SILICON (Si). Silicium. With the exception of oxygen, silicon is the most abundant constituent of our earth's crust. Its name is derived from silts, Latin for " flint," of which the essential component is silicon. The element silicon has great affinities for other elements, and hence does not exist, in nature, in the free state. Its common, and apparently sole, native form of combination is an oxide known as :ilex or silica. Rock crystal and white quartz are nearly pure varieties of silica; while calceslony, agate, opal, flint, and sand are chiefly Silica. The natural compounds of silica with oxides are almost innumerable. The individuality of siliceous minerals was recognised at a very early period, but their constitution was not demonstrated till the commence ment of the present century.
Silicon itself was first isolated only so lately as 1823. It may be prepared by reducing an alkaline silico-fluoride with potassium, in a glace or iron tube, at a high temperature. It may also be obtained by passing chloride of silicon vapour over potassium heated in a bulbed glass tube.
like Callao's; and BORON, exists in three distinct modifica tion& AS above prepared, it is a dull-brown powder ; insoluble in, and heavier than, water • is a non-conductor of electricity, is soluble in hydrofluoric acid, and in a warm solution of potash ; burns readily and brilliantly when heated iu the air ; and is moreover amorphous (Si7). If the amorphous silicon be strongly heated it becomes semi crystalline or graphitoidal (Sikl); is denser and darker in colour ; does not burn in oxygen : is not soluble in hydrofluoric acid ; and is a con ductor of electricity. Crystalline silicon (Sia) occurs in the form of six-sided prisms or pyramids, whenever the process for its prepara tion has included the application of the most intense heat of a wind furnace.
The equivalent of silicon has, in turn, been represented as 7 14, 21, and 23; but since the experiments of Marignac, who proved that the fluo-stannotes and fluo-silicates are isomorphous, it has been usual to consider the number 14 as the true equivalent of silicon.
Silicon and oxygen form two compounds :— 1. Hydrated protoxide of silicon . . nto, 3610 2. Sill& acid 810, 1. Hydrated protoxide of silicon (2H0, 3Si0).—When dry hydro. chloric said gas is passed over crystallised silicon, heated to incipient redness, bydrochlomte of protochloride of silicon (211C1,3SiCB is pro ducted, and may be condensed to the liquid state in a U-tube cooled b1 Ice ; hydrogen passes off carrying vapour of protochlorido with it ; the sae being allowed to bubble through water the chloride is decent posed, and a voluminous white precipitate of the oxide under con siclemtion is formed :— 2=1, asia + 5110 = 2110, 3SIO 511C1.
Ilydrated protoxide of silicon sinks in water but floats on ether the caustic alkalies and their carbonates dissolve it with evolution o hydrogen and formation of silicate ; It may be heated to 570* Fahr, without undergoing alteration, but at a higher temperature burns; an in contact with water undergoes oxidation, hydrogen being evolved, a any temperature above 32' Fehr.
2. Silicic acid (Si0;1, Silos, Silica, Binchride of allicon.—The physics and chemical properties of the many different forms of silica the occur in nature, as well as a lint of the minerals in which silica is characteristic constituent, already been treated of in the NATCRA 11ISTORT Divtatos of this elopedia, article SILICA.
Silicic acid is largely in the manufacture of glass, chinaware and porcelain. For these purposes it is obtained in a fine state c division by Igniting flints or colourless quartz to reduces, and the plunging iu cold water. The compact silica is thus split up into
riable mass, easily reducible to powder by grinding. Perfectly pure ilicic acid may be obtained by igniting hydrated silica.
Hydrates of *dick acid (x110, SiO,).—Finely powdered Silica is Outdo in strong alkaline solutions if heated with them under pressure; rem the resulting solutions hydrated silica is precipitated in a very ;elatinoue state on neutralising by hydrochloric acid. The alkaline ilicate may also be formed by fusing powdered flint, &c., with the arbonateuu of potash or soda ; if excess of the latter be used, the ilicate is soluble in water, and the solution furnishes hydrated silicic aid on the addition of hydrochloric acid. Perfectly pure hydrated ilica is formed in a very beautiful manner on passing gaseous fluoride ?f silicon into water, each bubble of gag forming a little balloon of ilica ; hydrotluosilicie acid (1IF, Si F„) is also formed at the ;same time, Ind remains dissolved in the water :— Isomeric conditions of silica—Professor Rose has recently directed attention to the two different states in which silica exists. Crystallised silica---including rock-crystal, quartz, calcedony, flint, ;sandstone, and luartzose sand—has a specific gravity, of about 2.9, and is only 'Backed with difficulty by potash, or hydrofluoric acid. Amorphous silica, on the other lumd,—including gelatinous silica, the pulverulent rariety that results from the decomposition of certain minerals, or of fluoride of silicon by water, opals, melted quartz, and silica from the tar-spaces of infusoria—is very readily soluble in alkaline solutions, is rapidly acted upon by hydrofluoric acid, and has n specific gravity of Silicates, as a general rule, arc insoluble in water. Alkaline silicates are however, soluble in that liquid, and their solutions have lately been used as a varnish for the stonework of buildings with the view of preventing decay. When thus exposed to the atmosphere, the silica, being but a weak acid, is replaced by carbonic acid ; the alkaline carbonate is removed by rain, and silicic acid filling up the pores of the stone is supposed to prevent ingress of moisture or other disinte grating matter. The fact is, however, that the decomposition alluded to, being but a slow one, a large portion of the silicate is washed away by the rain, and this process is consequently of but little value. A modification of the method, known as "nonsense's patent," consists in supplementing the application of the alkaline silicate by a wash of chloride of calcium; silicate of lime is hereby at once produced, and performs the office of a permanent varnish or cement, in a far more efficient manner than the mere silica before alluded to. Clay, talc, felspar,serpentine, mica, zeolite& hornblende, and many other minerals, consist of, or contain, silicates of lime, or magnesia, or alumina, or a mixture of those silicates. They are either scsguisilicates like meer schaum (231g0, 3S10, + 2H0), or neutral silicates, like Wollastonite (CaO, SiO,); or dibasic silicates, like olivine (2(31g, Fe)O, SiO,); or bi.silicates (MO, 2Si0,). [SILICA, in NAT. Hist Div. J Silicon and hydrogen form a hydride of silicon. Berzelitta first showed that the hydrogen which is evolved when crude silicon is washed with water, contains a hydride of silicon. This gas has not yet been pro cured in a pure state, but, according to 1Viihler and Buff, it is colourless and spontaneously inflammable. It occurs in the latter-condition when a solution of a chloride is clectrotised by a weak voltaic battery of which the positive pole is aluminium contaminated with silicon.