being dilute sulphuric or hydrochloric acid: Sodium, magnesium, zinc, iron, copper, silver, platinum. When a compound of two elements is electrolyzed, the electro-positive element appears at the negative electrode, and the electro-negative element at the positive electrode. It is impossible to make a single table of the electro-chemical order of the elements, as this is not the same under all circumstances, but it may be generally stated that oxygen is the most electro-negative element, and that next to it are the elements chlorine, bromine, fluorine, sulphur, etc., which form stable compounds with the metals.

ELECTRO-CHEMISTRY OR ELECTROLYTICS. The name electrolysis (breaking up by electricity) is given to the process of transmission of the electric current through liquids, when accompanied by the disruption of the molecules composing the circuit; the constituent radicals of the molecules being set free at the two poles.

The plates in the decomposition cells are called electrodes (electric ways); the plate connected to the+pole of the battery, usually copper, platinum, or carbon, is the anode (way up, as carrying the current out of the battery); the plate connected to the pole of the battery (the zinc) is the cathode (downward way).

The liquid undergoing decomposition is the electrolyte. The molecules of an electrolyte break up into two radicals, which are called ions (indicating individuality, and in another sense meaning "going"). Those ions which turn towards the anode are called anions. They are electro-negative or acid radicals, such as oxygen and chlorine. Those which turn towards the cathode are called cations. They are electro-positives or basic radicals, as hydrogen and metals. The same ion may belong at different times to each of these classes if united to one having a higher individuality in either direction, for there is no direct attraction between the electrodes and the ions themselves, but the relation depends simply upon the temporary polarity they assume in the circuit.

Ions or radicals may be single atoms or compounds, which act as radicals chemically, and these may even be incapable of actual separate existence as far as present knowledge goes. Hydrochloric acid is an electrolyte composed of two single atoms. In sulphuric acid two atoms of hydrogen form one ion, and the compound radical, SO,, the other. This radical cannot exist uncombined, so that sulphuric acid is an electrolyte only when in presence of something it can react on and combine with, such as water, although water itself is not an electrolyte. Ammonium, NH,, is also a compound ion strongly resembling potassium in its properties; it also cannot exist free, but breaks up into NH, (ammonia) and hydrogen, giving an apparent exception to the law of equivalence, by producing two free substances, each equivalent to the current producing them; but it must be considered that ammonia is not really a radical, for NH, may be considered as the equivalent of a complete molecule and is not capable of replacing hydrogen in salts.

We must regard the circuit as consisting of chains of molecules, some metallic, as in the plates and conductors; some liquid, as in the cells; and the transmission of electricity, as consisting of a motion of each molecule in the chain, accompanied with the breaking in halves of a molecule wherever the current passes from metal to liquid, or vice versa. We shall thus understand why there is equal current, equal quantity of electricity, or equivalent chemical action at every section of the circuit. Because there are the same number (or value, as will be seen presently) of molecular actions effected at every part, however the molecules themselves may differ in nature. Each cell is, therefore, a section of the conductor, and each has its own specific resistance, just as the wire portion has. But the cells are of two orders in one respect.

(1) Generating cells, in which energy is set free by chemical actions, and becomes electro-motive force, setting up the current. These are battery cells, represented by E in electrical formulæ. (2) Decomposition cells, in which energy is absorbed in doing chemical work. These may be simple resistances, where no ultimate change is made in the solution; such are most electro-plating and electro-metallurgical processes where the same metal is dissolved from the anode as is set free at the cathode. But if any ions are actually set free by the current, they tend to recombine and act as a cell of the first order, with their electro-motive force opposed to that of the battery. This "counter E M F" is represented in formulas by e, as is the electro-motive force of secondary batteries. See ELECTRICITY, STorage of. The feeblest electro-motive rce will send a current through the first of these classes of decomposition cells, but the second class require an E M F greater than that of opposition set up by the action itself, or electrolysis cannot take place, for the reason that no current will be produced if stopped by this counter E M F, as it is called. Except for this distinction of generating and decomposing, all the cells are under the same conditions. In each cell there is a plate or element, the zinc in the battery cells and the anode in the decomposition cells, and if the latter can unite to the chlorous radical of the electrolyte, it dissolves, just as the zinc does in the battery cells. In each cell there is the electrolyte which gives up its chlorous orion, at the plate, and transmits the molecular motion, which constitutes the current to the-plate where it also gives up its + ion. The plate then continues as the + pole or anode to the next cell, and ultimately to the pole or terminal zinc of the battery to complete the circuit. In fact, each pair of connecting plates in separate cells acts as though it were a metallic partition separating the two liquids with which the plates are in contact. In such a plate or conducting partition, one side would be and the other side —, and the two plates in different cells correspond to these two sides, united

