NOYES AND COOLIDGE. — ELECTRICAL CONDUCTIVITY. 183 



particles of graphite or dirt adhering to the flange and cover in the ■ 

 neighborhood of the gold packing ring are removed with absorbent 

 cotton saturated with benzene, and the screw thread on the lower part 

 is cleaned in the same manner. Both the upper and lower parts are 

 now rinsed thoroughly with good water, using the fine stream from a 

 wash bottle to remove more effectually any loose particles of graphite 

 which may have got into the bomb upon previously opening it. By this 

 means, too, water can be forced through the fine tube T v If the solu- 

 tion to be investigated is a dilute one, the rinsing muse be very thorough. 

 Finally, the bomb is rinsed out witli some of the solution, and as much 

 as possible of this is then shaken out. The bomb is then ready for use. 



Suppose now it is desired to make a series of measurements at the 

 temperatures up to 281°. An amount of solution which will almost, 

 but not cpuite, fill the bomb at this temperature is measured in from a 

 pipette previously graduated to contain this amount, as will be described 

 in Section V. A gold packing ring is annealed and cleaned by heat- 

 ing it in the flame of a burner, and it is placed in the groove. The 

 cover is then put in place, taking care not to disturb the ring. The 

 thread in the large nut is next washed out with benzene, to get rid of 

 any solid substance which may have condensed there in a previous heat- 

 ing. With a piece of cloth or absorbent cotton, a lot of finely powdered 

 graphite is then rubbed into the thread and onto the surface which bears 

 on the brass compensating washer. The nut is now screwed on by hand, 

 care being taken not to disturb the cover ; otherwise it might be raised 

 slightly, so that particles of graphite would enter the bomb. The appa- 

 ratus is next transported carefully to the large wrench, and the nut is 

 tightened up. The air pressure is then reduced to about 2 cm. by con- 

 necting the small tube with a Richards 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 con- 



