ZINC. 181 



The liberated metal is vaporized, and distils into suitable receivers, 

 where it solidifies. 



Zinc is a bluish-white metal, which slowly tarnishes in the air, 

 becoming coated with a film of oxide and carbonate ; it has a crys- 

 talline structure and is, under ordinary circumstances, brittle ; when 

 heated to about 130-150 C. (260-302 F.) it is malleable, and 

 may be rolled or hammered without fracture. Zinc thus treated 

 retains this malleability when cold ; the sheet-zinc of commerce is 

 thus made. When zinc is further heated to about 200 C. (392 F.), 

 it loses its malleability and becomes so brittle that it may be pow- 

 dered ; at 410 C. (760 F.) it fuses, and at a bright- red heat it 

 boils, volatilizes, and, if air be not excluded, burns with a splendid 

 greenish -white light, generating the oxide. 



Zinc is used by itself in the metallic state or fused together with 

 other metals (German silver and brass contain it) ; galvanized iron 

 is iron coated with metallic zinc. 



Zinc is a bivalent metal, forming but one oxide and one series of 

 salts, all of which have a white color. 



Zinc oxide, Zinci oxidum, ZnO = 81.1 (Flores zinci, Zinc-white), 

 may be obtained by burning the metal, but if made for medicinal 

 purposes, by heating the carbonate, when carbon dioxide and water 

 escape and the oxide is left : 



3[Zn(OH) 2 J.2ZnCO 3 = 5ZnO + 2CO 2 + 3H 2 O. 



It is an amorphous, white, tasteless powder, insoluble in water, 

 soluble in acids ; when strongly heated it turns yellow, but on 

 cooling resumes the white color. 



Zinc hydroxide, Zn(OH) 2 , is obtained by precipitating zinc salts 

 with the hydroxide of sodium or ammonium ; the precipitate, how- 

 ever, is soluble in an excess of either of the alkali hydroxides. 



Zinc chloride, Zinci chloridum, ZnCl 2 = 135.9. Made by dis- 

 solving zinc or zinc carbonate in hydrochloric acid and evaporating 

 the solution to dry ness : 



Zn + 2HC1 = ZnCl 2 -f 2H. 



It is met with either as a white crystalline powder, or in white 

 opaque pieces ; it is very deliquescent and easily soluble in water 

 and alcohol ; it combines readily with albuminoid substances ; it 

 fuses at about 115 C. (239 F.), and is volatilized, with partial 

 decomposition, at a higher temperature. 



