sometimes
coloured garnet-red, and sometimes honey-yellow, by the presence of
foreign matters. Their refrangibility can only be compared to that of
the diamond, and they present the same effects of reflected and
refracted light. They possess the quality of hardness, too, in such a
degree as to scratch the oriental ruby and corundum; and M. Froment has
used a crystal of boron to scratch the surface of a diamond.
The
cutting of the diamond with powder of boron was attempted by M.
Voorzanger, of Amsterdam, with entire success; only that a larger
quantity was used than would have been necessary of diamond-dust, and
the work was accomplished more slowly.
The
same success attended the cutting of an exceedingly hard diamond in
the collection of the Normal School at Paris. Its angular edges, and a
furrow which marred it, were removed by a wheel covered with powder of
boron. M. Guillot, who directed the experiment, confirmed the
observation of M. Voorzanger concerning the superlative qualifications
of boron-dust for cutting and polishing diamonds.
It
has been further observed that the greater number of the powerful
agents at the disposal of modern chemistry are without action upon
boron. " It is," says M. Malaguti, "the most unalterable of
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