Volume 1
A treatise on chemistry / by H.E. Roscoe and C. Schorlemmer.
- Henry Enfield Roscoe
- Date:
- 1877-1892
Licence: Public Domain Mark
Credit: A treatise on chemistry / by H.E. Roscoe and C. Schorlemmer. Source: Wellcome Collection.
572/792 page 556
![This substance was for a long time supposed to be the essen- tial principle of all earths, but it was found that it differed from them inasmuch as it has no power of neutralizing acids; and Tachenius, in the year 1G60, noticed that it possesses acid rather than alkaline properties, since it combines with alkalies. The true nature of silica was then unknown, but Lavoisier, in his chemical nomenclature, anticipates that the time may pro- bably soon arrive when this substance will be recognised as a compound body. After Davy’s discovery of the compound nature of the alkalies and alkaline earths in the year 1808, silica, which was then classed amongst the earths, was supposed to possess a similar constitution. Berzelius, in the year 1810, first obtained impure silicon by fusing together iron, carbon, and silica; and in 1823 he de- scribed the following method for obtaining this element1 in the pure state. Ten parts of dry potassium silico-tluoride mixed with eight to nine parts of metallic potassium are heated to redness in an iron tube. The following decomposition takes place:— K2SiF6+4K = 6KF + Si. Instead of potassium, sodium may be employed. As soon as the violent reaction which takes place is ended, the mass is allowed to cool, and then treated with cold, and afterwards with hot water, until all the potassium fluoride is dissolved. The residual silicium or silicon is found in the form of an amor- phous brown powder, which may likewise be obtained by passing the vapour of silicon tetrachloride through a red-hot tube over sodium.2 Prepared by either of these processes, silicon is a dark brown amorphous powder which when heated in the air easily takes fire, burning to the dioxide, Si02, which frequently fuses round the particles of the silicon, leaving a portion of this substance unburnt in the centre of the mass. Amorphous silicon is not attacked by sulphuric or nitric acid, but it readily dissolves in aqueous hydrofluoric acid. When it is heated to redness in absence of air, it becomes denser, and assumes a graphitic appearance, after which it oxidizes much less readily on heating. A crystalline modification of silicon is prepared by heating metallic aluminium with from twenty to forty times its weight i Pnrjrj. Ann. i. 169. 2 H. D^ville, Ann. Chim. rhys. [3] xlix. 68.](https://iiif.wellcomecollection.org/image/b28122409_0001_0574.jp2/full/800%2C/0/default.jpg)
