1803.} 
eomparative wear.of gold. .Thefe’ expe- 
riments were undertaken by Mr. Hatchett, 
_and Henry Cavendith, Efq. at the requelt 
of a committee of his Majefty’s molt ho- 
hourable Privy Council, who were ap- 
pointed to take into confideration the fate 
of the coins of this kingdom; and who 
having, among other circumitances, re- 
marked the confiderable lofs which the 
gold coin appeared to have fuftained by 
wear within certain periods, were defirous 
to afcertain whether this lofs was occa- 
fioned by any defect, either in the quality 
of the ftandard gold, ox in the figure or 
impreflion of the coins. 
Two queftions, then, were principally 
to be decided; 1. Whether very foft and 
duétile gold, or gold made as hard as is 
compatible with the procefs of coining, 
fuffers the moft by wear, under the vari- 
ous cireumftances of friétion to which 
coin is fubjected in the courfe of circula- 
tion? 2. Whether. coin with a flat, 
fmooth, and broad furface, wears lefs 
than coin which has- certain protu- 
berant parts raifed above the ground or 
general level of the pieces ? 
Concerning the firft queftion, opini- 
Ons were various, and the moft intelligent 
perfons were uncertain, whether very foft 
or very hard gold was to be preverred ; 
and, in refpeét to the fecond, though the 
prevalent opinion was in favour of flat and 
fmooth furfaces,which has been fince con- 
rmed, yet the faét had never been ex- 
perimentally and fatisfactorily afcertain- 
ed. 
The fir feries of experiments was in- 
tended to examine the effets which vari- 
ous metals produce upon gold, when com- 
bined with it in given proportions, be- 
ginning with 1-12th, which is the.tand- 
-ard proportion ofalloy, and gradually de- 
creafing to s5gth. part of the mafs. 
The refults drawn from thefe experiments 
were, that fine gold alloyed with /lver, 
with copper, and with ¢zz, did not fuffer 
any lofs during the experiment. That 
gold alloyed with /ead only loft three 
grains, chiefly by vitrification :—with 
iron it loft 12 grains which formed {co- 
ria:—with difmuth it loft alfo 12 grains 
chiefly by vitrification:—-with anéimony 
it loft the fame quantity partly by volati- 
lization, and partly by vitrification :— 
with zizc it loft a penny-weight by vola- 
tilization :—and with arfenic, it not only 
lo& the whole quantity of alloy, but alfo 
two grains of the gold which were carried 
eff in confequence of the rapid volatiliza- 
tion of the arfenic, . 
_ Hence it is likewile inferred that only 
Proceedings of Learned Societies. 
454 
two of the metals are proper for the alloy 
of gold coin, namely filver, and copper 9 
as all the others either confiderably alter 
the colour, or diminifh the dudfility of 
gold. In refpect to the latter quality the 
different metallic fubitances which were 
employed in this feries of experiments, 
appear to affect gold nearly in the follow. 
ing decreafing order. 
1. Bifmuth.—2. Lead.—3. Antimony. 
4. Arfenic. — 5. Zinc.— 6, Cobalt. — 7 
Mariganele.-—-8. Nickel.—g. Tin. — 105 
Tron, — 11. Platina. ~ 12. Copper, and 
13. Silver. 
The next fubject which engaged the 
attention of thefe gentlemen, related to 
the fpecific gravity of gold when alloyed. 
by various metals. 
The many difficulties which attend the 
making of experiments to a{certain the 
fpecific gravity of bodies with any tole~ 
rable degree of precilion, are fufficiently 
known to every experimental philofophera 
When the inaccuracies of balances, and 
the effects produced by the different 
heights of the column of water, and by 
the changes of temperature to which the 
water is expofed during the experiments 
are confidered, we have lefs reafon to be 
furprized at the frequent variation in the 
refults: and in addition to theie fources 
of error, if we confider the different 
texture of bodies, and the numberlefs 
interftices of them, often unequally ar- 
ranged, and which cannot at all times be 
penetrated by water, it is rather furprifing 
that fo much precifion has been attained. 
When metals are caft ina mould, they 
fpeedily become cold, and according te 
the quantity and quality of the metal, the 
figure and pofition of the mould, and the 
greater or lefs rapidity of cooling, metals 
may vary in texture, and in the relative 
proportion and arrangement of their ine 
terftices ; confequently the ma{s, in differ~ 
ent parts may be of unequal degrees of 
denfity. For a metal of an uniform qua- 
lity in other refpeéts, generally- becomes 
moft denfe in the bottom of the mould; 
efpecially when a long bar of heavy me- 
tal is caft in a vertical pofition. 
Thofe metals which are very duétile, 
may by hammering and rolling, be 
brought more nearly to a certain uniform 
denfity ; for the number and capacity of 
the interftices, or air-bladders in the inte~ 
rior of the mafs, are thus more or lefs di- 
minifhed, and although the brittle metals 
or femi-metals, as they are improperly 
called, cannot be thus treated, yet when 
reduced to powder, or into fmall frag~ 
ments, they expofe a large furface, and 
I conlequently 
