"The wire shall be capable of being wrapped in six. turns around wire of its own diameter, unwrapped and again wrapped in six turns around wire of its own diameter in the same direction as the first wrapping, without breaking; and shall be also capable of bearing the number of twists set down in the table, without breaking. "The twist-test will be made as follows: The wire will be gripped by two vises, one of which will be made to revolve at a speed not exceeding one revolution per second. The twists thus given to the wire will be reckoned by means of an ink mark which forms a spiral on the wire during torsion, the full number of twists to be visible between the vises." According to the above table, the mile-ohm of copper required is 878 pounds. This corresponds to a conductivity of 96.6 per cent., taking the value of the mile-ohm of 100 per cent. copper as 859. HARD-DRAWN COPPER WIRE.-(Continued.) required. Actual minimum. Actual Per square inch. Maximum. Minimum. Required. Minimum. Twists in six inches. tion in five feet. Per cent. elonga The strength of soft copper wire varies from 32 000 to 36 000 pounds per square inch, and of hard copper wire from 45 000 to 68 000 pounds per square inch, according to the degree of hardness. The above table is calculated for 34 000 pounds for soft wire and 60 000 pounds for hard wire, except for some of the larger sizes, where the breaking weight per square inch is taken at 50 000 pounds for 0 000, 000 and 00, 55 000 for 0, and 57 000 pounds for 1. |