WILLIAM D. HARKINS 



TABLE VII 



Flocculation Values 



173 



STABILITY OF AN EMULSION AND THE MONOMOLECULAR FILM 



An emulsion produced from equal volumes of water and oil by the use of sodium 

 oleate (a soap) as an emulsifying agent is found to be stable for a period of years if a 

 o.i-molal solution of soap is used, but changes greatly in a few days if produced by 



Fig. 22. — Shows how the change from the soap of a monovalent metal, such as sodium, to that 

 of a bivalent metal, such as calcium, may change the emulsion from one of oil droplets in water to an 

 emulsion of water droplets in oil. 



0.005-molal soap. In the latter case not enough soap is present to form a condensed mono- 

 niolecidar film around the particles of oil, so the droplets of oil unite in order to de- 

 crease the interfacial area and thus increase the concentration of the soap in the film. 

 With o.i-molal soap a condensed fikn of approximately monomolecular thickness is 

 present, and this gives a considerable degree of stability to the emulsion. If the soap 

 is the salt of a univalent metal, the droplets will be of oil, with water outside; but 

 with bi- or trivalent metals several hydrocarbon chains are present for each single 

 positive ion, and (Fig. 22) the droplets are of water, with oil outside. 



