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Theory of Surface Forces. 345 



For ether I find : 



A= {^- 4 ' 93 }^- • • • < u > 



At the temperature T = £T A , or & = J, or £=-39°-3 

 Celsius, we find thus for the thickness of the plane capillary 

 layer of ether : 



/t = 3'57 yLt^. 



If water was " conformable " with ether in the sense of 

 van der Waals, the proportion between the thickness of the 

 -capillary layers of water and ether at corresponding tem- 

 peratures would be equal to the expression : 



Pk ' 



4b >c Celsius, we 



The thickness of the capillary layer, calculated by the aid 

 of the formula (14), increases with the temperature. For a 

 temperature of 15° Celsius, we must therefore take a value 

 which is a little smaller than 2'4. Such a value would he 

 therefore in perfect accordance with the researches of Johonnott, 

 which give (see above) a value of the order of greatness of 2/ul/ju. 



§ 3. The surface-tension and the radius of small drops. 



In the same manner as I have demonstrated above for a 

 plane capillary layer, we can show that a spherical drop 

 is also fully determined by the pressure of the vapour 

 which surrounds it. Now, we have seen further that the 

 raetastabile phases of the Thomson-van der Waals Isotherm 

 might not be in equilibrium in the plane capillary layer if 

 the capillary layer was not limited at both sides by a homo- 

 geneous phase (of liquid and vapour), so that every plane 

 liquid film always consists of a liquid layer limited by two 

 complete capillary layers. In the same manner as we have 

 observed that the interior liquid layer of a plane liquid film 

 of which the thickness has its minimum value has a thickness 

 of the order of the radius of the sphere of action, and in the 



and we 



should have : 











"ether 

 "water 



23G 

 "151" 



circa 1*5. 





For < 



water at the tern 



perature 



T = \T K 



or 



should therefore calculate : 









h 



3 6 

 ~ 1-5" 



2-4 w. 





