NE SA 
(Jam 15, 
PROCEEDINGS OF LEARNED.SOCIETIES. 
EE 
ROYAL SOCIETY ‘OF LONDON. 
$Concluded jrom Page 4.53, of our laft.) 
‘NN puriuing his fubjeét Mr. Hatchet 
next treats of the comparative wear of 
gold, when alloyed by various metals, in 
onde to afcertain_which fuffers more, in a 
given time, either the duétile or the hard ; 
and he conceives that coin is fiabject 
chiefly, to three varieties of friétion: 1. 
that which arifcs between pieces of gold 
coin of a fimilar or of a different quality : 
2, of gold coin ating againft coin of other 
me tals, fuch as filver and copper: and 3. 
that which arifes from the action of cer- 
tain fubdftances, fuch as the particles or 
filings of metals, gritty powders, &c, 
The experiments made for this purpofe 
were numerous, and are very minutely de- 
fcribed, as well as the machinery ufed in 
the proceis ; the refult is, 1. That when 
equal friétion affitted by moderate pref- 
fure takes place between pieces of coin which 
are of a fimilar quality, then abrafion is 
moft commonly produced in. an oi ra~ 
tio to the degree of ductility. That the 
contrary effect happens en “pieces of 
different qualities rub againft each other ; 
for then the more ductile metal is worn by 
that which is harder. 3. That earthy 
powders and metallic filings produce fimi- 
_ Jar effets, and tend to wear the different 
kinds of gold in proportion to their re- 
{pective degrees of duétility. Hence it is 
concluded, that fine gold extremely foft 
and dete is not that which is the moft 
proper to be formed into coin: but gold 
of the oppolite quality, or, at leaf, that 
which is fo hard as to be juft ca ipatile of 
Being rolled and ttampet, feems to be 
equally improper for the purpole of coin. 
It follows therefore of courfe, that gold of 
nioderate ductility mult be the beit adapted 
for coin; and, as nothing ‘but filver or 
copper can be employed to alloy gold 
which is in tended to be coined, it oe be 
obferved, that'whatever might have becn 
the criginal motive for int troducing the 
prefent handard of 22 carats, yet it ap- 
pears from the experiments, that this pio- 
portion. of 3-12th of the ahove-inentioned 
metals is the beit, or at leaft as good a 
any which could have been chofen. 
There ts, however, a difference in the 
quality of gold, when allcyed with the 
ftandard proportion of filver, of filver and 
copper, and of copper. 
Gold alloyed | with r-r2th of filver is of 
a fine but~pale colour, very duétile, is 
eafily rolled, and may be oat without 
keing annealed ; it confequgntly does not 
require to be blanched : every part rea 
mains of an uniform quality, and in wear. 
it does not appear of d:fferent colours ; but: 
the objeStions to it are the additional ex- 
pence :—the extreme palenefs of colour; 
and its liabifity to have the impr:ffions 
effaced, 
Gold alloyed with filver and copper, 
when annealed, does not become black, 
but brown, a colour which is more eafily 
removed by the blanching liquor, or folu- 
tion of allum, than when the whole alloy 
confifts of copper. It may alfo be rolled 
and ftamped with great facility, and fuf- 
fers lefs by friétion, than gold alloyed by 
filver only, or by copper. The objection 
to itis, that afier it has been fubjeéted to 
the ordinary friétion which muft take 
piace during the circulation of money, it is” 
liable to appear of a deeper colour in thofé- 
parts which are prominent, and are con- 
fequently the moft expoled to friétion. 
The laft kind of flandard gold, which 
remains to be mentioned is that alloyed 
tie copper; which is of a deeper colour 
an thofe which have hitherto been no- 
Hea and harder; but the colour it ac« 
quires by annealing is not fo eafily remoy- 
-ed by the blanching liquor. It fuffers lefts 
by many of the varicties of friction, than 
gold which is alloyed with filver ; but, in 
fome cafes, it feems to wear pre ae more 
than gold alloyed with filver and copper, 
the difference is not however cenfid erable, 
This fort of (tandard gold, as well as 
that which is alloyed with filver and cop- 
per, appears, after a certain degree of wear, 
of a coppery colour, more or lefs deep, if 
thofe- parts which are moft prominent; 
and, when coin thus alloyed exhibits fuch 
an appearance, it is’ fometimes refufed, 
upon the fappofition that it is debafed.- 
Upon a comparifon of the different 
qualities of thefe threé kinds of flandard 
gold, it appears that gold made ftandard 
by filver and copper is rather to be pre- 
ferred for coin; but, as gold made ftan- 
dard by copper alone is not very much 
inferior in its general properties, it may 
be queftioned, ‘whether the {mall advan- 
tage thus gained, will compenfate the ad- 
ditional expenfe of the filver required for 
half the alloy. 
* 
By comparing the prefent experis” 
ments, there does not appear to” “be” 
any confiderable difference in the compa- 
rative wear of the three kinds of ftandard 
gold, all of which faffer abrafion flowly, 
and with much difficulty. For thefe rea- 
fons, itis evident that ‘the extragrdinary 
lefs 
