1823.] 



Crystalline Forms of Artificial Salts, 



41 



PonF 108° 16' 



P over the edge on 



theleft 104 15 



Vonz, 166 40 



P on 2^ 165 40 nearly 



«onP, orP' 122 00 



aony 90 00 



The planes % and y are generally striated, 

 and afford imperfect reflections ; and the 

 crystals are frequently elongated in the 

 direction of one of the edges of the base, so 

 that the plane P terminates in an edge instead 

 of a point, an irregularity of figure common 

 to all the classes of octahedrons. 



Sulphate of Potash and Magnesia, 



I have not found any cleavage of these 

 crystals, but the predominating form, 

 and which may be regarded as the pri- 

 mary, is an oblique rhombic prism, modi- 

 fied by the planes f, e, and h, and measur- 

 ing as follows : 



Lon M, orM' 102° 



MonM' 108 



Ponc^ 116 



P one, ore' 154 



'Ponh. 105 



20' 

 45 

 45 

 30 

 8 



Ferroprussiate of Potash. 

 The crystals are soft, flexible, and very 

 fissile parallel to the plane P of the an- 

 nexed figure, and there is not any distinct 

 cleavage that I have been able to perceive 

 m any other direction. There are, how- 

 ever, in some crystals, apparent natural 

 jomts parallel to the planes P of this 

 figure; these would give an octahedron for the primary form, 

 which, from the angles of the secondary planes, is found to 

 have a square base. The most distinct measurements are the 



P on P" 1370 



P orP'ona m 



o on/. 119 



a on e 90 



« on e' 90 



GO' 



30 



9 











