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, 4.6S 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; (/) 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 Brasswork

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

For Copper

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

Hard Solder

Hard solder 86.5 copper, 9.5 zinc, 4 tin.

Hard Solder For Gold

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

Hard Silver Solder

Hard silver solder (a) 4 parts silver, 1 copper; (b) 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 b, but will not "burn," is as fluid as water, and makes a far sounder joint.

Hard Spelter Solder

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

For Jewellers

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

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

For Pewterers

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

For Pewterers 148

For Sealing Iron In Stone

For sealing iron in stone 2 lead, 1 zinc.

For Sealing Tops Of Canned Goods

For sealing tops of canned goods 1 1/4 lb. lead, 2 lb. tin, 2 oz. bismuth; the lead 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

Soft solder 1 lead, 2 tin.

Soft Solder For Joining Electrotype Plates

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

For Steel

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

For Tinned Iron

For tinned iron 7 lead, 1 tin.

The following table exhibits the composition and characters of a number of solders: -

No.

Name.

Composition.

Flux.

Fluxing point.

1

Plumbers' coarse solder

Tin 1, Lead 3 .. ..

R

800 F. (427 C.)

2

" sealed "

" 1 " 2 .. ..

R

441 F. (227 C.)

3

" fine "

" 1 " 1 .. ..

R

370 F. (188 C.)

4

Tinners' solder ........

" 1 1/2 " 1 .. ..

R or Z

334 F. (168 C.)

5

" fine solder ......

" 2 „ 1 .. ..

R or Z

340 F. (171 C.)

6

Hard solder for copper, brass, iron

Copper 2, zinc 1 ..

B

7

" " " "

Good tough brass 5, zinc 1

B

8

" " " " more fusible than 6 or 7 ...

Copper 1, zinc 1 ..........

B

9

Hard solder for copper, brass, iron

Good tough plate brass ..

B

10

Silver solder for jewellers ........

Silver 19, copper 1, brass 1

B

11

„ „ „ plating .. ..

„ 2, brass 1

B

12

„ „ „ silver, brass, iron

" 1 " 1 .. .........

B

13

„ „ „ steel joints

„ 19, copper 1, brass 1

B

14

„ „ „ more fusible

„ 5, brass 5, zinc 5 ..

B

15

Gold solder...........

Gold 12, silver 2, copper 4

B

16

Bismuth solder...........

Lead 4, tin 4, bismuth 1

R or Z

320 F. (160 C.)

17

" " ...............

" 3 " 3 " 1

R or Z

310 F. (154 C.)

18

" " ........

" 2 " 2 " 1

R or Z

292 F.(144C.)

19

" " .........

" 2 " 1 " 1

R or Z

236 F. (113 C.)

20

" " ...........

" 3 " 5 " 3

R or Z

202 F. (94 C.)

21

Pewterers' solder .........

" 4 " 3 ,, 2

R or Z

Abbreviations : R, Rosin; B, Borax; Z, Zinc Chloride.

Advantage may be taken of the different degrees of fusibility of the solders in the table to make several joints in the same piece of work. Thus, if the first joint has been made with fine tinners' 3older, there would be no danger of melting it in making a joint near it with bismuth solder No. 16, and the melting-point of both is far enough removed from No. 19 to be in no danger of fusion during the use of that solder. Soft solders do not make malleable joints. To join brass, copper, or iron, so as to have the joint very strong and malleable, hard solder must be used. For this purpose, No. 12 will be found excellent; though for iron, copper, or very infusible brass, nothing is better than silver coin, rolled out thin, which may be done by any silversmith or dentist. This makes decidedly the toughest of all joints, and, as a little silver goes a long way, it is not very expensive. To obtain hard solders of uniform composition, they are generally granulated by pouring them into water through a wet broom. Sometimes they are cast in solid masses, and reduced to powder by filing.

Nos. 10, 11, 12, 13, 14, and 15 are generally rolled into thin plates, and sometimes the soft solders, especially No. 21, are rolled into sheets, and cut into narrow strips, which are very convenient for small work that is to be heated by lamp. Hard solders, Nos. 6, 7, 8, and 9, are usually reduced to powder, either by granulation or filing, and then spread along the joints after being mixed with borax which has been fused and powdered. It is not necessary that the grains of solder should be placed between the pieces to be joined, as with the aid of the borax they will sweat into the joint as soon as fusion takes place. The best solder for platinum is fine gold. The joint is not only very infusible, but is not easily acted upon by common agents. For German silver joints, No. 14 is excellent.

When brass is soldered with soft solder, the difference in colour is so marked as to direct attention to the spot mended. The following method of colouring soft solder is given by the Metallarbeiter: First prepare a saturated solution of copper sulphate (bluestone) in water, and apply some of this on the end of a stick to the solder. On touching it with a steel or iron wire it becomes coppered, and by repeating the experiment the deposit of copper may be made thicker and darker. To give the solder a yellower colour, mix 1 part of a saturated solution of zinc sulphate with 2 of copper sulphate, apply this to the coppered spot, and rub it with a zinc rod. The colour can be still further improved by applying gilt powder and polishing. On gold jewelry or coloured gold, the solder is first coppered as above, then a thin coat of gum or isinglass solution is applied, and bronze powder is dusted over it, which can be polished after the gum is dry, and made very smooth and brilliant; or the article may be electroplated with gold, and then it will all have the same colour.

On silverware, the coppered spots of solder are rubbed with silvering powder, or polished with the brush and then carefully scratched with the scratch-brush, then finally polished.