OIL FILMS ON WATER AND ON MERCURY.* 



By Henri Devaux, 

 Profe.fisnr on the Fdciilti/ of t^ciencps. at liordeaux.^ 



[With 7 plates.] 



Certain phenomena of daily observation are of great interest to 

 the physicist. Especially so is the expansion of oil over the sur- 

 face of water or of mercury. I have studied this matter for a long 

 while and from all my observations several unexpected facts stand 

 out. 



Films of oil tell us with the greatest nicety of the discontinuity 

 of matter, and the dimensions of molecules. They also give us val- 

 uable information as to the field of molecular action. For our 

 observations we will find that there is no need of complicated ap- 

 paratus ; basins, paper, threads of glass, a pipette, a sieve with some 

 talc powder, and finally some oil and benzole suffice for the greater 

 part of the experiments. As to measuring instruments, a double 

 decimeter will do, although its divisions be a million times greater 

 than the diameter of the molecules. Though it seems like measuring- 

 microbes with a surveyor's chain, we will see that the measures not 

 only can be made but made with great precision, because of a very 

 remarkable peculiarity of films of the thickness of one molecule. 

 We will yet further see that the smallest variation in homogeneity 

 engenders considerable differences in the surface tensions, causing 

 the molecules to become exactly equidistant. 



1 Translated by permission from Revue generale des Sciences pures et appliquges, Paris, 

 24th year, No. 4, Feb. 28, 1913. 



- This article gives a summai-y of all my researches upon oil films published since 

 190.3 ; it includes also several new results relating especially to films on mercury and 

 the interpretation of certain observed facts with them. The greater part of the figures 

 have not before been published. The following is a bibliography of my earlier researches : 

 Recherches sur les lames tres minces, liquides ou solides (Proc.-verb. Soc. Sc. Phys. do 

 Bordeaux, Nov.. 1903) ; Membranes de coagulation par simple contact de I'albumine 

 avec I'eau (1. c, Jan., 1904) ; Comparaison de I'epaisseur critique des lames trfe minces 

 avec le diametre theorique de la molecule (1. c, Apr., 1904) ; De I'epaisseur critique des 

 solides et des liquides reduits en lames tres minces (Bull, des stances de la Soc. franc. 

 de Phys., p. 24, 1904) ; Recherches sur les lames d'huile ^tendues sur I'eau (J. de Phys., 

 Sept., 1912, p. 699) ; Sur un proc^dS de fixation des figures d'evolution de I'huile sur 

 I'eau et sur le mercure (Journ. de Phys., Oct., 1912). Several physicists have honored 

 me by taking an interest for several years in my researches into molecular physics which 

 has greatly encouraged me in carrying them out. I especially wish to mention M. Ch. Ed. 

 Guillaume, president of the Soci^t6 de Physique and M. M. Brillouin, professor at the 

 College de France. 



261 



