and the Formal Ion of Liquid Films. 



103 



\ Diameter 



of 

 1 bubbles. 



"5 cm. 



Volume 

 of foam 

 (litres). 



Surface 

 removed 

 (square 

 metres). 



Resistance, 

 corrected 

 for tempe- 

 rature. 



Concen- 

 tration 



(gm.-mol. 



per litre). 



1 



Oleate 



removed 

 (gram-mol.). 



Surface 



Excess 

 (gm.-mol. 



per sq. cm.). 









1374 to 



•002056 









29-8 



90 



1456 



•001940 



117x10-° 



1-30X10- 10 





426 



128 



1467 



•001925 



134 .. 



1-05 ., 





570 



171 



1509 



•001S72 



1-86 „ 



1-09 .. 



"15 cm. 







1171 



002220 









445 



45 



1206 



•002156 



o-64xib-° 



1-42X10 -10 





11-16 



11-2 



1237 



•002102 



1-18 .. 



1-06 .. 





1724 



172 



1273 



002042 



1-78 ., 



103 ., 



Mean volume of solution, 100c.cs. 



The mean result — 1*2 X 10~ 10 gm.-mol. per sq. cm., or 

 •4 mgm. per sq. metre — is doubtless a moderately good 

 estimate for the surface excess at the moment of formation 

 of the bubbles, but it must necessarily be very much less 

 than the ultimate value of the excess. The curves of fig. 2 

 -how that at the concentration of these experiments the excess 

 is not fully formed until after the lapse of \ hr., while in the 

 bubbling the whole surface of the solution in the beaker was 

 renewed in about 2 seconds, — so that only a very small 

 fraction of the excess can have been formed. 



The existence of a surface excess having been confirmed 

 experimentally, a difficulty arises with regard to the theoretical 

 interpretation of the surface-tension curve. According to the 

 thermodynamieal equation (4\) an excess of the magnitude 

 found should cause a very considerable diminution of the 

 tension with the concentration ; but, as a matter of fact, the 

 ultimite values of the tension are practically independent of 

 the concentration. Since the application of the thermo- 

 dynamieal reasoning is limited only by the reversibility of the 

 processes concerned, we are driven to the conclusion that the 

 formation of the surface excess in oleate solutions is not a 

 reversible process. This idea is in conformity with the con- 

 clusion already arrived at, that the excess tends to be formed 

 however dibit i the solution ; for this means that the reverse 

 action (passage of the excess from the surface into the interior) 

 is very small if not actually zero. This leads us to expect 

 that, since the surface cannot take up an indefinite amount of 

 the oleate, it will ultimately in finite concentrations become 

 saturated, when irreversibility will be produced by the con- 

 tinuous precipitation of the oleate into another phase. Several 

 observations go to support this inference : — (1) It is well 

 known that an insoluble senm is formed on the surface of 



