Part IV.] Puran Singh : Preparation of Tannin Extracts . ii 
setting forth the commercial possibilities of the process. It may be 
pointed out here that though the decolourisation by nickel hydroxide 
entails some loss in the percentage of tannin which in chemical processes 
is always inevitable, yet it has no injurious effect on the original 
properties of the material. In this respect, the process combines in 
itself the effects of chemical decolourisation and mechanical clarification. 
This is an advantage, which very few processes of chemical decolourisa¬ 
tion possess. 
Considering the necessary defects that chemical treatment of the 
tannin extract entails, the latest view on the subject is that the processes 
bi decolourisation by chemicals are quite inconsistent with manufacture 
of good extracts. The authoritative opinion of Messrs. Dumsney and 
Noyer on this point may be quoted here : “ The decolourisation of the 
future does not lie in the use of chemical products, nor more or less 
complicated processes ; tanning is an industry already far too complex to 
stand it; it requires and will require, before and above all, pure extracts 
of a well-determined nature, with a high percentage of tannin, soluble in 
cold water and finally of as constant and uniform a composition as 
possible/’ (Wood Products, Distillates and Extracts by P. Dumsney 
and J. Noyer, page 205.) The same authors (loc. cit., page 206) com¬ 
menting upon a process of decolourisation based on the use of aluminium 
sulphate and sodium bisulphite make the following remarks :— 
“Notwithstanding the interesting aspects of these decolourisation 
processes, the authors maintain the opinion given above and add that they 
all have drawbacks, both for the extract manufacturer and the tanner; 
the first loses, whatever may be the process used, from 2 to 3 per cent, 
of tannin to the detriment of the yield in extract, and the percentage fails 
the second party, while the colour of his leathers is in no way altered. 
The authors can, in fact, affirm that, having had occasion to make import¬ 
ant analysis of the tannin in different leathers, where they had used 
decolourised extracts (either by blood or by nitrate), all the leathers tanned 
by these extracts were darker than those yielded by other and well clari¬ 
fied extracts, and that although the colouration of a 1 per cent, solution 
was less dark than solution of purified extract. Moreover, the tannery of 
the future will be that which utilises mixed processes of tanning with 
extracts manufactured in a genuine manner and judiciously used; the 
.opinion of Procter, the eminent English Chemist, is decisive on this 
point/'’ 
228 
