68 BEHAVIOUR OF IR<>N SALTS, IN THE PRESENCE OF 



(c) Experiments ivith potassium f&rric-ferrocyanide (soluble 



Prussian blue). 



It has already been mentioned in the introuacuon that, 

 under certain conditions, white of egg solution is capable 

 of decolourizing a solution of soluble Prussian blue. Neither 

 the egg albumen nor the serum albumen were found to decolour- 

 ize soluble Prussian blue >as readily as the white of egg solution. 



10 c. c. of 0.05$ soluble Prussian blue were mixed with 

 10 c. c. of the white of egg solution and the mixture kept at 

 60 for an hour. At the end of this time the deep blue solution 

 had become practically colourless. The fading of the blue colour 

 took place gradually. With pure white of egg, or at a higher 

 temperature, the decolonization of the soluble Prussian blue 

 was found to proceed with greater rapidity. When a mixture 

 of equal volumes of 0.05$ soluble Prussian blue and the white 

 of egg solution were kept at room temperature, no apparent 

 change in the intensity of the blue colour of the solution was 

 observed at the end of six hours. To some of the decolourized 

 solution haematoxylin was added; no precipitation occurred, 

 thus proving that the Fe m ion of soluble Prussian blue was no 

 longer present as such. The addition of dilute hydrochloric 

 acid or concentrated salt solutions to some of the decolourized 

 solution caused the precipitation of a white substance, which 

 gradually turned to a deep green blue colour on standing or on 

 treatment with hydrogen peroxide. ISTo change was observed 

 on the addition of hydrogen peroxide to some of the decolour- 

 ized soluble Prussian blue mixture. 



Like the foregoing mixtures of iron salts with albumen, a 

 solution of 0.05$ soluble Prussian blue and an equal volume 

 of the white of egg, which had been decolourized by heating 

 at 60-70, was stable to heat and could be boiled without the 

 albumen coagulating. Indeed, it was found that the substances 

 could be rapidly brought to boiling immediately after mixing 

 without precipitation taking place. At this temperature the 

 mixture became colourless in two or three minutes. 



