The Standard Electrical Dictionary Part 74

Frictional Electricity.

Electricity produced by friction of dissimilar substances. (See Electrostatic Series.) The contact theory holds that friction plays only a secondary r?le in this process; that it increases the thoroughness of contact, and tends to dry the rubbing surfaces, but that the charges induced are due to contact of dissimilar substances, not to friction of one against the other.

Frictional Heating.

The heating of a conductor by the pa.s.sage of a current; the Joule effect, q. v.

Fringe.

The outlying edge of a magnetic field.

Frog, Galvani's Experiment With.

A cla.s.sic experiment in electricity, leading to the discovery of current or dynamic electricity. If a pair of legs of a recently killed frog are prepared with the lumbar nerves exposed near the base of the spinal column, and if a metallic conductor, one half-length zinc and the other half-length copper, is held, one end between the lumbar nerves and the spine, and the other end against one of the muscles of the thigh or lower legs, the moment contact occurs and the circuit is completed through the animal substance the muscles contract and the leg is violently drawn upwards. Galvani, in 1786, first performed, by accident, this famous experiment, it is said, with a scalpel with which he was dissecting the animal. He gave his attention to the nerves and muscles.

Volta, more happily, gave his attention to the metals and invented the voltaic battery, described by him in a letter to Sir Joseph Banks, dated 1800.

Frog, Rheoscopic.

If the nerve or living muscle of a frog is suddenly dropped upon another living muscle so as to come in contact with its longitudinal and transverse sections, the first muscle will contract on account of the stimulation of its nerve due to the pa.s.sage of a current derived from the second muscle (Ganot). The experiment goes under the above t.i.tle.

263 STANDARD ELECTRICAL DICTIONARY.

Frying.

A term applied to a noise sometimes produced in a voltaic arc due to too close approach of the carbons to each other. It has been suggested that it may be due to volatilization of the carbon. (Elihu Thomson.)

Fulgurite.

An irregular and tubular ma.s.s of vitrified quartz, believed to be formed by melting under the lightning stroke.

Fig. 175. CRUCIBLE, ELECTRIC.

Furnace, Electric.

A furnace in which the heat is produced by the electric current. It has. .h.i.therto been practically used only in the extraction of aluminum and silicium from their ores. The general principle involves the formation of an arc between carbon electrodes. The substances to be treated are exposed to the heat thus produced. Sometimes the substances in the arc form imperfect conductors, and incandescence takes a part in the action.

Sometimes the substances are merely dropped through the arc.

[Transcriber's note: Silicium is silicon.]

Fuse Board.

A tablet on which a number of safety fuses are mounted. Slate is excellent material for the tablet, as it is incombustible, and is easily drilled and worked.

Fuse Box.

A box containing a safety fuse. Porcelain is an excellent material for its base. No combustible material should enter into its composition.

Fuse, c.o.c.kburn.

A safety fuse or cut off which consists of a wire of pure tin running from terminal to terminal, to whose centre a leaden ball is secured by being cast into position. The connection with the terminals is made by rings at the ends of the wire through which the terminal screws are pa.s.sed and screwed home. When the tin softens under too heavy a current the weight of the shot pulls it apart.

Fig. 176 c.o.c.kBURN SAFETY FUSE.

264 STANDARD ELECTRICAL DICTIONARY.

Fig. 177. ELECTRIC FUSE.

Fuse, Electric.

A fuse for igniting an explosive by electricity. There are two kinds. In one a thin wire unites the ends of the two conducting wires as they enter the case of the fuse. The larger wires are secured to the case, so that no strain comes on the fine wire. On pa.s.sing a current of sufficient strength the small wire is heated. In use the fuse is bedded in powder, which again may be surrounded by fulminating powder, all contained in a copper or other metallic case. Such a detonator is used for exploding guncotton and other high explosives.

The other kind of fuse is similar, but has no thin connecting wire. The ends of the conductors are brought nearer together without touching. In use a static discharge is produced across from end to end of the conductors, igniting a proper explosive placed there as in the other case.

The first kind of fuse is generally operated by a battery or small mechanical generator--the latter by a spark coil, frictional or influence machine or by a Leyden jar.

Galvanic. adj.

Voltaic; relating to current electricity or the electrolytic and electro-chemical relations of metals. (For t.i.tles in general under this head see Voltaic--or the main t.i.tle.)

Galvanic Element.

A galvanic couple with exciting fluid and adjuncts; a galvanic cell. The word element is sometimes applied to the electrodes of a cell, as the carbon element or zinc element.

265 STANDARD ELECTRICAL DICTIONARY.

Galvanic Polarization.

The polarization of a voltaic couple. (See Polarization.)

Galvanism.

The science of voltaic or current electricity.

Galvanization.

(a) Electroplating or depositing a metal over the surface of another by electrolysis.

(b) In medical electricity the effects produced on any part of the system by the current of voltaic battery. Various descriptive qualifications are prefixed, such as "general" galvanization, indicating its application as applied to the whole body, "local" for the reverse case, and so on.

Galvanization, Labile.

Application of the galvanic current in electro-therapeutics where one sponge electrode is employed which is rubbed or moved over the body, the other being in constant contact with the body.

Galvanized Iron.