﻿Thorium and Radium Emanations, 349 



The surprising result was found that the points were lying on 

 a totally new curve, that the emanation did not start to be 

 condensed until after —150° C, and that then it became 

 completely condensed very quickly. At the conclusion of 

 the experiment the vacuum of the tube had not appreciably 

 deteriorated. 



The only suggestion that can be made to explain the two 

 curves is that some quantity of gas had been liberated from 

 the walls of the tube which had a great effect on the con- 

 densation of the emanation. Whatever the cause, the results 

 show the great difficulty attaching to experiments of this 

 character. 



' Experiments at Low Pressure with Thorium Emanation, 



Apparatus. — For the thorium experiments the same pre- 

 paration of radio-thorium which had been used for the work 

 at atmospheric pressure was put into a small cylindrical brass 

 drum which was closed at the ends by filter-paper fixed on 

 with sealing-wax. For the first experiments a straight tube 

 was taken, fig. 7, at the bottom of which a small test-tube 



Fig- 7. 



£nd "TWio-rtonum. ^ eiad " 



filled with phosphorus pentoxide was placed, and a depression 

 was made in the glass so that this tube could not slide away 

 from its end. The radio-thorium drum was then introduced 

 and made to take up a position mid-way along the tube, 

 where it was fixed by sealing-wax. There was also a glass- 

 wool plug placed between the drum and the sealed end close 

 to the former. The total length of the tube was 60 cm. and 

 the diameter 1*5 cm. 



The tube was thoroughly evacuated by attachment over 

 night to a charcoal bulb cooled in liquid air, after which it 

 was sealed. The two ends of the tube will be distinguished 

 as the " P 2 5 end " and the " experimental end. 5 ' In this 

 experiment the large 7 electroscope, A, in the same position 

 as shown in fig. 3, was used to measure the activities of the 

 experimental end. For this purpose the tube was placed in 

 the lead cylinder with 10 cm. of that end projecting to 

 the right. 



The P 2 5 end was placed in liquid air and allowed to stand 



