INDIUM. 133 



For this purpose it must be in the state of a chloride, 

 or of a protoxide-salt mixed with hydrochloric acid, 

 and the solution must not contain more than 1 gramme 

 of thallium in 500 c.c. ; the permanganate solution 

 must be more dilute than for the estimation of iron. 

 The titration of the permanganate may be made with 

 pure iron, with thallium, or with a protoxide-salt (the 

 alum, for example); 2 at. iron (112 pts.) correspond to 

 1 at. thallium (204 pts.), inasmuch as the protochloride 

 HOI is converted by oxidation into a trichloride, HC1 3 , 

 so that 1 at. thallium takes up the same quantity of 

 oxygen as 2 at. iron. The solution of the protoxide 

 salt, diluted as above mentioned, is mixed with a few 

 drops of hydrochloric and a few drops of sulphurous 

 acid, and heated to the boiling-point to expel the 

 latter ; then left to cool, and mixed with the perman- 

 ganate. 



73. INDIUM. 



This metal was discovered in 1863 by Messrs. Reiqh 

 and Richter, in the zinc blende of Freiberg. It has 

 been investigated since that time by Mr. Clement 

 Winckler, from whose work we borrow the follow- 

 ing: 



The zinc obtained from the Freiberg blende contains 

 0.045 per cent, of indium, as well as small quantities 

 of lead, iron, arsenic, and cadmium. It was by the aid 

 of ammonia, in which the oxide of indium is entirely 

 insoluble, that Reich and Richter separated the indium 

 from the zinc. This process, which is excellent, be- 

 cause the oxide of indium is insoluble in the ammonia, 

 has the inconvenience of being much too expensive, 

 on account of the large- quantities of the reagent it is 

 necessary to employ. 

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