[ S39 ]

ounces of this glass in line powder were mixed with oneounce of platina, and the mixture melted in a close cru-cible for two hours. A brilliant regulus was obtained,greyish on the fracture, but when filed pretty white,weighing twenty-eight grains, or about one seventeenth,more than the platina: the scoria was of a dark browncolour.

Here the increase of weight is a full proof that thefusion of the platina was owing to its having imbibedeither lead or arsenic from the glass: in the brilliancy ofthe surface, and the grey colour of the internal part,Mr. Marggrafs metal agreed with our masses of arsenicatedplatina already described ; and probably the using of arse-nic in a slate of vitrification with substances which serveto detain it in the fire, may be the most effectual meansof combining this volatile metallic body with platina.

XV. General observations on the mixtures of platina with

other metals.

i. It appears from the foregoing experiments, that pla-tina, unfusible by itself in the strongest, fires of our fur-naces, and proof against the most active unmetallic fluxes,melts with, or is diffolved by, every one of the commonmetallic bodies: That the different metals dissolve it withdifferent degrees of force, and this not in proportion to thedegree of their own fusibility : That there are remarkabledifferences in its relation to different metals, in regard tothe change which it produces in the quality of the metal ;that it hardens, and diminishes the malleability of, all themalleable metals, but seems to communicate some degreeof toughness to one which of itself has none, viz. cast iron;that it diminishes the malleability of tin more, and of goldless, than of the other metals; that in certain quantities,tt debases the colour of all the metals, communicating to

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