1893.] Platinum Electrodes in Sulphuric Acid. 



FIG. 2. 



sation one of Lord Kelvin's quadrant electrometers was used, and 

 by an arrangement, described later, the breaking of the electro- 

 lysing current circuit and the switching of the electrodes on to 

 the terminals of the electrometer were done simultaneously. Before 

 switching as above, however, the needle of the electrometer was 

 deflected by making a difference of potential between the pairs of 

 quadrants, and this deflection was so adjusted by trial and error 

 that, when the electrodes were switched on, the needle was na 

 farther deflected. For deflecting the needle of the electrometer a 

 high resistance slide bridge was used. A difference of potential was 

 maintained between its two ends, and the difference of potential 

 between one end and the slider was used to deflect the needle, so 

 that by moving the slider one way or the other the deflection could 

 be increased or diminished at will. The electrolysing current was 

 kept constant throughout each experiment, being measured by one of 

 Lord Kelvin's electric balances and adjusted by a rheostat. One 

 terminal of the electrometer, one electrode, and one end of the 

 slide bridge were connected together and then put to earth. The 

 current for the electrolysis was got from eight large secondary cells, 

 and the difference of potential between the ends of the slide bridge 

 was maintained by two small secondary cells. The arrangement of 

 keys can be best understood from the diagram. By pressing the 

 key &', connexion was made between the slider and the unearthed 

 quadrants, and when the key fc was free, the circuit was complete 

 for the electrolysing current, but when k was pressed down the circuit 

 was broken, and the unearthed electrode was connected to the un- 

 earthed quadrants. 



