LIME, or CALCIUM OXIDE, CaO. A well-known compound of calcium and oxygen,- produced by heating some form of calcium carbonate or cal cium aitrate. Being all energetic base, lime readily combines with acids, even carbonic acid, and hence is not found free anywhere in nature. The forms of calcium carbonate technically used for the manufacture of lime, all more or less im pure, include limestone, marble, cab-spar, sea shells, etc. The best lime is yielded by the, densest limestones, the quality of the lime de pending further upon the duration of the heat ing process and the degree of heat to which the limestone is subjected. The heating process is carried nut in kilns, a good draught. being re quired to render it effective. It is well that the limestone should contain a certain amount of moisture, the latter aiding the decomposition of the carbonate., Various methods have been de vised for adding moisture to the carbonate dur ing the process of heating; thus, a current of steam passed over the carbonate, or a spray of water thrown upon it from time to thne, accele rates the process very effectively. The limestone was formerly heated in heaps or ditches, but at present this is scarcely ever practiced on a large scale, the process being carried out in either intermittent, or continuous kilns, the type of which is chosen according to the available fuel. The most efficient kiln is the ring kiln, or Iloff mann kiln. (Sec KILN.) Nearly as efficient. and more generally used, are vertical chamber kilns. (See KILN. section Continuous Kilns.) The kilns nay be provided with fireplaces, the fuel and the limestone being separated : or else there may be no separate fireplace, the limestone being charged together with the fuel. The latter form of kilns is convenient for most ordinary purposes: but if it is desired to produce a lime of high quality and of a pure white color, fireplace kilns alone should be employed. An economical form of kiln largely used at present is the iron-shell draw kiln, which holds the materials in a shell of heavy tank-iron.
Pure calcium oxide (quicklime. or burned lime) is a perfectly white substance having the specific gravity 3.15. It is not affected by heat. When 1»-ought into contact with water, it forms the hydroxide Ca commonly known as slacked lime, the ease with which the transformation takes place depending largely upon certain de tails of the process employed in the quick lime, such as the duration of the process, the degree of temperature, etc. Calcium hydroxide has a much lower specific gravity (2.05) than quicklime. When shaken up in water, it remains in suspension for a considerable length of time, forming what is knwn as 'milk of lime.' A
small amount of the lime actually goes into solu tion, and on filtering may he precipitated by carbonic-acid gas, with which the hydroxide read ily forms calcium carbonate, while quicklime refuses to absorb the gas at ordinary tempera tures. I vnlike that of most other substances. the solubility of lime in water decreases as the temperature increases. and hence clear 'lime water' becomes turbid wino boiled. Mien mixed with peroxide of hydrogen, lime-water yields an unstable hydrated calcium pc ro.ride, Cat),.311,0, which separates out in the form of minute crystals.
Lime is used for a variety of 1)119)05(.5 in the arts. It was formerly much used in the manu facture of sugar, the latter forming with it a chemical compound that can be readily sepa 1 tted from the molasses and purified. To reob tain the sugar, the lime compound was treated with carbonic-acid gas, which combined with the lime and set free the sugar. At present. how ever, strontia is generally used instead of lime. Lime is extensively used in making, mortars and cements for building purposes, and in manufac turing artificial stone and glass. It is also often employed as a medicinal agent, being prepared for this purpose from the purest varieties of calcium carbonate. It is prescribed mainly in the forms of lime-water (sometimes mixed with glycerin), lime liniment ('earron oil,' made by nixing equal volumes of lime-water and linseed oil), syrup of Hine (made up of lime, sugar. and water), and Vienna paste (lime and caustic potash). The last-named preparation is often used as a caustic for the removal of warts. I.ime liniment is used for burns, although a strong solution of pieric acid (q.v.) is preferred by many. A mixture of lime-water with glycerin is in weeping eczema. Lime-water (with milk) is also often administered internally. espe eMlly for the purpose of allaying vomiting in in fants. The carbonic-acid gas protiumd in the manufacture of lime may he collected and utilized. (See CAnnoxiC-AcmO GAS.) Consult: Frash, "Lime and Lime Burning," in Mineral Indus try York, ISO9)) ; Burnell, Rudimentary Treatise on. Limes, etc. London, t;illan1re, .1 Practical 7'reatise on Limes (New York, 1396). For information on the carbonates of limo. see 1.I\IEsToNE; iNlARnu.E; CALCITE ICELAND SPAR; and AQUEOUS ROCKS. For the sulphate of lime, see Gypsum and SCLrIIURIC ACM. For t he nitrate of lime, see NITRIC ACID. For the phosphates of lino'. soe FERTILIZERs. For chloride of lime, see BLEAcitING-PownEs.