While many investigators have tried to form alloys of copper and manganese by combining them in the metallic state (that is to say, by the simultaneous reduction of their oxides), the Hensler Bros., of Dillenburg, have found it best to first prepare the metallic manganese and then to alloy it in proper proportions with other metals. Their method consisted of reducing the pure pyrolusite in large plumbago crucibles, in the presence of carbon and an extra basic flux; the operation was carried on in a strong coke fire, and at the end of about six hours the crude manganese is poured out, having the following composition:
| Manganese | 90 | to | 92 |
| Carbon | 6 | to | 6.5 |
| Iron | 0.5 | to | 1.5 |
| Silicon | 0.5 | to | 1.2 |
By refining, the manganese can be brought up to 94 to 95 per cent. of purity. It is from this casting of pure manganese that is obtained the substance used as a base for the alloys. This metal is white, crystalline, when exposed to the damp air slowly oxidizes, and readily combines with copper to form the cupro-manganese of the variety having the composition—
| Copper | 70 |
| Manganese | 30 |
Cast in ingots or in pigs it becomes an article of commerce which may be introduced in previously determined proportions into bronze, gun metal, bell metal, brass, etc. It may also be used, as we have already mentioned, for the refining of copper according to Manhès's process.
Tests made from this standpoint at the works of Mansfield have shown that the addition of 0.45 per cent. of cupro-manganese is sufficient to give tenacity to the copper, which, thus treated, will not contain more than 0.005 to 0.022 of oxygen, the excess passing off with the manganese into the scorias.
On the other hand, the addition of cupro-manganese is recommended, when it is desirable to cast thin pieces of the metal, such as tubes, caldrons, kitchen utensils, which formerly could only be obtained by beating and stamping.
The tenacity obtained for tubes of only three centimeters in diameter and 1.75 millimeters in thickness is such that they are able to withstand a pressure of 1,100 pounds to the square inch.
The manganese bronze, which we have previously referred to, and which is used by the White Brass Company of London, is an alloy of copper, with from one to ten per cent. of manganese; the highest qualities of resistance, ductility, tenacity, and durability are obtained with one to four per cent. of manganese, while with twelve per cent. the metal becomes too weak for industrial uses.
| Manganese bronze. | Copper. | Manganese. | Weight of fracture in kilos per square mm. | Elongation |
|---|---|---|---|---|
| A | 96.00 | 4.00 | 19.00 | 14.60 |
| B | 95.00 | 5.00 | 20.62 | 10.00 |
| C | 94.00 | 6.00 | 20.80 | 14.60 |
| D | 90.00 | 10.00 | 16.56 | 5.00 |