Gravimetric Determination as Barium Sulphate

In order to eliminate any disturbing silicates, the water sample is evaporated to dryness after acidification with 3 ml hydrochloric acid (1.125 g/ml). 

The residue is heated to boiling point, after adding 5 ml of the same hydro- 

In the event of sulphites being present, the water sample is not acidified until the quantity of 0.1 m or 0.01 m iodine solution detected in determin- 

Silver nitrate solution, approximately 0.1 m Barium chloride solution  

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Gravimetric determination as barium sulphate after distillation General... 

Similar to hydrogen sulphide and sulphides, sulphur dioxide and sulphites can be determined by titration with iodine or by oxidation to sulphate followed by gravimetric determination as barium sulphate. Additionally a spectrophotometric method was developed based on the colour of p-nitroaniline which is discharged on acidification but is restored by adding formaldehyde and sulphur dioxide or sulphite. 

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