360 SECTIONAL TRANSACTIONS.—B. 
concerned with the shape of the pyranose ring; apart from its intrinsic 
interest this has considerable bearing on the linking of monose residues in 
polysaccharides. It is generally supposed that the pyranose ring possesses 
a ‘ strainless ’ puckered form ; this involves the unwarrantable assumption 
that the ‘ strainless ’ angle between the valencies of an asymmetric carbon 
atom is 1093° and ignores the different radius and valency angle of the oxygen 
atom. Since a hexo-pyranose of given configuration can possess no less 
than eight ‘strainless’ forms (excluding mirror image forms), direct 
experimental evidence is clearly desirable. ‘The X-ray results which have 
been obtained from about seventy crystalline carbohydrates will be dis- 
cussed. It appears that the five carbon atoms in the pyranose ring are co- 
planar or nearly so, the oxygen atom being displaced out of the plane. 
Various implications of this result will be discussed—e.g. such a ring-form 
requires the hydroxyl attached to the first carbon atom to be situated 
differently from the other hydroxyls with respect to the ring; this is in 
agreement with other evidence. The crystallographic results are found to 
confirm the configurations assigned to the « and 8 forms of various sugars. 
AFTERNOON. 
Visit to Printing Works of Messrs. Richard Clay & Sons, Ltd., 
Chaucer Lane, Bungay, and to Bungay Castle (2.0). 
Friday, September 6. 
Discussion on Surface phenomena, with special reference to substances 
which occur in nature (10.0). ; 
Prof. H. FREUNDLICH.—Displacement of chemical equilibrium at 
surfaces. 
Chemical equilibrium may be displaced by adsorption on surfaces. This 
is shown very directly by using indicators. The most convincing experi- 
ments are where the colour of an indicator changes, when a surface is 
produced by emulsifying one liquid in another, and where the original 
colour of the aqueous solution reappears, when the two phases separate again 
(Deutsch). If the second liquid is organic, the displacement is always 
in such a direction that the electrolytic dissociation of the indicator is 
decreased, compared with its state in the aqueous phase. The reverse 
takes place if an indicator, for instance a carbinol base, is dissolved in the 
organic liquid : on shaking with water, the change of colour may indicate 
the formation of more strongly dissociated substances. 
A similar displacement of equilibrium has been observed at surfaces 
between liquids and gases or solids (quartz, cellulose). 
Indicators may change their colour in presence of surfaces of colloidal 
particles. With colloidal electrolytes the following ‘sign rule’ holds: 
colloidal cations only influence the equilibrium of indicators where the 
colour change is due to a reaction between anions, and vice versa (G. S. 
Hartley). ‘The same rule applies to the influence of proteins on the colour 
of indicators (Thiel and Schulz). 
A displacement of equilibrium has also been found on charcoal with 
organic substances of low molecular weight, not indicators. 
The substances which are stable in adsorption layers may be very different 
from those stable in the bulk of a liquid. 
