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



tion was obtained containing a very small amount of free acid 

 and practically free from fluorides. This solution was then 

 diluted to 500 c. c, and 50 c. c. brought into a nesslerizing tube 

 and 2 c. c. of hydrogen dioxide added. About 40 c. c. of 

 water was added to another tube of the same dimensions and 

 then 2 c. c. of hydrogen dioxide. A solution of titanic acid, 

 prepared by evaporating potassium titanium fluoride with excess 

 of sulphuric acid and diluting with water until 1 c. c. equaled 

 one milligram of titanium oxide, was then run in until the 

 color in the two tubes was nearly alike. They were then 

 brought to the same volume and the standard solution of 

 titanium added drop by drop till there was no longer any dif- 

 ference in color discernible. The number of cubic centimeters 

 of the standard solution multiplied by ten gave the number of 

 milligrams of Ti0 2 in the solution analyzed. By calculating 

 the amount of permanganate solution necessary to oxidize the 

 Ti 2 3 formed by reduction of this amount of Ti0 3 the amount 

 of permanganate employed to oxidize the niobium was found 

 and from this the amount of niobium calculated. The tanta- 

 lum was found by subtracting the sum of the niobic and titanic 

 oxides from the sum of the three oxides. In this way the fol- 

 lowing amounts of each were found. 



Nb 2 5 Ta 2 5 Ti0 2 



Taken -3357 gr. -2246 gr. -0687 gr. 



Pound -3314 " -2289 " -0667 " 



It is necessary that during the reduction the heat should not 

 be too great, as the tantalic acid is liable to precipitate and to 

 carry with it both niobium and titanium and the reduction con- 

 sequently will be incomplete. If tantalum is not present the 

 solution can be boiled without danger. In order to analyze a 

 mineral containing these three elements the mixed oxides can 

 be obtained in the usual manner by fusing the finely ground 

 mineral with bisulphate of potassium, digesting with water, 

 filtering, heating the residue with ammonium sulphide, wash- 

 ing to remove tin and tungsten if present, treating the residue 

 with dilute sulphuric acid to remove iron, washing and igniting 

 with ammonium carbonate. After obtaining the joint weights 

 of the oxides, fuse with potassium bisulphate, digest with water, 

 and the residue, washed free from sulphates, dissolve in hot 

 hydrofluoric acid, evaporate nearly dry on the water bath and 

 proceed with the reduction and determination as just described. 

 An analysis of Branchville columbite by this method, gave the 

 following results: 



Ta 2 5 .18-95 19-44 Specific gravity 



Nb 2 6 60-95 60-46 5-73 



FeO .12-86 12-95 



MnO 7-07 7-00 Oxygen ratio 



1: 1-03 



99'83 99-85 



