316 Engelhart (yii the 



matter and other principles. If, as Berzelius says, iron exists 

 in the colouring particles in notable quantity, and not any where 

 else, Dr Engelhart conceives the presumption to be, that it is the 

 foundation of the red colour of the blood. If, on the other hand, 

 as Brande and Vauquehn insist, there is much less iron in the 

 colouring particles than Berzelius maintains, and not more than 

 in thefihrine and serum, the colour cannot be owing to the pre- 

 sence of that metal. 



The pure modified colouring matter, when charred in a cru- 

 cible, had a metallic lustre, and was attracted by the magnet ; 

 and when the charred matter was incinerated, it acquired a yel- 

 low colour, was almost entirely soluble in hydrochloric acid, 

 and then exhibited, with the ordinary re-agents, all the characters 

 of the hydrochlorate of iron. 



The pure serum and fibrine, when dried and charred, had 

 not a metallic lustre, and were not attracted by the magnet ; 

 and, when incinerated, gave a white powder, which, although 

 soluble in hydrochloric acid, evidently did not contain a trace of 

 iron. The only kind of blood which can be used for these ex- 

 periments is human blood, or that of the horse ; the blood of 

 the sow, sheep, ox, or turkey, does not yield a serum free from 

 colouring particles. If care be taken to avoid that fallacy, 

 therefore, it is found that iron exists in the colouring particles 

 only. 



Chemists have hitherto succeeded in detecting iron in the 

 blood, only by the process of incineration. But Dr Engelhart 

 has at length discovered a method of separating it in the humid 

 way ; and the result of his analysis gives the same proportion 

 as that formerly determined by Berzelius. His' method is, by 

 transmitting a stream of chlorine through a solution of the un- 

 modified particles, or through water containing the purer modi- 

 fied colouring matter in suspension. It has been already stated, 

 that, in this way, a white precipitate and colourless fluid are 

 procured. The fluid after being filtered evidently contains 

 iron in the state of a peroxide *. Two methods were em- 

 ployed for discovering its quantity. In one process, he threw 



• Care was taken that particles of iron did not pass over with the chlorine, — 

 supposing even that that was possible. 



