Effect of Sodium Hexametaphosphate on the Solution of Lead

Abstract

AT A joint meeting of the New England Health Institute, the New JLJL England Water Works Association and the New England Sewage Works Association, held in April 1941, Dr. L. T. Fairhall of the National Institute of Health questioned the use of sodium hexametaphosphate for corrosion control in systems containing lead pipe. Dr. Fairhall had found that concentrations of metaphosphate of about 1,000 ppm. produced large increases in the solubilities of some of the common lead salts. Ruchhoft and Kachmar (1) subsequently confirmed FairhalFs experiments, but allayed much of the anxiety that had been produced with respect to the use of metaphosphate by showing that in quantities of 1 to 10 ppm., the metaphosphate actually decreased the solubilities of lead salts. Hatch (2) published results on the effect of metaphosphate on the corrosion of lead wool, in which he showed that the solution of lead from the cleaned metal was markedly inhibited in waters of pH 6.0 or below. At and above pH 7.0, his results gave some indication that the metaphosphate slightly increased the solution of lead. It has seemed to the writers that the gravest question with respect to the introduction of metaphosphate into water systems containing lead pipe is that of the effect of this chemical on the deposits of lead salts previously formed in the pipe. Metaphosphate has been known to cause rapid removal of pipe deposits in some systems in which it has been introduced, and such removal would be particularly dangerous if the deposits contained a high percentage of lead. It has also seemed desirable to provide independent confirmation of the results of the investigators cited above, since the problem is significant to public health. In all experiments presented in this paper, the lead concentrations were determined by the dithizone method as described in Standard Methods (3). The only modification adopted consisted of the use of a Cenco-Sheard