gold 

 which covers each piece, it muft be evident, that when this 

 coating has been rubbed and removed from the raifed or pro- 

 minent parts, thefe will appear of a very different and deeper 

 colour than the flat part or ground of the coin. The reafon < 



therefore is fufficiently apparent, why gold which is alloyed 

 with filver only, cannot be liable to this blemifli. 



Upon a comparifon of the different qualities of the three Comparifon of 

 kinds of ftandard gold which have been lately mentioned, it ^ "^^ ' * 

 appears, (ftridly fpeaking,) that gold made ftandard by 

 filver and copper is rather to be preferred for coin ; but, 

 as gold^jnade ftandard by copper alone is not very much in-, 

 ferior in its general properties, it may be queftioned, whe- 

 ther the few advantages which are thus gained, will com- 



penfat« 



