544 SCIENCE PROGRESS 



in 1907 obtained the figure 8 per cent. ; in a later paper he states 

 that no a rays are produced, the mistake arising from the pre- 

 sence of /3 rays of small velocity. The question has not yet 

 been decided. Uranium X has a half-life period of twenty-two 

 days. In less than a year it has disintegrated almost completely. 

 Into what has it changed? 



Ever since Madame Curie succeeded in obtaining radium 

 from uranium minerals, and the theory of disintegration was 

 put forward, it has been considered highly probable that radium 

 is a descendant, in perhaps the third or fourth generation, of 

 uranium itself. Some experiments of Soddy in 1904 gave the 

 first proof of this statement. He took about two pounds of 

 uranium nitrate, dissolved it in water, and repeatedly added 

 barium solution, precipitating the barium as sulphate. In 

 this way the solution was practically freed from radium, 

 which is precipitated along with the barium sulphate. In 

 567 days the solution contained more than one hundred times 

 as much radium as it did immediately after this treatment. This 

 radium was identified by the decay rate of its emanation. The 

 actual amount of radium observed was only one-thousandth of 

 what it should be on the assumption that uranium X was the 

 parent of radium. Soddy postulated one or two intermediate 

 products. Boltwood criticised his method of procedure but after- 

 wards confirmed his results. In 1906 he suggested that the 

 intermediate product was actinium. Soddy and Mackenzie, and 

 also Rutherford, showed that this was impossible, pure uranium 

 nitrate neither giving rise to actinium nor its emanation. Ruther- 

 ford separated the actinium from solutions of commercial uranium 

 nitrate, and by passing ammonia and sulphuretted hydrogen 

 gases through the actinium solution, he effected the separation 

 of a new radioactive substance, which he considered to be the 

 actual intermediate product between uranium X and radium. 

 Boltwood confirmed this result. He found this new element 

 emits a rays (actinium is rayless) which are very easily absorbed, 

 and /3 rays of small penetrability. The activity is of the same 

 order as that of radium. He suggested the name Ionium. 

 Hahn has confirmed his conclusion by a different method. 



Radium was discovered by Madame Curie in 1898. Her 

 method of procedure has been indicated. Thoroughly examining 

 the different group precipitates in an analysis of pitchblende, 

 she found that the barium group precipitate was strongly active. 



