Flux Used on Food Containers.
—Killed spirits is objectionable as a flux for soldering vessels intended to contain food of any kind. Not only is this flux a poison, but it is liable to produce subsequent rusting wherever used unless all traces of it are thoroughly removed immediately after soldering. A good non-poisonous flux suitable for tin boxes may be made by dissolving resin in oil. Place a quantity of powdered resin in an iron vessel, add colza, olive, or any similar oil, and apply gentle heat, meanwhile stirring it until the resin is dissolved. Dissolve as much resin in the oil as possible without making the flux too thick (when cold) to apply with a brush. One or two small experiments will soon decide the required proportions. The resin is really the base of the flux; but the oil is added to facilitate its application and removal before and after the soldering process.
CHAPTER IV
Soft-soldering with the Copper Bit
Choice between Blowpipe and Bit.—The method of heating depends on the size of the work, or rather the area to be soldered, and the conveniences at the command of the worker. The soldering bit, although so commonly used, is not necessarily the best for the beginner to use for small work. A blowpipe flame—from a bunsen burner or a spirit lamp—is far more convenient and neat, and its effects can be applied and localised with the greatest precision, down to the merest pin point of heat applied at a definite spot. The bit is chiefly useful for long joints such as in tinplate work, and for pieces bound together to which the bit is applied to heat up and melt solder between them. But for work where the soldering area does not measure more than an inch or so (and there is a vast amount of this kind), the blowpipe flame is far preferable. It must be admitted, though, that this is a matter in which some workmen might have two distinct opinions; and, as already remarked, the bit is far more commonly used.
Fig. 2.—Soldering Bit
Fig. 3.—Pivoted Soldering Bit