166 METALS AND THEIR COMBINATIONS. 



Analytical reactions. 



1. To solution of a lead salt add hydrosulphuric acid or am- 

 monium sulphide: a black precipitate of lead sulphide is pro- 

 duced : 



Pb2N0 3 4- H 2 S = 2HN0 3 + PbS. 



2. Add sulphnric acid or soluble sulphate: a white precipitate 

 of lead sulphate is formed : 



Pb2NO 3 + Na 2 SO 4 = 2NaNO 3 + PbS0 4 . 



3. Add hydrochloric acid or soluble chlorides: a white pre- 

 cipitate of lead chloride is produced, which dissolves on the 

 addition of much water, as lead chloride is not entirely insoluble. 

 For the same reason, the precipitate is not formed when the 

 solutions used are highly diluted. 



4. Other reagents which give precipitates with lead solutions 

 are: 



Potassium chromate, producing yellow lead chromate ^chrome-yellow). 

 Potassium iodide, producing yellow lead iodide. 

 Alkaline carbonates, producing white lead carbonate. 

 Alkaline phosphates, producing white lead phosphate. 



Copper, Cu u = 63.2 (Cuprum). Found in nature sometimes in 

 the metallic state, generally, however, combined with sulphur or 

 oxygen. The commonest copper-ore is copper pyrites, a double 

 sulphide of copper and iron, CuFeS 2 or Cu 2 S.Fe 2 S 3 , having the 

 color and lustre of brass or gold. Other ores are : Copper glance, 

 cuprous sulphide, having a dark gray color and the composition 

 Cu 2 S; malachite, a beautiful green mineral, being a carbonate 

 and hydrate of copper, CuC0 3 .Cu2HO. The cupric and cuprous 

 oxide are also occasionally found. 



Copper is the only metal showing a distinct red color; it is so 

 malleable that, of the metals in common use, only gold and 

 silver surpass it in that respect; it is one of the best conductors 

 of heat and electricity. 



Copper is frequently used in the manufacture of alloys, of 

 which the more important are : 



