[JOHNSTONE] EMANATING POWER OF MINERALS 105 



India. It had a uranium content of 67.5 .per cent, and possessed an 

 emanating power of 8.4 per cent, at 18°C. 



In order to collect the emanation which was evolved from a 

 definite weight of the powdered mineral under the particular condi- 

 tions of experiment the following method was used: One end of a 

 piece of glass tubing (bore 0. 75 cm. and length 15 cm.) was tapered to 

 a point and sealed ofif in a flame. A small plug of cotton wadding 

 was then stuffed through the tube into the sealed-off end. A weighed 

 amount of mineral (2 gms.) was placed in the tube and on top of this 

 another plug of wadding. The remaining end of the tube was then 

 tapered out and sealed. To maintain the tubes at definite tempera- 

 tures for any given time, they were placed in a self-regulating, gas 

 thermostat in which temperatures twenty degrees above room tem- 

 peratures were obtainable. For temperatures higher than this an 

 electrically heated oven was utilized. To transfer the collected 

 emanation from the tube to the electroscope the latter was first 

 exhausted by a water pump. Both stopcocks were then closed. The 

 emanation tube was attached to the upper exit tube of the electroscope 

 by a short piece of thick-walled rubber tubing. The stopcock was 

 opened and closed again, then the tip of the emanation tube was 

 broken off inside the rubber tubing. The stopcock was opened 

 slowly and again closed. The other tip of the emanation tube was 

 then broken off, the stopcock opened gradually and air was drawn into 

 the electroscope through the emanation tube for about five minutes 

 when the stopcock was closed. The pressure of the air within the 

 electroscope was still considerably below that of the outside air, and 

 thus, if there were any tendency to leakage, it would be from the 

 outside to the inside. At the end of three hours the inside pressure 

 was raised to that of the outside air by allowing air to enter the 

 electroscope from the exterior and then closing the stopcocks. The 

 time taken for the gold-leaf to pass over a definite interval of the scale 

 was measured with a stopwatch. Both stopcocks were finally opened 

 and air was drawn through the electroscope for a half hour. In this 

 way the emanation was completely removed from the electroscope, 

 and when the active deposit had decayed and the natural leak was 

 determined, the instrument was ready for a new series of measure- 

 ments. 



A number of preliminary experiments were made which demon- 

 strated that by increasing the humidity of the air in the sealed tubes 

 the emanating power of the mineral was increased. In order to 

 eliminate any variations due to changes in the content of moisture 



