BOOK VIII.

321

concentrates are washed separately in different bowls from those which havesettled on the canvas. This bowl is smooth and two digits wide and deep,being in shape very similar to a small boat; it is broad in the fore part,narrow in the back, and in the middle of it there is a cross groove, in whichthe particles of pure gold or silver settle, while the grains of sand, since theyare lighter, flow out of it.

In some parts of Moravia, gold ore, which consists of quartz mixed withgold, is placed under the stamps and crushed wet. When crushed fine itflows out through a launder into a trough, is there stirred by a woodenscrubber, and the minute particles of gold which settle in the upper end ofthe trough are washed in a black, bowl.

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A —Stamps. B —Mortar. C—Plates full of holes. D —Transverse launder.

E —Planks full of cup-like depressions. F —Spout. G —Bowl into which the

CONCENTRATES FALL. H—CANVAS STRAKE. I—BOWLS SHAPED LIKE A SMALL BOAT.

K —Settling-pit under the canvas strake.

So far I have spoken of machines which crush wet ore with iron-shodstamps. I will now explain the methods of washing which are in a measurepeculiar to the ore of certain metals, beginning with gold. The ore whichcontains particles of this metal, and the sand of streams and rivers which