2 



Scientific Proceedings (55). 



Magnesium functions in a manner similar to calcium, one ion 

 being equivalent to two of OH; iron and aluminium exert a 

 greater effect, one ion being equivalent to three of OH, at the 

 critical point, provided equal volumes of oil and water have been 

 employed. NaCl exerts no effect on a system of this type. If 

 certain oil-water systems are slowly transformed through the 

 critical point to water-oil systems or vice versa, figures resembling 

 those in karyokinesis may be observed microscopically. 



Bancroft 1 concludes that the production of a stable emul- 

 sion depends on the formation of a concentration film or mem- 

 brane at all points of contact between the dispersed and con- 

 tinuous phases, and that the relative solubility of this film in 

 the aqueous and oil phases and the consequent surface tension 

 relations on its two sides determine the nature of the emulsion 

 formed. From the above experiments it appears probable that 

 positive ions adsorbed by a stabilizing fatty acid film render the 

 later relatively more soluble in the oil or less soluble in the water 

 phase thus lowering the surface tension on the oil as compared with 

 the water side. The tension on its two faces being unequal, the 

 membrane tends to develop a spherical curvature, the concave 

 side being presented to the water and the convex side to the oil 

 phase. This causes the production of a "water-oil" emulsion, 

 the number and size of the water globules formed depending on 

 the relative proportion of positive ions adsorbed by the film and 

 the consequent differences in surface tension on its two sides. 

 The adsorption of negative ions on the other hand renders the 

 membrane more soluble in the aqueous phase, and consequently 

 lowers the surface tension on that side causing the membrane to 

 curve in such a manner as to present its concave face to the oil 

 phase, an "oil-water" emulsion being formed. At the critical 

 point the proportion of positive and negative ions adsorbed by 

 the membrane must be such that the surface tension remains 

 practically the same on both sides of the film which consequently 

 fails to develop a curvature in either direction. Further support 

 is lent to this point of view by the fact that the fatty acid salts of 

 calcium, magnesium, iron, aluminium, etc., are relatively freely 

 soluble in oil and relatively insoluble in water. In order to deter- 



1 Journal of Physical Chemistry, 1913, 17, p. 501. 



