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The thermal decomposition of sodium dithionite (Na2S2O4) in the solid state was investigated by differential scanning calorimetry and the exothermic heat of decomposition was determined. The effect of isothermal pretreatment at various selected temperatures on the subsequently determined decomposition temperature was studied, together with the effect of sample weight on the decomposition temperature and degree of exothermicity.

The polymer is oxidised by a mixture of ceric ammonium sulphate and concentrated sulphuric acid in a closed system. The chlorine that is released then diffuses to a solution of ferrous ammonium sulphate, in which it is absorbed and reduced. The resultant chloride is then determined by the Volhard technique.AN important group of textile finishing materials comprises the polymers of vinyl chloride, vinylidene chloride and their copolymers with vinyl acetate, vinyl alcohol and acr ylonitrile. Since these polymers are unreactive chemically, differentiation is difficult, especially when only small amounts are available. Although their solubility in different organic solvents may give some clue to their identity, this is not very reliable and to make successive tests on small samples is not easy. However, it is sometimes possible to distinguish between these materials by means of their chlorine content, which serves, in many cases, to distinguish them from neoprene and rubber compounds containing chlorine. Characteristic values for a number of vinyl polymers and copolymers and for neoprene and two rubber compounds are given in Table I. TABLE I CHLORINE CONTENTS OF SOME UNPLASTICISED COMMERCIAL POLYMERS