[501 ] 



LXXV. On the Conversion of Benzoic Acid into Hippuric 

 Acid in the Animal Economy. By Mr. Alfred Baring 

 Garrod, of University College^^. 



A PAPER has appeared in the Medico-Chirurgical Trans- 

 ■^^ actions for last year, and also in the first Number of 

 the Pharmaceutical Transactions, by Dr. Alexander Ure, in 

 which it is stated, that by the internal administration of ben- 

 zoic acid, or any of its salts, hippuric acid is formed in the 

 system, and is eliminated from the kidneys in the form of a 

 soluble hippurate, and that this hippurate is formed by the 

 benzoic acid uniting with uric acid. It is also stated, that no 

 trace of uric acid, or any of its salts, could be found in the 

 urine after the administration of the benzoic acid. 



I have repeatedly performed Dr. Alex. Ure's experiment, 

 swallowing from a scruple to half a drachm of benzoic acid at 

 a time, and have always obtained a copious crop of crystals of 

 hippuric acid, amounting to from fifteen to twenty-nine grains, 

 by the addition of hydrochloric acid to the urine passed about 

 three or four hours afterwards (evaporated or not, according 

 to its state of dilution). These crystals possessed all the cha- 

 racters of hippuric acid, with the crystalline form, the small 

 solubility in cold water and aether, the ready solubility in al- 

 cohol, the evolution of nitrogen, and also the odour of the 

 tonquin bean when heated to destruction ; and my experi- 

 ments therefore so far confirm Dr. A. Ure's fundamental ob- 

 servation. He also mentions another test of hippuric acid, viz. 

 that when evaporated to dryness with dilute nitric acid, and 

 ammonia added, a beautiful purple colour is pi'oduced. This 

 is certainly true of the crystals obtained from the urine, but it 

 is not a character of pure hippuric acid. The cause of this 

 colour will be shown presently. 



Dr. A. Ure states that no trace of uric acid could be found 

 in the urine; but on examination I have always been able to 

 obtain a distinct trace of uric acid from a drop or two of the 

 urine, by adding a little nitric acid, carefully evaporating, and 

 holding the capsule containing it over ammonia, when a 

 distinct trace of murexide was formed; also, when the dish 

 containing the crystals of hippuric acid is carefully exa- 

 mined, minute grains are found at the bottom, which are uric 

 acid crystals; and on examining the crystals of hippuric acid 

 with the microscope, uric acid crystals are found adhering to 

 them in immense numbers, and this is the cause of the pro- 



18. 



Communicated by the Chemical Society, having been read January 



