PHASE REVERSAL IN EMULSIONS AND IN PROTOPLASM 135 



more than half of the volume of the gelatose emulsion. That portion 

 of the total volume which has been reversed into a water-in-oil system 

 does not separate out into a separate layer distinct from the remaining 

 oil-in-water emulsion, but instead, the two systems are dispersed one 

 within the other. The amperage of the partially reversed emulsion is 

 higher than that of the original, thus indicating that no reversal has 

 taken place. The color of the emulsion, however, has become deep red 

 (the oil phase being stained with Sudan III). One would, therefore, 

 with color alone as the criterion, say, without hesitation, that the emul- 

 sion has reversed into one of the water-in-oil type. Only a microscopi- 

 cal examination reveals the true state of affairs, namely, that both types 

 of emulsion exist. 



The most remarkable fact about the reversal of the emulsion with a 

 gelatose emulsifier is that the hydroxide causing reversal may be either 

 that of a mono- or bivalent cation. NaOH also partially reverses the 

 emulsion just as does Ba(OH) 2 . 



When an emulsion with a gelatose emulsifier is microscopically 

 examined after 6 cc. of M/10 NaOH has been added it is seen to consist 

 of the two types of emulsions, as just described. Further addition of the 

 hydroxide causes no further reversal but, on the contrary, a return 

 to the original oil-in-water system throughout the mixture. 



Leaving the unusual behavior of the emulsion with a gelatose emulsi- 

 fier out of consideration, it can be stated that both the chloride and the 

 hydroxide of barium and of calcium have the same effect in reversing oil 

 emulsions. 



When salts of sodium are added to water-in-oil emulsions which are 

 reversible with NaOH, no reversal takes place. Neither NaCl nor Na 2 

 S0 4 will cause any of the emulsions to reverse. It is quite evident, there- 

 fore, that it is not the cation Na which is alone responsible in causing 

 reversal. Nor can we say that it is the anion OH which is alone the 

 active ion in reversing water-in-oil systems, otherwise the hydroxide of 

 any cation should do, yet Ba(OH) 2 does not reverse water-in-oil systems, 

 but, on the contrary, behaves like BaCl 2 in reversing oil-in-water emul- 

 sions. 



The inability of NaCl to reverse the emulsions which can be reversed 

 with NaOH, is of special interest because of its bearing on the biologi- 

 cal significance of Clowes' hypothesis. It is this salt, NaCl, which has 

 been the classical example to illustrate the effect of a monovalent cation 

 on the permeability of protoplasm, and with CaCl 2 furnishes the funda- 

 mental evidence on which the theory of antagonism is based. If NaCl 

 has no apparent effect on the reversibility of oil emulsions, the hypothe- 

 sis of Clowes loses much of its weight. 



