484 PRACTICAL ORGANIC AND BIOCHEMISTRY 



Haemin. 



Haematin forms a hydrochloride which is insoluble in acetic acid 

 and is termed haemin. It crystallises in blue-black prisms and is very 

 easily prepared as a microscopical preparation : 



A drop of blood is placed on a glass slide and allowed to dry, or it 

 is dried by gently heating over a flame. The dry residue is scraped 

 into a little heap and a drop of glacial acetic acid added to it from the 



end of a glass rod. It is rubbed up 

 into a paste and a little is put on a 

 clean slide. A drop of glacial acetic 



.- 



' aci d is added, it is covered with a 



i-is ^ . \ cover slip and heated over a small 



\jff ^ff \JJ ' w c^* ^ rfjPT ' 



^T" ^ ^ ^*f x ^ flame till the acid just begins to boil. 



The slide is allowed to COC)1 and 

 //*' examined with a microscope. Small 

 4 ^" black or brownish-black crystals of 



* ^r V " haemin are seen as shown in Fig. 58. 



# . . ' If no crystals are visible, the glass 



slide is again heated and the heating 

 FIG. 58. Hsemm crystals. 



may be repeated two or three times. 



Haematoporphyrin. 



Haemoglobin and haematin are decomposed by the action of 

 strong acids and converted into haematoporphyrin. 



Haematoporphyrin is free from iron, whereas haematin still contains 

 this element. The removal of the iron from haematin in the absence 

 of reducing agents is accomplished only with difficulty and is only 

 effected by strong reagents, such as concentrated sulphuric acid, glacial 

 acetic acid saturated with hydrobromic acid, or hydrochloric acid, and 

 heated to 130 in a sealed tube. The haematoporphyrin obtained 

 by the action of sulphuric acid is haematoporphyrin anhydride. 



Haematoporphyrin is more readily formed from reduced haemo- 

 globin by the action of moderately concentrated hydrochloric acid. 



The iron is also readily removed from haemochromogen by dilute 

 acids and reducing agents of an acid nature easily set free hajmato- 

 porphyrin from haematin. Hence the stability of iron in haematin is 

 dependent on the presence of oxygen. 



It is very probable that the cells of the body deal with the blood 

 pigment in the reduced condition, which, as seen above, is easily 

 changed into haematoporphyrin. Its occurrence in the urine in cases 

 of haematoporphyrinuria can be thus accounted for. Alkaline h.-umato- 

 {><>rj>hyrin occurs in urine. 



Haematoporphyrin is soluble in dilute acids and alkalies giving 

 solutions of acid and alkaline haematoporphyrin. 



