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XXY. Researches on Silica. By Colonel Philip Yorke, F.R.S. 
Keeeived March 25, — Eead April 2, 1857. 
SixcE chemistry has been studied as a science, it has been an object with its cultivators 
to arrange the bodies which have been the subjects of their attention, into groups in 
which the individuals should have a natural relation to each other. Probably at no time in 
the history of the science has the importance of such a classification been more strongly 
felt than at the present day, not only on account of the number of known elements, but 
also from the number of compound bodies appearing to act as elements, which organic 
chemistry has made known. Although great advances have been made in this direction, 
the place of the element silicon in such a series as above alluded to, is very doubtful. 
Yet the binary compound of this element, silicon with oxygen, is familiar to every one ; 
it constitutes by itself a considerable portion of the crust of the earth, and enters into a 
long series of definite crystallized compounds. 
It has been satisfactorily determined that this substance, silica, belongs to the class 
of bodies designated as acids, but one essential point is wanting to enable chemists to 
give it, or its peculiar element, its proper position, and that is, the formula of this silica 
or silicic acid. 
Three different fonnulas have been proposed and made use of by different chemists, — 
SiOg, SiOa, SiO. 
The first was originally adopted by Berzelius, from a consideration of the composi- 
tion of felspar ; and subsequently it was supported by arguments deduced from a law 
relating to the boiling-points of the volatile compounds of chlorine and bromine, sug- 
gested by Hermajvn Kopp. The composition of a compound of chlorine, sulphur and 
silicon, discovered by Is. Pierre*, is also favourable to this formula. The second 
formula is adopted by Gmelin, and is supported by some experiments of H. PosEf , who 
found that when silica is fused with excess of carbonate of potash, the quantity of car- 
bonic acid driven off is such that the oxygen contained in the carbonic acid expelled is 
equal to that of the silicic acid used. This formula, SiOj, agrees with arguments 
derived from the specific gravity of the vapours of chloride and fluoride of silicon. The 
last formula, SiO, originally suggested by Dr. Thomson^, has been supported by 
M. Dumas §, and also by Ebelmen ||, from arguments suggested by the constitution of the 
sihcic ethers. 
* Ann. de Chim. &c. 3 ser. xxiv. 286. 
t On Titanium and its Compounds, Gilbert’s ‘ Annalen,’ Ixxiii. 83. 
X System of Chemistry, 5th ed. 1817. § Ann. de Chim. &c. 2 ser. xxxiii. 368. 
II Ann. de Chim. &c. 3 ser* xvi. 163. 
4 A 
MDCCCLVII. 
