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Lattice parameter data for MgO, CaO, and several isotropic compositions of LiH were measured from ~ 12 °K up to ~ 300 °K. Thermal expansion coefficients were derived by fitting the data to a second‐degree polynomial.

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The solubility of uranii~m(IV) hydroxide has bee11 nleasured in s o d i~~m hydroxide, water, and perchloric acid solutions. A possible reaction in sodium hydroxide solutions is evaluated.The purpose of this investigation was to measure the solubility of uraniurn(1V) hydroxide in dilute basic and dilute acidic media. Information pertaining to this subject is not available a t this time in the literature except for the,following:Kraus and Nelson (3) investigated the hydrolytic behavior of uranium(1V) ions in excess perchloric acid (above 0.2 11[) and in solutions of constant ionic strength ( p = 0.5). They concluded that the simple ion U+4 exists in excess acid and is associated witheight water molecules, U(H20)8+$ and that the principal hydrolysis reaction is u+q-H~O 6 u ( o H ) +~ + H+. They also found that uranium(1V) ions show a tendency to form rather stable polymeric solutions on hydrolysis, where the polymeric form has an approximate composition of U(OH)4. When uranium(1V) hydroxide is dissolved in a non-complexing acid, such as perchloric, solutions containing polymeric products result. The difference in color between the simple solutio~l and the polymeric form is very marked, being bright green for the former and almost black for the latter. PROCEDUREThe general procedure is similar to that described by Garrett and Heilts (2). An all glass apparatus was used.Water.-Conductivity water was prepared in a Barnstead coilductivity still, degassed by being boiled with nitrogen bubbling through it, and then stored under nitrogen.Perchloric acid solutions.-Approximately 1 molar acid was prepared from 70% G. F. Smith purified perchloric acid with degassed conductivity water and stored under nitrogen. Standard acid solutions were also made with conductivity water and standardized against standard sodium hydroxide.Sodi~~rn hydroxide so1z~tions.-Approximately 1 molar solutions of base were prepared under nitrogen by dissolving Balter and Adamson reagent pellets in degassed conductivity water in a paraffined flaslt. Barium hydroxide was added to just precipitate any carbonate, and the solutio~ls were stored under nitrogen. Standard base solutions were also prepared with coilductivity water and standardized against potassium acid phthalate using phenolphthalein indicator. 'ill/ analscript received J u l y 16, 1956

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