cement. Copper, 30 parts; mercury, 70 parts.
V.—Mirror metal.—Copper, 100 parts; tin, 50 parts; Chinese copper, 8 parts; lead, 1 part; antimony, 1 part.
Reflector Metals.
—I.—(Cooper’s.) Copper, 35 parts; platinum, 6; zinc, 2; tin, 16.5; arsenic, 1. On account of the hardness of this alloy, it takes a very high polish; it is impervious to the effects of the weather, and is therefore remarkably {73} well adapted to the manufacture of mirrors for fine optical instruments.
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.
—Alloys consisting of 2 parts of copper and 1 of tin can be very brilliantly polished, and will serve for mirrors. Good speculum metal should have a very fine-grained fracture, should be white and very hard, the highest degree of polish depending upon these qualities. A composition to meet these requirements must contain at least 35 to 36 per cent of copper. Attempts have frequently been made to increase the hardness of speculum metal by additions of nickel, antimony, and arsenic. With the exception of nickel, these substances have the effect of causing the metal to lose its high luster easily, any considerable quantity of arsenic in particular having this effect.
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.
II.—Palladium 6 parts, gold 18, silver 11, and copper 13, gives a reddish-brown, hard, and very fine-grained alloy, suitable for the bearings of pivots in clock works.
The alloys of most of the other platinum metals, so called, are little used on account of their rarity and costliness. Iridium and rhodium give great hardness to steel, but the commercial rhodium and iridium steel, so called, frequently contains not a trace of either. The alloy of iridium with osmium has great hardness and resistance and is recommended for pivots, fine instruments, and points of ship compasses.
Palladium Silver.
—This alloy, composed of 9 parts of palladium and 1 of silver, is used almost exclusively for dental purposes, and is well suited to the manufacture of artificial teeth, as it does not oxidize. An alloy even more frequently used than this consists of platinum 10 parts, palladium 8, and gold 6.
Palladium Bearing Metal.
—This alloy is extremely hard, and is used instead of jewel bearings in watches. It is composed of palladium 24 parts, gold 72, silver 44, copper 92.
Platinum Alloys.
Platinum has usually been alloyed with silver in goldsmith’s work, 2 parts silver to 1 of platinum being taken to form the favorite “platinum silver.” The object has been to produce an alloy having a white appearance, which can be polished, and at the same time has a low melting point. In addition to this platinum alloy the following are well known:
I.—A mixture of 7 parts platinum with 3 parts iridium. This gives to platinum the hardness of steel, which can be still further increased by taking 4 parts of iridium.
II.—An alloy of 9 parts platinum and 1 part iridium is used by the French in the manufacture of measuring instruments of great resisting power.
Compounds of copper, nickel, cadmium, and tungsten are also used in the construction of parts of watches; the latter acquire considerable hardness without becoming magnetic or rusting like steel.
III.—For this purpose a compound of {74} 62.75 parts platinum, 18 parts copper, 1.25 parts cadmium, and 18 parts nickel is much recommended.
IV.—Very ductile platinum-copper alloys have also been made, e.g., the so-called Cooper gold, consisting of 3 parts platinum and 13 parts copper, which is almost equal to 18-carat gold in regard to color, finish, and ductility. If 4 per cent of platinum is taken, these latter alloys acquire a rose-red color, while a golden-yellow color can be produced by further adding from 1 to 2 per cent (in all 5 to 6 per cent) of platinum. The last-named alloy is extensively used for ornaments, likewise alloy V.
V.—Ten parts platinum, 60 parts nickel, and 220 parts brass, or 2 parts platinum, 1 part nickel and silver respectively, 2 parts brass, and 5 parts copper; this also gives a golden-yellow color.
VI.—For
