Page:The New International Encyclopædia 1st ed. v. 12.djvu/303

lilME. 273 LIMEN. with a lliinner rind. The plant is a native of India and China, cultivated in the south of Kuiope, the West Indies, and Florida, where it is frequently found as an escape. The lime is chiefly valued as a source of citric acid, and for limejuioe, which is extensively used on ship- board as an anti-scorbutic. It is also used to make limeade, a pleasant beverage. The limes on the American markets are mostly derived from Fhu'ida or llie West Indies. The lime is projia- gated by cuttings or buds like the lemon, and re- quires similar treatment as an orchard jiiant. See Colored Plate of Citkus Fkuits. LIME, or Calcium Oxide, CaO. A well-known compound of calcium and oxygen, produced by healing some form of calcium carbonate or cal- cium nitrate. Being an 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, calc-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 out 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 time, accele- rates the process very elTectively. 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 Hoft'- mann kiln. (See Kiln.) Nearly as elfici<'nt. and more generally used, are vertical chamber kilns. (See KiL.N, section Continuous Kilns.) The kilns may 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 3.1o. It is not afTeeted by heat. When brought into contact with water, it forms the hydroxide Ca(OH),. commonly known as slnchcd lime, the ease with which the transformation takes place depending largely upon certain de- tails of the pi'ocess employed in making the quick- lime, such as the duration of the process, the degree of temperature, etc. Calcium hydroxide has a much lower specific gravity (2.0S) than quicklime. When .shaken up in water, it remains in suspension for a considerable length of time, forming what is known as 'milk of lime.' A small amount of the lime actually goes into solu- tion, and on filtering may be precipitated by carbonic-acid gas, with which the hydroxide read- ily forms calcium carbonate, while quickliiiie refuses to absorb the gas at ordinary tempera- tures. Unlike that of most other substances, the solubility of lime in water decreases as the temperature increases, and hence clear 'lime- water' becomes turbid when boiled. When mixed with peroxide of hydrogen, lime-water yields an unstable hydrated calcium peroxide, CaO,.8H,0, which separates out in the form of minute crystals. Lime is used for a variety of purpo.ses in the arts. It was formerly much used in the manu- facture of sugar, the latter forming with it a clicmical compound that can be readily sepa- rated 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 liuihling imrposes, and in manufac- turing artificial stone and glass. It is also often (■midoyed 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-w'ater (sometimes mixed with glycerin), lime liniment ('carron oil,' made by nii.xing equal volumes of lime-water and lin.seed oil), syrup of lime (made uj) of lime, sugar, and water), and Vienna paste (lime and caustic ])otash). The last-named preparation is often used as a caustic for the removal of warts. Lime liniment is used for burns, although a strong solution of picric acid (q.v. ) is preferred by many. A mixture of lime-water with glycerin is useful in weeping eczema. Lime-water ( with milk) is also often administered internally, espe- cially for the purpose of allaying vomiting in in- fants. The carl)onic-acid gas ])rodiiced in the manufacture of lime may be collected and utilized. (See Carhonic-Acid Gas.) Consult: Frash, "Lime and Lime Burning," in 77ie Mincrul Indus- try (New York, 1899) ; Burnell. Iiudimmlur;/ Treatise on JAmes, etc. London. 1887) : Gillmore. .1 Practical Treatise on Limes (New York. 1896). For information on the carbonates of lime, see Limestone; Marrle; Cai.cite; Icelano Spar; and Aqueous Rocks. For the sulphate of lime, sec Oypsum and Sulphuric .Acid. For the nitrate of lime, see Nitric Acid. For the phosphates of lime, si'c I'UOSPHORIS: Fertiuzkk.'S. I'or chloride of lime, see Bleaciiinq-Powdee. LIME, Chloride of. See Hypociilorous .Acid ; BLEAniiNfi-PowDER. LIME LIGHT. See Drummoxd Lioiit. LI'MEN (Lat.. threshold). A met.aphorical expression introduced into psychology by Herbart. The ideal boundary or limit, which ideas or representations ma}' be said to cross on becom- ing conscious, was termed by him the 'limcn of consciousness.' The word was then transferred by Fechncr to psychophysics. where it is em- ployed in two principal connections. ( 1 ) The eft'ect of a stimulus upon the organism may, for various reasons, be so slight as to produce no change in consciousness. A sound may be too faint, a point of light too small, a scent too weak, to arouse the corresponding sensation : or. on the afl'ective side, an occurrence in the outside world mav be of so little importance to us that we take it indifferently, are not 'affected' by it