CHAPTER IX 

 DISPERSE SYSTEMS 



II. SOAPS AND EMULSIONS 



" When we have faniiharised ourselves with the physico-eheniie and colloid- 

 chemie behaviour of systems of the type water-dissolved-in-x, we shall liiid ourselves 

 possessed also of the laws whieh govern the behaviour of protoplasm under physio- 

 logic and pathologic circumstances. Martin H. Fischer. 



Emulsions are systems consisting of two nuitually iiisoltible 

 liquids, one of which is very finely dispersed within the other. 



They may be regarded as emidsoids with somewhat larger 

 dispersed particles (microns). The term, as usually employed, 

 has, however, a narrower connotation, the disperse phase being 

 considered as a fat or fat-like substance distributed throughout 

 w^ater in such a way as to remain stable for an indefinite period. 

 Oil and water are two immiscible liquids, and no amount of 

 mechanical mixing will induce them to form a permanent emulsion. 

 It is true that after a prolonged beating of the two together a 

 maxinumi of 2 per cent, of the oil may be taken up by the water, 

 forming a stable dispcrsoid. Measurement of the particles, how- 

 ever, demonstrates that they are of the order of sub-microns, and 

 thus a true colloidal system has been formed. An example of this 

 is the condenser water of steam engines, which contains lubricating 

 oil in suspension. 



Analyses of natural and artificial emulsions, like milk, bile, 

 rubber, cod-liver-oil enuilsion, etc., demonstrate the presence of 

 more than merely oil and water. A colloid or semi-colloid must 

 be present. 



If the generic term oil is used to denote any liqind that is not 

 miscible w4th water, we may note that there are two entirely 

 different types of enmlsions, the one being drops of oil suspended 

 in water and the other being drops of water suspended in oil 

 (cf. sol and gel). For example, milk belongs to the former and 

 butter to the latter class. It is important to know under what 

 conditions each of these types is formed. One might at first 

 imagine that the governing factor wotdd be the relative amoimts 

 of oil in water, much water and little oil producing the 



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