Anhydrous sodium carbonate (soda ash, sal soda) is a white powder, which cakes and aggregates on exposure to air due to the formation of hydrates. The monohydrate, Na₂CO₃.H₂O, is a white crystalline material, which is soluble in water and insoluble in alcohol; r.d. 2.532; loses water at 109°C; m.p. 851°C.

The decahydrate, Na₂CO₃.10H₂O (washing soda), is a translucent efflorescent crystalline solid; r.d. 1.44; loses water at 32–34°C to give the monohydrate; m.p. 851°C. Sodium carbonate may be manufactured by the Solvay process or by suitable crystallization procedures from any one of a number of natural deposits, such as: trona (Na₂CO₃.NaHCO₃.2H₂O), natron (Na₂CO₃.10H₂O), ranksite (2Na₂CO₃.9Na₂SO₄.KCl), pirsonnite (Na₂CO₃.CaCO₃.2H₂O), gaylussite (Na₂CO₃.CaCO₃.5H₂O). The method of extraction is very sensitive to the relative energy costs and transport costs in the region involved. Sodium carbonate is used in photography, in cleaning, in pH control of water, in textile treatment, glasses and glazes, and as a food additive and volumetric reagent. See also sodium sesquicarbonate.