of vitriol;-very slightly by solution of potash, and not at all by anhydrous hyponitric acid. (Faraday.)

The conducting power of platinum is 2546680 times greater than that of a saturated solution of sulphate of copper. Assuming the latter = 1, that of a mixture of 1 measure of solution with 1 measure of water = 0.64, with 2 measures of water 044, with 4 measures of water = 0·31; that of a saturated solution of sulphate of zinc = 0.417; that of a mixture of water with nitric acid = 0·015; and that of pure water 0.0025. (Pouillet.)

The current of a 40-pair battery passed through pure water gives only as much detonating gas in a given time, as when the decomposing cell contains dilute sulphuric acid. (Faraday.)-Water becomes much more easily decomposible when mixed with sulphuric acid than when saturated with common salt. (Henrici.)

The current of a pair of zinc and copper plates in saturated solution of common salt, conducted by means of two gilt brass plates into the undermentioned liquids (all the solutions are saturated) produces the following deflections of an interposed galvanometer: Pure water, ; acetate of lead, 3...4°; sulphate of potash or soda, nitre, chloride of calcium, or chloride of lead, 5°; chlorate of potash, 7°; borax, chloride of manganese, tartrate of potash, tartar emetic, acetate of soda, or benzoate of potash, 10°; carbonate of potash or soda, 11°; green vitriol, nitrate of lead, or acetate of potash, 12°; oxalate of potash, 13°; aqueous ammonia of sp. gr. 0.980, or tartaric acid, 15°; protochloride of tin, 10...20°; alum or sulphate of copper, 20°; sulphate of zinc, 22; dilute phosphoric acid, 23°; strong vinegar, 25°; mixture of 1 part oil of vitriol and 4 parts water, 28°; nitrate of mercury, 30°; English oil of vitriol, 30...32°; nitrate of silver (solution not quite saturated), 35°; dilute nitric acid, sal-ammoniac, or sesqui-chloride of iron, 42°; bichloride of platinum, 45°; dilute hydrochloric acid, 50°.-When a large pair of zinc and copper plates is excited by solution of common salt, the deflections are stronger, but the differences with respect to the various liquids smaller. (Pfaff, Schw. 55, 258.)

The current of the same battery passed through various acids of different degrees of concentration, produces, according to Matteucci, the following deflections:

If the deflection produced by 1 part of sal-ammoniac in 100 parts of water amounts to 12°, it will be 22 with 2 parts of sal-ammoniac, 26° with 3 parts, and 27° with 4 parts.-If 1 part of sulphate of zinc in 100 of water gives 3° deflection, 2 parts of the same salt will give, 5°,-3 parts, 6.5-4 parts, 8°,-5 parts, 13,-6 parts, 17°,-7 parts, 23°,-and 8 parts, 24°. If a solution of 1 part of sal-ammoniac in 100 water gives a deflection of 12°, and a solution of 1 part of nitre in 100 water, a deflection of 8°, a solution of sal-ammoniac and 1 nitre in 100 water, will produce a deflection of 12° + 8° = = 20°. The same simple addition takes place with other aqueous and alcoholic solutions. Hence, when 1 part of sal

Since hydrochloric acid never has the sp. gr. 1.26, it is probable that the numbers annexed to hydrochloric acid really belong to nitric acid, and vice versa. (Vid. Ann. Chim. Phys. 66, 243.)

ammoniac is added to a cold saturated solution of nitre, which by itself produces a deflection of 21°, the deflection increases to 26°; by the further addition of 1 part of sulphate of copper, it is raised to 30°. (Matteucci.)

A constant battery of eight pairs of amalgamated zinc, copper, and dilute nitro-sulphuric acid, gives the following deflections, all the solutions containing 1 part of salt in 100 parts of water: Pure water, ; green vitriol, acetate of lead, or acetate of morphia, 2°; iodide of potassium or sulphate of copper, 3°; bicarbonate of potash, nitre, or chloride of calcium, 5°; bicarbonate of soda or nitrate of silver, 6°; carbonate of ammonia, 7°; carbonate of potash or soda, 8°; common salt, 10°; and sal-ammoniac, 12°. (Matteucci.)

The undermentioned salts give the following deflections, according as they are introduced into the current in a state of aqueous fusion or in saturated solution: Acetate of lead, 16° and 16°; chloride of calcium, 45° and 44°; alum, 42° and 42°; sulphate of zinc, 43° and 42°. Hence, the deflection is either the same in both cases, or rather stronger when the salt is in the fused state. If a saturated solution of nitre gives 30°, and of chloride of potash 38°, fused nitre will give a deflection increasing from 42° to 55°, and fused chlorate of potash, from 40° to 47°;-when solid matter begins to separate, the deflection increases to 55°. (Matteucci.)

A pair of zinc and copper plates excited by water sends a stronger current by means of copper-electrodes through dilute sulphuric acid, than a similar pair excited by dilute sulphuric acid sends through water.

Influence of the Temperature and Compression of the Electrolyte upon Decomposition.

