PAPERS PRESENTED AT GENERAL SESSIONS 43 



THE ATOM OF THE CHEMIST. 



W. H. EODEBUSH, UxmiESITY OF ILLINOIS. 



The chemist has believed in the existence of the atom 

 for more than one hnndred years. The fact that the 

 different elements combine to form compounds in certain 

 definite proportions by weight can be most easily ex- 

 plained by assuming each element to be made np of dis- 

 crete particles, all of the same mass in a given element 

 but of different masses for different elements. But 

 while this explanation of the laws of chemical combina- 

 tion was the only satisfactory one that could be offered, 

 nevertheless, until a few years ago, not a single direct 

 proof of the existence of atoms had been obtained. As 

 a matter of fact, about twenty years ago a school of 

 chemists arose, headed by Ostwald, who doubted the 

 existence of atoms. They said the atomic theory was 

 an attempt to explain nature by a crude mechanical 

 analogy, and that matter was not the coarse grained sort 

 of affair that these literal minded people made it out 

 to be. They said that the people who believed in atoms 

 did so because they had a psychological intuition which 

 they got from observing dust particles. One can divide 

 a dust particle into finer and finer particles, but the 

 imagination balks at continuing this process of di^T.sion 

 indefinitely. So these literal minded people said that 

 one must ultimately arrive at a particle of such fineness 

 that it could not be further divided and hence is the in- 

 divisible atom. Likewise, said the antagonists of the 

 atomic theory, these people think of a liquid like water 

 not as a fluid but as a discontinuous medium made up 

 of hard, solid molecules which were freer to slide over 

 one another, for the reason that the human mind grasps 

 the idea of particles of unchanging size and shape much 

 more readily than it does that of fluid matter. And so 

 a gas, instead of being a continuous medium able to ex- 

 pand indefinitely, must be made up of hard elastic par- 

 •ticles flj'ing about in space. 



On the other hand, these literal minded chemists, and 

 they comprised a great majority, went ahead serenely 



