B.—CHEMISTRY. 41 
he quickly realised that whether a current passes or not depends on the 
relative magnitudes of the chemical affinities of the reactions taking place 
in the battery and in the electrolytic cells. On February 19 he wrote: 
* Affinity is active at both points, but is as it were connected or related 
by the current of electricity in the communicating wires, or in other 
words affinity is electricity and vice versa.’ And three days later: ‘ Must 
make out what happens in cases of chemical action with no current.’ 
“We seem to have the power of deciding in certain cases of chemical 
affinity (as of zinc with the oxygen of water) which of two modes of action 
of the one power shall be exerted. In the one mode we can transfer the 
power on it being able to produce elsewhere its equivalent of action 
in the other it is not transferred on but exerted at the spot. The first 
is the case of Voltaic Electric production, the other the ordinary cases of 
chemical affinity. But both are chemical actions and due to one power 
or principle.’ 
In other words Faraday saw that a chemical reaction can be carried 
out in two ways, either by means of a voltaic cell in which the reactants 
- are separated by an electrolyte, or by their direct contact, and further, 
he identified the electromotive force of the cell with the chemical affinity 
of the reaction. Half a century was to elapse before the conception of 
chemical affinity assumed a definite form in chemists’ minds, but here 
Faraday anticipates our modern interpretation. His method of reasoning 
too, is an instinctive recognition of the Law of Conservation of Energy, 
and it was in connection with the chemical theory of the cell that he 
wrote in 1840, ‘in no case . . . is there a pure creation or production of 
power without a corresponding exhaustion of something to supply it.’ 
It is difficult for us to-day to realise the effect of Faraday’s work on the 
progress of electrochemistry, the clarity of ideas which came from his 
new nomenclature, the quantitative treatment of the problems which was 
made possible by his Laws of Electrolysis, the significance of his distinction 
between quantity of electricity and its tensity or potential, and his 
association of these two electrical quantities with the magnitude of the 
chemical change and of the chemical affinity respectively. 
Naturally, with so vast and complex a subject, so little understood, 
even Faraday made mistakes. He thought that in aqueous solutions 
hydrogen and oxygen were the ions that carried the current, other ions 
only appearing at the electrodes by secondary action, although in fused 
_ salts he knew that these secondary products acted as ions in his own sense 
of the word. Then, he supposed that only compounds containing one 
atom of each element could act as electrolytes, and he made rash state- 
ments about the existence of a binary oxide and sulphide of antimony. 
He thought, too, that an element could have only one electro-chemical 
equivalent, neglecting the different degrees of oxidation of metals. And 
he assumed that electrolytes possessed a certain measure of metallic con- 
ductivity subsidiary to their electrolytic conduction. 
It is interesting to read the criticism of Berzelius on Faraday’s discovery. 
_Berzelius was the foremost chemist of the day, a pioneer in electro- 
chemistry, a fine experimenter with encyclopedic knowledge, but con- 
servative in outlook. In a letter to Wohler, Berzelius criticises the paper, 
and says that it has diminished greatly his opinion of Faraday. He proved 
