596 Profs. B. B. Boltwood and E. Rutherford on 



emanation escaped from the solid salt and diffused into the 

 upper portion of the tube. A considerable proportion of the 

 a particles resulting from the disintegration of such free eman- 

 ation might be expected to embed themselves in the walls 

 of the tube and introduce an error which could not easily be 

 avoided. Measurements of the 7 radiation from the upper 

 portion of the tube when the lower portion containing the 

 radium salt was screened by a thick lead block, showed that 

 the amount of emanation in the upper part of the tube was 

 too small to be detected, although as little as 1 per cent, of 

 the total could have been easily observed. It was therefore 

 apparent that the escape of the emanation from the solid 

 salt did not need to be taken into consideration. Alter the 

 radium salt had been heated, a further series of measure- 

 ments of the 7 radiation was carried out, which indicated 

 that the emanation had been completely separated from the 

 salt by the heating process. It was therefore reasonable to 

 presume that the helium also was quite completely removed 

 at the same time. 



Helium from Radium Salt. 

 (Second Determination.) 



In order to leave no doubt as to the influence of the 

 hydrogen present in the first experiment, and to avoid all 

 possibility of incompleteness in the removal of the helium 

 from the salt, a second determination of helium was made 

 under distinctly different conditions. The tube T containing 

 copper oxide was introduced into the apparatus, and it was 

 found by experiment that the last traces of hydrogen could 

 be removed by passing a mixture of hydrogen with an excess 

 of oxygen through this copper-oxide plug heated to a low 

 red heat. 



The radium salt was sealed up for a further period of 

 132 days. At the end of this time the gases, consisting 

 chiefly of oxygen which had been introduced before sealing 

 up the salt, were pumped out and collected. The radium 

 salt was then removed from the glass tube in which it had 

 been sealed, the perforated cover was taken off the platinum 

 capsule, and the capsule was sealed into another glass tube 

 (fig- 3). 



The radium capsule was placed in the bottom of the cylin- 

 drical tube (fig. 3), the lower portion of this tube was 

 wrapped with wet paper to prevent any heat reaching the 



