Fusible Metal. Tin, bismuth and lead are metals which melt at comparatively low temperatures; and it has been shewn that the alloys of any two of them usually melt at lower temperatures than the mean, or even than the lower extreme. By analogy it might be inferred that an alloy of tin and lead fused with one of tin and bismuth, would melt below either of the two ingredients. It has been shewn that proportions of bismuth and lead of easiest fusion are 2 atoms bismuth with one of lead; this alloy melts at 250°. An alloy of 2 atoms of bismuth and 1 of tin melts at 260°; and so does that of 1 atom bismuth and 1 tin. These alloys being much more easily fused than any other proportions of these metals, it is from their combinations we are to expect a still further reduction of the fusing point. In fact, a combination of either of the tin and bismuth alloys, with the lead and bismuth alloy, produces almost exactly the same reduction of the fusing temperature.
Thus if 4 atoms of bismuth, 1 of tin and 1 of lead be fused together, the compound melts in boiling water or below 212°. It is equally the case if 3 atoms bismuth, 1 of tin and 1 of lead, are fused together.
The double alloy next to those above mentioned in regard to easy fusion is that of 2 atoms tin, and 1 bismuth. It fuses at 320°. This alloy, united to the one of 2 atoms bismuth and 1 lead, gives a compound of 3 atoms bismuth, 2 tin and 1 lead, which fuses very nearly at the same temperature as the above triple alloys.
In reference to weights, the above proportions for the most fusible metals will nearly be,
| Bismuth | 14 | parts | - | Lead | 5 | — tin | 3 |
| ——— | 10 | — | - | — | 5 | —— | 3 |
| ——— | 5 | — | - | — | 2½ | —— | 3 |
Most of the elementary books have given the proportions of 8 bismuth, 5 lead and 3 tin; or 5 bismuth 2 lead and 3 tin, which nearly agree with some of the above, and give an alloy fusing below 212°.
Wishing to investigate this subject more fully, and it being obvious from the preceding facts that there are only two proportions of tin and lead to be united with bismuth, to produce the desired effect, namely, either 1 atom of tin with 1 of lead, or 2 atoms of tin with 1 of lead, I proceeded as follows:
1 atom tin (52) + 1 atom lead (90) + 1 atom bismuth (62), were fused together; the fusing point was 270°. The alloy was flexible to a certain degree; and the fracture very small grained. To this alloy 31 grains of bismuth were added successively till it was evident the alloy was growing less fusible; the results were as follows:
| 1 | atom tin | + | 1 | lead | + | 1 | bismuth; | fuses at | 270° | semi fluid. |
| 1 | ——— | + | 1 | —— | + | 1½ | —— | —— | 235° | |
| 1 | ——— | + | 1 | —— | + | 2 | —— | —— | 205° | |
| 1 | ——— | + | 1 | —— | + | 2½ | —— | —— | 200° | |
| 1 | ——— | + | 1 | —— | + | 3 | —— | —— | 197° | |
| 1 | ——— | + | 1 | —— | + | 3½ | —— | —— | 200° | |
| 1 | ——— | + | 1 | —— | + | 4 | —— | —— | 220° | |
| 1 | ——— | + | 1 | —— | + | 4½ | —— | —— | 205° | |
| 1 | ——— | + | 1 | —— | + | 5 | —— | —— | 240° | semi fluid. |
| but it retains a little fluidity down to nearly 200° | ||||||||||
From this it appears that 3 parts by weight of tin, 5 of lead, and any proportion of bismuth from 7 to 14 will produce an alloy fusing below 212°; but of these the best is 10 or 11 parts.