Page:The American Cyclopædia (1879) Volume XVI.djvu/848

 818 ZINC der, dusted externally upon excoriations, &c., as a niild astringent and exsiccant. The na- tive carbonate, or smithsonite, formerly called calamine, one of the principal ores, is consid- ered below. Zincic chloride, or butter of zinc, ZnCU, is prepared by heating zinc in chlorine gas, or by dissolving it in muriatic acid. In the latter case hydrogen escapes, and the chlo- ride is left in the solution, which upon heat- ing gives off steam, until at 250 0. (482 F.) the anhydrous salt remains. But this is still fluid, and may be heated up to 371 0. (700 F.) without great volatilization. Hence this substance is used in the laboratory as a heat- ing bath for high temperatures. Pure zincic chloride is a white, semi-transparent, waxy substance, fusible, deliquescent, corrosive to the skin, and possessing even in weak solution a burning, nauseous, saline taste. It is em- ployed internally as an alterative and anti- spasmodic (in over doses, a corrosive poison, for which the alkaline carbonates are anti- dotes), and externally as a caustic, by some considered superior to argentic nitrate. In concentrated solution it is an antiseptic and preservative of vegetable fibre against decay. (See DISINFECTANTS, and PRESERVATION OF WOOD.) It absorbs ammonia freely, and unites with alkaline chlorides to form double chlo- rides, and with ZnO to form oxy chlorides. A concentrated solution of zincic ammonic chlo- ride is used to clean the surfaces of metals be- fore soldering, by removing the metallic ox- ides. A solution of zincic chloride containing iodine and potassic iodide is recommended in microscopy for giving to the cellulose of vege- table objects (for instance, to cotton) a violet or blue tint, without injury to their structure. An artificial filling for teeth ("bone filling") is made by intimately mixing one part of very fine glass powder with three parts of pulverized zinoic oxide ; then, in a different vessel, prepar- ing a concentrated solution of zincic chloride, to which about 2 per cent, of hot concentrated borax solution is added. With the compound solution, the powder is moistened to a paste just before using. In a few minutes (the bo- rax serving merely to retard the reaction somewhat) the mass " sets," by reason of the formation of oxy chloride, which, together with the glass powder, presents a degree of hard- ness at least equal to that of marble. Zincic sulphate, or white vitriol, occurs in mine wa- ters or as efflorescence in mines, where the sulphide (zinc blende) is among the ores. It is produced for use in the arts by calcining zinc blende in heaps, leaching, evaporating, crystallizing, &c. The commercial salt may contain sulphates of iron, copper, manganese, magnesia, or lime. Large quantities of the solution of zincic sulphate are produced in tel- egraph and other galvanic batteries in which dilute sulphuric acid acts upon metallic zinc. Its crystals are rhombic prisms, colorless, transparent, very soluble in water, and slight- ly efflorescent in the air. If prepared by slow evaporation, they are large; but when crys- tallized from a very concentrated solution, or stirred during the process, they appear as fine needles, like those of Epsom salts (magnesic sulphate), with which zinc vitriol is isomor- phous. They have a sharp metallic taste. Ordinarily the crystallized salt contains seven equivalents of water; but crystals can be formed with only six, five, two, and one. At 100 0. (212 F.) six equivalents escape, the last equivalent going only at higher tempera- ture. The number of parts of the sulphate dissolved by 100 parts of water at different temperatures is as follows: Centigrade. Fahrenheit. Anhydrous ult. CryitaU. 10' 20' so- so* 100 50 68* 86" 122' 212* 48-86 63-10 58-50 63-75 95-60 188-21 161-5 191-0 268-8 653-6 The great increase in the solubility of the crys- tals at the higher temperatures is due to their melting in their own water of crystallization. Medicinally zincic sulphate is tonic, astrin- gent ; in large doses a prompt emetic ; in over doses, an irritant poison, which, if not ex- pelled by vomiting, may be counteracted with bland drinks in largo quantities and the ad- ministration of opium. The solution is used externally as a styptio to bleeding surfaces, as a collyrium in diseases of the eye, as a gar- gle for ulcerated sore throat, and as an injec- tion upon inner excoriated surfaces. It is used as a mordant in cotton printing, and as a dryer for oil paints. It is the substance from which numerous zinc compounds are prepared. Its property of decomposing at high tempera- ture and leaving zincic oxide is made the basis of the preparation of the mixed zinc colors, in the various shades of which iron, manga- nese, cobalt, copper, nickel, and silver play a part. Zincic acetate is a medicinal prepara- tion similar in properties and uses to the sul- phate, and likewise employed as a mordant. History. The ancient Greeks and Romans made brass from ores of zinc and copper, but were not familiar with metallic zinc. Strabo speaks of a metal called "false silver," obtained by cal- cining and then melting with a certain earth a stone found near Andeira in the Troad. This metal, melted with copper, produced oricTutlcum, apparently the brass of the an- cient Romans, of which the coins of the com- mencement of the Christian era are composed. Some imperial Greek coins of the 2d century also contain zinc, though the Greek bronze was usually made of copper and tin, occasion- ally with some lead. Pliny speaks of an ore called cadmia, used in the smelting of copper (probably a mixture of the carbonates or sul- phides of copper and zinc), and describes the white, flocculent sublimate (pompholyx, zincic oxide) and the dense incrustation (spodos, now called cadmia or furnace calamine) forming