W. P. Headden — Tantalate from So. Dakota. 297 



Methods of Analysis. — There is no need to discuss these 

 as they were well known, conventional ones, except, per- 

 haps, the determination of titanic acid which was effected 

 by fusion with potassic bisulphate powdering the melt and 

 dissolving it in a mixture of sulphuric acid and hydrogen 

 peroxide. I used 5 parts of sulphuric acid, made by 

 diluting 3 parts of concentrated acid with 2 parts of 

 water; and 4 parts of 3% hydrogen peroxide. This 

 effects a perfect solution of the mineral which can be used 

 in the colorimeter without filtering after standing to allow 

 any bubbles of hydrogen peroxide to escape. This solu- 

 tion will remain clear for some hours, but eventually 

 tantalic acid begins to separate. I tried to separate the 

 acids from the salts introduced by this fusion by boiling 

 as usual and dissolving the separated acids in hydro- 

 fluoric acid, precipitating the hot solution by ammonia 

 and dissolving this precipitate in the acid hydrogen-per- 

 oxide mixture, but the acids did not go into solution. 

 Both of the acids, tantalic and columbic, are contam- 

 inated by titanic acid as separated in this analysis and the 

 titanic acid must be determined and deducted. I may 

 remark that the platinum that goes into solution in the 

 bisulphate fusions necessary in these analyses is an 

 annoyance. 



The determination of any cassiterite or quartz that may 

 be present is most easily made by fusion with bisulphate 

 and dissolving the melt in acid hydrogen peroxide. This 

 is much more satisfactory than taking the residue from 

 the solution of the mixed acids in hydrofluoric acid, which 

 invariably contains a little platinum. 



The analytical procedure was the same in the case of 

 the columbites. 



Columbites. 



The columbites presented in these notes have not been 

 described heretofore, and are from three localities ; two 

 of them are in Custer Co., the Old Mike Mica mine, and 

 Tin Mountain ; and one, Harney City, is in Pennington Co. 

 The minerals are typical columbites in habit, cleavage, 

 luster, etc. They are not quite so hard as the tantalates, 

 and are not brittle like them. They vary in color from 

 a brownish to a grayish black, in luster from submetallic, 

 shining in the case of the Old Mike samples, to dull sub- 



