Again, the Refraction of Camphire, Oil Olive, Linseed Oil, Spirit of
Turpentine and Amber, which are fat sulphureous unctuous Bodies, and a
Diamond, which probably is an unctuous Substance coagulated, have their
refractive Powers in Proportion to one another as their Densities
without any considerable Variation. But the refractive Powers of these
unctuous Substances are two or three Times greater in respect of their
Densities than the refractive Powers of the former Substances in respect
of theirs.
Water has a refractive Power in a middle degree between those two sorts
of Substances, and probably is of a middle nature. For out of it grow
all vegetable and animal Substances, which consist as well of
sulphureous fat and inflamable Parts, as of earthy lean and alcalizate
ones.
Salts and Vitriols have refractive Powers in a middle degree between
those of earthy Substances and Water, and accordingly are composed of
those two sorts of Substances. For by distillation and rectification of
their Spirits a great Part of them goes into Water, and a great Part
remains behind in the form of a dry fix'd Earth capable of
Vitrification.
Spirit of Wine has a refractive Power in a middle degree between those
of Water and oily Substances, and accordingly seems to be composed of
both, united by Fermentation; the Water, by means of some saline Spirits
with which 'tis impregnated, dissolving the Oil, and volatizing it by
the Action. For Spirit of Wine is inflamable by means of its oily Parts,
and being distilled often from Salt of Tartar, grow by every
distillation more and more aqueous and phlegmatick. And Chymists
observe, that Vegetables (as Lavender, Rue, Marjoram, &c.) distilled
_per se_, before fermentation yield Oils without any burning Spirits,
but after fermentation yield ardent Spirits without Oils: Which shews,
that their Oil is by fermentation converted into Spirit. They find also,
that if Oils be poured in a small quantity upon fermentating Vegetables,
they distil over after fermentation in the form of Spirits.
So then, by the foregoing Table, all Bodies seem to have their
refractive Powers proportional to their Densities, (or very nearly;)
excepting so far as they partake more or less of sulphureous oily
Particles, and thereby have their refractive Power made greater or less.
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