The Standard Electrical Dictionary Part 148

Streamlets, Current.

A conception bearing the same relation to an electric current that lines of force do to a field of force; elementary currents. If evenly distributed the current is of uniform density; if unevenly distributed, as in alternating currents, the current density varies in different parts of the cross section of the conductor. This evenness or unevenness may be referred to the number of streamlets per unit of area of cross-section.

[Transcriber's note: Streamlets per unit of area is redundant with current density.]

Stress.

Force exercised upon a solid tending to distort it, or to produce a strain.

496 STANDARD ELECTRICAL DICTIONARY.

Stress, Dielectric.

The condition of a dielectric when maintaining a charge; its two extremities are in opposite states of polarity, or are under permanent potential difference. As the two opposite polarities tend to unite a condition of stress is implied in the medium which separates them.

Stress, Electro-magnetic.

The stress produced upon transparent substances in an electro-magnetic field of force. It is shown in the modified optical properties of gla.s.s and similar substances placed between the poles of a strong electro-magnet.

Stress, Electrostatic.

The stress produced upon substances in an electrostatic field of force; the exact a.n.a.logue of electro-magnetic stress, and affecting transparent substances in the same general way.

Striae, Electric.

In Geissler tubes the light produced by the electric discharge is filled with striae, bright bands alternating with dark s.p.a.ces; these may be termed electric striae.

Striking Distance.

The distance that separates two conductors charged with electricity of different potential, when a spark starts between them.

Striking Solution.

In silver-plating a bath composed of a weak solution of silver cyanide-with a large proportion of free pota.s.sium cyanide. It is used with a strong current and a large silver anode. This gives an instantaneous deposition of metallic silver over the surface of the article which goes to insure a perfect coating in the silver bath proper. After a few seconds in the striking solution, the article is at once removed to the plating bath.

Stripping.

The removal of electroplating from an object. It may be effected in several ways. An object whose plating is to be removed is placed in a plating bath of the solution of the metal with which it is coated. It is connected as the anode to the positive plate of the battery or corresponding terminal of the generator. A kathode connected to the other terminal being placed in the bath, the coating is dissolved by electrolytic action. Sometimes simple treatment with acid is employed.

Different stripping baths are described under the heads of the different metals.

S. U.

Symbol or abbreviation for Siemens' Unit of Resistance. (See Resistance, Siemens' Unit of.)

Sub-branch.

A branch or lead of wire taken from a branch lead: a term used in electric distribution.

Sub-main.

In electric distribution a conductor connected directly to a main; a branch.

497 STANDARD ELECTRICAL DICTIONARY.

Subway, Electric.

A subterranean system of conduits for electric cables. As generally constructed in this country it includes manholes, q. v., at the street corners connected by ducts or pipes. These pipes are large enough to hold a cable. To introduce a cable into a duct, which latter may be two or three inches in diameter, and from two hundred to six or seven hundred feet long, a wire or rope is first pa.s.sed through the duct. This is done by a set of short wooden rods with screws at the end so as to be screwed together. Each rod must be shorter than the diameter of the manhole. A rod is thrust in, another is screwed to it and thrust in, and thus a set of rods is made to extend as far as desired. In pulling them out a rope is attached and drawn through. This rope or a larger one is used in drawing the cable through the duct. A windla.s.s is employed to draw the rope with cable attached through the ducts.

Sulphating.

In storage battery cells, the formation of a hard white basic lead sulphate, Pb2 S05. Its formation is due to over-exhaustion of the cells.

As long as the voltage is not allowed to fall below 1.90 volts per cell little of it forms. As it acc.u.mulates it is apt to drop off the plate and fall to the bottom, thus weakening the plate possibly, and depriving it of active material, and clogging up the cell. If it carries a film of metallic lead with it, there is danger of short circuiting the cell.

The presence of some sodium sulphate in the solution is said to tend to prevent sulphating, or to diminish it.

Sulphur Dioxide.

A compound gas, S O2; composed of Sulphur, 32 Oxygen, 32 Molecular weight, 64 Specific gravity, 2.21.

It is a dielectric of about the same resistance as air. Its specific inductive capacity at atmospheric pressure is: 1.0037 (Ayrton).

Synonyms--Sulphurous Acid--Sulphurous Acid Gas.

Sunstroke, Electric.

Exposure to the arc light sometimes produces the effects observed in cases of sunstroke. It is said that, in the case of workmen at electric furnaces, these effects are very noticeable. (See Prostration, Electric.)

[Transcriber's note: Effects are due to ultraviolet light.]

Supersaturated. adj.

A liquid is supersaturated when it has dissolved a substance at a temperature favorable to its solubility and its temperature has been allowed to change, the liquid being kept free from agitation or access of air, provided crystallization or precipitation has not taken place.

It expresses the state of a liquid when it holds in solution more than the normal quant.i.ty of any substance soluble in it.

Surface.

A galvanic battery is arranged in surface when all the positive plates are connected together and all the negative plates are also connected.

This makes it equivalent to one large cell, the surface of whose plates would be equal to the aggregate surface of the plates of the battery. It is also used as an adjective, as "a surface arrangement of battery."

498 STANDARD ELECTRICAL DICTIONARY.

Surface Density.

The relative quant.i.ty of an electric charge upon a surface.

Surface, Equipotential.