318 METALS AND THEIR COMBINATIONS. 



by the union of H* ions with (OH)' ions of the alkali. The equation in sim- 

 ple form is written, 9 

 Zn(OH) 2 + 2XaOH = Na. 2 ZnO 2 -f 2H 2 O. 



Cadmium, Cd = 111.6. 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 chemical properties. Cadmium differs from zinc by 

 forming a yellow sulphide (with hydrogen sulphide), insoluble in diluted acids. 

 Cadmium and its compounds are of little interest here; the yellow sulphide is 

 used as a pigment, the sulphate and iodide sometimes for medicinal purposes. 



Cadmium is a constituent of many alloys distinguished by very low fusing 

 points. 



30. LEAD -COPPER -BISMUTH. 



General remarks regarding the metals of the lead group. The 

 six metals belonging to this group (Pb, Cu, Bi, Ag, Hg, and Cd) are 

 distinguished by forming sulphides which are insoluble in water, 

 insoluble in dilute mineral acids, insoluble in ammonium sulphide ; 

 consequently they are precipitated from neutral, alkaline, or acid 

 solutions by hydrogen sulphide or ammonium sulphide. 



The metals themselves do not decompose water at any temperature, 

 and are not acted upon by dilute sulphuric acid ; heated with strong 

 sulphuric acid, most of these metals are converted into sulphates with 

 liberation of sulphur dioxide ; nitric acid converts all of them into 

 nitrates with liberation of nitric oxide. 



The oxides, iodides, sulphides, carbonates, phosphates, and a few of 

 the chlorides and sulphates of these metals are insoluble ; all the 

 nitrates, and most of the chlorides and sulphates are soluble. 



In regard to valence, they show no uniformity whatever, silver 

 being univalent, copper, cadmium, and mercury bivalent, bismuth 

 trivalent, and lead either bivalent or quadrivalent. 



Lead, Pb 11 = 2O5.35 (Plumbum). This metal is obtained chiefly 

 from the native lead sulphide (galena), PbS, by first roasting it, 

 whereby part is converted into oxide and sulphate. By heating this 



QUESTIONS. How is zinc found in nature, and by what process is it ob- 

 tained? Mention the properties of metallic zinc, and what is it used for? 

 Mention two processes for making zinc oxide. How does heat act on zinc 

 oxide? Show by chemical symbols the action of hydrochloric and sulphuric 

 acids on zinc. State the properties of chloride and of sulphate of zinc. AVhat 

 is white vitriol? Explain the formation of precipitated zinc carbonate, and 

 state its composition. Mention tests for zinc compounds. How many pounds 

 of crystallized zinc sulphate may be obtained from 21.7 pounds of metallic 

 zinc? i 



