Lime, oxide of calcium, or quicklime, a white, alkaline, earthy substance, obtained by calcining some of the various carbonates of lime, such as pure limestones, marbles, and marine shells. It is brittle and pulverizable, and has a specific gravity, depending on its porosity, from 2.3 to 3.8. Its symbol is CaO, containing 40 parts of the metal calcium and 16 of oxygen, by weight. It has not been decomposed by heat, and is only fused in the oxyhydrogen blowpipe and the voltaic arc. When subjected to this heat it gives out a most intense light (Drummond light). When lime is made from pure limestone or from pure dolomite (see Dolomite), it is called rich; when it contains impurities so as to diminish its value as an ingredient of mortar, it is called poor; when it contains silica and alumina in certain proportions which cause it to set quickly in the presence of water, it is called hydraulic lime. (For the preparation of mortar, see Cements, and Concrete.) The calcining or burning of lime is performed in kilns, of which there is a great variety, classified into periodic and continuous kilns.
Periodic kilns are those in which the limestone and fuel are mingled (most of the fuel being placed beneath), and after the operation is completed removed, which requires of course an intermission to clear out the kiln before repeating the process. These kilns are usually bowl-shaped, and are erected upon a slope of ground which admits of easy access to the top of the kiln. The sides are walled up with sandstone or granite, and an opening is left at one side of the bottom. In charging the kiln a quantity of wood, sometimes mingled with anthracite coal, is placed in the bottom, then a quantity of limestone broken into fragments is thrown in; then a layer of wood, and over this again a quantity of broken limestone, the alternation being repeated until the kiln is filled. It is then covered with turf or sod, and a flame kindled below. The continuous kiln is constructed in such a manner that the lime may be drawn off at one side without extinguishing the fire. These are to be preferred when fuel is expensive, because great loss of heat is involved in letting the fires go out.
There are several kinds of these kilns, for a description of which the reader is referred to the more strictly technological works. - Perhaps the most remarkable property of freshly burned lime is its affinity for water, with which it unites with great violence and evolution of heat, 100 parts of lime by weight requiring only 32 parts of water to produce a temperature of 300° F. This combination (slaking) forms a hydrate of the definite composition CaH202, or CaO,H20. This hydrate is a white soft powder, which gives off water at a red heat, being converted again into quicklime. It is slightly soluble in water, forming what is called lime water, or aqua calcis. It is more soluble in cold than in hot water; so that when a saturated solution is boiled some of the lime will be deposited. A much greater quantity than is soluble may be suspended in water in the form of milk of lime; when the mixture is of a creamy consistency it is called cream of lime. According to Dal-ton, lime water saturated at 00°, 130°, and 212° F. contains one grain of lime to 778, 972, and 1,270 grains of water respectively. A solution evaporated in vacuo over oil of vitriol deposits hydrate of lime in hexagonal prisms.
Lime water has the property of precipitating most of the metallic oxides from solutions of their salts, and of forming soapy mixtures with oils. When lime water is exposed to the air, it absorbs carbonic acid and soon becomes covered with a pellicle of carbonate, into which after a time all the lime is converted. - Salts. The salts of lime are numerous; the most important are the following. Hydrate of lime when exposed to the action of chlorine gas forms a mixture of chloride and hypochlorite of calcium. (See Bleaching Powder.) 1. Chloride of calcium, formerly called muriate of lime, is found in sea water and in some saline springs, often accompanied by traces of bromine and iodine. It is commonly made artificially by dissolving carbonate of lime in hydrochloric acid (CaC03 or CaO,C02 + H2Cl=Ca CI + H2O + CO2). The solution is evaporated to dryness and heated to redness to expel moisture. It must be preserved in air-tight bottles, because its attraction for water is so great that it soon becomes moist in the open air. It is on account of this property that it is so extensively used by chemists as a filter through which to pass gases to deprive them of aqueous vapor. It is also used to separate alcohol, ether, and other liquids from a mixture by distilling them off.
