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limit test is nothing but to identify the impurities present in the substance and compare it with the standard. Importance of Limit tests is to find out the harmful amount of impurities. Barium sulphate reagent contains barium chloride, sulphate – free alcohol and small quantity of potassium sulphate. The inclusion of the small quantity of potassium sulphate in the reagent increases the sensitivity of the test. Alcohol prevents super saturation and more uniform turbidity develops.