Citric Acid from Lemon Juice: Scheele's Process, Ure 1839

Carl Wilhelm Scheele first isolated citric acid from lemon juice. Andrew Ure (1839) gives his process: chalk turns the juice's acid into insoluble citrate of lime, which is washed and then split again by sulfuric acid, leaving gypsum behind and citric acid to crystallise. Twenty gallons of good juice gave Ure about ten pounds. The picture: citric acid crystals seen under polarised light.