52 HILLEBRAND, MERWIN AND WRIGHT. [April 25, 



the surrounding humidity is reduced practically to zero. When de- 

 hydrated over PoOg the color is no longer orange but dirty yellow. 

 After rehydration in moist air the color is much brighter yellow, but 

 without any trace of the original orange. 



As with hewettiteand metahewettite, the amount of water evolved 

 at and below 100° is almost exactly removable by exposure over 

 strong sulphuric acid at room temperature for one or two months 

 and much more rapidly in a vacuum. Above 100° further loss be- 

 gins, but is complete only at a temperature of perhaps 300°. No 

 experiments have been made as yet to trace the progress of dehydra- 

 tion at temperatures above 100°. Further tests on this mineral are 

 needed and will be made if opportunity offers. 



The arguments advanced (pp. 46-48) for hewettite and meta- 

 hewettite with respect to their chemical classification apply to pas- 

 coite also. In this case, if the assumptions made for the former 

 minerals are justified, we have normal calcium hexavanadate with 

 X molecules of water, at least 11 when the mineral was formed. 



Analytical Procedure. 



The methods of analysis need no special mention except as to 

 the separation and determination of the vanadium and molybdenum. 

 As a rule the portions used for water determinations served also 

 for the other constituents. They were treated in a glass tube, with 

 dry hydrochloric acid gas, after solution in nitric acid and evapo- 

 ration to dryness in a porcelain boat on a hot plate. The brown vapors 

 were collected in receptacles containing a little water. Two of these 

 in series were sufficient, but a third was sometimes used, all so con- 

 nected that no back suction of liquid was possible if the gas stream 

 slackened. The material in the boat is attacked instantly the acid 

 vapor reaches it, even without the aid of heat, but the reaction is 

 not complete in one operation even when heat is applied after vigor- 

 ous action ceases. It is necessary, usually, to remove the boat, to 

 reconvert the contents to nitrates and to repeat the treatment with 

 hydrochloric acid gas several times, and to wash out and dry the 

 glass tube between each operation. 



The molybdenum, less volatile than the vanadium, comes off only, 



