I905-] SMITH— COLUMBIUM AND TANTALUM. 157 



In this connection it may be added that, having freed the tanta- 

 lum and columbium oxides as thoroughly as possible from ordinary 

 contaminations, the problem of removing tungsten and tin con- 

 fronted us. After much experimentation, we found that the cer- 

 tainty of the removal of these impurities could only be had by 

 fusing the tantalum and columbium oxides with sodium carbonate 

 and sulphur. It is true that small quantities of tantalum and 

 columbium will be lost, being carried along with the tungsten and 

 tin, but as we were seeking a method of purification and not a sepa- 

 ration, we adopted this course. It is the one which was pursued 

 by Heinrich Rose. Our own experience leads us to say that the 

 removal of tungsten and tin from columbium and tantalum oxides 

 cannot be realized by digestion with ammonium sulphide. Indeed, 

 not only did we find the fusion with the sodium carbonate and sul- 

 phur necessary, but that working in large quantities of material, as 

 in our case, two and three refusions with these reagents were found 

 necessary. Another point of interest in connection with the puri- 

 fication of the tantalum and columbium oxides may be mentioned. 

 It has frequently been said that in crystallizing out the double 

 fluorides of these metals, if titanium be present with them, it will 

 be found in the potassium tantalum fluoride. We have encountered 

 no difficulty in getting potassium tantalum fluoride perfectly free 

 from what is supposed to be titanium by one or two crystallizations. 

 It has been assumed that as potassium titanium fluoride is rather 

 insoluble in water, it would naturally go with potassium tantalum 

 fluoride. This, however, seems to be an incorrect observation. It 

 masses with the columbium potassium fluoride ; at least the element 

 which gives the yellow color with hydrogen peroxide, or a rose red 

 with chromotropic acid is always found associated with the colum- 

 bium. How to free the columbium from titanic acid we do not 

 know. We are in precisely the same position as that of Marignac, 

 notwithstanding we have probably made greater efforts than he to 

 remove it from the columbium. It is this point in our investigation 

 upon which we have been continuously at work for the last year. 

 We have tried fractional precipitation with ammonia water, frac- 

 tional crystallization of the double fluorides, fractional chlorination 

 of the oxides in the presence of carbon and the action of numerous 

 organic bases, without finding any way of effecting a separation. 

 Indeed, the separation of columbium and titanium is a problem 



