A MICRO-ELECTRODE. 13! 



out to a bent tip, having a lumen of from three or more microns 

 in the active electrode, and five or more times this in the indif- 

 ferent one. The other end of the glass pipettes are more or less 

 bent. If they contain mercury, they have a platinum wire sol- 

 dered into them, and are fitted airtight with rubber tubing and 

 clamps. The rubber tubing and clamp are supported on a pulley 

 that allows this end to be raised or lowered, thus aiding in the 

 adjustment of the mercury in the bent tip. 



The pipettes are supported and regulated on the microscopic 

 stage of the Barber pipette holder, and their tips are operated 

 inside of a Barber moist chamber. 



The pipettes may contain mercury or some electrolytic solu- 

 tion. Or the indifferent one mercury and the active one a solu- 

 tion, or partly mercury and only the tip a solution. Or both 

 pipettes may contain fine wire. The active one connected with 

 Pratt's glass-coated platinum tip sharpened to a point of 8 mi- 

 crons, and the indifferent one platinum. Or it may be platinum 

 and the active one contain an electrolyte. When non-polarizable, 

 Porter boot electrodes are introduced in the circuit, the pipettes 

 and the dish containing the boots may be filled with sea water. 

 Or by means of pressure applied from the rubber capped end of 

 the pipette, mercury can be forced toward the tip. Then by 

 diminishing the pressure it can be brought back into the capillary 

 a certain distance, drawing after it some of the solution desired 

 from a hanging drop in the moist chamber. An equilibrium is 

 then established that will remain constant as long as the condi- 

 tions are not changed. Or the active pipette electrode may be 

 filled with mercury either in accordance with Barber's method, 

 or filled under pressure as far as possible and then placed with 

 the indifferent electrode in contact with a mercury hanging drop. 

 If now the circuit from a battery is closed, the current enter- 

 ing the anode traverses the hanging drop and the cathode. At 

 the moment of the establishment of the current, the equilibrium 

 of forces that holds the mercury at a certain point in the capillary 

 is disturbed. The end of the fine thread of mercury moves up- 

 ward or downward a certain distance owing to a change in sur- 



