548 



SCIENCE PROGRESS 



Hahn, in 1907, succeeded in showing that actinium is rayless, 

 its activity being due to its first product radio-actinium ; this 

 gives a rays only, corresponding to radiothorium. According 

 to Giesel it resembles the alkaline earth metals, and can be 

 precipitated from actinium solution by means of finely divided 

 sulphur. It disintegrates into actinium X, independently dis- 

 covered in 1905 by Giesel and Godlewski ; the separation is 

 similar to that employed for thorium X. The emanation was 

 observed by both Debierne and Giesel ; Godlewski proved that 

 actinium X was its immediate parent. Debierne has recently 

 noted the production of helium from this emanation ; Giesel has 

 confirmed the statement. The analysis of the active deposit 

 from the emanation is in great part the work of Miss Brooks. 

 Her work led to the recognition of actinium A and B ; Meyer 

 and Schweidler consider that C and D also exist. 



So far we have no clue to the atomic weight of actinium. 

 But it corresponds to lanthanum ; in that case it either comes 

 between radium and thorium, with an atomic weight of about 

 230, or has a greater weight than uranium. Actinium emanation 

 most probably belongs to the argon series, in the periodic 

 system, when it follows that radio-actinium corresponds to 

 radium (it resembles the alkaline earth metals) and actinium X 

 occupies the space below gold. With similar treatment of the 

 thorium products we can postulate some such arrangement as 

 the following for the higher members of the periodic system ; 

 it accepts the simplest hypothesis of disintegration — that it is 

 accompanied by loss of mass. 



