CHEMISTRY OF FLUORESCING URANYL SALTS. 211 



anhydride, N 2 0s. This was accomplished by having a reaction flask fitted 

 to the system by a ground-glass joint, in which were placed phosphorus 

 pentoxide and fuming (92 per cent) nitric acid in calculated amounts. From 

 this, on heating to 50, the N 2 O 5 distilled out and was condensed by freezing 

 mixture in the first U-tube, which served as a reservoir. When this was 

 filled with solid N 2 O 5 and a two-liquid layer of N 2 O 5 and HN0 3 , the flask was 

 removed, the joint covered by a cap, and the anhydride distilled over on 

 the uranic oxide by placing the reservoir tube in a bath of hot oil. No re- 

 action took place between the oxide and the acid until the oxide tube was in 

 turn put in the oil-bath and the anhydride boiled off into the last tube, which 

 served as a second reservoir for the acid. As soon as the acid began to boil 

 the reaction took place, producing a vivid green fluorescence and a light yel- 

 low color instead of the reddish oxide. The anhydride could be distilled off 

 and run back over while holding the tube with the uranyl nitrate at any 

 temperature. Also, any acid which did not solidify could be poured off and 

 the remaining N 2 5 run back over the nitrate, insuring absolute freedom from 

 water. The resulting compound was found to be stable up to 180, at which 

 temperature it broke up into N 2 05 and U0 3 , which could be recombined if the 

 temperature was lowered. Distilling the acid on and off was performed 

 several times with one specimen, examining the spectra each time, which 

 showed first the anhydrous salt fluorescence and then none for the oxide. 



DOUBLE NITRATES. 



Meyer and Wendel 1 prepared double salts of ammonium, potassium, rubi- 

 dium, caesium nitrates with uranyl nitrate. These crystals were described by 

 Steinmetz. 2 They were grown from a solution in nitric acid and were of the 

 type KUO 2 (N0 3 )3. Rimbach 3 endeavored to determine the solubility of these 

 salts in water at various temperatures. He found large crystals in the am- 

 monium and potassium solutions unlike those of Meyer and Wendel which 

 were measured by Sachs 4 and assigned formulae like those of Meyer and Wen- 

 del, but since they were alike were called isomorphous and the a forms of NH 4 

 and KU0 2 (NO 3 ) 3 . Examination of the spectra of these forms in the labora- 

 tory indicated and Sachs's data itself proves that the a form is simply uranyl 

 nitrate hexahydrate. 



In attempting to grow crystals according to Rimbach's method which would 

 not be uranyl nitrate, however, two new forms were discovered containing two 

 molecules of alkali nitrate to one of uranyl nitrate. In the process of growing 

 the potassium salt for experimental purposes, still a third was found, but so 

 rarely that it was not studied. 



In order to find out the conditions under which the various salts were formed, 

 a series of solubility determinations were undertaken, being run at constant 

 temperature of 20 C. in a thermostat, with varying percentages of aqueous 

 nitric acid as a solvent. 



From these incomplete results it will be seen that from solutions of less 

 than 30 per cent nitric acid and less than 1 molecule of uranyl nitrate to 1 of 

 potassium nitrate, potassium nitrate only will crystallize; that in a 1 to 1 



1 Meyer and Wendel, Ber. d. d. Ch. Ges., 36, 4055. 1903. 



2 Groth's Chem. Kryst, n, 150. 



3 Rimbach, Ber. d. d. Ch. Ges., 37, 472. 1904. 



4 Sachs, Zeit. f. Krys., 38, 497. 1904. 



