G-

l 553 I

nlain 697 parts of steel with 100 of platina, ana as 7,76parts of the mixt lose 1 in water, the gravity of the pla-tina comes out on calculation no less than 27,813.

It appears therefore that iron is very variable in its spe-cific weight, in the different circumstances of being meltedor forged, and impregnated more or less with phlogiston;but that probably some other cause also concurs in varyingthe gravity of mixtures of it with platina. This causestray perhaps be found in a remarkable property of iron,which the experiments related in the former part of thiswork (page 261) seem to have established. Melted iron,in the instant of its becoming solid, is dilated into a largervolume, and one of the marks of this dilatation is the con-vexity of its surface in circumstances wherein that of othermetals is depressed. Platina seems to destroy this powerin iron. In the first mixture I made of cast iron and pla-tina, the surface was as much hollowed as that of anymetallic mass I remember to have seen, nor was this phe-nomenon omitted in the account of the experiments printedin the Transactions. If then fluid iron expands in fixing,and the admixture of platina occasions it to contract, or toexpand less, we need not wonder at the increase of gravityin the hydrostatics experiments.

Specific Gravity

Platinas

T I N

By Exper.

7,180

By CakuJ.

Difference

Gravity

resulting

Platina 1, Tin 0,984

10,827

10,129

,698-f

21,649

Platina 1, Tin 1,966

8,972

8,920

,°32 +

I7,6l9

Platina 1, Tin 4 - -

7>79 4

8,117

>3 2 3 ~

Platina 1, Tin 8 - -

7 > 7°5

7,672

>°3 3+

18,613

Platina 1, Tin 12 - -

7,613

7 > 5 l 3

, 1 oo-|-

26,745

Platina 1, Tin24 - -

7'47i

7'349

, 122-j-

27,368

Th©