[ S°4 1

kept in a vehement fire, in a close crucible, for severalhours. The result was a vitreous, somewhat opal-likemass, inclining to a sea green: the platina, no otherwisealtered than in being made whiter, was dispersed partlyon the surface of the glass, and partly about the sides, andsurrounded with a distinct vitreous matter of a deep hy-acinth colour.

4. He tried also the powder separated from platina bycementation with nitre, as described in page 492. Sixgrains of this powder were mixed with a hundred andeighty grains of white sand, and ninety grains of salt oftartar. The mixture, melted with a vehement fire in aclose crucible, proved a porous, greyish, untransparent glass.

5. He prepared a precipitate from platina and tin toge-ther, and tried to vitrefy this mixt. A polished plate oftin being digested in solution of platina, part of the platinaprecipitated upon the tin in form of a blackish red pow-der, and the tin, in some days, was quite corroded : theliquor, of a dark coffee colour inclining to black, beingput into a filter, run through blackish. This compoundsolution of platina and tin was precipitated with salt oftartar: the liquor now passed the filter colourless, and thematter which remained on the paper, being well washedwith hot water and dried, was a black substance, almostresembling, in its fracture, broken pitch or fine pit-coal.Forty grains of this substance, sixty of calcined borax, ahundred and twenty of purified nitre, two hundred andforty of pure salt of tartar, and four hundred and eighty ofpowdered flint, were well mixed together, and melted ina very strong fire. They yielded a.greyish glass, in whichno metallic grains could be found: a thin piece of theglass, laid upon the nail and held up to'the fun, inclinedto an amethyst colour.

It