§ 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° to 200° C., and slightly below the melting-point (423° 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.