213 
oxides of members of the series H4 n), are tetragonal ; conse- 
quently, silicium does not belong to the series H 4m. 
By assigning to silicium the atomic weight 35, it forms 
with nitrogen and iron a triad similar to the first three 
members of Hn, H2 n, H3 n, H 5n. The position of Si = 35 
as the second member of the series H7 n, 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 0176* The determination 
was made with specimens of the metal of considerable size, 
and in a state of compactness and purity, to receive a polish 
which formed a perfect mirror. The above number multi- 
plied 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, Begnault 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 2 0 5 ; 
it would then resemble that of nitric, phosphoric, and 
arsenic acids. The atomic weight of silicium would then be 
35, and the product of this number and the specific heat 
wouldbenearly 6*25, which agrees with the analogous products 
which other simple bodies give. By assigning to silicium 
a higher atomic weight and a polybasic character like that 
of phosphorus or nitrogen, Begnault remarked that it is 
easy to explain the existence of the great number of sili- 
cates which nature presents in well defined and beautiful 
crystals, and to understand the existence of the natural 
hydro-silicates. 
Whichever view chemists may ultimately adopt in regard 
to the constitution of silicic acid, or whether its atomic 
* Annales de Chimie et de Physique, tome lxiii., 24-31, 1861. 
