for Measuring the Expojision of Solids. 265 



meroiis enough to enable us to deduce with precision the 

 general laws by which their expansions and points of fusion 

 are governed ; but enough is discernible to show that the sub- 

 ject is well worthy of further investigation. It appears 



1st. That the expansion of the compounds is not the mean 

 of the expansions of the simple metals of which they are com- 

 posed, but bears some proportion to their relative quantities. 

 Thus we may observe that the expansion of brass increases 

 with the quantity of zinc which it contains, as does bronze or 

 bell-metal with the quantity of tin. 



2ndly. That the expansion of brass is in an increasing ratio 

 to the increase of temperature till the quantity of zinc amounts 

 to one half, when it seems to assume a decreasing rate, as we 

 have reason to suppose is the case with pure zinc. On this 

 account the melting points both of this mixture and zinc ap- 

 pear to be higher when derived from their expansions to the 

 boiling point of mercury, than when calculated from their ex- 

 pansions 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. 



Srdly. 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 correspond- 

 ing 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 re- 

 duces 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 laismuth, 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 pro- 

 gressive linear dilatation by heat of such solids as I have mea- 

 sured 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 ap- 

 parent expansions by the register the corresponding expan~ 

 sion of the black-lead ; upon the assumption that the latter 

 continues at an etjual rate to temperatures above 662'' ; in 



Third Series. Vol. 1. No. 4. Oct. 1832. 2 M 



