A diminution in the number of positive ions would thus naturally be accompanied by a rise in potential gradient.
In 1887 Svante Arrhenius, professor of physics at Stockholm, put forward a new theory which supposed that the freedom of the opposite ions from each other was not a mere momentary freedom at the instants of molecular collision, but a more or less permanent freedom, the ions moving independently of each other through the liquid.
Thus the osmotic pressure, or the depression of the freezing point of a solution of potassium chloride should, at extreme dilution, be twice the normal value, but of a solution of sulphuric acid three times that value, since the potassium salt contains two ions and the acid three.
The rate of loss of charge is thus largely dependent on the extent to which ions are present in the surrounding air.
It depends, however, in addition on the natural mobility of the ions, and also on the opportunities for convection.