6i 



PROCEEDINGS OF THE ABIERICAN ACADEMY. 



TABLE I. 



Tlie Electrodes. — Pure silver wires served as electrodes. It was found 

 experimeutally that no special care need be taken as to the character of 

 their surface. In view of the irregularities shown by solid metal elec- 

 trodes in water solutions, this independence of the character of the surface 

 and previous treatment of the electrodes is quite remarkable. As a 

 matter of precaution the wires were scraped with a clean knife, washed, 

 and dried with filter paper before using. Tests were made on several 

 electrodes so treated by putting them into the same solution. They did 

 not give a difference of potential of more than 0.0001 volt. 



Measurement of the Potential Difference. — Above the cell tubes the 

 silver wires were soldered to copper ones, and the potential difference 

 measured by the Poggendorf method, using a Leclanche cell, an Ostwald 

 potential box, and a capillary electrometer. A previously standai-ilized 

 one-volt Helmholtz cell was taken as the standard of electromotive force. 

 The electrometer was read with a microscope, and would readily show a 

 difference of 0.0004 volt. 



No noticeable error could result from the possible difference in temper- 

 ature of the two copper-silver junctions. 



The Conductivity of Glass. — Although the temperatures used for these 

 nitrate cells were far below the softening point of glass, its conductivity 

 is, even at 200°, very considerable, being of about the same order of mag- 

 nitude as a j^iotfcT normal KCl solution. Measurements could indeed 

 be made with the capillary electrometer without having any liquid con- 

 nection between the two AgNOs solutions. The potentials so measured 

 (with the two cell tubes closed at the lower end) differed from the true 

 ones generally by about 0.02 volt. The conductivity, however, of tlie 

 fused salts is so great as to preclude any disturbance from conductivity of 

 the glass when the liquid connection is made. 



