An alloy of copper and tin in proportions varying from 3 to 5 parts of copper to 1 of tin. It is of a yellowish-grey colour, hard, brittle, and sonorous, and exhibits a fine-grained fracture. Cooled suddenly from a red heat, it becomes soft, but regains its hardness after being re-heated and cooled very slowly. Small house-bells are usually made of an alloy of 2 parts of copper with 1 of tin; but for larger bells a higher proportion of copper is needed.
The larger the proportion of copper in the alloy, the deeper and graver is the tone of the bells formed from it. The addition of tin, iron, or zinc causes them to give out a sharper tone. Where the quality of the tone is the chief object sought after, care must be taken to employ only commercially pure copper. The presence of lead, even in very small quantities, prejudicially affects the sonorousness of the alloy. Silver, on the contrary, is said to give sweetness to the tone. The presence of this metal has been detected in many old church bells, which, according to tradition, were cast from crucibles into which articles of silver had been thrown as votive offerings.
The composition of some varieties of bell-metal is shown below:-
(1) Copper, 39 parts; tin 11. This is the most sonorous of all the alloys of copper and zinc. (Standard.)
(2) Copper, 77 parts; tin, 21; antimony, 2. Paler and inferior to the above. (Founders' Standard.')
(3) Copper, 4 parts; tin, 1. Very deep-toned and sonorous.
(4) Copper, 3 parts; tin, 1. Used for church and other large bells.
(5) Copper, 17 parts; tin, 8. Best proportions for house-bells, hand-bells, &c.
(7) Copper, 6 lb.; nickel, 1 lb.; melted and cooled; add 1 lb. zinc and 1/2 oz. aluminium; melt and cool; melt again, and add 1/2 oz. mercury and 6 lb. melted copper. Said not to tarnish nor crack, and to be lighter in weight and give better sound.