90 



1^ C/. Boeseken, v. don Berg & Kerstjens, Rec. Trav. Chim. Pays Bns, 35, 

 320-345 (1916). Cellulose is regarded as (CcHi,0|i)n— (n— 1) H,0, and the 

 acetylation process is studied. As the molecule is hydrosed the acetyl number 

 increases from 62-5 for cellulose triacetate to 77 for dextrose pentacetate. The 

 molecule combines with 3«.+2 mols of acetic acid, giving a triacetate of aaolecular 



weight (162n+18) + (3n+2)42. The acetyl number = '43^4.^7 ■ from which 



n can be calculated. Values of n as high as 47-5 were found. 



" The viscous colloids are nearly all of vital origin. Cf. gelatin, rubber, 

 casein, the gums, etc. 



1*" See in this connection Miss Curm.ingham, Trans. Chem. Soc, 113, 173-181 

 (1918). 



1' Pictet & Sarasin, Compt. rend., 166, 38-39, (1918). • 



" Sarasin, Arch. Sci. Phys. Nat, IV., 46, 5-32 (1918). Starch and cellulose 

 are polymerides of 1-glucosan. 



HO— CH CHOH 



1 2 I 



HC8 O'— 'CH 



HaC^ O 8 «CHOH 



Polymers are found by the opening of the oxygen atom marked 8. This explains 

 the presence of 2 ■ 5 dimethyl furane in the products of decomposition. 



1' Irvine, Annual Reports (Chem. Soc), 69 (1918). The glucosan-polymeride 

 formula is criticised on the ground that it does not account for the particular 

 trimethyl glucose obtained from methylated cellulose by hydrolysis. (See 

 Denlmm & Woodhouse, Trans. Chem. Soc, 111, 244 (1917)). 



"" Compton (J. Franklin Inst., 185, 745-774 (1918)), concludes that in the 

 solid state, atoms are so intimately intermingled that particular molecules 

 cannot be said to have any real existence. 



^1 Eng. Pat. 114, 304 (H. Dreyfus) states that the higher the viscosity of 

 cellulose acetates, the greater the amount of plastifying or softening agents 

 which can be incorporated, and the stronger the resulting material from every 

 point of view. 



^^ In this connection see Bayliss, 2nd Report of this Committee. ' Protoplasm 

 and Cell Contents,' and 'The Nature and Permeability of the Cell Membrane.' 

 pp. 117-137. 



-' J. D. van der Waals, jnr. (K. Akad Amsterdam, Proc. 21, 5 pp., 743-755, 

 1919) points out this difference between gaseous and liquid friction. He attributes 

 liquid friction to the forces exerted by tlie molecules on each other, whereas in 

 gases it is due to the transfer of momentum from one layer to another. 



"'" The resistance to shearing stress gradvially increases as solvent is removed, 

 vmtil finally an elastic solid results. 



2« Trouton, Proc. Roy. Soc. 77, 426 (1906) and Trouton & Rankine, Phil. 

 Mag. [6], 8, 538 (1904). In the stretching of rods of highly viscous material the 

 following relation is found : — 



F /dv 



A/di-^ 

 WheFe F = stretching force. 



A = cross section of rod. 



V = velocity of given point of rod. 



X = distance of moving point from point of suspension. 

 From a chemical point of view it is unfortunate that Trouton worked with 

 substances of so indeterminate a nature as pitch and shoemakers' wax. The 

 use of a plastic material composed of a celluloid ester, a crystalline filler svich as 

 camplior, and alcohol, in a similar series of researches, would to some extent 

 simplify the interpretation of the phenomena. We do not know yet why 

 camphor is par excellence the solid solvent for nitrocellulose. It evidently 

 possesses a somewhat unique combination of chemical and physical properties. 

 Substitutes for camphor can only be accurately compared with it by some system 

 of physical tests of the resulting material such as these. The explanation of its 

 colloidal behaviour is not likely to be found until these experiments are done. 



