470 SECTIONAL TRANSACTIONS.—B. 
of the original twelve constant equation. Further work on these lines is 
likely in the near future to provide a clearer picture of the interaction within 
a molecule of atoms which are linked together and of atoms which are not 
linked in the chemical sense. 
Mr. C. N. HINsHELWoop, F.R.S. 
The curves showing the rate of reaction of certain gaseous substances as 
a function of pressure have proved to be composite in nature, although only 
one set of reaction products is formed. ‘Thus it must be concluded that 
a given molecule can be activated in more than one way for the same 
chemical transformation. This phenomenon presumably depends upon 
the localisation of the energy of activation in different modes of vibration, 
and should be correlatable with the information about the internal structure 
and vibrations of the molecules, as obtained from other methods of 
investigation. 
AFTERNOON. 
Visit to Messrs. Briggs’ Tannery, Leicester. 
Tuesday, September 12. 
Discussion on The chemistry of the tanning process (10.0) :— 
Dr. D. Jorpan Lioyp.—The chemistry of skin, and the problem 
confronting the tanner. 
Animal skin consists of a tissue of fibres which are the biological units. 
Each fibre has crystalline properties and is formed of packets of elongated 
molecules between which are planes of weakness. ‘The fibre can be split 
up at these planes into fibrils. This is an essential pre-tanning process since 
it increases the capillary space through which the colloidal tannins can diffuse 
and makes the polar groups of the protein accessible to the tan. Collagen 
carries postively and negatively charged polar groups, and collagen fibres 
contain both bound and free water. ‘Tanning consists in conferring chemical 
and physical stability on the collagen fibre by the suppression of the active 
groups and the elimination of water. 
Prof. Dr. K. FREUDENBERG.—TZannins and their behaviour towards 
proteins. 
It is known that phenols form molecular compounds with amines and 
amides (e.g. phenol itself with aniline or urea). ‘The amines and amides 
can be simple or complex, like proteins ; the phenols also can be simple or 
complex, as for example the tannins of the gallotannin or catechin groups 
(whose constitutions are discussed). It is therefore affirmed that, when a 
tannin and a protein particle come together, a molecular compound is 
formed first. In a single tannin particle there are available many phenolic 
groups capable of combining with the active groups of a protein particle. 
After the first contact the two particles combine in such a way that the 
greatest possible number of the phenolic and peptide groups are near one 
another. 
The first process is a contact at single points, the second is the mutual 
permeation of the parts. Until then the process is mainly reversible. 
The third process is the condensation of the neighbouring tannin particles 
te insoluble high molecular compounds. The two first steps may be 
Pn 
