﻿1154 Prof. E. K. Rideal on the Flow of 



column in motion is 7rr 2 . 

 lid ; hence 



irr 2 xhx = 27rry—8r).VTTti, 



The mass o£ the column in motion is 7rr 2 xh, where 8 is the 

 density of the liquid ; hence 



or 



Srx r 2 S ' 



■• j • b 

 or x -f ax = - . 



x 

 On integrating this expression, we obtain 



la , 1, 1 & 11 6 2 17?> 3 



Ct =^7^ log A* + ^ -=-5 + — -5-4 7-7 , 



297 , 8r\ SV 



For small values of r this equation reduces to the form given 

 by Washburn for a liquid wetting the tube wall or 



2^ 



Experiments on the rate of penetration of liquids moving- 

 through horizontal glass capillaries under their own capillary 

 pressure alone without any external force, indicated that when 

 the liquid wets the tube the angle of wetting is zero, and 

 that the penetration coefficient is given by the expression 



/V 



V v 



Experimental. 



A piece of capillary tube 1*2 metres long, of average 

 internal diameter 0*708 mm., chosen for uniformity of bore, 

 was mounted horizontally in a condenser tube maintained at 

 20° C. One end of the tube was fused into the side of a 

 wide boiling-tube containing the liquid to be tested. In each 

 experiment the boiling-tube was filled until the surface of 

 the liquid just covered the mouth of the capillary. The 

 liquid was drawn through the capillary by suction, and 

 forced back to within 15 cm. of the end by compressed air 

 so as to thoroughly wet the tube. This operation was per- 

 formed several times, the final removal of the liquid being- 

 accomplished very slowly to ensure removal of all excess 



