174 MINERAL RESOURCES, 1919—PART II.
tion
published by the South African Mining and Engineering Jour-nal,
Johannesburg, the bell of the caisson has a diameter of 15 feet, giving
ample space for several men to work. The bell is specially designed for
working in deep pools and can easily be shifted from one pool to
another, as the whole structure is attached to pontoons that can float
in shallow water from 12 to 18 inches deep. The bell is lowered into
the water by means of water ballast, and the water is displaced by air
pumped into the bell by compressed-air pumps. The interior is lighted
by electricity and has a telephone and signals for communication. The
gravel is hauled up by a compressed-air hoist and is handled by purely
mechanical means once it enters the skip. The apparatus is designed to
work in any depth of water less than 65 feet; the deepest pool in the
Vaal in the dry season is only about 30 to 40 feet deep. On the deck
there are boilers and a steam turbine for driving the machinery and an
air-compressor for supplying air to the bell. There is a bin to
accommodate the gravel brought up, a trommel for cleaning and
classifying the soil, gravitators for separating the diamonds, and a
sorting table. Previous attempts to obtain diamonds from the bed of
Vaal River have been made by means of breakwaters and suction or bucket
dredges, but the latter method is said to have proved unsuccessful
because the bed of the river is a natural concrete of bowlders and
clay. Recent advices indicate that the idea of recovering diamonds from
Vaal River by means of a caisson is not new.
CONTROL OF SOUTH AFRICAN DIAMONDS.
The
diamond-mining industry of South Africa has undergone a complete change
of control, as is shown by the following notes extracted from the
annual report of the De Beers Consolidated Mines (Ltd.) for 1919:
A
conference of the four largest producers of diamonds, consisting of the
German Southwest Africa, De Beers, Jagersfontein, and Premier
companies, met in London in July, 1914, with the object of regulating
the value of diamonds to be placed on the market and determining the
quota of each participant in the total annual sales. After long and
protracted negotiations lasting many days an agreement was arrived at
among the producers and terms made with the syndicate for the marketing
of the diamonds. Owing to the Avar all negotiations came to an end, but
during 1916 the diamond market began to show signs of a return to life,
and while the trade was slowly recovering the Union Government decided
to place a large quantity of German Southwest Africa (Southwest
Protectorate) diamonds on the market, for which it called for tenders
in London and on the Continent. The syndicate, feeling that if those
goods were forced on the dealers there would be a collapse, approached
the De Beers Co. and suggested tendering on joint account. The
proposition was accepted, and an arrangement was made on a
profit-sharing basis for the purchase of the German Southwest diamonds
until the conclusion of peace. In October, 1916, the syndicate came to
terms with the Premier Co. for the purchase of its output, so that from
February, 1917, the diamonds of the four big producers have been sold
through one channel.
