modern method of manufacturing the industrial alkali sodium carbonate, also known as soda ash. The process was devised and first put to commercial use by Ernest Solvay (Solvay, Ernest), who built a plant in 1865 in Couillet, Belg., and was improved in the 1870s by the German-born British chemist Ludwig Mond (Mond, Ludwig).

In the ammonia-soda (ammonia) process, common salt, sodium chloride, is treated with ammonia and then carbon dioxide, under carefully controlled conditions, to form sodium bicarbonate and ammonium chloride. When heated, the bicarbonate yields sodium carbonate, the desired product; the ammonium chloride is treated with lime to produce ammonia for reuse and calcium chloride.

For some years after its introduction, the ammonia-soda process encountered stiff competition from the older Leblanc process, but it ultimately prevailed because it produced soda ash more cheaply.