A: Infrared Absorption á197Kñ.

B: Heat a solution (1in 10)with 2Nsulfuric acid:formaldehyde is liberated,recognizable by its odor and by its darkening of paper moistened with silver ammonium nitrate TS.On the subsequent addition of an excess of 1Nsodium hydroxide to the solution,ammonia is evolved.

Chromotropic acid spot test solution— Suspend 100mg of chromotropic acid in 2mLof water,and cautiouslyadd 3mLof sulfuric acid.Allow to cool.Add 25mLof sulfuric acid,and mix.[NOTE—If excessive heat generated during mixing causes a violet color to appear in the solution,discard the solution and prepare another,taking precautions to avoid excessive heat.]

Procedure— Transfer about 1g of Methenamine,previously dried and accurately weighed,to a beaker.Add 40.0mLof 1Nsulfuric acid VS,and heat to a gentle boil,adding water from time to time if necessary,until the formaldehyde has been expelled.Test for the absence of formaldehyde by adding a drop of the assay solution to a glass fiber filter disk,on a watch glass,on which has previously been placed 3or 4drops of Chromotropic acid spot test solution.Formaldehyde produces a violet color with this reagent;repeat the test until no violet color is obtained on the warmed test filter disk upon comparison with a blank filter disk to which no assay specimen is added.Cool,add 20mLof water,then add methyl red TS,and titrate the excess acid with 1Nsodium hydroxide VS.Perform a blank determination (see Residual Titrationsunder Titrimetry á541ñ).Each mLof 1Nsulfuric acid is equivalent to 35.05mg of C6H12N4.