with an inert gas atmosphere has proven most successful. Both commercially pure and alloy titanium can absorb large amounts of cold-work without cracking. Practically anything that can be deep drawn in low-carbon steel can be duplicated in commercially pure titanium, although the titanium may require more intermediate anneals. IDENTIFICATION OF TITANIUM.—Titanium metal, pure or alloyed, is easily identified. When touched with a grinding wheel, it makes white spark traces that end in brilliant white bursts. When rubbed with a piece of glass, moistened titanium will leave a dark line similar in appearance to a pencil mark. Copper and Copper Alloys Most commercial copper is refined to a purity of 99.9 percent minimum copper plus silver. It is the only reddish-colored metal, and it is second only to silver in electrical conductivity. Its use as a structural material is limited because of its great weight. However, some of its outstanding characteristics, such as its high electrical and heat conductivity, in many cases overbalance the weight factor. Because it is very malleable and ductile, copper is ideal for making wire. In aircraft, copper is used primarily for the electrical system and for instrument tubing and bonding. It is corroded by salt water, but is not affected by fresh water. The ultimate tensile strength of copper varies greatly. For cast copper, the tensile strength is about 25,000 psi; and when cold-rolled or cold-drawn, its tensile strength increases, ranging from 40,000 to 67,000 psi. BRASS.—Brass is a copper alloy containing zinc and small amounts of aluminum, iron, lead, manganese, magnesium, nickel, phosphorous, and tin. Brass with a zinc content of 30 to 35 percent is very ductile, while that containing 45 percent has relatively high strength. “Muntz metal” is a brass composed of 60 percent copper and 40 percent zinc. It has excellent corrosion-resistant qualities when in contact with saltwater. Its strength can be increased by heat treatment. As cast, this metal has an ultimate tensile strength of 50,000 psi and can be elongated 18 percent. It is used in making bolts and nuts, as well as parts that come in contact with salt water. “Red brass,” sometimes termed bronze because of its tin content, is used in fuel and oil line fittings. This metal has good casting and finishing properties and machines freely. BRONZES.—Bronzes are copper alloys containing tin. The true bronzes have up to 25 percent tin, but those below 11 percent are most useful, especially for such items as tube fittings in aircraft. Among the copper alloys are the copper aluminum alloys, of which the aluminum bronzes rank very high in aircraft usage. They would find greater usefulness in structures if it were not for their strength/weight ratio as compared with alloy steels. Wrought aluminum bronzes are almost as strong and ductile as medium-carbon steel, and possess a high degree of resistance to corrosion by air, salt water, and chemicals. They are readily forged, hot- or cold-rolled, and some react to heat treatment. These copper-based alloys contain up to 16 percent of aluminum (usually 5 to 11 percent) to which other metals such as iron, nickel, or manganese maybe added. Aluminum bronzes have good tearing qualities, great strength, hardness, and resistance to both shock and fatigue. Because of these properties, they are used for diaphragms and gears, air pumps, condenser bolts, and slide liners. Aluminum bronzes are available in rods, bars, plates, sheets, strips, and forgings. Cast aluminum bronzes, using about 89 percent copper, 9 percent aluminum, and 2 percent of other elements, have high strength combined with ductility, and are resistant to corrosion, shock, and fatigue. Because of these properties, cast aluminum bronze is used in gun mounts, bearings, and pump parts. These alloys are useful in areas exposed to salt water and corrosive gases. Manganese bronze is an exceptionally high- strength, tough, corrosion-resistant copper zinc alloy containing aluminum, manganese, iron, and occasionally nickel or tin. This metal can be formed, extruded, drawn, or rolled to any desired shape. In rod form, it is generally used for machined parts. Otherwise it is used in catapults, landing gears, and brackets. Silicon bronze is composed of about 95 percent copper, 3 percent silicon, and 2 percent mixture of manganese, zinc, iron, tin, and aluminum. Although not a bronze in the true sense of the word because of its small tin content, silicon bronze has high strength and great corrosion resistance and is used variably. BERYLLIUM COPPER.—Beryllium copper is one of the most successful of all the copper-based alloys. It is a recently developed alloy containing about 97 percent copper, 2 percent beryllium, and sufficient nickel to increase the percentage of elongation. The most valuable feature of this metal is that the physical properties can be greatly stepped up by heat 1-33