"[A] considerable quantity of is used for the preparation of or caustic soda, which has also a very wide application. In large chemical works where sodium carbonate is manufactured from Na2SO4, it is usual first to manufacture , and then by its aid to convert common salt into , and lastly to convert the sodium sulphate thus obtained into carbonate and caustic soda. Hence these works prepare both alkaline substances (soda ash and caustic soda) and acid substances (sulphuric and s), the two classes of chemical products which are distinguished for the greatest energy of their reactions, and are therefore most frequently applied to technical purposes. Factories manufacturing soda in this manner are generally called alkali works."