Melanterite and Chalcanthite Groups. 231 



form under these conditions and a water determination 

 on the material gave 12.2 per cent and indicates the 

 monohydrate which theoretically contains 10.4 per cent 

 H 2 0. Material precipitated by slowly pouring a concen- 

 trated solution of CoS0 4 into concentrated H 2 S0 4 was no 

 doubt the same though it was not entirely homogeneous 

 and y appeared to be a little lower. This is probably also 

 the monohydrate although the tetrahydrate is said to 

 form when the solution is poured into H 2 S0 4 . 



The optical properties of the monohydrate formed with 

 the pentahydrate in a desiccator are sufficiently different 

 from the properties of the monohydrate crystallized on a 

 water bath, although the latter is too finely crystalline for 

 accurate measurements to justify the conclusion that 

 there are two forms of that hydrate. 



CoS0 4 crystallized from a solution at 23 °C in a desic- 

 cator under reduced pressure was in aggregates of car- 

 mine colored (Ridgway 1-i), tabular crystals with the fol- 

 lowing optical properties : Opt. — , 2V near 90°, dispersion 

 slight. 



a = 1.477' ± 0.003. p = 1.483 ± 0.003. y = 1.489 ± 0.003. 



The heptahydrate is said to be formed under these condi- 

 tions ; a water determination on this material gave 44.8 

 per cent and the theoretical water content of the heptahy- 

 drate is also 44.8 per cent. The optical properties are 

 similar to those of the members of the melanterite group 

 and the material is artificial bieberite. 



The hydrous Sulphates of Manganese. 



Artificial " manganese sulphate'' from the stock bottle 

 of the U. S. Geological Survey is made up of two forms : 

 pale pink, glassy crystals which are largely altered to 

 nearly white aggregates of minute crystals. The glassy 

 crystals have the following optical properties : Opt. — , 

 2V moderately large. 



a = 1.511 ± 0.003. p e= 1.519 ± 0.003. y = 1.521 ± 0.003. 



A determination of the water in this material gave 31.5 

 and indicates the tetrahydrate which theoretically con- 

 tains 32.3 per cent H 2 0. This form was crystallized from 

 solution at 45° and was formed from the alteration of the 

 pentahydrate. 



The nearly white alteration product in the stock bottle 

 is optically +, 2V is near 90°. 



a = 1.562 ± 0.003. p = 1.595 ± 0.003. y = 1.632 ± 0.003. 



