anodes are usually cast copper plates about (say) 3 ft. by 2 ft. by
3/4 or 1 in. The cathodes are frequently of electro-deposited copper,
deposited to a thickness of about 1/32 in. on black-leaded copper
plates, from which they are stripped before use. The tanks are
commonly constructed of wood lined with lead, or tarred inside, and
are placed in terrace fashion each a little higher than the next in
series, to facilitate the flow of solution through them all from a
cistern at one end to a well at the other. Gangways are left between
adjoining rows of tanks, and an overhead travelling-crane facilitates
the removal of the electrodes. The arrangement of the tanks depends
largely upon the voltage available from the electric generator
selected; commonly they are divided into groups, all the baths in each
group being in series. In the huge Anaconda plant, for example, in
which 150 tons of refined copper can be produced daily by the Thofehrn
multiple system (not the jet system alluded to above), there are 600
tanks about 8-1/4 ft. by 4-1/2 ft. by 3-1/4 ft. deep, arranged in
three groups of 200 tanks in series. The connexions are made by copper
rods, each of which, in length, is twice the width of the tank, with a
bayonet-bend in the middle, and serves to support the cathodes in the
one and the anodes in the next tank. Self-registering voltmeters
indicate at any moment the potential difference in every tank, and
therefore give notice of short circuits occurring at any part of the
installation. The chief differences between the commercial systems of
refining lie in the arrangement of the baths, in the disposition and
manner of supporting the electrodes in each, in the method of
circulating the solution, and in the current-density employed. The
various systems are often classed in two groups, known respectively as
the _Multiple_ and _Series_ systems, depending upon the arrangement of
the electrodes in each tank. Under the multiple system anodes and
cathodes are placed alternately, all the anodes in one tank being
connected to one rod, and all the cathodes to another, and the
potential difference between the terminals of each tank is that
between a single pair of plates. Under the series system only the
first anode and the last cathode are connected to the conductors;
between these are suspended, isolated from one another, a number of
intermediate bi-polar ele