Polarization of Platinum Plates. 489 



water-bath, and a thermometer, t, was suspended dipping 

 into the liquid of the voltameter. A battery of Grove cells 

 was used, the number of cells varying from 1 to 10. The 

 voltameter was a glass tube of an inch in diameter, and six 

 inches high. The electrodes were strips of platinum about 

 1J inch long and nearly \ inch wide, connected by pieces of 

 platinum wire which passed through the glass to binding- 



Fiff. 2. 





screws fixed on a wooden collar which surrounded the neck 

 of the instrument. The water-bath was contained in a copper 

 vessel, and heated by a Bunsen burner. 



The electrolytic liquid consisted of a 10-per-cent. solution 

 of pure sulphuric acid (sp. gr. 1*842) in distilled water. The 

 voltameter was emptied and refilled at the commencement of 

 each day's experiments, so that the solution never varied much 

 in strength. The thermometer employed was one whose 

 error had been previously found to be negligibly small ; and 

 it being necessary that the temperature of the liquid in the 

 voltameter should be accurately known, it was suspended 

 with its bulb dipping into the liquid. Some experiments 

 were made to see whether error was likely to be introduced 

 by this ; and it was found that when the stem of the thermo- 

 meter was actually between the electrodes, it had a small but 

 appreciable effect on the resistance of the column of liquid, 

 but when the bottom of the bulb was above the top of the 

 plates there was no measurable effect. It was concluded 

 that the thermometer might be placed with its bulb dipping 

 into the liquid but above the platinum plates, and that any 

 small alteration in its position from day to day would not 

 introduce sensible error. The voltameter was always filled 

 quite full, so that the introduction of the thermometer did 

 not alter the resistance by raising the level of the liquid. 



