14 PRESIDENT S ADDRESS. 



227.4 for the atomic weight of radium. It is as yet impossible to draw 

 any certain conclusion. 



The importance of the work which will enable a definite and sure 

 conclusion to be drawn is this: For the first time, we have accurate 

 knowledge as to the descent of some of the elements. Supposing the 

 atomic weight of uranium to be certainly 239, it may be taken as proved 

 that in losing three atoms of helium, radium is produced, and, if the 

 change consists solely in the loss of the three atoms of helium, the 

 atomic weight of radium must necessarily be 227. But it is known 

 that i8-rays, or electrons, are also parted with during tins change; and 

 electrons have weight.- How many electrons are lost is unknown; 

 therefore, although the weight of an electron is approximately known, 

 it is impossible to say how much to allow for in estimating the atomic 

 weight of radium. But it is possible to solve this question indirectly, 

 by determining exactly the atomic weights of radium and of uranium ; 

 the difference between the atomic weight of radium plus 12, i.e., plus 

 the weight of three atoms of helium, and that of uranium, will give the 

 weight of the number of electrons which escape. Taking the most pro- 

 bable numbers available, viz., 239.4 for uranium, and 226.8 for radium, 

 and adding 12 to the latter, the weight of the escaping electrons would 

 be 0.6. 



The correct solution of this problem would in great measure clear 

 up the mystery of the irregularities in the periodic table, and would 

 account for the deviations from Prout's Law, that the atomic weights 

 are multiples of some common factor or factors. I also venture to 

 suggest that it would throw light on allotropy, which in some cases at 

 least may very well be due to the loss or gain of electrons, accompanied 

 by a positive or negative heat-change. Incidentally, this suggestion 

 would afford places in the periodic table for the somewhat overwhelming 

 number of pseudo-elements the existence of which is made practically 

 certain by the disintegration hypothesis. Of the twenty-six elements 

 derived from uranium, thorium, and actinium, ten, which are formed 

 by the emission of electrons alone, may be regarded as allotropes or 

 pseudo-elements; this leaves sixteen, for which sixteen or seventeen 

 gaps would appear to be available in the periodic table, provided the 

 reasonable supposition be made that a second change in the length of the 

 periods has taken place. It is above all things certain that it would 

 he a fatal mistake to regard the existence of v such elements as irrecon- 

 cilable with the periodic arrangement, which has rendered to systematic 

 chemistry such signal service in the past. 



Attention has repeatedly been drawn to the enormous quantity of 

 energy stored up in radium and its descendants. That in its emanation, 

 niton, is such that if what it parts with as heat during its disintegration 



