paper itself deals in an interesting way with the theory
of the matter--however, the result is as follows.

(1) The aluminium articles are boiled for a few minutes in a strong
solution of ordinary washing soda. The aluminium surface is thus
corroded somewhat, and rendered favourable to the deposit of an
adherent film of copper. After removal from the soda solution the
aluminium is well washed and brushed in running water.

(2) The articles are dipped for thirty seconds or so in a hot 5 per
cent solution of pure hydrochloric acid.

(3) After dipping in the hydrochloric acid, the work is instantly
plunged into clean water for about one second, so as to remove nearly,
but not quite, all of the aluminium chloride.

(4) The work is transferred to a cold dilute (say 5 per cent) solution
of cupric sulphate slightly acidulated with sulphuric acid. The
degree of acidulation does not appear to be very important, but about
one-tenth per cent of strong acid does well.

If the preliminary processes have been properly carried out the
aluminium will become coated with copper, and the process is
accompanied by the disengagement of gas. It appears to be a rule that
if gas is not given off, the film of copper deposited is non-adherent.
The work must be left in the copper sulphate solution till it has
received a uniform coating of copper.

(5) When this is the case the work is removed--well washed so as to
get rid of the rest of the aluminium chloride, and then electroplated
by the battery in the ordinary copper sulphate bath.

If the operation (4) does not appear to give a uniform coat, or if gas
is not evolved from every part of the aluminium surface, I find that
operations (2) and (3) may be repeated without danger, provided that
the dip in the hydrochloric acid is shortened to two or three
seconds.

The copper layer obtained by Margot's method is perfectly
adherent--even when used as a base for ordinary solder--though in
this case it can be stripped if sufficient force is applied.

Since the solder recommended by M. Margot for aluminium contains zinc,
it does not run well when used to unite aluminium to copper, brass,
iron, etc. In this case, therefore, I have found the most
advantageous method of soldering to be by way of a preliminary
copper-plating.

The success of M. Margot's method depends in my experience on
obtaining just the proper amount of aluminium chloride in contact with
the aluminium when the latter is