Hillebrand — Occurrence of Nitrogen in Uraninite. 391 



Owing to the uncertainty of being able to determine with any 

 close approach to truth the proportions of U0 2 and UO s in the 

 presence of sulphides and compounds of arsenic and vanadium, 

 no quantitative analyses of specimens from those localities have 

 as yet been made. 



Hitherto the analyses have been considered without reference 

 to the nitrogen. It has been sought to show on grounds which 

 would be valid even without its presence that the ortho-uranate 

 formula is capable of no general application to uraninite, and 

 that in the one or two cases where it does seem to apply this 

 agreement is probably accidental. Taking into account the 

 low atomic weight of nitrogen as compared with uranium, 

 thorium, and lead, it is plain that it must play an important 

 part in the constitution of the molecule, and that therefore its 

 discovery without other evidence furnished by the analyses is 

 sufficient to invalidate entirely the practically identical formulae 

 of Comstock and Blomstrand. Throughout the whole list of 

 analyses in which nitrogen has been estimated the most striking 

 feature is the apparent relation between it and the U0 2 . This 

 is especially marked in the table of Norwegian uraninites re- 

 calculated, from which the rule might almost be formulated that, 

 given either nitrogen or U0 2 the other can be found by simple 

 calculation. The same ratio is not found in the Connecticut 

 varieties, but if the determination of nitrogen in the Branch- 

 ville mineral is to be depended on, the rule still holds that the 

 higher the U0 2 the higher likewise is the nitrogen. The Colo- 

 rado and North Carolina minerals are exceptions, but it should 

 be borne in mind that the former is amorphous like the Bohe- 

 mian and possesses the further similarity of containing no 

 thoria, though zirconia may take its place, and the North Car- 

 olina material is so much altered that its original condition is 

 quite unknown. 



In the absence of all positive knowledge as to the role which 

 nitrogen plays in the mineral it would be idle to speculate at 

 present upon the proper position of the latter in mineral classi- 

 fication. Much remains to be done before this question can be 

 elucidated. 



But two explanations seem possible to account for the wide 

 differences in the oxygen ratios for U0 3 and total bases, vary- 

 ing as they do, from I : 4"37 for the Branchville material of 

 analysis YI to 1 : 1 for Blomstrand's Broggerite and even to a 

 ratio indicating acidity for Nivenite. Either all the others are 

 alteration products of a mineral having the composition of the 

 Branchville occurrence, or even of some unknown body entirely 

 free from U0 3 ; or they are mixtures of two or more substances. 

 Fractional solution indicates this prettly clearly without decid- 



Am. Jour. Sci. — Third Series, Vol. XL, No. 239. — Nov., 1890. 

 25 



