Part IV.] Puran Singh: Preparation of Tannin Extracts. 9 
sodium bisulphite to 1,100 gallons of liquor at 4°B. The liquors so 
treated are decolourised by aluminium hydrate in nascent state, which 
agglutinates the resinoid particles of the liquor and falls with them to 
the bottom of the vat just like blood or albumen. Moreover the nascent 
sulphurous acid as it escapes during the reaction has an intensive de¬ 
colourising effect. Extracts thus made are soluble in cold water and 
.’etain an acid reaction. 
Sodium bisulphite forms the subject of various patents. In one of the 
patents the tannin extracts are treated with sulphurous acids, sulphites, 
bisulphites and hyposulphites, and also with a mixture of hypo- 
phosphorous acid and phosphorous acid, by means of which reduction and 
decolonisation takes place. 1 
In another process 2 milk, preferably butter milk, is added to the 
tannin extract and the mixture heated to 70°C. The albumen of the 
milk is thus coagulated and while settling, it takes with it the insoluble 
matter and part of the colouring matter of extract. 
Another patent 3 consists in the use of formaldehyde sulphoxylate, 
either pure or mixed, with formaldehyde bisulphite. For example, one 
litre of chestnut extract of 4°B is treated with about 5 gram of Ronga- 
lite C. (sodium formaldehyde sulphoxylate of about 90 per cent, strength), 
and evaporated to dryness in a vacuum. 
The writer while first trying his laboratory experiments on the de¬ 
colonisation of Mangrove bark in 1908, thought of utilising nascent 
hydrogen as a decolouriser of Mangrove bark tannin extract and, accord- 
ingly, he tried the effect of extracting the bark in contact with metals 
and weak acids such as tin, and zinc in contact with acetic, oxalic, formic 
acids, etc. A considerable improvement in the colour of the extract was 
observed. Acetic acid, however, had a bad effect on the tannin strength. 
Lactic acid and oxalic acids in small quantities were, therefore, preferred. 
Much of the effect and the reduction of the deep colour of the extract 
was due to the presence of free organic acids. It was also noticed that 
the contact of the metals tin and zinc with the bark while under treat¬ 
ment, even without the presence of free organic acids, produces an appre¬ 
ciable reduction in the colour of the resulting extract. This has been 
1 See Jour. Soc. Chem.-tnd., Vol. XXVI, 1907; p. 704. 
2 Loc. cit., Vol. XXVIII, 1909, p. 804. 
3 Loc. cit., Vol. XV, 1906, p. 770. 
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