7
inches per minute. Large quantities are used in electrical machines as
jewels for meters, etc. It is recorded that Solomon used diamonds to
cut the stones for the temple at Jerusalem, so that the enterprise of
our modern machinists may be but the resurrection of very ancient
methods, and it is not improbable that the Jewish King obtained his
diamonds from the same or neighboring sources, for there is evidence of
ancient mining in Rhodesia, in a section where late discoveries of
diamonds have been made.
Small pieces of bort, and crystals which are full of inclusions and fractures, are crushed to a powder for use as an abrasive.
Unlike
carbon, which is found with the gem diamond stones in one district only
in Brazil and to a very limited extent in Borneo, bort is found in all
diamond diggings the world over.
As
there has been no sustained effort, by controlling the output, to
maintain prices, the price of bort has varied considerably since the
discovery of the African diamond mines. It has depended largely on the
demand created by the use of it for mechanical purposes. In 1875 the
price for unassorted lots at the mines was about 50 cents per carat,
but as it was found useful for more purposes, and the number grew of
those who knew its value for their uses, the price rose gradually,
until by 1883 the mines were getting an average of about $2 per carat.
These are much less than the market prices for assorted goods during
the same period. Since then there has been considerable fluctuation,
but the tendency has been upward, especially since the rough was
marketed in London, though the opening of the Premier with its big out-
