Solder, such as used by the plumber, is composed of lead and tin.
The proportions in which these two metals are used vary considerably with the use to which it is to be put.
The plumber requires both bright solder and wiping solder, the proper consistency of the latter being a matter of great importance to him in the making of wiped joints. Bright solder is made of one part lead and one part tin.
The proportions for wiping solder are not so definite as for bright solder, as different workmen are accustomed to different degrees of fineness in their wiping solder. In general, however, the proportions may be laid down as three parts of lead and two parts of tin. Ten parts of lead and six parts of tin is a proportion sometimes used. Many of the best workmen make their own wiping solder, such a course enabling them to obtain solder that is suited to their individual requirements.
Nothing but the purest grades of lead and block tin should be used.
A test used by some plumbers to prove wiping solder, is to pour a small quantity of the melted metal onto a cold surface, when, if it is of about the right quality, it will have when cool a mottled appearance.
If it is too coarse - that is, if it has too much lead, it will have a granular appearance. If it is too fine - that is, if it has too much tin, it will have a very bright appearance.
While lead melts at about 612 degrees and tin at 442, the melting point of wiping solder is about 450 degrees, and of bright solder about 375 degrees.
There are certain substances which act very injuriously to wiping solder.
For instance, the presence in a pot of wiping solder of a very small amount of zinc, will make it entirely unfit for use.
Antimony and iron are also injurious.
The greatest amount of trouble, however, arises from the presence of zinc, for this metal is used extensively in the manufacture of plumber's brass work, such as bibbs, ferrules, nipples, solder unions, etc., and in wiping these fittings onto lead pipes, more or less of the zinc is taken up by the solder. This is especially true in the use of the cheaper grades of ferrules and nipples, which often contain large amounts of zinc. It is a customary practice of the plumber to dip his brass work into the wiping solder, in order to tin it, and this is one of the quickest ways in which the solder may be spoiled.
The experienced plumber can usually tell very quickly whether there is zinc in his wiping solder, as it works up roughly and crystallizes in a different manner than good solder. Solder is also often damaged by carelessly overheating it. This burns out the tin and leaves the solder coarse.
When impurities are known to be present, the solder may be purified in the following manner: Heat the solder red hot in the first place. If the solder is heated so as to appear red hot in the light, it is too hot, and should be heated only so that it shows a faint red in the dark. When this heat has been reached, throw into the solder a lump of sulphur, which will mix with the impurities of the solder when it is stirred, and carry them to the surface. Any oxidized tin or lead formed in overheating will also separate out in the form of a powder and rise to the surface. The impurities should be thoroughly skimmed off with the ladle, and after the solder has somewhat cooled, it is well to throw in some tallow, which will liberate the sulphur, and also a lump of rosin, which will further improve it.
After this refining process has been completed, the metal will usually be too coarse, owing to the burning out of some of the tin. Therefore the solder should be tempered with new metal until it has regained its right consistency.
When wiping solder is being used it should be stirred occasionally, in order to thoroughly mix the lead and tin, for the latter being the lighter, tends to rise to the top.