250 3Ir Purvis, The influence of dilution on the colour 



4 and 5 were wider than those in the 5 solution. The general 

 absorption was more marked in the 154 sokition than in the 



5 solution. The 154 solution of barium permanganate showed 

 that the bands 1, 2 and 3 had also become narrower, and the 

 bands 4 and 5 were wider; but the general absorption had not 

 altered much from the previous observation. The 310 solution 

 of barium permanganate was of a light brownish yellow colour 

 and perfectly clear. The 5 solution showed the five bands well 

 marked ; and the 310 solution showed that the bands 1, 2 and 3 

 had almost disappeared, whilst the bands 4 and 5 had quite 

 disappeared and just beyond these there was complete general 

 absorption. 



The colour of the 154 solution of potassium permanganate 

 was brown, and the solution was quite clear. The bands 1, 2 and 

 3 were much narrower than the corresponding bands in the 

 5 solution, whilst the bands 4 and 5 were a shade wider, and 

 just beyond band 5 there was complete general absorption ; 

 whereas there was little or no difference in the colour or the 

 general absorption in the 5 solution. In the 310 solution of 

 potassium permanganate the bands 1, 2 and 3 were only just 

 visible ; bands 4 and 5 had completely disappeared, and there was 

 complete general absorption just beyond; whilst in the 5 solution 

 the bands were just as before, and there was no apparent change 

 in the general absorption. 



The general results of the above observations indicate a 

 development of considerable differences in the more diluted 

 solutions both as regards colour and absorption bands. The 

 usual explanation is that light vibrations are the cause of such 

 changes. In order to test this, similar solutions of the perman- 

 ganates were made in the dark, and they stood covered up in 

 a dark cupboard so that no light could enter. The solutions were 

 examined after two days ; and the following notes describe the 

 observations. 



II. 



Solutions of permanganates of barium and potassium made in 

 the dark and allowed to stand for two days well covered up and 

 placed in a dark cupboard and then examined. 



The colours of the 154 solutions had changed from the well 

 known permanganate tint to a pinkish colour ; and the colours of 

 the 310 solutions had become a rose colour with a tinge of brown. 

 The strong 5 solution did not appear to have changed. The 

 absorption spectra of these solutions were also examined. 



D. Barium permanganate | ^^^ .^lutions. 

 rotassmm do. J 



do. do. 5 solutions. 



