2 Mr. J. Satterly on the Amount of Radium 



by screw-clips on the indiarubber connecting tube. The 

 air-stream was continued tor a certain time, and from a 

 knowledge of the time of exposure and the strength of the 

 air-stream the volume of air drawn through could he 

 calculated. At the end of the exposure the tube was taken, 

 placed on a gas-furnace, and connected up to an aspirator 

 formed of two bottles connected by rubber tubing, one of 

 which was filled with water. The tube was heated to redness 

 and the aspirator then started. The emanation absorbed by 

 the charcoal during the " exposure M to the air-stream was 

 driven off by the heat of the furnace, and drawn by the 

 current of air into the aspirator. Two aspirators were used 

 to make sure that all the emanation was withdrawn from the 

 charcoal. In practice, it was found that the air in the first 

 aspirator so collected contained nearly all the emanation 

 absorbed ; the air in the second one usually contained just 

 a little or none at all. 



The amount of emanation in the air in the aspirators was 

 measured by the increased electrical conductivity it imparted 

 to the air. To do this it was necessary to pass the air into 

 a testing vessel. 



The testing vessel consisted of a brass cylinder 40 cms. 

 long and 10 cms. wide. Down through the centre of the 

 vessel there passed an insulated brass wire whose upper 

 extremity was connected to the insulated quadrants of a 

 Dolezalek electrometer. The needle of the electrometer was 

 kept at +80 volts, and the sensitiveness was such that 

 1 volt of the insulated quadrants gave a deflexion of about 

 950 millims. on a scale 2 metres distant. The testing vessel 

 was kept at —320 volts. This ensured saturation for all the 

 leaks I had occasion to measure. The normal air-leak was 

 from *9 to 1*2 cms. per minute, it being practically constant 

 on any one day but varying from day to day. There were 

 two openings into the testing vessel : the upper one led to a 

 mercury manometer, and the lower one served as a means for 

 exhausting the vessel and refilling it with the air whose con- 

 ductivity was to be measured. 



The normal air-leak having been taken, the vessel was 

 exhausted, and the air collected in the second aspirator was 

 passed into the vessel*. The leak was again taken. The 

 difference between this leak and the normal air-leak is a 

 measure of the emanation in the air collected in the second 

 aspirator. The testing vessel was again exhausted and the 



* The volume of air collected in the aspirator was just a little less 

 than the volume of the testing vessel. Thus all the air in the aspirator 

 could be passed into the testing vessel. 



