CONTENTS xxi 



23. The Experiments of McBain and His Collabora- 



tors 561 



IX. Gibbs' Equation and the Structure of Adsorbed Films . . 566 



24. Impermeable or Insoluble Films 566 



25. The Work of Langmuir and Adam. The Concept 



of "Surface Pressure." Equations of Condition 



for Surface Phases 567 



26. Unimolecular Layers and the Dividing Surface . . . 572 

 X. Desorption 575 



27. Unimolecular Layers and Negative Adsorption. . . 575 



28. The Recent Experiments of McBain and Humph- 



reys on Slicing Off a Thin Layer at a Surface .... 578 

 XI. Adsorption of Gases and Vapors on Liquid Surfaces .... 579 



29. Form of Gibbs' Equation for Adsorption from a 



Gaseous Phase 579 



30. The Experiments of Iredale 581 



31. The Experiments of Micheli, Oliphant, and Cassel . 583 

 XII. The Thermal and Mechanical Relations Pertaining to 



the Extension of a Surface of Discontinuity 586 



32. Need for Unambiguous Specification of the Quanti- 



ties Which Are Chosen as Independent Variables. 586 



33. Alternative Method of Obtaining the Results in 



This Section. Total Surface Energy 588 



34. Empirical Relations Connecting a and t. Degree of 



Molecular Association in Liquids 592 



35. Heat of Adsorption 594 



36. Dependence of <r on the "Age" of a Surface 596 



XIII. The Influence of Gravity 597 



37. The Variation of p, <r, m, m, . . with Depth in a 



Liquid. An Apparent Inconsistency in Gibbs' 

 Argument. The Argument Justified 597 



XIV. The StabiUty of Surfaces of Discontinuity 605 



38. Conditions for the Stability of a Dynamical 



System 605 



39. Restricted Character of Such Conditions as Applied 



to a Thermodynamical System 607 



40. Stability of a Plane Portion of a Dividing Surface 



Which Does Not Move 608 



41. Three Conclusions Drawn from the Analysis in 



Subsection (40) 612 



42. Determination of a Condition Which Is Sufficient 



though Not Necessary for Stability when the 

 Dividing Surface Is Not Plane and Is Free to 

 Move 615 



43. Gibbs' General Argument Concerning Stability in 



Which the Difficulty Referred to in Subsection 

 (39) Is Surmounted 617 



