206 Value of Native Gold, é&c. 
between the weight in air and the weight in water is in point 
of fact the weight of a quantity of water equal in bulk to the 
specimen, and a simple proportion will thus give the specific 
gravity, or the weight of a cubic foot of the material experi- 
mented on, as follows :—As the difference between the two 
weights is to the weight of a cubic foot of water, or 1000, so 
is the weight of the specimen in air to its specific gravity ; 
or, more shortly, if W be the weight of the specimen in air, 
x 1000. 
w that in water, G the specific gravity G = W—w 
Where the specimen consisted of dust, a small silver scale 
was suspended by fine hairs to the under part of the prin- 
cipal scale, and exactly balanced when in the water by 
weights, the amount of which was recorded. The dust was 
then placed in the scale, and when the whole was accurately 
balanced, the sum of the weights in the opposite scale, less 
the recorded weight of the scale itself, gave the weight in 
water of the dust. 
The first experiments were made on coin :— 
Grains. 
No. 1, a sovereign weighed in air ....s.sssececresseee 123°12 
Ed 9? 9 in water Coeccecvevecececece 116:12 
Difference... 7 
Thus —— X 1000 = 17588 Specific Gravity. 
17589 Tabular Specific Gravity. 
1 Difference. 
Grains, 
No, 2, a Napoleon weighed in air secccccscessessoeeeee 99'S 
» ” ” IN, WALET ascaccccsersessc.s Gos, 
Differenc@vecccccccscscsieee Ondo, 
99°5 x 1000 = 17304 Sp. Gr. 
576 
French standard Gold is said to contain 1s of Copper 
