As the desulphurizing bath of the raw viscose silk, natrium sulphide is usually employed, and the reaction products in this case are polysulphide, Na₂S₂O₃, Na₂SO₄ and others. In this paper, the methods of analysis of the bath are related.
1. Natrium mono-and polysulphide. a) Determine the consumption of the total iodine as well as the iodine corresponding to Na₂S₂O₃ and Na₂SO₃. The difference of both values gives Na₂S. b) Take the sample with ammonia water and natrium acetate solution, and titrate it by standard ZnSO₄ solution containing ammonia water and ammonium chloride. The end point is determined by nickel sulphate paper. c) Take the sample with ammonia water and ammonium sulphate solution, and titrate it by standard AgNO₃ solution containing ammonia water and ammonium sulphate. The end point is determined by cadmium sulphate paper. These three methods give nearly the same values for mono-and polysulphide.
2. Natrium sulphite. Add barium chloride solution to the sample and filter, and determine the iodine consumption of the filtrate. The difference of the total iodine and this iodine consumption gives Na₂SO₃. Polysulphides and sulphite can not exist in one bath, and the practical desulphurizing bath does not contain the latter.
3. Natrium thiosulphate. Add natrium chloride, natrium acetate and zinc sulphate to the sample and filter, and determine the iodine consumption of the filtrate, and calculate Na₂S₂O₃.
4. Natrium carbonate. Titrate the sample with normal acetic acid using phenolphthalein as indicator. Add barium chloride to the other sample, and determine its alkali as above. The double of the difference of the two values gives Na₂CO₃.
5. Natrium sulphate. Add hydrochloric acid to the sample and evaporate to dryness, and on dissolving it in water, determine Na₂SO₄ by barium chloride.
6. Total alkali and natrium hydroxyde. Add an excess of the normal sulphuric acid to the sample and boil, and titrate it back with the normal alkali solutlon, the result of which gives total alkali. The difference between total iodine consumption and carbonate alkali and total alkali is assumed to be NaOH.
7. Total sulphur and polysulphides. Oxidize the sample with alkaline hypochlorite solution and determine the sulphur as barium sulphate. The difference between total sulphur and sulphur corresponding to sulphur compounds is the sulphur for polysulphide.
One example of the desulphurizing bath used practically in this analysis is as follows :
Na₂S 19.07g/l
Na₂CO₃ 3.39g/l,
Na₂S₂O₃ 32.39g/l,
NaOH 3.36g/l,
Na₂SO₄ 9.55g/l,
Total S 23.55g/l,
Polysulphide S 7.01g/l,

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