452% 
confequently the error produced by in- 
terftices is much reduced. 
But, neither hammering, rolling, nor 
pulverization, can be applied to thofe me- 
tallic fubfiances, whether fimple or mixed, 
which are neither fufficiently malleable 
to be rolled, nor fufficiently brittle to be 
reduced to powder ; and this laft diffi- 
culty mot frequently occurs in mixed or 
alloyed metals. 
Tt is well known that the fpecific gra- 
vity of an alloyed metal is feldom that 
which, by calculating the fpecific gravi- 
ties and proportions of the different me- 
tals would be therefult ; but it is greater 
or lefs than it ought to be according to 
calculation. 
After thefe obfervations Mr. Hatchett 
fays that his experiments were made with 
a very accurate balance, which when Joad- 
ed with tooo grains at each end turned 
with g$, th part of a grain. ‘The veffel 
containing diftilled water,t at 60° Fah- 
renheit, was covered with flannel, in or- 
der to avoid, as much as poflible, any 
change of temperature produced by the 
furrqunding air ; and every other precau- 
tion was taken, as is ufual when fuch ex. 
periments are to be made. ‘Then follow 
two tables with the refults of experi- 
ments of metals varioufly combined : the 
Jrft velates to the fpecific gravities of the 
metals in their pure ftate, and alfo after 
they had been compounded. From which 
it appears that the fpecific gravity of 
gold alloyed with different metals, is not 
only very different to what it ought to be 
according to calculations made on the re- 
fative proportions and f{pecific gravity of 
the alloy, but that it is alfo fubjeé& to 
many variations, partly occafioned by 
peculiar effeéts produced by certain pro- 
ortions of ome of the metals, and partly 
by effects peculiar to certain compound 
alloys ; fo that, by the proportions of 
certain metals, and by the combination 
of thefe with others, an immenfe com- 
plicated feries of alterations in fpecific 
gravity are produced, which have not 
been inveftigated by thofe philofophers 
who have written on the fpecific gravity 
of metals, 
The jecond table is added to fhow the 
comparative degrees of expanjion and con- 
traction which to k place in confequence 
of thefe combinations. 
From this, very little alteration appears 
to have been produced by alloying gold 
with r-12th of pure filver, for the alloy- 
ed mafs only differed from the natural 
bulk of the two metals by.10. But in 
gold alloyed with equal parts of filyer and 
Procesdings of Learned Societies: 
[ Dec. 1; 
‘copper, the expanfion amotinted to .673 
though when copper is ufed fingly the ex- 
panfion is only .66. Hence the com- 
pound alloy of filyer and copper, being 
added in the proportion of 1-12th to 
gold, caufes*a degree of expanfion fupe- 
rior to that produced by copper, although 
it might be previoufly imagined, that the 
filver would have diminifhed the expan- 
five property of copper. 
Iron in the proportion of 1-12th part 
caitfed an expanfion rather inferior to that 
of copper, but an alloy compofed of equal 
parts of iron and copper produced an ex- 
panfion lefs than the former. 
A contraction equal to .53 was ¢aufed 
when r-12th of tin was added to gold ; 
but with equal parts of tin and copper 
the contraétion was on .oz: when the 
copper amounted to 30 grains, and the 
tin only to 8 the expanfion was 14. The 
1-12th of lead produced alfo an expanfion 
of 14. ; when lead was in the proportion of 
4. grains to 34 of copper, or of even haif 
a grain to 37% of the fame metal, a very 
remarkable degree of expanfion took 
place, which feemed to be a pectiliar ef- 
feét of this compound alloy ; for ina fub- - 
fequent cafe when the lead was reduced 
to a quarter of a grain; the degree of ex- 
panfion was much lefs. 
Bifmuth, in its various properties very 
much refembles lead, in refpect to the ef- 
fe&ts which it produces upon gold, except- 
ing, that when employed fingly, and in 
the proportion of half, it occafioned a 
contraéion equal to 3s. But in fmaller 
quantities and in conjunétion with cop: 
per it produced expanfion, which became 
confiderable when bifmuth was added in 
the proportion of 4 grains, or of half a 
grain per ounce. 
When 1-12th of zinc was ufed the 
mafs contracted .o9, but the volatility 
of this metal renders the refults uncertain. 
From a general view of the table it ap- 
pears, that thofe metals which moft rea- 
dily render gold brittle, are thofe which 
heve the greateft tendency to produce con= 
tra€tions, when added to it in certain pro- 
portions. ; 
Mr. Hatchett proceeds to notice other 
caufes which more or lefs influence the 
fpecific gravity of what is called ftandard 
gold, of which the chief is the unequal 
diffufion of the alloy throughout the mafs 
of geld, fer he found that an exaét dif- 
tribution of the alloy is not fo eafily made 
as may be imagined, efpecially when a 
large quantity of gold is to be alloyed. 
In practice this dificulty has been con- 
fidered and an allowance made for it, 
which 
