[ 68 S 1 
?. Upon examining the cupelled matters hydro- 
jftatically, thofe, which appeared mod fpongy, were 
found nearly as ponderous as the crude platina. 
Among the more compadt, the gravity of one turned 
out 19.083 j of another 19. 13 6, and of a third 19.24,0. 
Remark. It appears from thefe experiments, that 
platina, like gold and filver, is intirely indeftrudti- 
ble by lead ; that probably the purer grains, or frag- 
ments, have fome heterogeneous admixtures, which 
are feparated in thefe operations ; and that, perfedtly 
pure, it is more ponderous than gold, fince, when 
mixed with a confiderable proportion of a lighter 
metal, it fell very little fhort of the gravity of pure 
gold. There is no reafon to fufpedt any increafe of 
its fpecific gravity from the mixture ; fince in all the 
compofitions with platina hitherto examined, there 
was conflantly a diminution of the fpecific gravity ; 
whether the proportion of the platina was large or 
fmall, the matter melted with a quick fire, or kept 
in fufion for many hours. 
6. A mixture of one part of platina and three of 
gold was cupelled with lead, under a muffle. The 
matter drove well for a confiderable time j at length 
collected into a bright hemifpherical lump, which 
by degrees became flatter, dull, and rough. The 
button, on being weighed, was found to retain a 
confiderable portion of lead. 
The experiment being repeated with a mixture of 
one part of platina and fix of gold, fome part of the 
lead was ftill retained. The bead proved rounder 
and brighter than the foregoing, and of a good golden 
colour on the outfide : It broke eafily under the ham- 
mer, and appeared internally greyifh: Some of the 
fragments 
