284 PHYSIOLOGICAL CHEMISTRY. 



ent. If the solution under examination contains only a trace of 

 hippuric acid the solution will appear smoky and faintly red in color 

 whereas if a larger amount of the acid be present the solution 

 will become opaque and of an orange or brown-red color. In either 

 case afte,r standing for some time the solution should clear up and 

 a light, finely divided precipitate should be deposited. This precip- 

 itate consists of earthy phosphates mixed with an amorphous orange 

 or brown-red substance of unknown composition. 



5. Formation of Nitro-Benzene. To a little hippuric acid in 

 a small porcelain dish add 1-2 c.c. of concentrated HNO 3 and 

 evaporate to dryness on a water-bath. Transfer the residue to a 

 dry test-tube, apply heat and note the odor of the artificial oil of 

 bitter almonds (nitro-benzene). 



6. Sublimation. Place a few crystals of hippuric acid in a dry 

 test-tube and apply heat. The crystals are reduced to an oily fluid 

 which solidifies in a crystalline mass upon cooling. When stronger 

 heat is applied the liquid assumes a red color and finally yields a 

 sublimate of benzoic acid and the odor of hydrocyanic acid. 



7. Formation of Ferric Salt. Render a small amount of a so- 

 lution of hippuric acid neutral with dilute potassium hydroxide. 

 Now add 1-3 drops of neutral ferric chloride solution and note the 

 formation of the ferric salt of hippuric acid as a cream colored 

 precipitate. 



COOH 



OXALIC ACID, | 



COOH. 



Oxalic acid is a constituent of normal urine, about 0.02 gram 

 being eliminated in 24 hours. It is present in the urine as cal- 

 cium oxalate, which is kept in solution through the medium of the 

 acid phosphates. The origin of the oxalic acid content of the urine 

 is not well understood. It is eliminated, at least in part, unchanged 

 when ingested, therefore since many of the common articles of 

 diet, e. g., asparagus, apples, cabbage, grapes, lettuce, spinach, 

 tomatoes, etc., contain oxalic acid it seems probable that the in- 

 gested food supplies a portion of the oxalic acid found in the urine. 

 There -is also experimental evidence that part of the oxalic acid 

 of the urine is formed within the organism in the course of protein 

 and fat metabolism. It has also been suggested that oxalic acid 

 may arise from an incomplete combustion of carbohydrates, espe- 

 cially under certain abnormal conditions. Pathologically, oxalic 



