Page:The American Cyclopædia (1879) Volume X.djvu/485

LIME 479 a corresponding phosphate of lime precipi- tates. 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 red- ness it emits a pale green light. There is gen- erally a small amount of fluoride of calcium present. Bodies known as coprolites, the ex- crements of fossil reptiles, contain large quan- tities of phosphate of lime; they are found throughout the lias formation in England, and in all strata which contain the remains of car- nivorous reptiles. These bodies resemble ob- long pebbles, and have a size corresponding to the cells of the intestines in which they were contained. (See COPEOLITES.) 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 agri- culture. Superphosphate or acid phosphate of lime (H 4 Ca2PO4) is formed by digesting phos- phate 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 phos- phorus and basic phosphate, the excess of acid being reduced. Superphosphate 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 quanti- ties. The economy of its use is however ques- tionable. 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 (Ca2NOs), 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 (CaCO 3 or CaO,CO 2 ), as has been ob- served, 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 decompo- sition of soluble lime salts and carbonates of other metals, as for instance between chloride of calcium and carbonate of potassium, CaCla -f K 2 CO 3 = CaCp 3 +KCl. When a stream of carbonic acid is passed into a solution of lime water, an insoluble carbonate is at first precipi- 498 VOL. x. 31 tated, but on continuing the operation the car- bonate 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 hy- drated boro-silicates of lime. Silicate of lime also enters into the composition of a large num- ber of native silicates, such as hornblende and augite, and forms an important part of mortars and hydraulic cements. (See CEMENTS, . and CONOEETE.) Lime is of great importance in agriculture, and is used in several forms, both separately and in combination with vari- ous other substances in artificial and farmyard manures. Its use in bone earth has been men- tioned. 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 mat- ter, causes decomposition, and moreover favors the decomposition of vegetable matter. Soils which are rich in f eldspathic 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 agri- cultural uses of lime are well set forth in John- ston'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 GAB.} Tests for Lime and its Salts. Lime water is distinguished from a solution of ba- ryta by not being thrown down by dilute sul- phuric 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, arid also by oxalic acid and oxalate