Waste sulphite liquor is a by-product of the wood pulp industry, and very large quantities are available in the countries where this industry is carried on. For every ton of cellulose about 10 tons of the liquor are produced. Among the substances present in it are dextrose and other sugars; xylose; acetic, sulphurous, and tannic acids; methyl alcohol; and nitrogenous and resinous bodies, together with calcium lignin-sulphonate, the chief by-product of the reaction involved in the production of the pulp.

The amount of fermentable sugars in the liquor varies rather considerably, but is usually between 15 and 2 per cent. An analysis by Klason gave dextrose 1.65, mannose 0.53, and galactose 0.27 per cent. Of these sugars, galactose ferments more slowly than the others, and the highest yields of alcohol obtained, namely, 1.4 per cent. of the volume of the liquor, corresponds approximately with the dextrose and mannose content.

1 Chem. and Metall. Eng., 1918, 19, 555. 2 U.S. P. 985725 and 985726. 3 F.P. 477077, 1914. 4 Helv. Chim. Acta, 1918, 1, 87.

Various processes are in use for utilising the waste liquor as a source of alcohol ("sulphite spirit"), but all are based upon the same principle. The free sulphurous acid, which is strongly toxic to yeast, is partly removed by evaporation and partly by neutralisation to a point of acidity favourable for fermentation. The hot liquor is neutralised in large vats, then cooled in towers, and aerated A yeast nutriment, such as malt extract, or dead yeast, is added to the cooled, neutralised liquor, which is then fermented. After the fermentation is finished, which takes three days or more, the yeast is separated and the liquid distilled in a continuous-action still. The alcohol obtained is already partly denatured, since it usually contains a little methyl alcohol derived from the original liquor, with some aldehydes and furfural, and sometimes acetone.

Ekstrom's process1 has been in operation for several years at Skutskar (Sweden), and that of Wallin at Forss, whilst others employed industrially are Landmark's and Marchand's. The difference in the various processes lies mainly in the method of neutralisation. It is not advisable to neutralise with lime alone, as a large excess is required, causing destruction of some of the sugar. In the Swedish plants which are operating under Ekstrom's and Wallin's patents, the neutralisation is partly effected with lime, and then finished with calcium carbonate. In Landmark's process, calcium carbonate only is employed, and in Marchand's, barium carbonate. The waste liquor does not contain sufficient nitrogen and phosphate for normal fermentation, and these must be supplied in a suitable form, with the yeast extract or otherwise. In Ekstrom's method, a yeast specially acclimatised to sulphite liquor is used. In Landmark's process, milk or whey is heated with acid, the precipitate separated, and the liquid portion added to the sulphite liquor, which can then be fermented directly with ordinary brewers' yeast. The cost of the milk is said to be covered by the "lignocasein" obtained, which can be used for sizing paper.2 A. V. Jernberg3 adds to the liquor a neutralising agent and a sufficient quantity of calcium cyanamide, previously treated with water or steam, to supply the deficiency in nitrogen.

The yield of alcohol is about 1 per cent. of the waste liquor, on an average, though rather greater yields are claimed for some of the methods.

1 B.P., 6741, 1910. 2 Bjarne Johnsen, J. Soc. Chem. Ind., 1918, 37, 131t.

3 U.S. P. 1221058, 1917.