i2-4> Mr. Hatchett’s Experiments on the various Alloys , 
the alloy, which predominated in the upper part of the mass 
when in the crucible, and consequently was. the first which 
entered and filled the lower part of the mould, so that the finer 
and more heavy gold, at the bottom of the crucible, was that 
which formed the upper part of the bar ; and it must be obvious, 
that the congelation was too rapid in the mould, to allow any 
very material change to take place after the metal was poured. 
The foregoing facts being considered, it is possible to con- 
ceive, that a bar of alloyed gold may be throughout of equal, 
specific gravity, and nevertheless not be of an uniform value 
or quality ; for the finer quality of the upper extremity, when 
not considerable, may at times be compensated by the superior 
density of the bottom ; but such effects can only take place 
within a very limited sphere. 
Exclusive of the causes lately enumerated, which occasion 
variations more or less considerable in the specific gravity of 
metals, there is another, which, I believe, has never been noticed ; 
it is true that its effects, when compared with those already 
mentioned, are but small; but still it appears proper that it 
should be taken into consideration, in the course of the present 
investigation. Long continued friction, is the cause to which I 
now allude; for I have always found, that it produced a dimi- 
nution in the specific gravity of those pieces of metal which 
had been subjected to it, as the following experiments will 
prove. 
Experiment i. 
In this experiment, forty-two pieces of gold, differently alloyed, 
and of the diameter of a guinea, were taken in the following 
order. 
