Plating Bath.
A vessel of solution for the deposition of metal by electrolysis as used
in electro-plating.
Plating, Electro-.
The deposition of metal by electrolysis so as to coat the conducting
surface of objects therewith. The full details of the many processes are
very lengthy and cannot be given here.
The general principle includes a battery or source of electric current.
The object to be plated is connected to the negative terminal and is
immersed in the solution. Thus with a battery the object is in
electrical connection with the zinc plate. To the other terminal a
metallic plate is connected. The object and the plate termed the anode
being introduced into a suitable bath, the metal whose solution is in
the bath is deposited upon the surface of the object.
The bath is a solution of the metal in some form that will lend itself
to the electrolytic action. The anode is often a plate of the metal of
the bath, so that it dissolves as fast as metal is deposited on the
object, thus keeping up the strength of the solution.
The objects to be plated must be scrupulously clean, and great care must
be taken to keep the bath uncontaminated.
When the object has a non-conducting surface, it is made conducting by
being brushed over with plumbago q.v. In addition iron dust is sometimes
dusted over it. This acts by precipitating the metal of the bath
directly and thus giving a conducting basis for the metal to deposit on.
To avoid getting iron in a bath the object may be dipped in copper
sulphate solution. This precipitates copper in place of the iron and
leaves the article in good shape for silver or other plating.
Electro-plating, if made thick enough, gives a reverse of the article
when separated therefrom. A direct copy can be got by a second plating,
on the first plating after separation, or a wax impression can be
employed.
Under the different metals, formulae for the baths will be found. (See
also Quicking--
Steeling--Plating Balance.)
Platinoid.
An alloy of copper, nickel, zinc in the proportions of German silver
with 1 or 2 per cent of tungsten. It is used for resistances. It has a
specific resistance (or resistance per centimeter cube) of about 34
microhms. Its percentage variation in resistance per degree C. (1.8° F.)
is only about .021 per cent., or less than half that of German silver.
This is its most valuable feature.