Dr. R. W. Boyle on the Volatilization of 



J t is known thai when emanation is condensed on the 

 inner wall oi' a vessel at any temperature, even down to the 

 liquid air temperature, the emanation can be practically all 

 removed by continuously pumping. The fact shows that 

 there is an appreciable vapour phase of the emanation at 

 all temperatures down to the temperature of liquid air. 

 Consequently, in an experiment by the Mow method, if the 

 emanation be at first condensed, and the temperature be kept 

 constant while the gas current is allowed to iiow indefinitely, 

 the molecules of emanation in the vapour phase will become 

 entrained in the gas current and be removed. More mole- 

 cules will then volatilize into the vapour phase from the 

 condensed layer, and these in turn will also be carried away. 

 This process will continue until all the emanation has been 

 removed. It follows, therefore, that with a temperature not 

 fixed but gradually rising, and with a constant gas flow, 

 the temperature at which all the emanation has just been 

 removed from the surface of the condenser will depend on 

 fl ) the quantity of emanation condensed, (2) the rate of rise 

 of temperature. Experiments by the flow method to com- 

 pare the influences of different surfaces on the process of 

 volatilization should be carried out with the conditions 

 regarding ( 1 ) and (2) at least approximately alike*. 



The quantities «>f emanation employed in the experiments 

 varied between the equilibrium amounts from 2 x 10~ 4 to 

 2x 10~ a mgm. of radium. Experience showed that the rate 

 of volatilization at the final temperature is increasing so 

 rapidly that variations in the quantity of emanation, much 

 larger than the above, give very similar results. The range 

 of accuracy in the experiments is considered to be +2° C. 



Curves 1. and II. of fig. 2, which represent the connexion 

 between ionization and temperature for spirals of lead and 

 of gla-<. me typical of the behaviour for all the substances 

 examined. The dotted curves represent the rise of tempe- 

 rature at the bottom of the bath with time. 



The maximum ordinates GH and IK of the ionization 

 curves give the temperatures at which the volatilization 

 of emanation from the condensing surface very rapidly 

 diminishes or ceases altogether. We may say that at these 

 temperatures the emanation is all removed from the surface. 



But the ordinates, such as AB, CD, EF, and also MN, 

 QR, show that at still lower temperatures there is appreciable 

 volatilization. This could no doubt be noticed down to 

 liquid air temperature if the electroscope could be kept from 



* It is not meant here that the quantity of emanation cannot be varied 

 from one amount over a range often or twenty times that quantity, hut 

 it should not he varied over thousands or tens of thousands of times. 



