1 88 Mr. Hatchett’s Experiments on the various Alloys , 
But, after it has been subjected to the ordinary friction which 
must take place during the circulation of money, it is liable 
to appear of a deeper colour in those parts which are promi- 
nent, and are consequently the most exposed to friction. This 
defect arises from a cause which will soon be explained, but it 
cannot be regarded as an objection of any weight. 
The last kind of standard gold which remains to be men- 
tioned, is that which is alloyed only by copper. This is of a 
much deeper colour than those which have been hitherto noticed, 
and it is slightly harder than either of them ; but nevertheless 
it is very ductile, provided that the copper be pure. It requires 
to be annealed, and then becomes nearly or quite black ; which 
colour is not so easily removed by the blanching liquor, as that 
which is produced by the process of annealing, upon gold alloyed 
with a mixture of silver and copper. 
It suffers less by many of the varieties of friction, than gold 
which is alloyed with silver; but, in some cases, it seems to 
wear rather more than gold alloyed with silver and copper ; the 
difference is not however very considerable. 
This sort of standard gold, as well as that which is alloyed 
with silver and copper, appears commonly, after a certain degree 
of wear, of a coppery colour, more or less deep, in those parts 
which are the most prominent ; and, when coin thus alloyed 
exhibits such an appearance, it is frequently and vulgarly said 
to have been in contact with copper money ; and sometimes 
guineas having this appearance have been refused, upon the 
supposition that they were debased. But the real fact is, that 
when copper constitutes part or the whole of the alloy, it be- 
comes oxidized or calcined upon the surface of the blanks, by 
the process of annealing ; and the blackish crust of copper, in 
