210 FLUORESCENCE OF THE URANYL SALTS. 



ing from the seed. Schultz-Sellack gives the melting-point as 120 and 

 Wasiljew as 121.5 C. It is really only a partial melting-point, as the dihy- 

 drate is not completely soluble in the resulting solution. The solubility of the 

 trihydrate in water above 60 or in nitric acid has not been determined, 

 although Ditte gives a solubility of 14.39 parts of the trihydrate in mono- 

 hydrated (91 per cent) nitric acid. 



URANYL NITRATE DIHYDRATE. 

 UO 2 (NO 3 ) 2 2H 2 O. 



Ordway describes the dihydrate as resulting by boiling off the fused 

 hexahydrate, which Lowenstein confirms. The latter finds it as the product 

 of 6 days' dihydration over sulphuric acid of over 80 per cent strength, al- 

 though Fourand finds 6 days required in a vacuum over strong sulphuric. 

 Lebeau finds powdered hexahydrate converted to dihydrate in a vacuum desic- 

 cator with concentrated sulphuric acid in 72 hours. Lebeau finds that on 

 treating the hexahydrate with ether, two layers are formed, of which the 

 ethereal layer can be dried with anhydrous calcium nitrate, which leaves the 

 dihydrate on evaporation. It is to be noted in this connection that the ethereal 

 solution, which is also used for separating uranium X, can not be boiled off, as 

 it decomposes with explosive violence after some heating, liberating copious 

 nitrous fumes. 1 Lebeau also obtains crystals with ether of crystallization at 

 10 and 70. The dihydrate may also be formed by adding dry U0 3 to 

 fuming nitric acid (92 per cent), from which solution it is readily recrystal- 

 lized. Wasiljew, crystallizing the dihydrate from fuming nitric acid (s. g. 

 1.502), finds quadratic tables of the rhombic system with strong fluorescence. 

 The author found yellow plates with marked fluorescence at lower tempera- 

 tures of probably rhombical pinacoid and pyramid, with some other forms. 

 The crystals weather so rapidly, having a vapor-pressure of 0.2 mm., accord- 

 ing to Lowenstein, that changing from one closed vessel to another usually 

 tarnishes them so that little can be done in the way of measuring, handling for 

 cleavage, etc. Wasiljew gives the melting-point as 179.3. The mixture of 

 dihydrate and solution obtained by melting the trihydrate goes over to solu- 

 tion at about 160 and then goes unchanged except for slight boiling to 240. 



URANYL NITRATE ANHYDROUS. 

 UO 2 (NO 3 ) 2 or UO 3 .N 2 O B . 



Marketos produced anhydrous uranyl nitrate by heating the nitrate to 170 

 to 180 C., since total decomposition took place at 200, and passing over it 

 dry carbon dioxide saturated with nitric-acid vapors by bubbling through 

 concentrated nitric and sulphuric acids. This produced a yellow amorphous 

 salt soluble in water which decomposed ether, with the liberation of nitrous 

 vapors. Forerand found that long heating above 125 C. in a current of dry 

 carbon dioxide produced basic anhydrous nitrate and below 100 only a 

 monohydrate. Twelve hours at 165 in a current of carbon dioxide charged 

 with nitric-acid vapors gave U0 2 (N0 3 ) 2 + 1/31H 2 U0 4 . 



The method evolved for producing anhydrous uranyl nitrate was to place 

 in a train of U -tubes a tube containing uranic oxide made by heating the 

 hydroxide or acid HVUC^ until it began to turn red and distilling over it nitric 



1 Muller, Chem. Ztg., 41, 439, 1917; 40, 30, 1916. 



