circulation. This law shows that quantity of electricity means number of equivalent molecular actions.

5. Those bodies only are electrolytes which are composed of a conductor and a non-conductor. This addition of Miller's is useful to remember, but can scarcely take rank as a law or principle of nature.

It is of importance to learn what is the quantity of matter which constitutes the equiv alent, as it is often considered to be what used to be called the chemical equivalent. If this were true, and if Faraday's theory were also true, that only molecules consisting of one equivalent of each radical are electrolytes, the old equivalent theory of chemistry would be almost impregnable; but neither of these ideas is true. The equivalent or lowest combining proportion of nitrogen is 14, that of hydrogen being 1; but when pure ammonia is electrolyzed, only 4 of nitrogen is given off for one of hydrogen. When cupric chloride, CuCl2, and cupreous chloride, Cu,Cl2, are electrolyzed in series, the first gives one equivalent, and the second two equivalents of copper for the same current which in the battery or other cell gives one of hydrogen.

For practical applications in this field, see ELECTRO-METALLURGY, ELECTRO-CHEMISTRY, ELECTRO-PLATING. See also Sprague's Electricity.

ELECTROCUTION. See ELECTRICITY, DEATH CURRENT OF.

ELECTROLYSIS. See ELECTRO-CHEMISTRY.

ELECTRO-METALLURGY AND ELECTRIC SMELTING. Electro-metallurgy is the art of treating metals by the use of electricity. The birth of electro-metallurgy as a distinct branch of science may be said to have occurred in 1807, in which year Sir Humphrey Davy succeeded in producing metallic sodium and potassium by electrolysis of the fused hydrates in the laboratory of the Royal Institution, London. This new branch of study was followed up by Faraday in the same laboratory during the period from 1812 to 1840, and the results of his experimental work placed the science upon a firm basis of accurately observed phenomena, and led to the formation of laws and theories which are still accepted after fifty years of further progress. In 1851 Charles Watt obtained an English patent for electrolytic processes by which caustic alkalis and chlorine, chlorates and pure metals could be produced on an industrial scale, but it was not until 1890 that electro-metallurgy attained a commercial development. The chief cause of this delay was undoubtedly the lack of a cheap source of electrical energy. Until the latter year copper refining was the one electrolytic industry, but since that date there has been a remarkable expansion in other directions, and there are now at least 18 distinct branches, while in Europe alone there are about 100 establishments in which these manufactures are carried on. In recent years, since currents of great power have been made available by the invention of powerful dynamos, electro-metallurgical processes have been successfully carried on on a very much bolder scale than formerly, when they were confined to electro-plating. Electrolytic actions, which are the foundation of metallurgy, can be carried on when substances are in the liquid form. This form may be obtained by raising the temperature of the substances until they are in a state of fusion, as well as by putting them in solution, as in the processes described in the article on ELECTROPLATING (q.v.). This process of electrical decomposition of substances, when fused, has lately received many applications. In one of these it has been applied, in a very ingenious electrical furnace, illustrated herewith, to the work of separating a few very refractory substances from their ores.

By the passage of the decomposing currents between the electrodes in this furnace sufficient heat is developed to melt the minerals, thereby bringing them into the liquid condition, when the same current, by its decomposing action, separates the substance sought for, from the others, with which it is in chemical combination. The particular furnace shown, which has been in practical use at Lockport, N. Y., for some years, was especially designed for extracting from their natural earths, aluminium and other minerals which are difficult to obtain. See ALUMINIUM.

By means of this furnace several substances which contain valuable metals, but which were very hard to decompose, are easily torn apart and the metals obtained. By this furnace the production of large quantities of the aluminium bronzes, at prices low enough to compete with brass, has been accomplished and is now being carried on, while formerly, before the use of electricity for the purpose, the prices of these alloys were so high as to put them out of the question.

