Quicklime—

Lime burning formerly took place in holes in the ground and kilns with wood, coal or peat as fuel, in which the limestone covered the fuel. These developed into the so-called shaft kilns . Limestone is ground into coarse particles (0 = ca. 60 to 120 mm) and loaded layer-wise with coal in the shaft kiln. The burning of the mixed-in coal produces a temperature of 900 to 1100°C, whereupon carbon dioxide is liberated. 

In addition to the different shaft kiln types, rotary kilns are often used for lime burning. This enables good quality quicklime to be obtained with cheap fuels. Smaller limestone particles (10 to 60 mm) are utilized. 

Calcimatic furnaces (rotary grate kilns) consist of a circulating grate on which the product to be burnt is fed as a thin layer through a stationary heating zone. Since the product is not moved during the calcining, very fine limestones can be burnt in these kilns. 

Dorr-Olivier have developed a unit in which the burning proceeds in a fluidized bed. 

In floating gas furnaces, the reaction is carried out in cyclones connected in series. This produces very reactive quicklime. 

---

Some carbonates are important industrial chemicals. Calcium carbonate occurs naturally in several forms, including limestone, and is used in the production of quicklime, calcium oxide CaO, slaked (or hydrated) lime, calcium hydroxide Ca(OH)2 and cement. 

It is best prepared by heating an intimate mixture of solid ammonium chloride and quicklime ... 

After drying over quicklime, calcium oxide CaO, the ammonia is collected by upward delivery. (N.B. Both of the common drying agents, calcium chloride and concentrated sulphuric acid, combine with the gas.)... 

Chemical methods may be employed if the reagent attacks only one of the components. Thus quicklime may be employed for the removal of water in the preparation of absolute ethyl alcohol. Also aromatic and unsaturated hydrocarbons may be removed from mixtures with saturated hydrocarbons by sulphonation. 

Sodium and potassium hydroxides. The use of these efficient reagents is generally confined to the drying of amines (soda lime, barium oxide and quicklime may also be employed) potassium hydroxide is somewhat superior to the sodium compound. Much of the water may be first removed by shaking with a concentrated solution of the alkali hydroxide. They react with many organic compounds (e.g., acids, phenols, esters and amides) in the presence of water, and are also soluble in certain organic liquids so that their use as desiccants is very limited... 

Alcohols Anhydrous potassium carbonate anhydrous magnesium or calcium sulphate quicklime. 

Organic bases (amines) Solid potassium or sodium hydroxide quicklime barium oxide. 

Absolute ethyl alcohol. Ethyl alcohol of a high degree of purity is frequently required in preparative organic chemistry. For some purposes alcohol of ca. 99 -5 per cent, purity is satisfactory this grade may be purchased (the absolute alcohol of commerce), or it may be conveniently prepared by the dehydration of rectified spirit with quicklime. Rectified spirit is the constant boiling point mixture which ethyl alcohol forms with water, and usually contains 95 6 per cent, of alcohol by weight. Wherever the term rectified spirit is used in this book, approximately 95 per cent, ethyl alcohol is to be understood. 

Extremely dry (or super-dry ) ethyl alcohol. The yields in several organic preparations e.g., malonic ester syntheses, reduction with sodium and ethyl alcohol, veronal synthesis) are considerably improved by the use of alcohol of 99-8 per cent, purity or higher. This very high grade ethyl alcohol may be prepared in several ways from commercial absolute alcohol or from the product of dehydration of rectified spirit with quicklime (see under 4). 

Ammonia. Small quantities of ammonia may be prepared with the aid of the apparatus depicted in Fig. II, 48,4. Concentrated ammonia solution (sp. gr. 0-88) is gently heated in the flask surmounted by an efficient reflux condenser. The gas is dried by passage through the tower which is loosely packed with soda lime or quicklime, and is then passed... 

The tert.-butyl alcohol should be dried over quicklime or anhydrous calcium sulphate and distilled. 

Place 200 ml. of absolute ethyl alcohol in a 500 ml. aU-glass wash bottle, and cool to — 5° by immersion in a bath of ice and salt. Pass a slow stream of ammonia, derived from a cylinder and dried by passage through a tower filled with small pieces of quicklime, into the alcohol until the... 

