EMULSIONS 127 



Fig. 81). Finally, they open up at the end of low surface tension, 

 pouring out their contents, which form the dispersion medium 

 of the new water-in-oil emulsion. In the meantime, the water, 

 the former continuous phase, has been breaking up into droplets 

 during the process of shaking. This change has been diagram- 

 matically represented by Clowes (Fig. 83). 



Compound Emulsions. — In the process of reversal with electro- 

 lytes, there is seldom a clean separation of oil and water at the 

 reversal point; that is to say, one type is always being formed 

 before the other type is fully done away with; consequently, 

 instead of the oil and the water being separated into two layers 

 at the reversal point, both types of emulsions usually exist side 



0/7 in i/Vaier Zone of Waier in Oil 



Reversal 

 Fig. 83. — Diagrammatic representation of phase reversal in an emulsion. 

 {Modified from Clowes.) At the extreme left is a fine oil-in-water emulsion; the 

 globules become larger, then pear-shaped (left center) , finally collapsing (center) 

 and emptying their contents (zone of reversal) ; the same takes place in the 

 water-in-oil emulsion (right) when reversing. The several stages given here 

 diagrammatically are fairly well illustrated in Fig. 81 where 6 is a fine water- 

 in-oil, d a coarse water-in-oil, and e the large pear-shaped water globules about to 

 open up to form the continuous phase of an oil-in-water emulsion. 



by side and one within the other (c, d, Fig. 81). Many interest- 

 ing things are to be seen in emulsions at or near the reversal 

 point. An oil globule, which is part of an oil-in-water emulsion, 

 may itself be a water-in-oil emulsion. This situation may reach 

 the extreme case of five emulsions, one within the other, like a 

 chest of Chinese boxes (/, Fig. 81). 



Theories of Emulsification. — Two hypotheses have been 

 advanced in an attempt to explain the behavior of emulsions — 

 the solubility, or surface-tension, hypothesis of the American 

 colloid chemist Wilder D. Bancroft, and the oriented molecular- 

 wedge hypothesis independently developed by the California 

 chemist J. H. Hildebrand and the Chicagoan Harkins. Both 

 hypotheses are ingenious interpretations of a little understood 

 and difficult problem. 



