108 



agent brings about an opposite condition, a "water in oil" emulsion will 

 result. Hence, to make an "oil in water" emulsion it is necessary to 

 use a water-soluble colloid ; and to make a "water in oil" emulsion an oil- 

 soluble colloid must be used. More briefly still, to get an "oil in water" 

 emulsion the emulsifying agent must be such that it is wetted more 

 by water than by oil. Potash and sodium soaps are such water-soluble 

 colloids. 



The excellence of an emulsion is judged primarily by its stability, 

 which is very dependent on its viscosity. Upon what then does the vis- 

 cosity depend? 



Possibly the greatest single factor affecting viscosity is the volume 

 ratio of the oil and water, or the concentration of the oil. While it is 

 possible to make an emulsion with potash-fish-oil soap and oil alone, or by 

 the addition of an unusual amount of water to the oil and soap, experi- 

 ment has shown that there is an optimum proportion of ingredients. 



Another factor affecting viscosity is the degree to which the in- 

 gredients are mechanically agitated. Orchardists have noted that the 

 more often the mixture is run through their pumps and the greater 

 the pressure, the more viscous is the product. This is due to the fact 

 that the oil is reduced to more minute globules and the extent of the 

 oil-water surface is thus greatly increased. 



A deficiency in the proportion of soap results in lower viscosity 

 owing to the prevalence of larger oil globules, regardless of agitation. 

 These large globules have a tendency to coalesce by breaking the film 

 which surrounds them. 



The size of the oil globules is further dependent on the tempera- 

 ture of the mixture when it is agitated. A cold mixture will yield an 

 emulsion physically inferior to a hot mixture. However, field and 

 laboratory tests have demonstrated that there is nothing to be gained 

 by continued application of heat. Heating facilitates emvilsification only 

 by lowering the viscosity of the mixture and reducing the interfacial ten- 

 sion between the two phases, thus aiding mechanical agitation. 



In comparative spray-tests we have often failed to take proper 

 cognizance of the fact that an emulsion undergoes some quantitative 

 changes during the process of manufacture. Unless these changes are 

 taken into consideration there is apt to be an element of doubt as to the 

 accuracy of our results. In this regard, it is well to keep in mind that 

 a mixture may, or may not, increase in volume with emulsification. 



INCREASE IN VOLUME OF BOILED EMULSIONS 



In making up the large series of emulsions which was necessary for 

 these experiments, it was noticed that there was a greater increase in 

 volume in the case of some boiled emulsions than in others, although 

 exactly the same proportions and length of time for boiling was allowed 

 in all cases. In one case the volume was increased by 13%, even though 

 the outlet hose was put into the liquid so that large amounts of air 



