views similar to that of Grotthuss. Becquerel (Ann. Chim. Phys.) supposes, as I do, that the atoms move in semicircles one over the other. According to Faraday (Phil. Trans. 1833, II., 675; also Pogg. 32, 401), who admits but one kind of electricity, electrolytic decomposition is the result of a peculiar corpuscular action developed in the direction of the current; it proceeds from a force which is either added to the affinity of the bodies present or determines the direction of that force. The decomposing body is a mass of acting particles, of which all that lie in the course of the current contribute to the terminal action; and in consequence of the affinity between the elements being weakened or partially neutralized by the current, parallel to its own course in one direction, and strengthened and assisted in the other, the combined particles acquire a tendency to move in different directions. The particles of one element a cannot travel from one pole to the other, unless they meet with particles of an opposed substance b ready to move in the opposite direction. For, in consequence of their increased affinity for these particles, and the diminution of their affinity for those which they have left behind them in their way, they are continually driven forward. Faraday, therefore, likewise supposes a transposition of particles. According to De la Rive (Ann. Chim. Phys. 28, 190), the positive electricity which enters a liquidwater for example-combines with the hydrogen, setting the oxygen free, and carries the hydrogen rapidly along with it through the whole mass of liquid till it reaches the negative wire; it then enters the wire, while the hydrogen combined with it escapes in the form of gas. At the same time, the negative electricity proceeding from the negative wire liberates hydrogen from the contiguous atom of water, carries the oxygen of the same atom over to the positive wire, enters the wire, and sets the oxygen free. Hence the oxygen gas evolved at the positive pole proceeds from two sources-half from the positive, and half from the negative current; similarly with respect to the hydrogen gas.-This view is mainly liable to the objection, that when the polar wires dip into two different liquids, the anions of the liquid which is in contact with the negative wire usually require a long continued action of the current to bring them to the positive pole, and sometimes do not reach it at all;-similarly, with regard to the passage of the cations of the other liquids towards the negative pole. For example, when solution of sulphate of magnesia is placed in contact with the positive pole and water in contact with the negative pole, no magnesia is set free at the latter, the whole of that substance being precipitated at the surface of separation of the two liquids. According to Biot, a liquid placed in the voltaic circuit divides itself into two halves, one of which acquires a positive the other a negative electrical tension. Each element of the liquid then goes towards that side which is charged with the kind of electricity opposite to its own, and thus decomposition ensues. But the evolution or precipitation of the elements does not take place throughout the two halves of the liquid-but, for the most part, solely at the polar wires.]

Electrolytes, Ions, and Products of Decomposition in general.

According to Faraday, only those compounds of the first order are directly decomposible, which contain one atom of one of their elements for each atom of the other,-e. g., compounds of 1 At. hydrogen or metal with 1 At. of oxygen, iodine, bromine, chlorine, fluorine, or cyanogen, &c. On the other hand, boracic acid (B O3), sulphurous acid (SO2), sul

VOL. I.

2 F

phuric acid (S O3), iodide of sulphur, chloride of phosphorus (P Cl3) and (P C15), chloride of sulphur (S2 C1), chloride of carbon (C CI), bichloride of tin (Sn Cl2), terchloride of arsenic (As Cl3), quintochloride of antimony (Sb C15), and acetic acid in the liquid but anhydrous state, are undecomposible and act as non-conductors. Oxide of antimony and terchloride of antimony, which are decomposible in the fused state (the latter however but slightly), form an exception not yet explained; so likewise does protiode of mercury (Hg I), which in the melted state conducts without suffering decomposition.-All compounds which are decomposible when dissolved in water, behave in the same manner when fused. (Faraday.)

Connell found that when the electric current was conducted into fused iodic acid (IO), the galvanometer was deflected and the acid decomposed: he considers however that the decomposition may be the result of heat, inasmuch as the fusing and decomposing points of the acid are near to one another. Liquid ammonia-possibly from containing a trace of water-conducts slightly the electricity of a battery of 250 pairs, so that an agitation is perceptible in it; but water placed in the same circuit is not decomposed. (Kemp.)-Liquid cyanogen does not conduct the electricity of a battery of 300 pairs of plates. (Kemp.)

Of the elements (and substances like ammonium and cyanogen, which replace them in their combinations), some are always evolved at the negative, others always at the positive pole, with whatever other substance they may be combined-hence they are divided into cations, which are evolved at the negative electrode, and anions which are evolved at the positive electrode.-The Anions are: Oxygen, fluorine, chlorine, bromine, iodine, and cyanogen,-probably also sulphur, seleninm and sulpho-cyanogen (For the acids also included in this class by Faraday, vid. Decomposition of Salts).—The Cations are: Hydrogen, the alkalimetals, magnesium, manganese, antimony, bismuth (?), zinc, cadmium, tin, lead, iron, cobalt, nickel, copper, mercury, silver, gold, platinum (and ammonium). The salifiable bases are also classed by Faraday under this head (vid. Decomposition of Salts).-All the elements are probably ions; but with respect to some among them, nothing has yet been determined by experiment. (Faraday.)

