ctrode plates of raw copper, each of these
plates acting on one side as a cathode, receiving a deposit of copper,
and on the other as an anode, passing into solution; the voltage
between the terminals of the tank will be as many times as great as
that between a single pair of plates as there are spaces between
electrodes in the tank. In time the original impure copper of the
plates becomes replaced by refined copper, but if the plates are
initially very impure and dissolve irregularly, it may happen that
much residual scrap may have to be remelted, or that some of the metal
may be twice refined, thus involving a waste of energy. Moreover, the
high potential difference between the terminals of the series tank
introduces a greater danger of short-circuiting through scraps of
metal at the bottom of the bath; for this reason, also, lead-lined
vats are inadmissible, and tarred slate tanks are often used instead.
A valuable comparison of the multiple and series systems has been
published by E. Keller (see _The Mineral Industry_, New York, 1899,
vol. vii. p. 229). G. Kroupa has calculated that the cost of refining
is 8s. per ton of copper higher under the series than it is under the
multiple system; but against this, it must be remembered that the new
works of the Baltimore Copper Smelting and Rolling Company, which are
as large as those of the Anaconda Copper Mining Company, are using the
Hayden process, which is the chief representative of the several
series systems. In this system rolled copper anodes are used; these,
being purer than many cast anodes, having flat surfaces, and being
held in place by guides, dissolve with great regularity and require a
space of only 5/8 in. between the electrodes, so that the potential
difference between each pair of plates may be reduced to 0.15-0.2
volt.

J. A. W. Borchers, in Germany, and A. E. Schneider and O. Szontagh, in
America, have introduced a method of circulating the solution in each
vat by forcing air into a vertical pipe communicating between the
bottom and top of a tank, with the result that the bubbling of the air
upward aspirates solution through the vertical pipe from below, at the
same time aerating it, and causing it to overflow into the top of the
tank. Obviously this slow circulation has but little effect on the
rate at which the copper may be deposited. The electrolyte, when too
impure for further