130 



PROTOPLASM 



the molecule is shaped like a wedge, then the row will bend 

 (Fig, 86). The way it bends will depend on which end of the 

 soap molecule is the larger. In the case of a sodium soap, it is 

 the metal end, of sodium, protruding into the water, which is the 

 larger, and the organic end, protruding into the oil, which is the 



--0 



Fig. 85. — Polar (stearic acid) molecules oriented at an oil (benzol) water interface. 

 - — - — tVater 





^Hydrocarbon 

 chain 



Fig. 86. — Sodium stearate (soap) molecules at the interface of oil globules in an 



oil-in-water emulsion. 



Fig. 87. — Calcium stearate (soap) molecules forming the stabilization membrane 



of a water-in-oil emulsion. 



smaller. Such a membrane will curve so that the larger sodium 

 ends form the outer surface. This will be on the water side, 

 and the membrane will surround oil on the inner side. The 

 resulting emulsion is, therefore, an oil-in-water one (Fig. 86). 

 Theory demands and experiment proves that a sodium soap 

 forms an oil-in-water emulsion. 



