402 



REPORT OF NATIONAL MUSEUM, 1899. 



Uses. — The various borax salts are used in the preparation of 

 boracic acid and the borate of sodium, the borax of commerce. 



XI. URANATES. 

 1. Uraninite; pitchblende. 



Composition very complex, essentially a uranate of uranyl, lead, 

 thorium, and other metals of the lanthanum and yttrium groups. 

 The mineral is unique in containing nitrogen, being the only one 

 among the constituents of the primary rocks of the earth's crust in 

 which the presence of this element has been thus far determined.^ 

 The analyses given below are for the most part by Hillebrand, to whom 

 is due the credit of a large share of the present knowledge on the 

 subject. 



Several varieties of uraninite are recognized, the distinctions being 

 based upon the relative proportions of the two oxides UO2 and UO3 

 (see analyses above). Inasmuch, however, as these variations may be 



ground from which these were taken the crust had been removed several times dur- 

 ing the preceding twelve years. 

 The analysis of samples gave the following results: 



From this list it will be seen that the first six months' growth is richest in borax, 

 and that the proportion of carbonate of soda to borax increases regularly. The 

 presence of so much sand as is here indicated is caused by the high winds that blow 

 at intervals, bringing in great quantities of that material from tbe mountains to the 

 west. This sand, it is supposed, facilitates the formation of the surface crust by 

 keeping the ground in a porous condition. 



>The mineral has since been found to contain some 0.23 per cent of the new ele^ 

 ments helium and argon. 



