49. Solder is an alloy of two or more metals. When melted, it adheres strongly to the clean surfaces of the other metals less fusible. Solders are hard or soft, according to their relative fusibility. The following table gives the compositions and fusing points of different varieties:

Table 3. Compositions And Fusing Points of Solder

Hard.

Soft.

Kind.

Zinc.

Copper.

Silver.

Tin.

Lead.

Bismuth.

Fusing Point

Spelter, hardest....

1

700°

Spelter, hard.....

2

3

550°

Spelter, soft................

1

1

Spelter, fine......

2

2

1/4

Silver, hard..............

1

4

Silver, medium....

1

3

Silver, soft......

1

2

Plumbers', coarse...

1

3

480°

Plumbers', ordinary........

1

2

441°

Plumbers', fine....

2

3

400°

Tinners'.......

1

1

370°

For tin pipe.....

3

2

330°

For tin pipe......

4

4

1

50. When solder becomes impure from use, it may be restored by heating it to 800°, and adding some sulphur, the mixture being well stirred. The sulphur, combining with the oxides and wastes of the metals, comes to the surface, where it can be skimmed off. By cooling to 400°, and putting in a little tallow to remove the sulphur, and adding tin, the proper quality may be restored.

Too much lead in solder produces a cellular joint and prevents its sweating properly.

Solder may be tested by melting, when, if a great many bright spots appear floating on top, it must be considered too soft or fine, while if the spots are totally absent, it contains too much lead. Tin spots about 3/8 of an inch in diameter indicate good solder.

51. Fluxes are used to aid in the fusion of solder, and to clean the surfaces of metals to be joined. Those commonly used, and the metals to which they are applied, are as follows:

Flux.

Metals to be Joined.

Rosin................

Lead, tin, or tinned metals; used with blowpipe.

Tallow......

Copper and iron; used with blowpipe or bit.

Sal ammoniac .........

Dirty zinc; used with copper bit.

Muriatic acid or Hydrochloric acid. .

Clean zinc, copper, tin, or tinned metals; used with bit or blowpipe.

Chloride of zinc ..

Lead and tin tubes; used with copper bit or blowpipe.

Borax................

Iron, steel, copper; used with blowpipe.

52. The melting points of the metals used in roofing are given in the following table:

Table 4

Metal.

Melting Temperature.

Tin............................................

446o

Copper.........................................

2,100°

Zinc...........................................

680°

Lead...........................................

626°

Wrought iron....................................

2,732°

The fusing point varies greatly, according to the purity of the metal, while the fusing points of alloys vary with their composition.