188 J. MORISON : ADDRESS 



distinct and successive stages. A body which has been exposed 

 to the radium emanation does not completely lose its activity 

 an hovy after it has been removed from the vicinity of the 

 radium, though the activity which remains is exceedingly small, 

 being after that time, according to Rutherford, less than one 

 millionth of that observed immediately after removal. This 

 small residual activity was first observed by Madame Curie. It 

 is at a minimum at first and continues to increase as time goes 

 on. The activity comprises both a and /3 rays, the latter being 

 present in a greater proportion than is observed in radium and 

 the active deposit of rapid change. The a rays reach a maximum 

 in about 240 days, and the /3 rays after about 50 days. 

 After this time the radiation appears to continue without marked 

 alteration for a lengthened period. Professor Rutherford's 

 investigations have shown that this residual activity is caused 

 by three more successive transformations of the radium product, 

 which he has termed collectively the active deposit of slow change. 

 The three stages have been called radium D, radium E, and 

 radium F. Radium D is produced by the transformation of 

 radiiun C. It emits no rays, is a comparatively stable body, and 

 has been calculated to have a period of about 40 years, but this 

 of course is only an approximative estimate. It is considered 

 by Rutherford to be identical with the so-called radio-lead, first 

 separated by Hofmann from pitch-blende residues. Radium D 

 is slowly transformed into radiiun E, which has a comparatively 

 short life, being half transformed in about six days ; radium E 

 emits only ft and 7 rays, and in its turn is changed into 

 radium F, which emits only a rays and has a period of 143 days. 

 There is good reason to think that radium F is identical with the 

 radio-tellm-ium of Marckwald and with the polonium which 

 was separated from pitch-blende by M. and Madame Curie. 

 Radium F, after emitting an a particle, is converted into the 

 final product, which, so far as we can tell, appears to be stable. 



All these different radium products are really to be looked 

 upon as totally distinct though temporary elements, with 

 different physical and chemical properties, and different atomic 

 constitutions. It has been calculated that the total period of 

 existence of a radium atom cannot on the average exceed a few 

 thousand years. Therefore, all the radium now existing on the 

 earth must have come into being within a comparatively recent 

 period, and will cease to exist as such at no extremely distant date. 

 So we appear to be drawn to the conclusion that radium is 

 constantly being formed, and is derived from the transformation 



