Sodium alizarin sulphonate, indicator

The yield of radioactive D.F.P. from 32P is necessarily small on the semi-micro scale (p. 75) it is better therefore to titrate the fluoride (obtained after the decomposition of D.F.P.) with thorium nitrate, sodium alizarin sulphonate being used as indicator.2 It is necessary, however, first of all, to remove the fluoride by distillation (p. 211). This method gives an accuracy of +1 per cent with 50 mg. of D.F.P. This degree of accuracy on a semi-micro scale3 may be considered fairly satisfactory. 

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