Hillebrand, Turner and Clarke — Roscoelite. 451 



Art. XLIX. — On Roscoelite ; by W. F. Hillebrand and 

 H. W. Turner, with a note on its chemical constitution by 

 F. W. Clarke. 



Analysis and Composition, by W. F. Hillebrand. 



The rare mineral roscoelite has greatly needed reexamina- 

 tion in order to reconcile the discrepancies between the analyses 

 of Roscoe and Genth and to establish* a satisfactory formula 

 for this supposed vanadium mica. To the kindness of Mr. 

 G-. W. Kimble of Placerville, Cal., I am indebted through 

 Mr. H. W. Turner for specimens from the Stockslager mine, 

 from which a limited amount of fairly pure material was 

 picked out. This was then laboriously purified by the aid of 

 Thoulet's solution, the result being a very nearly pure product 

 weighing only 1*2 grams and having after drying at 100° C. a 

 density of 2 ; 97 at 20° C. 



Notwithstanding the small amount, it was possible by the 

 exercise of care to make fairly satisfactory analyses. 



With regard to the methods employed little need be said 

 except as to the determination of the condition of the vana- 

 dium. For this purpose decomposition was effected by rather 

 dilute H 2 S0 4 in sealed tubes, the greatest care being taken to 

 expel every trace of air from the powder and acid and to seal 

 the tube during passage of a current of C0 2 . Otherwise it is 

 impossible to prevent oxidation of a considerable part of the 

 Y 2 3 . In one case, unfortunately, the air cannot have been 

 fully expelled, for the solution after decomposition was blue 

 instead of green and much less oxygen was required in titra- 

 tion than when the color was green. 



The contents of the tube, still warm, were poured into 

 fairly hot freshly boiled water and titrated rapidly. Iron and 

 vanadium were then reduced by H 2 S gas, the latter boiled out 

 in a current of 0O 2 , and titration repeated on the hot liquid. 

 The solution was then boiled with ammonia, the precipitate 

 fused with Na 2 C0 3 , leached with water, and the residue again 

 fused with Na 2 C0 3 and leached to remove the last of the 

 vanadium. This residue was then fused with KHS0 4 ,* dis- 

 solved in dilute H 2 S0 4 , boiled first with H 2 S and then in a cur- 

 rent of C0 2 , and the liquid titrated for total iron. The solu- 

 tion held titanium which was then estimated colorimetrically. 



The first of the titration results gave the effect of all iron, 

 assuming its existence as FeO, and of all vanadium that might 



* Any slight trace of vanadium remaining will impart a bright yellow color to 

 the cold KHS0 4 fusion, a test which proved useful more than once during the 



Am. Jour. Sci.— Fourth Series, Vol. VII, No. 42.— June, 1899. 

 30 



