Production of Fluorescent Rontgen Radiation. 359 



substances and from one another, and for the preparation of 

 several of these products completely free from radio-active 

 impurities. 



2. The relative activities of thorium B + C + D and thorium 

 X + Emanation + A was determined by preparing thorium X 

 entirely free from B + C-fD and determining its change of 

 activity with time. Knowing the periods of each of the 

 substances, the activity of B + G + D was found to be 0*427 

 of that of thorium X + Emanation + A. 



3. By determining the initial activity of pure radio- 

 thorium and its change of activity with time, it was found 

 that the products of radiothorium are 5*23 times as active as 

 the radiothorium itself. 



4. In order to make the calculations of the results of 3 

 and 4, it was necessary to know the periods of the various 

 radio-bodies accurately. As a result of new determinations, 

 the accepted periods of thorium X and thorium B were con- 

 firmed as 3*64 days and 10*60 hours respectively. The 

 period of thorium C w y as found to be G0'8 minutes instead 

 of 60*4 minutes (Lerch). 



5. It w T as shown that the accepted value of the range of 

 thorium X 5*7 cm. was incorrect, and that the true value 

 is 4*1 cm. This value is in good accord with that expected 

 from the period of this substance. 



6. It is shown to be theoretically probable that the total 

 ionization of an alpha particle is proportional to the % power 

 of its range. It is then shown that the activities found in 3 

 and 4 are in excellent agreement with those expected from 

 the ranges of the various active substances. 



Kent Chemical Laboratory, 

 University of Chicago, 

 October, 1912. 



XXXVIII. Production of Fluorescent Rontgen Radiation. By 

 J. Crosby Chapman, B.Sc, Tutor in Mathematics at King's 

 College, London, late Research Student of Gonville and 

 Caius College, Cambridge* . 



TO satisfy the corpuscular theory, Professor Bragg f has 

 recently suggested that not only ionization is an indirect 

 phenomenon due to f3 rays, but that in addition the fluorescent 

 X-rays themselves are possibly due also to action of the 

 /9-rays. That is, the fluorescent X-radiation is a tertiary and 

 not a secondary effect, being merely due to the expelled 



* Communicated by Professor C. G. Barkla. 



t Bragg and Porter, Proc. Boy. Soc. A. vol. lxxxv. p. 350. 



