It is not proposed here to describe the operations connected with soldering of different kinds, but one or two points may be noticed with advantage.2

The surfaces to be united must be perfectly clean, and freed from oxide, which would prevent adhesion and the formation of an alloy between the solder and the metal.

As the surfaces when heated are very easily oxidised they must be protected at the time - this is done by means of a flux which covers the surface and protects them from the air.

The materials used for fluxes are mentioned at p. 353.

1 Bloxam's Metals.

2 Every particular connected with soldering of all kinds is fully described in Holtzapffel's Mechanical Manipulation, whence much of the information here given has been taken.

Hard Solders - Of these there are two kinds in common use.

Spelter Solder made of copper and zinc in proportions which differ according to circumstances (see Table, below).

It is generally granulated by pouring it when melted through a bundle of twigs into water.

This solder is used for making joints in iron, copper, brass, and gun-metal; the process is known as brazing.

Silver Solder is a mixture of silver with copper, or brass in varying proportions (see Table).

It is used for making fine and neat joints in iron, steel, brass, and gun-metal - to prepare the surface of metals for welding, also for joints in silver and other light-coloured metals.