84 UNIVERSITY OF COLORADO STUDIES 



Time / 123456789 lo 20 30 180 



Measured Current 50.3 56.1 60.5 63.9 66.6 68.6 70.4 71.8 72-9 73.8 77.7 80.9 100 

 Calculated Current 50.3V55.9 60.3 63.6 66.4 68.7 70.4 71.7 72.9 73.8 78.3 80.8 ... 



The measured currents are the means of value obtained in ten separate 

 experiments, and, as a matter of fact, agree with the calculated values 

 to within | per cent during the first ten minutes and to within i per 

 cent during the following twenty minutes. 



In equation (2) i^ is the value of i when t=o, and in what follows 

 we assume that ?„ represents the saturation current due to the emana- 

 tion alone. /? is approximately equal to the ratio of the currents due 

 respectively to the induced activity and to the emanation when they 

 are in radio-active equilibrium, and ^/f^ is practically equal to the ratio 

 of the currents due, respectively, to the first and third of the successive 

 components of the induced radio-activity (in the theory of transforma- 

 tions.) 



The constants a, (i, ^ and [j- are functions of the dimensions of the 

 apparatus, although they vary little if large testing vessels are em- 

 ployed, such as was the case in the experiments described below. When 

 the current has reached its maximum value, about 42 per cent of it is 

 due to the emanation, 33 per cent to the first and 25 per cent to the 

 third of the components of the induced radio-activity. 



The quantity of emanation produced by a radium salt is propor- 

 tional to the weight of the salt and to the time. We define the unit 

 quantity of emanation to be that emitted during one second into a 

 large volume of air from a solution of small volume containing one 

 gram of radium bromide. If the time during which the emanation is 

 allowed to accumulate is not short, it is necessary to make a correction 

 for the amount of emanation transformed during that time. 



It is important to know the amount of ionization produced by the 

 unit quantity of emanation, for this datum may be used in quantitative 

 tests for radium. 



If the emanation is enclosed in a testing vessel a part of its radia- 

 tion is absorbed by the sides of the vessel. In order to determine the 

 effect produced by the sides, three cylindrical vessels of zinc were 

 constructed. In the axis of each cylinder an insulated zinc rod was 



