Page:The American Cyclopædia (1879) Volume X.djvu/484

478 LIME There are several kinds of these kilns, for a description of which the reader is referred to the more strictly technological works. Per- haps the most remarkable property of freshly burned lime is its affinity for water, with which it unites with great violence and evolu- tion of heat, 100 parts of lime by weight re- quiring only 32 parts of water to produce a temperature of 300 F. This combination (slaking) forms a hydrate of the definite com- position CaH 2 O 2 , or CaO,H 2 O. This hydrate is a white soft powder, which gives off water at a red heat, being converted again into quick- lime. It is slightly soluble in water, forming what is called lime water, or aqua calcis. It is more soluble in cold than in hot water ; so that when a saturated solution is boiled some of the lime will be deposited. A much greater quantity than is soluble may be sus- pended in water in the form of milk of lime ; when the mixture is of a creamy consistency it is called cream of lime. According to Dai- ton, lime water saturated at 60, 130, and 212 F. contains one grain of lime to 778, 972, and 1,270 grains of water respectively. A so- lution evaporated in vacuo over oil of*vitriol deposits hydrate of lime in hexagonal prisms. Lime water has the property of precipitating most of the metallic oxides from solutions of their salts, and of forming soapy mixtures with oils. When lime water is exposed to the air, it absorbs carbonic acid and soon becomes covered with a pellicle of carbonate, into which after a time all the lime is converted. Salts. The salts of lime are numerous ; the most im- portant are the following. Hydrate of lime when exposed to the action of chlorine gas forms a mixture of chloride and hypochlorite of calcium. (See BLEACHING POWDER.) 1. Chloride of calcium, formerly called muriate of lime, is found in sea water and in some saline springs, often accompanied by traces of bromine and iodine. It is commonly made artificially by dissolving carbonate of lime in hydro- chloric acid (OaC0 3 or OaO,OO a + 2H01=Ca Cla + HaO + COa). The solution is evapora- ted to dryness and heated to redness to expel moisture. It must be preserved in air-tight bottles, because its attraction for water is so great that it soon becomes moist in the open air. It is on account of this property that it is so extensively used by chemists as a filter through which to pass gases to deprive them of aqueous vapor. It is also used to separate alcohol, ether, and other liquids from a mix- ture by distilling them off. One part of wa- ter at 66 F. will dissolve four parts of dry chloride of calcium, but at 32 not more than two parts; while at 212 it will dissolve an al- most unlimited quantity. It is copiously sol- uble in alcohol, and in the cold crystals are formed containing about 60 per cent, of alco- hol instead of water of crystallization. 2. For fluoride of calcium see FLUOR SPAR. 3. Sul- phide of calcium (CaS) is formed by passing sulphuretted hydrogen (H 2 S) over red-hot lime (CaO + H a S=CaS + H a O). It is also formed by the action of charcoal or hydrogen on sul- Ehate of lime (gypsum) at a red heat. When reshly prepared it is phosphorescent (Can- ton's phosphorus). 4. Bisulphide of calcium (CaS 2 ) is produced by boiling sulphur and hy- drate of lime in equal parts in water ; the so- lution yields on cooling reddish yellow four- or six-sided prisms, which are permanent when dried in vacuo. Their water of crystalliza- tion is 33 '89 per cent., so that their formula is CaSa + 3H 3 O. 5. Pentasulphide of calcium (CaS 5) is a non-crystallizable salt, formed by boiling an excess of sulphur with quicklime and water; it is soluble in alcohol. By the action of heat it loses sulphur and becomes Erotosulphide. 6. For sulphate of lime (Ca 4 ) see GYPSIJM. 7. Sulphite of lime (Ca SOa) is formed by passing sulphurous acid through milk of lime. It is a white powder of sulphurous taste, and requires about 800 parts of water at 60 for solution. It is made soluble by excess of sulphurous acid, and then separates in hexagonal prisms, which dissolve with difficulty, and are converted into sulphate of lime on exposure to the air. 8. Hyposul- phite of lime (CaOSaOa) is formed by tritura-. ting in a mortar crystals of hydrated bisulphide of calcium; also by passing sulphurous acid through the yellow liquor obtained by boiling lime and sulphur in water, filtering, and evap- orating the solution at a temperature not above 140 F. Hexagonal crystals are obtained hav- ing the composition CaOS 2 Oa + 6H 2 0, which are decomposed at the boiling point into sul- phate of lime and sulphur. This salt is em- ployed in photography to remove silver salts. 9. Phosphuret of calcium (Ca 2 Pa) is a brown compound formed by passing the vapor of phosphorus over lime heated to redness. This compound is a mixture of phosphuret of calcium and phosphate of lime ; it decomposes water with the evolution of phosphuretted hydrogen. When lime is heated to redness its oxygen converts a part of the phosphorus into phosphoric acid, and the liberated calcium combines with another portion of phospho- rus to form phosphuret of calcium. 10. Hypo- phosphite of calcium (CaP a O 2 + 2H 2 0) is ob- tained by carefully boiling phosphorus in thin cream of lime, filtering the solution, and passing carbonic acid through it to separate excess of lime. It is also formed by boiling phosphuret of calcium in water, and treating the solution in the same way. When evapo- rated in vacuo, the solution furnishes rectan- gular prismatic crystals of the hyphosphite, insoluble in alcohol, but equally soluble in hot and cold water. 11. Phosphates of lime are definite compounds of lime with phosphoric acid, of which there are several, but the two following are the most important. Common phosphate, tribasic phosphate, or bone earth (Ca 3 2PO 4 ), is a salt found in the mineral king- dom and in bone ash. On adding chloride of calcium to the tribasic phosphate of soda,