specific Gravity, and comparative Wear of Gold. 105 
fracture, which had a porcellaneous appearance ; but, in the sub- 
sequent experiments, in proportion as the specific gravity was 
reduced, the grain of the fracture became coarser ; and, in the 
ivth Experiment, the porcellaneous or earthy appearance of the 
fracture began to give place to a certain degree of metallic lustre, 
which was increased in the vth Experiment ; at the same time, 
the alloyed gold, in both cases, became remarkably coarse- 
grained and spongy. 
The specific gravity was then found to be at the lowest de- 
gree ; for, in the vith or last Experiment, when only J of a grain 
of lead, or of bismuth, was present, the grain became compact, 
with complete metallic lustre ; and the specific gravity was so 
much increased, that when lead was employed, the difference 
between the vth and vith Experiments was 0,4,12; and, when 
bismuth was present, the difference was 0,315. 
From these and other experiments, I am induced to believe, 
that, in general, the specific gravity of gold alloyed with different 
metals, is not only very different to what it ought to be according 
to calculations made on the relative proportions and specific 
gravity of the alloy, but that it is also subject to many variations, 
partly occasioned by peculiar effects produced by certain pro- 
portions of some of the metals, and partly by effects peculiar to 
certain compound alloys ; so that, by the proportions of certain 
metals, and by the combination of these with others, an immense 
complicated series of alterations in specific gravity are produced, 
which as yet do not appear to have been investigated, by those 
philosophers who have written concerning the specific gravity 
of metals. 
MDcccm. 
P 
