| Tin % | Lead % | Melting point (C.) |
|---|---|---|
| 10 | 90 | 303° |
| 20 | 80 | 278° |
| 30 | 70 | 255° |
| 40 | 60 | 230° |
| 50 | 50 | 205° |
| 60 | 40 | 187° |
| 63 | 37 | 175° |
| 70 | 30 | 185° |
| 80 | 20 | 198° |
| 90 | 10 | 215° |
Hardness of Solders.
—According to the before-mentioned authority, Saposhniko, in 1908, determined the hardness of various lead-tin alloys by Brineli’s method, by which a steel cone is forced into the metal. The results he obtained are as follow:
| Lead | 100 | 90 | 80 | 70 | 60 | 50 | 40 | 34 | 33 | 32 | 30 | 20 | 10 | 0 |
| Tin | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 66 | 67 | 68 | 70 | 80 | 90 | 100 |
| Hardness | 3·9 | 10·1 | 12·16 | 14·5 | 15·8 | 15·0 | 14·6 | 16·7 | 15·4 | 14·6 | 15·8 | 15·2 | 13·3 | 4·1 |
These results, says Mr. Hiorns, show that the hardest alloy is the one with 66% (about 2 parts) of tin and 34% (about 1 part) of lead, which also is the one having the lowest melting point of all the lead-tin alloys. The results also show that tin is slightly harder than lead.
Compositions of Soft Solders.
—As already shown, solders vary in fusibility according to their composition, and the choice should be determined by the nature of the work and the properties of the metal to be soldered. Should a solder be used of too high a melting-point, the metal will itself be fused before the solder begins to flow.
A point to be particularly observed is that the introduction of a foreign substance into the solder—for example, the addition of a little zinc to a pot of “very fine” solder—will utterly spoil it and render it unworkable. To remove zinc from solder, melt the solder in a pot, take it off the fire and stir in powdered sulphur or brimstone until the whole is of the consistency of wet sand. Replace the pot on the fire and melt, but do not stir the contents. The sulphur and zinc will rise to the surface and form into a cake. Now take the pot off the fire and carefully remove the cake without breaking by employing two pieces of hoop iron with bent ends.
It is false economy to use a rough solder for fine work on the score of cheapness, since more solder is required for a given job on account of the rough particles of solder clinging to the work; moreover, the rough appearance of the soldering may completely spoil the job.
The [table] on the opposite page gives the fluxes and the compositions of soft solders suited to a number of different metals.