PHASE REVERSAL IN EMULSIONS AND IN PROTOPLASM 129 



reading, the rising or falling of the needle, and particularly the fluctua- 

 tions of the ammeter needle, are all indicators of what is taking place in 

 the emulsion. 



An Arrhenius or Ostwald conductivity cell can be conveniently used 

 for making the conductivity measurements, but equally satisfactory and 

 much less expensive is a simple apparatus consisting of two electrodes of 

 platinum foil 1 cm. wide and 10 cm. long supported by two glass rods 

 2 cm. apart. With this apparatus the emulsions to be tested are poured 

 into small glass vials, measuring 3 cm. in diameter and 9 cm. high with 

 a volume of 68 cc. The platinum electrodes are allowed to project 

 into the vials any convenient distance, but the same distance in every 

 case — in these experiments to a depth of 5 cm. in the emulsion. The 

 current used in this work was a 52 volt direct current. The ammeter 

 employed was a milliammeter reading to one milliampere, with a range 

 of 150 milliamperes. For readings in excess of 150 milliamperes a shunt 

 was inserted in the circuit which raised the value of the milliammeter 

 scale tenfold. 



The readings of the oil-in-water type of emulsions varied from 3 milli- 

 amperes in the case of the soap (sodium sterate) emulsions, to, with 

 one exception, 100 milliamperes in the case of the gelatose emulsions. 

 In those soap (sodium oleate) emulsions in which the aqueous phase is a 

 1M NaOH solution, the current reached the high value of 420 milliam- 

 peres. Higher amperage is obtained in all emulsions which have been 

 repeatedly reversed by alternate additions of mono- and bivalent 

 electrolytes. 



The color method for determining the type of emulsion consists in 

 adding a stain which is soluble in but one of the two phases. For this 

 purpose the oil soluble dye Sudan III may be used. When the emulsion 

 is of the oil-in-water type the color is a pale pink. When the emulsion 

 is of the water-in-oil type its color is a brilliant red, since the oil is then 

 the continuous phase. 



The microscopic method of determining the type of emulsion consists 

 simply in making a microscopic examination of a sample of the emulsion. 

 This method is not as convenient as the other two but should always be 

 employed to determine the precise state of an emulsion, especially 

 when it is incompletely reversed. It sometimes happens that the 

 electrical conductivity points clearly to an emulsion of the oil-in-water 

 type, while the color indicates equally clearly that the system is of the 

 reverse type. Only a microscopical examination reveals the true state 

 of affairs. 



Experimental. Sodium oleate. The first emulsion studied was the 

 same as that with which Clowes worked, namely, an emulsion in which 

 the emulsifier is sodium oleate. The sodium oleate is formed as a result 



THE AMERICAN 1 JOURNAL OF PHYSIOLOGY, VOL. 66, NO. 1 



