Standardization of the sodium peroxide bomb method with pure fluoroacetamide

Standardization of the sodium peroxide bomb method with pure fluoroacetamide 

The yield of radioactive D.F.P. from js necessarOy 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. 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 scale may be considered fairly satisfactory. 

The fluoride solution is diluted to lOO ml. with water, 8 drops of the indicator are added and the pink coloration just removed with 1/200 hydrochloric acid solution. Then I ml. of the monochloroacetate buffer solution is added and the solution is titrated with the thorium nitrate solu -tion to a faint pink coloration. This may be seen more easily by allowing the precipitate of thorium fluoride to settle, when the pink coloration collects at the bottom of the beaker. It is essential to use either bright sunlight or mercury vapour illumination, otherwise the end-point is indistinct. 

A Control reaction with the indicator must be carried out using the reagents as above, but with no fluoride present. This titration must be subtracted from subsequent titrations using fluoride solutions, thus giving the corrected titration . 

It is found that, after the eye has become accustomed to the end-point change in the titration, an accuracy of 1 per cent is obtainable with 5-10 mg. F. 

---