Experiments on various Liquids. 165 



afterwards with the Ruhmkorff 's coil. Formic acid is there- 

 fore purely negative, but a very weak insulator. It gives no 

 good effect at temperatures very near the freezing-point ; and 

 the same remark applies to acetic acid. 



7. Two of the so-called solid acids of the same series were 

 examined in the fusion-cell, and were found to be negative. 



Palmitic acid (n=16^, a transparent oil at or above 62° C, 

 acted well as a nonconductor. One turn of the plate gave an 

 intense restoration, whose purely negative character was very 

 little disturbed by movements in the liquid. When the tem- 

 perature was little above the point of fusion, and carefully 

 regulated, the initial extinction was very good without the 

 neutralizing plate, and there was no trace of disturbance by 

 currents. One eighth of a turn gave then a good effect which 

 was purely negative, strengthened by compression parallel to 

 lines of force, and extinguished by tension. 



Stearic acid (w = 18), a transparent oil at or above 70° C, 

 acted on the whole as well as the last, though there was rather 

 more disturbance by currents. One turn of the plate gave 

 always a strong effect which was purely negative, conspirino- 

 with compression parallel to lines of force, and neutralizing 

 tension. 



These results were very unexpected. I therefore tested 

 them at some length, working with new samples of the acids, 

 the purest that could be obtained, and comparing them suc- 

 cessively with paraffin and the fats. The facts never varied : 

 the two fused acids were always distinctly and purely negative. 



Other Alcohols and Acids. 



8. Allyl alcohol, C 3 H 5 HO, is distinctly though not quite 

 purely negative, and a good deal stronger than ethyl alcohol. 

 With good charges of the jar it gave a clear effect, which was 

 strengthened by compression parallel to lines of force, and 

 weakened almost to extinction by tension. There was always 

 some disturbance produced, partly by a feeble photogyric 

 action of the liquid, and partly by a special effect of electric 

 discharge. The flame was not simply restored in the polari- 

 scope by discharge, but was deformed as by an undulatory 

 movement in the liquid, and rendered also fibrous or thready 

 in appearance. This effect was probably due to heat ; for it 

 came out much more strongly afterwards with the Ruhmkorff ' s 

 coil, in which case three separate discharges were sufficient 

 to mask the electro-optic action completely by a permanent 

 heat-effect. 



Benzyl alcohol, C r H 7 HO, is purely negative. Tried in the 

 plate cell as a conductor, it gave a faint but good restoration 



