composition and treatment of the electrolyte is thus apparent. The
advantage of keeping the solution in motion is due partly to the
renewal of solution thus effected in the neighbourhood of the
electrodes, and partly to the neutralization of the tendency of
liquids undergoing electrolysis to separate into layers, due to the
different specific gravities of the solutions flowing from the
opposing electrodes. Such an irregular distribution of the bath, with
strong copper sulphate solution from the anode at the bottom and acid
solution from the cathode at the top, not only alters the conductivity
in different strata and so causes irregular current-distribution, but
may lead to the current-density in the upper layers being too great
for the proportion of copper there present. Irregular and defective
deposits are therefore obtained. Provision for circulation of solution
is made in the systems of copper-refining now in use. Henry Wilde, in
1875, in depositing copper on iron printing-rollers, recognized this
principle and rotated the rollers during electrolysis, thereby
renewing the surfaces of metal and liquid in mutual contact, and
imparting sufficient motion to the solution to prevent stratification;
as an alternative he imparted motion to the electrolyte by means of
propeller blades. Other workers have followed more or less on the same
lines; reference may be made to the patents of F. E. and A. S. Elmore,
who sought to improve the character of the deposit by burnishing
during electrolysis, of E. Dumoulin, and Sherard Cowper-Coles
(_Engineering Review_, 1905, vol. xiii. p. 392), who prefers to rotate
the cathode at a speed that maintains a peripheral velocity of at
least 1000 ft. per minute. Certain other inventors have applied the
same principle in a different way. H. Thofehrn in America and J. C.
Graham in England have patented processes by which jets of the
electrolyte are caused to impinge with considerable force upon the
surface of the cathode, so that the renewal of the liquid at this
point takes place very rapidly, and current-densities per sq. ft. of
50 to 100 amperes are recommended by the former, and of 300 amperes by
the latter. Graham has described experiments in this direction, using
a jet of electrolyte forced (beneath the surface of the bath) through
a hole in the anode upon the surface of the cathode. Whilst the jet
was playing, a good dep