Volatility of Thorium J). 801) 



-experiments with Th D were made when the active deposit 

 was chemically treated. 



In the experiments described below the volatilization of 

 Th D has been investigated in greater detail, particularly 

 with a view to providing more information on the process of 

 radioactive recoil. 



Experimental Arrangement. 



The active material was heated in an electric furnace lined 

 with a porcelain tube 30 cm. long, 4*5 cm. diameter, wound 

 with platinum strip. Variations of temperature from 100° C. 

 to 1200° C. could be measured accurately by means of a 

 platinum thermometer and Call end ar- Griffiths " bridge/'' 

 The coils of the " bridge " were carefully calibrated, and the 

 ice- and steam-points of the thermometer determined from 

 time to time. The " 8 coefficient " of platinum was assumed 

 to be 1'50. The bottom of the /3-ray electroscope employed 

 in all the activity measurements consisted of a sheet of tinfoil 

 of thickness sufficient to stop « particles of &6 cm. range and 

 soft /9 rays from Th B. The active deposit used in the experi- 

 ments was obtained by exposure to a source of radio- thorium. 



In all experiments the Th D, either " pure M or in equi- 

 librium with Th B and C, was heated on platinum foil, which 

 could be quickly placed on, or removed from, a fused silica 

 shelf fixed centrally on the furnace. To avoid unnecessary 

 complications, the time of heating in the furnace was kept 

 constant (4 minutes) throughout the experiments. This rather 

 short time of heating was necessary, owing to the decay of 

 Th D (period 3'1 minutes) in the furnace. 



The volatility of Th D obtained under the following con- 

 ditions has been examined : — 

 Case I. Thorium D, recoiling from ordinary actice deposit — 



then treated as follows: 



(i.) Undissolved in acid. 



(ii.) Dissolved in pure concentrated nitric acid, 

 (iii.) „ „ „ hydrochloric acid. 



Case II. (i.) Th D recoiling from active doposit which had 

 previously been treated with hydrochloric acid. 



(ii.) Th D recoiling from Th C (obtained from a solution 

 of active deposit in hydrochloric acid by von Lerch's 

 method — using polished nickel plates). 

 K Case III. Thorium I) in equilibrium with B and C, 

 (i.) Undissolved in acid, 

 (ii.) Dissolved in nitric acid, 

 (iii.) „ hydrochloric acid. 



Phil Mar). S. 6. Vol. 28. No. 168. Dec. 1914. ?> G 



