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It is the general opinion that platina is found in the fameform in which it is brought to us. The observations onthe appearance of the grains,, and the matters mixed withthem, mentioned at the beginning of this essay, induced me,on the first examination of it, to think that it had beenground in mills with quicksilver. Marggraf, whose pla-tina came from London, and probably from the sameparcel with that in which I had observed the drops ofquicksilver, seems to have entertained a suspicion of the.same kind; for he doubts whether the platina is a nativemineral, or a metallic recrement from which the Spaniard'shave extracted the perfect metal it contained. I have sincebeen informed that the quicksilver we observed among it,which doubtless influenced Marggraf as well as me, didnot come with it from the west Indies, but was added hereby the proprietor with a view to get out the golden particles-.

Some accounts however seem to countenance the aboveconjecture, that platina is found in large masses, and is re-duced into smooth grains by stamping and grinding. Asubstance in small grains, like the platina as brought to us,one should think could hardly be called a stone, as platinais by don Antonio d’Ulloa.

D’Ulloa is the first writer I have met with who mentionsplatina by name. In his voyage to South America, in1735 and the following years, speaking of the gold andsilver mines of Quito, he relates, that in the territory ofChoco there are mines, in which the gold is so envelopedin other mineral substances, bitumens, and stones, that theyare obliged to use quicksilver for its separation; that some-times they find mineral substances which; from their beingmixed with platina, they chuse to neglect 5 that this pla-tina is a stone (piedra) of such resistence, that it is noteasily broken by a blow upon an anvil; that it is not sub-dued by calcination; and that it is very difficult to extracttfce metal it contains even with much labour and expence,