ASPECTS OF ADSORPTION PHENOMENA 207 



inhibitory effect of the anion in the case of electro-negative dyes and 

 silk, whereas we see that the action of Mj;so 4 is rather greater in the 

 case of silk than in that of paper. 



The troublesome stain which appears on the surface of glass 

 containing electro-positive dyes is no doubt due to the negative charge 

 of the glass. This film is so adherent that water will not remove it, 

 and I have found it necessary, when working with these dyes, to rinse 

 all flasks used with concentrated nitric acid, in order to obtain con- 

 cordant results. 



Another fact receives its explanation from the negative charge of 

 paper, viz., that from alcohol more negative dye is taken up than 

 from water, in one experiment : 



From 50 % alcohol - 65 % taken up 

 water ~ 53 % 



Since alcohol has a lower dielectric-constant than water it would 

 naturally be expected, since the negative charge of paper is due to the 

 difference between its dielectric-constant and that of the fluid in which 

 it is immersed, that the negative charge would be greater the greater 

 this difference is, and therefore in alcohol the charge would be less 

 than in water and the attachment of a negative dye less difficult. On 

 the other hand, less + dye is taken up in the presence of alcohol, 



thus : 



From 50 % alcohol 5 % taken up 



water - 80 % 



Finally, I may refer to the action of acid in preventing the 

 favouring action of electrolytes on adsorption of a negative dye, for 



example : 



CONGO- RED 



From water 17 % adsorbed 



75% 



+ ~ H ' so < - 3i % ,, 



2000 



This result is probably to be explained by the fact that in the 

 presence of sulphuric acid the colour-acid is set free from congo- 

 red. This colour-acid is, no doubt, more strongly electro-negative 



