Soft solder is applied in several different ways.

For joints in lead the surfaces to be soldered are carefully cleaned and covered with tallow - the space around is smeared with a mixture of size and lampblack, called soil, to prevent the solder from adhering - melted solder is then poured on and the excess wiped off with a cloth or in other ways.

In joining thin sheets of tinned iron, zinc, copper, and other metals, the edges are cleaned and sprinkled with powdered rosin; a tinned copper bolt or soldering iron is made hot and applied so as to heat the edges of the plates; the stick of solder is at the same time forced against the bolt, and the solder as it melts is dropped into the joint.

The copper bolt is also used to supply the heat in soldering light work in lead, such as lattices. The soldering iron cannot be used for thick pieces of metal, as it will not impart sufficient heat to their edges.

Wben joints are to be made between thicker pieces, the latter must have their surfaces first tinned separately and then the solder run in between them.

A blowpipe flame is sometimes used as the source of heat in soldering the metals.

1 Seddon.

2 Bloxam.

Solder for use with the copper bolt is cast in strips called "strap-solder," or in thin cakes for gasfitter's work.1

Table Showing The Proportions Of Ingredients Of Different Solders - Melting Points - Purposes For Which Used

Description of solder.

Constituents and their melting points.

Uses.

Tin.

Lead.

Zinc

Copper.

Bismuth.

Silver.

Anti-many.

Melting point of solder,

Fahr.

446°

617°

773°

2000°

507°

1873°

1150°

Hard Solders. Brazing -

Very fine .

2

...

...

...

...

..

1

..

Fine . . .

1

..

3

4

..

..

..

..

Spelter - soft .

...

...

1

1

..

..

.....

For ordinary brass work.

Do. hard. Silver solders -

...

...

2

3 to 6

...

...

...

••

For copper, iron, and steel.

Hardest.

..

..

...

1

...

4

..

..

For silver, copper, and brass.

Harda . .

...

..

1a

..

3

..

..

Soft . . .

...

..

...

1

..

2

..

...

Soft Solders. Plumber's -

Fine. . .

1

1-1 1/2

..

..

..

..

..

385

Ordinary * .

1

2

...

...

441°

For lead work, cisterns, jointing pipes.

Coarse solder Tinman's -

1

3

..

..

..

..

..

482°

Used with copper soldering bolt.

Ordinary solder

2

1

..

...

..

..

..

340°

Very fusible do.

4

1

..

..

..

..

...

320°

Pewterer's - Fine . . .

2

1

..

..

1

..

..

201°

Used by pewterers.

a The brass is put into the melted silver, or the zinc would evaporate. One brass wire instead of one copper witli 2 silver is used for soldering silver.

b Also called "pot metal;" is assayed by the Plumbers' Company, stamped as genuine, and sold in ingots, hence called "Plumber's sealed solder."

Fluxes

The fluxes used are as follows : - For hard soldering - Borax.

For soft soldering - (with solders of about 2 tin, 1 lead) - the flux is varied according to the metals to be united, as shown below : - 1

Metals.

Fluxes.

Cast-iron, malleable iron, steel .

Borax or Sal ammoniac.2

Copper, brass, gun-metal .

Sal ammoniac, chloride of zinc, or rosin.

Tinned iron .....

Chloride of zinc or rosin.

Zinc ......

Chloride of zinc.

Pewter ......

Gallipoli oil.

Lead with coarse solder .

Tallow.

„ fine solder

Rosin.

Soldering fluid is a concentrated solution of chloride of zinc.

1 Seddon.

2 Ammonium chloride.