Page:Outlines of Physical Chemistry - 1899.djvu/203

 68-8 - 96 - ark

— of antimony, 85*5 of CI

Faraday's law concerning the phenomena of electro- lysis states that, when equal quantities of electricity pass through different electrolytes^ equivalent quantities of these electrolytes are decomposed. The equivalent x of an ion is equal to its atomic weight divided by its valency. Suppose that in the circuit of an electric current we place solutions of silver nitrate, copper sulphate, and antimony trichloride, we find that the elements or radicals separated are in the following proportion :

108 of silver, 62 of NO, (^^ ?* £fP osit ^

on the cathode. The acid

radicals generally react on

the solvent water and evolve

an equivalent quantity of

v oxygen.

The electro-chemical equivalent of an element is subject to the same variations as its valency. Thus for

fiO»Q

copper we have -— or 63*3, according as the copper is

A

present in the compound in the cupric or cuprous state. From the ferrous and ferric salts we get the equivalents

lr and — for iron. In potassium ferrocyanide the equi-

valent of the negative radical is e .^ 6, whilst in the ferri-

cyanide it is V^ 6.

Let us now return to the electrical units and see how

they are applied to electrolytic phenomena. Kohlrausch

and Lord Bayleigh have found that a current of one

amp&re acting for one second on a silver solution deposits

0*001118 gram of silver on the cathode. One coulomb

therefore sets free the 96540th part of an equivalent of

1 The term equivalent has been used in most of our theories. We meet it here for the third time, but this time it has a profound theoretical meaning.

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