Part 41

827. ii. If one ion be combined in right proportions (697.) with another strongly opposed to it in its ordinary chemical relations, i.e. if an anion be combined with a cation, then both will travel, the one to the anode, the other to the cathode, of the decomposing body (530, 542. 547.).

828. iii. If, therefore, an ion pass towards one of the electrodes, another ion must also be passing simultaneously to the other electrode, although, from secondary action, it may not make its appearance (743.).

829. iv. A body decomposable directly by the electric current, i.e. an electrolyte, must consist of two ions, and must also render them up during the act of decomposition.

830. v. There is but one electrolyte composed of the same two elementary ions; at least such appears to be the fact (697.), dependent upon a law, that only single electro-chemical equivalents of elementary ions can go to the electrodes, and not multiples.

831. vi. A body not decomposable when alone, as boracic acid, is not directly decomposable by the electric current when in combination (780.). It may act as an ion going wholly to the anode or cathode, but does not yield up its elements, except occasionally by a secondary action. Perhaps it is superfluous for me to point out that this proposition has no relation to such cases as that of water, which, by the presence of other bodies, is rendered a better conductor of electricity, and therefore is more freely decomposed.

832. vii. The nature of the substance of which the electrode is formed, provided it be a conductor, causes no difference in the electro-decomposition, either in kind or degree (807. 813.): but it seriously influences, by secondary action (714.), the state in which the finally appear. Advantage may be taken of this principle in combining and ions collecting such ions as, if evolved in their free state, would be unmanageable.

It will often happen that the electrodes used may be of such a nature as, with the fluid in which they are immersed, to produce an electric current, either according with or opposing that of the voltaic arrangement used, and in this way, or by direct chemical action, may sadly disturb the results. Still, in the midst of all these confusing effects, the electric current, which actually passes in any direction through the body suffering decomposition, will produce its own definite electrolytic action.

833. viii. A substance which, being used as the electrode, can combine with the ion evolved against it, is also, I believe, an ion, and combines, in such cases, in the quantity represented by its electro-chemical equivalent. All the experiments I have made agree with this view; and it seems to me, at present, to result as a necessary consequence. Whether, in the secondary actions that take place, where the ion acts, not upon the matter of the electrode, but on that which is around it in the liquid (744.), the same consequence follows, will require more extended investigation to determine.

834. ix. Compound ions are not necessarily composed of electro-chemical equivalents of simple ions. For instance, sulphuric acid, boracic acid, phosphoric acid, are ions, but not electrolytes, i.e. not composed of electro-chemical equivalents of simple ions.

835. x. Electro-chemical equivalents are always consistent; i.e. the same number which represents the equivalent of a substance A when it is separating from a substance B, will also represent A when separating from a third substance C. Thus, 8 is the electro-chemical equivalent of oxygen, whether separating from hydrogen, or tin, or lead; and 103.5 is the electrochemical equivalent of lead, whether separating from oxygen, or chlorine, or iodine.

836. xi. Electro-chemical equivalents coincide, and are the same, with ordinary chemical equivalents.

837. By means of experiment and the preceding propositions, a knowledge of ions and their electro-chemical equivalents may be obtained in various ways.

838. In the first place, they may be determined directly, as has been done with hydrogen, oxygen, lead, and tin, in the numerous experiments already quoted.

839. In the next place, from propositions ii. and iii., may be deduced the knowledge of many other ions, and also their equivalents. When chloride of lead was decomposed, platina being used for both electrodes (395.), there could remain no more doubt that chlorine was passing to the anode, although it combined with the platina there, than when the positive electrode, being of plumbago (794.), allowed its evolution in the free state; neither could there, in either case, remain any doubt that for every 103.5 parts of lead evolved at the cathode, 36 parts of chlorine were evolved at the anode, for the remaining chloride of lead was unchanged. So also, when in a metallic solution one volume of oxygen, or a secondary compound containing that proportion, appeared at the anode, no doubt could arise that hydrogen, equivalent to two volumes, had been determined to the cathode, although, by a secondary action, it had been employed in reducing oxides of lead, copper, or other metals, to the metallic state. In this manner, then, we learn from the experiments already described in these Researches, that chlorine, iodine, bromine, fluorine, calcium, potassium, strontium, magnesium, manganese, &c., are ions and that their electro-chemical equivalents are the same as their ordinary chemical equivalents.

