INDIUM. 135 



the mixture allowed to stand; all the indium will be 

 precipitated with a little, oxide of iron, but free from, 

 oxide of zinc. 



II. Purification of Indium. 



After having separated by one of the preceding 

 methods the oxide of indium from the greater part of 

 the zinc, the metal is then purified. Winckler recom- 

 mends the use of the precipitate obtained by process a. 



This sponge is dissolved in nitric acid, and the 

 greater part of the lead separated by the aid of sul- 

 phuric acid. Hydrosulphuric acid is passed into the 

 filtrate until the lead, cadmium, arsenic, &c., are com- 

 pletely precipitated. 



The hydrosulphuric acid is driven off by boiling. 

 The iron is oxidized by adding chlorate of potassa and 

 precipitated by ammonia. The greater part of the 

 zinc remains in solution, the precipitate of oxide of 

 iron and oxide of indium contain very little of it. 



After washing, the precipitate is dissolved on the 

 filter in warm dilute acetic acid, and the whole of the 

 indium is precipitated, at the same time a little of the 

 iron and zinc by the hydrosulphuric acid. 



It is very difficult to separate all the iron and the 

 zinc, even by repeating the process ten times. 



In order to obtain absolutely pure indium it is better 

 to employ the precipitate obtained by the carbonate 

 of baryta. The iron in this case should be in the state 

 of protoxide, because the peroxide of this metal is pre- 

 cipitated by the carbonate of baryta. 



The sulphur of impure indium is dissolved in dilute 

 hydrochloric acid. It is heated in order to drive off 

 the hydrosulphuric acid dissolved in the liquid, and a 

 solution is obtained which contains iron in the state of 

 protochloride. 



After cooling, a sufficient quantity of carbonate of 



