. £ ss° 3

platina not perfectly dissolved by the rest. I took all pos-sible precautions for preparing a set of mixtures of thesetwo metals on purpose for this examination, but they al-ways sputtered up so much about the crucible, that no de-pendence could be had upon the proportions of the twoin the remaining mass..

Sped acBy Exper.

Gravity

By Calcul.

Difference

Piatinas

Gravity

COPPERPlatina 1, Copper 0,969

8,830

I 1,400

I 1,869

,469-

resulting

Platina 1, Copper 2 - -

10,410

10,514

,104 —

Platina 1, Copper 4 - -

9,908

9,768

19,364

Platina 1, Copper 5 - -

9 > 6 93

9'598

.095 +

18,970

Platina 1, Copper 8 - -

9,30°

9,328

,028 —

Platina 1, Copper 1 2 - -

9> 2 5 i

9,168

,083 +

21,607,

Platina 1, Coppers - -

8,970

8,996

,026 —

Mr. SchefFer remarks that copper of itself can never becast close; that when melted with a weak heat, it proves,so incompact as not to bear the hammer; and that whenmelted in a strong heat, with the addition of inflammablematter, in order to render it malleable, it proves cavernulouson the outside. The irregularity in the above set of ex-periments seems to shew that something of the same kindhappens in the mixtures of copper and platina; since fourmixtures out of the seven were lighter than they ought tohave been, and this not from any uniform action of thetwo metals on one another, but apparently from accidentalporosity. I melted some of the mixtures a second time,and found their gravities considerably altered; that of11,400 was increased to 11,693; und that of 9,231 was-diminifhed to 8,985. Little therefore can be concluded'from these mixtures, in regard either to the gravity of theplatina, or its effect in varying the gravity of copper.

IRON