in Mercury by Deoxidation. 495 



Thus, by changing the direction of the battery, the electro- 

 lytic liquid could be transferred at pleasure from one limb to 

 the other, rising on that side in which the positive wire was 

 inserted, whilst the mercury globule never moved more than 

 -^ inch from its original position. 



With a U-tube of 1*3 centim. bore, the acid water attained a 

 difference of level of 1*8 centim. when no resistance was inserted 

 in the circuit, and the niveau rose 1*3 centim. in twenty seconds. 



With a U-tube 0*6 centim. diameter, the acid water attained 

 the following differences of level : — 



Resistance inserted. Difference of level, 



ohms. centim. 



2-27 



1000 2-05 



5000 1-60 



10000 1-30 



The times (noted with a stop-watch) which the column took 

 to travel from 0'5 centim. below to 0*5 centim. above the zero 

 of the scale were as follows : — 



Resistance inserted. Time taken to alter 



ohms. level 1 centim. 



4'6 seconds. 



1000 5*9 



10000 25-5 



5000 16-2 



From this, the rate at which the liquid is pumped by the cir- 

 culating mercury drop appeared to be almost proportional to 

 the current. 



When the quantity of mercury in the U-tube was increased 

 so that its level was 2 or 3 inches up the tube, the quantity of 

 acid water which it pumped was extremely small, on account 

 of the increased resistance of the passage between the mercury 

 column and the glass. But instead of this, the level of the 

 mercury in the two sides of the U-tube was altered, rising on 

 that side in which the negative wire was plunged until the 

 altered level balanced the force exerted by the circulation of 

 the mercury. 



This brings us to the experiment published by Draper 

 (1845), in which he employed a U-tube, one limb of which 

 was of larger diameter than the other, the narrower one only 

 containing acid water above the mercury. With this appa- 

 ratus Draper observed the alteration of level in question when 

 the current was sent through ; and he ascribed the phenome- 

 non to a supposed alteration in the capillary constant of the 

 mercury. A modification of Draper's apparatus was intro- 



