Leblanc
Leblanc :
Also written LeBlanc and Le Blanc. An obsolete, two-stage process for making sodium carbonate from sodium chloride. In the first stage, the “salt cake” process, salt was heated with sulfuric acid, yielding sodium sulfate (salt cake) and gaseous hydrogen chloride: 2NaCl + H2SO4 = Na2SO4 + 2HCl. In the second stage, the “black ash process,” the sodium sulfate was reduced to sodium sulfide and then converted to sodium carbonate by calcining with limestone and coal in a rotating kiln known as a black ash furnace or revolver: Na2SO4 + 4C = Na2S + 4CO; Na2S + CaCO3 = Na2CO3 + CaS. The black product was extracted with water and the sodium carbonate in it was recovered by concentration and crystallization. The residue, chiefly calcium sulfide, known as “galigu,” was dumped on land and created an environmental nuisance for many years because it never hardened
