77 
specific Gravity , and comparative Wear of Gold. 
“ « Of tin and lead, the most minute portions, even the va- 
« pours which rise from them in the fire, though not sufficient 
“ to add to the gold any weight sensible in the most delicate 
“ balance, make it so brittle, that it flies to pieces under the 
“ hammer/ Lewis’s Philosophical Commerce of Arts, p. 85.” 
There must have been, undoubtedly, some cause from whence 
originated the general and universal opinion, that tin was so 
injurious to the ductility of gold, although it is now evident that 
this opinion is, within certain limits, erroneous ; and it appears 
to me very probable, that the chemists and metallurgists who 
first promulgated the idea that the ductility of gold was de- 
stroyed even by the fumes of tin, made their experiments with 
tin which contained a small portion of bismuth, lead, antimony* 
or zinc ; and, as the foregoing experiments have proved, that 
even less than f 9 r 2b of the three first of these metals is suffi- 
cient to make gold very brittle, and that gold in fusion attracts 
and combines with them, when in a state of vapour, we may 
suspect these to have produced the principal part of the effect 
which has been attributed to tin, and which has been s^> gene- 
rally asserted and believed. 
As to the difference of opinion between Mr. Alchorne and 
Mr. Til let, it seems that both these gentlemen have just 
grounds for their assertions ; and that the different degree of 
annealing heat, employed by the one and by the other, has been 
the cause, why the results of their experiments appear to be so 
opposite. 
GOLD ALLOYED WITH IRON. 
The effects of iron upon gold seem to have been less under- 
stood, and more erroneously stated, than even those of tin. For 
