106 



Most formulae for oil emulsions have been the result of practical 

 experience, for we know but little in regard to the various theories 

 involved in a study of colloids, but some knowledge of the theory of 

 emulsification is necessary if we would proceed intelligently. 



THE THEORY OF EMULSION 



The theory of emulsion is based on the assumption that we are 

 dealing with two-phase systems, the oil and the water being the re- 

 spective phases. The oil is the disperse or internal phase, the water is 

 the continuous or external phase, and the two phases of the system are 

 separated by surfaces of contact, or interfaces. 



The external phase may be either a solid or a liquid. The first 

 part of this discussion is concerned with a system in which both phases 

 are liquids ; but the latter part, with a system in which one phase 

 is a liquid and the other a solid. 



An emulsion is defined by Clayton as a system containing two 

 liquid phases, one of which is dispersed as globules in the other. Mak- 

 ing lubricating oil emulsion is essentially a mechanical process which 

 has for its purpose the breaking up of the oil in the water, but as oil 

 and water are immiscible an emulsifying agent is needed, and here again 

 there may be two kinds of emulsions, "oil in water" and "water in oil", 

 depending upon the nature of the emulsifying agent. The lubricating 

 oil emulsions are of the former kind. 



THE USE OF A SOLID AS AN EMULSIFIER 



It has been long known that any substance that will go into the 

 interface and thus increase viscosity, will cause emulsification. In other 

 words, the insoluble solid, if finely enough divided, will yield results 

 similar to those produced by a gelatinous colloid, such as soap. Picker- 

 ing was one of the first to point out that the basic sulfate precipitated 

 in Bordeaux mixture consists of just such particles. These particles 

 have only a slight tendency to unite with one another, and are more 

 readily wetted by water than by oil. When the oil is added to the 

 Bordeaux mixture and broken up by agitation, the finely divided pre- 

 cipitate surrounds the oil globules, thus holding them in suspension. 

 Theoretically there seems to be no reason to ex])ect unfavorable results 

 with the soapless emulsions. Indeed, in instances where a weak Bor- 

 deaux is advised when the soap emulsions are to be diluted with hard 

 water, we get, in reality, what amounts to a soapless Bordeaux-oil 

 emulsion. 



THE USE OF SOAP AS AN EMULSIFIER 



Bancroft holds that if the emulsifying agent is such that it will 

 lower the interfacial tension of the water more than that of the oil 

 so that the film bends convex to the oil, there will be a tendency to 

 emulsify the "oil in water," but if the absorption of the emulsifying 



