Dielectric Constants of certain Frozen Electrolytes. 301 



and outer cones. After the liquid is frozen, if desired, the nut work- 

 ing on the screw pin may be loosened, the inner cone is then free to 

 follow up the contraction of the dielectric and always keeps up a 

 perfect contact between the metal cones and the conical layer of 

 dielectric. The whole arrangement is perfectly rigid, and can be 

 taken to pieces, and put together again in exactly the same position 

 by releasing the three screws which attach the three-spoke carrier 

 to the outer cone. 



In order to determine the temperature of the frozen dielectric a 

 platinum wire thermometer was fixed in the interior of the inner cone 

 with the wire pressed against the wall of: the cone, and was held there 

 by partly filling the interior of the inner cone with paraffin wax or 

 fusible metal. Leading-in wires were then brought out to enable the 

 resistance, and therefore the temperature of this platinum thermo- 

 meter, to be instantly determined on a slide wire bridge. 



The condenser was then suspended in such a way by silk strings 

 that it could be lowered into the interior of a very large vacnum 

 vessel, 60 cm. deep and 7 cm. wide in interior diameter, and capable 

 of holding several litres of liquid air. The two cones of the con- 

 denser were connected with the galvanometer, battery and vibrating 

 contact maker controlled by an electrically driven tuning-fork, just 

 as described in a previous communication.* f 



The arrangement of circuits is shown in fig. 2. 



Fig-. 2. — Arrangement of connections for measurement of dielectric constants. 



B, Battery of lithanode cells. Gr, Galvanometer. S^, Change-over switch. 



C, Cone condenser. V, Vibrating contact maker. 



By means of a switch SiS 3 the position of the galvanometer can be 

 instantly changed from the charge to the discharge circuit, so as to 



* See a " Note on the Dielectric Constant of Ice and Alcohol at very low Tem- 

 peratures," 4 Roy. Soc. Proc.,' vol. 61, p. 2, February, 1897. 



