PROPERTIES OF FERRIC COMPOUNDS 219 



of a mixture of denatured globin hemichrome with some alkaline 

 hematin (c/. Section 2.4.4.)- 



This has led Holden and Hicks {1323) to suggest that hemtglobin hydroxide 

 is an equilibrium mixture of a native globin hem/chrome with a substance 

 in which hematin is not bound to the globin through the iron. This might 

 explain the anomalous magnetochemical behavior of hem?globin hydroxide, 

 but it is doubtful whether it can satisfactorily explain the potentiometrie 

 data. 



The magnetic susceptibility measurements put this compound in 

 a class by itself. Four dsj)^ covalent bonds are considered as resonat- 

 ing among the six adjacent atoms, making the bond approximately 

 two-thirds covalent and one-third ionic. Reaction: 



HiOH + H+ ^ Hi+ + H2O 



has a pK value of 8.1, whether measured by spectrophotometry 

 (99,1155) or magnetochemical titration {502). 



On account of the spectral change when hemiglobin hydroxide is 

 formed, this compound is less readily detectable in the presence of 

 excess oxyhemoglobin than is hemiglobin, and the pH should always 

 be shifted to 6 or 7 before making spectroscopic examination of 

 blood for the presence of hemzglobin. 



2.3.3. Hemiglobin Fluoride (HiF). Fluoride ions combine with 

 hemiglobin to form hemtglobin fluoride. The solutions are red in 

 color with a band at 610 niju and bands in the green. Hemtglobin 

 fluoride was first crystallized by von Zeynek in 1901 {3177; cf. 

 Haurowitz, 1155). The affinity of hemiglobin for fluoride is small 

 and dependent on the pH. The reaction Hi"*" + F~ ;=i HiF is insen- 

 sitive to pH changes between 5 and 7. The equilibrium calculated 

 from spectophotometry (Lipmann, 1756; Havemann, 1188) agrees 

 well with the equation log Khif = — 2.23 + 0.59 V/i, deduced from 

 magnetochemical data {502), m being ionic strength. As the solutions 

 are made more alkaline, the reaction becomes: 



HiOH + F-;^HiF + OH- 



[HiOH] [F-] 

 and the equilibrium: ThfI TOH^l 



has a K value of 0.78 X 10^ 



2.3.4. Hemiglobin Cyanide (Cyanmethemoglobin, Ferrihemo- 

 globin Cyanide). Hemiglobin cyanide was discovered by Haldane 



