Experiments on various Liquids. 159 



stroyed. Although I never recovered any thing like the very 

 strong and fine effects which I have described, I have no 

 doubt that fused sulphur is purely and strongly positive. 



Hydrocarbons. 



4. Those of the hydrocarbons that I have examined up to 

 this time, the nine or ten mentioned in my former paper, and 

 the eight which here follow*, are all nonconductors, electro- 

 optically active, and purely positive. 



Amy I hydride, C 5 H^, is interesting as one of the lightest 

 of known liquids. Tested for insulation in the plate cell, it 

 gave a spark hardly \ inch long. Tried optically as a non- 

 conductor, it gave a sure but extremely faint restoration from 

 pure extinction. "When the hand-compensator was introduced 

 beforehand, and strained steadily, the effect of electric force 

 was brought out more strongly, and with great purity — an 

 increase of light in the case of tension parallel to lines of force, 

 and a decrease to extinction in the case of compression. There 

 was no increase of effect when the liquid was tried as a con- 

 ductor, with or without the Leyden jar. 



Hexyl hydride, or trityl, C 6 H u . For a specimen of this 

 liquid, prepared from petroleum-oil, I am indebted to the 

 kindness of Dr. Gladstone. It was examined immediately 

 after amyl hydride, for the purpose of comparison. Of the 

 two, the hexyl compound appeared to be somewhat stronger 

 both in insulating and in electro-optic power. Both bodies 

 exert very faint but perfectly pure actions as positive non- 

 conductors. 



Cinnamol, C 3 H 8; tried in the plate cell as a nonconductor, 

 gave an intense and purely positive effect. The action was 

 strong enough to give definite and very black extinction- 

 bands, like those in my old experiments with CS 2 and the 

 stronger hydrocarbons. 



Caprylene, C 8 H 16 , acts in the plate cell as a positive non- 

 conductor. Most of the plates of this liquid were somewhat 

 dirty, and easily traversed by spark discharge ; but the effect 

 was always manifest, and always purely positive. In the 

 cleaner plates the action was very fine, and apparently a good 

 deal stronger than that formerly observed in the lighter olefme, 

 amylene. 



Caoutchoucin, or empyreumatic oil of caoutchouc. — My 

 specimen of this liquid was of a deep red colour, and a mode- 

 rately good insulator ; so that it could be tried in the plate cell 



* All of them pure hydrocarbons, except caoutchoucin and oil of resin, 

 which contain a little oxygen. 



