1 66 Mr. Hatchett’s Experiments on the various Alloys , 
between hard and brittle metal. If a metal is disposed to crack 
when rolled, without requiring any extraordinary force to 
enable it to pass the rollers, then it may be regarded as brittle ; 
but, if it requires an extraordinary force to make it pass the 
rollers, and is not disposed to crack, then it may be considered 
as hard. 
The latter quality, or hardness, appears however in some 
degree to be produced, when a very brittle metal is gradually 
rendered ductile; at least it is difficult to distinguish a certain 
degree of hardness from a certain degree of brittleness, when 
the extremes of ductility and brittleness are nearly in equilibrio; 
and this was found to be the case, when gold was required to be 
made only so brittle as still to be capable of being rolled and 
stamped. 
Some of the Swedish copper dollars were found to make gold 
very brittle, when employed as the alloy in standard proportion; 
but then this extreme brittle quality was incompatible with 
rolling and stamping. The standard gold, therefore, which was 
thus become so very brittle, was mixed with different propor- 
tions of very ductile standard gold, which had been alloyed 
with fine Swedish copper ; and, after several trials, it appeared, 
that a mixture of equal parts of the very brittle standard gold 
and of that which was ductile, formed a metal the best adapted 
to the present purpose, as it then remained but just sufficiently 
ductile to be rolled and stamped. 
