ORIGIN OF ELEMENTARY SUBSTANCES. 131 



and similar alternations in other natural groups have been 

 recognized in the arrangement of elements proposed by 

 Mr. Newlands"^ and Mendeleefff. 



Just as Cu=62, Ag=io8j and 57=154, alternate with 

 Rb = 85j Cs=i3i, and ^=177, in the series Hn; and Zn 

 = 64, Cd= 1 12_, and x= 160, alternate with Sr = 88, Ba= 

 136, and ^=184; so in the series H^^"} ^^ x=6q, Yt = 

 123, and Eb=i77, alternate with w = ()6, In=i50, and 

 Tl=204. Again, just as K, Rb, Cs, and ^=154, are 

 analogues of each other in the series Hn, so are 57 = 42, 

 a!=g6, In, and Tl, analogues of each other in the series 

 H3»i, and are in homologous positions with the alkaline, 

 and alkaline-earth metals in the series Hn, and H2n. The 

 specific gravities of analogous members of these two series, 

 except glucinum, which is anomalous, increase in the order 

 of their atomic weights, and so far as the specific gravities 

 of the members of the series H^n have been ascertained, 

 they follow the same order. Now, M. Lecoq de Boisbau- 

 dran has shown that the new metal which he has discovered, 

 and named gallium |, is, from its spectral reactions and 

 other properties, the analogue of indium and thallium. 

 The position of the new metal in the series H3re, should 

 therefore be either — =42, homologous with Ca, and K, 

 or — =96, homologous with Sr and Rb. In comparing 

 the alkaline metals of the series Hn, the specific gravity of 

 sodium (o'97), as will be seen, is greater than that of 

 potassium (o"86), although Na has a less atomic weight; 

 and the same inversion of specific gravities in relation to 

 atomic weights is observable in their homologues of posi- 

 tion Mg (sp. g. 174), and Ca (sp. g. I'sS), in the series 



* Chem. News, vol. xii. p. 83 ; vol. xiii. p. 113. 



t Die periodische Gesetzmafsigkeit clex* chemischen Elemeute. — Ann. Chem. 

 Pharm. Suppl. Band. viii. pp. 133-229 (1872); Pliil. Mag. 5th ser. vol. i. 



P- 543- 



X Oomptes Rendiis, tome l.wxi. pp. 403, 1000 (1865). 



k2 



