Transition from gaseous to coherent films condensation phenomena in two dimensions

8 These subsequently collapse to aggregates visible under dark-ground illumination. 4 Proc. Roy. Soc. A, 110, 423 (1926). 

Bideal found, for one of these acids, that the vapour film was associated into double molecules. 

As the area is diminished below some thousands of sq. A., where the molecules cover only a small fraction of the surface, the surface pressure rapidly becomes much smaller than that of a perfect gas, and in the four acids with the longest chains becomes constant over a considerable region. The curves are indeed a very faithful reproduction of Andrews s curves for the relation between pressure and volume, for carbon dioxide, at temperatures near the critical. The horizontal regions in the curves correspond to the vapour pressure of liquids, and indicate the presence of an equilibrium between two surface phases, the vapour film, and islands of liquid, coherent film. 

It has now been shown unquestionably, by measurement of surface 1 Proe. Soy. Soe. A, 110,423. 

Zocher and Stiebel,8 examining surfaces covered by films in the two-phase region, by dark-ground illumination, considered that they could see the outlines of some of the islands of coherent film by the lines of dust particles which these collected round their boundaries as they floated about on the surface. 

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