88 B. B. Bolt wood — Ultimate Disintegration Products, etc. 



formation. The constituents of this mineral* are in part as 

 follows : Th0 9 , 66-26 per cent ; Ce0 2 , 7*18 per cent ; Zr0 2 , 2-23 

 per cent ; TT0 2 , 0"46 per cent. No lead at all is indicated as 

 present, and the amount to be expected from the uranium is 

 only O'OS per cent, which was probably overlooked in making 

 the analysis. A similar result was obtained in an examination 

 by the writer of a specimen of thorite from Norway, which con- 

 tained only O40 per cent of uranium, 52*0 per cent of Th() 2 

 and less than 0*10 per cent of lead. No mention is made of 

 the presence of helium in the former of these thorites and in 

 the specimen examined by the writer no indications of the 

 presence of helium in measurable quantities were obtained. 

 Although it has been stated by Ramsayf that the relatively 

 large amount of helium contained in the thorianite from the 

 Sabaragamuwa province is conclusive evidence of the produc- 

 tion of helium by thorium, it seems quite probable that the 

 evidence furnished by this mineral is quite the contrary, since 

 it appears to contain only half of the amount of helium which 

 would be produced by the disintegration of the uranium alone. 



Summary. 



Evidence has been presented to show that in unaltered, pri- 

 mary minerals from the same locality the amount of lead is 

 proportional to the amount of uranium in the mineral, and in 

 unaltered primary minerals from different localities the amount 

 of lead relative to uranium is greatest in minerals from the 

 locality which, on the basis of geological data, is the oldest. 

 This is considered as proof that lead is the final disintegration 

 product of uranium. 



It has also been shown that, on the basis of the experimental 

 data at present available, the amounts of helium found in 

 radio-active minerals are of about the order, and are not in 

 excess of the quantities, to be expected from the assumption 

 that helium is produced by the disintegration of uranium and 

 its products only. 



The improbability that either lead or helium are disintegra- 

 tion products of thorium has been pointed out. 



December 27, 1906. 



*Dunstan and Blake, I. c. f Jour. Cheni. Phys., iii, 617, 1905. 



