Michael Faraday, His Life and Work

by Silvanus P. Thompson

The “former occasions” is a reference to an earlier suggestion that a current might mean anything progressive, whether a flow in one direction or two fluids moving in opposite directions, or merely vibrations, or, still more generally, progressive forces. He had expressly said that what we call the electric current “may perhaps best be conceived of as an axis of power having contrary forces, exactly equal in amount, in contrary directions.”

ELECTRO-CHEMICAL LAWS.

He then suggests as a measurer of current the standard form of electrolytic cell ever since known as the voltameter. He preferred that kind in which water is decomposed, the quantity of electricity which had flowed through it being measured by the quantity of the gas or gases evolved during the operation. Before adopting this he undertook careful experiments in which his fine manipulative skill, no less than his chemical experience, was called into service to verify the fact that the quantity of water decomposed was really proportionate to the quantity of electricity which has been passed through the instrument. Having this standard, he investigated numerous other cases of decomposition by the current, and so arrived at a substantial basis for the doctrine of definite electro-chemical action. Speaking of the substances into which electrolytes are divided by the current, and which he had called ions, he says: “They are combining bodies; are directly associated with the fundamental parts of the doctrine of chemical affinity; and have each a definite proportion, in which they are always evolved during electrolytic action.... I have proposed to call the numbers representing the proportions in which they are evolved electro-chemical equivalents. Thus hydrogen, oxygen, chlorine, iodine, lead, tin are ions; the three former are anions, the two metals cations, and 1, 8, 36, 125, 104, 58, are their electro-chemical equivalents nearly.”

This fundamental law being set upon an impregnable basis of facts, he goes on to speculate upon the absolute quantity of electricity or electric power belonging to different bodies; a notion which only within the last few years has found general acceptance.

In developing this theory he uses the following language:—

According to it [i.e. this theory], the equivalent weights of bodies are simply those quantities of them which contain equal quantities of electricity, or have naturally equal electric powers; it being the ELECTRICITY which determines the equivalent number, because it determines the combining force. Or, if we adopt the atomic theory or phraseology, then the atoms of bodies which are equivalents to each other in their ordinary chemical action, have equal quantities of electricity naturally associated with them. But I must confess I am jealous of the term atom....

Here we find the modern doctrine of electrons or unitary atomic charges, clearly formulated in 1834. In the course of this speculation he remarks that “if the electrical power which holds the elements of a grain of water in combination, or which makes a grain of oxygen or hydrogen in the right proportions unite into water when they are made to combine, could be thrown into the condition of a current, it would exactly equal the current required for the separation of that grain of water into its elements again.” And all this years before there was any doctrine of the conservation of energy to guide the mind of the philosopher! The passage just cited contains the germs of the thermodynamic theory of electromotive forces worked out a dozen years later by Sir William Thomson (now Lord Kelvin), by which theory we can predict the electromotive forces of any given chemical combination from a knowledge of the heat evolved by a given mass of the product in the act of combining.

ANOTHER UNSUCCESSFUL QUEST.

The eighth series of the researches, which was read in June, 1834, deals chiefly with voltaic cells and batteries of cells. He is now applying to the operations inside the primary cell the electrochemical principles learned by the study of electrolysis in secondary cells. His thoughts have been incessantly playing around the problem of electrolytic conduction. He was convinced that the forces which shear the anions from combination with the cations and transfer them in opposite directions must be inherent before the circuit is completed, and therefore before any actual transfer or movement takes place. “It seems to me impossible,” he says, “to resist the idea that it [the “transfer,” or “what is called the voltaic current”] must be preceded by a state of tension in the fluid. I have sought carefully for indications of a state of tension in the electrolytic conductor; and conceiving that it might produce something like structure, either before or during its discharge, I endeavoured to make this evident by polarised light.” He used a solution of sulphate of soda, but without the slightest trace of optical action in any direction of the ray. He repeated the experiment, using a solid electrolyte, borate of lead, in its non-conducting state, but equally without result.

During the time of these electrochemical researches in 1833 and 1834, Faraday’s activities for the Royal Institution were undiminished. In 1833 he gave seven Friday discourses, three of them on the researches in hand, one on Wheatstone’s investigation of the velocity of the electric spark, and one on the practical prevention of dry rot in timber, which was afterwards republished as a pamphlet, and ran to two editions. In 1834 he gave four Friday discourses; two on his electrochemical researches, one on Ericsson’s heat-engine, and the other on caoutchouc.