66 BEHAVIOUR OF IRON SALTS, IN THE PRESENCE OF 



stable towards heat. When potassium ferrocyanide is present, 

 however, the complex is precipitated bv boiling the solution. 

 A mixture consisting of equal parts of the white of egg and 

 l.O/o ferric chloride solution, was found to be more stable 

 towards heat than a pure albumen solution of the same con- 

 centration; whereas the mixture did not commence to coagulate 

 until the temperature was raised to 65°, the pure albumen 

 solution became cloudy at 61.5°. 



(b) Experiments with potassium ferricyanide. 

 White of egg solution, egg albumen, and serum albumen 

 were all found to prevent ithe precipitation of potassium ferri- 

 cyanide, in dilute solution, by ferrous salts. On the addition of 

 a few drops of ammonium ferrous sulphate to a mixture con- 

 sisting of 2 c. c. of O.lfc potassium ferricyanide and 5 c. c. of 

 the white of egg solution only a very faint blue colouration was 

 produced. When the concentration of the potassium ferricyanide 

 was smaller than this, a blue colouration did not occur on the 

 addition of the ammonium ferrous sulphate. 5.0 c. c. of 0.1^ 

 potassium ferricyanide were mixed with 25 c. c. of the white 

 of egg solution. Ammonium ferrous sulphate solution was then 

 added drop by drop to the pale yellow mixture until it became 

 colourless. This disappearance of the yellow colour points to 

 the occurrence of chemical change on the addition of the 

 ammonium ferrous sulphate, and is probably due to the dis- 

 appearance of the ion ito which the colour of the solution is 

 due. A blue black colouration appeared when a few drops 

 of haematoxylin w^ere added to part of the decolourised solution. 

 The decolourised solution turned blue on the addition of a drop 

 of dilute hydrochloric acid. Excess of hydrochloric acid caused 

 a blue precipitate to separate slowly from the solution. 



With solutions containing no albumen and the above con- 

 centrations of potassium ferricyanide, ammonium ferrous sul- 

 phate gave deep blue precipitates. 



To a mixture of 5 c. c. of 0.1^ potassium ferricyanide and 

 25 c. c of the white of egg solution, sufficient dilute hydro- 



