ed cathode of iron is by no means
easily polished either by fine emery, tripoli, or rouge.
Consequently, as in the case of brass, if a polished surface is
desired, it must be first prepared on the unplated cathode. In this
case, even if the deposit appears dull, but not gray, it may be easily
polished by tripoli and water, using a cork as the polisher.
Scratch-brushing with brass wire, however, though possibly not with
German silver wire, brightens the deposit, but discolours it. When
the deposit becomes gray I have not succeeded in polishing it
satisfactorily.

Soldered brass or iron may be satisfactorily coated with nickel by
giving it a preliminary coating of copper in the cyanide bath. On the
whole, I recommend in general that iron be first coated with copper in
the alkaline bath, scratch-brushed, and then nickel-plated, and this
whether the iron appears to be uniform or not. Much smoother,
thicker, and stronger coats of nickel are obtained upon the
copper-plated surface than on the iron one, and the coating does not
become discoloured (? by iron rust) in the same way that a coating on
bare iron does. The copper surface may be plated for at least an hour
at a density of ten amperes per square foot without scaling.

Scales or circles divided on brass may be greatly improved in
durability by nickel--plating. For this purpose the brass must be
highly polished and divided before it is nickelled.

The plating should be continued for a few minutes only, when a very
bright but thin coat of nickel will be deposited; it then only
remains to wash and dry the work, and this must be done at once. If
the nickel is deposited before the scale or circle is engraved, very
fine and legible divisions are obtained, but there is a risk that
flakes of nickel may become detached here and there in the process of
engraving.

142. Miscellaneous Notes on Electroplating.

Occasionally it is desirable to make a metallic mould or other object
of complex shape. The quickest way to do this is to carve the object
out of hard paraffin, and then copy it by electrotyping. Electrotype
moulds can be made in many ways. The easiest way perhaps is to take a
casting in plaster of Paris, or by means of pressure in warm
gutta-percha.

In cases where the mould will not draw, recourse must be had to the
devices of iron-founders, i.e. the plaster cast must be made in
suitable pieces, and these afterwards fitted together. This process
can