LEAD- COPPER- BISMUTH. 185 



28. LEAD -COPPER-BISMUTH. 



General remarks regarding 1 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 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. 



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 = 206.4 (Plumbum). This metal is obtained almost 

 exclusively from the native sulphide of lead, called galena, PbS, by 

 roasting until it is converted into oxide, and smelting this with coke 

 in a blast furnace. 



Lead owes its usefulness in the metallic state chiefly to its softness, 

 fusibility, and resistance to acids, which properties are of advantage 

 in using it for tubes or pipes, or in constructing vessels to hold or 

 manufacture sulphuric acid. Lead is a constituent of many alloys, 

 as, for instance, of type-metal, solder, britannia metal, shot, etc. 



Experiment 31. Dissolve 1 gramme of lead acetate or lead nitrate in about 

 200 c.c. of water, suspend in the centre of the solution a piece of metallic zinc 

 and set aside. Notice that metallic lead is deposited slowly upon the zinc in a 

 crystalline condition, whilst zinc passes into solution, which may be verified by 

 analytical methods. The chemical change taking place is this : 



Pb(NO 3 ) 2 + Zn = Zn(NO 3 ) 2 + Pb. 



The formation of the crystallized lead is called generally a lead-tree. 



i 



Lead oxide, Plumbi oxidum, PbO = 222.4 (Litharge). Obtained 

 by exposing melted lead to a current of air, when the metal is 

 gradually oxidized with the formation of a yellow powder, known 

 as massicot; at a high temperature this fuses, forming reddish-yellow 



