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CALCIUM [symbol Ca, atomic weight 40....

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Originally appearing in Volume V04, Page 972 of the 1911 Encyclopedia Britannica.
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CALCIUM [See also:symbol Ca, atomic See also:weight 40.0 (o= x6)] , a metallic chemical See also:element, so named by See also:Sir See also:Humphry See also:Davy from its occurrence in See also:chalk (Latin calx). It does not occur in nature in the See also:free See also:state, but in See also:combination it is widely and abundantly diffused. Thus the sulphate constitutes the minerals See also:anhydrite, See also:alabaster, See also:gypsum, and selenite; the carbonate occurs dissolved in most natural See also:waters and as the minerals chalk, See also:marble, See also:calcite, See also:aragonite; also in the See also:double See also:carbonates such as See also:dolomite, See also:bromlite, See also:barytocalcite; the fluoride as fluorspar; the fluophosphate constitutes the See also:mineral See also:apatite; while all the more important mineral silicates contain a proportion of this element. Extraction.—Calcium See also:oxide or See also:lime has been known from a very remote See also:period, and was for a See also:long See also:time considered to be an elementary or undecomposable See also:earth. This view was questioned in the 18th See also:century, and in 18o8 Sir Humphry Davy (Phil. Trans., 1808, p. 303) was able to show that lime was a combination of a See also:metal and See also:oxygen. His attempts at isolating this metal were not completely successful; in fact, metallic calcium remained a laboratory curiosity until the beginning of the 20th century. Davy, inspired by his successful See also:isolation of the metals See also:sodium and See also:potassium by the See also:electrolysis of their hydrates, attempted to decompose a mixture of lime and mercuric oxide by the electric current; an See also:amalgam of calcium was obtained, but the separation of the See also:mercury was so difficult that even Davy himself was not sure as to whether he had obtained pure metallic calcium. Electrolysis of lime or calcium chloride in contact with mercury gave similar results. See also:Bunsen (See also:Ann., 1854, 92, p. 248) was more successful when he electrolysed calcium chloride moistened with hydrochloric See also:acid; and A.

Matthiessen (Jour. Chem. See also:

Soc., 1856, p. 28) obtained the metal by electrolysing a mixture of fused calcium and sodium chlorides. See also:Henri See also:Moissan obtained the metal of 99% purity by electrolysing calcium iodide at a See also:low red See also:heat, using a See also:nickel See also:cathode and a See also:graphite anode; he also showed that a more convenient See also:process consisted in See also:heating the iodide with an excess of sodium, forming an amalgam of the product, and removing the sodium by means of See also:absolute See also:alcohol (which has but little See also:action on calcium), and the mercury by See also:distillation. The electrolytic isolation of calcium has been carefully investigated, and this is the method followed for the commercial See also:production of the metal. In 1902 W. Borchers and L. Stockem (Zeil. See also:fur Eleclrochemie, 1902, p. 8757) obtained the metal of 90 % purity by electrolysing calcium chloride at a temperature of about 780°, using an See also:iron cathode, the anode being the graphite See also:vessel in which the electrolysis was carried out. In the same See also:year, O. See also:Ruff and W.

See also:

Plato (Ber. 1902, 35, p. 3612) employed a mixture of calcium chloride (too parts) and fluorspar (16.5 parts), which was fused in a See also:porcelain crucible and electrolysed with a See also:carbon anode and an iron cathode. Neither of these processes admitted of commercial application, but by a modification of Ruff and Plato's process, W. Ruthenau and C. Suter have made the metal commercially available. These chemists electrolyse either pure calcium chloride, or a mixture of this See also:salt with fluorspar, in a graphite vessel which serves as the anode. The cathode consists of an iron See also:rod which can be gradually raised. On electrolysis a layer of metallic calcium is formed at the See also:lower end of this rod on the See also:surface of the electrolyte; the rod is gradually raised, the thickness of the layer increases, and ultimately a rod of metallic calcium, forming, as it were, a continuation of the iron cathode, is obtained. This is the See also:form in which calcium is put on the See also:market. An See also:idea as to the advance made by this method is recorded in the variation in the See also:price of calcium. At the beginning of 1904 it was quoted at 5s. per See also:gram, £250 per kilogram or £110 per See also:pound; about a year later the price was reduced to 21S. per kilogram, or I 2S. per kilogram in quantities of too kilograms.

