URINE 563 



Procedure. The 24-hour specimen of urine is treated with 30 c.c. of concen- 

 trated iron-free nitric acid and then evaporated to low volume in a large evaporating 

 dish on the water-bath. Transfer to a small evaporating dish. Heat to dryness on 

 the sand bath and then char, using a small flame. Transfer the charred mass by 

 means of a glass spatula to a crucible. The remaining material in the evaporating 

 dish is transferred with the aid of a little hot water and a rubber "policeman" to a 

 second crucible. Evaporate to dryness on the water-bath and then ash the material 

 in both crucibles. Dissolve the ash in about 30 c.c. of iron-free hydrochloric acid, 

 transfer to an Erlenmeyer flask, add 2 c.c. of hydrogen peroxide and boil for three- 

 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. 



