The Deacon process, invented by Henry Deacon, is a process used during the manufacture of alkalis (the initial end product was sodium carbonate) by the Leblanc process.  Hydrogen chloride gas was converted to chlorine gas, which was then used to manufacture a commercially valuable bleaching powder, and at the same time the emission of waste hydrochloric acid was curtailed.  To some extent this technically sophisticated process superseded the earlier manganese dioxide process.