sorting
tables; or, from 12,000 loads, which is about the daily average of the
quantity washed at De Beers and Kimberley mines, 160 cubic feet had to
be assorted by hand.
The
first question usually asked by visitors is, What is the cause of this
amazing discrimination ? This is a very difficult question to answer
with positive assurance. It is possible that the secret of the affinity
may lie in the fact that water adheres to or enters into all minerals
composing the concentrate except precious stones. These present
comparatively dry faces to the grease and quickly adhere to it, while
the wet stones flow over the table. The grease has no affinity for a
piece of glass, which, when dropped on the table, flows away in the
tailings.
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 any extraneous
matter, such as small particles of adhering blue ground, by boiling
them in a mixture of nitric and hydrochloric acids (aqua regia), or,
still better, in fluoric acid. When the stones are cleaned, they are
carefully assorted with reference to size, color, and purity, and made
up in parcels for sale, formerly to local buyers, who represented the
leading diamond merchants of the world. For several years past De Beers
Company has sold in advance its annual production to a syndicate of
London diamond merchants who have representatives residing in
Kimberley.