Electro-metallurgical and electro-chemical processes have made remarkable progress in the last ten years, and in 1897 there were in Europe and the United States 142 plants in operation, in which various products were made electrolytically. These may all be regarded as permanent industries, whose natural growth is assured by the purity and cheapness of the materials so manufactured. Besides these industries already established, new processes in this field are constantly being discovered. Among the more important processes are those for producing aluminium, copper, zinc, gold, silver and nickel, besides which there are a large number of materials such as sodium, potassium, white lead, calcium carbide, carborundum, etc., to which electrolytic processes are specially adapted.

Copper refining has become a very important industry, and the electrical process is an ideal one for extracting small amounts of impurities from commercial copper. There are 35 establishments for producing electrolytic copper, of which 16 are in the United States. The production of gold and silver by electrolytic methods is an assured industry, as in no other way can they be so easily and cheaply refined. In all gold mining districts where the cyanide extraction process is used the electrolytic method will be found extending. There are two such plants in Germany, 5 in the United States and 8 in the Transvaal. The manufacture of white lead will probably become an important one because the evils arising from lead poisoning in operating the older process have only been tolerated because no other satisfactory and economical method was formerly known. The cheapening of the cost of electrical energy has been alluded to as the principal incentive to the extension of electro-metallurgical operations. The recent use of waterpowers in this connection is very noticeable. In Europe there are in actual operation 16 companies which are utilizing water-powers for the manufacture of metallurgical products, and at the present time (1897) there are eight water-powers in course of development for similar processes.

In the United States the development of the water-power at Niagara Falls has led to the establishment of a number of metallurgical operations in that neighborhood. Large plants are established there for the manufacture of aluminium and carborundum, and a new plant has just been completed for the manufacture of sodium peroxide, which is used in the manufacture of hydrogen peroxide solution. The latter is extensively used for bleaching, and the peroxide of sodium is said to contain 12 times as much oxygen available for bleaching as the ordinary hydrogen peroxide solution.

The possibilities of electro-metallurgy seem almost infinite, and the field in this direction for new and valuable applications of electricity seems very promising, more especially as electrolysis seems to afford a means of accomplishing some chemical actions which are otherwise impossible.

ELECTROPHONE, an instrument devised by Dr. Strethill Wright for producing sound by electric currents of high tension. In its simplest form, the electrophone consists of two metallic plates separated by a sheet of cartridge-paper, the whole being closely pressed together by a heavy weight or screw. Such an instruinent, when its plates are connected with the terminals of a small induction-coil, forms a sonorous condenser, the note of which varies with the rapidity of action in the electrotome or contact-breaker. The more complicated electrophone communicated to the royal Scottish society of arts, 25th April, 1864, by Dr. Wright, is composed of four curved plates of the thinnest sheet zinc, each 2 by 4 ft., and each separated from its neighbor by a double layer of imitation silvered paper, the silvered sides being in apposition to the zinc. The first and third and second and fourth plates are connected by fine wires, which also connect the instrument with the induction-coil. When this instrument is connected with a small coil, the terminals of which afford a spark almost inaudible, it becomes charged and discharged with each impulse of current, each charge being attended by a sonorous tap given out by the whole mass of metal thrown into vibration, and the rapid succession of taps producing a prolonged trumpet-note, the power of which may be increased by adding battery-power to the coil. The electrophone has been recommended by its author for use as a telegraphic relay capable of giving two or four signs with a single wire, with the advantage over other relays that perfection of contact was not necessary to its working. Fig. 1 shows the mode of working the electrophone as a double relay with four signals and the galvanometer of Thomson; A represents the needle of the galvanometer, B and C the wires communicating with an electrophone. When the needle is deflected to the right, it falls on the points B and C, and sounds the electrophone through B, A, C. The signals are produced by long and short contacts, as in the code of Morse. The

FIG. 1.

