440 W. F. Hillebrancl — Danger in Mineral Separations. 



Mineral treated by 

 Mineral untreated. Thoulet solution. 

 Per cent Per cent 



V 2 5 18*03 18-31 



U0 3 - 53-71 55-37 



CaO 5-20 1-72 



K 2 -24 6-08 



CuO 4-16 4-22 



Si °A' P l?"*l?' n V 2-45 1-91 



A1 3 3 , MgO, Na,0 



I 



H 2 and loss 16-21 12-39 



100-00 100-00 



sium. The decrease in the water content of the treated portion 

 practically accounts for the somewhat higher values for vana- 

 dium and uranium in it. The difference in the water values 

 may, however, not be real, since it is now known that the water 

 content of the mineral may vary several per cent, according as 

 the weather is dry or humid. Striking is the fact that the 

 copper does not seem to have been affected by the heavy solu- 

 tion. Whether complete replacement of the calcium would 

 have resulted from longer treatment has not been determined 

 by reason of lack of material and opportunity. It was noted 

 in earlier tests of treated specimens that the calcium had not 

 been wholly displaced. This is in agreement with the obser- 

 vation that the copper vanadate probably carries calcium, and, 

 since the copper of that mineral has not suffered removal, it is 

 not improbable that whatever other bases it may carry were 

 also retained. 



The yellow calcium mineral, when treated with Thoulet 

 solution, showed, according to Mr. H. E. Merwin, a decrease in 

 the optic axial angle of 25° as compared with untreated mate- 

 rial of approximately the same state of hydration. 



The observation detailed above shows how important it is 

 in the use of heavy solutions to assure oneself that chemical 

 changes of the kind shown are not incurred. Question natur- 

 ally arises as to the validity of the compositions that have been 

 assigned to one and another mineral which has been separated 

 from others by heavy solutions before analysis. 



The calcium carnotite experimented with is probably iden- 

 tical with the tuyamunite of Nenadkeviclv* and will form the 

 basis for detailed description by Mr. Merwin and myself in a 

 later paper. 



Bureau of Standards, 



Washington, D. C, Feb. 



* Bull. Acad. Sci. St. Petersburg, 1912, p. 945. 



