[ S55 ]

have more or less than its due proportion of platina. Inthe mixtures with some metals, as lead, this unequal distri-bution, or separation of the platina, is very visible; and itmay be presumed to happen in a greater or less degree inthe mixtures with all the metals, though it cannot alwaysbe distinguished by the eye. Compositions of platina withzinc, tin, and copper, by all which the platina seemsbe uniformly enough dissolved, were poured into narrowcylindrical mould? : the cylinders being broken in two,the lower half of each was found to be of considerablygreater gravity than the upper.

Thus much however the experiments demonstrate, thatin some instances, in the mixtures with silver at least,there is a true diminution of gravity, from the action ofthe ingredients upon one another : and if they do not de-monstrate, they render it extremely probable, that in somecafes, particularly in the mixtures with iron, there is a trueincrease of gravity. If an increase or diminution happenin the mixtures with one metal, we cannot be certain butthey may happen also in those with another; and conse-quently the specific gravity of platina cannot be inferredwith certainty, or even with probability, from that of anymixture of it with any metal.

Of a variation of gravity produced by mixture, there aresome remarkable instances in the other metals also.Copper, whose specific gravity was 8,830, was meltedwith half its weight of tin whose gravity was 7,180: therewas a little loss in the fusion, which we need not here re-gard, for the mixture was specifically heavier than the hea-viest of the metals by itself, its gravity being 8,898: boththe mixture, and a piece of the copper, were examined bysome other gentlemen, who all reported the mixture to bethe heaviest, although, as is usual in trials of this kind,there were some differences in the numbers: if, from the

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