Solders are divided, according to their fusibility and special uses, as follows:

1. Soft Solder, or Tin Solder. - Subdivisions of this class are pure tin solder and the so-called" bismuth solder. Soft solder is the most fusible kind, requiring, therefore, the least heat for soldering. As a matter of fact, soft solders can be prepared which will melt at a heat below the boiling point of water.

2. Hard Solder. - Some very different substances are brought together under this name; but the one distinguishing characteristic of the group is that all its members have a considerably higher fusing point than the soft solders, and thus can be used in soldering articles which are to be exposed to higher temperatures. The principal varieties of hard solder are:

Copper solder. Brass solder, with its varieties known as hard and soft brass solder, white, half-white, and yellow-white solder. German silver solder. White nickel solder. Soft and hard silver solder. Gold solder. Enameling solder. Aluminium solder.

Several of these solders can be used for soldering other metals than those which the name indicates. It would be entirely possible, for example, to solder German silver with hard brass solder; but as this is yellow and German silver white, the seams would show and give the article a bad appearance.

To have the color of the solder as nearly as possible the same as that of the metal to be soldered, metallic mixtures are used, and it is also an object, as far as practicable, that the alloy should have similar properties. It is apparent that a large number of different solders are necessary, to correspond with the number of different metals and alloys.