��ELECTROLYTES.
��CHAP.
��transportation, the so-called metallic conduction, went on simultaneously, and by this there was no decomposition of the substance. However, very exact investigations have proved that always so much salt is decomposed as is required by Faraday's law. Occasionally it is found that the quantity of hydrogen or oxygen evolved is too small, but this is due to the solubility of the gases in the liquid ; and diffusion of the dissolved gases takes place, so that some of the hydrogen parses to the positive pole, and some oxygen to the negative pole, and there (by contact action of the platinum) partial recombination to water takes place!
Faraday termed an ion that product which is formed at a pole independently of whether it is the result of a primary or secondary action. Amongst the ions he therefore included not only chlorine and potassium, but also hydrochloric acid, caustic potash, and oxygen, but not the compound hydroxyl (OH), because this could not be obtained in the free state.
We now understand by ions those parts of an electrolyte which, electrically charged, wander through the liquid towards the electrodes, whether they sufiTer a secondary change at the electrodes or not.
Application of Ohm's Law to Solutions. — ^Let us again consider a current passing through a parallel-sided trough
(Fig. 27) with two pole- J^ v - plates, A being the posi-
tive, and B the negative. Suppose, further, that the electrodes are non-polar- isable, as would be the case if we take amalga- mated zinc plates in a
solution of zinc sulphate. The electricity is then trans-
+ + ported by the ions Zn and SO4, of which the former, the
cation, goes to the negative pole B, and the latter, the
anion, goes to the positive pole A,
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Fig. 27.
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