4 STUDIES IN GELS II3 



of the amorphous part, x = the fraction of crystalline material. 

 Substituting 1.55 for the density of the cellulose fibre (determined 

 in toluene), 1.59 for that of crystalline cellulose and 6% less for 

 amorphous cellulose (compare butyl alcohol), Hermans (1946) cal- 

 culated X = 0.61 for ramie fibres and 0.18 — 0.32 for regenerated 

 cellulose. In other words, only 1/5 to 1/5 of the cellulose in rayon fibres 

 is crystalline. Whereas this result is quite acceptable, the amount of 

 crystalline cellulose in ramie is likely to be greater than 60%. Otherwise 

 the difference between the birefringence of ramie fibres and that of 

 crystalline cellulose ought to be greater than actually determined 

 (Frey-Wyssling and Speich, 1942; according to our measurements it 

 amounts to 4.4% and, based on the double refraction 0.0705 of 

 crystalline cellulose determined by Hermans 1949, to 7.3 %). 



The crystallinity of a gel can also be determined by X-rays. Since 

 amorphous substances scatter the X-ray beam, they cause a diffuse back- 

 ground blackening of the film in the X-ray camera. The photometer curve 

 (cf. Fig. 70, p. 102) taken from such films permits computation of the amount 

 of the amorphous fraction in the gel under investigation. By this method 

 Hermans and Weidinger (1949) find 70% crystalline cellulose in ramie 

 and 39 % in regenerated cellulose. There is a third means of estimating 

 the amount of the two fractions. As the hydrolysis velocity of amorphous 

 cellulose is much greater than that of crystallized cellulose, the quantitative 

 relation between them can be derived from a suitable hydrolysis/time curve. 

 Philipp, Nelson and Ziifle (1947) calculate by this method 95% crystal- 

 linity for ramie fibres and about 70 % for rayon. As the three methods 

 mentioned (optical. X-ray and chemical) yield different values for the 

 crystallinity of the same gel, we must conclude that there is no net difference 

 between crystallized and amorphous cellulose; hence the non-crystallized 

 fraction is rather to be considered 2lS paracrystalline (cf. Fig. 54, p. 70). 



Hermans criticizes the opinion that dry xerogels are porous bodies 

 on the ground that no one speaks of submicroscopic spaces in the case 

 of glasses either, notwithstanding the lower density than in the crystal- 

 line state. This comparison, however, does not seem quite justified 

 to me, since certain liquids (such as water, alcohols and aldehydes in 

 the case of cellulose) are capable of penetrating into xerogels, whereas 

 this does not occur in glasses. Thus, clearly, there must exist a differ- 

 ence in the order of magnitude of the "empty spaces" present. In 

 the swollen state xerogels definitely possess a loose structure, and it 

 is not likely that the micellar framework loses this structure completely 



