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      §9. Whosoever first light on a parcel of that sort of Substance,
we denote by the word Gold, could not rationally take the Bulk and
Figure be observed in that lump, to depend on its real Essence, or
internal Constitution. Therefore those never went into his Idea of
that Species of Body; but its peculiar Colour, perhaps, and Weight,
were the first he abstracted from it, to make the complex Idea of
that Species. Which both are but Powers; the one to affect our Eyes,
after such a manner, and to produce in us that Idea, we call Yellow;
and the other to force upwards any other Body of equal bulk, they
being put into a pair of equal Scales, one against another. Another,
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perhaps, added to these, the Ideas of Fusibility, and Fixedness, two
other passive Powers, in relation to the operation of Fire upon it;
Another, its Ductility, and Solubility in Aqua Regia, two other
Powers, relating to the operation of other Bodies, in changing its
outward Figure or Separation of it, into insensible Parts. These, or
part of these, put together, usually make the complex Idea in Men’s
Minds, of that sort of Body we call Gold.
Locke Hum II, 31, §9, pp. 381-382