ON THE IONIZATION DUE TO THE EMANATION OF RADIUM 85 



fastened to serve as an electrode. The largest cylinder contained 

 51 liters of air and the smallest about one-half a liter. The length of 

 each cylinder was about twice its diameter. The saturation currents 

 in these vessels were measured at intervals after the introduction of 

 a known quantity of emanation, and from these data the initial value 

 of the current was calculated by means of equation (2). These initial 

 currents are quite accurately represented by the equation 



I=Io-kl (3) 



5 being the surface of the vessel, V its volume and /„ and k constants. 

 If each vessel contains unit quantity of emanation, the value of k is 

 .326 and that of 7o .63 in electrostatic units and at 18" C. and 76 cm. 

 pressure. 



Equation (3) may be interpreted as follows: We may assume that 

 the radiation absorbed by the sides and the secondary radiation pro- 

 duced at the metal surface are proportional to the area of the surface 

 and to the quantity of emanation contained in a cubic centimeter of 

 air. If each vessel contains the same total quantity of emanation, the 

 quantity per cubic centimeter is inversely proportional to the total volume. 

 The effect produced by the sides is therefore proportional to the ratio 

 of S to V. The quantity /<, is the saturation current that would be 

 produced by the unit quantity of emanation, if all its rays were 

 absorbed in air. The constant k is positive, which shows that the 

 absorbing effect of the sides is greater than the effect caused by any 

 secondary radiation that may be produced. 



In obtaining the above values of /„ and k the emanation evolved 

 during two hours by a solution of .0001096 gram of radium bromide, 

 i. e., about .79 of a unit, was used. The volume of the solution was 

 one cubic centimeter and that of the reservoir of glass that contained 

 it about thirty cubic centimeters. In order to establish a permanent 

 state the precaution was taken of drawing air several times through 

 the reservoir at intervals of two hours before collecting the emanation 

 for use in the experiments. Two other solutions also have been used 

 containing respectively .000110 gram and .0000127 gram of radium 

 bromide dissolved in five cubic centimeters of water. The correspond- 



