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fill out the molds, without the formation of blowholes, and present no difficulties in casting.
Cupromanganese is suitable for many purposes for which nothing else but bronze can advantageously be used, and the cost of its production is no greater than that of genuine bronze. In preparing the alloy, the copper is used in the form of fine grains, obtained by pouring melted copper into cold water. These copper grains are mixed with the dry oxide of manganese, and the mixture put into a crucible holding about 66 pounds. Enough space must be left in the crucible to allow a thick cover of charcoal, as the manganese oxidizes easily. The crucible is placed in a well-drawing wind furnace and subjected to a strong white heat. The oxide of manganese is completely reduced to manganese, which at once combines with the copper to form an alloy. In order to prevent, as far as possible, the access of air to the fusing mass, it is advisable to cover the crucible with a lid which has an aperture in the center for the escape of the carbonic oxide formed during the reduction.
When the reduction is complete and the metals fused, the lid is removed and the contents of the crucible stirred with an iron rod, in order to make the alloy as homogeneous as possible. By repeated remelting of the cupromanganese a considerable quantity of the manganese is reconverted into oxide; it is, therefore, advisable to make the casts directly from the crucible. When poured out, the alloy rapidly solidifies, and resembles in appearance good German silver. Another reason for avoiding remelting is that the crucible is strongly attacked by the cupromanganese, and can be used but a few times.
The best kinds of cupromanganese contain between 10 and 30 per cent of manganese. They have a beautiful white color, are hard, tougher than copper, and can be worked under the hammer or with rolls. Some varieties of cupromanganese which are especially valuable for technical purposes are given below:
| I | II | III | IV | |
|---|---|---|---|---|
| Copper | 75 | 60 | 65 | 60 |
| Manganese | 25 | 25 | 20 | 20 |
| Zinc | — | 15 | 5 | — |
| Tin | — | — | — | 10 |
| Nickel | — | — | 10 | 10 |
Manganin.
—This is an alloy of copper, nickel, and manganese for electric resistances.
Mirror Alloys:
Amalgams For Mirrors.
—I.—Tin, 70 parts; mercury, 30 parts.
II.—For curved mirrors. Tin, 1 part; lead, 1 part; bismuth, 1 part; mercury, 9 parts.
III.—For glass balls. Tin, 80 parts; mercury, 20 parts.
IV.—Metallic 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