EMULSIONS 



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milliamperes go through at a voltage of 110, the emulsion is an 

 oil-in-water one, because the water, with its electrolytes, is the 

 continuous phase and acts as a fair conductor; if no current 

 passes, then oil, a nonconductor of electricity, is the continuous 

 phase, and the emulsion is a water-in-oil one. 



Fig. 82. — An oil-in-water (left), a "broken" (center), and a water-in-oil 

 (right) emulsion in bulk; the oil phase is stained red, therefore the left sample is 

 pink, the center one, red above and white below, and the right one red. 



Phase Reversal. — Most emulsions can be reversed from one 

 type to the other — from oil in water to water in oil, and vice 

 versa. The addition of a suitable electrolyte (salt, acid, or base) 

 will usually do it. If the emulsion is one of olive oil in water, 

 stabilized by the soap sodium oleate, it can be reversed by adding 

 a little calcium chloride. The water-in-oil system thus formed 

 can now be thrown back to the original oil-in-water type by 

 adding sodium hydroxide. Under favorable conditions, rever- 

 sals may be repeated eight or ten times. While some emulsions 

 can be frequently reversed, others will not budge. The above 

 olive-oil emulsion reverses readily if soap or casein is the emulsi- 

 fier but refuses to change type if albumin or saponin is used. 

 Why, it is at present impossible to say. It is possible that pre- 

 sumably irreversible emulsions could be made to change type if 

 the right electrolyte or other agent were found. As the mem- 

 brane is the seat of the mechanism of reversal, it is also possible 

 that the substance of which it is formed, i.e., the emulsifier, is pre- 



