138 



THE ELECTRICAL RESLSTAXCE AND 



^o/ycfi on' cfcr- 



,'*!ercijryCont&c'f 



Fig. 7. 



temperatures througii whicli it T\-as to be used iu the experi- 

 ment, viz. — from 5" to — 12 °C. 



Ii Tvas found very difficult to freeze the ^vater in the ^'U" 

 tube in the method described, without the tube being broken 

 by the expansion of the ice. To obviate this difficulty a piece 

 of rubber tubing, about .5 cm. in diameter and 15 cm. in leng'th, 

 and very carefully cleaned by boiling, etc., was closed at one 

 end, by means of a glass stopper. The other end was also 

 closed with the exception of a small hole, the size of a pin-head. 

 This tubing was placed inside the '"U" tube, care being 

 taken to prevent any quantity of water entering through the 

 opening in the one end. When the water expands on freezing, 

 it can be seen that a certain amount of freedom is allowed it, 

 by its being able to push in the lateral stirface of the rubber 



