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DIAMOND.
known. It is therefore employed for sawing and boring the hardest
stones, and for engraving seals. For this purpose it is reduced to
powder.
This powder is uſed in the fame manner as sand, emery, or other
cutting powders, are employed by the lapidaries, viz. by moistening
it with empyreumatic oil, and applying it to their wheel or drill ;
or the metal point used by the seal engravers, like a crayon. The
metal employed for this purpose is the purest and softest iron. This
takes faſt hold of the diamond powder,—it being pressed into it by
the force exerted in the operation : And the little particle never
quits its place to roll about, but is carried along by the tool, acting
like the tooth of a file, and tearing up whatever it touches. There
is something curious in the way in which diamond acts in cutting
common glaſs. The glazier’s diamond is by no means ſharp pointed.
I have seen them as blunt and round and fmooth as the head of a
large pin ; yet this, with a moderate preffure, causes the plate to
ſhiver under it wherever it is drawn. This is by no means a crack;
but the glafs being made somewhat weaker there, splits imme
diately, when gently patted on the other side with a hard body.
4. The diamond is still more distinguished from the rest of the
gems by its chemical properties, or the effects produced on it by
heat and mixture with other bodies. The utmost violence of heat,
even that of a burning mirror, does not induce the leaft appearance
of fusion. Its asperities are not perceptibly rounded, as has been
obferved in the ruby. The only effect of simple heat is, to dissipate
some foulnesses which sometimes taint its purity, or water, as it is
called by the jewellers ; but it makes no change in its texture, if
the diamond has been free from previous cracks or flaws.
Nor does the utmost violence of fimple heat volatilize the dia
mond. If it be protected from the action of the air, it fuffers no
diminution of its weight by the longest continuance in the fire. But
if it be fubjected to intense heat, and to a current of free air, it will