272 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 1913. 



TABLE OF RESULTS. 



The following table gives a summary of the pre^dous results and 

 allows us to make useful comparisons. 



THEORETICAL REPRESENTATION OF BLACK FILMS AND OF MOLECULES. 



Greatest and least thicknesses of stable oil films expanded upon water. The thicknesses are multiplied 

 by one million (1 mm. represents 1 /i/i.) 



1. 13 nil Theoretical size of oil molecules (trioleate of glycer- 

 ine),' calculated from Perrin's data. 



1.10/i;:i Minimum thickness of a stable oil film found ex- 

 perimentally. 



1.15 to Maximum thickness of a stable film without £;lob- 

 1.53/1^ ules, or the minimum thickness of a film with 

 globules, found experimentally. 



■™« 2 to 3 iiii Maximum thickness of a film in stable equilibrium 

 with great globules or with masses of oil of 1 mm. 

 or greater in tliickness. 



6 im 1st minimum thickness of film of soap-bubbles. 



12 till 2nd minimum thickness of films of soap-bubbles 

 or maximum thickness of the black spot. 



Black spot of oil 

 films. 



Black spot of soap- 

 bubble films. 



V. OIL FILMS ON MERCURY. 



Oil placed on mercury shows very similar results to those obtained 

 upon water.^ There is still a very sharp limit to the extension, and 

 the thickness of the films at the limits is sensibly the same. When 

 the oil is abundant enough, it forms a thick colored film which grows 

 rapidly with the production of black spots surrounded with globules 

 (pi. 7) and finally becomes a very thin film dotted with droplets. 

 Other liquids (sulphuric acid, soap water, distilled water) give upon 

 mercury analogous growths. We have therefore here a very general 

 class of phenomena.^ 



VI. CONCLUSIONS. 



We see now that a concept which at first seemed chimerical — that 

 is, the reduction of substances to perfectly homogeneous films onlj'^ one 

 molecule in thickness — has become an experimental reality. And in- 



1 See Devaux, 1. c, November, 1912. 



- Devaux, Journal de Physique, November, 1912. 



3 Karl Fischer in his inaugural dissertation (Die geringste Dicke von Fliissigkeitschich- 

 ten, Miinich, 1S96), studied the extension of two oils and other liquids upon mercury. 

 He gives numerous measures of the thickness of films before their rupture. The thin- 

 est had thicknesses less than 3 lin (rapeseed oil) and 1 nn (sulphuric acid). 



