The relations between surface tension, the potential difference and the electrostatic capacity of fluids in contact. Although nominally in contact such surfaces are separated by about one-twenty-millionth of a centimeter (1/50000000 inch) ; thus a globule of mercury and water in which it is immersed const.i.tute an electrostatic acc.u.mulator of definite electrostatic capacity. Again the mercury and water being in electric connection differ in potential by contact (see Contact Theory). A definite surface tension is also established. Any change in one of these factors changes the other also. A current pa.s.sed through the contact surfaces will change the surface tension and hence the shape of the mercury globule. Shaking the globule will change its shape and capacity and produce a current. Heating will do the same. (See Electrometer, Capillary; and Telephone, Capillary.) Mercury and water are named as liquids in which the phenomena are most conveniently observed. They are observable in other parallel cases.

Electro-chemical Equivalent.

The quant.i.ty of an element or compound liberated from or brought into combination, electrolytically, by one coulomb of electricity. The electro-chemical equivalent of hydrogen is found by experiment to be .0000105 gram. That of any other substance is found by multiplying this weight by its chemical equivalent referred to hydrogen, which is its atomic or molecular weight divided by its valency. Thus the atomic weight of oxygen is 16, its valency is 2, its equivalent is 16/2 = 8; its electro-chemical equivalent is equal to .0000105 X 8 = .000840 gram.

Electro-chemical Series.

An arrangement of the elements in the order of their relative electrical affinities so that each element is electro-negative to all the elements following it, and electro-positive to the elements preceding it. The usual series begins with oxygen as the most electro-negative and ends with pota.s.sium as the most electro-positive element. There is, of course, no reason why other series of compound radicals, such as sulphion (SO4), etc., should not also be constructed. For each liquid acting on substances a separate series of the substances acted on may be constructed. Thus for dilute sulphuric acid the series beginning with the negatively charged or most attacked one is zinc, amalgamated or pure, cadmium, iron, tin, lead, aluminum, nickel, antimony, bis.m.u.th, copper, silver, platinum. In other liquids the series is altogether different.

Electro--chemistry.

The branch of electricity or of chemistry treating of the relations between electric and chemical force in different compounds and reactions. (See Electrolysis--Electrochemical series--Electro-chemical Equivalent .)

210 STANDARD ELECTRICAL DICTIONARY.

Electro-culture.

The application of electricity to the cultivation of plants. In one system wires are stretched or carried across the bed under the surface, and some are connected to one pole and others to the other pole of a galvanic battery of two or more elements. In some experiments improved results have thus been obtained.

Another branch refers to the action of the electric arc light on vegetation. This has an effect on vegetation varying in results.

Electrode.

(a) The terminal of an open electric circuit.

(b) The terminals of the metallic or solid conductors of an electric circuit, immersed in an electrolytic solution.

(c) The terminals between which a voltaic arc is formed, always in practice made of carbon, are termed electrodes.

(d) In electro-therapeutics many different electrodes are used whose names are generally descriptive of their shape, character, or uses to which they are to be applied. Such are aural electrodes for the ears, and many others.

(e) The plates of a voltaic battery.

Electrode, Indifferent.

A term in electro-therapeutics. An electrode to which no therapeutic action is attributed but which merely provides a second contact with the body to complete the circuit through the same. The other electrode is termed the therapeutic electrode.

Electrodes, Erb's Standards of.

Proposed standard sizes for medical electrodes as follows: Name. Diameter.

Fine Electrode, 1/2 centimeter .2 inch Small " 2 " .8 "

Medium " 7.5 " 3.0 "

Large " 6X2 " 2.4 X .8 "

Very large " 16x8 " 6.4 x 3.2 "

Electrodes, Non-polarizable.

In electro-therapeutics electrodes whose contact surface is virtually porous clay saturated with zinc chloride solution. The series terminate in amalgamated zinc ends, enclosed each in a gla.s.s tube, and closed with clay. Contact of metal with the tissues is thus avoided.

Electrode, Therapeutic.

A term in electro-therapeutics. An electrode applied to the body for the purpose of inducing therapeutic action, or for giving the basis for an electric diagnosis of the case. The other electrode is applied to complete the circuit only; it is termed the indifferent electrode.

Electro-diagnosis.

The study of the condition of a patient by the reactions which occur at the terminals or kathode and anode of an electric circuit applied to the person. The reactions are divided into kathodic and anodic reactions.

211 STANDARD ELECTRICAL DICTIONARY.

Electro-dynamic. adj.

The opposite of electrostatic; a qualification of phenomena due to current electricity.

Synonym--Electro-kinetic.

Electro-dynamic Attraction and Repulsion.

The mutual attraction and repulsion exercised by currents of electricity upon each other. The theory of the cause is based upon stress of the luminiferous ether and upon the reaction of lines of force upon each other. For a resum? of the theory see Induction, Electro-magnetic.

Electro-dynamics.

The laws of electricity in a state of motion; the inter-reaction of electric currents. It is distinguished from electro-magnetic induction as the latter refers to the production of currents by induction. The general laws of electro-dynamics are stated under Induction, Electro-magnetic, q. v.

Synonym--Electro-kinetics.

Fig. 143. DIAGRAM OF CONNECTIONS OF SIEMENS' ELECTRO-DYNAMOMETER.

212 STANDARD ELECTRICAL DICTIONARY.

Electro-dynamometer, Siemens'.

An apparatus for measuring currents by the reaction between two coils, one fixed and one movable, through which the current to be measured pa.s.ses. It is one of the oldest commercial ammeters or current measurers. It comprises a fixed coil of a number of convolutions and a movable coil often of only one convolution surrounding the other. The movable coil is suspended by a filament or thread from a spiral spring.

The spring is the controlling factor. Connection is established through mercury cups so as to bring the two coils in series. In use the spring and filament are adjusted by turning a milled head to which they are connected until the coils are at right angles. Then the current is turned on and deflects the movable coil. The milled head is turned until the deflection is overcome. The angle through which the head is turned is proportional to the square of the current. The movable coil must in its position at right angles to the fixed one lie at right angles to the magnetic meridian.

Thus in the diagram, Fig. 143 A B C D is the fixed coil; E F G H is the movable coil; S is the spiral spring attached at K to the movable coil.

The arrows show the course of the current as it goes through the coils.

Electrolier.

A fixture for supporting electric lamps; the a.n.a.logue in electric lighting of the gasolier or gas chandelier. Often both are combined, the same fixture being piped and carrying gas burners, as well as being wired and carrying electric lamps.

Electrolysis.

The separation of a chemical compound into its const.i.tuent parts or elements by the action of the electric current. The compound may be decomposed into its elements, as water into hydrogen and oxygen, or into const.i.tuent radicals, as sodium sulphate into sodium and sulphion, which by secondary reactions at once give sodium hydrate and sulphuric acid.