840. Propositions iv. and v. extend our means of gaining information. For if a body of known chemical composition is found to be decomposable, and the nature of the substance evolved as a primary or even a secondary result (743. 777.) at one of the electrodes, be ascertained, the electro-chemical equivalent of that body may be deduced from the known constant composition of the substance evolved. Thus, when fused protiodide of tin is decomposed by the voltaic current (804.), the conclusion may be drawn, that both the iodine and tin are ions, and that the proportions in which they combine in the fused compound express their electro-chemical equivalents. Again, with respect to the fused iodide of potassium (805.), it is an electrolyte; and the chemical equivalents will also be the electro-chemical equivalents.

841. If proposition viii. sustain extensive experimental investigation, then it will not only help to confirm the results obtained by the use of the other propositions, but will give abundant original information of its own.

842. In many instances, the secondary results obtained by the action of the evolved ion on the substances present in the surrounding liquid or solution, will give the electro-chemical equivalent. Thus, in the solution of acetate of lead, and, as far as I have gone, in other proto-salts subjected to the reducing action of the nascent hydrogen at the cathode, the metal precipitated has been in the same quantity as if it had been a primary product, (provided no free hydrogen escaped there,) and therefore gave accurately the number representing its electro-chemical equivalent.

843. Upon this principle it is that secondary results may occasionally be used as measurers of the volta-electric current (706. 740.); but there are not many metallic solutions that answer this purpose well: for unless the metal is easily precipitated, hydrogen will be evolved at the cathode and vitiate the result. If a soluble peroxide is formed at the anode, or if the precipitated metal crystallize across the solution and touch the positive electrode, similar vitiated results are obtained. I expect to find in some salts, as the acetates of mercury and zinc, solutions favourable for this use.

844. After the first experimental investigations to establish the definite chemical action of electricity, I have not hesitated to apply the more strict results of chemical analysis to correct the numbers obtained as electrolytic results. This, it is evident, may be done in a great number of cases, without using too much liberty towards the due severity of scientific research. The series of numbers representing electro-chemical equivalents must, like those expressing the ordinary equivalents of chemically acting bodies, remain subject to the continual correction of experiment and sound reasoning.

845. I give the following brief Table of ions and their electro-chemical equivalents, rather as a specimen of a first attempt than as anything that can supply the want which must very quickly be felt, of a full and complete tabular account of this class of bodies. Looking forward to such a table as of extreme utility (if well-constructed) in developing the intimate relation of ordinary chemical affinity to electrical actions, and identifying the two, not to the imagination merely, but to the conviction of the senses and a sound judgement, I may be allowed to express a hope, that the endeavour will always be to make it a table of real, and not hypothetical, electro-chemical equivalents; for we shall else overrun the facts, and lose all sight and consciousness of the knowledge lying directly in our path.

846. The equivalent numbers do not profess to be exact, and are taken almost entirely from the chemical results of other philosophers in whom I could repose more confidence, as to these points, than in myself.

847. TABLE OF IONS.

Anions.

Oxygen 8 Chlorine 35.5 Iodine 126 Bromine 78.3 Fluorine 18.7 Cyanogen 26 Sulphuric acid 40 Selenic acid 64 Nitric acid 54 Chloric acid 75.5 Phosphoric acid 35.7 Carbonic acid 22 Boracic acid 24 Acetic acid 51 Tartaric acid 66 Citric acid 58 Oxalic acid 36 Sulphur (?) 16 Selenium (?) Salpho-cyanogen

Cations.

Hydrogen 1 Potassium 39.2 Sodium 23.3 Lithium 10 Barium 68.7 Strontium 43.8 Calcium 20.5 Magnesium 12.7 Manganese 27.7 Zinc 32.5 Tin 57.9 Lead 103.5 Iron 28 Copper 31.6 Cadmium 55.8 Cerium 46 Cobalt 29.5 Nickel 29.5 Antimony 61.67 Bismuth 71 Mercury 200 Silver 108 Platina 98.6? Gold (?)

Ammonia 17 Potassa 47.2 Soda 31.3 Lithia 18 Baryta 76.7 Strontia 51.8 Lime 28.5 Magnesia 20.7 Alumina. (?) Protoxides generally. Quinia 171.6 Cinchona 160 Morphia 290 Vegeto-alkalies generally.

848. This Table might be further arrange into groups of such substances as either act with, or replace, each other. Thus, for instance, acids and bases act in relation to each other; but they do not act in association with oxygen, hydrogen, or elementary substances. There is indeed little or no doubt that, when the electrical relations of the particles of matter come to be closely examined, this division must be made. The simple substances, with cyanogen, sulpho-cyanogen, and one or two other compound bodies, will probably form the first group; and the acids and bases, with such analogous compounds as may prove to be ions, the second group. Whether these will include all ions, or whether a third class of more complicated results will be required, must be decided by future experiments.