SIMPLE AND COMPLEX COACERVATES 3O5 



bound to them and are rigidly orientated relative to the 

 colloidal particles. 



Thus, according to Bungenberg de Jong, coacervates form 

 a special class of colloidal sols in which the molecules of water 

 (or other solvent) are, to a certain extent, rigidly orientated 

 with regard to the particles of the colloid and in which, 

 therefore, a real boundary is formed between them and the 

 free molecules of the equilibrium solution. 



However, in view of the extreme complication of the 

 phenomenon of coacervation, its theory cannot yet be held 

 to be fully worked out. In order to elucidate the nature of 

 the processes occurring we must turn to a study of some of 

 the simpler cases of coacervation. At present, solutions of 

 organic substances of high molecular weight are generally 

 regarded as thermodynamically stable molecular solutions 

 conforming to the phase rule.^* For practical purposes they 

 may be considered as ordinary liquids which contain very 

 large molecules. As early as 1904 G. Galeotti^^ showed that 

 the phase rule is applicable to protein solutions, and this was 

 later confirmed by H. Chick and C. J. Martin'' in 1910-13 

 and by other later workers. The same applicability was first 

 demonstrated for a number of other substances, including 

 gelatin, by V. Kargin and his collaborators.'^ If two simple 

 liquids of low molecular weight can be dissolved in one 

 another in all proportions (e.g. benzene and toluene or water 

 and acetone) then, naturally, there will be no layering out. 

 There exists, however, a large number of pairs of liquids 

 ^vhich are only soluble in one another to a limited extent 

 (e.g. water and phenol or water and aniline). If we mix two 

 such liquids and shake up the mixture it will quickly separate 

 out into two layers, one of which might consist of a solution 

 of water in phenol and the other of a solution of phenol in 

 water. When this takes place, the difference between the 

 composition of the two layers at room temperature is very 

 great. As a result of this, the surface tension at the boundary 

 between the droplets formed by shaking and the surrounding 

 medium will also be very great and the droplets will coalesce 

 to form a continuous layer, thereby diminishing their surface 

 area and with it the surface energy. As the temperature rises, 

 the mutual solubility of the liquids increases, the difference 



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