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 alone is deposited from a solution of lead containing small
quantities only of free nitric acid.
The lead peroxide deposited is at first light brown or dark red, and
becomes constantly darker and finally taking a velvet-black. As its
stratification upon the platinum is unequal, it forms beautifully
colored rings.
Experiments show that the quantity of peroxide deposited depends on
the nature of the solution and the strength of the current. In case of
very feeble currents and slight acidity, its quantity is so small that
it does not need to be taken into consideration. If the lead solution
is very dilute scarcely any current is observed, lead solutions _per
se_ being very bad conductors of electricity.
Faintly acid concentrated lead solutions give loose peroxide along
with much spongy metallic lead. Free alkali decreases the separation
of peroxide; feebly alkaline solutions, concentrated and dilute, yield
relatively much peroxide along with metallic lead, while strongly
alkaline solutions deposit no peroxide.
Dried lead peroxide is so sparingly hygroscopic that it may be weighed
as such; its weight remains constant upon the balance for a long time.
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