398 PHYSIOLOGICAL CHEMISTRY 



In this reaction the uric acid is oxidized to dialuric acid and alloxan. 

 These two substances condense to form alloxan tin. This alloxantin 

 reacts with ammonium hydroxide to form purpuric acid. The purple 

 color is due to the formation of ammonium pur pur ate or murexide. 



5. Phosphotungstic Acid Reaction (Folin). To 20 c.c. of saturated sodium 

 carbonate solution in a small beaker add a small amount of uric acid. , Stir 

 the solution until the uric acid has dissolved, then add i c.c. of Folin's uric 

 acid reagent (see Chapter XXVII). A blue color results. 



6. Silver Reduction Test (Schiff). Dissolve a small amount of pure uric acid 

 in sodium carbonate solution and transfer a drop of the resulting mixture to a 

 strip of filter paper saturated with silver nitrate solution. A yellowish-brown 

 or black coloration due to the formation of reduced silver is produced. 



It is claimed that chlorides interfere with this test. 



7. Ganassini's Test. 1 Dissolve a small amount of uric acid in sodium carbon- 

 ate. Precipitate the dissolved uric acid by means of zinc chloride, filter off the 

 precipitate, and permit it to stand in contact with the air. A sky-blue color will 

 develop, a color change which may be hastened by sunlight. A similar reaction 

 may be obtained by treating the original precipitate with K 2 S 2 8 . 



8. Influence upon Fehling's Solution. Dilute i c.c. of Fehling's solution 

 with 4 c.c. of water and heat to boiling. Now add slowly, a. few drops at a 

 time, 1-2 c.c. of a concentrated solution of uric acid in potassium hydroxide, 

 heating after each addition. From this experiment what do you conclude re- 

 garding the possibility of arriving at an erroneous decision when testing for sugar 

 in the urine by means of Fehling's test ? 



9. Reduction of Nylander's Reagent. To 5 c.c. of a solution of uric acid 

 in potassium hydroxide add about one-half a cubic centimeter of Nylander's 

 reagent and heat to boiling for a few moments. Do you obtain the typical black 

 end-reaction signifying the reduction of the bismuth? 



NH CO 



CREATININE, C = NH 



N(CH 3 ).C] 



Creatinine is the anhydride of creatine and is a constituent of normal 

 human urine. The theory that creatinine is derived from the creatine 

 of ingested muscular tissue as well as from the creatine of the muscular 

 tissue of the organism has been proven to be incorrect by Folin, 

 Klercker, and Wolf and Shaffer. Shaffer believes that creatinine is 

 the result of some special process of normal metabolism which takes 

 place to a large extent, if not entirely, in the muscles, and further that 

 the amount of such creatinine elimination, expressed in milligrams per 

 kilogram body weight, is an index of this special process. 2 He further 



1 Ganassini: Boll, soc., 1908, No. i. 



2 He proposes to designate as the "creatinine coefficient" the excretion of creatinine- 

 nitrogen (mg.} per kilogram of body weight. 



