Of this last kind is the Whiteness of Froth, Paper, Linnen, and most
white Substances; of the former I reckon that of white Metals to be. For
whilst the densest of Metals, Gold, if foliated, is transparent, and all
Metals become transparent if dissolved in Menstruums or vitrified, the
Opacity of white Metals ariseth not from their Density alone. They being
less dense than Gold would be more transparent than it, did not some
other Cause concur with their Density to make them opake. And this Cause
I take to be such a Bigness of their Particles as fits them to reflect
the white of the first order. For, if they be of other Thicknesses they
may reflect other Colours, as is manifest by the Colours which appear
upon hot Steel in tempering it, and sometimes upon the Surface of melted
Metals in the Skin or Scoria which arises upon them in their cooling.
And as the white of the first order is the strongest which can be made
by Plates of transparent Substances, so it ought to be stronger in the
denser Substances of Metals than in the rarer of Air, Water, and Glass.
Nor do I see but that metallick Substances of such a Thickness as may
fit them to reflect the white of the first order, may, by reason of
their great Density (according to the Tenor of the first of these
Propositions) reflect all the Light incident upon them, and so be as
opake and splendent as it's possible for any Body to be. Gold, or Copper
mix'd with less than half their Weight of Silver, or Tin, or Regulus of
Antimony, in fusion, or amalgamed with a very little Mercury, become
white; which shews both that the Particles of white Metals have much
more Superficies, and so are smaller, than those of Gold and Copper, and
also that they are so opake as not to suffer the Particles of Gold or
Copper to shine through them. Now it is scarce to be doubted but that
the Colours of Gold and Copper are of the second and third order, and
therefore the Particles of white Metals cannot be much bigger than is
requisite to make them reflect the white of the first order. The
Volatility of Mercury argues that they are not much bigger, nor may they
be much less, lest they lose their Opacity, and become either
transparent as they do when attenuated by Vitrification, or by Solution
in Menstruums, or black as they do when ground smaller, by rubbing
Silver, or Tin, or Lead, upon other Substances to draw black Lines. The
first and only Colour which white Metals take by grinding their
Particles smaller, is black, and therefore their white ought to be that
which borders upon the black Spot in the Center of the Rings of Colours,
that is, the white of the first order. But, if you would hence gather
the Bigness of metallick Particles, you must allow for their Density.
For were Mercury transparent, its Density is such that the Sine of
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