SULPHATES. 



53 



In both cases the curves b showed the water bands at 1.5 and 2/t, 

 beyond which there was complete opacity. 



GROUP III : MISCELLANEOUS COMPOUNDS. 



It has been noticed elsewhere that in the examination of selenite the 

 large absorption band at 4.55 /* is shifted, and too deep to belong to 

 water ; also that it was suspected to be due to the SO 4 groups of atoms. 



The band has further been noticed in discussing selenite and anhy- 

 drite (fig. 3), and in thaumasite and blodite (fig. 13). Under the 

 present heading will be discussed the absorption spectra of simple sul- 



80% 



E 

 n 



c 



0/234567 



FIG. 39. Barite(a); Glauberite. 



phates formed by the combination of a metallic oxide and sulphur 

 trioxide, all of which show a band at 4.55 p., while several have another 

 band in common at 6.5 //,. 



SULPHATES. 

 BARITE (BaSCy). 



(Orthorhombic; section parallel to c; translucent; ^ = 0.25. Curve a, fig. 39. 



From Cheshire, Connecticut.) 



The barite curve is quite opaque, due in part to numerous cracks. 

 There are bands at 3, 4.6, 6.2, and 6.5 p. Konigsberger's curves show 

 that the band at 4.6 ju, is wide, and shifts for different directions of vibra- 

 tion of polarized light. 



