406 PHYSIOLOGICAL CHEMISTRY 



rapidity of crystallization. Pure hippuric acid melts at i87C. The 

 most satisfactory method for the isolation of hippuric acid from the 

 urine in crystalline form is that proposed by Roaf (see below). It 

 is easily soluble in alcohol or hot water, and only slightly soluble in 

 ether. The output of hippuric acid is increased in diabetes owing prob- 

 ably to the ingestion of much protein and fruit. Plums, prunes and 

 cranberries in particular increase the hippuric acid output considerably 

 due to their relatively high content of benzoic acid. Hippuric acid 

 is decreased in fevers and in certain kidney disorders where the synthetic 



FIG. 130. HIPPURIC ACID. 



activity of the renal cells is diminished. It may be determined quan- 

 titatively by methods given in Chapter XXVII. 



EXPERIMENTS ON HLPPURIC ACID 



i. Separation from the Urine. (a) First Method. Render 500-1000 c.c. 

 of urine of the horse or cow 1 alkaline with milk of lime, boil for a few moments and 

 filter while hot. Concentrate the filtrate, over a burner, to a small volume. Cool 

 the solution, acidify it strongly with concentrated hydrochloric acid and stand it 

 in a cool place for 24 hours. Filter off the crystals of hippuric acid which have 

 formed and wash them with a little cold water. Remove the crystals from the 

 paper, dissolve them in a very small amount of hot water and percolate the hot 

 solution through thoroughly washed animal charcoal, being careful to wash out 

 the last portion of the hippuric acid solution with hot water. Filter, concentrate 



1 If urine of the horse or cow is not available human urine may serve the purpose fully 

 as well provided means are taken to increase its content of hippuric acid. This may be con- 

 veniently accomplished by ingesting 2 grams of ammonium benzoate at night. (See 

 chapter on Metabolism.) The fraction of urine passed in the morning will be found to have 

 a high content of hippuric acid. The ammonium benzoate is in no way harmful. In case 

 ammonium benzoate is not available sodium benzoate may be substituted. 



