[ 6 74 ] 
oefs. Like the others, it could not be broke whilft 
cold, without extreme violence j but proved very brit- 
tle when heated red. 
4. The foregoing compofitions, efpecially thofe in 
which the proportion of platina was large, received 
a fine polifli ; and did not ruft or tarnifh on being 
expofed to the air in a dry room for feveral months. 
5. A compofition of one part of platina and four 
©f iron was treated with fubftances, which produce 
notable alterations in pure iron. Surrounded with 
Reaumur’s fieel- making mixture (compofed of char- 
coal-powder, foot, wood-afhes, and common fait), 
and cemented in a clofe luted crucible for twelve 
hours, it gained an increafe of one-thirty-ninth its 
weight, yielded to the file more eafily than at firft, 
feemed to receive no additional hardnefs on being 
ignited and quenched in water, and difcovered none 
of the qualities of fleel. A piece broke off from 
the fame ingot, treated in the fame manner, with 
the powder for foftening caff iron (viz. bone-afh, 
with a fmall proportion of charcoal), was found in- 
creafed in weight about one-thirty-fourth, proved 
lefs hard to the file than at fir#, but manifeftly 
harder than the part cemented with the fteel- mak- 
ing mixture. 
Platina 
Platina 3, Iron 4 
Platina 3, Iron 12 
Platina 3, Iron 16 
Platina 3, Iron 36 
Iron 
■Specific Gravity. 
By Experiment. 
1 7. OOO 
By Calculation. 
Difference. 
s>- 
917 
IT. 
3+3 
I. 426 
8. 
700 
5 >- 
080 
O. 380 
8. 
202 
8. 
663 
O. 46I 
7 - 
7- 
800 
IOO 
7 - 
862 
0. 062 
General 
