URIC ACID. 161 



conical flask (Erlenmeyer) which contains exactly 10 cubic centi- 

 meters of the standard acid (not the concentrated!). Continue 

 the distillation until at least half has been distilled over and the 

 distillate coming from the condenser no longer turns red litmus- 

 paper blue. 



Then find how much ammonia has been taken up by the 

 standard acid. To do this add a few drops of Congo-red solution to 

 the distillate. It will be colored red, because of the acid reaction. 

 From a burette add the standard ammonia, stirring meanwhile, 

 until the red just changes to a blue, when the liquid is neutral. 

 Subtract the number of cubic centimeters of ammonia used from 

 the number which are required to neutralize 10 cubic centimeters 

 of the standard acid. The difference represents the volume of 

 standard ammonia equal to that which was distilled from the 

 oxidized urine. Calculate the weight of NH 3 in this. Fourteen- 

 seventeenth of the NH 3 is the weight of the nitrogen in 5 cubic 

 centimeters of urine. Calculate the percentage. 



URIC ACID ("LITHIC ACID"). 



Uric acid is normally present in solution in the urine 

 of mammals. With birds and snakes it is the principal 

 nitrogenous excretory product. Its formula is C 5 H 4 N 4 3 

 and the constitution of the molecule is probably 



CO 



It is consequently 2-6-8-trioxypurin. 



The daily amount varies much, but averages from 0.2 

 to 0.8 gramme. Except that it must be formed from the 

 nitrogenous compounds in the body, we know little of its 

 production or of the cause and significance of its variations. 



