﻿346 



Mr. A. Fleck on the Condensation of 



only conclusion that can be deduced is that the vapour pressure 

 of the emanation is lower at some temperature slightly higher 

 than that of liquid air, than it is within certain limits of 

 temperature intermediate between these two. That this low 

 value of the vapour pressure is not lower than the value at 

 liquid air temperature is shown by the fact that the emana- 

 tion, no matter how long it is exposed to very low temper- 

 atures, will not collect completely in the region beyond the 

 liquid air. 



These observations, therefore, form further evidence of 

 the existence of a maximum, probably the one at —161° C, 

 found in the quantitative measurements with the straight 

 tube. 



Experiments by another method in a two-limb tube. — Further 

 experiments were made with radium emanation in a two-limb 

 tube of the form shown in fig. o. The greatest length of the 



tube was 70 cm., while the short limbs were each 18 cm. 

 long and were 15 cm. distant from one another. As before, 

 10 cm. of the long tube projected beyond the lead cylinder 

 (the same as used previously) and the activity of the un- 

 screened portion could be measured on either the small 7 or 

 on the /3 electroscopes, which occupied the same positions as 

 previously described. 



The end of limb A was always immersed in liquid air 

 except when an experiment at some low temperature was in 

 progress, while limb B was enclosed in the larger gas-tight 

 tube D, through which a current of air, freed from C0 2 by 

 soda-lime and from moisture by sulphuric acid, could be 

 drawn by a water-pump. The taps T x and T 2 regulated the 

 gas stream, and the end of the thermocouple was at the same 

 level as the end of limb B. 



The tube was charged with 11 millicuries of emanation. 

 The advantage of this tube was that it was unnecessary to 

 remove it from its position under the electroscope to make a 

 determination. 



