Wool sulphur dioxide

Thionyl chloride method. Mix 100 g. of pure p-nitrobenzoic acid and 126 g. (77 ml.) (1) of redistilled thionyl chloride in a 500 ml. round-bottomed flask. Fit the flask with a double surface reflux condenser carrying a calcium chloride (or cottou wool) guard tube and connect the latter to an absorption device e.g., Fig. II, 8, 1. c). Heat the flask on a water bath with occasional shaking for 1 hour or until the evolution of hydrogen chloride and sulphur dioxide ahnost ceases. Allow the reaction mixture to cool, transfer it cautiously to a Claisen flask connected with a water-cooled condenser and a receiver (compare Fig. II, 13, 1). Distil off the excess of thionyl chloride (b.p. 77°) slowly and continue the distillation until the temperature rises rapidly to about 120° this will ensure that all the thionyl chloride is remov. Allow to cool, and distil the residual p-nitrobenzoyl chloride under diminished pressure as detailed in the Phosphorus Pentachloride Method. The resulting p-nitrobenzoyl chloride (a yellow crystalline solid) weighs 107 g. and melts at 72-73°. 

Sulphur dioxide can be removed at 450° using silver wool combined with a plug of platinized quartz wool. Halogens are removed by using Mg, Zn or Cu, heated to 450°. 

The free sulphur in the issuing gas may be removed by condensation and filtration through glass wool. Carbon disulphide vapour may be absorbed in ethereal triethylphosphine. The maximum formation of the disulphide is at 850° to 900° C., the sulphur from the sulphur dioxide then being distributed as follows —... 

Bleaching of wool with sulphur dioxide (stoving process)... 

This was carried out extensively in this country until 1940 when, owing to the scarcity of sulphur, it fell out of use and it is doubtful whether it has been revived to any great extent. It did, however, give an adequate bleach for lower quality goods, was extremely cheap, and only required simple equipment. The process was known as stoving because the wool was exposed to sulphur dioxide in what was called a stove. 

As well as flowers, silk, straw, wool, etc., may be bleached by the action of sulphur dioxide. 

The content of cystine, cysteine and sulphur dioxide (which gives a reduction wave between the anodic cysteine wave and the cathodic cystine wave) has been determined in wool destroyed in alkaline, acidic, oxidizing and reducing media. 

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