[ 191 ] 



XXVII. On the power of conducting Electricity assumed by Insu- 

 lators at High Temperatures. By W. Beetz*. 



THE accounts given by several physicists concerning the 

 property which many substances possess of passing from 

 the condition of insulators to that of conductors,, by increase of 

 temperature, have reference to bodies so heterogeneous that it 

 appears almost impossible to reduce the phsenomena to one cause. 

 Davy's experiments f prove that the conducting power of metallic 

 conductors is decreased by heating them ; whilst, according to 

 Ohm's observations t, a decrease of resistance takes place in 

 electrolytic conductors under similar circumstances. Hence the 

 passage of a body by means of heat from the condition of a 

 non-conductor, i. e. of a very bad conductor, to that of a con- 

 ductor, or better conductor, can be very well explained if the 

 body be a compound one, but not at all if it be an elementary 

 one. In the following pages I have described the experiments 

 by means of which I hope to have secured a common point of 

 view for all these several statements. 



Of the elementary bodies which are liquid at the usual tem- 

 peratures, the one, quicksilver, deports itself in every respect as 

 a conductor of the first class, and hence, as shown by E. Bec- 

 querel's§ measurements, its conducting power is decreased by 

 heating. The other, bromine, according to Balard's experi- 

 ments ||, is a non-conductor of galvanic electricity; a stratum 

 from 3 to 4 lines thick, when introduced into the circuit of a 

 battery, caused every perceptible action in a decomposition ap- 

 paratus to cease. De la Rive^ obtained the same result, and 

 mentions at the same time that, according to a verbal communi- 

 cation of Faraday's, liquid chlorine is a non-conductor, and is 

 not acted upon by a battery. Solly** found that bromine did 

 not conduct, but was at first of opinion that chlorine was a con- 

 ductor ; after carefully washing the tube in which it was con- 

 tained, however, he found it to be a perfect non-conductor. 

 When sufficiently well freed from admixed water, I have also 

 found bromine to be a perfect non-conductor of galvanic elec- 

 tricity. Those elements which are made liquid by fusion are 

 generally metallic in the solid state, and consequently lose con- 

 ducting power when heated. Of the non-metallic bodies, 



* Communicated to the Academy of Sciences, Berlin, June 13, 1854. 



t Phil. Trans. 1821, p. 431. 



+ Pogg. Ann. vol. Ixiii. p. 403. 



§ Ann. de Chim. et de Phys. 3 ser. vol. xvii. p. 234. 



II Ibid. vol. xxxii. p. 345 ; Pogg. Ann. vol. viii. p. 123. 



IF Ann. de Chim. et de P%s.vol.xxxv.p.l60j Pogg.^WTi.vol.x. p. 307. 



** Phil. Mag. S. 3. vol. viii. p. 130; Pogg. Ann. vol. xxxvii. p. 420. 



