32 T. H. LABY. 



The Saxony mineral contained also N(i.e. He), MnO, 

 Na 2 0, P 2 O s , As,0 5 , V 2 O s , W0 3 , Mo0 3 , S0 3 in small 

 quantities. Neither mineral contained rare earths. 



The chief difference between the two pitchblendes lies in 

 the greater density, and presence of less water in the New 

 South Wales one. In these respects it approaches the 

 crystalline uraninites — a brilliant and well-defined example 

 of which was found by Hillebrand 1 to contain 13*3 U0 3 + 

 72*2 UO a = 85'5, Th0 2 Zr0 2 7% PbO 4'3, H 2 '7, S.G. 9'7. 

 But the absence of rare earths, the presence of CuO, Bi 2 O s , 

 As a 3 , the high proportion of U0 3 , and the massive and 

 non-crystalline form of the New South Wales mineral 

 indicate that it is probably a secondary pitchblende. 



Radio-Activity.— The radio-activity of the mineral was 

 measured by placing a uniform thick layer of it in the form 

 of a powder in a flat circular lead dish between the plates 

 of a condenser separated by 5 cms. of air. The ionization 

 it produced with a saturation voltage was 3*15 times that 

 obtained when the mineral was replaced in the lead dish 

 by black oxide of uranium CJ 2 5 . Thus the radio-activity 

 of the mineral is 4*4 times that which it would have solely 

 on account of the uranium which it contains. McCoy 2 (who 

 allows for the absorption of the a particles in the layer of 

 radio-active matter which I did not do), has shown that for 

 the uranium minerals he examined the above number is 4'15« 

 The radio-activity above that contributed by the uranium 

 is known to be due to ionium, radium and its products. 

 Since this extra activity is slightly above its normal value, 

 it follows that Bennett's pitchblende contains at the least 

 the normal amount of radium for that variety of mineral. 

 This was confirmed by comparing its activity directly with 

 that of a Bohemian pitchblende — the New South Wales 

 mineral was the more active by If. 



1 U.S.G.S., No. 78, p. 64 (1891). * Phil. Mag., Jan. 1906, p. 176. 



