TH E ATOM 89 



oughly established than the fact that, as first 

 taught by Dalton in 1808, the atom is the unit in 

 chemical changes. The overwhelming proof consists 

 in the demonstration whereby in numerous instances 

 the quantitative analysis of a substance has been 

 followed by the synthetic production of that sub- 

 stance. In the laboratory synthesis of the substance, 

 the atoms may be gathered from various sources and, 

 combined according to the ratios indicated by the 

 analysis, will produce and approximately duplicate 

 the substance. As is well known, there are now many 

 synthetic substances, some of which are of great 

 industrial importance. And the work of chemical 

 analysis and synthesis is going steadily on, ac- 

 cording to no haphazard methods. 



The valency properties of the atoms are experience 

 facts. Long before the intricacies of atomic structure 

 were even suspected, the "loves and hates" of the 

 atoms were known, and the elements were grouped 

 according to their chemical combining power, or 

 valency, as determined by experimental data. Chem- 

 istry reckons with principal valencies, with residual 

 valency, and with free valency, besides recognizing 

 nulvalent atoms. 



According to J. D. Main Smith, "Professors Thorpe 

 and Morgan both agree that the time is not yet ripe 

 for the application of general electronic theories to or- 



