48 HILLEBRAND, MERWIN AND WRIGHT. [April 25. 



and the other eight are water of crystalHzation. Against two of the 

 eight being regarded as water of crystalHzation might be advanced 

 the difficulty of removing the seventh and eighth molecules, but this 

 can not be considered a weighty argument. Neither can the fact 

 that the water content is so markedly afifected by outside humidity 

 and is susceptible of repeated removal and restoration be brought 

 as a conclusive argument against the assumption of water of crystal- 

 lization, for it must be remembered that loss of water is not accom- 

 panied by rupture of the crystalline structure, as is usually the case 

 with true hydrates. On the other hand, in favor of water of crys- 

 tallization, as opposed to water of absorption, must be placed the 

 breaks in the curves of dehydration observed when the minerals are 

 rapidly heated above 100°, and the fact that the content of water at 

 a fixed atmospheric temperature does not bear a continuous relation 

 to the outside humidity. 



On the whole we are disposed to adopt the view that eight of the 

 nine molecules represent water of crystallization and to report the 

 formulas of both minerals as examined by us to be CaHaVgOiy' 

 8H„0. Under natural conditions mixtures of this and another salt 

 of much lower hydration may and do often occur. 



Inspection of the formulas of the artificial alkali and alkaline- 

 earth hexavanadates throws no light on this problem, since the range 

 in number of molecules of water is very wide for the normal alkali 

 salts and the number is reported as 14 for the normal barium salt 

 and 9.5 for the normal magnesium salt. Acid salts of bivalent metals 

 do not seem to have been prepared, unless Ditte's calcium " trivana- 

 date" CaO,3Vo05,i2H20, is such a salt, perhaps identical with one 

 of the minerals described by us. Its description, however, does not 

 fit our minerals, since it is reported as very soluble in water and as 

 having the luster of gold. The evidence of the salts mentioned 

 points, however, to the possibility that hewettite and metahewettite 

 may have held more than nine molecules of water when formed, 

 unless the fact that only slight changes occur in their water content 

 with high atmospheric humidity at summer temperatures negatives 

 such a possibility. 



Under the name alaite K. A. Nenadkevich has given a very brief 



