THE NITROGENOUS EXCRETION. URINE. 



373 



It appears, therefore, that in this kind of solution 2 mole- 

 cules of copper oxide are required to oxidize i molecule of 

 creatinine. The 2 molecules of copper oxide yield i atom of 

 oxygen. It will be recalled that 5 molecules of copper oxide 

 are used up in oxidizing i molecule of dextrose. For equal 

 weights the reducing power of dextrose is about twice as great 

 as is that of creatinine. 



Reducing Power of Uric Acid. With the same reagent 

 the reducing power of uric acid may be measured, the uric acid 

 being dissolved with a little alkali to form a soluble urate. 

 The table below illustrates the relation of the reducing and 

 oxidizing solutions : 



From this it appears that i molecule of uric acid requires 3 

 molecules of copper oxide for oxidation under the conditions 

 of the test, or 1.5 atoms of oxygen. This is a larger amount 

 of oxygen than would be required for the oxidation of uric 

 acid to urea and alloxan. This requires i atom : 



C 6 H 4 N 4 O 3 + O + H 2 O = CON 2 H 4 + C 4 H 2 N 2 O 4 . 



But secondary reactions also take place, and a partial oxida- 

 tion to parabanic acid may be represented in this way : 



2C 5 H 4 N 4 O 3 + 3O + 2H-O = 2CON 2 H 4 + CH 2 N : O 4 + C 3 H 2 N 2 O 3 + CO.. 



This possibly represents the course of the reaction with such 

 a solution. 



With these reducing values established it is possible to esti- 

 mate the fraction of the total urine reduction which is not due 

 to these two most important substances besides sugar. To do 

 this it is necessarv to find the amount of uric acid and creatinine 



