246 



Profer^sor A. W. Bilcler 



[Marcli 20, 



The coiiclnsion was thus arrived at that the specific resistance of 

 the liquid of which a soaji film is formed does not difier from that of 

 the same liquid in mass, at all events when the thickness is greater 

 than 374 x 10"'^ mm, and that comparatively small changes in the 

 temperature or hygroscopic state of the air in contact with the film 

 are attended with great alterations in the specific resistance, which 

 indicate a considerable change in composition. 



The method of experiment made it possible to determine the 

 amoimt of this change. Solutions were made up representing 

 " liquide glycerique " which had lost or gained given percentages of 

 water, their specific resistances were determined at various tempera- 

 tures, and approximate formulae obtained by which the percentage of 

 water present could be calculated if the specific resistance and 

 tempei'ature were known. 



The results of the application of this method of analysis to a film 

 are shown in the accompanying figure. The abscissae represent time, 

 the ordinates of curve I. represent the average thickness of the film. 



Fig. 1, 



It will be observed that the film continued to get thinner during the 

 whole time that it was under observation. The electrical observations 

 however, proved that at first the jiroduct of the resistance and thick- 

 ness steadily increased, indicating a continuous loss of water. Curve II. 

 shows the numl)cr of parts of water in 100 of the solution lost at the 



