Abstract
The side reactions between sulphide and sulphite which take place at the neutralization of those mixtures and the total alkali titration method of kraft liquors were studied. The results are summarized as follows :
1. When total alkali of a sample containing sulphite in great quantities is titrated without aldehyde, the side reactions pointed out by D. R. Moltzau are taken place distinctly and result a decrease in alkalinity.
2. On the contrary, it is possible to titrate whole of sulphite (not a half of sulphite, as usually supposed) when titration is made rapidly with 1 N-acid using methyl orange indicator on a 50 ml of diluted sample by twenty times of the original liquor containing Na2 SO3 about 5 g/l or less, and nearly at the end point promote the reaction which increases alkalinity at acidic medium by heating and then cooling to the room temperature, and again titrate to the final end point.
Total alkali obtained in such way, therefore, is expressed as follows :
NaOH+ Na2S + Na2CO3+ Na2SO3+ Na2SiO3
And in this way, no addition of furfural is neccessary.
3. The side reaction which decreases alkalinity is expressed in the next chemical equation.
2NaHS+4NaHSO3=3Na2S2O3+3H2O
And the reaction by which whole of sulphite are neutralized is expressed as follows :
NaHSO3+3H2S=NaHS+3S+3H2O
or
2NaHSO3+2H2S=Na2SO3+3S+3H2O
