ANALYSIS FOR SMALL AMOUNTS OF CALCIUM, MAGNESIUM, BARIUM, AND SULPHATE USING PHTHALEIN PURPLE

For the determination of sulphate ion in samples containing 3 to 20 mgm., it was found that the standard precipitation techniques did not give sufficiently accurate results, and were time consuming. Reference to the literature showed that with certain modifications a complexometric method proposed by Schwarzenbach etal. for samples containing 20 to 50 mgm. of sulphate was most likely to give accurate results rapidly. In this method the sample is passed through a cation exchange column and washed with distilled water into a flask. This solution is boiled and precipitated with excess standard disodium ethylenediaminetetracetate in the presence of alcohol and ammonia using phthalein purple indicator. Provided that the details of procedure described in this paper are closely adhered to, accuracy is usually within two per cent. Calcium, magnesium, and barium may also be titrated directly using the phthalein purple indicator.