246 WIEDEMANN ON THE MOTION OF LIQUIDS 



§7. 



The disturbing influence which the different friction of the 

 liquids in the pores of the porous diaphragms exerted on the 

 results last given, may also have effected in some measure the 

 laws previously expressed. It has already been mentioned, that, 

 by employing clay plates of different densities, other conditions 

 being equal, different quantities of liquid were transported by 

 the same current in the same time ; in the pores of the clay 

 plates, owing to their different densities, a different friction was 

 encountered, and the generality of the results would be thus 

 impaired. In order to eliminate such disturbance, or to be able 

 to draw conclusions independent of the friction of the liquids 

 in the pores of the diaphragm, the former experiments were 

 somewhat modified; so that in place of the quantities of 

 Uquid transported in equal times through the clay cylinder of 

 the apparatus described in § 3, the force by means of which the 

 galvanic current transported the liquid w^as measured directly. 

 To this end a certain hydrostatic counter-pressure was applied 

 within the clay cylinder. Its effect alone would have been to 

 force the liquid out of the clay cylinder ; but an attempt was 

 made so to arrange its intensity, that it and the transporting 

 action of the galvanic current exactly equilibrated each other. 



The above-described apparatus was accordingly thus modified. 

 The tube a (fig. 3.) attached to the clay cylinder was provided at 

 its upper end with a brass cap, which could be closed air-tight by 

 a screw. The efflux tube e, attached to the tube a by means of 

 the blow-pipe, was then connected, by a strong caoutchouc tube, 

 with a manometer, p m, partly filled with mercury ; the height 

 of which could be read off on a suitable scale. When the clay 

 cylinder and surrounding cylinder, h, were filled with a liquid, 

 the screw at the upper end of d closed air-tight, and the galvanic 

 current set in action ; the liquid entering the clay cylinder 

 pressed down the mercury in the shorter leg p of the mano- 

 meter, and thereby caused it to ascend in the longer leg m. 

 The mercury continued to ascend until its difference of level in 

 the two legs p and m exerted on the liquid within the clay 

 cylinder a hydrostatic pressure sufficient to force in a given time 

 through the pores of the latter into the wider cylinder h, as much 



