CARBOHYDRATES, CHITIN AND CUTIN 



321 



0.074 



0.013 



tural elements of starch have been found with the electron microscope 

 (unpublished data) so that its texture must be amicroscopic. On the 

 other hand, those spaces must be fairly wide, since they are accessible 

 to the big molecule I.^ whose diameter measures 2.7 and 5.3 A, and 

 to organic dyestuffs. It is doubtful whether these molecules can be 

 inserted into the intermolecular spaces of the crystal lattice shown in 

 Fig. 158, where the cross-section of the starch chains is not drawn in 

 its actual dimensions, but is merely symbolized by a black dot. 

 However, there is the possibility of gaps in the chain lattice, or of 

 a widening of the crystal lattice by water, in the same way as is known 

 to occur in zeolites. 



The analysis of the rodlet 

 birefringence supports this view\ 

 Series of aldehydes, monovalent 

 alcohols and polyvalent alcohols 

 (glycol, glycerol) including wa- 

 ter give three different curves of 

 rodlet birefringence (Fig. 159), 

 disclosing different intrinsic 

 double refractions in these three 

 groups of liquids. This is due to 

 the different interaction of these 

 compounds with the starch 

 chains. Lipophilic liquids (amyl- 

 bromide, xylene, toluene, ben- 

 zene, chlorobenzene, bromoben- 

 zene, and a-bromonaphthalene) 

 do not penetrate into the starch 

 grain, because they have no affin- 

 itv for starch ; the double refrac- 

 tion therefore does not change in 

 a series of lipophilic liquids with 

 increasing refractive power. 



Since crystallized starch attracts water molecules which penetrate 

 between the molecular chains, the starch grains ought to dissolve in 

 water. 



Such a dissolution is possible with another reserve carbohydrate, viz., 

 mannan, which is obtained from the tuber of Amorphophallus konjak and is 



0012 



OOII 



1.60 ni" 



Fig. 159. Rodlet birefringence curves of 

 potato starch (Speich, 1941). A in lipophilic 

 liquids; B in aldehydes; C in monovalent 

 alcohols (except ethanol); D in water, 

 ethanol, glycol, glycerol and their mixtures. 



