The present paper is the third in a series presenting the results of an investigation carried out in coiiperation with the Joint Research Committee on Boiler Feedwater Studies dealing with the solubility of sodium sulfate in various solutions in the temperature range from 150 to 350". The first paper5 gave solubility data for sodium SUIfate, in sodium hydroxide-sodium chloride solutions, and the secondfi for sodium sulfate in SOdium hydroxide-sodium carbonate solutions. This paper presents data for (1) a design for a new high temperature solubility bomb, ( 2 ) the solubility of trisodium phosphate in water and in sodium hydroxide solutions, (3) data for the system sodium sulfate-trisodium phosphate-water, (4) the solid phases in this system, and (5) the effect of sodium hydroxide on the system. These studies involving the phosphate are the most complicated, and perhaps the most interesting, of the three solubility investigations. High Temperature Solubility BombThe bomb originally used in the study of the high temperature solubility equilibria of sodium sulfate has been described in the first paper5 of this series. As the investigation proceeded several disadvantageous features were found in this equipment. It has been redesigned and the difficulties have been corrected in the bomb shown in Fig. 1. The body is open a t both ends to make for easy machining] with the sampler as well as the bottom held in place by studs. The necessary seals are formed by metal-to-metal contact between seats machined a t 60" so that no gaskets or material other than the bomb metal comes in contact with the solution. The valve (I) Published by permission of the Director, U. S. Bureau of Mines. (Not subject to copyright.) (2) Research chemical engineer, Joint Research Committee on Boiler Feed-Water Studies, attached to Eastern Experiment Station, stem is large enough to eliminate sticking and danger of twisting off. SQUARE FOR WRENCH ~ PACKING Fig. l.-Solubility bomb (dimensions in inches) : firessure, 200 atmospheres or 3000 lb. per sq. in.; volume, L U L~I W I L U saiiryicr 111 p a c e YJU CC., UCIUW aamyirr IYW CF., above sampler 110 cc., sampler 18 cc.The sampler is enclosed in the bomb to ensure sampling a t the operating temperature, and the end may be equipped with a filter of carbon or 843-849 (1936) ' fine wire screen if this is desirable. Crane pack-

In 1934, Powell (1) estimated the cost of repairs and replacement on boilers damaged by intercrystalline cracking or embrittlement during the preceding four years at approximately 200,000 dollars per year. In spite of this outlay no extensive experimental work was in progress on this specific problem, although a related investigation concerning the solubility of sodium sulphate in boiler water salines was under way at the Bureau of Mines. This situation existed because many operators believed a satisfactory solution to the difficulty was available if conditions believed to be correct were maintained in boilers. These conditions which had been accepted as correct involved principally the maintenance in the boiler water of such concentrations of sodium sulphate and alkalinity that the ratios suggested by the A.S.M.E. for the prevention of embrittlement were satisfied. These ratios it will be recalled were based upon data gathered from boilers throughout the country and were later supported by the important pioneer work of Parr and Straub. On the other hand many competent engineers believed that the use of sodium sulphate for protection was based on contradictory operating data.The solubility studies at the Bureau of Mines under the auspices of the Joint Research Committee on Boiler Feedwater Studies attempted to establish an accurate basis for the use of sodium sulphate

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Vol. 59 droxide decreases the solubility of all the solid ious phases are increased markedly.phases. At 350°the solubilities of the var-College Park, Md.

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