and the absorption spectra of various permanganates. 255 



with an almost complete obliteration of the absorption bands and 

 a greatly increased general absorption ; (4) a shift of the bands 

 of the 5 solutions to the red end of the spectrum as compared 

 with their positions in the 154 and -310 solutions, and this 

 shift appeared to decrease with increased refrangibility of the 

 absorbed rays. 



In order to explain the different positions of the bands of the 

 different solutions, the observations of H,, Becquerel* show that 

 such differences depend upon the concentration — the greater the 

 concentration, the greater the shift of the bands towards the red 

 end of the spectrum. 



With regard to the other changes, attention is again called to 

 the observations that the changes take place whether the solutions 

 are subjected to the action of light or whether they are kept io the 

 dark, although light accelerates the changes. One explanation 

 is that the dissolved gases, the atmospheric gases, particularly 

 carbon dioxide, may have been the influencing causes. Against 

 this view is the fact that carbon dioxide usually converts man- 

 ganates to permanganates very rapidly; and oxygen would scarcely 

 act as a reducing influence, whilst nitrogen is completely inert. 

 Nor could the changes have been caused by any dissolved organic 

 substances, for the solutions were made in distilled water, and 

 from pure crystallised salts ; and also, all the glass vessels were 

 well washed before use with a warm mixture of hydrochloric and 

 nitric acids. Nor could any organic substances have entered the 

 solutions, for the latter were always kept well covered up. Never- 

 theless, in order to eliminate the action of any extraneous gases or 

 dirt, another series of solutions of potassium permanganate was 

 made, and the glass bottles were filled to overflowing. The contents 

 were isolated from the air by well ground stoppers. The bottles 

 of one series were filled in the dark, and they stood in cupboards 

 to which no light could penetrate. A similar series of bottles 

 stood in a well lighted room and they were exposed to the full 

 action of light. The changes in the colour of the solutions were 

 exactly the same as in the earlier observations ; but those of the 

 solutions exposed to the action of light were much quicker. Besides 

 the colour changes, a small bubble of gas collected in the bottles. 

 The absorption spectra were not observed. 



The explanation which seems to account for the changes 

 is that the dissociating force of the water slowly acted upon the 



dissolved permanganates, so that the ionic condition of K, and 



+ 

 Mn04, where R represents the metallic ion, broke down. One 



may imagine that the Mn04 ioii undergoes further dissociation 



* Gompt. Rend. Vol. cii. p. 106. 



