The `bronzes* used in the economic arts are the three-metal or poly-metal alloys, made by adding other metals to the true copper-tin bronzes, and in several mixtures dispensing with the tin altogether. The metals chiefly in use in these alloys with bronze are lead, zinc, phosphorus, manganese and aluminum. In general, lead gives to bronzes a superior ma chining quality, and a dull bronzy polish highly esteemed in statuary. The lead alloy is called °plastic bronze.* Its ultimate lead content is 30 per cent — with copper, 65 per cent, and tin, S per cent. This bronze, though soft, stands up well in heavy locomotive bearings. There is some difficulty in making this due to the segregation of the metals, but this has been remedied by adding about 1 per cent of nickel. Zinc added to bronze gives greater ease in cold rolling and forging. In most maganese bronzes zinc takes the place of tin, so that these bronzes are really brasses. Examples of copper-tin zinc bronzes are the United States °Standard Bronze No. (copper, 88 per cent ; tin, 10 per cent, and zinc, 2 per cent), and °Admiralty gun metal* (copper, 86 per cent ; tin, 13 per cent, and zinc, 1 per cent). The addition of phos phorus to bronze imparts greatly increased hardness and wearing qualities, but if the proportion is not kept low the tensile strength and elastic limit are impaired. In the malleable phosphor-bronzes the top limit for tin is 8 per cent, and for phosphorus 0.8 per cent. The phosphorus alloys generally consist of about 90 per cent of copper, 9 of tin and from 0.5 to 0.75 of phosphorus. By varying the proportion of the constituents, the hardness, tenacity and elasticity of the alloy may be modified at pleas ure. Its special characteristics are resistance to corrosion by salt water, which affects all zinc alloys to some extent, its resistance under abrasion and its high qualities as a constructive material. • Great hardness and tenacity with little elasticity can be conferred on it for the making of ordnance, and hardness and tenacity combined with permanent elasticity can be given to it for the making of parts of machines, etc. In the elastic condition it is peculiarly well adapted for the bearings of machinery, since it produces very little friction. The standard phosphor-bronze used for bearings in railway cars is composed of 76.8 per cent of copper, 8 per cent of tin, 15 per cent of lead and 02 per cent of phosphorus. For large castings the pro portions are: Copper, 90 to 92 per cent; tin, 7.4 to 9.7 per cent; phosphorus, 0.3 to 0.6 per cent. For braiding the covering of submarine electric cables the proportions are: Copper, 92.9 per cent; tin, 6.55 per cent, and phosphorus, 0.32 per cent. The addition of phosphorus has another imrtant effect. When the proportion po exceeds 0.5 per cent it gives a warmer color to the bronze, making it resemble gold largely alloyed with•copper. This form is therefore largely used for works of art. Arsenic may be substituted for phosphorus in all the phosphor bronze formulas with practically the same effect. Manganese bronze, as has been noted, is really a form of brass. If it contains any tin at all, the amount is small. Iron is often added to this bronze to impart a high elastic limit. It has a low melting point and is readily cast into the most intricate forms. For sheets and forgings, manganese bronze carries 60 parts of copper, 39 parts of zinc and 2 parts of steel alloy; for sand casts, 56 parts copper, 43 parts zinc and 2 parts °steel alloy.' This &steel alloy° is com posed of tin, 29.03 per cent; wrought iron, 58.06
per cent, and of 80 per cent ferro-manganese, 12.91 per cent. Manganese bronze is classed as red and yellow: the red is composed of copper, 80 parts; tin, 10 parts, with 10 parts of a 20 per cent manganese-copper alloy. It is used for gear wheels; the yellow is composed of 50 parts of copper, 6 parts of 20 per cent manganese-copper and 44 parts zinc, and is used for gun mechanism, automobile castings, motor-boat shafts and propeller blades, as it is non-corrodible in sea water. It is also used for the vanes or blades in steam turbines where the erosive action of the steam is severe. A special type of this alloy is called °Naval Manganese Bronze*: it consists of copper, 57 per cent; zinc, 40 per cent; iron, 1 per cent; manganese, 0.75 per cent; aluminum, 0.75 per cent; tin, 0.50 per cent. A very fine bell metal is composed of copper, 90 parts; tin, 5 parts; zinc, 5 parts, and manganese, 1 part. °White Manganese Bronze)) is a quite different alloy: it contains copper, 68 per cent; manganese, 18 per cent ; zinc, 13 per cent, and aluminum, 1 per cent. The tensile strength of cold rolled man ganese bronze is 95,000 pounds per square inch; of castings, 70,000 pounds per square inch. aTurbandium Bronze' is the trade name for an alloy containing copper, 48 per cent; zinc, 46 per cent; iron, 1 per cent; manganese, 1.75 per cent; nickel, 2 per cent; tin, 0.5 per cent; alu minum, 0.2 per cent. It is non-corrodible by sea water and is especially valued for ships' pro pellers. Aluminum bronzes carry from 9 to 11 per cent of aluminum and are of a golden color. They are very viscous in the liquid state even at the highest temperature. They pour thick and sluggish, owing to a tenacious film of oxide of the aluminum which invariably covers the surface. For this reason they are poured very slowly and so as to enter the bot tom of the mold. In large castings risers are necessary to overcome the shrinkage of the alloy. The temperature should not be higher than from 100° ,to 150° above the setting tem perature of the alloy. Aluminum bronze has properties very similar to Swedish Bessemer steel, and withstands *fatigue from 9 to 15 times longer than the best manganese bronze. The addition of titanium tends to remove the troublesome oxidation and reduces segregation. Thus titanium-aluminum bronze is the hardest of all the bronzes, but of little use in the arts as it cannot be worked. The proportions of the alloy are copper, 76 per cent; titanium, 12 per cent, and aluminum, 12 per cent. It is made by adding the titanium to aluminum bronze. Its tensile strength is 100,000 pounds per square inch. A form of this bronze offered in the market under the trade name of 'Titan Bronze° has a tensile strength of 110,000 pounds. It is extremely plastic and is forgeable and is sup plied in hot-rolled bars, hot and cold-rolled sheets, castings and recasting ingots. °Chro max Bronze' is a trade name for a chrome nickel bronze, white in color and capable of taking a high polish. It has a denser structure and greater compression strength than man ganese bronze, and can be rolled into sheets and drawn into wire. Its tensile strength is 79,000 pounds per square inch. °Tobin Bronzes is another commercial bronze, composed of cop per, 59 per cent; zinc, 38 per cent; tin, 2 per cent, an lead, as per cent. The name °steel bronze° is given to bronze condensed and hard ened artificially, as in the making of cannon the i bore of which is enlarged and the metal com pacted by forcing in several strong steel cylin ders of gradually increasing sizes in succession. See BRONZES.