It is necessary to distinguish, as Faraday does, between direct and indirect decomposition by the electric current. The former arises from the immediate action of the current; but the substances thereby liberated at the electrodes, may, when the liquid is a mixture of several compounds, exert a decomposing action on a compound upon which the current does not act directly. Thus, aqueous ammonia is resolved by the electric current into hydrogen gas at the negative and nitrogen gas at the positive pole. It may be supposed that the water alone is directly decomposed; and that the oxygen separated at the positive pole, abstracts hydrogen from the ammonia and sets free the nitrogen of the same compound. It cannot however be positively determined, either in this or in many other cases, which decomposition is direct and which indirect.

Degree of Decomposition.

When the electric current continues for a sufficient length of time, the decomposition is complete. If the two electricities be conducted into two cups containing dilute solution of sulphate of potash, and connected by a moistened wick of asbestus, which is washed twice a day, so that no salt may be deposited upon it,-the positive cup is found, after three

days, to contain all the sulphuric acid, and the negative cup all the potash. (H. Davy.)

Place of Decomposition.

The separation of the ions takes place only in the immediate neighbourhood of the electrodes, not at any part of the liquid at a distance from them. (H. Davy, De la Rive.) If a solution of common salt, coloured with infusion of violets, be divided into three portions by two membranous partitions the electrodes dipping into the outermost divisions-the colour of the liquid changes in these divisions alone, not in the middle. (De la Rive.)

When a number of currents, either equally or unequally strong, pass simultaneously through the same liquid, either in the same or in opposite directions, neither of them is disturbed by the rest. (Marianini.)

Relation between the Quantity of the Electric Current and the Quantity of Liquid decomposed.

A battery which retains a platinum wire of an inch thick in a state of constant ignition during the whole time occupied by the decomposition, decomposes one grain of water in 3 minutes: this quantity of electricity is perhaps equal to that of a powerful stroke of lightning. (Faraday.)

The quantity of electricity which enters the liquid is directly proportional to the quantity of liquid decomposed. Hence, the quantity of electricity in the current may be determined from the quantity of the products of decomposition. (Faraday, De la Rive.) The greater therefore the quantity of electricity which the apparatus employed yields in a given time, the greater will be the quantity of liquid decomposed, provided that the electricity possesses the requisite tension. Hence the batteries of Grove, Daniell, Sturgeon, Smee, and others, have the strongest decomposing action, the electrical machine the weakest..

Faraday's Volta-electrometer or Voltameter. Into the lower part of a graduated tube closed at the top (App. 28) are inserted, opposite to each other, two platinum wires, to the ends of which are attached two small plates of platinum placed upright in the tube. The open end of the tube is inserted into one aperture of a vessel, two-thirds filled with dilute sulphuric acid of sp. gr. from 1.25 to 1336, the other aperture being closed with a stopper. The tube is filled with liquid by inverting the apparatus. It is then placed upright, and the two platinum wires connected with the poles of the battery, in order to determine the quantity of detonating gas evolved in a given time. The decomposition must not be allowed to go on long enough to bring the gas in contact with the platinum plates, because these plates would give rise to a slow re-union of the gases.-In many liquids, as in hydrochloric acid, only hydrogen gas has to be collected, in others only oxygen, as in the case of sulphate of copper. In such cases, the voltameter may be formed of a graduated tube, having a platinum wire inserted into its upper and closed end, filled with the liquid, and inverted in a glass vessel into which the other electrode is introduced (App. 29). Other arrangements are likewise described by Faraday.

Whether the quantity of electricity in the current be measured by the voltameter or by the galvanometer (in proportion to the tangent of the

deflection, and therefore by means of Nervander's compass) or by the electro-magnetic balance, the proportion obtained is invariably the same. (Jacobi.)

An atom of any one electrolyte requires for its decomposition the same quantity of electricity as an atom of any other, whether the combination be held together by strong or by feeble affinity.

If the current of a battery be passed through the voltameter, and thence -by means of a platinum wire entering at the upper end and conveying positive electricity-into a glass tube containing fused protochloride of tin, and having inserted into its lower end, a platinum wire, which serves as the negative electrode, then, for every 9 parts of water decomposed in the voltameter, 58.53 parts of tin are deposited on the last-mentioned wire (the atomic weight of tin is 59).-When fused chloride, iodide, oxide, and borate of lead, were treated in a similar manner, the quantity of lead obtained was too small in proportion to the water decomposed, viz. to 9 parts of water, 100-8, 89, 93-2 and 1013 lead, whereas the atomic weight of lead is 103.8. The cause of the deficiency is probably that a portion of the precipitated lead was redissolved by the anion. When two silver wires are introduced as electrodes into fused chloride of silver, the weight of the positive electrode diminishes almost exactly by 108-1 parts of silver for every 9 parts of water decomposed in the voltameter, whilst that of the negative electrode increases by the same quantity. Chloride and iodide of lead treated in the same manner, lead being used as the positive electrode, give 101-5 and 103.5 lead for every 9 parts of water. (Faraday.)

