40 SECTIONAL ADDRESSES. 
naturally associated with the particles of matter, gives them their com- 
bining power, is able, when thrown into a current, to separate those 
particles from their state of combination; or in other words, that 
the electricity which decomposes, and that which is evolved by the 
decomposition of a certain amount of matter, are alike.’ 
In this way the theories of combination in definite proportions and of 
electro-chemical affinity were brought into harmony. 
Faraday pointed out that ‘if we adopt the atomic theory or 
phraseology then the atoms of bodies . . . have equal quantities of 
electricity associated with them.’ Had he been a believer in the atomic 
theory he might have made the deduction that electricity, like matter, 
is atomic in nature. ‘I must confess,’ he said, ‘that I am jealous of the 
term atom ; for, though it is very easy to talk of atoms, it is very difficult 
to form a clear idea of their nature.’ And it was left to Helmholtz, in his 
Faraday lecture of 1881, to point out this most startling result of Faraday’s 
laws: ‘If we accept the hypothesis that the elementary substances are 
composed of atoms, we cannot avoid concluding that electricity also, 
positive as well as negative, is divided into definite elementary portions, 
which behave like atoms of electricity.’ 
As soon as the work for the great paper was ended Faraday returned 
to a topic that had constantly been in his mind, the long-disputed question 
of the source of electricity in the voltaic cell, whether it was due to chemical 
action or to the contact of dissimilar metals. The inquiry was linked with 
the question of the intensity, or, as we call it, the electromotive force, of 
the cell, and the relation of this to the power of cells to produce electrolysis. 
On January 18, 1834, he made some experiments when Daniell was 
present on the number of cells necessary to electrolyse sulphuric acid, 
which showed him ‘ that the number of decompositions which on the one 
hand excite or produce the current and on the other retard it constitute 
the essential point.’ ‘ Beautiful,’ he writes, ‘I think I see it all, but 
must go on with fluorine first.’ For three weeks he tried to isolate fluorine, 
and on February 10 thought he had obtained it by the electrolysis of fused 
lead fluoride. ‘ Must now lay this subject aside for a while and go to the 
trough.” On April 7, less than two months later, his paper ‘On the 
Electricity of the Voltaic Pile’ reached the Royal Society. In it he 
presents fresh experimental evidence for the chemical theory of the voltaic 
cell, including a direct proof that a current may flow when there is no 
direct contact between the two metals, a slip of paper moistened with 
potassium iodide being interposed between them. In this paper Faraday 
first points out clearly the distinction he makes between the quantity of 
the current and its intensity, or electromotive force, and the relation of 
the latter to the chemical affinity of the reaction which is producing the 
current or opposing its passage. During the two months Faraday carried 
out a large number of experiments on the intensity required to produce 
electrolysis by varying the number of cells in the battery and seeing how 
many were required to produce and electrolyse various compounds in 
solution or in a fused state. On February 10 he notes ‘The power of 
decomposing water a good unit of intensity in voltaic apparatus.’ 
It is clear from his note-book that his mind was concentrated on the 
relation between chemical action and the production of electricity, and 
