100 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1757. 



Gravity, 

 By experiment. By calculation. Difference. 



Platina 17-000 



Platina 

 Platina 

 Platina 

 Platina 

 Platina 

 Platina 



gold 



gold 



gold 



gold 



gold 



gold 23. . . 

 Platina 1 gold 31... 

 Platina 1 gold 47. . . 



1. 



3. 



5 

 11. 

 15. 



. 0. 02" 



.0.101 



. 0.092 



. 0.259 ^ diminution. 



. 0.224 



y mcrease. 



18.140. .. . 18.142. 



I8.613 I8.714. 



18.812 I8.904. 



18.835 19.094. 



I8.9I8. . . . 19.142. 



I9.O89 19.1 89 0.100 



19.128 19.213 0.085 



19.262 19.237 0.025' 



Platina 1 gold 95 19-273 I9.261 0.012. 



Gold 19.285. 



Exper. 3. — As a mixture of platina with an equal quantity of gold has been 

 reported to be specifically heavier than gold itself, but turned out otherwise ia 

 the above experiments; some further trials were made on that head. ^o'> 



1. Instead of the crude mineral, whose gravity is but 17, we took platina, 

 that had been cupelled with lead, one of the neatest of the buttons formerly 

 mentioned, which, though retaining a portion of the lead, was nearly as pon- 

 derous as fine gold, viz. 19.240. This was melted with equal its weight of the 

 gold, in a strong fire, and continued in fusion for about an hour; the mass 

 proved spongy, and very light. We remelted it several times with vehement 

 degrees of fire, suffering it to cool leisurely in the crucible; and, in order to 

 separate as much as possible of the lead, to which its sponginess seemed owing, 

 boiled it in aquafortis, and repeatedly injected corrosive sublimate on it during 

 fusion ; the mass, nevertheless, still turned out cavernulous and brittle, and spe- 

 cifically lighter than either the gold or platina by themselves. 2. Mr. L. like- 

 wise endeavoured to combine platina with small proportions of gold. By vehe- 

 mence of fire, it was made to unite, though not perfectly, with half its weight 

 and less; but the mixtures were extremely spongy and brittle; in specific gravity 

 one scarcely 16, another less than 15. 3. As a cast metalline body from the 

 Spanish West Indies, of which some account will be given hereafter, appears to 

 have been confounded with the mineral platina, this also was melted with an 

 equal quantity of gold. They united with great ease, by a moderate fire, into 

 a uniform compound, tolerably compact, but whose specific gravity was only 1 6^; 

 which is nearly the mean gravity of the 2 ingredients. 



^Exper.A. — Asa small portion of copper somewhat heightens the colour of 

 pale gold, platina was melted with 8 times its weight of standard gold made with 

 copper alloy. The fusion was performed, as in the preceding experiments, in a 

 close crucible, with a strong fire, but without any flux, and continued for about 

 an hour. The metal appeared covered with a black scurf, and had lost about 

 -ri-r. It was much duller coloured, harder to the hammer, and cracked sooner 