Recovery of the wopropyl alcohol. It is not usually economical to recover the isopropyl alcohol because of its lo v cost. However, if the alcohol is to be recovered, great care must be exercised particularly if it has been allowed to stand for several days peroxides are readily formed in the impure acetone - isopropyl alcohol mixtures. Test first for peroxides by adding 0-6 ml. of the isopropyl alcohol to 1 ml. of 10 per cent, potassium iodide solution acidified with 0-6 ml. of dilute (1 5) hydrochloric acid and mixed with a few drops of starch solution if a blue (or blue-black) coloration appears in one minute, the test is positive. One convenient method of removing the peroxides is to reflux each one litre of recovered isopropyl alcohol with 10-15 g. of solid stannous chloride for half an hour. Test for peroxides with a portion of the cooled solution if iodine is liberated, add further 5 g. portions of stannous chloride followed by refluxing for half-hour periods until the test is negative. Then add about 200 g. of quicklime, reflux for 4 hours, and distil (Fig. II, 47, 2) discard the first portion of the distillate until the test for acetone is negative (Crotyl Alcohol, Note 1). Peroxides generally redevelop in tliis purified isopropyl alcohol in several days. 

Its natural and prepared compounds are widely used. Quicklime (CaO), which is made by heating limestone that is changed into slaked lime by carefully adding water, is the great base of chemical refinery with countless uses. 

Acid rhodamines are made by the iatroduction of the sulfonic acid group to the aminoxanthene base. The preferred route is the reaction fluorescein (2) with phosphorous pentachloride to give 3,6-dichlorofluoran (fluorescein dichloride) (23), which is then condensed with a primary aromatic amine in the presence of 2inc chloride and quicklime. This product is then sulfonated. For example, if compound (23) (fluorescein dichloride) is condensed with aniline and the product is sulfonated. Acid Violet 30 Cl45186) (24) is produced. 

In North America, quicklime was produced locally as early as 1635 in Rhode Island. It was not until 1733, when lime was shipped by boatioad from Rockland, Maine, to Boston, that lime manufacture was estabUshed as a significant iadustry in commerce. The commercial hydration of lime is a relatively recent development initiated in 1904. Technical progress has allowed the industry to advance rapidly during the latter part of the twentieth century. 

The term lime also has a broad coimotation and frequently is used in referring to limestone. According to precise definition, lime can only be a burned form quicklime, hydrated lime, or hydraiflic lime. These products are oxides or hydroxides of calcium and magnesium, except hydraiflic types in which the CaO and MgO are chemically combined with impurities. The oxide is converted to a hydroxide by slaking, an exothermic reaction in which the water combines chemically with the lime. These reversible reactions for both high calcium and dolomitic types are Quicklime... 

Ca(OH)2 + heat high calcium high calcium quicklime hydrate... 

Mir-slaked lime contains various proportions of the oxides, hydroxides, and carbonates of calcium and magnesium which result from excessive exposure of quicklime to air that vitiates its quaUty. It is partially or largely decomposed quicklime that has become hydrated and carbonated. 

Mvailable lime, the total free lime (ie, CaO) content in a quicklime or hydrate, is the active constituent of a lime. It provides a means of evaluating the concentration of lime. 

Dead-burned dolomite is a specially sintered or double-burned form of dolomitic quicklime which is further stabilized by the addition of iron oxides. Historically, it was used as a refractory for lining steel furnaces, particularly open hearths, but as of this writing is used primarily in making dolomite refractory brick (see Refractories). 

Fluxing lime is lump or pebble quicklime used as flux in steel (qv) manufacture the term may also be appHed more broadly to include fluxing of nonferrous metals and glass (qv). It is a type of chemical lime. 

Ground burnt lime refers to ground quicklime used for agricultural liming. 

Hard-burned lime is a quicklime that is calcined at high temperature and is generally characterized by relatively high density and moderate-to-low chemical reactivity. 

Dump lime is a physical shape of quicklime, derived from vertical kilns. 

PefractoTy lime is synonymous with dead-burned dolomite, an unreactive dolomitic quicklime, stabilized with iron oxides, that is used primarily for lining refractories of steel furnaces, particularly open hearths. 

Many lime plants are able to reduce the impurities in their lime product by careful screening and selecting of stone for burning. Because 9 kg of limestone produce only 5 kg of quicklime, the percentage of impurities in a quicklime is nearly double that in the original stone. Analyses of typical samples of high calcium, magnesian, and dolomitic limestones found in the United States are Hsted in Table 1. 

Quicklime is usually white of varying intensity, depending on chemical purity some species possess a slight ash-gray, buff, or yellowish cast. Invariably quicklime is lighter in color than the limestone from which it is derived. Hydrated limes, except for hydrauHc and impure hydrates, are extremely white in color, invariably whiter than their quicklimes. 

Texture. All limestones are crystalline, but there is tremendous variance in the size, uniformity, and arrangement of their crystal lattices. The crystals of the minerals calcite, magnesite, and dolomite are rhombohedral those of aragonite are orthorhombic. The crystals of chalk and of most quick and hydrated limes are so minute that these products appear amorphous, but high powered microscopy proves them to be cryptocrystalline. Hydrated lime is invariably a white, fluffy powder of micrometer and submicrometer particle size. Commercial quicklime is used in lump, pebble, ground, and pulverized forms. 

---