Deniges’ test

Denig s test for citric acid in the saponification liquor is as follows —... 

Deniges s test Add 0-5 ml acid mercury(II) sulphate solution to 3 ml citrate solution, heat to boiling and then add a few drops of a 0-02m solution of potassium permanganate. Decolourization of the permanganate will take place rapidly and then, somewhat suddenly, a heavy white precipitate, consisting of the double salt of basic mercury(II) sulphate with mercury(II) acetone dicarboxylate... 

Citrate, (i) Deniges s test (IV.39, 5). (ii) Cadmium acetate solution test (IV.39, 4), and negative results with resorcinol and copper hydroxide tests (IV.38, 6, 7). 

Mercury(II) sulphate reagent (0.2m) (for Deniges s test). To 40ml water add cautiously 10 ml concentrated sulphuric acid with constant stirring. Dissolve in this mixture 2.2 g mercury(II) oxide. 

In determining the ester value of the oil, it should be carefully watched for the first five or ten minutes. The clear liquid will very soon become turbid, on account of the separation of potassium citrate (which is not very soluble in alcohol), if citric acid esters are present, and eventually become clear again. Denig s has devised a test by which the presence of citric acid can be positively decided. 

Small amounts of strychnine may be determined colorimetrically by applying Malaquin s colour test as modified by Deniges. In this test the alkaloid, dissolved in dilute hydrochloric acid, is reduced with zinc amalgam and then treated with sodium nitrite. The red colour produced is then matched against a series of standards prepared by application of the test to solutions of strychnine sulphate of known concentration. 

Deniges reagent Mix 5 g of yellow mercuric oxide with 40 ml of water, add, slowly while stirring, 20 ml of concentrated sulphuric acid followed by 40 ml of water and stir until all the mercuric oxide has dissolved. Test for the absence of mercurous mercury as follows To 10 ml add... 

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