1911 Encyclopædia Britannica/Decolourizing

DECOLOURIZING, in practical chemistry and chemical technology, the removal of coloured impurities from a substance. The agent most frequently used is charcoal, preferably prepared from blood, which when shaken with a coloured solution frequently precipitates the coloured substances leaving the solution clear. Thus the red colour of wines may be removed by filtering the wine through charcoal; the removal of the dark-coloured impurities which arise in the manufacture of sugar may be similarly effected. Other “decolourizers” are sulphurous acid, permanganates and manganates, all of which have received application in the sugar industry.