These quotations apply to See also:

Germany; in the See also:United See also:Kingdom the price (1905) varied from 27s. to 30S. per kilogram (12s. to 13S. per lb.). See also:Pro perties.—A freshly prepared surface of the metal closely resembles See also:zinc in See also:appearance, but op exposure to the See also:air it rapidly tarnishes, becoming yellowish and ultimately See also:grey or See also:white in See also:colour owing to the formation of a surface layer of calcium See also:hydrate. A faint See also:smell of See also:acetylene may be perceived during the oxidation in moist air; this is probably due to traces of .calcium See also:carbide. It is rapidly acted on by See also:water, especially if means are taken to remove the layer of calcium hydrate formed on the metal; alcohol acts very slowly. In its chemical properties it closely resembles See also:barium and See also:strontium, and to some degree See also:magnesium; these four elements comprise the so-called metals of the " alkaline earths." It combines directly with most elements, including See also:nitrogen; this can be taken See also:advantage of in forming almost a perfect vacuum, the oxygen combining to form the oxide, CaO, and the nitrogen to form the nitride, Ca3N2. Several of its See also:physical properties have been determined by K. See also:Arndt (Ber., 1904, 37, p. 4733). The metal as prepared by electrolysis generally contains traces of See also:aluminium and See also:silica. Its specific gravity is 1.54, and after remelting 1.56; after distillation it is 1.52. It melts at about 800°, but sublimes at a lower temperature. Compounds.—Calcium hydride, obtained by heating electrolytic calcium in a current of See also:hydrogen, appears in See also:commerce under the name hydrolite.

Water decomposes it to give hydrogen free from See also:

ammonia and acetylene, i gram yielding about 'co See also:cos. of See also:gas (Prats Aymerich, Abst. J. C. S., 1907, ii p. 460). Calcium forms two oxides —the monoxide, CaO, and the dioxide, CaO,. The monoxide and its hydrate are more familiarly known as lime (q.v.) and slaked-lime. The dioxide was obtained as the hydrate, CaO2.8H2O, by P. See also:Thenard (Ann. Chim. Phys., 1818, 8, p. 213), who precipitated lime-water with hydrogen peroxide.

It is permanent when dry; on heating to 130° C. it loses water and gives the anhydrous dioxide as an unstable, See also:

pale See also:buff-coloured See also:powder, very sparingly soluble in water. It is used as an antiseptic and oxidizing See also:agent. Whereas calcium chloride, bromide, and iodide are deliquescent solids, the fluoride is practically insoluble in water; this is a See also:parallelism to the soluble See also:silver fluoride, and the insoluble chloride, bromide and iodide. Calcium fluoride, CaF2, constitutes the mineral fluor-spar (q.v.), and is prepared artificially as an insoluble white powder by precipitating a See also:solution of calcium chloride with a soluble fluoride. One See also:part dissolves in 26,000 parts of water. Calcium chloride, CaC12, occurs in many natural waters, and as a by-product in the manufacture of carbonic acid (carbon dioxide), and potassium chlorate. Aqueous solutions See also:deposit crystals containing 2, 4 or 6 molecules of water. Anhydrous calcium chloride, prepared by heating the hydrate to 200° (preferably in a current of hydrochloric acid gas, which prevents the formation of any oxychloride), is very hygroscopic, and is used as a desiccating agent. It fuses at 723°. It combines with gaseous ammonia and forms crystalline compounds with certain See also:alcohols. The crystallized salt dissolves very readily in water with a considerable absorption of heat; hence its use in forming " freezing mixtures." A temperature of -55° C. is obtained by mixing io parts of the hexahydrate with 7 parts of See also:snow. A saturated solution of calcium chloride contains 325 parts of CaCl2 to too of water at the boiling point(179.5°).

Calcium iodide and bromide are white deliquescent solids and closely resemble the chloride. Chloride of lime or " See also:

