H3 
specific Gravity , and comparative Wear of Gold. 
to me to be more accurate, than if the experiments had been 
made upon part of a large mass or ingot. In the latter case there 
are many sources of error, which either have been or will be 
noticed in the present Paper ; and the observations made upon 
them apply to the subject under immediate examination, as 
well as to the specific gravity of compound or alloyed metals 
in general. 
If Mr. Brisson made his experiment upon part of a large 
bar or ingot, (which probably was the case,) it will not be 
difficult to conceive the reason why he found the specific gravity 
to be 17,486. For, the unequal diffusion of the alloy, the quantity 
of the metal, with the nature, form, and position, of the mould, 
will always produce variations in specific gravity. 
In some experiments, when copper was present in rather a 
less proportion than the above, still a very conspicuous degree 
of expansion prevailed, even in that part of the mass which was 
subjected to the pressure of a considerable quantity of superin- 
cumbent metal, and even when the whole was cast in a mould 
of iron, which, from repeated experiments, I have found to be 
unfavourable to the expansion of metals. As a proof of this, I 
shall state an experiment which will again be found in a sub- 
sequent part of this Paper, but which may here be anticipated 
with propriety, as it tends to elucidate the present subject. 
Experiment. 
A quantity of gold, 23 car. grs. fine, was alloyed with fine 
Swedish copper, in such a proportion as to form an uniform mass, 
which, by assays made upon both extremities, proved to be 8 
Troy grains in the pound better than standard. 
Iwo pounds of this alloyed gold were cast in a mould of 
mdccciii. O 
