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



constant results were obtained by pouring the reduced solution 

 into ferric .sulphate, but these varied too widely to give any 

 promise of a satisfactory method. Hydrochloric acid was then 

 tried and iodine solution added till a drop gave a blue color 

 with a drop of starch solution, then sodium thiosulphate solu- 

 tion in. slight excess, then a few drops of starch solution and 

 iodine added till a blue color appeared. It was found, how- 

 ever, that a dark brownish color was formed near the end of 

 the titration which so obscured the blue of the starch that very 

 unsatisfactory results were obtained. 



I then tried potassium dichromate for titrating, pouring the 

 reduced solution into ferric chloride but without success. 



Potassium permanganate was then returned to and man- 

 ganese sulphate or magnesium sulphate added to prevent the 

 action of the hydrochloric acid on the permanganate. It was 

 afterward found that by sufficient dilution the end point could 

 be obtained with all the accuracy desirable without the addi- 

 tion of either magnesium or manganese sulphates. The results 

 are shown in the following table. The reduction was assumed 

 to be to Nb 2 O s . 



Amount of 

 Amount of acid used. NbOF 3 2KFH 2 0. 



50 c. c. HC1 sp. gr. 1*1 



40 c. c. 



30 c. c. 

 50 c. c. 



25 c. c. 



n-, ^ 



(cone.) 



(cone.) 



5155 

 4652 

 4932 

 5900 

 5561 

 6614 

 4926 

 5896 

 4982 

 4161 

 5291 

 5219 

 8122 

 4256 

 7152 

 4421 

 5162 

 3910 

 0592 



9274 

 6734 

 6861 

 5980 

 5828 

 7611 

 6530 



Time of 



Percentage 



reduction. 



of Nb a O s . 



§ hour 



34-24 



ti 



35.21 



II 



35-58 



" 



34-90 



it 



34*50 



(1 



35-24 



1£ hour 



34 01 



(i 



3460 



§ hour 



34-27 



" 



34-13 



■J hour 



3356 



f hour 



37-68 



" 



38-41 



" 



36-74 



i. 



37-65 



a 



3697 



u 



37-54 



if 



37-40 



ti 



38-07 



1 hour 



37-56 



" 



35-90 



£ hour 



38-58 



i. 



38-78 



ii 



38-30 



u 



38-70 



u 



37-68 



a 



38-07 



In the above analyses the fluorides 

 were dissolved in water and the 

 acid added. In the following 

 concentrated acid was added di- 

 rectly- to the fluorides 



The amount of Nb 2 E 

 Nb0F 3 2KFH 2 O is 



1-1023 " 



•8395 

 corresponding to the niobium in the 



39-03 



38-86 



44-48 



