LIME. CaO. Syn. Oxide of calcium; Chaux, Fr.; Kalk, Ger. Lime, when pure, and as a chemical and medical reagent, will be found treated of under Calcium (Oxide of). It is prepared on the large scale for commerce by calcining chalk, marble or limestone, in kilns, and is called quicklime, caustic lime, burnt lime, stone lime, &c. The lime kilns are usually of the form of an inverted cone, and are packed with alternate layers of limestone and fuel, and the burnt lime raked out from the bottom. The lime thus obtained is a pale yellow powder, combining eagerly with water, and crumbling to a light white powder, “slaked lime,” with the evolution of much heat. Lime which slakes well is termed “fat lime,” while if it slakes badly is termed “poor lime.” The slaked lime, the Calcis hydras of the B. P., is fresh lime sprinkled with water till it falls to powder.
Lime, Salts of. See under Calcium.
Lime, Pyrolignite of. An impure acetate of calcium used for making mordants in dyeing and calico printing, as a substitute for the more expensive acetate of lead.
Lime, Chloride of. Syn. Bleaching powder, Chlorinated lime, Hypochlorite of calcium.
This article was formerly believed to be a compound of lime and chlorine (CaO.Cl), and consequently received the name of ‘chloride of lime.’ We now know, however, that it is not a definite substance, but a mixture of calcium hypochlorite, calcium chloride, and calcium
hydrate. The value of this preparation is due to the readiness with which the calcium hypochlorite is decomposed by acids, even by the carbonic acid of the air, with the evolution of hypochlorous acid which abstracts hydrogen from many vegetable colouring matters, badly smelling gases, &c.: the former are thereby bleached and the latter deodorised.
Chloride of lime is most extensively used for bleaching linen, calico, and similar fabrics, thousands of tons being made near Newcastle alone every year. It is also largely employed as a deodoriser.
Prep. Freshly slaked lime is thinly spread out in a proper vessel and exposed to an atmosphere of chlorine gas until it is saturated. Now included in the Materia Medica.
Slaked lime (fresh), 20 parts, common salt, 1 part, are mixed together, and the powder placed in long earthenware vessels into which chlorine is passed until the mixture begins to grow damp, or until one part of it, dissolved in 130 parts of water, is capable of decolouring 41⁄2 parts of sulphate of indigo (see Chlorimetry), when the whole is transferred to dry bottles.
(Wholesale.) The chlorine is generated from the usual materials mixed in leaden vessels, heated by steam, and the gas, after passing through water, is conveyed by a leaden tube into an apartment built of siliceous sandstone, and arranged with shelves or trays, containing dry fresh slaked lime, placed one above another, about an inch asunder. The process, to produce a first-class article, is continued for 4 or 5 days. During this time the lime is occasionally agitated by means of iron rakes, the handles of which pass through boxes of lime placed in the walls of the chamber, which thus act as valves.