164 



ATOMS, IONS, SALTS, AND SURFACES 



molecule. This area is found to be nearly the same for long-chain compounds of from 

 16 to 30 carbon atoms long, which indicates that the molecules in the film are oriented. 

 The thickness of such a film, calculated on the basis of the idea that its density is that 



s& 



'f2- 



3^ 



Fig. 16.— Adhesional work, ergs per square centimeter, between organic liquids and water. (The 

 names of the substances represented by the curves are given at the right while the names given in the 

 middle of the diagram represent substances for which the values are given at 20° only.) 



of the pure organic substance, indicates that each CH2 group adds about 1.4 A to the 

 thickness of the film, while X-ray measurements on the solid substance give a mean 

 value of about 1.15 A. 



FILMS ABSORBED FROM LIQUIDS 



The best evidence at present available indicates that the films on water of butyric 

 acid, amyl amine, octyl alcohol, phenol, resorcinol, and all analogous substances are 



