590 



Profs. B. B. Boltwood and E. Rutherford 



to dryness in a silica dish on a water-bath and the residue of 

 radium-barium chloride was heated gently to remove the 

 excess of hydrochloric acid and water. The dry salt was 

 then placed in a cylindrical platinum capsule which was 

 closed by a perforated cover. The capsule was next sealed 

 up in a tube of Jena " combustion'" glass (a, fig. 1). One 



Fig. 1. 



end of this tube was ground to fit into a tube of soft glass b 

 and the extremity of the tube a, extending into the joint 

 at 6, terminated in a slightly curved, narrow, closed, 

 capillary tube. An inward depression in the tube b near the 

 joint made it possible, by rotating the tube a in the joint b, 

 to break off the capillary extension of a and thus establish 

 communication between a and b when desired. This arrange- 

 ment was designed to facilitate the removal of the helium at 

 the end of the period of accumulation. The Jena glass tube 

 was completely exhausted of air through the tube c, which 

 was then sealed off. 



Determination of Radium in Salt. 



The amount of radium present in the salt contained in the 

 capsule was determined by the measurement of the y radi- 

 ation emitted after a period of over two months from the 

 time of sealing up the tube. Using a thick-walled, lead 

 electroscope, the 7 ray activity of the salt in the tube was 

 compared with the 7 ray activity of the 3*69 milligram 

 radium bromide standard of this Laboratory both directly 

 and by a comparison with a third specimen of radium salt 

 containing approximately 32 milligrams of radium bromide 

 calibrated in terms of the small standard. The comparisons 

 of the radium quantities were made at various distances and 

 under different conditions, and gave the amount of radium 

 in the salt used in the experiment as .191 milligrams (equi- 

 valent to 326 milligrams of radium bromide). 



