600 Profs. B. B. Boltwood and E. Hutherford 



on 



By the courtesy o£ Sir James Dewar we were enabled to 

 compare the amount o£ radium employed in his experiments 

 with our working standard. It was found that the quantity 

 of radium used by Sir James Dewar, which was taken as 

 70 milligrams of pure radium chloride, was on our standard 

 equivalent to 12 milligrams of RaCl 2 . Expressed in terms 

 of our standard, the rate of production of helium observed 

 by Dewar comes out to be 164 instead of 169 millimetres 

 per year. This is somewhat higher than our value, but is in 

 substantial agreement with it. 



The Production of Helium by Radium Emanation. 

 A determination was also made of the amount of helium 

 produced by the disintegration of a known quantity of 

 radium emanation. The radium emanation was obtained 

 from a solution of radium salt, and was puiified and separated 

 from other gases by condensation at the temperature of 

 liquid air. A soft glass tube was prepared, about 10 milli- 

 metres inside diameter and about 8 centimetres in length. 

 At one end of this tube was a ground joint with a capillary 

 termination similar to that on the tube a (fig. 1). This 

 ground joint fitted into another tube similar to b (fig. 1). 

 The glass tube was filled about half full of melted sulphur, 

 was completely pumped out and the sulphur allowed to cool. 

 The purified radium emanation was introduced into this tube 

 and the tube was sealed by fusion of the glass. The tube 

 was warmed until the sulphur melted. It was then allowed 

 to cool and was tipped and turned in the meantime so that 

 a continuous layer of solid sulphur about three millimetres 

 thick w r as formed over the inner surface of the glass. The 

 object of the sulphur was to provide an inner coating in which 

 the a particles expelled by the emanation and active deposit 

 would be embedded and from which the helium could be 

 easily displaced when the sulphur was melted. About liji 

 hours after the emanation had been introduced into the tube, 

 the 7 radiation from the tube was measured and compared with 

 that emitted by the radium standard. The results indicated 

 that the amount of emanation in the tube at the start was 

 equivalent to the quantity in equilibrium with 126 milligrams 

 of radium. 



Twenty-one days after the radium emanation had been 

 introduced, the tube was warmed until the sulphur had 

 melted and the capillary at the end of the tube was clear. 

 The tube was then attached by means of the ground joint 

 to the measuring apparatus, the apparatus was completely 

 evacuated down to the joint, the capillary tube w r as broken 



