An obsolete process for manufacturing sodium carbonate. The raw materials were sodium chloride, sulphuric acid, coke, and limestone (calcium carbonate), and the process involved two stages. First the sodium chloride was heated with sulphuric acid to give sodium sulphate:2NaCl(s)+H2SO4(l) → Na2SO4(s)+2HCl(g) The sodium sulphate was then heated with coke and limestone:Na2SO4+2C+CaCO3 → Na2CO3+CaS+2CO2 Calcium sulphide was a by-product, the sodium carbonate being extracted by crystallization. The process, invented in 1783 by the French chemist Nicolas Leblanc (1742–1806), was the first for producing sodium carbonate synthetically (earlier methods were from wood ash and other vegetable sources). By the end of the 19th century it had been largely replaced by the Solvay process.
2NaCl(s)+H2SO4(l) → Na2SO4(s)+2HCl(g)
Na2SO4+2C+CaCO3 → Na2CO3+CaS+2CO2