74 Mr. Henry Wilde on the 



titanium, as the oxide Si0 2 agrees with titanic acid Ti0 2 . 

 Now, if silicon 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 Yi^n) are tetragonal. 



Through the classical researches of Regnault the 

 specific heat of silicon was found to be O'l 76.* The 

 determination was made with specimens of the metalloid 

 of considerable 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 &2$. 



In discussing the cause of the anomalous atomic heat 

 of silicon, Regnault 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 

 Si20 5 ; it would then resemble that of nitric, phosphoric, and 

 arsenic acid. The atomic weight of silicon 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 that other simple bodies give. By assigning to 

 silicon a higher atomic weight, and a polybasic character 

 like that of phosphorus or nitrogen, Regnault remarked 

 that it is easy to explain the existence of the great number 

 of silicates which nature presents in well defined and 

 beautiful crystals, and to understand the existence of the 

 natural hydro-silicates. 



It will be seen from my table that the atomic weights of 

 nitrogen, silicon and iron, beside being whole numbers, are 

 exact multiples of H7 ; and in all the formulae proposed for 

 the constitution of silica, the atomic weight of silicon is a 



* Aniiales de Chemie et de Physique tome LXIII. pp. 24 — 31 (1861). 



