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The author gives a review of the literature and methods for the determination of free and combined sulphurous acid. Sulphurous acid combines with aldehyde and ketone groups in foods and can be separated from the combination rapidly on addition of alkali and more or less slowly on distillation with acid. Distillation according to one or other of the various modifications proposed is the only reliable method for the majority of foods. Titration of the sulphur dioxide in the distillate, either as such or after oxidation to sulphuric acid, gives accurate results if precautions are taken to eliminate volatile organic compounds. Distillation in a current of carbon dioxide through a reflux condenser into pure hydrogen peroxide, and titration of the sulphuric acid formed, can be applied with satisfactory results to all foods. With dried fruits the last traces of sulphur dioxide are given off with extreme slowness on boiling, even in
The Determination of Sulphur Dioxide in Foods.. JAMA. 1927;89(19):1627. doi:10.1001/jama.1927.02690190065031