before
the waters, increased in volume, suddenly destroy it. The fall of water
from the artificial sluice is often employed to turn a wheel to keep
the old channel pumped dry, but little use is made of this power for
other purposes. When the river bed has thus been laid bare, search is
made with a long iron rod for huge pot-holes, known as caldeiros, which
experience has shown are more likely to contain quantities of diamonds
than the ordinary river bed. This is natural, since the diamonds resist
longer than other stones the constant wear due to the whirling about of
the water in the pot-holes and hence gather there. It is said that
sometimes on removal of a little sand large aggregations of pure
diamonds are to be seen. A single small pot-hole is said to have
yielded 8,000 carats, or about 6 pounds of diamonds. The caldeiros have
now been nearly all dug over, however, and the finding of a new one is
rare. The separation of the diamonds from the accompanying sand and
gravel is usually performed by washing, in the manner thus described by
Gorceix :*
"
The sands are placed," he says, " in portions of two hundred to two
hundred and fifty pounds, in a kind of hod or rectangular trough, only
three sides of which are inclosed. The hods are arranged by twos,
fours, or sixes by the side of a trough of water about a foot and a
half deep so that their bottoms shall be slightly inclined toward it. A
workman standing in the trough before each hod dashes water upon the
sand in it. The clay and the very fine sands are carried away and the
first separation is made. The larger pieces remaining in the top of the
sand are picked away. The diamond is to be found in the two upper
thirds of the mass that is left, the lower part being nearly sterile.
The washing is afterward finished in bowls a little deeper and a little
more conical than those used by the gold-washers. The washer puts the
sand in the bowl and fills it with water; then by whirling the bowl and
shaking it up and down while the sand is floating around in it, and
being careful to stir it from time to time with his hand, he determines
a classification in the order of density. This work would be easy if he
were washing gold, for that metal is heavier than the substances with
which it occurs, and always goes to the bottom. The diamond, however,
having a density only about three and a half times greater than that of
water, not much more than that of quartz and tourmaline, and less than
that of the oxides of iron and titanium, its constant companions,
settles in the middle layers. The washer, after several rinsings,
removes the upper particles, hardly looking at them; and when he has
reached a certain level, which his
* Popular Science Monthly, Vol. XXI., p. 616.
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