Theory of Surface Forces. 351 



For ether we have : 



p k = 35*6 atm. (S. Young) = 4*5092 x 10 6 dyne per cm. 2 



The equation (21) gives by the substitutions of the 

 'calculated values : 



Pvap. = 3*178 x 10° dyne per cm. 2 



Further, the equation (20 a) gives : 



p liq = 3G*411 x 10 G dyne per cm. 2 



By the aid of the formula of Kelvin, we calculate thus 

 finally : 



H 2x1 0-3 



i = - - =-.„. --,: : , - A —q x 10 ~ 6 = 1>01 x 10 " 6 cm - = 10'ififi. 



i?liq.~/?vap. 36-411 —0*3178 



We find therefore again a value of the order of greatness of 

 the thickness of the plane capillary layer at the same tempera- 

 ture. If water was conformable in the sense of van der 

 Waals with ether, 0° Celsius for ether would correspond to 

 100° Celsius for water, and the thickness of their capillary 

 layers at the considered temperatures would be proportional 

 to the values of the expression : 



v 



That is about 1*5. At 100° Celsius the value of the radius R 

 in the formula of Kelvin for a drop of water of minimal size 

 would be thus about or 7 millicrons. R being a mean value 

 between the radii of the two spheres which envelop the 

 spherical capillary layer of the drop, I put for the effective 

 radius of a water-drop of minimal size at 100° Celsius : 



R = 10 pp. 



In the same manner as we have determined the order of 

 greatness of the radius of a liquid drop, which has its minimal 

 size, we can treat a spherical bubble of minimal size in the 

 interior of a mass of liquid. We shall make the calculation 

 again for ether at the temperature T = 0'844T^. or t = 121°*5 

 Celsius. The pressures _/.>i iq . and /> vap . are in this case given 

 by the ordinates of the points A, and Ci of fig. 1. The 

 equality of the thermodynamical potentials gives here in the 

 same manner as above : 



(n + v 1 ')(pi-pu q ) = (tV+«»')(Pi-lw)» • (20) 



"where i\ and v 2 have the same meaning as above, while Vi 

 and v s ' are respectively the abscissae of the points A x and C x 



2B 2 



