DETERMINATION OF FLUORIDES IN WATER BY MEANS OF A PHOTOELECTRIC COLORIMETER

Abstract

A method has been developed for the determination of small amounts of fluorides by means of a photoelectric colorimeter. The method is based on the bleaching of the lake formed from a zirconyl salt and sodium alizarin sulphonate by the action of fluoride ion. The photoelectric colorimeter used is of the direct reading type based on that developed by Evelyn but differs in that the light passes vertically through a long absorption cell rather than horizontally through an absorption cell consisting of a large test-tube. By calibrating the galvanometer scale against solutions containing known amounts of fluoride, the number of parts per million of fluorides in water can be determined. A comparison of the results obtained in the photoelectric colorimeter with those from the corresponding visual method show that the two sets of data are in agreement with each other.