1 18 Mr. Hatchett’s Experiments on the various Alloys , 
I was desirous to examine the specific gravity of some bars of 
gold, which had been made standard by the addition of various 
kinds of copper ; and, as every usual precaution had been taken 
to mix the alloy properly with the gold, the pieces which were 
to be hydrostatically weighed were taken from the ends of the 
bars, without any discrimination whether the pieces were cut 
from the end of the bars which, when cast, had been formed near 
the mouth of the mould, or from that end which had been formed 
at the bottom. The following were the results. 
1. Gold made standard by the best Swedish copper, 
the bar being cast in a mould of iron - 17,372 
2. The same bar melted again, and cast in sand - 17,312 
3. Gold made standard by common Swedish copper, 
cast in sand - 16,225 
4. Gold made standard by Swedish dollar copper, 
cast in sand - 16 ,977 
5. Gold made standard by British copper, cast in iron 17,281 
6. The same, cast in sand - - 1 6,994 
7. Gold made standard with another sample of 
British copper, cast in sand - - 16,979 
From these experiments it was evident, that when the same 
metal was cast in iron and in sand, a difference was to be 
observed in the specific gravity, which was always the most 
considerable when moulds of iron were employed ; but, allowing 
that this might have operated at certain times, yet so great a 
variation was discovered in other instances, that it was thought 
requisite to make a new series of experiments, in order to ascer- 
tain the cause ; and, as there was reason to suspect, that part, at 
least, of this difference in specific gravity arose from an unequal 
