Page:Popular Science Monthly Volume 27.djvu/556

538 ground as ordinary wires do, but, by virtue of their high elasticity, will spring back and coil up close to the standards.

It has long been known that the hardness of bronze could be increased by adding iron to it, but that quality appears to be acquired at the expense of ductility and toughness, and for that reason, probably, such alloys have never come into general use. Mr. Alexander Parkes, and the late Mr. J. D. Morries Stirling, were probably the first to propose and carry into practice the use of manganese for improving the quality of bronze. Mr. Parkes combined manganese alone with copper, and used this alloy to form improved alloys of brass and yellow metal, of which to make sheathing, rods, wire, nails, and tubes. Mr. Stirling, in 1848, proposed to employ manganese in various brass alloys in which iron was present; and a metal introduced by him was used for some time in railway-carriage bearings. It, however, lacked strength, hardness, and ductility, and has long since been superseded.

A manganese-bronze having all the requisites of a useful alloy was introduced in 1876 by Mr. P. M. Parsons. It is prepared by mixing a small proportion of ferro-manganese with copper, after which various alloys are formed. The ferro-manganese is melted in a separate crucible, and is added to the copper when in a fluid state. The effect of this combination is similar to that produced by the addition of ferromanganese to the decarburized iron in a Bessemer converter. According to Mr. Parsons, while a part of the manganese cleanses the copper of any oxides it may contain by combining with them and forming a slag, another part, with the iron, becomes permanently combined with the copper, whereby the strength, hardness, and toughness of the compound are modified, according as the proportions of the constituents are varied. Five different qualities of manganese-bronze are made. In the number one quality the zinc alloyed with the copper is considerably in excess of the tin. It may be worked hot or cold, and has great tensile strength and elasticity. Manganese-bronze number two is stronger, and can be cast in sand for special purposes where strength, hardness, and toughness are required; but it has to be melted in crucibles. One of its most important applications is to the production of articles cast in metal molds under pressure; and the articles thus made have the strength, toughness, and hardness of cast-steel, without any of its defects. It is perfectly homogeneous, and, while not possessing a fibrous texture derived from rolling or hammering, is still fibrous in character, in all directions alike, and, when broken, shows a beautiful silky fracture. It can be cast upon any object, on which it will shrink with a force equal to its elastic limit, and, when released, will show an amount of resilience about double that of steel. Its hardness is about equal to that of mild steel.

The number three quality is composed chiefly of copper and tin in about the same proportions as gun-metal, combined with a large percentage of ferro-manganese. Its chief characteristics are great