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various sizes were not consistent with each other in the same table, and that no two tables seemed to agree in regard to the specific gravity of the material.
This table is calculated from the formula, weight per mile=D2 X .013 9, which seems to be the most likely value for galvanized iron wire. This corresponds with a specific gravity of 7.73, and a weight per cubic foot of 483 pounds.
Steel wire is slightly heavier, and it is probable the constant in the above formula should be .014 for galvanized steel wire.
The following average values of the mile-ohm were
E. B. B.,
7 000 The breaking weight of any wire equals its weight per mile multiplied by 3 for E. B. B., 3.3 for B. B., or 3.7 for steel, all annealed and galvanized. This corresponds to 53 100 pounds, 58 410 pounds, and 65 490 pounds per square inch, respectively.
The strength of steel wire varies from 50 000 pounds per square inch to over 300 000 pounds, according to the kind of material and its treatment.
By taking 100 000 pounds per square inch as the breaking strain of steel wire, the breaking strain of any other wire may easily be computed from the table. For a wire of 80 000 pounds per square inch breaking strain, take eight-tenths of the tabulated breaking strain for that size wire at 100 000 pounds per square inch given in the table.
GALVANIZED IRON TELEGRAPH WIRE.
Western Union Telegraph company's specifications.
(Condensed). “1. The wire to be soft and pliable, and capable of elongating 15 per cent. without breaking, after being galvanized.
“2. Great tensile strength is not required, but the wire must not break under a less strain than two and onehalf times its weight in pounds per mile.
“3. Tests for ductility will be made as follows: The piece of wire will be gripped by two vises, 6 inches apart, and twisted. The full number of twists must be distinctly visible between the vises on the 6-inch piece. The number of twists in a piece of 6 inches in length not to be under 15.
“4. The weight per mile for the different gauge wires to be: for No. 4,730 ibs.; No. 6,540 lbs.; No. 8, 380 lbs.; No. 9, 320 lbs.; No. 10, 250 ibs., or, as near these figures as practicable.
“5. The electrical resistance of the wire in ohms per mile, at a temperature of 68° Fahrenheit, must not exceed the quotient arising from the dividing the constant number 4 800 by the weight of the wire in pounds per
mile. The coëfficient .003 will be allowed for each degree Fahrenheit in reducing to standard temperature.
“6. The wire must be well galvanized, and capable of standing the following tests : The wire will be plunged into a saturated solution of sulphate of copper, and permitted to remain one minute, and then wiped clean. This process will be performed four times. If the wire appears black after the fourth immersion, it shows that the zinc has not been all removed, and that the galvanizing is well done; but if it has a copper color, the iron is exposed, showing that the zinc is too thin."
GALVANIZED IRON TELEGRAPH WIRE.
British Post-office specifications.
“The wire shall be well galvanized with zinc spelter, and this will be tested by an officer appointed by the Postmaster-
The mile-ohm is 5 323.