208 - Value of Native Gold, ce. 
these two coins approximat every nearly to each other, but 
their actual value depends upon the character of the metal 
with which the Gold is alloyed. This is a matter of import- 
ance, and the more so as an impression may very probably 
exist that the more valuable the metal combined with the 
Gold the more valuable the compound will be; whereas 
the reverse is the case. 
I have shown before that the specific gravity of pure Gold 
which, when cast, is 19258, and when hammered 19361, is 
reduced to 17486 in the one case, and to 17589 in the other, 
by an admixture of one-twelfth part of Copper at a specific 
gravity of 8878. Now the value of Copper in the state of 
coin as compared with Gold may be taken at 100; and as 
the value of £80 grains of Standard Gold, consisting of £49 
grains of pure Gold and 40 of Copper, is 77s. 10°5d., the 
Gold in the compound is worth 77s. 10°42d., while the 
Copper is not worth more than ‘08 of a penny. Pure Gold 
may then be taken to be worth 2°1237d. per grain, and in 
all the calculations into which the value of Gold enters this 
will be used as representing it 
When, however, Gold is alloyed with any other metal, of 
course a separate calculation will be required; and as the 
Gold of California and Australia is combined very generally 
with Silver, it will be desirable to determine the amount of 
that metal which, when mixed with pure Gold, will bring 
down the specific gravity to that of the standard, viz., 
17486. The specific gravity of Silver is given in the Tables 
as 10474; and the following formula will, when the proper 
substitutions are made, give the amount of Silver contained 
in any specimen of mixed Silver and Gold whose specific 
gravity is known. Let 2 be put for the weight of Silver in 
the compound, 8 the specific gravity of Gold = 19258. s the 
specific gravity of Silver = 101474. f the specific gravity 
