specific Gravity , and comparative Wear of Gold. 6 7 
Experiment iv. 
To eighteen pennyweights and ten grains of gold, alloyed 
with one pennyweight and thirteen grains of copper, one grain 
of bismuth was added. 
The colour of the metal was like that of Exper. 111. it was 
very brittle, and, in the fracture, shewed a much coarser grain . 
Experiment v. 
Eighteen pennyweights of the fine gold, alloyed with one 
pennyweight and fourteen grains of copper, being completely 
melted, the button formed by Exper. iv. was added, and mixed. 
In the two ounces of metal, one grain only of bismuth was 
present; nevertheless, the ingot was extremely brittle, and the 
grain of the fracture was remarkably coarse and spongy. 
Experiment vi. 
To eighteen pennyweights and ten grains of fine gold, al- 
loyed with one pennyweight and fourteen grains of copper, 
when in fusion, one ounce of the metal formed by Exper. v. 
was added. There now was, at most, not more than £ of a grain 
of bismuth in each ounce ; but the metal was still brittle, al- 
though rather in a less degree than before. 
The grain was not spongy ; and, as well as the colour, was 
similar to gold made standard by copper. 
From these experiments it appears, that i of a grain of bis- 
muth in one ounce Troy of standard gold, or of the mass, 
is capable of destroying all ductility; and there is reason to 
believe, that even a smaller quantity would produce a coi^si- 
derable effect. 
K 2 
