 Castner's only asset then was his cheap sodium and he worked to develop uses for this, including the manufacture of sodium peroxide, a bleaching agent, and sodium cyanide which was used in the gold mining industry.In 1890 Castner devised a new method for producing very pure caustic soda by the electrolysis of brine in a rocking cell containing mercury.This process also produced the useful by-products, chlorine and hydrogen.