Compounds of Short-lived Radioactive Elements. 127 



described later the mean distance between two atoms of the 

 material deposited on a platinum wire is about 10,000 times 

 as large as their radii. 



Volatilization of Actinium JB. 



According to the work of Levin *, actinium B is non- 

 volatile below 400° but is completely volatilized at 750° in 

 about 10 minutes from a surface of platinum. In the present 

 paper this subject has been examined in greater detail. It has 

 been found impossible to get perfect agreement in different 

 experiments, but results have been obtained sufficiently defi- 

 nite to test whether any considerable change in volatility could 

 be effected by chemical treatment of the active substance. 



Experimental details. — A platinum wire 0*13 mm. thick, 

 10 cm. long, was bent into a loop the ends of which were 

 welded to two thick platinum wires. The latter were 

 soldered to copper rods fitting into two brass rods C, which 

 were connected to the terminals of a battery. By means of 



Ammeter 



Variable /?esjst/ince 



MERCURr PUMP 



screws perfect contact was ensured. The disposition is shown in 



the figure. The temperature of the wire was found by 



comparing the fall of potential along the wire with that 



* M. Levin, PMjs. Zeitschr. vol. vii. p. 812 (1906; . 



