the
blue ground minerals, adhered to grease, while all else would flow off
with water as tailings. The improved shaking tables now used at the
South African mines are corrugated, and while a first table fails to
detain one third of the diamonds a second table recovers these, almost
to the last diamond; so that this invention is practically as certain
in its accomplishments as the human eye and hand, while proving a
great economy in its operation. It has been demonstrated also that
these greased shaking tables will hold other precious stones of high
specific gravity and hardness. The diamonds which are heavily coated
with grease, of about the consistency of axle grease, by their
experience with this process, are cleaned by boiling them in a solution
of caustic soda. The quantity of deposit (diamonds) which reaches the
sorting tables equals but one cubic foot in 192 cubic feet.
From
the sorting tables the diamonds are taken daily to the general office
under an armed escort and delivered to the valuators in charge of the
diamond department. These experts clean the diamonds of extraneous
matter by boiling them in a mixture of nitric and hydrochloric acids,
or in fluoric acid. When cleaned
