LEAD COPPER BISMUTH. 321 



Lead nitrate, Plumbi nitras, Pb(NO 3 ) 2 328.49. Obtained by 

 dissolving the oxide in nitric acid : 



PbO + 2HN0 3 = H 2 + Pb(N0 3 ) 2 . 



Lead nitrate is the only salt of lead (with a mineral acid) which is 

 easily soluble in water ; it has a white color, and a sweetish, astrin- 

 gent, and afterward metallic taste. It is insoluble in strong nitric 

 acid ; hence lead is insoluble in this acid. 



Experiment 39. Heat 30 c.c. of dilute nitric acid, but not to the boiling- 

 point, and dissolve in it, with stirring, small portions of lead oxide, until no 

 more is taken up. Filter the solution if necessary, and let it cool to crystallize. 

 If no crystals form, concentrate further. The crystals are octahedra. Examine 

 their appearance and form. Which one of the methods of forming salts does 

 this experiment illustrate ? 



Heat some of the dried and powdered crystals in a porcelain crucible mod- 

 erately. Note the brown fumes of nitrogen tetroxide and residue of brown lead 

 oxide, which becomes yellow on cooling. This experiment illustrates the 

 instability of most nitrates when heated, and the method by which some oxides 

 are obtained : 



Pb(N0 3 ) 2 = PbO + N 2 4 + O. 



Lead carbonate, PbCO 3 , occurs in nature as the mineral cerussite, 

 and may be obtained by precipitation of a lead acetate solution with 

 sodium bicarbonate. While this normal salt is scarcely used, the basic 

 lead carbonate or white lead of the approximate composition 2PbCO 3 . 

 Pb(OH) 2 is used very largely as a constituent of paints. It is man- 

 ufactured on a large scale directly from lead, by exposing it to the 

 simultaneous action of air, carbon dioxide, and vapors of acetic acid. 

 The latter combines with the lead, forming a basic acetate, which is 

 converted into the carbonate (almost as soon as produced) by the 

 carbon dioxide present. 



The action of acetic acid on lead or lead oxide will be considered 

 in connection with acetic acid. 



Lead carbonate is a heavy, white, insoluble, tasteless powder ; the 

 white-lead of commerce frequently is found adulterated with barium 

 sulphate, gypsum or lead sulphate. 



Lead iodide, Plumbi iodidum, PbI 2 = 457.15. Made by adding 

 solution of potassium iodide to lead nitrate (Plate III., 6) : 

 Pb(NO 3 ) 2 + 2KI = 2KNO S + PbI 2 . 



It is a heavy, bright yellow, almost insoluble powder, which ma/ 

 be distinguished from lead chromate by its solubility in ammonium 

 chloride solution on boiling, lead chromate being insoluble in this 

 solution. 



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