second set of signals is produced by the reversal of the line-current, which throws the needle on the points of the arrangement D connected with a second electrophone of differ. ent tone. The electrophone has been employed as a lecture-table instrument to report to a large audience results of processes which can only be rendered sensible by the most delicate galvanometric apparatus. Fig. 2 shows the adaptation of the electrophone to the galvanometer. AB represents the needle of the galvanometer suspended by a silk fiber, C; D is a small vessel of mercury communicating by a fine wire with the center of the needle; while a similar wire, attached to the end of the needle B, dips into the curved trough EF, containing distilled water. The wires inserted into D and F connect the coil with the electrophone, the current passing through F, E, B, D. When the needle is deflected, the tract of water between E and F is shortened, and the electrophone gives forth a gradually increasing sound. By a delicate ystem of levers attached to the wrist, as in the sphygmograph (q.v.), the rhythm and character of the human pulse, and its variation in disease, may be indicated to the class by the physician. Further, the electrophone may be adapted to the telephone by making the telephone membrane act the part of a make-and-break for the current circulating in the primary wire of inductioncoil. This can easily be done by leading the current through the membrane, and through a spring carrying a platinum point, which presses lightly against a piece of platinum attached to the center of the membrane. If the sounds uttered into the telephone be sufficiently strong to make the membrane so to vibrate as to cause actual separation between the platinum surfaces, they will be reproduced with great loudness in the electrophone; but if, as in the case of speaking, they be merely able to cause variations of pressure at the surfaces, they will be but imperfectly heard. Hence the electrophone succeeds best with singing (see TELEPHONE), and a song gently sung in one place may be repeated in trumpet-tones in another hundreds of yards distant.

FIG. 2.

electric

ELECTROPHORUS. This generally consists of a tin mold filled with shellac, and a movable metal cover, with a glass handle. The shellac is poured in when melted, and it is mixed with some other substance, to make it less brittle. Five parts of shellac, one of wax, and one of Venice turpentine, is given as a good mixture. When used, the surface of the cake of shellac is smartly beaten with a cat's fur or foxtail. The cover is then put on, and touched with the finger, which receives a slight spark of ity, just before contact takes place; and after the finger is removed, the cover, when lifted by its insulating handle, gives a brisk spark of electricity to anything presented to it. This can be repeated for several minutes without any apparent exhaustion of the source of electricity; and in dry weather, sperks can be g in this way hours, and frequently days after the cake has been beaten.

The action of the electricity may be thus accounted for. When the surface of the cake of shellac is beaten, the friction excites electricity on it. This acts inductively all round, but the tin mold being the nearest conductor, and shellac a good dielectric, the induction becomes concentrated on it, electricity becoming fixed on the side next the shellac, and electricity being sent to the ground. The electricity of the upper surface of the shellac is thus fixed by the electricity of the mold. When the cover is put on the cake, the contact between the two is not sufficient to allow the latter to communicate its charge to the former. The cover is thus acted on inductively, not conductively. The electricity of the cake, then, has the choice of two channels for its induction, either through the cake to the mold, or through a very thin film of air to the cover. The latter, from its offering so short a passage through the dielectric, has the preference, and the inductive action of the charge is diverted from the mold to the cover, and the electricity on the other side of the cake is thus liberated and lost in the ground. The cover being strongly polarized, electricity is induced and fixed on its lower surface, and electricity on its upper, this last being transmitted to the ground by the finger. When the finger is withdrawn, and then the cover, the electricity of the latter is free to discharge itself by spark, and inductive action again takes the direction of the mold, once more attracting + electricity to it. The induced polarity of the cover is attended with no loss to the charge of the shellac, which can thus continue to act with the same efficiency. The loss of electricity that all charged bodies experience in air, and especially when moist, at length discharges the cake, but this takes place all the less readily, that when the electricity is not needed to act on the cover, it is kept bound by the electricity induced by it in the mold. In order that the electricity of the mold should have liberty, so to speak, to come and go, the electricity must not be insulated; and when it is so, the action on the cover is feeble, if at all perceptible.

ELECTRO-PLATING. The decomposition of salts by the battery has received a most important application in electro-plating, or galvano-plastics, by which is meant

the art of precipitating certain metals from their solutions by the slow action of a galIvanic current, by which means the salts of certain metals are decomposed, the metal being deposited on the negative pole, while the acid is liberated at the positive. The art was discovered independently by Spencer in England, and by Jacobi in Petersburg.

