ORIGIN OF ELEMENTARY SUBSTANCES. 139 



with titanic acid TiO^. Now, if siliciura were the true 

 analogue of titanium, the oxides of these elements should 

 be isomorphous, whereas the crystalline form of quartz is 

 hexagonal, while rutile, anatase, brookite, zirconia and 

 tinstone (similar oxides of members of the series H4ra), 

 are tetragonal ; consequently, silicium does not belong to 

 the series H4W. 



By assigning to silicium the atomic weight 35, it forms 

 with nitrogen and iron a triad similar to the first three 

 members of Hw, H2w, Ji'^n, H^n. The position of Si= 35, 

 as the second member of the series Hyn, not only throws 

 new light on the disputed atomicity of this element, but 

 also explains the anomalous atomic heat which has been 

 assigned to it. 



Through the classical researches of Regnault the specific 

 heat of silicium was found to be O'lyb^. The determi- 

 nation was made with specimens of the metal of consi- 

 derable size, and in a state of compactness and purity to 

 receive a polish which formed a perfect mirror. The 

 above number multiplied by 28, the highest atomic weight 

 assigned to Si, gives the product 4*93, while the law of 

 Dulong and Petit requires the value 6"25. 



In discussing the cause of the anomalous atomic heat 

 of silicium, Eegnault pointed out that in order that it 

 might enter into the law of the specific heat of other 

 elements, it would be necessary to write the formula of 

 silicic acid Si^O^ ; it would then resemble that of nitric, 

 phosphoric, and arsenic acid. The atomic weight of 

 silicium would then be 35, and the product of this number 

 and the specific heat would be nearly 6" 25, which agrees 

 with the analogous products which other simple bodies 

 give. By assigning to silicium a higher atomic weight 



* ' Annales cle Chimic et cTe Physique,' tome Ixiii. pp. 24-31 (1861). 



