LEAD. 163 



cal properties. Cadmium differs from zinc by forming a yellow 

 sulphide (with hydrosulphuric acid), soluble in diluted acids. 

 Cadmium and its compounds are of little interest ; the yellow 

 sulphide is used as a pigment, the sulphate and iodide some- 

 times for medicinal purposes. 



QUESTIONS. 



261. How is zinc found in nature, and by what process is it obtained ? 



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



263. Mention two processes for making zinc oxide. 



264. How does heat act on zinc oxide? 



265. Show by chemical symbols the action of hydrochloric and sul- 

 phuric acids on zinc. 



266. State the properties of chloride and sulphate of zinc. 



267. What is white vitriol ? 



268. Explain the formation of precipitated zinc carbonate, and state 

 its composition. 



269. Mention tests for zinc compounds. 



270. How many pounds of crystallized zinc sulphate may be ob- 

 tained from 22.63 pounds of metallic zinc? 



28. 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 diluted mineral acids, insoluble in ammonium 

 sulphide ; they are consequently precipitated from neutral, 

 alkaline, or acid solutions by hydrosulphuric acid or ammonium 

 sulphide. 



The metals themselves do not decompose water at any tem- 

 perature, and are not acted upon by diluted 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 

 nitrogen dioxide. 



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. 



