THE CHEMICAL PROBLEMS OF TO-DAY. 369 



and the structure of this work. What these men created has since 

 become generally known ; they showed that the properties of the elements 

 are functions of their atomie iceights. Mendelejeff taught us to predict 

 the existence and the properties of chemical elements as yet unknown 

 with a certainty that reminds us of Le Verrier's prediction of the dis- 

 covery of the planet Neptune. We can say with confidence that even 

 to-day numerous elements, the qualities of which, as well as the place 

 which they will occupy in the system, can be minutely foretold, wait 

 merely to be discovered. 



The natural S3 stem has imposed upon us a problem of the greatest 

 significance in the new determination of the atomic weights, the numer- 

 ical values of which are now of increased interest. But numerous other 

 problems are presented by the new system of the elements. Above all 

 we are at a loss to discern the cause of the inner nexus of the elements 

 as the system offers it. Also by diligent work the less studied elements 

 must be properly brought within the system. Fortunate circumstances 

 may allow us to discover the numerous elements indicated by the peri- 

 odic law. Here let us note a peculiar coincidence. We know to-day 

 about seventy elements, but Mendelejeff's table indicates so far — two 

 small periods of seven elements each, and five large ones of seventeen 

 elements, respectively. To these must be added hydrogen, forming a 

 " group" in itself. 



By addition of these figures, (2 x 7) -f (5 x 17) + 1, we obtain exactly 

 the number 100. 



It is true that no one can say whether the missing elements will 

 really be discovered, or if furtlier new periods might not be indicated 

 by which this number 100 would be exceeded. But, as far as positive 

 data are at hand, they indicate exactly the number mentioned and 

 nothing points beyond it, — an odd coincidence which seems to ally 

 the number of the existing elements with the number of our fingers. 



The discovery of the system of the elements leads us back to the 

 question whether the chemical elements are separate worlds in them- 

 selves or whether they represent different forms or conditions under 

 which one ultimate substance exists, a question that has occupied the 

 philosophical mind since very early times. The sam3 question was 

 raised anew by the discovery of spectral analysis. Whosoever regards 

 the numerous lines of the spectrum of a metal will hardly be convinced 

 that the metal from which they emanate should be an eternally un- 

 decomposable element. In a similar manner the compound nature of 

 the elements is indicated by comparison of the regularities in numbers 

 of the atomic weights with the homologous series of organic chemistry. 



In the pursuit of this question, which, since Proat's hypothesis and 

 the surprises offered by Stas's determinations of atomic weights, has not 

 been allowed to rest, positive results are not to be found. The decom- 

 position of substances called elements into simpler ones has not been 

 accomplished. 



H. Mis. 129 24 



