TIN AND LEAD. 73 



latter evaporated, the solution diluted with hot water, 

 and the undissolved binoxide of tin filtered off. The 

 copper is precipitated from the filtrate by caustic po- 

 tassa, at a boiling-heat. 



If the bronze contain also zinc, lead, and iron, the 

 lead is precipitated by sulphuric acid, and the copper 

 by sulphuretted hydrogen. The solution filtered from 

 the sulphide of copper is heated with some chlorate of 

 potassa in order to peroxidize the iron, and the sesqui- 

 oxide of the latter metal precipitated by an excess of 

 ammonia. The oxide of zinc remains dissolved in the 

 alkali, and is precipitated by sulphide of ammonium. 

 Or the method described in No. 31 may be followed. 



II. A surer method of obtaining the binoxide of tin. 

 free from other metals consists in oxidizing the alloy 

 with nitric acid, evaporating to complete dryness, 

 moistening with hydrochloric acid, and after some time 

 adding water, the mass dissolves completely and the 

 binoxide of tin is precipitated by sulphuric acid. After 

 it has fully settled, it is filtered, washed, and ignited. 



III. A very accurate analysis may also be effected 

 by heating the alloy in a current of dry chlorine, when 

 the tin and a part of the iron are volatilized as chlo- 

 rides, which are conducted into water, and chloride of 

 copper, chloride of zinc, and chloride of lead are left. 

 (See Tetrahedrite.) 



48. TIN AND LEAD. 

 (Pewter, Soft Solder.) 



The alloy is oxidized with moderately strong nitric 

 acid, which leaves the tin undissolved in the form of 

 binoxide ; after heating and diluting with water, the 

 binoxide of tin is filtered off, washed, dried, and ignited. 



From the filtrate the lead is precipitated by dilute 

 7 