Electrophon

by a connecting wire instead of by the mass of metal of the plate itself. It is of the utmost importance to bear in mind this distinction of plates or elements related to the liquid within their own cell, and of poles or electrodes related to another cell, and to the direction of the polarity they set up, or the current they transmit. Leaving out of sight the distinction of cells, as those setting up and those absorbing energy, that plate in each cell which is to its own liquid, or the positive plate of the cell, is the anode or electrode of the cell to which it is connected, and completes the circuit from the plate of this cell. Hence it is that the anode in the decomposition cell represents the zinc in the battery cell, for, like the zinc, it is to the liquid, and gives up energy to the liquid (though that energy is derived from the current itself in this cell), and, like the zinc, it dissolves if made of materials which can combine with the negative or - radical of the solution. For this reason some prefer to call the anode the zincode. The laws of electrolysis usually accepted are those of Faraday, who also originated the terms described. These laws are:

1. No elementary substance can be an electrolyte. That is to say, the two ions must be differently composed.

2. Electrolysis occurs only while the body is in the liquid state. This state may be due to either fusion or solution; in the latter case many substances which are not electrolytes of themselves may become electrolytes by a secondary action.

3. During electrolysis the components of the electrolyte are resolved into two groups; one group takes a definite direction towards one of the electrodes, the other group takes a course towards the other electrode. They turn towards the several electrodes in polar order, but are not attracted or moved towards them by a direct attraction of the polar electrodes. Faraday held that only substances containing single equivalents of each radical could act as electrolytes, but this is now superseded by more general conceptions.

4. The amount as well as the direction of electrolysis is definite, and is dependent upon the degree of action in the battery being directly proportional to the quantity of electricity in 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 equivalent, 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,Cl,, 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.

The general subject of electro-chemistry is too long, as well as too indirect in its practical applications, to admit of further consideration here.

For practical applications in its field, see ELECTRO-METALLURGY, ELECTRO-CHEMISTRY, ELECTRO-PLATING. See also Sprague's Electricity: Its Theory, Sources, and Applications.

ELECTROLYSIS. See ELECTRO-CHEMISTRY.

ELECTRO-METALLURGY AND ELECTRIC SMELTING. Electro-metallurgy is the art of treating metals by the use of electricity. In recent years, since currents of great power have been made available by the invention of powerful dynamos, electrometallurgical 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 ELECTRO-PLATING (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. Into opposite sides of a brick retort are inserted very large carbon rods about the size of a man's arm. The current is led from the generator to these rods by large cables connected to heavy copper heads, which are cast solid on the outer ends of the carbon rods for the purpose of making good connections. A very strong current is passed through the substances with which the retort is filled, passing

from the end of one rod to the other, and heating the contents to any desired degree. The advantages of this arrangement as a method of applying heat are that substances which, when heated, would attack and destroy a retort as ordinarily used, may be melted without harm in this, because the molten part is surrounded by cooler material, which

does not affect the retort. Unlike other retorts, in which the bottom is thin in order that the heat from the fire below may reach the interior, this is made strong and thick for the purpose of holding the heat. It therefore requires very much less expense in electric currents for fuel than it would if the heat were applied externally. It has been possible to perform chemical manufacturing processes successfully in this retort, which were not practicable before on account of the destructive nature of the substances to be treated.

Another feature of the process is the use of charcoal mixed with the substances, for the double purpose of carrying the electricity through the substances, and converting it into heat as it passes across the retort, and causing the charcoal to absorb the oxygen from and refine the substances, or causing it to act as a " reducing agent," as it is called in metallurgy. 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.

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. 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

The

FIG. 1.