I9I4] 



HYDROUS CALCIUM VANADATES. 



43 



The value for V0O5 in I. becomes 3.00 if enough is deducted to 

 form an equi-molecular compound with the V2O4. 



Before discussing the formulas of the minerals we must present 

 a number of considerations bearing on their specific differentiation, 

 in the course of which certain experimental data essential to a 

 proper understanding of the subject will be given. 



Evidences of Specific Distinction of Hewettite and 

 Metahewettite. 



The evidence which impels us to give different names to the 

 Peruvian and North American minerals, in spite of the fact that 

 they seem to have the same empirical formula, will now be set forth. 



Optical and Crystallographic Differences. — Metahewettite is 



Fig. 2. Showing the course of dehydration of hewettite and metahewet- 

 tite over sulphuric acid of different concentrations at room temperatures, and 

 of metahewettite at temperatures above 100°. 



