Radioactivity of the Leinster Granite. 



109 



is first closed and C, opened, so that the air is drawn entirely 

 through the measuring flask. The end of the tube T x is 



Fifif. 3. 



SKki 



then dipped below the surface of the water in the vessel V 

 placed in position for the purpose, and the time of filling to 

 the fixed mark noted. The friction opposing the entry of 

 the water into the measuring flask is compensated for by 

 lengthening the inner limb of the tube at M', so that this 

 takes the character of a siphon and a slight static head is 

 given to the entering water. The additional length — about 

 3 cms. — was found by trial and error, the exact length being 

 hit when no motion of the oil in the gauge was observed to 

 attend the flow of water into the flask. 



The air flow was regulated by means of the stopcock X, 

 which was then allowed to remain untouched throughout the 

 remainder of the work. The standard height of the oil in 

 the gauge was adhered to as far as possible throughout the 

 successive experiments, by regulation of the vacuum-pump. 

 The stopcock C is of course allowed to remain permanently 

 open, and G 1 closed until it is thought necessary to again test 

 the velocity of influx. 



The height of the thoria solution in the flask is marked, 

 and is as far as possible maintained in successive estimations. 

 Flasks of various sizes may thus be used, and standardized 

 to a particular velocity of air-current. It was found possible 

 to maintain a violent ebullition. The current of air entering 

 the electroscope from the boiling flask is first dried by passage 

 through the tube D, containing coarsely granulated calcium 

 chloride, and finally through the tube U, filled with phos- 

 phorus pentoxide. 



An asbestos card A was used to prevent the admission of 

 gases from the flame along with the air-current, A small 

 piece of the bulb of the electroscope was remov 



ea ana 



