IX, A, 1 Wright and Smith: Radium Emanation 55 



The electroscope. — The testing apparatus used was a Spindler 

 and Hoyer aluminum-leaf electroscope with an ionization cham- 

 ber attached. The aluminum leaf in these electroscopes has a 

 fine quartz fiber attached to one edge which makes it possible 

 to obtain very accurate readings with the aid of the reading 

 microscope. The ionization chamber was 38 centimeters high 

 and 7.8 centimeters in diameter, giving a volume of 1,820 cubic 

 centimeters, and was provided with both an inlet and an outlet 

 tube so that the chamber could easily be exhausted and refilled 

 with the air containing the emanation. The electroscope with 

 the attached ionization chamber had an electrical capacity of 

 8.7 e. s. units, the range of the scale of 100 divisions being 

 approximately from 368 to 302 volts. Therefore, the voltage 

 on the leaf was suflficient to produce saturation currents in a 

 chamber of the size used. The natural leak was almost abso- 

 lutely constant at 0.022 division per minute. 



The ionization chamber was permanently attached through 

 one opening to a mercury manometer and through the other 

 opening to a Geryk oil pump and to 2 aspirator bottles, all 

 connected in parallel, so that any one could be put in direct 

 connection with the chamber. Between the pump, aspirators, 

 and chamber were placed two tubes, one containing calcium 

 chloride and the other phosphorus pentoxide, permitting all the 

 air passing into the chamber to be thoroughly dried. 



Method of taking readings. — For comparative measurements 

 it is essential that a definite course of procedure be adopted 

 and adhered to throughout the entire investigation. After a 

 few preliminary experiments, we adopted the following method 

 of taking measurements on the emanation collected. The air- 

 emanation tubes were connected in parallel to one aspirator and 

 heated to a bright red heat, the temperature for the different 

 determinations being practically the same, equal currents being 

 always passed through the electrical furnace for the same length 

 of time. The tubes were then rapidly but thoroughly flushed 

 until the aspirator was filled down to a definite mark. The air 

 containing the emanation was then passed into the ionization 

 chamber through the calcium chloride and phosphorus pentoxide 

 tubes, care being taken finally to flush the tubes with air so 

 that all the emanation would be carried into the ionization 

 chamber. The chamber had been made with the necessary 

 volume to accomodate all the gas driven off from 140 grams 

 of charcoal with a liberal margin for flushing. The electroscope 

 readings were always taken over practically the same region 

 of the scale, the reading being started as nearly as possible 



