RUBBER WIRE.

'E MANUFACTURE rubber insulated wires for all

WE purposes, including wires and cables for aerial,

underground, and submarine use. The copper conductor is tinned, and then covered with a cement of pure rubber, which causes the succeeding coat of rubber to adhere firmly to the wire. This layer consists of white rubber without sulphur. Over this is a layer of vulcanized rubber, and the whole is covered with a finishing braid of cotton saturated with a Weatherproof compound, which protects the rubber from mechanical injury, and from the action of the air. A poor quality of rubber insulation is inferior to Weatherproof, and we would recommend our Fire and Weatherproof insulation for inside work, rather than an inferior rubber wire.

A good rubber wire should have its conductor central, the insulation should adhere firmly to the wire, it should not crack or become brittle after use, and it should show, after immersion in water for twenty-four hours, the same insulation resistance per mile as when tested after being first put in water. The absolute number of megohms per mile depends on the age of the rubber used, together with other details of manufacture, and is not always a sure guide to the quality of the insulation. Uniformity of insulation among several coils of wire made at the same time, or among the various conductors of a cable, is a much more valuable aid in detecting a poor piece of wire, as in this case an insulation lower than the average shows a local defect, which, in time, will be likely to cause trouble.

THE

MAGNET WIRE.

'HE BARE COPPER intended for Magnet wire is specially drawn and annealed, great care being taken to have it true to gauge, and soft.

A difference from the standard, of one mil, is allowed on sizes larger than No. 10 B. & S. G.; from No. 10 to No. 14, three-fourths of a mil variation is allowed, and any wire smaller than No. 14, one-half a mil variation is allowed.

The insulation is smooth and uniform, and is kept true to gauge to within one mil of the required diameter.

We manufacture any special kind of Magnet wire required, flats, squares and strands.

We understand that a No. 6 B. & S. square Magnet wire measures 162 x 162 mils.

Flats are designated by their width and thickness. Thus a flat Magnet wire 340 mils wide and 40 mils thick would be designated as a 340 x 40 flat Magnet wire.

Strands can be furnished of any size, insulated with double or triple windings of cotton, or any combination of braids and windings that may be desired.

The resistance of German silver wire varies according to the method of manufacture and the materials used. From actual tests on wire with eighteen per centum of nickel, extending over ten years, it seems that eighteen times the resistance of copper, at 75° F., represents very closely the resistance of this alloy. This value is rather under than over the average results of the tests.

For the thirty per centum alloy, we have to depend on the results of a single series of tests, and while the results are believed to be correct, they are not as reliable as those given for the eighteen per centum German silver wire. We take the resistance of the thirty per centum alloy at twenty-eight times the resistance of copper, at 75°.

The International ohm is taken as the unit of resist

ance.