334 T. B. Osborne — Quantitative determination of 'Niobium. 



of about 80° C. for three quarters of an hour. The amounts 

 obtained were as follows : 



Ain't of mixed Amount of 



oxides taken. Nb 2 6 found. 



•6400 46-99 



•6652 Nb 2 6 present 47-45 



•7455 v , ' 46-70 



•7663 47-36 per cent. 46-64 



•8323 46-97 



In the above determinations the reduction was evidently to 

 Nb 2 O a . Marignac states that alkali fluorides impede the re- 

 duction, and this would explain why the reduction in the fore- 

 going determinations was complete while in those where the 

 potassium fluoride of niobium was used it was incomplete ; as 

 the amount of alkali fluoride was always in the same propor- 

 tion to the amount of tantalum and niobium constant results 

 might be expected, but it is remarkable that so small an amount 

 of alkali fluoride should exert so great an influence on the re- 

 duction, and that the hydrofluoric acid added to dissolve the 

 niobic acid did not also interfere with the reduction. Two 

 analyses were made in order to throw light on this point by 

 adding weighed amounts of potassium fluoride to a mixture of 

 tantalic and niobic acids free from fluorides and containing 

 45-99 per cent of Nb 2 6 . 



Weight of Weight ]Srb Q 5 Nb 2 5 



mixed acids. of KF. found. present. 



5696 • -0900 43-83 45"99 



5405 -3728 43-87 



From this it would appear that the amount of alkali fluoride 

 exerted no influence, but that its presence did. In this case, 

 however, the reduction is proportionally greater than when 

 NbOF 3 2KF was used. 



The influence of titanium was next studied. Titanic acid 

 was treated exactly as the niobic acid and the following results 

 were obtained. 



Ti0 2 found by 

 reduction and titration. Present. 



20-38 20-36 20'48 



In order to determine whether both niobium and titanium 

 would reduce together as well as separately, the oxides were 

 mixed together and the niobium determined by deducting from 

 the amount of permanganate used the amount necessary to 

 oxidize all the reduced titanium and calculating the niobium 

 corresponding to the balance. In this way I obtained the 

 amounts given below. 



Mixture of Titanic acid Nb 2 6 Nb 2 5 



three acids. present. present. found. 



1-1798 gr. -0859 gr. -4928 gr. "4907 



•8145 -0687 -3357 '3314 



