92 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



ing until the fused mass solidifies. Cool the test-tube and 

 add a few c.c. of water and NaOH drop by drop until 

 the residue is all in solution. Add now a drop or two of 

 very dilute CuS0 4 solution. To what reaction does this 

 correspond? What substance is formed from the urea? 

 Write the equation. 



(c) To 5 c.c. of NaOH add some bromine water and 

 drop in a crystal of urea. What is the reaction which takes 

 place? 



HN CO 



I I H 

 URIC ACID, CO C N\ 



>CO 



HN C X 



II 



Uric acid is a diureide and structurally is composed of 

 two urea groups attached to a 3-carbon chain. It is closely 

 related to the purine bases being built up from the "purine" 

 type. 



Uric acid acts as a weak dibasic acid and forms three 

 types of salts neutral, biurate, and quadriurate. 



The neutral salts which are formed by the replacement 

 of two hydrogen atoms of the acid by two atoms of the base 

 are very unstable. 



The biurates have only one of the hydrogens replaced 

 and form very stable compounds. They present the chief 

 type in which uric acid exists in the urine. 



The quadriurates stand between the other urates as re- 

 gards stability. They are formed by a weak combination 

 of uric acid and biurate molecule for molecule. They 

 therefore contain in the molecule one-fourth the quantity 

 of base that exists in the neutral urate. When uric acid 

 separates out spontaneously from a urine, it is caused by an 



