958 Dr. R. W. Boyle on the Volatilization of 



Throughoul the above operations the Dewar cylinder was 

 kept nearly full of liquid air, bur immediately they were 

 finished the cylinder was rapidly drawn away from the 

 pentane bath, quickly emptied of its liquid air contents, and 

 then set back in place over the bath. The stop-cocks of the 

 electroscope were then opened. Under these conditions the 

 temperature of the hath rose very slowly — about 0° 4 C. 

 per minute at the bottom. 



A- soon as the electroscope stop-cocks were opened there 

 \\;i> a slight rise in ionization. This was due to slight 

 amounts or a neon den sea emanation not completely expelled 

 from the spiral and the conducting tubes. This initial rise 

 was in no way connected with the relatively large increase 

 in ionization which marked the volatilization at the tem- 

 peratures present ly shown. 



Aa already mentioned, pentane was used as a temperature 

 hath. The pentane employed became very viscous at about 

 —150 C, and consequently could not bestirred below this 

 temperature. On this account the temperature of the hath 

 was not uniform throughout but increased gradually from 



• Mom to the top. 



Under these conditions the temperature required must be 

 that of the coldest part of the condensing spirals, namely, 

 the bottom coil. This must certainly be the ease, for the 



Writer has found from a few special experiments in which 

 emanation was condensed in U-tubos, that condensation takes 

 in the limb of the tube through which tin; air current 

 carrying the emanation enters. (The fact uas ascertained 

 by noting that the phosphorescence caused by the emanation 

 and active deposit was confined to this limb of the U-tube.) 

 Similarly with spirals : condensation takes place in that half 

 of the spiral through which the air current enters. If, when 

 the process of warming has started, any emanation volatilizes 

 in the upper and warmer coils of the spiral, the air current 

 bears it to the lower and colder coils, where it immediately 

 recondenses provided that the temperature rises slowly. It 

 is therefore necessary that the air current should be very slow, 

 and that the spiral should rise very slowly in temperature. 



For the above reason, the temperature of the bottom coil 

 of the spirals was measured in all experiments ; but oppor- 

 tunity was taken whenever possible to probe the other parts 

 of the bath with a thermo-couple in order to acquire some 

 information regarding the temperature distribution. 



The temperatures w 7 ere measured by means of thermo- 

 couples ; the sensitiveness of the two element copper- 

 eonstantan set. used in most of the experiments, was. on an 



