162 METALS AND THEIR COMBINATIONS. 



If zinc be added to strong sulphuric acid, no decomposition 

 takes place ; no sufficient explanation has as yet been given for 

 this fact. 



Zinc sulphate forms small, colorless crystals, which are iso- 

 morphous with magnesium sulphate; it is easily soluble in 

 water. 



Zinc phosphide, Zinci phosphidum, Zn 3 P 2 = 256.7 (Phosphide of 

 zinc}. The two elements zinc and phosphorus combine readity 

 when the latter is thrown upon melted zinc, forming a grayish 

 black powder, or minutely crystalline, friable fragments, having 

 a metallic lustre on the fractured surface. 



Antidotes. Soluble zinc salts (sulphate, chloride) have a 

 poisonous effect. If the poison have not produced vomiting, it 

 should be induced. Milk, white of egg, or, still better, some 

 substance containing tannic acid (with which zinc forms an 

 insoluble compound) should be given. 



Analytical reactions. 



1. Add to solution of a zinc salt ammonium sulphide : a 

 white precipitate of zinc sulphide is produced. (Zinc sulphide 

 is the only white insoluble sulphide.) 



ZnSO 4 + (NHJ 2 S = (NH 4 ) 2 S + ZnS. 



2. Add ammonium, sodium, or potassium hydrate : a white 

 precipitate of zinc hydrate, Zn2HO, is produced, soluble in 

 excess of the reagent. 



3. Soluble carbonates and phosphates give white precipitates 

 in neutral solutions of zinc. 



4. Potassium ferrocyanide gives a white precipitate of zinc 

 ferrocyanide. (This test may be used to distinguish compounds 

 of zinc from those of magnesium or aluminium.) 



5. Zinc is the only heavy metal whose compounds are all color- 

 less. The oxide, carbonate, phosphate, and ferrocyanide are in- 

 soluble ; the chloride, nitrate, and sulphate soluble. 



Cadmium, Cd = 111.8. Found in nature associated (though 

 in very small quantities) with the various ores of zinc, with 

 which metal it has in common a number of physical and chemi- 



