Some optical and crystallographical properties of the alkali zinc uranyl acetates

Abstract

The optical properties and crystal form of the zinc uranyl acetates of sodium, lithium, and potassium were determined. The lithium and sodium zinc uranyl acetates belong to the monoclinic system and are isomorphous. They are capable of forming a series of solid solutions, as is evidenced by the homogeneity and the intermediate optical properties and X-ray pattern of a mixed sodium and lithium zinc uranyl acetate. The potassium zinc uranyl acetate belongs to the tetragonal system and differs from the lithium and sodium zinc uranyl acetates in optical properties and crystal form. In studying the application of the Barber and Kolthoff method l for the quantitative determination of sodium to the analysis of glass, 2 a casual examination of the crystalline precipitate showed that the crystals were, in general, very well formed and were characterized by twinning. Barber and Kolthoff stated that part of the potassium and most of the lithium are precipitated with the sodium salt when they are present. Glaze has recently substantiated Barber and Kolthoff's statement that lithium cannot be separated from sodium, but has shown that potassium can be separated from sodium if proper precautions are taken. 3 Hence it seemed desirable to make a detailed study of the three salts to see if they can be readily distinguished by their optical properties. The crystalline compounds used in this work were prepared as follows: One volume of a solution of cp alkali chloride was mixed with 10 volumes of the zinc uranyl acetate reagent 4 and stirred frequently during 30 minutes. The precipitate was filtered and washed free from the excess reagent with 95 percent alcohol and finally with etber. The precipitate was dissolved in a minimum amount of distilled water and recrystallized by slowly concentrating the solution in a dessicator over sulphuric acid. In the case of the potassium salt a few drops of acetic acid were added to prevent hydrolysis. Microscopic examination of the sodium and lithium salts showed them to be perfectly homogeneous and without visible impurity. Analyses of these two salts were made as follows: The uranium was converted to sulphate by fuming with sulphuric acid, reduced in a Jones reductor, oxidized to quadrivalent uranium with air and i Jour. Am. Chem. Soc, vol. 50, pp. 1625-1631, 1928. « F. W. Glaze, Jour Am. Cer. Soc, vol. 14, no. 6, pp. 450-453, 1931. 3 B.S. Technical News Bulletin No. 94, p. 68, June 1933. * Barber and Kolthofi, op. cit., p. 1626. 471 472 Bureau oj Standards Journal of Research [Vol. IB titrated with permanganate. The zinc was precipitated from a 0.008 N sulphuric acid solution by hydrogen sulphide. The precipitate was dissolved and reprecipitated until white in color, filtered, and ignited to the oxide. The alkali was determined as sulphate on a separate sample after removing the uranium and zinc as sulphides from an ammoniacal solution. On the lithium salt water was determined at 100 C and 3 mm pressure and the acetic acid was determined by distilling from a phosphoric acid solution and titrating with standard sodium hydroxide. The results of the analyses are given in table 1 together with the compositions calculated from the formulas (see footnote 4).