[ 54 * 3

nical principles, to produce by their simple junction ; andas such new properties seem to be in no metallic mixturdmore conspicuous than in those which platina affords; itfollows, that the dissolution of platina by metals is by ndmeans a superficial mixture, but as perfect and intimate acoalition as we have grounds to believe that of any onemetal to be with any other.

SECT. VI.

Of the specific gravities of mixtures of platina nvith different

metals .

\ MONO the experiments communicated to thejs\ Royal Society by Mr. Wood, there is a remarkableone of the specific gravity of a mixture of equal parts ofplatina and gold. The gravity of the heaviest: platina heexamined was to that of water as 15 to i ; and the gravityof gold, as we have seen in the history of that metal, isabout 19-rv. If 15,0 parts of platina lose one on beingimmersed in water, and 19,3 parts of gold lose 1 ; then,if the two metals be mixed in equal quantities, 34,3 partsof the compound should lose 2; whence, dividing 34,3 by2, we have 17,130 for the gravity of the compound. Suchought the gravity to be, if the two metals were joined su-perficially, and each preserved its own proper volume ; butwhen melted together, the specific weight of the mass issaid to have been considerably greater, amounting to noless than 19. If this be the cafe, 19 parts of the meltedmass must occupy no more space than 17-nrJ- did beforethe fusion ; so that near a fourth part of one metal is re-ceived into the pores of the other, without increasing thebulk of the mass. It may be suspected, that the substancewhich Mr. Wood weighed by itself under the name of;platina was the lighter cast metal mentioned at the begin-

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