In order to obtain a galvano-plastic reproduction of a medal or any other object, a mold must first be made on which the layer of metal is deposited by the electric current. For this purpose several substances are in use, and one or the other is preferred, according to circumstances. For medals and similar objects which can be submitted to pressure, gutta-percha may be used with advantage. The gutta-percha is softened in hot water, pressed against the object to be copied, and allowed to cool, when it can be detached without difficulty. For the reproduction of engraved wood blocks or type, wax molds are now commonly used. They are prepared by pouring into a narrow flat pan a suitable mixture of wax, tallow, and Venice turpentine, which is allowed to set, and is then carefully brushed over with very finely powdered graphite. While this composition is still somewhat soft, the wood block or type is pressed upon it either by a screw press or, still better, by hydraulic pressure. If plaster of Paris molds are to be made use of, it is essential that they be first thoroughly saturated with wax or tallow, so as to become impervious to water.

In all cases, whether the molds be of gutta-percha, of wax, or any non-conducting substance, it is of the highest importance that the surface be brushed over very carefully with graphite, and so made a good conductor. The conducting surface thus prepared must also be in metallic contact with a wire or a strip of copper by which it is connected with the negative electrode. Sometimes the molds are made of a fusible alloy, which may consist of 5 parts of lead, 8 of bismuth, and 3 of tin. Some of the melted alloy is poured into a shallow box, and just as it begins to solidify, the medal is placed horizontally on it in a fixed position. When the alloy has become cool, a slight shock is sufficient to detach the medal. A copper wire is then bound round the edge of the mold, by which it can be connected with the negative electrode of the battery, and then the edge and the back are covered with a thin non-conducting layer of wax, so that the deposit is only formed on the mold itself.

The most suitable arrangement for producing an electro-deposit of copper consists of a trough of glass, slate, or of wood, lined with india-rubber or coated with marine glue. The figure shows one of glass. This con

tains an acid solution of copper sulphate, and across it are stretched copper rods, a and e, connected respectively with the negative and positive poles of a battery. By their copper conductors, the molds BBB are suspended in the liquid from the negative rod, while sheets of copper, a a a, presenting a surface about equal to that of the molds to be covered, are suspended from the positive rod at the distance of about 2 in., directly opposite to them.

The battery employed for the electric deposition of metals ought to be one of great constancy, and Daniell's and Smee's are mostly in use. The currents of electricity fu:nished by magneto-electrical machines of a special construction are also used in large establishments.

The copper plate suspended from the positive pole serves a double purpose: it not only closes the circuit, but it keeps the solution in a state of concentration, for the acid liberated at the positive pole dissolves the copper and reproduces a quantity of copper sulphate equal to that decomposed by the current.

Another and very simple process for producing the electric deposit of copper consists in making use of what is in effect a Daniell's cell. A porous pot or a glass cylinder covered at the bottom with bladder or with vegetable parchment is immersed in a vessel of larger capacity containing a concentrated solution of copper sulphate. The porous vessel contains acidulated water, and in it is suspended a piece of amalgamated zinc, of suitable form and having a surface about equal to that of the mold. The latter is attached to an insulated wire connected with the zinc, and is immersed in the solution of copper sulphate in such a position that it is directly opposite to the diaphragm. The action commences by the mold becoming covered with copper, commencing at the point of contact with the conductor, and gradually increasing in thickness in proportion to the action of the Daniell's element thus formed. It is, of course, essential in the process, to keep the solution of copper sulphate at a uniform strength, which is done by suspending in it muslin bags filled with crystals of this salt.

The extreme delicacy which such electric deposits can attain appears from the fact that galvano-plastic copies of the greatest accuracy can be made of daguerreotypes.

