OXIDES OF MANGANESE, IRON> AND ZINC. 59 



is converted into Cu 2 S. The oxide of zinc is heated 

 and precipitated with carbonate of soda. 



This method may be used also for the separation of 

 iron and copper. 



The brass sometimes contains traces of tin. It is 

 then dissolved in hot nitric acid, which leaves the bin- 

 oxide of tin (containing a little copper) untouched. 



In order to detect a small quantity of lead which 

 frequently occurs in brass, the sulphide of copper pre- 

 cipitated by sulphuretted hydrogen is oxidized with 

 fuming nitric acid, the mass dried, and treated with 

 water, which leaves thq sulphate of lead undissolved. 

 Should this contain sulphur, it must be burnt off. 



Or the brass may be dissolved in nitric acid, a little 

 sulphuric acid added, the solution evaporated to dry- 

 ness, and the mass treated with water. 



If the brass be placed in a little porcelain boat, and 

 heated to redness in a porcelain tube through which a 

 rapid stream of hydrogen is passed, all the zinc rnay 

 be volatilized. 



34. OXIDES OF MANGANESE, IRON, AND ZINC. 



The solution, which must contain the iron in the 

 form of sesquioxide, is mixed with carbonate of soda 

 until a permanent precipitate begins to appear; it is 

 then boiled with acetate of soda, when all the sesqui- 

 oxide of iron is precipitated. 



The filtrate is mixed with acetic acid, and the zinc 

 precipitated by sulphuretted hydrogen. 



The manganese may be precipitated, after neutrali- 

 zation, with an alkaline hypochlorite, or by boiling 

 with an alkaline carbonate. 



