464 



Determination of Capacity. — In the same equations if c is known, that 

 is, if c is a cylindrical condenser, then C can be obtained. Note that C is 

 the capacity of the "leaf" system plus the charging system. Knowing the 

 sum, the capacity of the "leaf" can be had by getting the ratio of the two 

 by an operation similar to the above. 



Removing the Emanation Gas from the Solution. — The emanation can be 

 removed from a solution by the boiling method. The solution is boiled, 

 driving off the dissolved gases with the steam. The steam is condensed and 

 the gases are trapped in suitable glass tubes over mercury. The ionization 

 chamber is then evacuated and the emanation is sucked into the electroscope. 

 The entire amount of emanation is placed in the chamber by washing the 



glass tube with air until the pressure of the ionization chamber of the electro- 

 scope is at normal pressure. This method is accurate but requires elaborate 

 apparatus which can be used only in the laboratory. 



Where the greatest accuracy is not wished Schmidt's shaking method 

 can be used. (Phys. Zeit., Vol. 6, p. 561, 1905.) This method admits of 

 determinations being made at the spring with apparatus which easily can 

 be carried by the observer. The shaking method consists of taking a known 

 volume of water and shaking it vigorously for two minutes in a closed vessel 

 with a known volume of air. Then the emanation which was originally dis- 

 solved in the water is mixed in the air and water in a known proportion, de- 

 pending upon the temperature of the water. Then this air is pumped through 



