Friedel and Crafts on the Ethers of Silicic Acid. 157 
ment in their favor in the brilliant researches of Marignac on 
the isomorphism of fluosilicates, fluotitanates, and fluostannates.* 
en the progress of organic chemistry forced the chemists, 
after Gerhardt, to double the atomic weights of oxygen and car- 
bon, leaving that of hydrogen =1, which was nothing else than 
returning to the old relations of Berzelius and Dumas, the ques- 
tion arose, whether silica ought to be written 
SiO (Si=14, 0=16) or SiO, (Si=28). 
Gerhardt answered the question implicitly in favor of the 
latter formula, when he wrote silicic ethert 4(SiO), 4(C «HO, 
and without doubt his only motive for retaining the atomic 
weight of Ebelmen (Si=7) was the same, which prevented him 
from changing those of carbon and oxygen in his work on or- 
ganic chemistry. In order to have been consistent with his own 
theoretic views, he need only have gone back to the formula of 
Gaudin. Odlingt has done this, and writes silica Si®,, and 
considers SiH, ®, as the normal hydrate of silicic acid, to which 
the ethers correspond. 
Odling, as well as Gerhardt and Gaudin before him, have de- 
duced these formule: from the consideration of the vapor-density 
of the chlorid of silicium and of silicic ether. This must be 
regarded as an important argument in their favor, and to deny 
its value it would be necessary to forget the admirable order in- 
troduced by Gerhardt in the classification of organic compounds 
in the place of the confusion which reigned before the vapor- 
density was employed as a criterion to determine the molecular 
Weight of compounds. It would be necessary, also, to ignore 
the important results obtained by various chemists, particularly 
by Wurtz§ and Cannizzaro,|| in the fixation of molecular weights 
according to the same law. 
evertheless we must remember that the ideas of Avogadro 
and Ampére are nothing more than a physical hypothesis; and 
although this hypothesis has been fruitful in accurate conclu- 
Slons, even from the stand-point of a chemist, it must yield 
before purely chemical considerations in the determination of 
a " 
hope of obtaining results which would enable us to resolve, on 
mi 
firming by our research the conclusions drawn from the law of 
Ampére, : 
* Ann. des Mines, [5], xv, 221. + Traité de Chimie Organique, ii, 363. 
Lee pbical Magazine, xviii, 368 ae 
e i imi 5 
Sunto di un Corso di Filosofia Chimica; Pisa, 1858. 
Am. Jour. Sc1.—Szconp Serres, Vou. XLII, No. 128.—Manrce, 1867. 
21 
