Films of fatty substances with double bonds

A double bond in the aj8 position to the carboxyl group lowers the expansion temperature much less than in the middle of the chain (c). Hughes3 has shown that it approximately doubles the surface potential, however, presumably through the displacement of electrons near the carboxyl head rendering the a carbon more negative and the jS more positive than in the saturated chain. A double bond in the middle of the chain increases the surface potential of the molecule only slightly, but there is still a slight increase in dipole moment when a double bond is present in the middle of the chain. 

Further very interesting studies of films of fatty acids and glycerides with from one to three double bonds in the chains come from Rideal s laboratory at Cambridge.4 The fatty acids with from one to three double bonds, at points in the chain remote from the end group, form liquid-expanded films of which the limiting area increases with the number of double bonds in the molecule. One double bond gives about 55 sq. A. three, in the elaeostearic acids 

A triple bond, in stearolic acid, remote from the end group, gives such an increase in attraction for the water, combined with little increase in the lateral adhesion between the chains, that the films are vapour-expanded. This triple bond produces a considerable increase of surface potential. 

Hughes obtained some very remarkable results with the compounds formed by adding maleic anhydride to the two elaeostearic acids (Fig. 20).1 The 

Knight and Stamberger1 find that addition of sulphur to double bonds in the 

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