S. Tciber — Growth of Crystals. 



539 



difference in their tendency to form cavities and raise the 

 growing crystal. 



One of the deepest hollows (2*93 millimeters) obtained by 

 growing a crystal of alum in a solution that was allowed to 

 cool down over night, was formed around an artificial plain 

 surface which had been previously ground on the crystal in a 

 direction not parallel to any of the natural faces. During the 



Fig. 2. 



Fig. 2. Plan and cross-section of a large alum crystal with nucleal crys- 

 tal colored with chrome alum. Crystal shows terraced pyramidal form and 

 well-developed hollow on under surface. 



growth of the crystal no appreciable change in the slope of the 

 upper surface, which was a natural crystal face, could be 

 observed. 



When a crystal about 2 centimeters in diameter was placed 

 upside down (i.e. with the hollow up) in a warm saturated 

 solution, it grew a smooth surface on top similar in every way 

 to the crystal that had not been reversed. Underneath the 

 crystal a hollow, 0'6 millimeter in depth, was formed by the 



