163 



meterscale. I< is a connexion-tube made of gold or platinum. It is 

 necessary to use one of these metals in order to avoid an evolution 

 of gas, as the metal is in contact with the acid. Even the minutest 

 trace of gas will spoil the measurements. 



After having repeatedl}^ charged and discharged the plates (this 

 was continuously done for 4 weeks) it was necessary to evacuate 

 the apparatus several times after having filled it with the acid. 

 Only in this way we were able to secure that the accumulator 

 remains free of gas during its decharge by a w^eak current. 



After these manipulations the apparatus was ready for use. 



As the whole forms a very sensitive thermometer the temperature 

 at the beginning and the end of the experiment must be absolutely 

 the same. It was therefore placed in a thermostat which was heated 

 electrically and whose temperature was kept very carefully at 15°. 00 

 within 0^005. 



The procedure was now as follows: The accumulator was inserted 

 in a circuit which contained a rheostat, a milliammeter and two 

 silver-coulometers. After the temperature and the position of the 

 meniscus in the capillary tube had been noted, the current was turned 

 on and the apparatus was kept at work for 20 hours. During this 

 time the meniscus slowly moved forward, indicating an increase of 

 volume. After turning off the current the coulometers were carefully 

 washed, dried and weighed. In this way the quantity of electricity 

 which had i)assed the cell was known. 



In order to determine the increase of volume which accompanied 

 the reaction, the volume of that portion of the capillary tube through 

 which the meniscus had moved, was ascertained by filling it with 

 mercury and weighing the metal. In this way the following data 

 were obtained: 



Experiment I. 



Displacement of the meniscus 40.6 mm. = 14.92 mm\ 



Silver deposit in grams : 



Goniometer 1. Goniometer 2. 



0,4304 0,4304 



Increase of volume per gramaequivalent (Ag = 107.93) 



3.74 cc. 



Experiment TI. 



Displacement of the meniscus 35.3 mm. = 12.98 mm^ 



Silver deposit in grams. 



Goniometer 1. Goniometer 2. 



0,4098 0.4095 



11* 