bleaching powder " is a calcium chlorhypochlorite or an equimolecular mixture of the chloride and hypochlorite (see See also:ALKALI MANUFACTURE and BLEACHING). Calcium carbide, CaC2, a See also:compound of See also:great See also:industrial importance as a source of acetylene, was first prepared by F. See also:Wohler. It is now manufactured by heating lime and carbon in the electric See also:furnace (see ACETYLENE). Heated in See also:chlorine or with See also:bromine, it yields carbon and calcium chloride or bromide; at a dull red heat it See also:burns in oxygen, forming calcium carbonate, and it becomes incandescent in See also:sulphur vapour at 500°, forming calcium sulphide and carbon disulphide. Heated in the electric furnace in a current of air, it yields calcium See also:cyanamide (see CYANAMIDE). Calcium carbonate, CaCO3, is of exceptionally wide See also:distribution in both the mineral and See also:animal kingdoms. It constitutes the bulk of the chalk deposits and See also:limestone rocks; it forms over one-See also:half of the mineral dolomite and the See also:rock magnesium limestone; it occurs also as the dimorphous minerals aragonite (q.v.) and calcite (q.v.). See also:Tuff (q.v.) and travertine are calcareous deposits found in volcanic districts. Most natural waters contain it dissolved in carbonic acid; this confers " temporary hardness " on the water. The dissipation of the dissolved carbon dioxide results in the formation of " fur " in kettles or boilers, and if the solution is falling, as from the roof of a See also:cave, in the formation of See also:stalactites and stalagmites.

In the animal kingdom it occurs as b4~th calcite and aragonite in the tests of the See also:

foraminifera, echinoderms, See also:brachiopoda, and See also:mollusca; also in the skeletons of See also:sponges and See also:corals. Calcium carbonate is obtained as a white precipitate, almost insoluble in water (I part requiring io,000 of water for solution), by mixing solutions of a carbonate and a calcium salt. Hot or dilute See also:cold solutions deposit See also:minute orthorhombic crystals of aragonite, cold saturated or moderately strong solutions, hexagonal (See also:rhombohedral) crystals of calcite. Aragonite is the least See also:stable form; crystals have been found altered to calcite. Calcium nitride, Ca,N2, is a greyish-yellow powder formed by heating calcium in air or nitrogen; water decomposes it with See also:evolution of ammonia (see H. Moissan, Comp'. Rend., 127, p. 497). Calcium nitrate, Ca(NO,)2.4H2O, is a highly deliquescent salt, crystallizing in.See also:monoclinic prisms, and occurring in various natural waters, as an efflorescence in limestone caverns, and in the See also:neighbour-See also:hood of decaying nitrogenous organic See also:matter. Hence its synonyms, " See also:wall-See also:saltpetre " and " lime-saltpetre "; from its disintegrating action on See also:mortar, it is sometimes referred to as " saltpetre rot.' The anhydrous nitrate, obtained by heating the crystallized salt, is very phosphorescent, and constitutes " Baldwiq's See also:phosphorus." A bask nitrate, Ca(NO3)2•Ca(OH)2.3H20; is obtained by dissolving calcium hydroxide in a solution of the normal nitrate. Calcium phosphide, Ca3P2, is obtained as a reddish substance by passing phosphorus vapour over strongly heated lime. Water decomposes it with the evolution of spontaneously inflammable hydrogen phosphide; hence its use as a marine See also:signal See also:fire (" See also:Holmes See also:lights "), (see L.

Gattermann and W. Haussknecht, Ber., 189o, 23, p. 1176, and H. Moissan, Compt. Rend., 128, p. 787). Of the calcium orthophosphates, the normal salt, Ca3(PO4)27 is the most important. It is the See also:

principal inorganic constituent of bones, and hence of the " See also:bone-ash " of commerce (see PHOSPHORUS) ; it occurs with fluorides in the mineral apatite (q.v.) ; and the concretions known as See also:coprolites (q.v.) largely consist of this salt. It also constitutes the minerals ornithite, Caa(PO4)2.2H20, osteolite and sombrerite. The mineral brushite, CaHPO4.2H2O, which is isomorphous with the acid arsenate pharmacolite, CaHAsO4.2H20, is an acid phosphate, and assumes monoclinic forms. The normal salt may be obtained artificially, as a white gelatinous precipitate which shrinks greatly on drying, by mixing solutions of sodium hydrogen phosphate, ammonia, and calcium chloride. Crystals may be obtained by heating di-calcium pyrophosphate, Ca2P2O7, with water under pressure.

