2q. Conductivity of Aqueous Solutions. Part II. 



absorbent cotton, a lot of finely powdered graphite is then rubbed into 

 the thread and upon the surface which bears on the brass compensating 

 washer. The nut is now screwed on by hand, care being taken not to dis- 

 turb the cover; otherwise it might be raised slightly, so that particles of 

 graphite would enter the bomb. The apparatus is next transported care- 

 fully to the large wrench, and the nut is tightened up. The air pressure 

 is then reduced to about 2 cm. by connecting the small tube with a Rich- 

 ards water pump, the valve is screwed down, the lead-wires bolted on, 

 and the bomb is ready for the measurements. 



The conductivity is first measured at 26. To hasten the equalization of 

 the temperatures, the cold bomb was usually introduced after bringing the 

 bath to about 30. The other vapor baths are heated up meanwhile. 



The bomb is then immersed in the 140 bath, whereupon the conduc- 

 tivity increases very rapidly. The minimum in the telephone is at first 

 greatly disturbed by the boiling of the solution, which takes place strongly 

 at the lower electrode, owing to the fact that this is at the start, because of 

 its position, the hottest part of the bomb. But as the temperature of the 

 solution approaches that of the bath the disturbance decreases, and finally 

 ceases altogether. When the temperature has become almost constant, 

 which is indicated by the constancy of the conductivity, the bomb is 

 removed from the bath, shaken, and returned as quickly as possible. To 

 shake it while hot, a piece of asbestos cloth, with a piece of woolen cloth 

 outside, is used. If the shaking is omitted, the measured conductivity 

 may be too high by as much as 0.5 per cent. This was found to be due to 

 the following facts : At 140 there is still a considerable vapor space left 

 in the bomb, the entire cover being above the liquid surface. During the 

 first part of the heating the xylene vapor is condensed so rapidly by the 

 bomb that it extends up only for a little distance above the bottom 

 of the bomb, leaving the upper part completely out of it. This causes an 

 evaporation of pure water and a condensation of it all over the colder 

 cover, leaving the solution too concentrated. If the bomb is shaken after 

 reaching the temperature of the bath and quickly returned, the same action 

 does not repeat itself, since the top is now as hot as the bottom. The 

 bridge readings are now continued (usually for about 30 minutes) till 

 one perfectly constant for 10 to 15 minutes is obtained. 



The bomb is then transferred to the naphthalene bath. Shaking was 

 found to have no effect at this temperature, owing, doubtless, to the fact 

 that the liquid level has then risen almost to the cover, so that large drops 

 can not adhere to the latter, and to the fact that the surface tension has 

 diminished, so that less water is held clinging to the walls of the narrow 

 chamber in the cover. 



