Part I V.] Puran Singh: Preparation of Tannin Extracts. 17 
For cooling tan liquors, a supply of cold ivater say at about 15 to 
18°C must be available in the factory , and this should be borne in mind 
in choosing the factory site. 
(6) Heating of tan liquors for longer than is absolutely necessary is 
another factor which has a very detrimental effect in changing the com¬ 
position of the extract owing to the formation of non-tannins and oxidation 
products. It will be seen from what has been given in Chapter I, that 
the Single Effect system of vacuum pans and even the Double and Triple 
effect systems, one after another, have been given up in favour of Kestner*s 
evaporators, as improvements were effected in the machinery used in 
tannin extract according to the needs and experience of the manufac¬ 
turers in Europe. In Kestner’s evaporators of multiple effect the 
maximum of water is evaporated with the minimum of steam and in 
the minimum of time. 
Of all the extracts, as has been pointed out, mangrove bark extract 
is the most sensitive and is liable to develop a dark colour through oxida¬ 
tion, heat and alkaline water, it seems essential that the mangrove Tannin 
Extract Factory should be equipped with Kestner’s evaporators of multiple 
effect. 
(7) Storing for any great length of time, even of good mangrove 
extracts, results in the reduction of their tannin strength. It is due to 
slow oxidation resulting in the formation of insoluble products. For 
example, the writer observed that mangrove extracts made at the Ran¬ 
goon Tannin Factory in the year 1904-05 were reduced for the most part 
by 1910-11 to insoluble oxidized products of a blackish brown colour 
with dull earthy fracture. To take a recent example, the mangrove extract 
made in February 1911 showed a decrease of 3 per cent, of tannin after 
four months* storing. This rapid change in the percentage of tannin is 
possibly due to the presence of the mineral matter present in the natural 
water used for extraction, but it admits of little doubt that all tannino* 
materials do deteriorate on storage. 
For the reasons cited, it is therefore advisable to secure a regular 
marJcet for the fresh extracts as they come to hand and never to keep a 
large stock in the factory. 
234 
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