I. FANKUCHEN AND H. MARK 



comparable with many paint brushes the handles of which are all 

 parallel. Using a somewhat abbreviated and oversimplified expres- 

 sion, one can also say that the diagram indicates that the sample con- 

 tains a multitude of oriented crystallites of silk protein. The fact that 

 each of the spots is larger than the actual geometric projection of the 

 irradiated part of the fiber bundle and that their boundary is somewhat 

 diffuse indicates that the highly organized areas consist of only a limited 

 number of strictly periodically arranged elements, such as atoms, 

 groups of atoms, molecules, etc. In other words, the oriented "crystals" 

 of the fiber protein (or, in our analogy, the bundles of pencils) are very 

 small. The presence of the intensive halo around the incident beam 

 ■ — compare Figure 1 — shows that there exist in this sample struc- 

 tural heterogeneities the dimensions of which are larger than the wave 

 length of the irradiated light. Cu Ka radiation has a wave length of 

 about 1.5 A., and the structural heterogeneities as indicated by the 

 central blackening have dimensions of about 100 A. Finally, the gen- 

 eral diffuse background of the pattern is caused by the presence in the 

 sample of a certain amount of disordered material which may, but 

 need not necessarily, be chemically different from the more highly 

 ordered constituents. This would be comparable to a situation in 

 which the bundles of pencils mentioned above are embedded in a mass 

 of randomly arranged pencils pointing in all possible directions. 



Using the same simplicity and abbreviation as above, we may 

 summarize by saying that the qualitative inspection of a diagram such 

 as shown in Figure 1 leads to the conclusion that the investigated ma- 

 terial consists of very small, highly oriented crystallites, which are em- 

 bedded in an amorphous matrix in such a way that certain long-range, 

 quasiperiodic spacings are somewhat accentuated. Each of these 

 statements corresponds to a special feature of the diagram, as repre- 

 sented in Table I. 



It may, perhaps, be appropriate to add a few brief remarks about 

 the justification of the use of "crystallites" and "amorphous areas" 

 in the qualitative interpretation of x-ray diagrams of this kind. With 

 reference to the crystallites, or micelles, we shall consider these to be 

 small volumes of somewhat indefinite size and shape, inside of which 

 the long-chain molecules are arranged according to a fairly regular 

 three-dimensional periodic pattern. There are also, however, in every 

 sample of a high polymer, certain portions which are not crystallized. 



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