The change in solubility in water with time of a and ß calcium sulfate hemihydrate and of /3-soluble anhydrite and "insoluble" anhydrite were determined over the temperature range of 35°to 110°C. The solubility of the hemihydrates goes through a maximum with time, which is related to modifications in the calcium sulfate phase present. The a-hemihydrate is less soluble but more stable than the ß form. The stability of a and ß hemihydrate increase as the transition temperature, 99°C. for gypsum-a-hemihydrate and 103°C. for gypsum-/3-hemihydrate, is approached. At temperatures above 45°C. the solute content in contact with "insoluble" anhydrite, prepared by igniting gypsum at 890°C., surprisingly increased with time well beyond the values previously reported for anhydrite solubility.Three FORMS of calcium sulfate have long been recognized, CaS04-2H20 (gypsum), CaS04-M2H2O (hemihydrate), and CaS04 (anhydrite). Various modifications of these forms have also been postulated, but after a careful study and review of previous work, Kelley, Southard and Anderson (9) in 1941 concluded that the only unique and reproducible forms were: CaS0v2H20, a-CaS04• V2H2O, ß-CaSOv V2H2O, a-and /3-soluble anhydrites, and insoluble anhydrite. The -hemihydrate is prepared, for example, by dehydration of gypsum in an atmosphere of saturated steam. The /3-hemihydrate is formed by dehydration of gypsum under a lower water vapor pressure, and it shows a higher solubility than the -hemihydrate. a-and ß-anhydrites are prepared by further dehydration of a-and /3-hemihydrates, respectively; both rehydrate

The change in solute concentration with time of 0.25m or 1.0m NaCI in contact with gypsum, fl-hemihydrate, /¡-soluble anhydrite, or insoluble anhydrite was determined over the temperature range of 25°to 105°C. Accompanying changes in the solid phase were also determined. Under thermodynamically favorable conditions, /S-hemihydrate and fl-soluble anhydrite rapidly hydrate to form gypsum. The dehydration rate of gypsum at 95°and 105°C. to form insoluble anhydrite is much faster in 1.0m NaCI than in pure water. Some changes in solubility and solid phase composition occur

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Radium can be separated from barium-radium mixtures in ratios as high as 4440 to 1 by a single elution from a cation exchange resin. Barium elution characteristics from Dowex 50 resin, position of elution maxima, and maximum barium loadings are correlated with citrate concentration and pH by the use of citrate complex equilibria. Ammonium citrate, 0.32M at pH 5.6, is the most satisfactory eluent of those used from the standpoints of separation factor and freedom from precipitation in the column. Conditions affecting the precipitation of slightly soluble barium citrate during elution with ammonium citrate are discussed.Eluting above 25°C.decreases separation factors and permissible barium levels.

An apparatus for continuously recording the deposition or dissolution of radioactive material upon a radiationtransparent electrode during potential change is described.