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E. van der Ven1 conducted a series of experiments to determine the value of phosphor-bronze and silicon-bronze for electrical purposes, chiefly as materials for telephone wires, and came to the conclusion that phosphor-bronze has about 30 per cent of the conductivity of copper, and siliconbronze about 70 per cent, while that of steel has only 10.5 per cent the conducting power of copper. Comparing their tensile strengths with that of steel, he finds that a steel wire, 2 millimetres diameter, with quadruple security, and the conventional "sag " of 0.7 millimetre, can have a stretch from pole to pole of 130 metres. The stretch of a phosphorbronze wire, 1 millimetre diameter, under the same conditions would be 106 metres, and for silicon-bronze 91 metres. These alloys, with a diameter of 1·18, and 0.77 millimetres respectively, have the same electrical resistance as a steel wire 2 millimetres diameter.

Silicon-bronze is valuable on account of its great strength and tenacity, high conductivity, and resistance to corrosion by atmospheric influences; and is therefore one of the very best mediums for transmission of electrical force. It can be made nearly as strong as steel, and yet possess treble its conductivity. The manufacture of this alloy has been greatly improved since its introduction, the latest kinds possessing less conductivity for electricity, but a higher tensile strength, which allows the wire to be more tightly stretched, and the supports wider apart. Wires of silicon-bronze are largely used on the continent for telephone purposes, and will stand the force of violent storms remarkably well, which is in some measure due to the small diameter of the conductor. In one case, at Rheims, a line having a span of 1000 feet was exposed to the action of the wind blowing directly across it, and stood the test admirably. The Italian General Telephone Company have employed silicon-bronze wires for some time without an accident occurring. Railway engineers have proved its efficacy for resisting a weight of snow in cold and hilly districts. When the wires have been 1 Musée Teyler, and Electrotech. Zeitsch. 1883.

covered with snow, and "sagged" considerably, they have immediately assumed their normal deflections when the snow has been removed. The poles of an Austrian railway company, using silicon-bronze, are from 328 to 720 feet apart across flat country, and from 160 to 500 feet apart in hilly districts. 1 Mr. Robey states that the blizzard, which did so much damage to telegraph wires in the United States in 1887, did not break those made of siliconbronze.

Silicon-copper and silicon-bronze are made, according to Weiller, the inventor of these combinations, in the following manner. He recommends the following proportions: potassium silico-fluoride 450 parts by weight, powdered glass 600 parts, common salt 250 parts, carbonate of soda 75 parts, carbonate of lime 60 parts, and dried chloride of calcium 500 parts. The mixture is heated in a covered plumbago crucible to a temperature a little below the point when they begin to act on each other, when the mixture is added to the molten copper or bronze, as the case may be; the reduced silicon combining with the metal or alloy.

The action of silicon on copper and bronze is similar to that of phosphorus. It acts as a deoxidiser, and the silica formed being an acid, is a valuable flux for any metallic oxides remaining unreduced. Silicon also enters into chemical combination with the alloy.

MANGANESE-BRONZE

§ 75. This is a new combination introduced by Mr. P. M. Parsons, to whom the author is indebted for much of the following information.2 Copper and iron unite at high temperatures in various proportions, forming alloys of great

1 Paper read before the Cleveland Inst. of Engineers, December 2 Brit. Assoc. Report, 1883.

1888.

hardness, and when the iron is present in certain proportions the tenacity and elasticity of the copper is increased. The same remarks apply to brass and bronze. It should be stated, however, that the above properties are acquired at the expense of ductility and toughness. The effect of iron being so decided, led some metallurgists to try the influence of manganese by reducing oxide of manganese with carbon in the presence of copper. Mr. Stirling and Mr. A. Parkes both used manganese to alloy with copper, brass, and other alloys. Mr. Everitt of Birmingham has introduced manganese into yellow-metal for sheathing and similar purposes.

