298 Boll/wood — Radio-activity of Uranium Minerals. 



less marked variations when the relative activities are measured 

 in an ionization chamber of different size and dimensions from 

 that of the electroscope used in these experiments. In a 

 smaller ionization chamber the relative activity of the products 

 emitting- a particles of longer ranges will be less, while in a 

 larger chamber the ionizing effects due to the various /3 radia- 

 tions will be proportionately greater. Without special defini- 

 tion, therefore, the numbers as derived above can not be 

 considered as approximating to definite constants. 



The values found indicate that the activit}^ of the uranium 

 is about 2*22 times that of the radium with which it is in 

 radio-active equilibrium. It seems very certain that the range 

 of the a particles from uranium is not greater than the range 

 of the a particles from radium itself,* and the number found 

 is, therefore, not the one which would be expected on the basis 

 of the simple disintegration theory, in which it is assumed that 

 the same number of a particles is emitted per second by 

 equilibrium amounts of successive products. It is possible, 

 however, that two distinct a ray changes may exist in ordinary 

 uranium, although the assumption of two such products does 

 not entirely obviate the difficulty. The problem is evidently 

 too complicated to permit of any simple explanation of the 

 relations for the present. 



In so far as these experiments throw any light on the 

 question of a genetic relation between actinium and uranium, 

 I think that the constancy of the activity of the different 

 minerals and the fact that quite appreciable amounts of actinium 

 can be separated from all of theinf make it necessary to assume 

 that the amounts of actinium in a mineral are proportional to 

 the quantity of uranium present. It is therefore extremely 

 probable that actinium is a disintegration product of uranium, 

 although its position in the uranium-radium series is still to be 

 determined. 



New Haven, Conn., 



February 14, 1908. 



* Bragg, Phil. Mag., xi, 754, 1906. McCoy and Ross, Jour. Am. Chein. 

 Soc, xxix, 1698, 1907. 



f I have had no difficulty in demonstrating the presence of actinium in 

 carnotite. 



