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Of the methods currently in use for determining the fluoride ion concentration in water, the electrode and colorimetric methods are believed to be the most satisfactory. We have devised a laboratory experiment for students in general chemistry based upon the SPADNS Colorimetric Procedure.1 The method is based upon the reaction of fluoride ion with a zirconium dye-lake. The ion reacts with the dye-lake to destroy it and form a colorless complex anion, (ZrF62~). As the concentration of the fluoride ion in the solution to be analyzed increases, the intensity of the color of the solution becomes progressively lighter. The intensity of the color is measured quantitatively with a spectrophotometer.

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A freshman laboratory experiment for medically and biologically oriented students Colorimetric or spectrophotometric methods based upon the reaction of glucose with primary aromatic amines in glacial acetic acid have been utilized clinically with different degrees of success.1,2 Perhaps the most successful is the selective reaction of glucose with o-toluidine, a primary ar-