MOLECULES. 



Fig. 64. 



If we apply our knife again to the line i A*, k I, I m, 

 m 2, fig. 64, and strike in the direction of n, we may 

 remove the remaining solid angles of the cube, and 

 we shall then obtain the regular octahedron iklmno. 



Fig. 65. 



The position of this octahedron in the cube is 

 shewn by fig. 65. 



This octahedron is the primary form of Jluate of 

 limey and it may obviously be cleaved in a direction 

 parallel to its own planes. 



Fig. 66. 



To illustrate more perspicuously the relation we 

 are about to trace between the octahedron and tetra- 



