The Literature on the Solubility of Calcium Sulfate A search of the literature, complete up to May, 1928, covering references to the solubility of any of the various forms of calcium sulfate, was made and the original data abstracted from these articles were compared. Such as seemed significant have been utilized in conjunction with the determinations described in the present paper.For the purposes of this paper all concentrations have been expressed in parts of CaS04 per million parts of solution. Conversion from original data has been carried out with the use of the density measurements of Hulett and Allen3 on calcium sulfate solutions, although in view of the low solubilities encountered this is a refinement well within the experimental error.The Solubility of Gypsum,-The lower curve of Fig. 1 represents the solubility of gypsum as determined by the values of Raupenstrauch,4 Hulett and Allen,3 Melcher,6 and Cavazzi.6 The excellent agreement of the four sets of data is checked by individual determinations at various temperatures made by other recent investigators.It should be noted here that Raupenstrauch has never received the credit due him for the first accurate determination of the gypsum solubility curve. His article antedates the well-known and equally excellent work of Hulett and Allen by seventeen years but it has been quite generally ignored.The Solubility of Calcium Sulfate Hemihydrate.-Marignac,7 Potilit-zin8 and Cavazzi6 found the solubility of dehydrated gypsum at room tempera time to be approximately five times that of fully hydrated gypsum. That these values represent the solubility of calcium sulfate hemihydrate 1 This paper forms part of the dissertation submitted by Dr. Partridge in partial fulfilment of the requirements for the Ph.D. degree at the University of Michigan. Acknowledgment is made to The Detroit Edison Company which sustained this work through a fellowship.

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Threshold treatment system is shown a t left. Effluent cooling water from mash coolers is then softened and used for bailer feed, which is further conditioned with sodium sulfite and sodium metaphosphate.

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