In treating of soft solders, it was shown that the fusing point of these compositions varies considerably. The variations are still greater in the case of hard solders, whose composition is such that they melt only on being brought to strong red heat. Some of them can be melted in the ordinary way, with the aid of a soldering iron, while in the case of others, a special apparatus, such as a bellows, must be employed, or the whole object to be soldered must be strongly heated. The numerous kinds of hard solders, with different fusing points, are made necessary by the difference in the nature of the various metals and metallic compositions which may require soldering.

If metals are to be soldered which are very difficult of fusion, brass itself may be used directly as a solder; a very hard solder may he made by melting brass and mixing in copper. There are numerous formulas for hard solders, hut not all of them are reliable; a few will he given here, all of which have been well tested and found excellent. The hardest are given first.

Yellow Hard Solders (Very Hard) Appelbaum's Compositions

I.

Copper ..................................... 58

Zinc ....................................... 42

II.

Sheet brass ................................. 85.42

Zinc ....................................... 13.58

Karmarsch's Composition III

Brass ...................................... 7

Zinc ....................................... 1

P'Rechtl's Composition

IV.

Copper .................................... 53.30

Zinc ....................................... 43-10

Tin ........................................ 1.30

Lead ...................................... 0.30

The foregoing compositions have the yellow color of brass, are very strong, and require very high temperatures for melting, so that they can be used for copper, bronze, steel, and all kinds of iron. The ones next given melt more easily than the first, and are suitable for all kinds of work with brass.

I.

Sheet brass................................. 81.1 2

Zinc ....................................... 18.88

II.

Copper ..................................... 54.08

Zinc ....................................... 45.29

III.

Brass....................................... 3 to 4

Zinc....................................... 1

IV.

Brass ...................................... 78.26

Zinc ....................................... 17.41

Silver ..................................... 4.33

IV. is somewhat expensive on account of the silver, but has the valuable property of being at once tenacious and ductile, and can be worked into wire with hammer or rollers.

Still softer are:

I.

Brass ...................................... 5

Zinc ....................................... 2.5

II.

Brass.................................. 5

Zinc....................................... 5

Half-White

I.

Copper..................................... 53.3

Zinc ..'..................................... 46.7

II.

Brass...................................... 12

Zinc....................................... 4 to 7

Tin........................................ 1

III.

Brass ...................................... 22

Zinc ..................................... 10

Tin ........................................ 1

IV.

Copper ................................... 44

Zinc ...................................... 49

Tin ........................................ 3.20

Lead ...................................... 1.20

I. (Yolk's hard solder) and IV. (Prechtl's half-white) are quite readily fusible.

While

I.

Brass ...................................... 20

Zinc....................................... 1

Tin........................................ 4

II.

Brass ...................................... 11

Zinc....................................... 1

Tin........................................ 2

III.

Brass ...................................... 6

Zinc ....................................... 4

Tin........................................ 10

IV.

Copper .................................... 57.44

Zinc ....................................... 27.98

Tin ........................................ 14.58

A. Krupp, in his excellent work, gives the following table of the compositions of hard solders, all of which have been verified in practice. The proportions are given in percentage. The terms "hard" and "soft" refer, of course, to the respective degrees of fusibility, being simply comparative, as the whole class of solders which we are now considering are called in general "hard."