L32 Dr. Hans Schrader on tlie Existence of Chemical 



dropped into the quartz tube. The temperature at the 

 bottom of the tube was usually higher than 900°, so that 

 the greater part of the material volatilized and was deposited 

 again on the cooler parts of the tube and on the mica. 

 After some minutes the latter was removed and cut into 

 parts of equal lengths which were measured on both sides in 

 an a-ray electroscope. 



Experiments were conducted in air and in hydrogen. In 

 experiments with the latter the tube was filled first with 

 carbon dioxide and then with hydrogen. By means of a 

 special device the active wire was dropped into the tube 

 without opening it. The interval of time which was allowed 

 to elapse between inserting the wire and removing the mica 

 varied from 5 to 15 minutes in different experiments. 



Volatility in Air. — The experiments showed the unex- 

 pected result that actinium B, after volatilization in air, 

 becomes much less volatile than it had been when the experi- 

 ments were conducted in vacuo. The details of one experi- 

 ment are given in the following table : — 



Interval of time between insertion of the active wire and 

 removal of the mica, 5 minutes. 



Length No. Temperature. Activity 



1 m rhv. per mm. 



Greater than 1090° 



1200 



1 1075° to 1090° 



100 



2 1045° to 1075° 



2 



3, &c less than 1045° 







When a platinum strip was used instead of a mica one, an 

 appreciable amount of activity was obtained above 1000°. 



It thus follows that all the volatilized actinium B is 

 deposited in air at temperatures above 1000°, although it 

 begins to volatilize from a surface at 600°. Experiments 

 with thorium B and C give the same results. A. S. Russell 

 has carried oui experiments for radium (J and has shown that 

 its behaviour is similar. 



Volatility in Hydrogen. — The distribution of activity along 

 the mica strip was found to be entirely different when the 

 volatilization was carried out in an atmosphere of hydrogen. 

 In contrast to the experiments with air the activity con- 

 densed on cooler parts of the mica, the maximum amount of 