One part of water at 66° F. will dissolve four parts of dry chloride of calcium, but at 32° not more than two parts.; while at 212° it will dissolve an almost unlimited quantity. It is copiously soluble in alcohol, and in the cold crystals are formed containing about GO Per cent. of alcohol instead of water of crystallization. 2. For fluoride of calcium see Fluor Spar. 3. Sulphide of calcium (CaS) is formed by passing sulphuretted hydrogen (H2S) over red-hot lime (Cal + H2S=CaS + H2O). It is also formed by the action of charcoal or hydrogen on sulphate of lime (gypsum) at a red heat. When freshly prepared it is phosphorescent (Canton's phosphorus). 4. Bisulphide of calcium (CaS2) is produced by boiling sulphur and hydrate of lime in equal parts in water; the solution yields on cooling reddish yellow four- or six-sided prisms, which are permanent when dried in vacuo. Their water of crystallization is 33.89 per cent., so that their formula is CaS2 + 3H20. 5. Pentasulphide of calcium (CaS5) is a non-crystallizable salt, formed by boiling an excess of sulphur with quicklime and water; it is soluble in alcohol.
By the action of heat it loses sulphur and becomes protosulphide. 6. For sulphate of lime (Ca S04) see Gypsum. 7. Sulphite of lime (Ca S03) is formed by passing sulphurous acid through milk of lime. It is a white powder of sulphurous taste, and requires about 800 parts of water at 60° for solution. It is made soluble by excess of sulphurous acid, and then separates in hexagonal prisms, which dissolve with difficulty, and are converted into sulphate of lime on exposure to the air. 8; Hyposulphite of lime (CaOS202) is formed by triturating in a mortar crystals of hydrated bisulphide of calcium; also by passing sulphurous acid through the yellow liquor obtained by boiling lime and sulphur in water, filtering, and evaporating the solution at a temperature not above 140° F. Hexagonal crystals are obtained having the composition CaOS202 + 6H20, which are decomposed at the boiling point into sulphate of lime and sulphur. This salt is employed in photography to remove silver salts. 9. Phosphuret of calcium (CaP2) is a brown compound formed by passing the vapor of phosphorus over lime heated to redness. This compound is a mixture of phosphuret of calcium and phosphate of lime; it decomposes water with the evolution of phosphuretted hydrogen.
When lime is heated to redness its oxygen converts a part of the phosphorus into phosphoric acid, and the liberated calcium combines with another portion of phosphorus to form phosphuret of calcium. 10. Hypo-phosphite of calcium (CaP202-f 2H20) is obtained by carefully boiling phosphorus in thin cream of lime, filtering the solution, and passing carbonic acid through it to separate excess of lime. It is also formed by boiling phosphuret of calcium in water, and treating the solution in the same way. When evaporated in vacuo, the solution furnishes rectangular prismatic crystals of the hyphosphite, insoluble in alcohol, but equally soluble in hot and cold water. 11. Phosphates of lime are definite compounds of lime with phosphoric acid, of which there are several, but the two following are the most important. Common phosphate, tribasic phosphate, or bone earth (3CaO,P05), is a salt found in the mineral kingdom and in bone ash. On adding chloride of calcium to the tribasic phosphate of soda, a corresponding phosphate of lime precipitates. Hydrochloric and nitric acids, and also acetic acid and water saturated with carbonic acid, readily dissolve bone phosphate. Caustic ammonia added to these solutions reprecipi-tates the original phosphate. Native phosphate of lime occurs in apatite.
