Spelter.—The alloy used for this purpose is termed "spelter," and brass, zinc and tin are its usual components. The hard solders are used for uniting brass, bronze, copper, and iron.
Whether soft or hard solder is used, it is obvious that it must melt at a lower temperature than the parts which are to be joined together.
There is one peculiarity with respect to alloys:[p. 119] They melt at a lower temperature than either of the metals forming the alloys.
Soldering Acid.—Before beginning the work of soldering, the parts must be cleaned by filing or sandpapering, and coated with an acid which neutralizes the oxygen of the air.
This is usually muriatic acid, of which use, say, one quart and into this drop small pieces of zinc. This will effervesce during the time the acid is dissolving the zinc. When the boiling motion ceases, the liquid may be strained, or the dark pieces removed.
The next step is to dissolve two ounces of sal ammoniac in a third of a pint of water, and in another vessel dissolve an ounce of chloride of tin.
Then mix the three solutions, and this can be placed in a bottle, or earthen jar or vessel, and it will keep indefinitely.
The Soldering Iron.—A large iron is always better than a small one, particularly for the reason that it will retain its heat better. This should always be kept tinned, which can be done by heating and plunging it into the soldering solution, and the solder will then adhere to the iron and cover the point, so that when the actual soldering takes place the solder will not creep away from the tool.
By a little care and attention to these details, the work of uniting metals will be a pleasure. It is so[p. 120] often the case, however, that the apparatus for doing this work is neglected in a shop; the acid is allowed to become dirty and full or foreign matter, and the different parts separated