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The consequence is that in large mines the nests of vanners comprise scores or even hundreds of machines. When shaking tables are used, without the addition of the endless moving bands, good work can also be done; but the waste of power is still excessive. The vanning spade and shallow washing dish are the prototypes of this kind of ore-dressing machinery.
The main essential in this particular application of the art of vanning is simply that the water should move or drift transversely to lines of ore passing, while held in suspension with water, down a smooth sloping surface.
The method is to pump the liquid from the tanks in which it is stored and to allow it to flow back by way of the vanning apparatus, thus providing not only for catching the grains of gold by the concentrating machine, but also for the dissolving of the fine impalpable gold dust, or natural precipitate, by the action of the cyanide of potassium.
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