BLOOD. 233 



mixture of three volumes of concentrated sulphuric acid 

 and two volumes of water, warm until dissolved, and dilute 

 to 50 to 100 cc. To determine the iron hi the solution we 

 make use of the reaction of potassium permanganate on a 

 solution of ferrous sulphate containing free sulphuric acid. 

 This takes place according to the following equation : 



10FeS0 4 + 2KMn0 4 + 9H 2 S0 4 = 



Ferrous Potassium Sulphuric 



sulphate permanganate acid 



5Fe a (S0 4 ), + 2MnS0 4 + 2HKS0 4 + 8H 2 0. 



Ferric Manganous Monopotassium 



sulphate sulphate sulphate 



In the solution obtained above, however, the iron is pres- 

 ent as a ferric salt. If we wish to determine the iron by 

 titration with potassium permanganate, we must first con- 

 vert it into a ferrous salt. This may be m?st readily accom- 

 plished by means of some metallic zinc (weighed quantity 

 about 1 g.). The reduction is made in an atmosphere of 

 carbon dioxide and is continued until the fluid has become 

 perfectly colorless and the zinc has completely dissolved 

 (some dilute sulphuric acid must eventually be added). Let 

 the contents of the flask cool completely in the atmosphere 

 of carbon dioxide, and titrate with a solution of potassium 

 permanganate whose strength has been accurately deter- 

 mined. To prepare this solution weigh off accurately 0.32 

 g. of pure potassium permanganate, dissolve in water, and 

 dilute to the volume of one liter. This solution may be 

 standardized by means of either oxalic acid or ferrous ammo- 

 nium sulphate. 



Standardization with Oxalic Acid. Weigh off accu- 

 rately 0.63 g. of perfectly pure oxalic acid which has not 

 effloresced, dissolve hi water, and dilute to one liter. Add 

 to 25 cc. of this solution a few cubic centimeters of dilute 

 sulphuric acid, heat in a flask on the wire gauze to boiling, 

 and let the permanganate solution run in from a burette 



