THE PROGRESS OF CHEMISTRY DURING THE LAST 

 QUARTER OF A CENTURY 



William McPherson 



To give any comprehensive account of the growth of 

 chemical science during the last quarter of a century within the 

 limits of the time assigned me is entirely out of the question. 

 It has seemed to me appropriate, therefore, that under the con- 

 ditions imposed I should not attempt to follow the many avenues 

 along which the science has progressed but rather select for dis- 

 cussion a few topics which are of primary importance, fully 

 realizing the inadequacy of this method to give any connected 

 or systematic' treatment of the subject as a whole. 



The Constitution of Matter. — Radioactiznty. If not the 

 most important at least the most sensational of the discoveries 

 made during the last quarter of ?. century lie within that great 

 field of science largely developed in recent years and known as 

 "Physical Chemistry". The development of this line of investi- 

 gation has effaced all traces of a boundary line between Physics 

 and Chemistry. It follows, therefore, that both the physicist 

 and the chemist are equally interested in many of the facts that 

 have been discovered as well as in the theories that have been 

 developed in this field of investigation. 



Included in this field of inquiry is the question of the con- 

 stitution of matter — a question not only of fundamental im- 

 portance but one of universal interest. Perhaps the cjuery most 

 often put to the chemist at the present time by workers in other 

 fields of science is "What changes have the results of modern 

 investigation compelled us to make in our ideas concerning the 

 Daltonian atom?" These changes have been largely the out- 

 growth of the discoveries included in that newly developed region 

 known as "radioactivity". 



(370) 



