Products of the Radio-active Elements. 259 



In the greater number of instances where water is found 

 present in these minerals, it is quite impossible to explain how 

 it could have penetrated into them from without, since their 

 close-grained and impervious nature is impressively indicated 

 by the very notable quantity of helium which they have 

 retained. Moreover non-radio-active minerals which occur 

 associated with the radio-active species, and which have been 

 subjected to the same external influences, are often quite 

 anhydrous, e. g., apatite, magnetite, etc. The mineral thorite 

 has been called to the attention of the writer by Professor S. 

 L. PenfLeld. This mineral frequently occurs in very perfect 

 crystals, which however exhibit only the optical properties of 

 an isotropic and amorphous compound. This species has been 

 long regarded as having undergone alteration, but that the 

 causes of the alteration existed within and not without the 

 crystals is, I believe, a new and somewhat novel explanation. 



It is a significant fact that results obtained* in the examina- 

 tion of certain radio-active minerals indicate that hydrogen 

 occurs as one of the gaseous constituents of many of these com- 

 pounds. A further interesting point bearing on this question 

 is mentioned by Hillebrand,t who observed that when urani- 

 nite was mixed with sodium carbonate and fused in an atmos- 

 phere of carbon dioxide, the lead present was apparently 

 entirely reduced and collected in globules. Mixtures of cor- 

 responding proportions of lead oxide (litharge) and U 3 8 or IJ0 2 , 

 when treated in an identical manner, showed no reduction of 

 the litharge to metallic lead. This distinctive difference in 

 behavior is strongly indicative of the presence of hydrogen as 

 a constituent of uraninite. 



Argon. 

 Results obtained by Ramsay and Traversal may further indi- 

 cate that another of the disintegration products of radio-active 

 substances is the inert gas argon. It is stated by these authors 

 that most minerals which evolve heliiun also evolve argon in 

 small quantity. It may not be impossible that some of the 

 rayless changes which have been observed by Rutherford to 

 take place in radio-active bodies, may be accompanied by the 

 expulsion of alpha particles consisting of argon, which owing 

 to their relatively high mass are projected at too low velocities 

 to cause ionization of the surrounding gases and to permit 



* Ramsay, Collie and Travers, Jour. Chem. Soc, Lond., lxvii, 684 (1895), 

 state that hydrogen in varying quantities was evolved by yttrotantalite, 

 samarskite. Melinite, fergiisonite, tantalite, monazite, xenotime, columbite, 

 perofskite, euxenite, orthite, gadolinite and cerite. Also Ramsay, Proc. Eoy. 

 Soc. Lond., lix, 325 (1896). 



f Bulletin of the U. S. Geological Survey, No. 78, p. 59 (1891). 



% Proc. Roy. Soc. Lond., lii, 316 (1898). 



