positive pole; the oxide existing in
solution is brought to a higher degree of oxidation, and is separated
out. Its formation may be decreased or entirely prevented by the
addition of readily oxidizible bodies, such as organic acids, lactose,
glycerine, and preferably by an excess of oxalic acid; but only until
the organic matter is transformed into carbonic acid. In this manner
Classen separates other metals from manganese in order to prevent the
saline solutions from being retained by the peroxide.

With solutions of silver, bismuth, nickel, and cobalt, it is often
practicable to prevent the separation of oxide by giving the current a
greater resistance--increasing the distance between the electrodes.

The proportion between the quantities of metal and of peroxide
deposited is not constant, and even if we disregard the concentration
of the solution, the strength of the current and secondary influences
(action of nascent hydrogen) is different in acid and in alkaline
solutions. In acid solutions much peroxide is formed; in alkaline
liquids, little or none. The reason of the difference is that ozone is
evolved principally in acid solutions, but appears in small quantities
only in alkaline liquids, or under certain circumstances not at all.
The quantity of peroxide deposited depends also on the temperature of
the saline solution; at ordinary temperatures the author obtained more
peroxide--the solution, the time, and the strength of current being
equal--than from a heated liquid. The cause is that ozone is destroyed
by heat and converted into ordinary oxygen. With the exception of lead
and thallium the quantity of metal deposited from an acid solution is
always greater than that of the peroxide.

_Lead._--Luckow has shown that from acid solutions--no matter what may
be the acid--lead is deposited at the anode as a mixture of anhydrous
and hydrated peroxide of variable composition. Only very strongly acid
solutions let all their lead fall down as peroxide; the precipitation
is rapid immediately on closing the circuit, and complete separation
is effected only in presence of at least 10 per cent. of free nitric
acid. As the current becomes stronger with the increase of free acid,
there is deposited upon the first compact layer a new stratum of
loosely adhering peroxide.

In presence of small quantities of other metals which are thrown down
by the current in the metallic state, such as copper, mercury, etc.,
peroxide alo