318 THE DIAMOND
increases in the following order, it is said: Gold, silver, copper, brass, bronze, platinum, nickel, iron, crucible steel.
"
Splints" are sharp-pointed splinters of diamond crystal. They are
obtained from the refuse of the cleaving and cutting establishments and
also, since the use of the grease-table, from the mines, with the
unbroken crystals. As noted elsewhere, the matrix of the African mines
contains many fractured crystals, and the grease-tables hold small
splintered pieces which formerly escaped attention when hand picking
was the custom. They are used for small drills, for turning jewels for
watches, electrical machinery and similar purposes, and at present
bring from $3 to $10 per carat.
In
the use of diamond in any form for mechanical purposes, care must be
taken to avoid crushing or overheating. The hard fragments of a broken
diamond involved in machinery turning rapidly, do serious damage
almost instantaneously, and overheated, the crystal loses consistency
and carbonizes the soft iron of the setting, turning it at once into
hard steel. This applies particularly to carbon when used for deep
borings. A hard blow will often crush carbon to fragments, and heat
injures the quality. A stoppage of the supply of water to the borer has
been known to change the hard carbons of the drill to a mass
resembling black glass which yielded to a file, while the soft iron of
the bit was at the same time turned to steel. Great skill and care is
necessary also in the setting of the carbons in a drill for deep
boring. If one gets loose, it quickly tears itself and the bit to
pieces, and fishing for a loose car-
