Editing Sodium carbonate (section)

===Leblanc process===
{{Main|Leblanc process}}
In 1792, the French chemist [[Nicolas Leblanc]] patented a process for producing sodium carbonate from salt, [[sulfuric acid]], [[limestone]], and coal. In the first step, sodium chloride is treated with sulfuric acid in the [[Mannheim process]]. This reaction produces [[sodium sulfate]] (''salt cake'') and [[hydrogen chloride]]:
{{block indent|2NaCl + H<sub>2</sub>SO<sub>4</sub> → Na<sub>2</sub>SO<sub>4</sub> + 2HCl}}

The salt cake and crushed [[limestone]] ([[calcium carbonate]]) was reduced by heating with [[coal]].<ref name=Ullmann>{{cite encyclopedia|author=Christian Thieme|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley-VCH|location=Weinheim|year=2000|doi=10.1002/14356007.a24_299|isbn = 978-3527306732|chapter = Sodium Carbonates}}</ref> This conversion entails two parts. First is the [[carbothermic reaction]] whereby the coal, a source of [[carbon]], [[Redox|reduces]] the [[sulfate]] to [[sulfide]]:
{{block indent|Na<sub>2</sub>SO<sub>4</sub> + 2C → Na<sub>2</sub>S + 2CO<sub>2</sub>}}

The second stage is the reaction to produce sodium carbonate and [[calcium sulfide]]:
{{block indent|Na<sub>2</sub>S + CaCO<sub>3</sub> → Na<sub>2</sub>CO<sub>3</sub> + CaS}}
This mixture is called ''black ash''. The soda ash is extracted from the black ash with water. Evaporation of this extract yields solid sodium carbonate. This extraction process was termed [[Leaching (chemistry)|lixiviating]].

The hydrochloric acid produced by the [[Leblanc process]] was a major source of air pollution, and the [[calcium sulfide]] byproduct also presented waste disposal issues. However, it remained the major production method for sodium carbonate until the late 1880s.<ref name="Clow52"/><ref name="Kiefer">{{cite journal |last1=Kiefer |first1=David M. |date=January 2002 |url=http://pubs.acs.org/subscribe/journals/tcaw/11/i01/html/01chemchron.html |title=It was all about alkali |journal=Today's Chemist at Work |volume=11 |issue=1 |pages=45–6}}</ref>