The solders thus classified, as their name implies, are used principally for soldering German silver. This alloy contains nickel and is very hard and white, and it requires solders which have corresponding qualities. German silver belongs among the alloys which are very difficult of fusion, and the solders used for it are those which have very high fusing points, and belong therefore to the general class of hard solders. They have great strength, and are used for other purposes, in cases where the object to be soldered is exposed to heavy strain. German silver solder can be given a color very much like that of steel, and is much used in steel work.

In regard to its composition, it bears this relation to ordinary hard solders, that while these may be considered to be brass with an admixture of zinc, German silver solder may be called a mixture of zinc and German silver. It is softer or harder according to the greater or less amount of zinc contained in it; but if this exceeds a certain limit, the solder becomes very brittle.

There are two principal varieties of German silver solder, called, relatively, hard and soft. The former is exceedingly strong, on account of the large amount of nickel it contains, and is sometimes called "steel solder," being quite generally used for soldering steel.

Soft German Silver Solders

I.

Copper ...................................... 4.5

Zinc........................................ 7.0

Nickei...................................... 1.0

II.

Copper ..................................... 35.0

Zinc........................................ 56.5

Nickel...................................... 8.5

III

German silver ............................... 5

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

I. and II. are quite similar in composition, and have correspondingly similar properties; in III., German silver, that is, a compound of copper, zinc, and nickel, is used directly, and in preparing this solder it is necessary to know the exact composition of the alloy, or to try the solder in small quantities, in order to judge of the correct amount of zinc to be added. It may be assumed that the proportions are correct, when the metallic mixture is lustrous, and brittle enough to allow of pulverizing when hot, and when it will become fluid in contact with a red hot soldering iron.

Hard German Silver Solders (Steel Solders)

I.

Copper ...................................... 35

Zinc ....................................... 56.5

Nickel ...................................... 9.5

II.

Copper ..................................... 38

Zinc ........................................ 50

Nickel ...................................... 12

I. requires a very hot flame for melting, and II. can usually be melted only by applying bellows to the flame.

In preparing German silver solder by direct melting together of the three metals, the copper is first to be melted, then the zinc and nickel added simultaneously. It can also be made by melting German silver together with zinc, a method which is not only more convenient, but has other advantages, especially if the solder is needed only in small quantities. The temperature required for melting this solder is so high that some of the zinc, which is very volatile, will evaporate if used pure, and it is difficult to obtain a mixture containing the proper amount of zinc.

The German silver is first melted, and heated very hot, and about six-tenths of the quantity of zinc is then thrown in. The. melted mass is immediately stirred with an iron rod and a sample of it is taken out, by means of an iron spoon with a beak, and poured upon a cold stone or iron plate. As soon as it has stiffened, it is put into a mortar to be pulverized. If a few vigorous strokes will accomplish this, the alloy is of the right composition; but if it cannot be pulverized, there is too little zinc. If, on the other hand, the alloy is so brittle, while still hot, that a blow of a hammer will break it to pieces, and if it is very easily powdered in the mortar, an excess of zinc is indicated, and it will not only be too soft, but lose in strength. Too much zinc is also shown by a very high luster.

More zinc can be added as required, and if there is already too much, this can be remedied in either of two ways; either the alloy is kept a long time in fusion, so that a certain quantity of zinc evaporates, or more German silver is added-. This method is preferable, as it saves consumption of fuel, and no zinc is lost. The German silver should be added in the form of filings, as it is obtained from the manufactories of German silver articles, in order to insure quick and thorough mixture. The filings are to be scattered over the alloy, and stirred in with a hardwood stick. When this is dipped into the melted mass, the wood begins to decompose, on account of the great heat, and gases are developed which have a reducing effect, and cause an intimate mixture of the constituents.

In soldering German silver articles, which are not to be exposed to very high temperatures, the soft German silver solders are generally used, and the correct composition is hardly to be distinguished from the German silver itself, since the color is nearly the same. The solder is employed in the form of a fine powder, which has the advantage that it can be applied quickly and no more used than necessary.

It is best to heat the mortar, in which the solder is pulverized, very hot, and to pour out the melted solder upon a large iron plate, in a thin layer, which is at once broken in pieces with a hammer and thrown into the mortar. The powder, which will be in grains of uneven size, is put through a hair sieve, and the fine portions are used for solder, the larger particles being ground over again.

The process of pulverizing German silver solder, as just described, is a very troublesome one, as it not only requires a great expenditure of strength, on account of the tenacious nature of the alloy, but must be done within a short time, that is. while the metal is still hot. The following method of preparing the powder is preferable:

A cast-iron mold is made, in two parts exactly fitting together, and allowing the casting of a cylinder 20 or 30 centimeters long and 8 or 10 in diameter. This cylinder is rubbed on the inside with oil and lampblack, to prevent the alloy from adhering, and filled with the metallic mixture. After it has become entirely cold the cylinder is placed in a mechanical turning lathe, and the turning chisel so adjusted that very fine filings are shaved off, which are then heated and pulverized. The cylinder may also be pressed against a rapidly-revolving steel disk, cut like a file, and the filings procured in this way.