Chemical factory. External view of a chlor-alkali chemical factory used in the production of caustic soda (sodium hydroxide) & chlorine gas. These chemicals are mainly used to make other chemicals. The sodium hydroxide and chlorine are made by passing an electric current through a solution of common salt (sodium chloride), a process known as electrolysis. Photograph of the DCM Shriram plant at Jhagadia, Bharuch in Gujarat, India.