Electrophoric Action.

The action of an electrophorous; utilized in influence machines. (See Electrophorous.)

Fig. 159. ELECTROPHOROUS.

Electrophorous.

An apparatus for the production of electric charges of high potential by electrostatic induction, q. v. It consists of a disc of insulating material B, such as resin or gutta percha, which is held in a shallow metal-lined box or form. The disc may be half an inch thick and a foot or more in diameter, or may be much smaller and thinner. A metal disc A, smaller in diameter is provided with an insulating handle which may be of gla.s.s, or simply silk suspension strings. To use it the disc B is excited by friction with a cat-skin or other suitable substance. The metallic disc is then placed on the cake of resin exactly in its centre, so that the latter disc or cake projects on all sides. Owing to roughness there is little real electric contact between the metal and dielectric. On touching the metal disc a quant.i.ty of negative electricity escapes to the earth. On raising it from the cake it comes off excited positively, and gives a spark and is discharged. It can be replaced, touched, removed and another spark can be taken from it, and so on as long as the cake stays charged.

The successive discharges represent electrical energy expended. This is derived from the muscular energy expended by the operator in separating the two discs when oppositely excited. As generally used it is therefore an apparatus for converting muscular or mechanical energy into electric energy.

231 STANDARD ELECTRICAL DICTIONARY.

Electro-physiology.

The science of the electric phenomena of the animal system. It may also be extended to include plants. The great discovery of Galvani with the frog's body fell into this branch of science. The electric fishes, gymnotus, etc., present intense phenomena in the same.

Electroplating.

The deposition by electrolysis of a coating of metal upon a conducting surface. The simplest system makes the object to be plated the negative electrode or plate in a galvanic couple. Thus a spoon or other object may be connected by a wire to a plate of zinc. A porous cup is placed inside a battery jar. The spoon is placed in the porous cup and the zinc outside it. A solution of copper sulphate is placed in the porous cup, and water with a little sodium or zinc sulphate dissolved in it, outside. A current starts through the couple, and copper is deposited on the spoon.

A less primitive way is to use a separate battery as the source of current; to connect to the positive plate by a wire the object to be plated, and a plate of copper, silver, nickel or other metal to the other pole of the battery. On immersing both object and plate (anode) in a bath of proper solution the object will become plated.

In general the anode is of the same material as the metal to be deposited, and dissolving keeps up the strength of the bath. There are a great many points of technicality involved which cannot be given here.

The surface of the immersed object must be conductive. If not a fine wire network stretched over it will gradually fill up in the bath and give a matrix. More generally the surface is made conductive by being brushed over with plumbago. This may be followed by a dusting of iron dust, followed by immersion in solution ot copper sulphate. This has the effect of depositing metallic copper over the surface as a starter for the final coat.

Attention must be paid to the perfect cleanliness of the objects, to the condition of the bath, purity of anodes and current density.

Voltaic batteries are largely used for the current as well as special low resistance dynamos. Thermo-electric batteries are also used to some extent but not generally.

Electro-pneumatic Signals.

Signals, such as railroad signals or semaph.o.r.es, moved by compressed air, which is controlled by valves operated by electricity. The House telegraph, which was worked by air controlled by electricity, might come under this term, but it is always understood as applied to railroad signals, or their equivalent.

232 STANDARD ELECTRICAL DICTIONARY.

Electropoion Fluid.

An acid depolarizing solution for use in zinc-carbon couples, such as the Grenet battery. The following are formulae for its preparation:

(a) Dissolve one pound of pota.s.sium bichromate in ten pounds of water, to which two and one-half pounds of concentrated sulphuric acid have been gradually added. The better way is to use powdered pota.s.sium bichromate, add it to the water first, and then gradually add the sulphuric acid with constant stirring.

(b) To three pints of water add five fluid ounces of concentrated sulphuric acid; add six ounces pulverized pota.s.sium bichromate.

(c) Mix one gallon concentrated sulphuric acid and three gallons of water. In a separate vessel dissolve six pounds pota.s.sium bichromate in two gallons of boiling water. Mix the two.

The last is the best formula. Always use electropoion fluid cold. (See Trouv?'s Solution--Poggendorff's Solution--Kakogey's Solution-- Tissandrier's Solution--Chutaux's Solution.)

Electro-positive. adj.

Appertaining to positive electrification; thus pota.s.sium is the most electro-positive of the elements. (See Electro-negative.)

Electro-puncture.

The introduction into the system of a platinum point or needle, insulated with vulcanite, except near its point, and connected as the anode of a galvanic battery. The kathode is a metal one, covered with a wet sponge and applied on the surface near the place of puncture. It is used for treatment of aneurisms or diseased growths, and also for removal of hair by electrolysis. (See Hair, Removal of by Electrolysis.)

Synonym--Galvano-puncture.

Electro-receptive. adj.

A term applied to any device or apparatus designed to receive and absorb electric energy. A motor is an example of an electro-receptive mechanism.

Electroscope.

An apparatus for indicating the presence of an electric charge, and also for determining the sign, or whether the charge is positive or negative.

The simplest form consists of a thread doubled at its centre and hung therefrom. On being charged, or on being connected to a charged body the threads diverge. A pair of pith b.a.l.l.s may be suspended in a similar way, or a couple of strips of gold leaf within a flask (the gold leaf electroscope). To use an electroscope to determine the sign of the charge it is first slightly charged. The body to be tested is then applied to the point of suspension, or other charging point. If at once further repelled the charge of the body is of the same sign as the slight charge first imparted to the electroscope leaves; the leaves as they become more excited will at once diverge more. If of different sign they will at first approach as their charge is neutralized and will afterwards diverge.

The gold-leaf electroscope is generally enclosed in a gla.s.s bell jar or flask. Sometimes a pair of posts rise, one on each side, to supply points of induction from the earth to intensify the action. (See Electrometer, Quadrant--Electroscope, Gold leaf, and others.)

233 STANDARD ELECTRICAL DICTIONARY.

Electroscope, Bennett's.

A gold-leaf electroscope, the suspended leaves of which are contained in a gla.s.s shade or vessel of dry air. On the inside of the gla.s.s shade are two strips of gold leaf, which rise from the lower edge a short distance, being pasted to the gla.s.s, and connected to the ground. These act by induction to increase the sensitiveness of the instruments.

Electroscope, Bohenberger's.

A condensing electroscope (see Electroscope, Condensing) with a single strip of gold leaf suspended within the gla.s.s bell. This is at an equal distance from the opposite poles of two dry piles (see Zamboni's Dry Pile) standing on end, one on each side of it. As soon as the leaf is excited it moves toward one and away from the other pile, and the sign of its electrification is shown by the direction of its motion.

Electroscope, Condensing.

A gold leaf electroscope, the gla.s.s bell of which is surmounted by an electrophorous or static condenser, to the lower plate of which the leaves of gold are suspended or connected.

In use the object to be tested is touched to the lower plate, and the upper plate at the same time is touched by the finger. The plates are now separated. This reduces the capacity of the lower plate greatly and its charge acquires sufficient potential to affect the leaves, although the simple touching may not have affected them at all.

Electroscope, Gold Leaf.

An electroscope consisting of two leaves of gold leaf hung in contact with each other from the end of a conductor. When excited they diverge.

The leaves are enclosed in a gla.s.s vessel.

Fig. 160. GOLD LEAF ELECTROSCOPE.