SECTIONAL TRANSACTIONS.—B. 471 
compared with the adsorption of indigo-white on the fibre; the third 
resembles in some way the production of the insoluble indigo itself on the 
fibre, and this process is irreversible. The third step, that is the self- 
condensation of the tannin, is portrayed in this connection, 
Dr. P. MairLanp.—The chemistry of Quebracho tannin. 
The hypothetical stem substance of Quebracho tannin, the so-called 
Quebracho-catechin, whose formula was suggested by Freudenberg in 1925, 
has now been prepared synthetically from the corresponding pyrylium salt. 
This new catechin is very similar to ordinary catechin itself, and has been 
condensed to a product which shows many similarities to the purified 
Quebracho tannin of natural origin. 
The ‘ phlobaphene ’ reaction of the catechins has also been studied, and 
some light thrown on its probable mechanism. 
Prof. Dr. M. BERcMANN.—The chemistry of skin, and the catechol 
tannins. 
Skin is altered by tanning in such a way that it becomes more resistant 
to putrefaction. ‘The chemical groups of the skin are also so altered by 
tanning that they can better resist the chemical attack of the proteolytic 
enzymes of the organisms of putrefaction. 'This resistance to enzymes is, 
however, only limited in vegetable-tanned leather. According to the 
tanning material used, the pre-tanning treatment of the skin and the manner 
of tanning, the leather can be digested by the proteolytic enzymes to a 
greater or less extent. The measure of this digestion is a measure of the 
quality of the tanning. There appears to have been found here a new 
analytical means for the investigation of leather since progress of tanning 
can be measured by a falling away of a particular chemical characteristic. 
By simple experiment it can be shown that liming and bating with enzymes 
have a quite recognisable influence on the colloidal condition of the skin 
which must make itself felt during the course of tanning. 
The behaviour of a tannin during the tanning process depends directly 
on its general chemical character. By sulphiting, the chemical nature is 
altered and it then produces leather of different properties from non-sulphited 
tans. Even the molecular size of the tannin is of fundamental importance 
in the tanning process. 
These particular lines of thought and experimental methods show the 
way to a rational method of leather manufacture. The properties of the 
leather can be altered at will by selected variations of the methods of tanning. 
Dr. H. Puitiies.—The nature of the vegetable tanning process. 
Gelatin in solution combines instantaneously with tannins, hide powder 
less rapidly, whilst the structurally intact hide tans slowly. The speed of 
tannage is thus governed by the rate of diffusion of the tannins into the hide. 
This rate of diffusion is dependent on the following inter-related factors : 
(a) the size of the intermolecular spaces in the hide ; (b) the intensity of the 
electrical charge on the protein molecules ; (c) the size of the tannin mole- 
cules ; (d) the charge on the tannin molecules ; (e) the degree to which the 
tannin molecules are hydrated. The non-tannins in vegetable tanning 
“materials play an important part in the process since they influence the size 
of the intermolecular spaces in the hide and also modify the properties of 
the tannins. Vegetable tanning materials vary in character, and the tanner 
blends and manipulates the tan liquors so that penetration of the hide by 
