228 PHYSIOLOGICAL CHEMISTRY. 



tioned, by the treatment with strong acids, and also by various 

 other reactions. The product from reduced hemoglobin is 

 known as hemochromogen, while from oxyhemoglobin oxy- 

 hematin or common hematin is obtained. The relations may 

 be thus illustrated : 



globin C + HC1 = herain 



Q = hemochromogen 



Fe hematoporphyrin 



Hematin is usually obtained as an acid combination or ester. 

 In one process frequently followed blood is warmed with an 

 excess of glacial acetic acid. Crystals containing acetic acid 

 separate on cooling. In another process the hydrochloride is 

 obtained ; in either case the free hematin is secured by saponi- 

 fication with weak sodium hydroxide solution. Several for- 

 mulas have been given for hematin; the one most commonly 

 accepted is 



while for hemin crystals the formula 



C 32 H 3 oN4FeO 3 HCl 



has been given. It is possible that different analysts have 

 obtained, not the same, but closely related products. Hemin 

 is secured in minute brownish crystalline plates, hematin as 

 an amorphous bluish black insoluble powder. The spectrum, 

 which is important, will be referred to later. 



Hematoporphyrin. This is a derivative obtained by the 

 action of acids on hematin. In this treatment the iron is re- 

 moved, as illustrated by the following reaction, when hydro- 

 bromic acid is employed as the decomposing agent : 



C 32 H 32 N4FeO4 + 2H 2 O + 2HBr = 2Ci6Hi8N a O8 + FeBr 2 -f H 2 . 



The substance appears to be related to and isomeric with bili- 

 rubin. The alkaline solutions of hematoporphyrin are deep 



