Determining Columbium and Tantalum. 399 



filtered, washed with water, and treated several times with 

 yellow ammonium sulphide. The insoluble residue of bismuth 

 sulphide was dissolved in nitric acid, precipitated with ammo- 

 nium carbonate, filtered, washed, ignited and weighed as 

 BijOj. The solution of antimony sulphide in ammonium 

 sulphide was precipitated with sulphuric acid, (in the case of 

 the two gram sample one tenth of the solution was used,) 

 filtered in a porcelain Gooch crucible and washed with water. 

 The crucible was supported in a triangle on a sand bath and 

 covered with a 300" flask whose bottom had been removed. 

 A glass tube and thermometer were fitted into the neck of 

 the flask through a rubber stopper. The air in the flask was 

 displaced by a rapid stream of carbon dioxide entering through 

 the neck of the flask and escaping through the sand at the 

 bottom. The temperature was raised to 240° and maintained 

 for two hours, while carbon dioxide was passed in. At the 

 end of this time all free sulphur had been removed from the 

 Sb^Sj precipitate, as was shown by the weight remaining con- 

 stant after further treatment. The crucible was allowed to 

 cool in the atmosphere of carbon dioxide, its weight taken, 

 and SKS3 calculated into terms of Sb^Og. 



The filtrate from the precipitation with hydrogen sulphide 

 contained columbium and tantalum in solution in hydrofluoric 

 acid. It was evaporated to dryness, moistened with concen- 

 trated sulphuric acid, and heated until all hydrofluoric acid 

 was expelled. Water was added and the solution made alkaline 

 with ammonia, filtered, the precipitate washed, ignited, and 

 weighed. After heating over a blast lamp for an hour the 

 density was determined. In experiments 2 and 3 the hydro- 

 fiuoric acid solutions containing tantalum and columbium were 



^h 



united in order to obtain enough material for a reliable deter- 



*ft^ 



mination of density. The results of the analysis are as follows 



12 3 Average 



Sb^Og - 40-98 40-98 40-91 40-95 



Bi^O, 0-50 0-69 0-60 



Ta,0^ 41-53 42-30 42-30 41-92 



Cb„0, 16-56 15-82 15-82 16-19 



99-60 99-72 99-66 



Density of mixed 1 



oxides of \ 7-191 7-282 7-282 7-236 



Ta and Cb ) 



Ratio of pfT^T^ TTT^ = 0-92 



