244 INDIUM AND THALLIUM IN 



in equilibrium at room temperature with a solution widely 

 differing in composition from that represented by the formula 

 of the salt, the concentration of the solution had to be varied 

 till the required salt was found to crystallise. On dissolving 

 thallous oxide in the halogen acid, any thallous ions present 

 go to form insoluble thallous halide ; consequently the 

 difficulties which attend investigations on the thallic sulphates 

 on account of the continuous reduction in the solution of 

 thallic ions to thallous ions, were obviated here. So long as an 

 excess of acid is present, practically no thallous ions can 

 remain in solution. Excess of acid also prevents hydrolysis 

 from taking place ; in the case of the indium solutions, 

 precipitation of the hydroxide was only prevented by main- 

 taining the solutions decidedly acid, during the process of 

 crystallisation. 



The analyses were carried out as follows. After being 

 carefully crushed, and dried at room temperature, the salt was 

 gradually heated in a drying oven, and weighed at intervals, 

 all precautions being taken to avoid overheating and conse- 

 quent disintegration. On constant weight being attained, the 

 water of crystallisation was estimated. The salt was dissolved 

 in water, and the thallic or indie hydroxide precipitated by 

 addition of ammonia. Meyer (13) found that only two-thirds 

 of the chloride in a thallic chloride solution is precipitated by 

 silver nitrate in strong nitric acid, a fact which points to the 

 formation of complex ions in the solution. It is therefore 

 necessary to remove the thallium or indium from the solution 

 before estimating the halogen. Indium was estimated as 

 In 2 O 3 , precautions being taken to ensure that no sublimation 

 took place during the heating of the hydroxide. Thiel and 

 Koelsch (2), on investigating this method of estimating indium, 

 found that at a temperature of 850 C. no loss of weight took 

 place through sublimation, while at 1000 C. the sublimation 

 was considerable. Unless in the case where the solution con- 

 tained a large amount of ammonium nitrate, it w r as found that 



