464 
Determination of Capacity—In the same equations if ¢ is known, that 
is, if ¢ 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 
