, that the "vanner," or moving endless
band with a stream of water running on it, was invented with the
special object of treating the finer stuff.

Jiggers and vanners form the staple of the miner's ore-dressing
machinery at the present day. The efficiency of the latter class of
separating machines, working on certain kinds of finely crushed ore,
is already so great that it may be said without exaggeration that it
could hardly be much improved upon, so far as percentage of extraction
is concerned; and yet the waste of power which is involved is
something outrageous. For the treatment of a thin layer of slimes,
perhaps no thicker than a sixpence, it is necessary to violently
agitate, with a reciprocating movement, a large and heavy framework.
Sometimes the quantity of stuff put through as the result of one
horse-power working for an hour is not more than about a
hundredweight. 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. Let any one place a line of
finely-crushed wet ore on a flat spade and draw the latter quickly
through still water, at the same time shaking it, and the result on
inspection, if the speed has not been so great as to sweep all the
fine grains off the surface, will be that the heavier parts of the ore
will be found to have ranged themselves on the side towards which the
spade was propelled in its progress through the water. A sheet of
glass serves for the purpose of this experiment even better than a
metal implement; but the spade is the time-honoured appliance among
miners for testing some kinds of finely crushed ore by mechanical
separation.

It is to be observed that, besides the shaking motion imparted to the
apparatus, the only active agency in the distribution of the particles
is the sidelong movement of the spade relatively to the water. But it
makes little or no difference whether the water moves sidelong on the
spade or the latter progresses through the liquid; the ore will range
itself accurately all the same. Consequently, if a circular tank be
used, and if the water be set in rotary motion, the ore on a sheet of
glass, held steady, will arrange itself in the same way. If the ore be