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XII. Platina with vitreous bodies.

r. Half an ounce of a precipitate thrown down fromlblution of platina by tin, was ground in an iron mortar,with eight times its weight of common hint glass, andthe mixture put into a crucible, which was covered andluted, and placed in a wind furnace. The.fire was gra-dually raised, and kept up extremely strong for about tenhours.: the crucible being then taken out and broken, thematter proved of a dark blackish colour, untransparent,friable, interspersed with a bright whitish substance appa-rently metallic. It is probable that this metallic matterwas the platina, and that the glass owed its opacity anddark colour, not to this metal, but to tin in the precipitate,or some particles of iron worn off from the mortar, orother accidental causes.

2. I ground in a glass mortar a quarter of an ounce ofa precipitate of platina made by alcaline salt, with twelvetimes its weight of powdered flint glass, and committedthe mixture to the same fire as the foregoing. The resultwas a compact cloudy glass, pretty transparent in thinpieces, covered in part with a thin whitish coat. Towardsthe upper, part, and all round the sides, were observed se-veral particles of metal, which appeared to the eye likebright platina, and proved hard to the point of a knife;In this, as in. the foregoing experiment, the glass seems tohave received nothing from the platina, the change beingno other than what flint glass is found to undergo froma flight introduction of inflammable matter.

3. Mr. Marggraf gives an account of three experimentsof the mixture of platina with vitreous bodies. Fivedrams of pure salt of tartar, twelve drams of clean sandcalcined and washed, one dram of calcined borax, two ofnitre, and two of crude- platina, were mixed together, and

kept