Bell, Electric. A bell rung by electricity. The current excites an electro-magnet, attracting or releasing an armature which is attached to a vibrating or pivoted arm, on the end of which the knocker is fastened.
Bichromate of Potash. A strong, yellowish-red chemical, used chiefly in battery fluids and electrolytes.
Bifilar Winding. The method followed in winding resistance-coils. To prevent them from creating fields of force, the wire is doubled and the looped end started in the coil. Since the current passes in opposite senses in the two lays of the winding, no field of force is produced.
Binding. Unattached wire wound round armature-coils to hold them in place.
Binding-post. An arrangement for receiving the loose ends of wires in an electric circuit and securing them, by means of screws, so that perfect contact will be the result.
Bi-polar. Possessing two poles.
Bi-telephone. A pair of telephones arranged with a curved connecting arm or spring so that they can be simultaneously applied to both ears.
Blasting, Electric. The ignition of a blasting charge of powder, dynamite, or other high explosive by an electric spark, or by the heating, to red or white heat, of a thin wire imbedded in the explosive.
Block System. A system of signalling on railroads. Signal-posts are arranged at stated spaces, and on these signals appear automatically, showing the location of trains to the engineers of trains in the rear.
Bluestone. A trade name for sulphate of copper in a crystallized state.