URINE 429 



due principally to the latter class of substances. The carbonates of 

 the alkaline earths are often found in amorphous urinary sediments. 



Iron 



Iron is present in small amount in normal urine. It probably occurs 

 partly in inorganic and partly in organic combination. The iron con- 

 tained in urinary pigments or chromogens is in organic combination. 

 According to different investigators the iron content of normal urine will 

 probably not average more than 1-5 mg. per day. After splenectomy 

 there is an increased loss of iron from the body particularly by way of 

 the feces (Asher). 



EXPERIMENT 



Detection of Iron in Urine. Evaporate a convenient volume (10-15 c - c -) f 

 urine to dryness. Incinerate and dissolve the residue in a few drops of iron-free 

 hydrochloric acid and dilute tne 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 presence 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 substances are all found in traces in human urine under nor- 

 mal conditions. Nitrates are undoubtedly introduced into the organ- 

 ism in the water and ingested food. The average excretion of nitrates 

 is about 0.5 gram per day, the output being the largest upon a vege- 

 table diet and smallest upon a meat diet. Nitrites are found only in 

 urine which is undergoing decomposition and are formed from 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. 



