Micro-Determination of Fluorine

Abstract

The author's1 modification of the Willard-Winter2 method has been adapted to the determination of small quantities of fluorine. The distillation of H2SiF6 is carried out in the usual manner except that a 50 cc. distilling flask, 0.1 gm. quartz and 5 cc. 60% perchloric acid are employed. The temperature of the flask contents is maintained at 140°, and 150 cc. of distillate are collected. The water employed is freshly boiled after redistillation from alkali. The distillate is made alkaline to phenolphthalein, evaporated to a small volume, rendered just acid to the indicator, and diluted to 10 cc. One cc. aliquots are transferred to 5 cc. vials (such as those in which dentists receive gold foil). The addition of an equal volume of alcohol is omitted in order to permit a direct relationship between the fluorine content of the aliquots and the volume of Th(NO3)4 solution used for their titration and to render inoperative the effect of HClO4 on the determination of more than 5γ (micrograms) F. If the sample con...