he
plumber's shave-hook. The shave-hook is merely a peculiarly shaped
hard steel scraping knife on a handle (Fig. 79).

Fig. 79

With tin plate the soldering of long joints is often necessary. The
plate must be temporarily held in position either by binding with iron
wire, fastening by clamps, or holding by an assistant. The flux is
applied and the iron run slowly along the joint. Enough solder is
used to completely float the tip of the iron. By arranging the joint
so that it slopes downward slightly, and commencing at the upper end,
the solder may be caused to flow after the iron, and will leave a
joint with the minimum permissible amount of solder in it. By
regulating the slope, heat of iron, etc, any desired quantity of
solder may be run into the joint.

Sec. 97. Soldering Zinc.

Zinc alloys with soft solder very easily, and by so doing entirely
spoils it, making, it "crumbly," dirty, and preventing it running.
Consequently, in soldering up zinc great care must be taken to prevent
the solder becoming appreciably contaminated by the zinc. To this end
the zinc surfaces are cleaned by means of a little hydrochloric acid,
which is painted on instead of chloride of zinc. Plenty of solder is
melted on to the work, and is drawn along over the joint by a single
slow motion of the soldering bit. The iron must be just hot enough to
make the solder flow freely, and it must never be rubbed violently on
the zinc or allowed to linger in one spot; the result of the latter
action will be to melt a hole through the zinc, owing to the tendency
of this metal to form an easily fusible alloy with the solder.

The art of soldering zinc is a very useful one in the laboratory. The
majority of physicists appear to overlook the advantages of zinc
considered as a material for apparatus construction. It is light,
fairly strong, cheap, easily fusible, and yet hard and elastic when
cold. It may be worked as easily as lead at a temperature of, say,
150 deg. to 200 deg. C, and slightly below the melting-point (423 deg. C.) it is
brittle and may & powdered. The property of softening at a moderate
temperature is invaluable as a means of flattening zinc plate or
shaping it in any way. During the work it may be held by means of an
old cloth. Zinc sheet which has been heated between iron plates and
flattened by pressure retains its flatness very fairly well after
cooling.

Sec. 98. Soldering other Metals.

Iron.

The iron