520 0. H. Warren — Niobium and Tantalum. 



Art. XLY. — Note on the Estimation of Niobium and Tan- 

 talum in the presence of Titanium / by C. H. Warren. 



The obtaining of a strong reaction for niobium in the mineral 

 described in the previous paper and the failure to obtain more 

 than a fraction of a per cent of niobium by means of the acid 

 potassium sulphate fusion and leaching in cold water, naturally 

 led to an examination of the methods for estimating these ele- 

 ments quantitatively in the presence of each other. 



So far as the writer can ascertain, the most common method 

 followed is that involving a fusion with bisulphate of potash 

 followed by leaching with cold water, these operations being 

 repeated until all the titanium has passed into solution, while the 

 niobic and tantalic oxides remain behind. In his System of 

 Qualitative Analysis,* page 218, Dr. A. A. Noyes states that 

 when treated in this manner fairly large quantities of niobium 

 and tantalum pass into solution with titanium when much of 

 the latter is present. With this statement in mind a few exper- 

 iments were made to gain some further idea of the magnitude 

 of the error involved in the method. 



Pure Ti0 2 was prepared from selected crystals of rutile by 

 the usual chemical methods. Nb 2 5 and Ta 3 5 were prepared 

 from the columbite of Branchville, Conn., after the method 

 described by Osborne,+ except that the precipitated oxides were 

 digested for some time with ammonium sulphide to insure the 

 removal of any tungsten or tin which might be present. The 

 final products were subjected to the most careful qualitative 

 examination and no impurity other than a trace of iron could 

 be detected. 



The attempts at separating these oxides, quantitatively, when 

 mixed together were very unsatisfactory, and although few in 

 number seem to thoroughly confirm Dr. Noyes' statement. 

 Indeed, considerable quantities of niobium may be made to pass 

 into solution with the titanium, as the figures given below show. 

 In the first three experiments, the fusion and leachings were 

 thrice repeated. In each case the fusion was mashed to a pow- 

 der under cold water in an agate mortar and allowed to stand 

 with from 250 to 300 cc of water for twenty-four hours. The 

 titanium was precipitated from the combined filtrates with 

 ammonium hydroxide, filtered, washed free from sulphates 

 and ignited to a constant weight. The residues from the first 

 two leachings gave a strong reaction for titanium with hydro- 

 gen peroxide, and a small amount of titanium always remained 

 in the last residue. 



* Technology Quarterly, vol. xvii, No. 3, 1904. 

 f This Journal (3), xxx, 330, 1885. 



