Fluorine and Its Determination

A brief discussion of the geological formation of minerals containing fluorine is given, and an attempt is also made to show the economic importance of fluorine. The discussion shows that in some cases the compounds of fluorine are beneficial to man and in other cases detrimental.A critical review of the methods for the determination of fluorine shows that most of them are applicable only to pure solutions. Few can be used in the analysis of fluorspar or of such complex materials as glasses and enamels.Indirect methods serve best in the analysis of fluorspar. The sources of error in such methods are discussed, and improved procedures are given in detail. The methods described were checked against synthetic mixtures of known calcium fluoride content.In the development of methods for the analysis of glasses and enamels various methods of determining silica in the presence of fluorine were tested, but only the procedure developed by Berzelius or some modification was found to be reliable. In the methods described the procedure of Berzelius was modified so as to eliminate (1) the long precipitation period with ammonium carbonate and the difficult filtration which follows; and (2) the slow and troublesome neutralization with small portions of nitric acid. It was also found that for quantities of fluorine between 0.01 and 0.10 g the precipitation of fluorine as lead chlorofluoride is much more convenient and rapid, and as accurate as the precipitation of a mixture of calcium fluoride and calcium carbonate followed by extraction of the latter with acetic acid.The lead chlorofluoride method succeeds in the presence of moderate quantities of ammonium nitrate, and boric, chromic, sulphuric, or phosphoric acids, As written, it is not suitable for determining fluorine in phosphate rock. The presence of much magnesium tends to yield slightly low results.The effects of various other contaminants, such as oxides of tin, antimony, iron, aluminum, nickel, cobalt, manganese, and lead, are shown, and a routine method for determining fluorine in glasses and enamels is given. The studies and experiments of this thesis show quite conclusively that methods of separation of fluorine from other elements rather than methods of determinations are needed.