FOR MEASURING THE EXPANSION OF SOLIDS. 
455 
to be higher when derived from their expansions to the boiling point of mer- 
cury, than when calculated from their expansions to the boiling points of water. 
With this exception, there is great reason to suppose that the melting points of 
the alloys, from the higher rate of expansion, cannot be very far removed from 
the true temperatures. 
3rdly. That the melting point of copper is reduced by an admixture of one 
fourth of zinc to nearly the average which results from the proportions of the 
two ingredients ; but by an admixture of an equal quantity of tin it is reduced 
in a much greater proportion. The temperature derived from the average with 
zinc would be 1690°, and the corresponding temperature in the Table is 1750°. 
The temperature derived from the average with tin would be 1607°, but the 
corresponding temperature is only 1446°. 
4thly. That a similar power in tin to depress the melting point of another 
metal is exhibited in pewter ; in which we may observe that a mixture of one 
fifth of tin with lead reduces the melting point actually below that of either of 
the pure metals ; and we may recall to recollection the fact, that an alloy of 
eight parts of bismuth, whose fusing point is 476° ; five of lead, whose fusing- 
point is 612° ; and three of tin, whose fusing point is 442°, — liquefies at 212°. 
I shall here subjoin a Table, in the usual form, of the progressive linear di- 
latation by heat of such solids as I have measured with the pyrometer to the 
boiling point of water, the boiling point of mercury, and their respective 
melting points, where they have been ascertained. I have added to their 
apparent expansions by the register the corresponding expansion of the black- 
lead ; upon the assumption that the latter continues at an equal rate to tempe- 
ratures above 662° ; in which it is not probable, from the preceding observa- 
tions, that there is any error of material importance. 
3 N 
MDCCCXXXI. 
