The mechanical qualities demanded of the metal for such purposes as telegraph work may be indicated by the two specifications of wire for the British Post Office, which are appended:—
- A. Post Office Specification.
- Weight, 150 lbs. per mile.
- Minimum diameter, ·95½".
- Maximum diameter, ·98".[1]
- Minimum breaking strain, 490 lbs.
- Minimum number of twists, 25 in 3 inches.
- Wraps required, 6 times round wire of its own diameter, unwrapped, and again wrapped without breaking.
- Maximum resistance per mile at 60° F., 5·857 ω.
- B. Post Office Specification.
- Weight, 500 lbs. per mile.
- Minimum diameter, ·135¼".
- Maximum diameter, ·138¾".
- Minimum breaking strain, 950 lbs.
- Minimum number of twists, 30 in 6 inches.
- Wraps required, 6 times round wire of its own diameter, unwrapped, and again wrapped without breaking.
- Maximum resistance per mile at 60° F., 2·928 ω.
The following figures afford some indication of the increasing demand for copper in two branches only of electrical industry:—
| 1902. | 1907. | ||
| Mileage of wire for | telegraph purposes, | 3·9 | 5·3 |
| "" | telephone purposes, | 10·9 | 28·2 |
| (in million of miles) | |||
(b) Engineering Uses.—Metallic copper finds application in marine shipbuilding and engine work, as well as in railway and locomotive work, where the metal is particularly employed for steam pipes, and for fire-box plates and stays, sometimes also for boiler tubes, on account of its high conductivity for heat, combined with toughness. The questions of suitable composition, and the other requirements of the metal intended for these purposes, has been a subject for discussion by some of the leading marine and locomotive engineers. Useful information on the subject will be found in the reports of some of these discussions at the Institution of Mechanical Engineers.
The following tests are required for copper plate (best quality) intended for locomotive fire-boxes on the Lancashire and Yorkshire Railway, taken from standard specifications given by their Chief Mechanical Engineer at the Institute of Metals:—
Bending Test.—Pieces of the plate shall be tested both cold and at a red heat by being doubled over on themselves— that is, bent through an angle of 180°—without showing either crack or flaw on the outside of the bend.
Flanging.—Plates must not show any defects in flanging.
Tensile Test.—Ultimate breaking load, 14 tons per square inch; Elongation, 35 per cent. in 8 inches.