Crystallized apatite is found in Cornwall and Devonshire, England, and in Spain and Bohemia. It is one of the most beautiful of phosphorescent minerals, and when placed upon iron heated just below redness it emits a pale green light. There is generally a small amount of fluoride of calcium present. Bodies known as coprolites, the excrements of fossil reptiles, contain large quantities of phosphate of lime; they are found throughout the lias formation in England, and in all strata which contain the remains of carnivorous reptiles. These bodies resemble oblong pebbles, and have a size corresponding to the cells of the intestines in which they were contained. (See Coprolites.) Phosphate of lime exists in small quantities in all fertile soils, and also in the vegetables which they produce, and through them it finds its way into the bodies of the animals that feed upon them, a fact having an important bearing upon agriculture. Biphosphate of lime (CaP206 or CaO,P203) is formed by digesting phosphate of lime in phosphoric, muriatic, or nitric acid. It is deliquescent, soluble in water, with an acid reaction, and does not crystallize on evaporating the solution. When biphosphate of lime is distilled with charcoal, it yields phosphorus and basic phosphate, the excess of acid being reduced.
Biphosphate of lime is an ingredient of several artificial manures, and is valued as being more immediate in its action than bone ash, and required in smaller quantities. The economy of its use is however questionable. Lime, or the metal calcium, also unites with bromine and iodine, bromic, iodic, chloric, and perchloric acids, forming bromide and iodide, bromate, iodate, chlorate, and per-chlorate of calcium. 12. Nitrate of calcium, or nitrate of lime (CaN03), is conveniently formed when carbonate of lime is dissolved in nitric acid. It is found in old mortars, and sometimes occurs in spring and river waters. It is soluble in alcohol. It fuses on exposure to heat, and on cooling forms a phosphorescent substance called Baldwin's phosphorus. When heated, the nitric acid is driven off and pure oxide of calcium remains. 13. Carbonate of lime (CaC03 or CaO,C02), as has been observed, exists in a native state in limestones and marine shells. It may be formed artificially by passing carbonic acid gas through lime water, or otherwise exposing hydrate of lime to the action of carbonic acid; or by double decomposition of soluble lime salts and carbonates of other metals, as for instance between chloride of calcium and carbonate of potassium, CaCl2 + KC03 = CaC03 + KCl2. When a stream of carbonic acid is passed into a solution of lime water, an insoluble carbonate is at first precipitated, but on continuing the operation the carbonate becomes dissolved, a supercarbonate being formed, which is more soluble.
It also appears that a dicarbonate exists, from the fact that in burning lime one half of the carbonic acid is more easily driven off than the other half. 14. Silicates of lime are found in nature in several forms; apophylite is a hydrated po-tassio-silicate; datalyte and botryolite are hydrated boro-silicates of lime. Silicate of lime also enters into the composition of a large number of native silicates, such as hornblende and augite, and forms an important part of mortars and hydraulic cements. (See Cements, and Concrete.) - Lime is of great importance in agriculture, and is used in several forms, both separately and in combination with various other substances in artificial and farmyard manures. Its use in bone earth has been mentioned. It is a constituent of some of the salts in all the excrements of animals; the ash of nearly all plants contains it in some form, and it is furnished to the soil in the products of their decomposition. One of the principal agricultural uses of lime, however, is not alone to supply the growing plants with their needed constituents, but so to act upon the soil as to unlock its riches to them.
For this purpose it is applied usually in the form of freshly slaked hydrate, which, acting upon the mineral matter, causes decomposition, and moreover favors the decomposition of vegetable matter. Soils which are rich in feldspathic minerals, or those containing silicates of potash and soda, are particularly benefited, after they have been worn, by the application of caustic lime, which acts by combining with the silica, forming a silicate of lime and liberating the alkali, which is now free to enter into the composition of the growing plants. As a rule those soils are the richest (supposing them to contain sufficient organic matter) which are abundantly supplied with alkaline salts. The principles of the agricultural uses of lime are well set forth in Johnston's "Agricultural Chemistry," and also in Liebig's letters and works on chemistry. Other uses of lime and its salts are various. The hydrate is largely used in coating the plastered walls of buildings; by the tanner in removing hair from hides; and by the paper maker, in conjunction with alkaline carbonates, in the preparation of pulp. It acts not only directly upon the vegetable fibre, but also abstracts carbonic acid from the alkali, rendering it caustic.
