314 METALS AND THEIR COMBINATIONS. 



Zinc chloride, Zinci chloridum, ZnCl 2 = 135.26. Made by dis- 

 solving zinc or zinc carbonate in hydrochloric acid and evaporating 

 the solution to dryness : 



Zn + 2HC1 = ZnCl 2 + 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 115C. (239 F.), and is volatilized, with partial 

 decomposition, at a higher temperature. 



Liquor zinci chloridi, U. S. P., is an aqueous solution of zinc chloride, con- 

 taining 50 per cent, of the salt. 



Zinc oxychloride is used extensively for dental purposes, and is made by 

 mixing zinc oxide with a strong solution of zinc chloride. At first a plastic 

 mass forms, which rapidly hardens. The proportions in which the two sub- 

 stances are mixed differ widely, the weights corresponding all the way from 3 

 to 9 molecules of zinc oxide for each molecule of zinc chloride. Whether or 

 to what extent the oxychloride of zinc is a true chemical compound is not 

 known. 



Zinc oxyphosphate is a preparation used similarly to the oxychloride. It 

 is made by mixing zinc oxide with phosphoric acid. The acid used is either 

 ortho- or metaphosphoric acid, or a mixture of both. In all cases a zinc phos- 

 phate is formed, but as the quantity of zinc oxide used is larger than needed 

 for saturating the acid completely, the mass as used by dentists is generally a 

 mixture of zinc phosphate with zinc oxide. 



Zinc bromide, Zinci bromidum, ZnBr 2 = 223.62. Obtained 

 analogously to the chloride by dissolving zinc in hydrobromic acid ; 

 it is a white powder, resembling the chloride in its properties. 



Zinc iodide, Zinci iodidum, ZnI 2 = 316.7. The two elements 

 zinc and iodine combine readily when heated with water ; the color- 

 less solution when evaporated to dryness yields a powder whose 

 physical properties resemble those of the chloride. 



Zinc carbonate, Zinci carbonas prsecipitatus, 2ZnCO 3 .3Zn(OH) 2 

 (Precipitated carbonate of zinc). Solutions of equal quantities of zinc 

 sulphate and sodium carbonate are mixed and boiled, when a white pre- 

 cipitate is formed, which is a mixture of the carbonate and hydroxide 

 of zinc, corresponding more or less to the formula given above. 

 5ZnSO 4 + 5Na 2 CO 3 + 3H 2 O = 3CO 2 + 5Na 2 SO 4 -f 2(ZnCO 3 ).3Zn(OH) 2 . 



Precipitated zinc carbonate is a white, impalpable powder, odorless 

 and tasteless, insoluble in water, soluble in acids and in ammonia water. 



Experiment 37. Dissolve 10 grammes of the zinc sulphate obtained in Experi- 



