42 SECTIONAL ADDRESSES 
The tendency for inulin to undergo this change is best understood from 
writing the complete constitution of this carbohydrate in the following 
way. In no case can the constitution of inulin be represented as a flat 
model, inasmuch as the stereochemical arrangement necessitated by the 
1 : 2 junctions demands that the model should be spaced in either of the 
following ways : 
(2) oH 0 
Ho GH ) CH, 
i woke Gy eco 
¥ H ~, 
2 
(2 
Brot cE ens 
mommy ON Ney Papi 
H Ho Se if 
“ho SoMa) ie big ne meaner, raed [es 4 
0 0) 0 
te dhe <n 
Qoney- 
In the second of these formule for inulin, which are really identical 
constitutions differing only in the draughtsmanship employed to represent 
them, it will be seen that a simple cleavage along the dotted lines in a 
hydrolysing medium will liberate pairs of fructo-furanose units which 
can readily combine as the difructofuranose anhydride shown above. 
From what has been said of the stereochemical arrangement of inulin, 
and the difficulty of compressing the model within a linear chain, it is 
perhaps not surprising to learn that acetyl inulin and methylated inulin 
give altogether fallacious results for molecular size by the viscosity method 
and the Staudinger formula, from which it would appear that the molecular 
weight is of the order of 1,300. The end group method of assay of 
methylated inulin shows the molecular weight to be about 5,000 and the 
chemical molecule to be composed of 30 fructose units. Alternative 
methods of measurement of molecular weight confirm this value. The 
ebullioscopic method gives indeed an identical value and it has recently 
been found that the osmotic pressure exhibited by inulin derivatives fully 
confirms this figure. I have invited Dr. S. R. Carter to give some account 
of the experimental equipment and the choice of membranes which have 
already been of service in the case of one or two other polysaccharides - 
in determining the molecular weight of high polymers. These constitu- 
tional models for inulin and levan illustrate how wide a disparity there is 
between the several carbohydrates which may occur in one and the 
same plant. It must be conceded that in no other natural products 
does the factor of stereochemistry enter so largely as in the carbohydrate 
