﻿of the common Surface of two Liquids. 377 



influence of the same on the magnitude of the capillary constants 

 or tension of the surface, no mathematical expression for the 

 form of the drops of liquid in the experiments now described 

 can be constructed. 



I will, however, expressly observe that the liquids are not per- 

 fectly moveable, as was presupposed in the theoretical considera- 

 tions, consequently the motion of the particles of liquid against 

 one another is prevented by a certain friction. Hence it is pos- 

 sible that liquid 3 spread itself out on a very thin adsorbed layer 

 of liquid 2 on the surface of liquid 1, and thereby occasioned the 

 difference between theory and experience (compare §§18 and 27). 



III. Capillary elevations in submerged tubes. 



15. The best-known experiment on capillarity is very likely 

 the elevation of liquids in tubes which, filled with air, are im- 

 mersed in a liquid 1. 



Liquid 1 then rises above the horizontal level of the liquid 



(that is, the open plane surface of liquid 1) to a mean height 



(compare § 4) 



7 2 a. cos a) 



n= j 



a r 



in which a is the capillary constant of the open surface, <r the 

 specific gravity of the liquid, &> the marginal angle, and r the 

 radius of the tube. 



The air which is above the capillary meniscus and the plane 

 surface of liquid 1 can be replaced by a liquid 2, which also now 

 covers the upper end of the vertical capillary tube. According 

 to whether the angle &> 12 < or > 90°, an elevation or a depres- 

 sion is observed of the meniscus forming the common limit of 

 liquids 1 and 2 in the capillary tube, above or below the hori- 

 zontal plane in which 'the liquids 1 and 2 outside the capillary 

 tube touch one another in the wider vessel which contains them. 



Although Laplace* has treated this case theoretically, yet, 

 to my knowledge, no experiment with regard to it has hitherto 

 been made. 



According to the axioms given in § 1, the weight of liquid 

 borne by the capillary meniscus of the common surface, as well 

 as the periphery of the tube, must be multiplied by « ]2 cosft> 12 . 

 If A 12 denotes the mean elevation of the capillary meniscus above 

 the plane limit of liquids 1 and 2 of specific gravities cr x and <r 2 

 respectively in a vertical tube of radius r, then we have 



(<Xj — o- 2 )A ]2 .r 2 7r=2r7r. a 12 .cosft) 12 ,^ 

 , __ 2 ^ a 12 cosft> 12! > . . (15) 



h *~ g x -* 2 r J 



* Supplement au liv.x. de laMec. Cel., CEuvres, vol. iv. p. 491. 



