PROPERTIES OF COMPLEX COACERVATES 307 



its solubility, so that the solution separates out into two layers 

 and forms a coacervate on warming to 50° C. 



Simple coacervates may also be obtained from other pro- 

 teins such as amandin (a globulin foinid in almonds)'* by 

 dialysis in cold Avater, when the coacervate will dissolve again 

 on heating ; from alcoholic solutions of prolamines (cereal 

 proteins) by diluting them with water ; from alkaline solu- 

 tions of protamines by adding alcohol and so forth. In all 

 these cases the coacervate is formed under conditions in 

 which the solubility of the protein is diminished. These 

 simple coacervates, however, do not interest us nearly so 

 much as the complex coacervates w^hich are formed on mixing 

 solutions of t^vo or several colloids with different charges'^ 

 such as gelatin and gum arable. 



The structure and properties of 

 complex coacervate drops. 



Bungenberg de Jong^" believes that w^hen such coacervates 

 are formed the electrostatic forces act in the opposite sense 

 to those of hydration. The effect of hydration tends to stabilise 

 the solution ^vhile the electrostatic forces are acting to draw 

 together the colloidal particles bearing opposite charges. 

 When the mutual attraction of the oppositely charged part- 

 icles reaches a certain intensity it can overcome the effect 

 of hydration and the particles combine to form a complex 

 coacervate. Thus such a coacervate is always under the 

 influence of two opposing forces, the electrostatic ones which 

 keep it together and those of hydration which tend to drive 

 the colloid back into solution. 



One can, however, treat the formation of complex co- 

 acervates from the point of view w^hich has already been 

 discussed, as occurring under conditions of limited mutual 

 solubility of the components of the system. This approach 

 is particidarly applicable to such a coacervate as that of 

 gelatin and gum arable. The isoelectric point of gelatin is 

 at pH 4-82 but the coacervate can only exist at pH levels 

 between 1-23 and 4-82. Within these pH limits gelatin is 

 positively and gum arable negatively charged. Under these 

 conditions the charges can neutralise one another and the 

 solubility is thereby reduced. It is know^n that at the iso- 



