At the present day, however, two kinds of electric forces are recognised, and distinguished as negative and positive, but they are both assumed to be analogous in principle, and very generally assumed to be simply due to different analogous motions of matter. For a full exposition, however, the reader must refer to some of the especial works on the subject.
ELECTRICITY, Iron reduced by. Gelatin capsules of the size of a 2-grain pill, filled with powdered blacksmith scales (black oxide of iron). (Hager.)
ELECTRO-CHEM′ISTRY. That branch of chemistry which treats of the agency of electricity in effecting chemical changes.
ELECTRO-ETCH′ING. See Etching.
ELECTROL′YSIS. (-trŏl′-e-sĭs). Electro-chemical decomposition. The voltaic current has the power of loosening and separating the constituents of certain compound bodies when these are interposed in the circuit. The substances which are thus susceptible of decomposition are termed electrolytes. They are all binary compounds, containing single equivalents of their components, which are held together by very powerful affinities. The amount of electrical power required to effect decomposition varies greatly with different electrolytes: solution of iodide of potassium, melted chloride of lead, hydrochloric acid, water mixed with a little sulphuric acid, and pure water, demand very different degrees of decomposing force, the resistance increasing from the first-mentioned substance to the last, which latter it has been denied can be decomposed. One of the indispensable conditions of electrolysis is fluidity. When a liquid is electrolysed its components are discharged solely at the limiting surfaces, where, according to the usual figurative mode of speech, the current enters and leaves the liquid, all the intermediate portions appearing quiescent. The terms ‘anode’ and ‘cathode’ have been proposed respectively for the surfaces which are supposed to receive and let out the current of positive electricity. The anode is therefore directly against or opposite the positive pole of the battery, or, according to the improved nomenclature, the positive electrode; and the cathode against the negative pole, or electrode. The bodies which are set free by the action of the current are termed ions; those which go to the anode and appear at the positive electrode being distinguished by the term anions, and those which go to the cathode and appear at the negative electrode by the term cathions. This nomenclature has, however, been but partially adopted, and is making but slow way, if any, many preferring the old terms of electro-positive for anions, and electro-negative for cathions.
The relative decomposing effects produced by the same current in different electrolytes are exactly expressed by the chemical equivalents of the electrolytes. Thus, if a current be made to traverse acidulated water, iodide of potassium, and chloride of lead, these three electrolytes will suffer decomposition at the same time, but by no means to the same extent; for the current which decomposes but 9 parts of water will separate into their elements 166 parts of iodide of potassium and 139 parts of chloride of lead. The electrolysis of metallic salts is now carried out on a large scale in the beautiful arts, which we notice under the general head of Electrotype.
ELECTROMOTIVE ESSENCE (Romershausen). An embrocation for restoring the suspended functions of the skin by stimulating the flow of vital electricity and the functions of the nerves. A solution of oils of turpentine and rosemary in the ninth dilution of alcohol previously coloured red with some vegetable dye. (Reithner.)
ELECTRO-PLA′′TING and GILDING. See Electrotype.
ELECTROPH′ORUS. A simple instrument for exciting electricity, generally used in the chemical laboratory for charging small Leyden jars when gases have to be exploded by the electric spark. To construct it, a plate of tinned iron is made into a circle of about 12 inches diameter; a raised border is then turned up for about half an inch, and the extreme edge is turned outwards over a wire to avoid a sharp border. A mixture of equal parts by weight of shell-lac, Venice turpentine, and resin, is made by gently heating them together with stirring until well fused and thoroughly incorporated. This composition is poured into the plate, to quite fill it, and kept melted until all bubbles have disappeared. Another portion of the instrument, serving the same purpose as the conductor of an electric machine, is a circle of wood, rather smaller than the resinous plate, rounded at the edge, and neatly covered with tin-foil. An insulating handle, formed of a piece of stout glass rod, is cemented into the centre of this wooden disc. Before using the instrument it must be carefully dried and slightly warmed. The resinous surface is excited by beating it obliquely with a folded piece of warm flannel. When this has been done for about a minute, the warm dry cover of the instrument is to be placed upon the resinous plate, and touched with the finger. If the cover is then raised a few inches, and the knuckle approached, a powerful spark of positive electricity will pass; and if the cover be again replaced, touched, and raised, a second spark will pass. This may be repeated many times without again exciting the resinous plate. By receiving the sparks with the knobs of a Leyden jar, a charge strong enough to give a powerful shock, or explode a gaseous mixture, may be rapidly obtained. Other forms have been given to the instrument, but the essential part of every one is a plate of some resinous substance.
ELECTROTYPE. Syn. Electro-met′allurgy, Galvan′o-plas′tic. The art of working in metals by the aid of electricity. Strictly speaking, the term electrotype is only applicable to one branch of ‘electro-metallurgy’—that which relates to the production of copies of engraved plates, medals, coins, and other works—but it is now commonly employed in the sense indicated by our definition. According to this extended signification of the term, the