180 



From the plot one obtains the following values : 



Surface tension at 0° C.=75.5 dynes per cm. 

 Surface tension at 18° C.=72.6 dynes per cm. 

 Surface tension of 80° C.=62.6 dynes per cm. 

 Temperature coefficient=.161 dynes per cm. 

 T. Proctor HalP gives the following values : 

 Tension at 0° C.=75.48 dynes. 

 Tension at 18° C.^72.96 dynes. 

 Tension at 80° C. (calculated) =64.28 dynes. 

 Temperature coefficient;=.14 dynes. 

 Hall tabulates the results of nineteen different investigations by 

 fourteen investigators giving a mean of all of Tension=75.4 dynes at 0° C. 

 and temperature coefficient ranging from .141 dynes to .204 dynes per cm. 

 Hall adopts .14 dynes as the most probable value. 



It will be observed that the author's result for the tension at zero 

 temperature agrees with the results obtained by others, but that his values 

 at higher temperatures are considerably lower, giving a much larger tem- 

 perature coefficient. The differences are entirely too large and too regular 

 to be attributed to experimental errors. 



Hall claims that absorbed gases tend to raise the surface tension of 

 water and to increase the temperature coefficient. He claims also that the 

 sui-face tensions of different samples of water are not the same. The 

 author rather inclines to the view that the smaller values obtained at 

 higher temperatures in this investigation are due to the fact that the 

 measurements were made on water in contact with air saturated with 

 watery vapor, while the conditions under which most of the other investi- 

 gations have been made give the tension of water in contact with moist 

 air, but not saturated air. Perhaps the actual temperature of the film 

 under such conditions is not given correctly by a thermometer placed in 

 the liquid. Evaporation into the air lowers the temperature of the surface 

 film — possibly considerably below the temperature of the body of the 

 liquid. Whatever the actual magnitude of this efi:ect may be, it tends al- 

 ways to give too high values for the surface tension at high temperatures — 

 the drier the air the higher the values. 



2 New method of measuring surface tension. Philosophical Magazine, Novem- 

 ber, 1893, Vol. 36, p. 412. 



