THE CHEMICAL ELEMENTS RAMSAY. 189 



atomic weight of lead is 207.1, and not 206.4; however, it is possible 

 that the atomic weight of radium is 227.1, and not 226.4. 



We have another method of approaching the same subject. It is 

 practically certain that the progenitor of radium is uranium, and that 

 the transformation of uranium into radium involves the loss of 3 

 alpha particles; that is, of 3 atoms of helium. The atomic weight 

 of helium may be taken as one of the most certain; it is 3.994, as 

 determined by Mr. Watson, in my laboratories. Three atoms would 

 therefore weigh 11.98, practically 12. There is, however, still some 

 uncertainty in the atomic weight of uranium; Richards and Merigold 

 make it 239.4; but the general mean, calculated by Clarke, is 239. 

 Subtracting 12 from these numbers, we have the values 227, and 

 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 3 atoms of helium, radium is produced, and, if 

 the change consists solely in the loss of the 3 atoms of helium, the 

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

 that /?-rays, or electrons, are also parted with during this 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 3 atoms of helium, and that of uranium, will give the 

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

 probable numbers available, viz, 239.4 for uranium, and 226.8 for 

 radium, and adding 12 to the latter, the weight of the escaping elec- 

 trons 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, accompa- 1 

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

 gestion 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 

 26 elements derived from uranium, thorium, and actinium, 10, which 

 are formed by the emission of electrons alone, may be regarded as 



