64 FUNDAMENTALS OF S UBMIC RO SCOPIC MORPHOLOGY I 



are of particular importance in biology, become increasingly pro- 

 nounced beyond a certain degree of polymerization. 



It is only from the low molecular weight members of a homologous 

 polymeric series that uniform substances of definite molecular weight 

 can be obtained by recrystallization, fractional precipitation, etc. In 

 the members of higher molecular weight this is no longer possible. 

 In the series of paraffins, in particular, it has been found that fraction- 

 ation gives mixtures of substances of molecular weights which are 

 only approximately equal. The determination of the degree of polymeri- 

 zation therefore yields only an average value ; the actual chain lengths 

 are spread more or less around this value according to the method 

 of fractionation. Such mixtures are called polymer uniform substances 

 ("'polymer einheitliche Stoffe") by Staudinger (1936b). Whether 

 the high polymers occurring in nature are also polymer uniform, or 

 whether life always builds chains of exactly the same length cannot 

 be decided at present. 



Although the representatives of a homologous series behave quite 

 differently from a physical point of view, they show the same, or 

 at least a very similar chemical behaviour, in conformity with their 

 uniform structure. For instance, the alcoholic OH-groups of all re- 

 presentatives in Table VIII and, further, those of the polysaccharide 

 molecules shown in Fig. 50 and even those of the polygalacturonic 

 acid chains (Schneider and co-workers, 1936; Deuel, 1947b) can 

 be etherified and esterified (methylated, acetylated, nitrated, etc.) with- 

 out measurable change in the degree of polymerization. The polymer 

 mixture formed in this way from the polymer uniform substance con- 

 cerned has the same average chain length as the original material 

 (it is an "analogous polymer", Staudinger, 1936b). On esterifica- 

 tion, the cellulose chains lose their polar, hydrophilic properties, 

 acquire a more homopolar lipophilic character and on account of their 

 solubility in organic liquids are then more accessible to osmotic ex- 

 periments. 



b. Structural Viscosity 



Anomalous flow. The four fractions of the series of homologous 

 cellulose polymers yield colloid solutions of an entirely different 

 nature. Staudinger divides them into "almost, meso-, hemi- and eu- 

 -colloid" (Tabic VIII). In the two former cases the chain molecules in 



