=256. The Oxidation Method.=—The removal of the reducing sugars may be accomplished by oxidation instead of fermentation. The process of analysis is in all respects similar to that described in the foregoing paragraph, substituting oxidation for fermentation.[212] For the oxidizing agent mercuric cyanid is preferred, and it is conveniently prepared by dissolving 120 grams of mercuric cyanid and an equal quantity of sodium hydroxid in water mixing the solutions and completing the volume to one liter. If a precipitate be formed in mixing the solutions it should be removed by filtering through asbestos. For the polarization, ten grams of the sugars in 100 cubic centimeters is a convenient quantity. Ten cubic centimeters of this solution are placed in a flask of water marked at fifty cubic centimeters, a sufficient quantity of the mercuric cyanid added to remain in slight excess after the oxidation is finished (from twenty to twenty-five cubic centimeters) and the mixture heated to the boiling point for three minutes. The alkali, after cooling, is neutralized with strong hydrochloric acid and the passing from alkalinity to acidity will be indicated by a discharge of the brown color which is produced by heating with the alkaline mercuric cyanid. The heating with the mercury salt should be conducted in a well ventilated fume chamber. The calculation of the results is conducted by means of the formulas given in the preceding paragraph. In the original paper describing this method, it was stated that its accuracy depended on the complete oxidation of the reducing sugar in a manner leaving no optically active products, and on the inactivity of the reagents used in respect to the dextrin present. These two conditions are not rigidly fulfilled, as is shown by Wilson.[213] According to his data maltose leaves an optically active residue, which gives a somewhat greater right hand rotation than is compensated for by the diminished rotation of the dextrin. Wilson, however, confesses that the dextrin used contained reducing sugars, which would not be the case had it been prepared by the process of treating it with alkaline mercuric cyanid as above indicated. Upon the whole, the oxidation of the reducing sugar by a mercury salt gives results which, while not strictly accurate, are probably as reliable as those afforded by fermentation. The author has attempted to supplant both the oxidation and fermentation methods by removing the reducing sugars with a precipitating reagent, such as phenylhydrazin, but the methods are not sufficiently developed for publication.