THE TRANSFORMATION OF ELEMENTS 225 



Giesel performed somewhat similar experiments, and also 

 confirmed the production of helium. 



In view of these numerous experiments by different workers, 

 all leading to the same result, the change of radium through its 

 emanation into helium must be regarded as finally proved. It is 

 of interest to see what other radioactive substances produce 

 helium. 



Debierne in 1905 repeated Ramsay and Soddy's work with 

 about 10 milligrams of radium bromide. His methods were 

 very similar, and he obtained the same results in numerous 

 experiments carried out during a period of six months. He 

 then substituted very active actinium salts for the radium 

 bromide. A solution of actinium chloride disengaged hydrogen 

 and oxygen in quantity comparable as regards activity with that 

 from a radium salt solution. Treating the gases in the usual 

 way, he succeeded in identifying the helium spectrum visually 

 and photographically. After specially purifying his solution 

 from radium, he still obtained the same results ; helium was 

 also observed in the gas produced by heating some dry actinium 

 fluoride. Debierne states that the quantity of helium formed 

 is in all cases comparable with that derived from radium of the 

 same degree of activity. He checked his results by carrying out 

 blank experiments with other gases, especially electrolytic gas ; 

 helium was never observed. 



In 1907, Giesel, using the methods he had employed for 

 radium salts with a strongly active actinium preparation, 

 succeeded in identifying the D 3 line of helium. 



Ramsay has obtained some indications of the formation of 

 helium from thorium solutions, but this cannot yet be regarded 

 as proved. In this connection Strutt's work on thorium 

 minerals, which will be dealt with in the third section, is of 

 great importance. 



Greinacher and Kernbaum have carried out observations 

 during eleven months with polonium (radium F) preparations 

 enclosed in evacuated spectrum tubes of small capacity. No 

 trace of helium was observed. 



Hofmann and Wolfl state that when radio-lead, or radium 

 D sulphate is placed in a completely exhausted capillary tube, 

 after several months the yellow, green, and blue helium lines 

 become visible, although all attempts with radium E and F 

 have given negative results. 



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