more
and more serious because of the different depths to which different
claims were carried. The walls of the outlying areas disintegrated
rapidly, and fell from time to time in great masses, causing sad loss
of life. Moreover, the immense output of diamonds, and extensive
competition between the different producers, caused a lowering of the
price which made it unprofitable to work many of the poorer parts of
the mines. A consolidation of interests seemed the only way out of
these difficulties, and this was finally accomplished under the
leadership of Cecil Rhodes. In 1888 a joint stock company, known as
the De Beers Consolidated Mines, Limited, was formed to operate the
important diamond properties in the region of Kimberley. The workings
of this company have proved highly satisfactory, both in promoting a
safe and economical extraction of the diamonds and in limiting their
output. Under the new management the system of open-cut workings has
been abandoned in all the mines except the Premier, and the diamond -
bearing ground is mined by a system of tunnels at various levels. From
these it is hoisted to the surface through shafts, and then spread out
over large areas, called floors, to disintegrate. The disintegration
is accomplished by exposure to sun and rain, huge harrows being drawn
frequently over the floors to assist in the work. The time required for
proper disintegration varies from three to six months according to the
nature of the rock. When sufficiently disintegrated, the rock is
carried to machines which wash away the finer particles and
mechanically concentrate that of a size likely to contain diamonds of
value.
For
a long time the diamonds were picked out from this concentrate by
hand, the assortment of pebbles being spread on tables and picked over.
It has lately been found, however, as already noted, that by running
the concentrate over percussion tables the surfaces of which are
covered with a thick coat of grease, that the diamonds are caught and
held by the grease while the valueless minerals pass on. In this way a
more nearly complete as well as more rapid extraction of the diamonds
is secured than when the concentrate is sorted by hand.
After
being sorted out the diamonds are cleaned by boiling in a mixture of
nitric and sulphuric acids, rinsing in water, and finally washing in
alcohol. They are then assorted according to quality into about ten
classes, ranging from the finest, called " close goods," to the
poorest, called " boart." The diamonds belonging to the first eight of
these classes are then again assorted according to color, the " blue
whites" standing first and the "yellows" last. They are then wrapped in
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