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electric spark was passed through air. Similar experiments were made 
by Cavendish and Von Marum with decomposed ammonia. It is not, how- 
ever, till after the discovery of the voltaic cell that the subject of electro- 
lysis really begins. I have already referred to the discovery of Nicholson 
and Carlisle in 1800 and to the subsequent work of Davy and Faraday. 
The peculiar phenomena of the appearance of separated elements only at 
the end plates in the electrolytic cell led to considerable speculation and 
was explained by Grothuss on the supposition that the molecules sepa- 
rated into two parts, one positively and the other negatively electrified, 
and that these parts formed a chain between the plates along which chem- 
ical action traveled by a continual interchange of mates, the end parts 
going to the plates. This theory was held for many years and is still to 
be found in some text books. I: ‘aday’s work is by the far the most 
valuable of the early contributions to this subject. He gave the following 
laws: 
“The amount of chemical decomposition in electrolysis is proportional 
to the current and the time of its action. 
“The mass of an ion liberated by a definite quantity of electricity is 
directly proportional to its chemical equivalent weight. 
“The quantity of electricity which is required to decompose a certain 
amount of an electrolyte is equal to the quantity which would be pro- 
duced by recombining the separated ions in a battery.” 
These laws are all of the greatest importance, and the last one clearly 
points out the reversibility of the electrical process. By forcing a current 
through an electrolyte it is decomposed and the mutual potential energy 
of the components consequently increased. By allowing the components 
to recombine in a battery the mutual potential energy is reduced and a 
current of electricity is the result. An excellent illustration of this action 
is exhibited by the secondary battery. 
In 1857 Clausius gave a theory of electrolysis and at the same time re- 
viewed the weaknesses of the hypotheses of Grothuss and others. Clausius 
assumes that the molecules of the liquid are in continual motion, that im- 
pacts frequently occur which produce temporary dissociation, leaving 
atomic groups charged with opposite electricities, and that during these 
separations any directive agency such as an e. m. f. is able to cause a 
motion of these atoms in opposite directions. This is probably the first 
