22 



Conductivity of Aqueous Solutions. Part II. 



never be a leak at this point. It is also better to use a fresh steel ball each 

 time. The screw K should fit well, but still turn easily with the fingers ; 

 for, if there were much friction here, it would be impossible to tell how 

 much of the force employed in screwing it down was being communicated 

 to the ball and how much was wasted in friction in the screw. Smearing a 

 little vaseline on the screw prevents air from leaking in while the bomb is 

 being evacuated. 



The edge of the lining is fastened to the cover by eight steel screws, in 

 the same way as the flange of the lining of the body of the bomb is secured, 

 the only difference being that it is not necessary at the top to recess the 

 edge of the platinum. Care must, of course, be taken that the screws in 

 the top do not come opposite those in the lower part when the top is put 

 on. Two reference marks enable the experimenter to bring the cover 

 always into the same position with respect to the bottom. 



The cover lining is forced into place and tested, just as was the lining 

 of the lower part of the bomb, by means of the Cailletet pump, making 

 the pump connection with a metal piece like that shown in fig. 6, which 

 takes the place of the lower part of the bomb. 



The construction of the 

 auxiliary electrode is simi- 

 lar to that of the lower one ; 

 it will be evident from fig. 

 7. The part a has to be 

 made just as small as is 

 consistent with making the 

 joint tight on the end of the 



crystal. The platinum covering consists of a little plati- 

 num box similar to that used on the lower electrode, a 

 short piece of tubing b and a piece of platinum wire c. 



The gold packing-rings are made as follows : A piece 

 of g-old wire about 3 mm. shorter than the circumference 

 of the finished ring is cut off and the ends fused together 

 in a small oxy-gas flame. (The ends of the wire were 

 originally filed flat and then soldered with coin gold; but this method 

 besides being much more laborious had the disadvantage of bringing 

 base metal into the gold.) The joint made in this way is slightly thicker 

 thsn the rest of the ring, but not enough so to do any harm. The 

 ring is then annealed and placed on a cast-iron spreader. By pushing a 

 tapered brass plug into this spreader, it is expanded and the ring stretched. 

 By placing a reference mark on the tapered plug, the ring can be stretched 

 to just the same size every time. It, of course, comes off perfectly round, 



Fig 6. 



