584 RICE ART. L 



This work was carried out at a water surface. However, 

 Micheli also experimented with a mercury-air interface, sub- 

 stantially confirming Iredale's conclusion that at this surface 

 the amount adsorbed approaches a definite limiting value as the 

 partial pressure of the hydrocarbon vapor increases, and that 

 the values of the area per molecule obtained from T, in this 

 case agreed well with Adam's value for benzene already referred 

 to and, in the case of pentane, hexane, heptane and octane, 

 with the values also found by Adam for closely packed mole- 

 cules of straight-chain alphatic acids or alcohols oriented at a 

 water-air interface so that the OH or CO OH groups are attached 

 to the surface. One feature of Iredale's work with benzene, 

 Micheli did not obtain; this concerned the point of inflexion 

 obtained by Iredale on his (a, log p) curve for benzene, indicat- 

 ing a maximum adsorption before saturation was reached, with a 

 subsequent diminution. Micheli remarks that such an effect 

 would not be probable, and draws attention to the curves of 

 Schofield and Rideal concerning the adsorption of ethyl alcohol 

 from an aqueous solution on which we have already commented 

 and where a similar apparent maximum exhibits itself. Micheli 

 states that the observed maxima really indicate that conditions 

 exist which render the Gibbs equation inapplicable, and is 

 obviously suggesting that we must look for an explanation of 

 Iredale's result, if it really exists, along the lines already referred 

 to in our previous comments on this point. 



It is interesting to observe that Gibbs' own footnote on page 

 235 is concerned with adsorption from a vapor phase. He 

 quotes some figures of Quincke for the tension of mercury in 

 contact with air (which he takes to be practically the same as 

 for contact with its own vapor free of water vapor), and for the 

 interfacial tension of water and mercury and of water and its 

 vapor. They are, when expressed in present-day units, 539, 

 417 and 81 dynes per cm. Assuming that the tension of 

 mercury in contact with the saturated vapor of water is the sum 

 of the two latter, which is tantamount to assuming that at 

 saturation pressure of water vapor the adsorbed film is begin- 

 ning to have the properties of water condensed in mass, the 

 reduction in the tension of mercury by adsorption of water 



