Calcium chloride is formed when calcium carbonate is dissolved in hydrochloric acid. It is exceedingly soluble, but upon evaporation of its solution it separates in white, needle-like crystals having the formula CaCI, 61120. When these are heated to about 400° F. they lose two-thirds of their water of crystallization and become converted into CaCh+ 2H2O, in which form the chloride is commonly used. Thus prepared, calcium chloride is a white, porous solid, which absorbs moisture with great avidity, and hence is exceedingly valuable to the chemist and physicist for drying air and other gaseous bodies. It forms crystalline com pounds with ethyl and methyl alcohols, which are again resolved, by the addition of water, into calcium chloride and the free alcohol. On account of this property it has been used for the preparation of these alcohols in the pure state. See also CALCIUM CHLORIDE.
Calcium hyperchlorite is a bleaching agent which is more stable than ordinary bleaching powder (chloride of lime), yielding a clear solution in water and containing from 80 to 90 per cent of available chlorine. (See BLEACH ING). It is made by passing chlorine gas into milk of lime at a temperature not exceeding 90° F., and then concentrating the solution to crystallization. Besides its bleaching properties it is used in very large quantities for the purifi cation of water in reservoirs for drinking purposes.
Calcium sulphate occurs native in the an hydrous form, as the mineral anhydrite; and, combined with two molecules of water, it also occurs abundantly as gypsum. It is soluble in 400 parts of water, and, like the carbonate, it occurs quite generally in the waters of wells and springs. Like the carbonate, too, it makes the water in which it occurs hard; but the hardness due to the presence of the sulphate cannot be removed by boiling, and it is therefore said to be Calcium sulphate produces deposits in steam boilers that are far more troublesome and injurious than those due to the carbonate, since the sulphate is deposited in a hard, compact, stony form, and can be re moved only with difficulty.
When gypsum is moderately heated it loses its water of crystallization and becomes con verted into a substance that is commercially known as plaster of Paris, from the fact that the gypsum from which it is prepared (and which is also called plaster of Paris, though rarely) occurs abundantly in the Tertiary formations of the Paris basin. Plaster of Paris, when moistened by the addition of the proper quantity of water, takes up two molecules of water again, and rapidly sets into a hard, solid mass which expands somewhat at the instant of solidification. It is much used in making casts and molds. These are harder and better when the plaster is wetted with a solution of alum than they are when pure water is used for this purpose. If equal weights of the an hydrous sulphates of calcium and of potassium are wetted with about four parts of water, the mixture sets like plaster of Paris, with the formation of a double sulphate of calcium and potassium, having the formula CaSO4.KISO, 1-120. The casts so obtained exhibit polished surfaces, superior to those obtained with pure plaster.
Calcium fluoride, CaF,, occurs native as fluor spar, or fluorite, and is used to some extent as a flux in metallurgical operations, to which circumstance it owes its name (Latin fluor, a flux). It is also used in the manufacture of vases and other ornamental articles and as a source of hydrofluoric acid, which is set free when the fluorine is treated with warm sul phuric acid.
Calcium carbide, CaG, has long been known, and was prepared by Wohler in 1862 by melting an alloy of zinc and calcium in the presence of carbon. Its importance, however, dates from the discovery made by Mr. T. L Willson in 1892, that it can be formed by the direct combination of lime and carbon at the temperature of the electric furnace. Large quantities of it are now made by this process at Niagara Falls, at Spray, N. C., and elsewhere. Calcium carbide in its commercial form is a dark-gray substance, often almost black. It is hard, infusible and incombustible, with a specific gravity of about 2.24. Its value in the arts depends upon the fact that when it is thrown into water a double decomposition occurs, by which acetylene gas is formed, in accordance with the equation CaCi 2H2O C,H, Ca (OH). See ACETYLENE' CARBIDE.
Calcium phosphide, CasPs, has the property of decomposing instantly when thrown into water with the evolution of phosphuretted hy drogen which takes fire spontaneously. It is used in several forms of marine signal lights and also in naval target practice at night.
Calcium sulphite, CaSO,, is formed and pre cipitated as a white powder when a solution of a calcium salt is added to a solution of an alka line sulphite. The sulphite so formed requires 800 parts of pure water to effect its solution. It is far more soluble in sulphurous acid, however, and it is believed that the sulphurous acid acts upon it to produce a new but comparatively unstable compound, CaS0*.S0,, to which hypo thetical substance the name calcium bisulphate, or bisulphite of lime, has been given. Upon exposure to air the bisulphite solution gradually deposits crystals of the monosulphite, having the composition CaS0.2H20. On the commer cial scale the bisulphite solution is prepared by passing sulphur dioxide gas (SO,) through of lime" (that is, water containing slaked lime in suspension). The monosulphite of lime is first formed, and by the continued action of the sulphur dioxide this passes into solution in the form of the bisulphite. The usefulness of bisulphite of lime in the arts depends upon the power of dissolving the gums and resins by which the fibres of wood are cemented together. Thus, in the sulphite process of manufacturing wood pulp, chips of wood are submerged in a solution of the bisulphate and heated for some hours in closed digesters, by the action of steam. By this means the chips are disin tegrated, they connective materials being entirely and the wood being thereby reduced to a mass of separate fibres, which after simple washing and bleaching are ready for use in the manufacture of paper. See ELECTROCHEMICAL INDUSTRIES.