214 FLUORESCENCE OF THE URANYL SALTS. 



DIPOTASSIUM URANYL NITRATE. 

 (5 form) K 2 U0 2 (NO 3 ) 4 . 



These crystals appeared, after a year of effort to obtain crystals from neutral 

 solution which were not hexahydrate, in a slightly acid solution containing an 

 excess of potassium nitrate. It shows marked reluctance to appear and does 

 not grow well if the room temperature is below 20 C., the hexahydrate forming 

 instead, but above that temperature gives fine crystals, especially if seeded, 

 although it does not grow as rapidly as the other members of the group. 



System monoclinic; axial ratio a : b : c = 0.6394 : 1 : 0.6190; /3 = 90 . 



These axes are probably not those of the space lattice, being taken from 

 the first habitus observed, which formed in a solution having barely enough 

 potassium nitrate to produce this phase, and consisted of e (001), o (133), and 

 p (331) meeting in a point in front which was sometimes cut off by a (100), 

 usually accompanied by d (101). TT sometimes occurred between o (133) 

 and p (331) and q (131) between o 133 and p 311; b (010) and m (230) were 

 found in measurement. One crystal showed c, o, p, d, and d' (101), a and 

 probably q and (111). Most of the crystals grown later had a prismatic or 

 needle habitus in which p (331) was the predominant form, with small e 

 faces on the ends and occasionally some of the other forms. All faces on these 

 crystals gave reflections which appeared in the goniometer as a flattened 

 figure 8, and best agreements were found in the angles taken from the outside 

 of every pair of readings. In case the whole figure did not appear, results 

 were unsatisfactory. 



On dissolving a large crystal in the mother-liquor by heat, c (001) was un- 

 touched, d (101) was left even and a little pitted, and the edge between p (331) 

 and o (133) was rapidly dissolved, leaving the deepest etching where these 

 met at d (101). 



No conspicuous cleavage was noticed. 



The specific gravity was found to be 3.359. 



On heating crystals of this phase, they first decrepitate to an opaque yellow 

 powder at 200 C., which, at 260 C., flows together. Above this temperature 

 decomposition sets in, with the evolution of nitric fumes. Various colored 

 masses result, deep red U 3 O 8 , bright red U0 3 , bright yellow K 2 UO 4 , and on 

 cooling a beautiful rose pink pervades the mass. 



This phase does not change over concentrated sulphuric acid, i. e., has zero 

 vapor-pressure at 20 C., but over acid corresponding to 11 mm. of mercury 

 of partial pressure of water-vapor it turns whitish without becoming moist, 

 probably due to the formation of KN0 3 and UO 2 (N0 3 ) 2 6H 2 0. This is the 

 same pressure at which the diammonium salt deliquesces. 



The refractive index of dipotassium uranyl nitrate given by the faces (001) 

 and d (101) were found to be 1.5422 for light vibrating parallel to the 6 axis 



