[ 641 ] 
be to that of water as ifi.poy to 1.000. The quan- 
tity weigh’d for this purpofe was no lefs than a 000 
Troy grains. 
The larger grains of platina, feparated as much as 
poflible from the other matters by the fieve, and 
cleans’d by heating, boiling in aqua fortis, mixing 
them with fal ammoniac, and forcing off the fait by 
f re, and afterwards wafhing them 5 weigh’d in air 
64.2, in water 600.7 S : whence their gravity turns out 
18.213. The microfcope dill difcover’d a confider- 
able portion of blackifh matter in their cavities. 
Thefe trials were feveral times repeated on differ- 
ent parcels of platina : the refult was nearly the fame 
in all. 
Remark. The gravity of this mineral, great as it 
appears to be from the foregoing experiments, would 
probably turn out dill greater upon a farther purifi- 
cation of the platina, fince it is manifedly mix'd with 
fome of the lighter heterogeneous matters. 
Experiment 4. 
1. A quantity of platina, containing its ufual ad- 
mixture of magnetic dud, was kept for fome time of 
a moderate red heat in an iron ladle. The bright 
particles became fomewhat duller-colour’d ; the mag- 
netic ones were no longer attracted. In other refpedts 
there was no fenfible alteration. 
2. An ounce of platina was urg’d with a drong 
fea-coal fire, in a blad -furnace, for above an hour: 
the heat was fo vehement, that the black-lead cru- 
cible vitrify’d, and the dip of Windfor brick, which 
cover’d it, melted, and ran down. The grains of 
platina were found fuperficially cohering into a lump, 
4 M of 
