and corners of the cathode.

If the deposit becomes markedly irregular, the best plan is to stop
the process and file the face of the deposit down to approximate
smoothness. In coppering it is of the utmost importance that the
cathode be clean and free from grease; it must never be touched (by
the finger, for instance) from the time it is scratch-brushed till it
is immersed in the plating bath. Any grease or oxidation tends to
prevent the copper deposit adhering properly.

A copper deposit oxidises very easily when exposed to the air.
Consequently if the surface be required free from oxide, as, for
instance, when it is to be silvered or gilt, it must be quickly washed
when withdrawn from the coppering bath, scratch-brushed, and
transferred immediately to the silvering or gilding bath.

If the surface is to be dried, as in electrolysis calibrations, it
must be rinsed quickly with boiling water and pressed between sheets
of filter paper. Another method which has been recommended is to
rinse the copper in--water slightly acidulated with sulphuric acid
(which prevents oxidation), then in distilled water, and to dry by
blotting paper and in front of a fire, taking care not to make the
plate too hot. The wash water is sufficiently acidulated by the
addition of two or three drops of acid per litre. So far as I know,
the method of washing in acidulated water was first proposed by Mr. T.
Gray.

Sec. 138. Coppering Aluminium.

A good adherent deposit of copper on aluminium used to be considered a
desideratum in the days when it afforded the only means of soldering
the latter. Many receipts have been published from time to time, and
I have tried, I think, most of them. On no occasion, however, till
this year (1896), have I succeeded in obtaining a deposit which would
not strip after it was tinned and soldered, though it is not difficult
to get apparently adherent deposits so long as they are not operated
upon by the soldering iron. The best of the many solutions which have
been proposed in years gone by is very dilute cupric nitrate with
about 5 per cent of free nitric acid.

The problem of electroplating aluminium which I have indicated as
awaiting a solution has at last found one. In the Archives des
Sciences physiques et naturelles de Geneve for December 1895 (vol.
xxxiv. p. 563) there is a paper by M. Margot on the subject, which
discloses a perfectly successful method of plating aluminium with
copper. The