'914.] HYDROUS CALCIUM VANADATES. 41 



Molecular Ratios. 



In calculating molecular ratios for the minerals one is con- 

 fronted with difficulties arising from the presence of vanadium of 

 lower valence than 5, of molybdenum, and of small amounts of con- 

 stituents other than calcium. These different problems will be taken 

 up in order. 



Vanadium. — In hewettite the presence of vanadium in the quad- 

 rivalent state may be regarded as probable in view of its existence 

 in many of the specimens representing much less complete oxida- 

 tion of patronite. In these cases it may be assumed with consider- 

 able probability that there exist vanadyl-vanadic oxides or salts, since 

 artificial compounds of the kind are known. If a compound of this 

 nature exists in hewettite, it demands a portion of the V2O5, and, if 

 hydrated, a considerable percentage of water. 



In metahewettite, however, there is great reason to believe that 

 the vanadium of lower valence is trivalent. That it exists as a con- 

 stituent of a silicate containing also aluminum and potassium was 

 pointed out on p. 34. It will be so regarded. This stand is taken 

 with full knowledge that a characteristic black ore from Paradox 

 contains much of its vanadium in the quadrivalent state, as men- 

 tioned in our preliminary paper. ^^ 



Molybdenum. — The presence of molybdenum hampers some- 



la. Pet Cent. Mol. Ratio, 



VoOs 66.8 4.79 



V.O. 7 



M0O3 2.8 .26 



CaO 43 100 



HoO ( 100° — ) 13.9 10.03 



H.O ( 100° -f ) 6.9 4-97 



Fe.Oa, etc 2-2 



SiO, 1.2 



99-9 



This analysis is given chiefly to show how deceptive the evidence afforded 

 by sharp molecular ratios may be, for microscopical examination showed the 

 material to be very far from pure. It also serves to show what different 

 compositions similar appearing materials may have. 



''■^ Jour. Washington Acad. Sci., 3, 158, 1913. 



