Alloys employed for joining metals together are termed "solders," and they are commonly divided into two classes: hard and soft solders. The former fuse only at a red heat, but soft solders fuse at comparatively low temperatures.

One of the most easily fusible metals is an alloy of 2 parts bismuth, 1 tin, and 1 lead; tin is the most fusible of these three metals, melting at 455° F. (235° C), but this alloy melts at 199 1/2° F. (93° C), or a little below the boiling point of water. By diminishing the quantity of bismuth in the alloy, the point of fusion may be made to vary between 212° F. (100° C.) and 329° F. (200° C), and thus it is an easy matter to form a solder which shall fuse at any required temperature between these limits, for electrical purposes, steam-boiler plugs, etc. The following are the best recipes for the common solders:-For aluminium-bronze: (a) 88.88 gold, 4. 68 silver, 6 • 44 copper; (b) 54• 4 gold,27 silver, 18.6 copper. (c) Melt 20 parts of aluminium in a suitable crucible, and when in fusion add 80 of zinc. When the mixture is melted, cover the surface with some tallow, and maintain in quiet fusion for some time, stirring occasionally with an iron rod.

Then pour into moulds. (d) 15 parts aluminium and 85 of zinc; (e) 12 aluminium and 88 zinc; (f) 8 aluminium and 92 zinc; all of these alloys are prepared as (c). The flux recommended consists of 3 parts copaiba balsam, 1 of Venetian turpentine, and a few drops of lemon-juice. The soldering - iron is dipped into this mixture.

For brass-work: (a) equal parts of copper and zinc; (b) for the finer kinds of work, 1 part silver, 8 copper, 8 zinc.

For copper: (a) 3 parts copper, 1 zinc; (6) 7 copper, 3 zinc, 2 tin.

Hard solder: 86. 5 copper, 9 . 5 zinc, 4 tin.

Hard solder for gold: 18 parts 18 carat gold, 10 silver, 10 pure copper.

Hard silver solder: (a) 4 parts silver, 1 copper; (6) 2 silver, 1 brass wire; these are employed for fine work; the latter is the more readily fusible; (c) equal parts copper and coin silver; requires higher temperature than 6, but will not " burn," is as fluid as water, and makes a far sounder joint.

Hard spelter solder: 2 parts copper; 1 zinc; this solder is used for iron-work, gun-metal, etc.

For jewellers: (a) 19 parts fine silver, 10 brass, 1 copper; (6) for joining gold, 24 parts gold, 2 silver, 1 copper.

Middling hard solder: 4 parts scraps of metal to be soldered, 1 zinc.

For pewterers: (a) 2 parts bismuth, 4 lead, 3 tin; (6) 1 bismuth, 1 lead, 2 tin; the latter is best applied to the rougher kinds of work.

For sealing iron in stone: 2 lead, 1 zinc.

For sealing tops of canned goods : 1 1/4 lb. lead, 2 lb. tin, 2 oz. bismuth; the head is melted first, the tin added next, and finally the bismuth stirred in well just before pouring. This makes a soft solder, and the cans do not take much heat to open them.

Soft solder: 1 lead, 2 tin.

Soft solder for joining electrotype plates: 67 parts lead, 33 tin.

For steel: 19 parts silver, 3 copper, 1 zinc.

For tinned iron: 7 lead, 1 tin.