CHAPTER XV.

Oxidation and Reduction Elements. Secondary Elements.

Becquerel's Experiments — Becquerel (1) has shown that when two platinum or gold electrodes are surrounded, one with an oxidising and the other with a reducing agent, a current passes in the liquid from the reducing to the oxidising agent. Ostwald and his pupils haye made a study of these so-called oxidation and redtoction elements. Bancroft (2) found an electromotive force for the ele- ment —

Pt in SnCla | NaCl | NaCl + Bra at Pt

of 1-171 volts.

In place of stannous chloride, any reducing agent, such as sulphurous acid or ferrous sulphate, may be used; and instead of bromine, any oxidising agent, like gold or mercuric chloride, potassium permanganate, etc. ; in this way quite considerable electromotive forces can be obtained. Bancroft arranged the oxidising and reducing agents examined in this way in a series which describes well their chemical position.

In these elements we have evidently a direct trans- formation of chemical into electrical energy. Ostwald terms this " chemical action at a distance." The oxidation and reducing agents which, when mixed, react chemically on each other, are here separated, and can only react when an electric current passes through the liquid and brings

�� �