A novel process of electro-plating animals, flowers, tissues, and other natural objects, has been brought out in France. Slugs or snails are washed in water to clean them and then placed in distilled water until they give off their albuminous matter. This liquid is filtered and boiled for an hour; then distilled water is added to make up for that lost by boiling, and in addition about 3 per cent. of nitrate of silver. The solution is kept

Elements.

in a dark place, in hermetically sealed bottles until required for use, when about 30 grammes of the liquid are mixed with about 100 grammes of distilled water. The objects to be electro-plated are then immersed for a few moments in the liquid, are next placed in a bath consisting of about 20 per cent. of nitrate of silver dissolved in distilled water, and are finally submitted to the action of sulphuretted hydrogen gas by which the nitrate of silver on the albumen-coated object is reduced. The organic object is thus fitted to receive the electro-deposited metal, and the layer obtained is of superior fineness and delicacy.

ELECTRO-POSITIVE ORDER OF THE ELEMENTS. As a voltaic current is produced whenever two metals are placed in metallic contact in a liquid which acts more powerfully upon one than upon the other, there is a great choice in the mode of producing such currents. In reference to their electrical deportment, the metals have been arranged in what is called an electro-motive series, in which the most electro-positive are at one end, and the most electro-negative at the other. Hence when any two of these are placed in contact in dilute acid, the current in the connecting wire proceeds from the one lower in the list to the one higher. The principal metals are as follows:

It will be seen that the electrical deportment of any metal depends on the metal with which it is associated. Iron, for example, in dilute sulphuric acid is electro-negative towards zinc, but is electro-positive towards copper; copper, in turn, is electro negative towards iron and zinc, but is electro-positive towards silver, platinum, or graphite.

The relative positions in this scale of the substances depend, somewhat upon the nature of the liquid in which they are placed.

ELECTROSCOPE is any instrument for the detection of the presence of electricity. It depends for its action on the principle that bodies charged with like electricity repel, while those charged with unlike electricity attract each other. The ordinary pith-ball is the simplest form of the instrument. The most perfect form is Bennet's gold leaf electroscope, but Cavallo's, Volta's condensing, and Bohnenberger's electroscopes are also used.

ELECTROTYPE, PHOTOGRAPHIC. Much thought and labor have been expended in producing a relief-plate to take the place of wood-engraving, and various` methods of etching on metal by the aid of photography have been brought to light. The earlier of these never were successful, because after the acid has eaten or etched below the surface protected by the asphaltum, there is nothing to prevent it from undermining the lines, as the acid will eat in one direction as well as another, thus weakening them to such an extent that they often break down in printing. With the gelatine process, the gelatine must be of a thickness compatible with the depth desired. A gelatine of this thickness will become nearly, if not quite insoluble before it is dry, through the action of bichromate alone. Also the color of the gelatine, after the bichromate has been added, is such as to prevent the action of light from penetrating to the proper depth in the time during which it can be exposed. These are the almost insurmountable reasons why a relief-plate in gelatine has not been obtained till the advent of a new process called photo-electrotype. W. H. Mumler, of Boston, Mass., has now succeeded in overcoming these obstacles. After printing upon his gelatine, through a negative, the necessary time to secure all the details, the parts unaffected are dissolved away to a slight depth. The interstices are then filled with a black paste, when it is again exposed to light; the soluble parts that were protected by the opacity of the negative in the first printing are now protected from the action of light by the black paste that covers them. The second exposure may be continued for a length of time sufficient to allow the light to penetrate its entire depth; and the action of light being to render the gelatine insoluble, it can readily be seen that the protected parts can be dissolved away to the depth to which the light has penetrated. The gelatine relief is then placed in a drying closet for a few hours, when it becomes as hard as horn. From this an electrotype is taken in precisely the same manner as from a wood-cut. It is then mounted on mahogany blocks, type high, when it is ready for the press. The result is an electrotype plate with a surface as smooth as polished plate-glass, and a depth far exceeding that of ordinary wood-cuts. See PHOTO

GRAPHY.

ELECTROTYPING. The process of forming exact reproductions of type, woodcuts, and so forth by means of the process of electro-plating (q.v.). See also ELECTROMETALLURGY; ELECTRO-CHEMISTRY. Electrotypes are very much used in printing on account of their furnishing inexpensive and perfectly accurate reproduction of the original. By their use many complete sets of type for printing are quickly obtained, and the original type is saved from the great wear which would result from the direct printing from them of many thousands of copies.