732 Behaviour of Radium Emanation at Loiv Temperatures. 



writer made a number of experiments with the object of deter- 

 mining quantitatively the vapour pressures at temperatures 

 upwards from — 180° C. The experiments were not successful, 

 but they may be briefly referred to. 



The emanation was condensed in a manner somewhat 

 similar to the one described on p. 725, in the bottom of a 

 narrow glass tube connected to the side of a larger vessel 

 which terminated at the top in a series of small bulbs. 

 The whole apparatus was exhausted to a charcoal vacuum 

 before the emanation was introduced. After condensing 

 the emanation and securing temperature conditions as steady 

 as possible, the condensing tube was opened to the larger 

 vessel for half an hour in order to ensure a constant dis- 

 tribution of the emanation. The connexion was then closed, 

 and the emanation distributed in the larger volume was 

 compressed over mercury into the topmost small bulb. This 

 bulb was then sealed off, the mercury was lowered to its 

 original position, and the same process was repeated at 

 another temperature. After a set of experiments, the ema- 

 nation contents of the different bulbs were measured, and 

 from them could be calculated the vapour pressures corre- 

 sponding to the different temperatures employed. 



The result of these experiments supported the conclusions 

 arrived at from the former experiments, and showed that the 

 pressures were of such small orders as the figures of column 4, 

 Table I., would suggest. But the numerical results were 

 very irregular, and they could not be even approximately 

 repeated under the same conditions. There was great dif- 

 ficulty in maintaining constant temperatures ; but the chief 

 cause of the failure was due to the action of the emanation 

 in producing, in the course of an experiment, appreciable 

 quantities of carbon dioxide and other gases from the im- 

 purities introduced into the apparatus by the mercury 

 and the stop-cocks. The emanation behaved as if it con- 

 densed along with these gases, thereby becoming entrapped 

 and not being able to escape until the gases escaped also. 

 The experience showed that in this type of experiment special 

 apparatus will have to be used to prevent any foreign gas 

 entering the condensing chamber. It is hoped that the 

 experiments may be taken up again in the near future. 



The writer is greatly indebted to Prof. Rutherford for the 

 loan of apparatus and supplies of emanation, and also for 

 his helpful suggestions and advice throughout the course of 

 the experiments. 



