THE GROWTH OF OUR KNOWLEDGE OF HELIUM. 257 



DR. HILLEBRAND'S RESEARCHES ON URANINITE, 1888. 



In this year Dr. Hillebrand, one of the officials in the 

 Geological Department at Washington, was engaged upon 

 the chemical examination of specimens of the mineral 

 uraninite from various localities. 



He dealt with crystals which he put in a vessel contain- 

 ing some sulphuric acid and water. He found that bubbles 

 of gas were produced out of the crystal by means of the 

 sulphuric acid. He collected this gas and came to the 

 conclusion that it was nitrogen. 



This result was new. He thus wrote about it : — 



"In consequence of a certain observation " [the one I 

 have just referred to] " and its results, an entirely new 

 direction was given to the work, and its scope wonderfully 

 broadened. This was the discovery of a hitherto un- 

 suspected element in uraninite, existing in a form of com- 

 bination not before observed in the mineral world." 



It is not needful here to follow -Dr. Hillebrand through 

 all the painstaking and patient labour he cut out for him- 

 self to explain this anomalous behaviour. Needless to 

 say he did not omit to employ the spectroscope to test the 

 nature of the new gas. 



His observations were thus described : — 1 



"In a Geissler tube under a pressure of ten milli- 

 metres and less, the gas afforded the fluted spectrum of 

 pure nitrogen as brilliantly and as completely as was done 

 by a purchased nitrogen tube. In order that no possibility 

 of error might exist, the tube was then reopened and 

 repeatedly filled with hydrogen, and evacuated till only the 

 hydrogen lines were visible. When now filled with the 

 gas and again evacuated, the nitrogen spectrum appeared 

 as brilliantly as before, with the three bright hydrogen lines 

 added." 



On this paragraph I may remark that it has long been 

 known that gases like nitrogen give us quite distinct spectra 

 at different temperatures — one fluted, another containing 



1<( On the Occurrence of Nitrogen in Uraninite," Bulletin, No. 78, 

 U.S. Geol. Survey, 1889-90, p. 55. 



