156 Mr. R. Appleyard on Dielectrics. 



Resistance during Melting. 



If the temperature of paraffin-wax is raised much higher 

 than is indicated in Table I., the change of state, as melting is 

 approached, is characterized by a corresponding decrease in 

 resistance. In order to examine this effect, a special con- 

 denser consisting of two horizontal circular plates, 11 in. 

 diameter, was used. The lower plate was provided with a 

 projecting rim to retain the wax, and was rather larger than 

 the top plate. Three small wafers of thin ebonite sheet 

 (16 mils) were used as distance-pieces. Melted wax was 

 then poured in, tilling the space between the plates. 



There are so many disturbing influences affecting the resist- 

 ance during the change of state, connected with the latent 

 heat of solidification, the unequal melting, the absence or not 

 of " electrification/'' and the contractions and expansions of 

 the wax, that only qualitative results can be given. 



Heating. — Starting at about 20° C. below the melting- 

 point, the resistance rapidly diminishes until actual melting 

 begins ; there is then a definite fall to something like one 

 third of what the resistance was just before melting. If heat 

 is still applied to the condenser, the resistance keeps steady 

 until the melting is complete ; after which the resistance 

 again diminishes steadily. So far as I am able to discover 

 there is no " electrification " while the wax is in the melted 

 condition. 



The spark-resisting power of the melted wax is at least 

 one third that of the solid. The melted wax in this particular 

 condenser broke down under 1200 steady volts: the insulation 

 heals, as in the case of oil, to break down again in a few 

 seconds. 



Cooling. — A converse process occurs during cooling ; and 

 as the cooling is more uniform than the heating the effects 

 can be more easily noted. The resistance of the melted wax 

 gradually increases until the first crystals appear, at which 

 stage it remains more or less constant until the process is 

 nearly complete, when it very rapidly increases to about 

 three times the value it had during the partial crystallization; 

 it then behaves as solid wax. 



Appendix I. 



When an extra wire (fig. 1) is added from the -testing- 

 battery to some point near the middle of the cleaned end of 

 the lead, intercepting the path of leakage (a) at that end, the 

 circuits can be represented by fig. 2. The (a) leakage is 



