Solubility of Radium Emanation. 811 



is established, and the amount of Ra C is proportional to the 

 emanation present. 



The simplicity and fair accuracy of the instrument are 

 great advantages, but the chief advantage is that measure- 

 ments can be quickly and easily taken without actually 

 drawing the emanation into the electroscope. Much time 

 and labour are thereby saved, and there are no corrections to 

 be applied for loss of emanation in the conducting tubes, and 

 in the necessary drying of the gas in which the emanation is 

 contained. 



Von Traubenberg was the first to find that radium emana- 

 tion distributed itself in a definite manner between water 

 and air in contact with one another. From the behaviour 

 of the emanation in experiments which he performed he 

 concluded that the emanation, like other oases, was absorbed 

 by a liquid, and on a basis of the validity of Henry's law he 

 determined the coefficient of absorption or solubility. 

 Henry's law states that the amount of gas absorbed is pro- 

 portional to the pressure, and from it follows the law of 

 distribution, viz., that the ratio of the concentrations of the 

 gas within and without the liquid is a constant. In this 

 sense the coefficient of solubility is defined as the ratio of 

 these concentrations. 



In the case of the radioactive emanations it is, of course, 

 difficult to work without some gas acting as carrier of the 

 emanation, and the coefficient of solubility is defined as 

 follows : — Let a volume of liquid t?i be in contact with a 

 volume of gas r 2 , and let a quantity of emanation distribute 

 itself between them, so that after equilibrium is established 

 ei will be the emanation contained in the liquid, and e 2 that 



in the gas. Then - will be the concentration of emanation in 



e Vl 

 the liquid, and — the concentration in the gas. The ratio 



of these concentrations, viz. — — is the coefficient of 

 solubility. l ' 



By Henry's law this ratio, at any one temperature, should 

 be independent of the concentration of the emanation, and 

 of the nature and pressure of the containing gas ; it should 

 depend only on the nature of the absorbent. The ratio, 

 however, should decrease as the temperature rises. It is 

 known that Henry's law fails as the liquid approaches satu- 

 ration. Practically the law only holds for dilute solutions 

 in the case of gases which do not react chemically with the 

 absorbing liquid. These two conditions are fulfilled ideally 

 by radium emanation, and in consequence we should expect 