If the same current be made to pass through fused chloride of lead and solution of Glauber's salts, one atom of Glauber's salt is decomposed for every atom of lead reduced. If instead of Glauber's salt a solution of common salt be used, the electricity being conducted into it by means of a weighed tin plate, then for every atom of lead reduced, one atom of soda is separated, and one atom of tin dissolved. (Daniell.)

If the current of a battery be passed through a number of metallic solutions connected by platinum wires, the metals are precipitated in the ratio of their atomic weights,-e. g., about four times as much silver as copper. (Matteucci.)

For Berzelius's objections to Faraday's law-that equal numbers of atoms of liquid require equal quantities of electricity to decompose them— vid. Berzelius' Jahresb., 15, 34.

The quantity of electricity which an atom of liquid requires to decompose it, is equal to the quantity which an atom of the same liquid evolves during its electro-chemical decomposition by ponderable bodies. (Faraday.)

If an atom of hydrogen has given up a quantity of negative electricity, denoted by x, and an atom of oxygen the same quantity of positive electricity, in combining to form water, this same quantity of electricity must be restored to each of them by the current.-When an atom of water is decomposed by an atom of zine which combines with its oxygen, a units of negative electricity are set free from the zinc,-while the atom of hydrogen evolved on the copper, takes x units of negative electricity from it, and sets free x units of positive electricity, which flow through the connecting wire to the x units of negative electricity liberated from the zinc].

The following experiments afford an approximate demonstration of this law; but the quantity dissolved in each cell of the battery in proportion to 9 parts (1 Át.) of water in the voltameter, was always greater than

32-2 parts (1 At.), on account of pure chemical action, which could not be altogether prevented.

9

When a Daniell's constant battery, with amalgamated zinc was used, 33.6 parts of zinc were dissolved in each cell of the battery for every parts of water decomposed. (Jacobi.)

With batteries containing only one liquid, the loss of zinc is greater. When the form of the battery and the nature of the liquid are varied, the following differences are observed,-F. denoting Faraday's apparatus, with double copper surface (p. 424); Tg. the common trough-battery, with single copper surface; QZ. the surface of the plates in square inches, PZ. the number of pairs; 1 Tr. the number of atoms of zinc dissolved in one trough during the decomposition of one atom of water; and Tot. the number of atoms of ziuc dissolved in all the troughs taken together. In both batteries, the liquid used was a mixture of 200 measures of water, 4.5 of oil of vitriol, and 4 of strong nitric acid.

QZ. PZ. 1 Tr. Tot. QZ. PZ. 1 Tr. Tot. QZ. PZ. 1Tr. Tot. F... 3 40

2.25

Tg.. 4 40 3.54

88.4

4

20

3.7 74

4

10 6.76 67.6 10 15.5 155.0

141-6 4 20 5.5 110

When different liquids are used in a Faraday's battery of forty pairs, the quantities of zinc dissolved in each cell for one atom of water decomposed are as follows: With 200 measures of water mixed with 8 of strong nitric acid, 1.85 At.; the same quantity of water with 16 nitric acid, 1.82; with 32 nitric acid, 2.1 At.; with 16 measures of strong hydrochloric acid, 3.8; with 9 measures of oil of vitriol, 4.66; with 16 measures of strong hydrochloric and 6 of nitric acid, 2:11; with 45 measures of oil of vitriol and 4 of nitric acid, 2.26; with 9 measures of oil of vitriol and 4 of nitric acid, 2.79; and with 9 measures of oil of vitriol and 8 of nitric acid, 2.26 At. zinc. Nitric acid is therefore the best for this battery; and different degrees of dilution of this acid do not affect, to any considerable extent, the proportion between water decomposed and zinc dissolved. (Faraday.)

If the current from about four pairs of zinc and copper be made to pass into a solution of nitrate of silver, and the quantity of zinc dissolved be the same one time as another, the quantity of silver separated will likewise be constant,-whether the zinc be quickly dissolved by the use of strong and warm acid, and the galvanometer strongly deflected by the current-or the zinc be slowly dissolved by cold, weak acid, and the galvanometer feebly deflected. The same quantity of electricity passes through the liquid in both cases, though in different times: hence the quantity of silver precipitated is likewise the same. Similar results are obtained with a battery of copper, platinum, and nitric acid.—If a pile a be constructed of lead and platinum plates, and a pile of copper and platinum, the weight of the lead plates being to that of the copper plates in the ratio of the atomic weights of the metals, viz., as 103.8: 32,-and the currents of both batteries be passed through solution of nitrate of silver contained in separate vessels, then, when all the copper and lead are dissolved, the quantities of silver separated in the two vessels will be found to be equal. (Matteucci.)

Since an electrical machine developes much less electricity in a given time than a galvanic battery, even with very small plates, it does not readily produce decomposition, notwithstanding its high tension. When the machine is employed for this purpose, the two electrodes are connected with the two coatings of the electrical battery, or one with the conductors and the other with the rubber or the ground. The excessive tension of