T. B. Osborne — Quantitative determination of Niobium. 331 



arate as an oxyfluoride. None was found. Analyses of the 

 NbOF 3 2KFH 2 thus obtained gave the following results. 



Calculated. 

 H„0 5-92 5-90 5-97 

 NbO 36-92 36-84 36-87 

 K 2 26-07 26-13 25-97 

 F 5 31-09 81-13 31-19 

 Ti trace trace 



100-00 100-00 100-00 



This analysis shows that the salt was practically pure. The 

 trace of titanium was found by testing with H 2 2 and amounted 

 to only -0066 per cent. 



Tantalum when treated with zinc and hydrochloric acid does 

 not reduce. Niobium on the other hand forms apparently 

 several reduction products or at least exhibits colors varying 

 according to treatment. When zinc is added to a dilute hydro- 

 chloric acid solution of niobium, a blue color is formed in the 

 cold; if the acid is strong a brown color is obtained which, if 

 the acid is allowed to act on the zinc until nearly neutralized, 

 changes to blue and an indigo blue precipitate separates out. 

 When heated to 100° only quite dilute acid solutions give a 

 blue color which speedily turn brown. Those containing more 

 acid give a brown color at once. If sulphuric acid is used in- 

 stead of hydrochloric, the blue color appears at first, but on 

 heating with much acid this passes into a brown differing 

 slightly in color from that produced in the hydrochloric acid 

 solution. A grass-green color is often obtained in the cold, 

 with both sulphuric and hydrochloric acids, which appears to 

 be intermediate between the blue and the brown as the blue 

 passes into green and this into brown. All solutions strongly 

 acidified with sulphuric or hydrochloric acid give on heating a 

 dark brown color, which evidently indicates the lowest reduc- 

 tion attainable, while the blue color marks a higher oxide than 

 the brown or else an incomplete reduction. 



The solution reduced with sulphuric acid and zinc is much 

 less stable than that with hydrochloric acid, for on pouring it 

 while warm into water, if ^the amount of reduced niobium is 

 sufficient, an evolution of hydrogen takes place from the decom- 

 position of the water. With hydrofluoric acid and zinc a 

 violet color is produced similar to that given by titanium with 

 zinc and sulphuric acid. Under similar conditions titanium 

 gives a green color. 



The first attempts at a quantitative determination of niobium 

 were made with sulphuric acid solutions of NbOF 8 2KF, as sul- 

 phuric acid is better suited for titration with potassium perman- 

 ganate than hydrochloric. It was found, however, that the 

 amount of reduced niobium was very far from constant. More 



