r 272 ] 



XXXV. On the Determination of J'emperature-'Coeffi.cients for 

 Insulating Envelopes. By Thomas T. P. Bruce Warren, 

 Analytical Chemist to the India-rubbery Gutta-percha^ and 

 Telegraph-Worhs Company, Limited^. 



AT the Exeter Meeting of the British Association I read a 

 paper on Electrificationt; in which I endeavoured to 

 show that the rate of variation in the insulation resistance of 

 a core or cable under changes of temperature could be deter- 

 mined for any period of contact. 



A statement was made in that paper which has led to the 

 belief that india-rubber has the same constant for correcting 

 from one temperature to another and for any period of con- 

 tact. Professor Fleeming Jenkin, Mr. Latimer Clark, and 

 others have pointed out that this phenomenon is not met with 

 in gutta percha or any other insulator with which they are 

 acquainted. This has led me to reexamine the matter, and to 

 consider carefully the experimental data upon which the paper 

 w^as founded. 



The method of representing graphically the decrease of 

 resistance due to increase of temperature corresponding to one 

 minute's electrification can be followed out for two, three, or 

 any number of minutes. In this way a series of logarithmic 

 curves are obtained for any required duration of contact. These 

 curves are generated by a constant which must first be ascer- 

 tained by experiment for changes of temperature at the end 

 of one, two, three, &c. minutes. This was omitted in the pre- 

 vious paper, or at least not dealt with as fully as the importance 

 of the subject required. 



The phenomenon of electrification, from what has just been 

 pointed out, must appear to every electrician to have received 

 additional importance, and no longer to be regarded as an unin- 

 telligible or inapplicable fact. One very important consequence 

 of its being reducible to an intelligible variation is, that we 

 can now calculate not only the changes in the resistance of an 

 insulator due to variation of temperature, but we can ascertain 

 with the same precision any required change due to prolonged 

 contact at any required temperature. 



The resistances at different temperatures under different 

 durations of contact will, when tabulated, represent a series of 

 logarithms, the base of each system being the ratio between 



■^- Communicated b;r the Aiitlior, liaving- been read in Section A of the 

 British Association at Plymouth, August 1877. 



t This paper was reprinted in this Mag-azine, Decein1)er 1809. 



