GENERAL AND PHYSICAL CHEMISTRY NERNST. 253 



charge five electroscopes, sufficient to enable him to study (with a 

 sufficient experimental accuracy) the most important radio-active 

 properties of each element. 



The extreme sensitiveness of this reagent for radio-active substances 

 has been the only factor which has permitted the discovery of several 

 radio-active elements which had heretofore escaped notice because of 

 their very small quantity or because of the brief period of their exist- 

 ence (in the sense of the hypothesis of atomic decomposition). 



It is often easy to write history, but it is always more difficult to 

 learn anything from the history after it is written. If I dare make 

 a modest attempt in this direction, I should say perhaj)S that the 

 chemist with such a mass of material to work on is destined in the 

 future to prepare new compounds and to study the reactions of those 

 already known as in the past, but that the methods of experimental 

 and theoretical physics will be more and more called into requisition 

 to supplement purely chemical research. 



