[ 649 ] 
fome hours, the fublirhate was found to have entirely 
arifen, leaving the platina of its original weight, as 
well as appearance. 
y. Fifty grains of a mixture of one part of platina 
and two of gold, well neal’d, and cautioufly ham- 
mer’d into a thin plate, were furrounded with regal 
cement, the veftel cover’d, clofely luted, and kept 
for a confiderable time in a red heat. Upon exa- 
mining the metal, it was found to retain the white- 
nefs and brittlenefs, which gold conftantly receives 
from fo large a proportion of platina ; and to have 
loft in weight about half a grain, or one- hundredth. 
Remark. The lofs here appears to have proceeded, 
not from the platina, but from alloy in the gold em- 
ploy’d, which was above ftandard, but not perfectly 
fine : For the metal cemented a fecond time, with 
frefh mixture, fuffer’d no farther diminution. If the 
marine acid were capable of diffolving platina, in- 
ftead of one-hundredth, nearly one-third would have 
been exeded. , This experiment therefore determines, 
with certainty, the refiftance of platina to the marine 
fumes ; and that the regal cement, fo call’d from its 
being fuppos’d to purify gold from all heterogeneous 
metallic matters, is incapable of feparating platina 
from it. 
’Experiment 3. 
Platina with the nitrous acid. 
1. Spirit of nitre diluted with water, proof aqua 
fortis , and the ftrong nitrous fpirit, were digefted fe- 
parately, with one-third their weight of platina, in a 
gentle heat, for feveral hours. During- the digeftion, 
4 N fome 