Hot water is more abundantly decomposed by the electric current than cold water. (Gay-Lussac & Thénard.)-The deflection of the galvanometer increases considerably as the electrolyte is heated: but this increase reaches its limit at a certain temperature, which is so much the higher as the conducting power of the electrolyte is less. On subsequent cooling, the liquid still retains a little of the increased conducting power which it had acquired by heating. (Matteucci.)-In a larger volume of water exceeding an inch in diameter, the influence of heat is imperceptible. In dilute sulphuric acid, a very feeble current of 12° is increased to 30 by igniting both the electrodes, or only the negative one, whereas heating the positive electrode alone has no effect whatever. Similarly with nitric acid, the deflection is increased from 12° to 80° by heating the negative electrode. (De la Rive.) [The application of heat to the negative electrode probably liberates the bubbles of hydrogen gas which cover that electrode in large quantities, and hinder the transference of electricity.]-The deflection of the needle is likewise increased by heating the positive electrode. (Faraday.)- Heating the positive electrode increases the current, only when the temperature is raised to the boiling point of the liquid-the heat then acting by mechanical agitation and removing from the negative electrode the substances (gas-bubbles) which have been carried towards it: hence the deflection is likewise increased by shaking the negative electrode. (Vorsselman de Herr, Pogg. 49, 109.)

The decomposition of water goes on in a sealed glass tube containing two platinum wires, even when the water is subjected by the accumulated detonating gas to a pressure of eleven atmospheres, the deflection of the

galvanometer even increasing a little under these circumstances. (Jacobi.) The development of gas still goes on when the water is subjected to a pressure of 150 atmospheres, till at length the tube bursts. (Degen, Pogg. 38, 454.)

Influence of the Relative Volume of the Electrolyte on Decomposition.

When the current from two pairs of zinc and platinum excited by dilute sulphuric acid, is conducted by means of two platinum plates into dilute sulphuric acid, the strength of the current is the same, whether the platinum plates are at the distance of six inches from one another or separated only by the thickness of a sheet of paper. (Faraday.) [With pure water, a greater difference would probably be found.]

The thinner the film of liquid which the current has to traverse, the greater is the deflection produced. The increase of deflection caused by diminishing the thickness of the liquid, is the more considerable as the conducting power of the liquid is less [i. e. as the resistance to the transposition of atoms is greater]. When, however, by enlarging the platinum plates, the current has been raised to its maximum, the deflection is no longer increased by bringing the electrodes nearer together. (Matteucci.)

The distance between the electrodes remaining the same, the deflection is augmented up to a certain point by increasing the height and breadth of the liquid; but when the increase in dimension is carried further, the deflection diminishes. The deflection is stronger when the positive electricity enters by the narrower part of the liquid, and the negative by the wider, than in the contrary case. (Matteucci.)

Influence of the Chemical Nature of the Electrodes on Decomposition.

The greater the tendency of the electrodes to combine with those elements of the liquid which are set free upon them, the more easily does the decomposition takes place.

If the quantity of electricity in the current of a single pair of zinc and copper plates in dilute sulphuric acid be equal to 1000 when the circuit is closed by good metallic conductors, it will amount to the following quantities when the current is conducted by the under-mentioned electrodes into the following liquids: zinc plates in water, 0-8; in fuming oil of vitriol, 647; in a mixture of 1 part of sulphuric acid and 3 parts water, 851;-platinum electrodes in hydrochloric acid, 2:6; in nitric acid, 17.7; in aqua regia, 338 3. Hence it appears that those liquids which do not act chemically on the electrodes offer the greatest resistance. (Fechner.)

If the cups a, b (App. 2), contain dilute sulphuric acid, o consisting of zinc, p of copper, and ghi of one of the following metals, no hydrogen gas is evolved at the end p when ghi consists of platinum, and only a trace when it is formed of gold; next follows silver, then copper, then tin, then iron, and lastly zine, which yields most of all. If, however, the two cups contain ammonia, the deflection is stronger when ghi consists of copper than when it is formed of iron. (De la Rive.)

When the positive electricity of a pair of zinc and platinum is conducted by zinc into dilute sulphuric acid, the quantity of the current is the same as when the circuit is metallically closed without the interposition of a liquid. (Faraday: vid. 441.)

Influence of the Surface of the Electrodes upon Decomposition.

Electrodes of small surface evolve as much detonating gas from acidu lated water in a given time as those of a larger surface. (Faraday.) When, however, the current is strong, the decomposition diminishes if the electrode be too small to allow free passage to the current; thus, a Daniell's battery of ten pairs yields 2-7 cubic inches of detonating gas, whether the electrodes are formed of broad plates of platinum, or of wires; but if the latter are covered with resin to within a quarter of an inch of their points, the quantity of gas per minute is reduced to 2-3 cub. in.; and when they are coated up to their points, it is only 0.8 cub. in.: in this last case, the gas is driven into the liquid with some force. (Daniell.) -With currents of small quantity, on the contrary, the decomposition is increased by diminishing the size of the electrodes, and thereby concentrating the current. (Wollaston, Matteucci.) The deflection is likewise stronger when the positive electricity enters by a narrower, and the negative electricity by a wider electrode, than in the contrary case [because a greater quantity of gas is evolved at the negative electrode]. (Matteucci.)

