578 PHYSIOLOGICAL CHEMISTRY 



quarters of an hour. After cooling, 2 grams of potassium iodide and a few drops of 

 fresh starch paste are added. The liberated iodine is titrated with N/ioo thiosul- 

 phate solution. Controls should be run on reagents. A correction of 0.32 mg. is 

 usually necessary for the undecomposed hydrogen peroxide. The thiosulphate solu- 

 tion is made up as needed from an N/io stock solution by dilution. It is standard- 

 ized against an iron solution containing 2 mg. of iron in 10 c.c. The number of 

 cubic centimeters of thiosulphate used in titration of the iodine set free from the 

 ash solution is multiplied by the iron equivalent of i c.c. of the thiosulphate (about 

 0.2 mg.) to obtain the total amount of iron in the 24-hour specimen of urine. From 

 1-5 mg. of iron are usually excreted per day. 



