304 PHYSIOLOGICAL CHEMISTRY. 



EXPERIMENT. 



Detection of Iron in Urine. Evaporate a convenient volume 

 ( 10-15 c.c.) of urine to dryness. Incinerate and dissolve the residue 

 in a few drops of iron-free hydrochloric acid and dilute the acid 

 solution with 5 c.c. of water. Divide the acid solution into two 

 parts and make the following tests: (a) To the first part add a 

 solution of ammonium thiocyanate; a red color indicates the pres- 

 ence of iron, (b) To the second part of the solution add a little 

 potassium ferrocyanide solution; a precipitate of Prussian blue 

 forms upon standing. 



Fluorides, Nitrates, Silicates and Hydrogen Peroxide. 



These substance are all found in traces in human urine under 

 normal conditions. Nitrates are undoubtedly introduced into the 

 organism in the water and ingested food. The average excre- 

 tion of nitrates is about 0.5 gram per day, the output being the 

 largest upon a vegetable diet and smallest upon a meat diet. Ni- 

 trites are found only in urine which is undergoing decomposition 

 and are formed from the nitrates in the course of ammoniacal 

 fermentation. Hydrogen peroxide has been detected in the urine, 

 but its presence is believed to possess no pathological importance. 



