208 FLUORESCENCE OF THE URANYL SALTS. 



For making triple sodium acetates, some material was precipitated as the 

 sodium uranate, dissolved in sodium carbonate, and the solution treated with 

 acetic acid, from which the sodium uranyl acetate crystallizes, leaving the 

 sodium acetate in solution with very little waste uranyl salt. 



NITRATES. 

 URANYL NITRATE. 



This is the commonest and best known of the uranyl salts, crystallizing 

 ordinarily as the hexahydrate, which readily forms large, clear crystals by 

 cooling or evaporation. It is prepared by dissolving either the uranic oxide 

 or hydroxide H 2 U04 or the uranous uranic oxide U 3 8 in nitric acid and crystal- 

 lizing. This salt shows strikingly the property of most of the uranyl salts 

 of strong acid, of dissolving noticeable amounts of the oxide in the neutral 

 solution, so that a clear solution may be strongly basic. This oxide pre- 

 cipitates on heating or evaporation. 



URANYL NITRATE HEXAHYDRATE. 

 U0 2 (N03) 2 6H 2 O. 



The complete description 1 of the crystal properties of this hydrate are given 

 in Groth's Chemische Krystallographie, II, page 142. 



System rhombic; axial ratio a : b : c = 0.8737: 1: 0.6088. Forms b (010), 

 a (100), making short rectangular prisms with pyramidal ends formed by 

 b (111), usually cut also by q (Oil), making a a six-sided face and b eight- 

 sided. The prism (110) was observed on one crystal which was deformed by 

 growing near another. Specific gravity, according to Boedeker (1860), is 

 2.807. 



No statement is made as to cleavage, but it was found that very slight 

 temperature changes produce a spontaneous cleavage, generally along q (Oil), 

 so that the crystals can not be handled on a cold day and immersion in liquid 

 air completely powders them. 



The optical properties are double refraction +, plane of axes 6 (010), acute 

 bisectrix the c axis, apparent angle of optic axes 67 to 69, mean index 

 /3 1.495 to 1.502. The pleochroism, according to Schabus, gives bright yel- 

 low-green parallel to a, b greenish yellow, c deep citron yellow. 



The fluorescence and absorption were investigated by Stokes 2 , E. Becquerel, 

 Hagenback, 3 and H. Becquerel. 4 The tribo-luminescence was noticed by 

 Herschel. 5 Wasiljew 6 gives the melting-point of the hexahydrate as 60.2 C. 

 and gives the solubility curve for the hexahydrate in water. Silliman 7 gave 



1 de la Provostage, Ann. der Chim. Phys. (3), 5, 48. 1842. 

 Schabus, Preischr. Wien (1855), 40. 



Sitz. berichte d. A. d. W. Wien, 27, 41. 1857. 



Rammelsberg, Neust. Fortsch. in de Kryst. Chem. Leipzig, 58. 1857. 



Lang, Sitz. ber. Wien, 31, 120. 1858. 



des Cloiseau, Annales des Mines (5), 14, 348. 1858. 



Quercigh, Riv. Min. crist. Ital., 4, 6-14. 1915. 



2 Stokes, Phil. Trans., 142, 517, 520. 1852. 



3 Hagenback, Poggendorff's Annalen, 146, 395. 1872. 



4 H. Becquerel, Ann. Chim. Phys. (6), 14, 230. 1888. 

 6 Herschel, Nature, 60, 29. 1899. 



6 Wasiljew, Chem. Zentralblatt 14, 2, n, 1527. 1910. Jour. Russ. Phys. Chem. Ges. 42, 



577. 1910. 



7 Silliman, Amer. Jour. Science (2), 27, 14. 1859. 



