Hillebrand — Occurrence of Nitrogen in JJraninite. 393 



whereas there should have been a large loss if the nitrogen 

 had been expelled. No other explanation seems possible than 

 that the nitrogen has entered into some other state of combi- 

 nation from which it is not set free by the usual means. A 

 somewhat similar change seems to result from heating the min- 

 eral in hydrogen. All U0 3 is reduced to TJ0 2 and the usual 

 tests show that the percentage of nitrogen decreases very slowly 

 as the heating is prolonged, but the total loss is by no means 

 equal to the sum of water plus oxygen of U0 3 reduced to U0 2 

 plus the nitrogen that has disappeared ; it is slightly, if any, in 

 excess of water and oxygen from UO s alone. Ammonia is not 

 formed. Practically no loss in weight occurs on heating the 

 mineral in C0 2 beyond that representing the water. 



Briefly summarized the conclusions are as follows : 



First. Nitrogen exists in uraninite in quantities up to over 

 2 '5 per cent, and seems generally to bear a relation to the 

 amount of U0 2 present. This is the first discovery of nitro- 

 gen in the primitive crust of the earth. 



Second. The condition in which the nitrogen exists is un- 

 known, but it is entirely different from any hitherto observed 

 in the mineral kingdom. 



Third. Analysis of uraninite from various localities has 

 shown that, with in general the same constituents, the mineral 

 varies widely in composition, and that its physical character- 

 istics and its behavior toward certain solvents are often as dis- 

 tinct as the chemical differences. 



Fourth. The formulae of Comstock and Blomstrand are inap- 

 plicable to the zirconia, thoria, and yttria uraninites of North 

 America and Norway, among which are to be reckoned 

 Broggerite, Cleveite, and Nivenite, and probably to the varie- 

 ties free from earths. 



Fifth. Extended and most careful examination of uraninite 

 specimens from all possible localities is necessary before any 

 conclusion worthy of acceptance can be reached as to the char- 

 acter of the chemical combination or combinations represented 

 by them. The work in this direction should likewise cover a 

 study of the nitrides and oxynitrides of uranium and thorium, 

 with synthetical experiments aiming at the artificial produc- 

 tion of uraninite. 



Work will continue in this laboratory as opportunity may 

 offer. It is earnestly to be hoped that those possessing or in a 

 position to secure uraninite specimens will take the trouble to 

 examine them on the lines suggested in the foregoing pages, 

 or if unable to do so, will kindly contribute material for exam- 

 ination here. The interest in the matter is not confined 

 merely to a solution of the composition of this one mineral ; 

 it is broader than that, and the question arises, may not nitro- 



