SIMPLE AND COMPLEX COACER\ ATES 303 



separates into two layers, one rich in colloidal substances and 

 another, clearly demarcated from it, which is almost free 

 from colloids. 



For many years this phenomenon has been studied in 

 detail by H. G. Biuigenberg de Jong^ and his collaborators, 

 and recently also by many other scientists in various coun- 

 tries.* To distinguish it from ordinary coagulation, Bungen- 

 berg de Jong called this phenomenon ' coacervation '. The 

 colloid-rich liquid was referred to as a ' coacervate ' and the 

 colloid-poor liquid in equilibrium with it was referred to 

 as the ' equilibrium liquid '. In many cases the coacervate 

 does not separate out as a continuous layer but appears in 

 the form of very small droplets which are readily seen 

 under the microscope, floating in the equilibrium liquid. In 

 Bungenberg de Jong's experiments with protein coacervates^ 

 the diameters of the droplets were between 2 and 670 p.. 



Moreover, it is not only proteins which form coacervates, 

 they may also be formed by other hydrophilic and even 

 hydrophobic colloids, both organic and inorganic.*^ For 

 example, they are formed by complex salts of cobalt,^ by 

 sodium silicate and ammonia,* by such organic substances as 

 polyvinyl derivatives, by solutions of acetylcellulose in chloro- 

 form or benzene,® and so forth. 



The phenomenon of coacervation is particularly interest- 

 ing from our point of view in that, during the process of 

 evolution of organic substances, it must have been a powerfvil 

 means of concentrating compounds of high molecular w^eight, 

 in particular protein-like substances, dissolved in the hydro- 

 sphere. 



It is well known that a coacervate may be obtained experi- 

 mentally from solutions of as little as o-ooi per cent of gelatin. 

 When this takes place there is a considerable increase in the 

 concentration of the protein in the droplets of coacervate, 

 which is particularly significant at very low concentrations.^" 

 For example, if a coacervate is formed from a 1 per cent 

 solution of gelatin, about 93 per cent of the gelatin is to be 

 foimd in the coacervate layer, but when the concentration 

 is lower the proportion of gelatin in the coacervate to that 

 in the equilibrium liquid is very much greater. It is hardly 

 possible to find any other equally effective means for con- 