No comparative experiments as to the strength, hardness, and ductility, or other qualities of these alloys, appear to have been published. The effect of manganese is to add somewhat to the ductility and toughness of copper alloys and allow copper, zinc, etc., of commoner quality to be used for definite purposes. In 1876 Mr. Parsons introduced his method of manufacturing manganese brass and bronze by mixing ferro-manganese with copper, and using this triple alloy for making various copper alloys, such as brass and bronze.

§ 76. Cupro-Manganese.--Copper and manganese unite in various proportions, forming alloys which may be red like copper, or silvery-white in colour, depending upon the amount of manganese present. They possess considerable hardness and tenacity, some are very ductile, and more fusible than ordinary bronze. They are distinguished by the property of soundness when cast into moulds, the castings being free from blow-holes. The great difficulty in producing alloys containing much manganese is owing to the great affinity that this metal has for oxygen, and the high temperature required for the reduction of manganese from its oxides, which are used as a source of the metal. This renders the production of homogeneous alloys, with a required amount of manganese, very difficult.

Pure oxide of manganese is not found in nature, at any rate only in rare cases: the most frequently occurring ore is pyrolusite, generally containing oxides of other metals, which are reduced along with the manganese and enter into the composition of the alloy. Pyrolusite is used for the manufacture of chlorine gas, and the bye product can be used to obtain oxide of manganese in a comparatively pure form, and this is employed for the production of cupro-manganese, by reducing it in contact with copper.

The copper is finely granulated, mixed with charcoal and dry oxide of manganese, in alternate layers in a plumbago crucible, and the whole covered with a thick layer of charcoal powder. A lid is then placed on to prevent admission of air, the crucible put into a wind-furnace, and exposed to the highest temperature of the same for some hours. The oxide is gradually reduced to the metallic state, and alloys with the copper forming cupro-manganese, which settles to the bottom of the crucible. When the operation is completed the pot is removed from the furnace, and the contents vigorously stirred with an iron rod to thoroughly incorporate the ingredients and produce a homogeneous alloy. The metal thus obtained is silver-white in colour, resembling German silver.

Cupro-manganese is considerably altered in composition by repeated remelting, the manganese being so readily oxidised, and as metallic manganese is not a commercial article, the metal cannot be added to make up the loss in the same way as zinc is added to brass. Moreover, the crucible is strongly attacked by oxide of manganese, which has a strong affinity for silica, forming a liquid slag. Alloys containing from 15 to 30 per cent of manganese have a white colour, are hard, very tough, and can be forged and rolled.

In making alloys of brass, bronze, or German silver containing manganese, the cupro-manganese must be rapidly melted under charcoal, and added to the alloy, then the whole well mixed and poured as soon as possible. The following are useful proportions :-

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$77. Cupro-ferro-Manganese.-Mr. Parsons prepares this alloy by mixing a certain proportion of ferro-manganese (an alloy of iron and manganese) with copper, and the product is afterwards made into alloys similar to bronze, brass, and other copper alloys. The ferro-manganese and the copper are melted in separate crucibles, and the ferro-alloy added to the copper. The effect of this combination is similar to that produced by the addition of ferro-manganese to the decarburised iron in the Bessemer converter. The manganese and iron in the metallic state, having a great affinity for oxygen, cleanse the copper of any oxides-it may contain, by combining with the oxygen, and rising to the surface, in the form of slag, and thus render the metal dense and homogeneous. A portion of the iron and manganese is utilised in this manner, and the remainder becomes permanently combined with the copper, and plays an important part in improving and modifying the quality of the bronze and brass alloys, afterwards prepared from the copper thus treated. The effect is greatly to increase their strength, hardness, and toughness, the degrees of all of which can be modified at will, according to the quantity of ferro-manganese used and the proportions of iron and manganese it contains. It will be seen from the above that this process of making manganese-bronze is altogether different from that previously described, and that iron is added in addition to manganese.

Another point of great importance which the inventor claims, is the nicety with which both the iron and

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