Water cannot be decomposed when in a state of ice, and other substances, as oxide of lead and chloride of silver, require for electrolysis to be fused to give them conducting power. 2. The energy of electrolytic action is the same in all parts of the current. 3. The same quantity of electricity de: composes chemically equivalent quantities of all the electrolytic constituents through which it passes. That is to say, the same current will in the same time decompose 165 parts of iodide of potassium, 101 of nitrate of potash, 59 of chloride of sodium, and 9 of water. The decomposition which takes place in electrolysis creates a resistance to the current, and tends to generate a current in an opposite direction, the action being similar to what would be the case if one of the cells of the battery were to be reversed, so that the current would be forced to pass through the liquid from the copper to the zinc. This is in agreement with the doctrine of conservation of forces. A certain amount of the power generated by the consumption of the positive element of the battery, that is to say, by the combination of the acid with the zinc, may be expended in one way or another in the conductors which are traversed by the current.

A certain amount of decomposition or electrolysis may be effected in one part, a certain amount of heat in another, and a certain quantity of mechanical power in another; the sum of all the forces expended being precisely equal to the original electromotive force.-Polarization of Electrodes. After protracted electrolysis, if the electrodes are disconnected from the battery and placed in a conducting liquid and connected externally by a wire, a current will flow in a direction opposite to that which was generated by the battery. Suppose, for instance, that in fig. 27 a battery decomposes sulphate of soda by a current passing in the liquid from A to B. If after a time the battery is removed and the wires attached to the electrodes are connected and coiled around a magnetic needle as shown in fig. 28, it will be found that the current is now flowing in the liquid from B to A, or in a direction opposite to that urged by the battery. The action may be explained as follows: During electrolysis potash collects on the electrode B, and sulphuric acid on A. The battery being removed and a connecting wire substituted, the acid and alkali tend to unite and produce an electromotive force in an opposite direction.

In the electrolysis of water, or any body which causes oxygen to be evolved at one electrode and hydrogen at the other, a thin film of gas becomes attached to either plate, having sufficient electromotive force to send a current in the contrary direction when the battery is removed and a connecting wire introduced. Such currents, produced by polarized plates, are called secondary currents; and upon this principle Prof. Grove constructed a gas battery which is capable of producing a continuous current. Two glass tubes (fig. 29), closed at the top and each containing a strip of platinum of the length of the tube having a surface of finely divided platinum, which is suspended by a platinum wire passing through the top of the tube, which is closely sealed, are filled with dilute sulphuric acid, and their lower ends, which are open, are placed in the same liquid in the vessel a a. The platinum strips are then connected with the poles of a battery, and by electrolysis hydrogen is collected in one tube and oxygen in the other.

Upon removing the battery and connecting the platinum strips either through a galvanometer or an easily decomposed electrolyte, as iodide of potassium, a current will flow from the oxygen to the hydrogen tube, and in the opposite direction to that produced by the battery used in evolving the gases, while during the action the gases in the tubes will gradually disappear, the hydrogen twice as fast as the oxygen. Ritter's secondary pile is constructed upon the same principle. A number of disks of the same metal are separated by pieces of moistened cloth. After passing for a time a galvanic current through the system, on removing the battery and connecting the ends of the pile a current will be found passing in the opposite direction to the battery current.-Prof. Clau-sius proposes a molecular theory of electrolysis," which may be briefly stated as follows. An electromotive force urges the constituents of the compound molecules of an electrolyte in opposite directions. The components being joined together in pairs by chemical force, an electrolytic force sufficient to tear them asunder is hardly conceivable, and therefore an additional power is sought for. The molecules of an electrolyte, as of all bodies, are constantly in a state of more or less intense vibration.

In electrolytes, which are fluids, the molecules, which exist in pairs, are constantly striking against each other. Sometimes the components of a pair are separated, and it is at this time, according to Clausius, that the electromotive force causes the molecules of one kind to move in one, and those of the other kind in the opposite direction.-The identity of frictional electricity and galvanism is regarded as established, but the expression is rather indefinite when it is considered that at the same time a wide difference in the phenomena is recognized. That the particles of ponderable matter, or of ether, whichever may be the media of electrical action, assume motions of an entirely different character, and which may also be transformed one into another in accordance with the influence of other forces and conditions, is not only probable, but is a view whose acceptance can scarcely be resisted. Moreover, having accepted the doctrine that ethereal heat vibrations are communicated to ponderable matter, and from ponderable matter again to the ether, it is natural to believe that electrical motion in ether may propagate or generate motion in ponderable matter, which we recognize as another form of electricity.