The atoms separated from each other by the electric current were called ions by Faraday; those going to the anode being anions, and those going to the cathode being kathions.

Anions are generally regarded as electro-negative, because they move as if attracted to the positive electrode, while kathions are regarded as electro-positive.

In order to explain the transfer of electricity and the transfer of matter through the electrolyte, Grotthuss put forward the hypothesis that when two metal plates at different potentials are placed in a cell, the effect produced in the liquid is that the molecules of the liquid arrange themselves in innumerable chains, as shown in fig. 91, in which every molecule has its atoms pointing in a certain direction, the electro-positive atom being attracted towards the cathode and the electro-negative towards the anode. An interchange then takes place all along the line, the free atoms appearing at the electrodes, and every atom discharging a minute charge of electricity upon the electrode at which it is liberated.

Electro-chemical Series.—This is an arrangement of the metals in a series in such a manner that the most electro-positive is at one end and the most electro-negative at the other.

The order of the metals varies with the electrolyte in which the metals are tested.

The following table shows such series for the most common metals, in three different solutions:

Sulphuric acid.Hydrochloric acid.Caustic potash.
ZincZincZinc
CadmiumCadmiumTin
TinTinCadmium
LeadLeadAntimony
IronIronLead
NickelCopperBismuth
BismuthBismuthIron
AntimonyNickelCopper
CopperSilverNickel
SilverAntimonySilver
Gold
Platinum

Faraday stated several laws of electrolysis, as follows:

1. The quantity of an ion liberated in a given time is proportional to the quantity of electricity that has passed through the voltameter[10] in that time.

2. The quantity of an ion liberated in a voltameter is proportional to the electro-chemical equivalent of the ion.