It is insoluble in water; slightly soluble in solutions of carbonic acid and See also:

common salt, and readily soluble in concentrated hydrochloric and nitric acid. Of the acid orthophosphates, the mono-calcium salt, CaH4(PO4)2, may be obtained as crystalline scales, containing one See also:molecule of water, by evaporating a solution of the normal salt in hydrochloric or nitric acid. It dissolves readily in water, the solution having an acid reaction. The artificial manure known as " superphosphate of lime " consists of this salt and calcium sulphate, and is obtained by treating ground bones, coprolites. &c., with sulphuric acid. The di-calcium salt, Ca2H2(PO4)2, occurs in a concretionary form in the ureters and See also:cloaca of the See also:sturgeon, and also in See also:guano. It is obtained as rhombic plates by mixing dilute solutions of calcium chloride and sodium phosphate, and passing carbon dioxide into the liquid. Other See also:phosphates are also known. Calcium monosulphide, CaS, a white amorphous powder, sparingly soluble in water, is formed by heating the sulphate with See also:charcoal, or by heating lime in a current of sulphuretted hydrogen. It is particularly noteworthy from the See also:phosphorescence which it exhibits when heated, or after exposure to the See also:sun's rays; hence its synonym " See also:Canton's phosphorus," after See also:John Canton (1718-1772), an See also:English natural philosopher. The sulpliydrate or hydrosulphide, Ca(SH)2, is obtained as colourless, prismatic crystals of the See also:composition Ca(SH)2.6H20, by passing sulphuretted hydrogen into See also:milk of lime. The strong aqueous solution deposits colourless, four-sided prisms of the hydroxy-hydrosulphide, Ca(OH)(SH).

The disulphide, CaS2, and pentasulphide, CaSSi are formed when milk of lime is boiled with See also:

flowers of sulphur. These sulphides form the basis of See also:Balmain's luminous paint. An oxysulphide, 2CaS•CaO, is sometimes See also:present in " soda-See also:waste," and See also:orange-coloured, acicular crystals of 4CaS•CaSO4.18H2O occasionally See also:settle out on the long See also:standing of oxidized " soda- or alkali-waste " (see ALKALI MANUFACTURE). Calcium sulphite, CaSO3, a white substance, soluble in water, is prepared by passing sulphur dioxide into milk of lime. This solution with excess of sulphur dioxide yields the " bisulphite of lime " of commerce, which is used in the " chemical " manufacture of See also:wood-pulp for See also:paper making. Calcium sulphate, CaSO4, constitutes the minerals anhydrite (q.v.), and, in the hydrated form, selenite, gypsum (q.v.), alabaster (q.v.), and also the adhesive See also:plaster of See also:Paris (see See also:CEMENT). It occurs dissolved in most natural waters, which it renders " permanently hard." It is obtained as a white crystalline precipitate, sparingly soluble in water (Too parts of water dissolve 24 of the salt at 15° C.), by mixing solutions of a sulphate and a calcium salt; it is more soluble in solutions of common salt and hydrochloric acid, and especially of sodium thiosulphate. Calcium silicates are exceptionally abundant in the mineral kingdom. Calcium metasilicate, CaSiO3, occurs in nature as mono-clinic crystals known as See also:tabular spar or See also:wollastonite; it may be prepared artificially from solutions of calcium chloride and sodium silicate. H. Le Chatelier (Annales See also:des mines, 1887, p. 345) has obtained artificially the compounds: CaSiO3, Ca2SiO4, Ca3Si2O7, and CasSiOs.

(See also G. Oddo, Chemisches Centralblatt, 1896, 228.) Acid calcium silicates are represented in the mineral kingdom by gyrolite, H2Ca2(SiO3)3•H2O, a lime zeolite, sometimes regarded as an altered form of See also:

apophyllite (q.v.), which is itself an acid calcium silicate containing an alkaline fluoride, by okenite, H2Ca(SiO0)2•H2O, and by xonalite 4CaSiO3•H2O. Calcium silicate is also present in the minerals: See also:olivine, pyroxenes, amphiboles, See also:epidote, felspars, See also:zeolites,to a Bunsen See also:flame, which when viewed through See also:green See also:glass appears to be See also:finch-green; this distinguishes it in the presence of strontium, whose See also:crimson coloration is See also:apt to See also:mask the orange-red calcium flame (when viewed through green glass the strontium flame appears to be a very faint yellow). In the spectroscope calcium exhibits two intense lines—an orange See also:line (a), (X 6163), a green line (3), (X 4229), and a fainter See also:indigo line. Calcium is not precipitated by sulphuretted hydrogen, but falls as the carbonate when an alkaline carbonate is added to a solution. Sulphuric acid gives a white precipitate of calcium sulphate with strong solutions; ammonium oxalate gives calcium oxalate, practically insoluble in water and dilute acetic acid, but readily soluble in nitric or hydrochloric acid. Calcium is generally estimated by precipitation as oxalate which, after drying, is heated and weighed as carbonate or oxide, according to the degree and duration of the heating.

End of Article: CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

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