238 WIEDEMANN ON THE MOTION OF LIQUIDS 



some time in dilute hydrochloric acid^ and subsequently washed 

 with distilled water until all soluble materials were removed. 

 By this means the cylinders were preserved from any change 

 which the solution of extraneous matter in their pores might 

 have effected. 



When the whole apparatus was filled with distilled water, so 

 that within the porous cylinder the water stood at the level of 

 the tube e, or rather exactly filled it, then in consequence of 

 capillary attraction no water issued from e. Further, when the 

 outer cylinder, h, was also filled to the brim with water, the dif- 

 ference of pressure within and without the tube d was so small 

 that during many hours no perceptible change in the level of 

 the water in the tube d took place. We may therefore assume 

 that the action of the difference of pressure, though extended 

 over many hours, is equal to zero. 



If the end of the wire, k, be connected with the positive pole, 

 the end of the wire, f, with the negative pole of the galvanic 

 battery, the water soon ascends in the tube d, above the level of its 

 junction with the tube e. The hydrostatic pressure thus pro- 

 duced overcomes the capillary attraction at the mouth of e, and 

 hence the water flows out into the vessel, /, placed to receive it. 

 The principal cause of this phaenomenon is, as we have already 

 said, the galvanic current, by means of which the water is 

 forced from, the outer cylinder, h, into the clay cylinder. The 

 simplicity of this action is nevertheless disturbed by many 

 other circumstances. 



The hydrogen gas, liberated in consequence of the chemical 

 action of the current, collects on the inner surface of the 

 clay cylinder on the platinum plate g, and on the bell-shaped 

 glass c, and thus displaces a certain quantity of water. Never- 

 theless, as soon as a maximum amount of gas has thus col- 

 lected, it afterwards escapes through the tube d, and causes no 

 further ascent of the water in this tube unless the current has 

 in the mean time exceeded a certain intensity. In order to 

 measure the pure transferring action of the galvanic current, it 

 is necessary therefore to wait until this maximum amount of 

 gas has collected. Moreover, with distilled water the quan- 

 tity of gas liberated is so small in comparison to the quan- 

 tity of water transported, that the gas bubbles from time to 



