384 Hillebrand — Occurrence of Nitrogen in Uraninite. 



before and after every weighing, and during the entire series 

 of experiments the greatest variation was '0001 grams. 



For weighing the boats used in the second and third series of 

 experiments, light glass tubes, with accurately fitting stoppers 

 of glass, were made. Two boats were used in every experi- 

 ment, one as a counterpoise. The boats, while still warm, 

 were placed in the tubes and the tubes stoppered. When quite 

 cold the stoppers were momentarily loosened to restore the 

 atmospheric equilibrium inside the tubes. 



The balance used was most accurate and highly sensitive, of 

 the short arm pattern, with an aluminium beam. With a 

 load of 30 grams in each pan. the resting point was displaced 

 two whole divisions by '0001 grams. The weights were 

 adjusted with the utmost care, especially for this work. The 

 weighings in all experiments were reduced to the vacuum 

 standard. 



University of Pennsylvania, 



Art. XLIX. — On the occurrence of Nitrogen in draninite 

 and on the composition of Uraninite in general. Con- 

 densed from a forthcoming Bulletin of the TJ. S. Geological 

 Survey • by W. F. Hillebrand. 



The following pages contain in much condensed form the 

 results of chemical work thus far done by myself on uraninite 

 from various localities in North America and Europe, of 

 which brief notices have already from time to time appeared.* 

 For various reasons it has been impossible to bring the investi- 

 gation as far forward as was expected, and the results are in 

 some respects incomplete and in others difficult of interpreta- 

 tion, but so much time has elapsed since the work was begun 

 that it seems advisable to make public now what has been 

 achieved, without waiting an indefinite and probably long 

 time for the sake of then presenting the subject in a more 

 finished and satisfactory form. 



At an early stage of the work it was found that to the 

 North American varieties could by no possibility be applied 

 the formula obtained by Comstockf for the Branch ville 

 Conn., mineral, and by Blomstrand X for the Norwegian and 

 Bohemian varieties. Comstock's analysis was shown to be 

 incorrect, he having found no thoria where about 7 per cent 



* This Journal, III, xxxvi, 295, xxxviii, 329, and Bull. U. S. Geol. Survey, No. 

 GO, p. 131. 



f This Journal, III, xix, 220. 



\ Geol. For. Forh., vii, 59, and Journ. prakt. Chem., xxix, 191. 



