428 



Mr. J. Buchanan. 



[May 27, 



methylated spirit was used to give the apparatus a thorough cleansing 

 from all traces of oil, &c. 



As a valuable test of the proper working of the apparatus, oil of 

 turpentine was constantly in use. If everything was going well, the 

 effect of adding a small quantity of the oil to the distilled water in 

 the feeder-tube was to make the boiler positive, and the steam nega- 

 tive. On continuing to blow out, the boiler quickly passed on to 

 negative. 



This was repeated as a rule between the testing of each pair of sub- 

 stances. 



It will be observed in the list given below that there are three 

 persistent apparent exceptions to the rule that holds for all the other 

 substances tried ; these are turpentine, sperm oil, and chloroform. 



The extremely uncertain composition of the first and second of 

 these three bodies did not allow their exceptional behaviour to 

 assume much importance in my eyes. But that chloroform should 

 remain an exception to the rule appears to indicate that either the 

 influence of the water masks that of the chloroform (vide remarks by 

 Faraday on Alcohol, "Exper. Res." §2115, 2116), or that there has 

 been a change of sign in the electro- optical position of the body due 

 to rise of temperature. These points, together with some others 

 that have been raised in my mind in connexion with the present 

 application of the theorem of Part I, I hope to be able to clear up 

 by experiments in a different direction from those recorded here. It 

 may be desirable to state also, that I began experiments in which dry 

 compressed air was used instead of steam, but was not able to con- 

 tinue them. 



In conclusion 1 desire to record my thanks to Prof. Foster, for the 

 valuable criticisms with which he has favoured me during the pre- 

 paration of this paper. 



Note. — In the experimental results which follow, the sign of the 

 electrification is that assumed by the body to whose name it stands 

 opposite when rubbed on the material whose name is at the top of 

 the column. 