Decomposition of Individual Compounds.

Nicholson and Carlisle discovered the decomposition of water, Hisinger & Berzelius that of salts, Sir H. Davy that of the alkalis.

Water.

The electric current acts more readily on water contained in a bundle of asbestus fibres than on a column of that liquid of equal length and thickness in a U-tube. (H. Davy.)

Many substances which are soluble in water favour its decomposition (p. 443); but with a powerful battery, the same quantity of detonating gas is obtained in a given time, whether the water is mixed with a large or a small quantity of sulphuric acid, or holds in solution, potash, soda, carbonate of potash, sulphate of ammonia with excess of ammonia, or sulphate of soda. Dilute sulphuric acid of sp. gr. from 1.25 to 1.336 is best adapted for the purpose. Acid of 1·495 sp. gr. yields a somewhat greater quantity of gas, because it retains less oxygen gas in solution. With acid of still greater strength, e. g. 2 measures of oil of vitriol to 1 measure of water, only 0.57 volume of oxygen gas is obtained for every 2 volumes of hydrogen,-possibly because the predisposing affinity of the sulphuric acid favours the production of peroxide of hydrogen. (Faraday.) Connell likewise obtained with these different solutions, and also with that of boracic acid, constantly the same quantity of detonating gas.

When water is divided by a membrane into two portions, and one of the electrodes of a powerful battery immersed in each of them, the water rises in the negative and sinks in the positive division. (Porret.)—This effect is exhibited by distilled water and rain-water, which are bad conductors, but not by saline solutions, and is due to the resistance which the water opposes to the passage of positive electricity. (De la Rive.)On the contrary: This effect seen only in water which holds in solution some salt, by the decomposition of which, alkali collects in the negative and acid in the positive division; and the rise of the water is not a

direct consequence of the action of the electric current, but is produced by endosmose. (Dutrochet, Pogg. 28, 36; comp. Schweigger, Schw. 16, 383.)

Water not freed from atmospheric air yields, in consequence of the nitrogen which it contains, nitric acid in the positive gold cup, and ammonia in the negative gold cup connected with the former by means of asbestus, the nitrogen combining with oxygen at the anode and with hydrogen at the cathode: the quantity of the nitric acid continually increases, but that of the ammonia soon reaches a maximum. If the receiver under which the gold cups are placed be exhausted of air, then filled with hydrogen, and again exhausted, neither acid nor ammonia appears in the water. (H. Davy.)

When platinum electrodes are used, somewhat less than one measure of oxygen gas is obtained for every two measures of hydrogen; for the former is more readily absorbed by water,-partly because it is evolved in smaller bubbles, partly because water is essentially capable of absorbing oxygen gas in greater quantity than hydrogen; perhaps also a small quantity of peroxide of hydrogen is formed at the anode. The detonating gas likewise contains nitrogen, which was previously dissolved in the water. (Faraday.)-Just at the commencement of the decomposition, the detonating gas contains less than its normal quantity of oxygen, because the positive platinum wire oxidates on the surface: the latter portions of detonating gas contain almost exactly the proper quantity of oxygen. If both the platinum plates have been previously cleansed (by rubbing them while hot with hydrate of potash, dipping them in oil of vitriol, and washing with water out of contact of air), the negative plate immediately evolves gas, the positive plate not till after some few seconds, because the first portions of oxygen are retained by the platinum: if, on the other hand, the platinum plates have been exposed to the air for some time, gas is immediately disengaged on the positive plate. but often not till after twenty seconds on the negative plate,-because the first portions of hydrogen set free have to reduce the oxide of platinum. (De la Rive.)

Clean platinum wire used in rapid alternation as positive and nega tive electrode becomes covered with a black powder, consisting of finely divided metallic platinum; for the metal, in conducting positive electricity, takes up a trace of the liberated oxygen and forms an oxide, which, when afterwards used as a cathode, is reduced by the hydrogen to the state of finely divided platinum.-If the electrode a consists of a thin platinum wire, and the electrode b of a broad plate of the same metal, the volumes of oxygen and hydrogen gas evolved from water acidulated with sulphuric acid are in the exact proportion of 1: 2, when a is used as the anode, because the small surface of the wire can take up but a trifling quantity of oxygen; but when b is used as anode, the quantity of oxygen is deficient; and if b be then put in the place of the cathode, the quantity of hydrogen appears deficient, because a portion of that element is employed in reducing the oxide previously formed on b. Hence, when platinum which has been used as anode is afterwards made to conduct negative electricity, some seconds elapse before hydrogen gas appears on its surface, because the first portions enter into combination with the oxygen of the oxide of platinum. This power possessed by platinum of fixing oxygen on its surface explains the fact announced by Peclet, viz. that platinum may be positive with regard to gold. Gold wire used as the anode in dilute sulphuric acid acquires a reddish tinge from oxidation, -and, when the poles are changed, becomes pulverulent on the surface, in