CHEMISTRY OF FLUORESCING URANYL SALTS. 



215 



and 1.5349 for light vibrating in the ac plane 26 34|' from a toward c in the 

 "acute" angle /3. 



The composition was investigated by igniting to K 2 U04 and by washing 

 out the K2S0 4 from sulphuric-acid solution precipitated with NH 4 OH and 

 weighing the resulting U 3 8 and K 2 SO 4 . 



The best crystals were obtained by cooling solutions supersaturated 1 

 gram in 100 c.c. 



MONOAMMONIUM URANYL NlTRATE. 



form NH 4 UO 2 (NO 3 ) 3 . 



This salt forms from solutions containing uranyl nitrate and ammonium 

 nitrate at room temperature if the acid-content is high and from water at 

 higher temperatures. 



System trigonal; axial ratio a :c = 1: 1.0027 (a 976 / ). The forms are 

 prismatic combinations of prism a (1120) with the rhombohedron r (1101) on 

 the end, on the edges of which,occur s (1012). 



The column headed Theory gives the values for a substance having an axial 

 ratio a :c = 1:1, the close approximation to which makes this a remarkable 

 case and probably indicates something concerning the structure. 



Twins were observed in which the contact plane was s 1102 and the twin- 

 ning axis, the axis of reference to which s was parallel, making the angle be- 

 tween the two unique axes 11954' and giving the crystal the appearance _pf a 

 flat hemimorphic orthorhombic crystal. The angle between the two r (lIOl) 

 faces was calculated to be 2132' and found to be 21 == . 



Crystals of this form are stable in dry air, but begin to deliquesce and 

 change to a light yellow chalky mass if the vapor-pressure of water is above 

 9 mm. Hg. 



Intense pleochroism was observed in crystals about 0.01 mm. thick on a 

 microscope slide, when they occurred lying on a prism face, the light vibrat- 

 ing parallel to the unique axis appearing white, i. e., less yellow than the 

 mother-liquor in which the crystal lay, while that ordinary ray appeared a 

 deep yellow. 



The monopotassium and monoammonium crystals separate from the same 

 solution, there being no tendency to form mixed crystals. 



The composition of the crystals was checked as being the same as that 

 given by Meyer and Wendel by igniting to the oxide. Theory, 59.22 per 

 cent found, 58.97, and 58.86. 



