348 Prof. J. J. Thomson on the 



Potassium Iodide. 



Strength of Solution. Deflexion. 



Water 390+ 



•04 gramme of KI in 100 o.c. of H 2 70- 



•12 „ „ „ „ 100- 



°32 „ „ „ ,, 110 



A similar reversal to that shown by chromium trioxide. 



Potassium Permanganate. 



Strength of Solution. Deflexion. 



Water .... 230 + 



•025 gramme of permanganate in 100 c. c. of H 2 ... 145 — 



Thus the addition of potassium permanganate produces a 

 reversal of the electrification. 



Though the addition of mineral salts and acids produces a 

 very decided effect on the electrification, this effect is not 

 nearly so large as that produced by very dilute solutions of 

 organic compounds. We have seen an instance of this already 

 in the case of phenol, which produced an enormous increase 

 in the electrification of the drops. An equally remarkable 

 effect is produced by methyl violet, but in this case the elec- 

 trification of the drop is reversed : the merest trace of methyl 

 violet is sufficient to reverse the electrification, and in fact a 

 weak solution is much more effective than a strong one, a 

 very strong solution being almost neutral. The effect of 

 methyl violet is so great that when a funnel has been used 

 for this substance, many litres of water have to be run through 

 it before distilled water when running through it gives the 

 normal effect. The following measurements show the large 

 effects produced by small quantities of methyl violet : the 

 standard solution mentioned below was distinctly, though not 

 deeply, coloured. 



Methyl Violet. 

 Strength of Solution. Deflexion. 



Water 350+ 



2 drops of standard solution in 100 c. c. of H 2 ... 450— 

 •2 c. c. „ „ „ „ „ ... 370 — 



'■* J5 >} }> >> >> >5 ••• OiV) 



l'O ,, ,, „ ,, ,, „ ... 2o0 — 



10-0 „ „ „ „ „ „ ... 210- 



40-0 „ „ „ „ „ „ ... 100- 



E-osaniline also produces an effect of the same character as 

 methyl violet, though not quite to the same extent : thus, when 

 the distilled water gave a deflexion 200 + , a weak solution 

 of rosaniline gave a deflexion 370— ; stronger solutions 



