This is one of the most important of the alloys. While its usual constituents, copper and zinc, combine in any proportion, the range of useful proportions varies from about 60 to

89% of copper. A widely used formula for brass is about 2/3 copper and 1/3 zinc.

The range of composition of brass offers a material suitable for a great number of particular uses. Zinc gives brass its hardness, and tin in small quantities increases this. Experiment shows that the tensile strength of cast brass is greatest (about 50,000 lbs. per sq. in.) when the composition is about 62% copper and 38% zinc; and that ductility and malleability are greatest for about 70% copper and 30% zinc. These properties, however, are improved by adding a small amount of tin for hardness, or lead for ductility.

Brass may be considerably hardened by rolling or hammering, hot or cold, or by drawing it into wire. Its strength and rigidity are by these means increased, and brass thus treated is used for springs, but these effects may be removed by annealing, which consists of heating to a cherry-red and cooling slowly, or rapidly, if its composition will not cause cracking. Thoroughly annealed brass has no springiness and may be bent like lead.