W8 Mr. A. B. Wood on the 



The relations used in deriving these results are strictly 

 applicable in the cases of (1) gases, (2) dilute solutions. 



It must be admitted, however, that the mechanism de- 

 rived demands conditions (of collision, &c.) which occur 

 readily in the liquid and the solid state as well as in the 

 gaseous; and it is difficult to conceive how the mechanism 

 can apply in the one case and not in the others. 



It would seem, therefore, that a general law has been 

 obtained, which has been derived rigidly in the case of gases 

 only. 



My thanks are due to Professor Lyle for the criticism and 

 encouragement he has given, and to I. 0. Masson, Esq., M.Sc, 

 for kindly reading the proofs. 



The University, Melbourne, 

 August 1914. 



LXXXV1II. The Volatility of Thorium D. With a Note 



on the Relative /3 Activities of Thorium C and 1). By 



A. B. Wood, M.Sc, Oliver Lodge Fellow, University of 

 Liverpool *. 



Introduction. 



RECENT work on the volatility of radio-active substances 

 has shown clearly the possible existence of definite 

 compounds of these substances with other elements. Expe- 

 riments by Schrader f on the volatiliiy of the active deposit 

 of actinium have given evidence of the formation of chlorine 

 compounds of the active deposit ; and those of Russell J of 

 the existence of an oxide of radium C. In some recent work 

 of Barratt and Wood § similar results have been obtained 

 with the various members of the active deposit of thorium. 



These observers agree that the temperatures of volati- 

 lization of the chlorine compounds of the active deposit are 

 considerably lower than the corresponding temperatures for 

 the active deposits obtained by exposure to emanation and 

 not subjected to any definite chemical treatment. Barratt 

 and Wood give a short account of experiments on the 

 volatility of Th D. It was found that this substance begins 

 to volatilize at a temperature of about 500° C. 



In their experiments, however, the results were com- 

 plicated somewhat by the presence of Th B and C, and no 



* Communicated by Prof. L. R. Wilberforce, M.A. 



t Schrader, Phil. Mag. xxiv. p. 125 (1912). 



X Russell, Phil. Mag. xxiv. p. 134 ( 1912). 



§ Barratt & Wood, Proc. Phys. Soc. Lond., June 1914. 



