SILICA  , in See also:

• CHEMISTRY
• CHEMISTRY (formerly "chymistry"; Gr. xvµela; for derivation see ALCHEMY)

chemistry, the name ordinarily given to amorphous See also:

• SILICON [symbol Si, atomic weight 28.3 (0= 16)]

silicon dioxide, SiO2 . This chemical See also:

• COMPOUND
• COMPOUND (from Lat. componere, to combine or put together)

compound is widely and most abundantly distributed in nature, both in the See also:

• FREE

free See also:

• STATE
• STATE, GREAT OFFICERS OF

state and in See also:

• COMBINATION (Lat. combinare, to combine)

combination with metallic oxides . Free silica constitutes the greater See also:

• PART

part of See also:

• SAND
• SAND, GEORGE (1804-1876)

sand and sandy rocks; when fairly pure it occurs in the large crystals which we know as See also:

• QUARTZ

quartz (q.v.), and which, when coloured, See also:

• FORM (Lat. forma)

form the See also:

• GEM (Lat. gemma, a bud,—from the root gen, meaning " to produce,"—or precious stone; in the latter sense the Greek term is > d>os)
• GEM, ARTIFICIAL

gem-stones See also:

• AMETHYST

amethyst, See also:

• CAIRNGORM

cairngorm, See also:

• CATS, JACOB (1577-1660)

cats'-See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye and See also:

• JASPER

jasper . See also:

• TRIDYMITE

Tridymite (q.v.) is a rarer form, crystallographically different from quartz . Amorphous forms also occur: See also:

• CHALCEDONY, or CALCEDONY (sometimes called by old writers cassidoine)

chalcedony (q.v.), and its coloured modifications See also:

• AGATE

agate, See also:

• CARNELIAN

carnelian, See also:

• ONYX

onyx and See also:

• SARD

sard, together with See also:

• OPAL

opal (qq.v.) are examples . Amorphous silica can be obtained from a silicate (a compound of silica and a metallic See also:

• OXIDE

oxide) by fusing the finely powdered See also:

• MINERAL

mineral with See also:

• SODIUM [symbol Na, from Lat. natrium; atomic weight 23.00 (0=16)]

sodium carbonate, decomposing the sodium silicate thus formed with hydrochloric See also:

• ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid, evaporating to dryness to convert the colloidal silicic acid into insoluble silica, and removing the soluble chlorides by washing with hot See also:

• WATER

water . On drying, the .silica is obtained as a soft See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white amorphous See also:

• POWDER (through O. Fr. puldre, modern poudre, from Lat. pulvis, pulveris, dust)

powder, insoluble in water and in all acids except hydrofluoric; it dissolves in hot solutions of the See also:

• CAUSTIC (Gr. rcavvraubs, burning)

caustic alkalis and to a less extent in See also:

• ALKALI

alkali See also:

• CARBONATES

carbonates . It melts at a high temperature, and in the electric See also:

• FURNACE

furnace it may be distilled, the vapours condensing to a bluish-white powder . By See also:

• HEATING

heating a See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution of sodium silicate in a See also:

• GLASS
• GLASS (O.E. glees, cf. Ger. Glas, perhaps derived from an old Teutonic root gla-, a variant of glo-, having the general sense of shining, cf. " glare," " glow ")
• GLASS, STAINED

glass See also:

• VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel the glass is attacked (an acid silicate being formed) and silica separates at See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary temperatures in a hydrated amorphous form, at higher temperatures but below 18o° as tridymite, and above 18o° as quartz . Silicates.—These compounds are to be regarded as salts of silicic acid, or combinations of silicon dioxide and metallic basic oxides; they are of See also:

• GREAT

great importance since they constitute the commonest See also:

• ROCK
• ROCK (O.Fr. rake, Sp. rota, Ital. rocca; possibly from a Lat. form rupica, from rupes, rock)
• ROCK, DANIEL (1799–187t)

rock-forming and many other minerals, and occur in every petrographical See also:

• SPECIES

species . The See also:

• PARENT, SIMON NAPOLEON (1855– )

parent acid, silicic acid, was obtained by T . See also:

• GRAHAM, SIR GERALD (1831–1899)
• GRAHAM, SIR JAMES ROBERT GEORGE
• GRAHAM, SYLVESTER (1794-1851)
• GRAHAM, THOMAS (1805-1869)

Graham by dialysing a solution of hydrochloric acid to which sodium silicate had been added; a colloidal silicic acid being resained in the dialyser .

This solution may be concentrated until it contains about 14°f° of silica by open boiling, and this solution on evaporation in a vacuum gives a transparent See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass of metasilicic acid, H2SiOa . The solution is a tasteless liquid having a slight acid reaction; it gradually changes to a clear transparent jelly, which afterwards shrinks on drying . This coagulation is brought about very quickly by sodium carbonate, and may be retarded by hydrochloric acid or by a solution of a caustic alkali . Several hydrated forms have been obtained, e.g . 2SiO2•See also:

• H2O (combined)

H2O, 3SiO2•H2O, 4Si02•H2O, 8SiO2•H2O; these are very unstable, the first two losing water on exposure whilst the others absorb water . The natural silicates may be regarded as falling into 5 classes, viz. orthosilicates, derived from Si(OH)4; metasilicates, from SiO(OH)2; disilicates, from Si2Oa(OH)2; trisilicates, from Sia06(OH)2; and basic silicates . These acids may be regarded as derived by the partial dehydration of the ortho-acid . Another See also:

• CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification is given in METALLURGY; a See also:

• LIST (O.E. lisle, a Teutonic word, cf. Dut. lust, Ger. Leiste, adapted in Ital. lista and Fr. lisle)
• LIST, FRIEDRICH (1789-1846)

list of mineral silicates is given in See also:

• MINERALOGY

MINERALOGY, and for the synthetical See also:

• PRODUCTION (Lat. productionem, from producere, to pro-duce)

production of these compounds see also See also:

• PETROLOGY

PETROLOGY .