62 Messrs. J. H. L. Johnstone and B. B. Boltwood on the 



We will now proceed to a consideration of the two alterna- 

 tives (a) and (b) mentioned in the preceding paragraph. 

 As a preliminary to this the relative activities of the other 

 members of the main-line series can be calculated from the 

 ratio experimentally determined for the uranium and radium. 

 Geiger's equation is employed 



I = N/,B, 



and the results obtained are given in Table V. The calcu- 

 lations are made on the assumption that the simplest 

 (1 : 1) relation exists between all the products following and 

 including ionium. 



Table V. 



Range of a-particle Relative Activity 



Element. in cm. (at 0° C.) Calc. Found. 



Uranium 1 2*37 



Uranium II 275 1-00 1-00 



Ionium 295 0'46 



Radium 313 049 0'49 



Emanation 394 0'57 



Radium A 4"50 0-62 



Radium C G"57 O80 



Radium F 364 0*53 



Sum = 4-47 

 Relative activity of actinium and 

 actinium products as determined 

 experimentally by Boltwood* =0*28 



Total = 4-75 



Total activity as determined (p. 57). 



4-73 



The very close agreement between the total activities as 

 calculated and as found is purely accidental and merely 

 indicates that the value given for the activity of the actinium 

 products by difference (4*73 — 4*47 = 0*26) is practically 

 the same as that suggested by Boltwood as a result of his 

 experiments. 



The ranges of the a-particles from uranium, radium, and 

 each of the actinium products and also the value of the two- 

 thirds power of the range are given in Table VI. 



* Am. Journ. Sci. xxv. p. 297 (1908). 



