508 PHILOSOPHICAL TRANSACTIONS. [aNNO 1754. 



previously melted, were exposed in crucibles closely luted, to a strong fire in a 

 wind furnace, which was steadily kept up for 8 hours. When taken out, they 

 were all found to have suffered some diminution, amounting to about -^ of the 

 tin. In appearance and quality, there was no sensible alteration, except that the 

 mixture seemed more uniform, and the grain a little finer. 



8. The remarkable gravity of platina induced us to examine the several mix- 

 tures hydrostatically. Here it was found, that the specific weight of the com- 

 pound constantly turned out less than the medium of the gravities of the two 

 ingredients; and generally the more so, as the proportion of the platina was the 

 greater. 



Specific graTity. 

 By experiment. 

 17.000 

 10.827. .. 

 8.972... 



7.794... 

 7.705. . . 

 7.613.., 

 7.471... 

 7.180. 



Remarkn. It appears from the foregoing experiments, that platina melts with 

 at least equal its weight of tin ; that it destroys the malleability of near 4 times 

 its weight: that with larger proportions it forms compounds tolerably ductile, but 

 renders the texture of the tin coarser, and debases its colour. The difference in 

 colour of these compositions was much less conspicuous on the touchstone, than 

 when the fractures of the ingots were examined; though, on close inspection, 

 they appeared all sensibly duller and darker than pure tin, and the more so, in 

 proportion as the platina prevailed. They all tarnished in the air; those least, 

 which had a very small or a very large proportion of platina. 



It is remarkable, that though tin is a metal very readily destructible by fire, 

 yet in most of the preceding fusions, there was scarcely any sensible loss of 

 weight. This is to be attributed not solely to the admixture of the platina, but 

 also to the flux made use of, and more particularly to the celerity and short con- 

 tinuance of the heat. In N° 2 and 7, the only ones in which the loss was at all 

 considerable, the fire was slowly raised, and long continued. 



jirt. 2. — Patina with Lead. 1 . Equal parts of platina and lead were injected 

 -into a mixture of black flux and common salt, previously melted together; and 

 the fire hastily raised by bellows. A much stronger heat was requisite than for 

 the fusion of platina with an equal quantity of tin; and the loss was considerably 

 greater, amounting to about -^. The metal yielded difficultly to the file; broke. 



