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THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Akt. XVII. — A Modification of the Periodic Table; by 

 Ingo W. D. Hackh. 



About fifty years ago Newland 1 recognized a certain 

 periodicity among the elements and compiled his well 

 known i i octaves. ' ' At that time chemical knowledge had 

 progressed so far, that Lothar Meyer 2 and MendeleefP 

 could express it in the form of the periodic system. But 

 it was still somewhat fragmentary, that is to say while 

 the periods were clearly recognized as such, there was 

 a certain discrepancy in connecting them. In other 

 words, there was a missing link, which was not found 

 until the discovery of the rare gases by Ramsay, Ray- 

 leigh, Travers and Cleve in 1894 and 1895. These ele- 

 ments seemed at first to have no place in the system and 

 aroused much controversy as to their position in the 

 periodic system. But in spite of the fact that some, e. g. 

 Dennstedt, 1 believed argon to be a kind of nitrogen=N 3 

 (like ozone = 3 ) they were placed either in a new group, 

 the zero group, or in the eighth group by Thomson, 5 

 Ramsay, 6 Crookes 7 and others. 



As Thomson has pointed out, the electropotential of 

 these rare gases may be regarded as ± or ± oo . ' Thus 

 they farm the connecting link between the periods, viz. 

 the halogens and the alkali metals, and we obtain a con- 

 tinuous line of elements when arranged with increasing- 

 atomic weights. 



But there was still some uncertainty as to the limits of 

 the periodic system (compare Losanitsch s ) which was not 



1 For references see the end of this paper. 



Am. Jour. Sci.— Fourth Series, Vol. XLVI, No. 273.— September, 1918. 



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