Faraday as a Discoverer HTML version

Chapter 6
Laws of electro-chemical decomposition.
In our conceptions and reasonings regarding the forces of nature, we perpetually make
use of symbols which, when they possess a high representative value, we dignify with the
name of theories. Thus, prompted by certain analogies, we ascribe electrical phenomena
to the action of a peculiar fluid, sometimes flowing, sometimes at rest. Such conceptions
have their advantages and their disadvantages; they afford peaceful lodging to the
intellect for a time, but they also circumscribe it, and by-and-by, when the mind has
grown too large for its lodging, it often finds difficulty in breaking down the walls of
what has become its prison instead of its home.[1]
No man ever felt this tyranny of symbols more deeply than Faraday, and no man was
ever more assiduous than he to liberate himself from them, and the terms which
suggested them. Calling Dr. Whewell to his aid in 1833, he endeavoured to displace by
others all terms tainted by a foregone conclusion. His paper on Electro-chemical
Decomposition, received by the Royal Society on January 9, 1834, opens with the
proposal of a new terminology. He would avoid the word 'current' if he could.[2] He does
abandon the word 'poles' as applied to the ends of a decomposing cell, because it suggests
the idea of attraction, substituting for it the perfectly natural term Electrodes. He applied
the term Electrolyte to every substance which can be decomposed by the current, and the
act of decomposition he called Electrolysis. All these terms have become current in
science. He called the positive electrode the Anode, and the negative one the Cathode,
but these terms, though frequently used, have not enjoyed the same currency as the
others. The terms Anion and Cation, which he applied to the constituents of the
decomposed electrolyte, and the term Ion, which included both anions and cations, are
still less frequently employed.
Faraday now passes from terminology to research; he sees the necessity of quantitative
determinations, and seeks to supply himself with a measure of voltaic electricity. This he
finds in the quantity of water decomposed by the current. He tests this measure in all
possible ways, to assure himself that no error can arise from its employment. He places in
the course of one and the same current a series of cells with electrodes of different sizes,
some of them plates of platinum, others merely platinum wires, and collects the gas
liberated on each distinct pair of electrodes. He finds the quantity of gas to be the same
for all. Thus he concludes that when the same quantity of electricity is caused to pass
through a series of cells containing acidulated water, the electro-chemical action is
independent of the size of the electrodes.[3] He next proves that variations in intensity do
not interfere with this equality of action. Whether his battery is charged with strong acid
or with weak; whether it consists of five pairs or of fifty pairs; in short, whatever be its
source, when the same current is sent through his series of cells the same amount of
decomposition takes place in all. He next assures himself that the strength or weakness of
his dilute acid does not interfere with this law. Sending the same current through a series
of cells containing mixtures of sulphuric acid and water of different strengths, he finds,