HIPPURIC ACID. 165 



filtrate, 125 cubic centimeters each, pour them into beakers, add 

 5 cubic centimeters of concentrated ammonia and let the precipi- 

 tated urates stand until the next day. Filter and wash the urates, 

 using a 10-per-cent. ammonium sulphate solution for this as well 

 as for transferring to the filter. Then spread out the paper and 

 wash off the precipitates into beakers, using about 100 cubic centi- 

 meters of water for each. Add 15 cubic centimeters of concen- 

 trated sulphuric acid and titrate immediately with one-twentieth 

 normal potassium permanganate, containing 1.57 grammes per 

 liter, stopping when the solution is first pink throughout. For 

 each cubic centimeter of permanganate 0.00375 gramme of uric 

 acid has been oxidized. Calculate the amount in the urine, adding 

 a correction of 0.003 gramme for every 100 cubic centimeters of 

 urine employed because of the solubility of the urates. 



Heintz's Method for the quantitative determination of uric 

 acid is less accurate. It consists in adding to 200 cc. of urine 

 which contains no albumin or sugar 20 cc. of concentrated hydro- 

 chloric acid; the precipitated crystals are collected on a weighed 

 filter, washed with water until the drop of the filtrate shows no 

 chlorin reaction with a drop of silver nitrate and nitric acid, then 

 washed with alcohol. After drying three hours at 110 the uric 

 acid is to be rapidly weighed on the paper. It is customary to 

 add to the weight 0.00038 grm. for each 10 cc. of filtrate and wash 

 water as a correction for the acid which is dissolved. 



HIPPURIC ACID (C 6 H 5 COHNCH 2 C0 2 H). 



This occurs normally in the urine, but in that of 

 human beings only in very small quantities. It is found 

 here in larger amounts after the internal use of benzoic 

 acid. It increases with a vegetable diet and is abundant 

 in the urine of herbivorous animals. It forms translucent, 

 four-sided prisms, somewhat soluble in water. The acid 

 can be made synthetically by heating benzoic anhydrid, 

 (C 6 H B CO) 2 0, with glycocoll, NH 2 CH 2 C0 2 H: 



(C 6 H 5 CO) 2 + 2NH 2 CH 2 C0 2 H = 2C 6 H 5 CONHCH 2 CO 2 H +H 2 O . 



