II.—(Duppler’s.) Zinc, 20 parts; silver, 80 parts.
III.—Copper, 66.22 parts; tin, 33.11 parts; arsenic, 0.67 part.
IV.—Copper, 64 parts; tin, 32 parts; arsenic, 4 parts.
V.—Copper, 82.18 parts; lead, 9.22 parts; antimony, 8.60 parts.
VI.—(Little’s.) Copper, 69.01 parts; tin, 30.82 parts; zinc, 2.44 parts; arsenic, 1.83 parts.
Speculum Metal.
The real speculum metal seems to be a combination of the formula Cu4Sn, composed of copper 68.21 per cent, tin 31.7. An alloy of this nature is sometimes separated from ordnance bronze by incorrect treatment, causing the so-called tin spots; but this has not the pure white color which distinguishes the speculum metal containing 31.5 per cent of tin. By increasing the percentage of copper the color gradually shades into yellow; with a larger amount of tin into blue. It is dangerous to increase the tin too much, as this changes the other properties of the alloy, and it becomes too brittle to be worked. Below is a table showing different compositions of speculum metal. The standard alloy is undoubtedly the best.
| Copper | Tin | Zinc | Arsenic | Silver | |
|---|---|---|---|---|---|
| Standard alloy | 68.21 | 31.7 | — | — | — |
| Otto’s alloy | 68.5 | 31.5 | — | — | — |
| Richardson’s alloy | 65.3 | 30.0 | 0.7 | 2. | 2. |
| Sollit’s alloy | 64.6 | 31.3 | 4.1 | Nickel | — |
| Chinese speculum metal | 80.83 | — | — | 8.5 | Antimony |
| Old Roman | 63.39 | 19.05 | — | 17.29 | Lead |
Palladium Alloys.
I.—An alloy of palladium 24 parts, gold 80, is white, hard as steel, unchangeable in the air, and can, like the other alloys of palladium, be used for dental purposes.