COLOURING MATTERS. 41 



the other elements, and fonns a chloride of iron, while the 

 atom of metal thus removed is replaced by six atoms of chlorous 

 acid, and a compound is formed, which is represented by the 

 fonmda C,, H., N, 0, + 6 CI O . 



44 'Z'2 3 3 



During this process the red colouring matter is destroyed, 

 and the new compound appears as a white flocculent precipitate. 

 It must not, however, be assumed from this experiment that the 

 red colour of the blood is dependent on the iron, for that con- 

 stituent may be removed from the haematin without materially 

 affecting its tint, as may be shown in the following manner. 

 Let some dried blood be mixed with concentrated sulphuric 

 acid, and after standing for some days let water be added. 

 Hydrogen gas is evolved by the action of the acid on the 

 dried blood, and sulphate of the protoxide of iron is formed. 

 If the blood, after this process, be carefully washed, a mixture 

 of alcohol and sulphuric acid will extract from it red hsematin 

 in combination with sulphoproteic acid, but perfectly free 

 from iron. Van Goudoever has deduced the following formula 

 for this compound : 



Cgj H57 Ng Ojj, S03=C^^ H22 Ng Og (the organic part of haematin,) 

 -fC^j H3J Nj 0,2, SO3 (sulphoproteic acid,) 

 +4 HO. 



Although this experiment affords conclusive evidence that 

 the red coloui* of the haematin is not dependent on the iron, 

 yet this metal is very firmly combined with the four organic 

 elements of this constituent. Well prepared hsematin may be 

 submitted for several days to the action of dilute hydrochloric 

 or sulphuric acid, Anthout the iron diminishing in the slightest 

 degree. 



Hajmatin treated in this manner, left after incineration 

 9"49g of peroxide of iron,' the amount that is always yielded 

 by well- purified hsematin. 



Peroxide Metallic 

 of Iron. Iron. 

 ' In 100 parts of haematin from human blood, Lecanu found . lO'OO = 6"93 



,, „ from blood of ox „ „ . 12-85 = 8-90 



„ „ from arterial blood of ox, Mulder found, 9'60 = 6-66 



„ „ from venous blood of ox „ „ . 9'82 = 6-75 



„ „ from blood of ox, Simon found . 11-50 = 7*97 



„ „ from blood of sheep, Mulder found . 9'30 =: 6*45 