On account of this action it is also used in the manufacture of caustic potash and soda. The hydrate is also largely consumed in the purification of illuminating gas. (See Gas.) - Tests for Lime and its Salts. Lime water is distinguished from a solution of baryta by not being thrown down by dilute sulphuric and fluosilicic acids. Unlike baryta or strontia, lime is deposited from a saturated solution by boiling. The soluble salts of lime are precipitated by alkaline carbonates and bi-carbonates, and also by oxalic acid and oxalate of ammonia. The latter salt will detect one part of lime in 50,000 of water. Chloride of calcium imparts an orange red color to alcohol flame, which by spectrum analysis is resolved into green and orange bands. - Medical Uses of Lime. Several salts of lime are used in medicine. The hydrate, when mixed with an equal weight of caustic potassa, constitutes the potassa cum calce of the United States Pharmacopoeia, or Vienna caustic. Lime water is often used as an antacid, especially for children. It prevents the too rapid coagulation of the milk used in their food, and has besides a restraining effect upon diarrhoea, so that it is sometimes called astringent.
Combination with sugar renders lime more soluble in water, and a saccharine solution or sirup may be used, which contains a much larger quantity of lime than lime water. Lime water with milk is often used in diseases of the stomach; a combination which is sometimes borne, especially in the nausea of pregnancy, when no other food can be retained. As lime water has some power in dissolving the false membrane of croup, it has been employed in that disease, both by projection of its spray into the fauces, and by the inhalation of the vapor arising from slaking lime. The various carbonates of lime, such as prepared chalk, precipitated carbonate, prepared oyster shells, crabs1 claws, and "crabs' eyes," are used to neutralize acid in the stomach both in indigestion and in poisoning by acids. They are specially called for in oxalic acid poisoning. Chloride of calcium has been used as a tonic, but is less employed than formerly. Phosphate of lime or bone earth has been considerably used in medicine, to increase the supply of this salt for the formation of bone and the promotion of the general nutrition. (See Hypopiiosphites.) - The following works on the uses of lime, besides those already mentioned, may be consulted: Hassenfratz, Traite theorique et pratique de l'art de calciner la pierre calcaire et de fabriquer toutes sortes de matieres, ciments, betons, etc. (Paris, 1825); Vicat, " Treatise on Calcareous Mortars and Cements," translated from the French by J. T. Smith (London, 1837); Dumas, Chimie ap-pliquee aux arts, vols, liv., lv., chap. viii.; Regnault, Cows de chimie, vol. ii. (1849); Burnell, "Treatise on Limes, Cements, Mortars, Concretes," etc. (in Weale's "Rudimentary Series," 1850); Gen. Q. A. Gillmore, "Lime, Hydraulic Cements, and Mortars " (New York, 1872); and Beckwith, " Report on the Hydraulic Lime of Theil" (New York, 1873).
Lime, a fruit resembling a miniature lemon, produced by a species or variety of citrus. As mentioned under Lemon, there is great difficulty in defining the species of citrus, and some botanists incline to regard nearly all the cultivated ones as forms of C. medica. The books generally refer the lime to C. limctta, but that produces a very different fruit from the one known in our commerce as the lime; some authors refer our fruit to G. lima, others to C. acida, while Grisebach ("Flora of the British West Indies ") regards it as a dwarf, spiny, and small-fruited variety (var. spinosis-sima) of the common orange, C. aurantium; it is considered as indigenous to the West Indies, and is there used as a beautiful and serviceable hedge plant. The fruit varies much in size, sometimes being only an inch long; the skin is thin, greenish yellow, and the abundant juice very sour, with a slight bitterness; the juice is used for the same purposes as lemon juice. Large quantities of lime juice are exported from the West Indies for the manufacture of citric acid, and for use as an anti-scorbutic upon long sea voyages.
For the botanical characters of the genus, see Orange.