Placed
in the hydrostatic balance, it loses two-fifths of its weight, and this
is the sole point of resemblance between it and the white topaz of
Brazil, excepting the colour.
The
different specific gravity of the Tarions diamonds under the same form
is clearly produced by the different degrees of colouring, proceeding
from the metallic oxides, which are heavier than the crystalline
substance which contains them. It seems, however, that those contained
in the American diamond are less pure, and therefore lighter.
One of the most beautiful qualities of the diamond is its power of refraction ; that of water is 0-785 ; that of the ruby, 0.739 ; that of the rock crystal, 0.654 ; that of the diamond, l-396.
The
refraction of the diamond is single in the entire crystals ; when
broken, it possesses double, but imperfect refraction, in the thin
layers.
The polarization of light gives in the topaz an angle of 31° ; in the Strass, 35° ; in the diamond, 22°.
The
purest diamonds, that is, those of the finest quality, are quite devoid
of colour ; in other words, when facetted, they reflect all the
prismatic colours.
In
the mines, however, these were only found in the proportion of
one-fifth ; those of the second quality, and much less esteemed, are in
the proportion of one-fourth, and are covered with a yellowish,
greenish or bluish colour ; the remainder present the most varied
colours.
The colouring principles are due to oxides and me-
