CHEMISTRY OF FLUORESCING URANYL SALTS. 213 



rather low acid concentration was necessary to produce this form. These 

 higher ratios of ammonium nitrate should be investigated. 



These results do not check well with those of Rimbach, who presumably 

 crystallized considerable portions of the salt, instead of determining the phase 

 with which the solution was in equilibrium by the addition of seeds of known 

 phases. They do not, however, materially conflict with those of Engel 1 in the 

 case of the solubility of potassium nitrate in nitric acid, where the solubility 

 is found greater at 20 than at in dilute solutions and less in highly acid 

 solution. 



The mono or acid forms of the double potassium ammonium salts and the 

 corresponding rubidium and caesium salts were found to be as described by 

 Sacks from the preparation of Meyer and Wendel. There is no indication 

 that the corresponding double salts containing 2 atoms of rubidium or caesium 

 could not be produced by using solutions similar to that used for the dipotas- 

 sium salt. 



Other double uranyl nitrates with other bases than the four alkalies dis- 

 cussed do not seem to form, with the exception of thallium, which is reported 

 by Meyer and Wendel as forming but being non-fluorescent, as the double 

 thallous sulphate is. Sodium nitrate crystallizes side by side with the hexa- 

 hydrate or trihydrate, according to the acidity of the solution, but no con- 

 ditions were found under which the two salts would crystallize together. 

 Silver, cadmium, zinc, calcium, barium, and magnesium were also tried with- 

 out success, although a modification of the hexahydrate spectrum was pro- 

 duced by the calcium and magnesium. Meyer and Wendel also tried lithium, 

 sodium, and the bivalent metals without formation of double salts. 



MONOPOTASSIUM URANYL NlTRATE. 



(y form) KUO 2 (NO 3 ) 3 . 



These crystals were prepared by Meyer and Wendel by crystallizing potas- 

 sium nitrate and uranyl nitrate in equal proportions from a nitric-acid solu- 

 tion. The crystals were examined by Steinmetz. 



System rhombic; axial ratio 0.8541: 1: 0.6792. 



Thick tabular combinations of c (001), m (110), with subordinate forms of 

 b (010), s (102), o (111), sometimes a (100), and rarely a (Oil) and 122. 

 Steinmetz and Sykes report good cleavage on 6, and good cleavage was also 

 observed on a. The specific gravity was found to be 3.503. Crystals of this 

 form are stable at 20 if the partial pressure of the water-vapor is not over 

 9 mm. Hg, but at that point begin to deliquesce, changing to a whitish yel- 

 low chalky mass. On heating the crystals, yellow crusts begin to form on the 

 crystals at 150, violent decrepitation begins at 200, and decomposition with 

 liberation of nitrous fumes at 270 C. 



According to Steinmetz, the plane of the optical axes is c (001), acute 

 bisectric a. Axes visible through (110). 



The best crystals were obtained by cooling of hot solutions supersaturated 

 2 grams in 50 c.c. in glass-stoppered bottles. 



The composition as determined by Meyer and Wendel was KU0 2 (N0 3 )3. 

 An ignition run to check this gave 65.13 and 64.82 per cent, the theoretical 

 form K 2 U20 7 being 67.29, the low values being due to loss by decrepitation. 



1 Engel, Comptes Rendus, 104, 913. 1887. 



