136 INDIUM. 



is added, and is left to digest for twenty-four 

 hours stirring it frequently: 



The precipitate which contains all the indium is 

 carefully filtered and washed, while the whole of the 

 iron and zinc are found in the liquid. 



The precipitate is decomposed by sulphuric acid, 

 which gives some sulphate of baryta and some sulphate 

 of oxide of indium, from which the ammonia precipi- 

 tates entirely pure oxide of indium. 



III. Preparation of Metallic Indium. 



The oxide of indium is heated to a low temperature 

 in a porcelain crucible, into which a current of hydro- 

 gen is passed. A little indium is always lost, on 

 account of the volatility of the metal. If the gas is 

 passed slowly at first, in such a manner that it does 

 not burn between the cover and the crucible, very little 

 of the indium is lost, and the current of gas can then 

 be increased without fear of carrying off' much of the 

 metal. The crucible is left to cool in the current of 

 gas, and little metallic globules are obtained at the 

 bottom of the vessel. In order to unite them in one 

 mass fused cyanide of potassium is added heated to 

 redness and the union of the globules is aided by 

 inclining the crucible in different directions. 



The mass is freed from the cyanide of potassium, 

 which adheres to it, by washing with hot water. 



IV. Properties of Indium. 



The color of indium is similar to that of platinum, 

 has marked metallic characteristics, and is much sof- 

 ter than lead can be easily separated into thin lami- 

 na it marks paper it does not tarnish on exposure 

 to the air it is soluble in dilute hydrochloric and 

 sulphuric acid ; but, when in contact with concentrated 

 sulphuric acid, is given off sulphurous acid. Nitric 



