34 FUNDAMENTALS OF SUBMICROSCOPIC MORPHOLOGY I 



If a plane is drawn through two body diagonals, the arrangement of 

 lattice points obtained is as represented in Fig. 31a. In this cross- 

 section the C-atoms are joined by a zig-zag line whose links enclose 

 the so-called tetrahedron angle of 109°. 5. On parallel planes, further ar- 

 rays of such zig-zag chains are found, one of which has been represented 

 by dotted lines. It is linked up with the other two by primary valencies. 



.^ , 



I / 



7.45^ 



Fig. 31. «) Diamond lattice (primary valency lattice) as compared 



with Fig. 30a by 45° inclined, b) Paraffin lattice (molecule lattice); 



V = valency angle = 109°. 5 



Aliphatic compounds (chain lattice). The zig-zag arrangement described 

 is fundamental to the morphology of saturated carbon compounds; 

 for it has been found that all aliphatic molecules represent such kinked 

 chains. In paraffin molecules, for instance, the increase in chain length 

 for each additional C-atom is 1.27 A instead of 1.54 A. It can easily 

 be calculated that this is in conformity with the zig-zag chains show- 

 ing the tetrahedron angle. In this way two carbon atoms reach a 

 spacing of 2.54 A, which is the intramolecular period of the paraffins 

 (Hengstenberg, 1928; MiJLLER, 1929; Halle, 193 i). 



In Fig. 31b it is shown how, by parallel alignment, such chains 

 combine into the rhombic crystal lattice of the paraffins. It seems 



