power
differ but little from the diamond, are frequently cut into roses and
brilliants, and sold for diamonds. A proof of this fact is furnished by
the commercial price of the colourless topaz, which is much greater than it could obtain as topaz. It is valued in the secret hope that after cutting it may be sold for diamonds.
At
the present day there are means—such as the scales for determining
specific gravity, polariscopes, &c.—for distinguishing with
mathematical certainty the diamond from the sapphire or topaz; but
these tests are of modern origin; and in the middle ages not only
colourless topazes, but those whose tint had been removed in different
ways, principally by the action of fire, frequently passed current for
diamonds. Nay more than this, under the influence of the ideas that
then prevailed concerning transmutation, the successful experimenters
belfeved that they had actually transformed rubies and topazes into
diamonds.
Cardan
furnishes some very curious details on this subject. He gives a receipt
by which " a limpid sapphire of a faint colour" may be boiled in melted gold and converted into a true diamond.
SEMI-STONES OR DOUBLETS. This mode of imitating real stones, though vary-
