586 



PHYSIOLOGICAL CHEMISTRY 



per day. The urine of herbivorous animals contains much larger quan- 

 tities. This acid is formed in the animal body, by synthesis from ben- 

 zoic acid and glycocoll which takes place in the kidneys and elsewhere. 1 



Experiment. Ingest 2 grams of sodium benzoate or ammonium benzoate 

 before retiring at night. Collect the first fraction of urine voided the next morn- 

 ing. The benzoate has been synthesized with glycocoll to form hippuric acid. 



FIG. 172. BERTHELOT-ATWATER BOMB CALORIMETER. 



The urine will therefore be found to contain much more of this acid than is nor- 

 mally present. Isolate the hippuric acid by one of the following methods : 



(a) First Method. Render the urine 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 

 1 Kingsbury and Bell: Jour. Biol. Chem., 21, 297, 1915. 



