I 593 J

the pulverisation may be facilitated by means of heat,both the grains of platina itself, and mixtures of themwith other metals, being considerably more brittle whenhot than when cold. Or what is still better and easier,the mixt may be melted with a suitable quantity of lead,and this compound submitted to the trituration with mer-cury and water. If there is any truth in the report, thatcertain gold mines are neglected, on account of their in-tractableness from platina contained in them, this last pro-cess may turn out a very important and advantageousone.

II. Precipitation by vegetablesixt Alcalies.

As gold is totally precipitated by sixt alcaline salts, butplatina only in part, and as a minute portion of platinaremaining dissolved tinges a furprizingly large quantity ofthe fluid of a yellow colour; it was presumed that a smalladmixture of platina with gold might by this means bereadily discovered. A few drops of a solution ot platinawere therefore mixed with above a hundred times the quan-tity of a solution of gold, and a pure sixt alcaline salt gra-dually added so long as it occasioned any effervescence orprecipitation. The remaining liquor was still so yellow,that it was judged the platina would have discovered itself,though its proportion had been less than one thousandthpart of that of the gold. It may be observed, that thoughit is customary to dilute metallic solutions pretty largelywith water in order to their precipitation, yet here, as wewant only to fee whether any colour remains in the liquorafter the precipitate has settled, the less dilute the liquoris, the less quantity of colouring matter we shall be able to-distinguish.

It has been objected to the above experiment, thatthough the platina is discoverable when thus mingled su-perficially