ASPECTS OF ADSORPTION PHENOMENA 213 



rose was less in the case of calcium and barium than in that of 

 potassium or strontium, the calcium, etc., being more completely 

 held by the paper. In the case of a solution of iodine in KI, while the 

 latter rose nearly as far as water, the iodine was kept back in the 

 lower third. These facts were explained by Schonbein as capillary 

 attraction, but, as Ostwald remarks, there is no doubt that it is 

 really an adsorption process that causes the separation of the bodies in 

 question, capillarity only occasions the transport of the separated 

 fractions. 



These results of Schonbein have been extended and employed as 

 a means of analysis by Goppelsroeder. 1 



It is well known to histologists how certain tissues take up 

 particular dyes in preference to others. In certain cases, as for 

 example, the differences between paper and silk, as to their respective 

 behaviour towards congo-red and methylene blue, this is probably to 

 be accounted for by the fact of the electrical charge in the two dyes 

 being opposite in sign combined with the negative charge of the 

 substance to be stained, as already pointed out. 



Acid fuchsin is used in Van Gieson's stain to show connective- 

 tissue. In view of this, I thought it of interest to try the behaviour 

 of gelatin in sheet towards this dye and toluidin blue respectively. 

 The same amount of gelatin was found to take up 72 per cent, 

 of the acid-fushin and only 32 per cent, of the blue. It is possible 

 here that the electrolytes of the gelatin were responsible for the 

 difference, since they would increase the -adsorption of the acid dye 

 and diminish that of the basic dye. This possibility is excluded when 

 we compare the amounts of congo-red and acid fuchsin, both electro- 

 negative dyes, taken up by gelatin or filter-paper. The following are 

 the results of an experiment: 



Equimolecular concentrations of dye. 

 Equal weights of gelatin and filter-paper. 



Filter-paper from Congo-red ... 3 1 % 



,, ,, acid-fuchsin ... 32 % 



Gelatin Congo-red ... 49 % 



,, acid-fuchsin ... 95 % 



I. Mitt. d. teckn. Ge-wcrbe Museums, Wien, 1899, and Studien uber die Ani-uendung d. Capillar 

 analyse, Basel, 190^.. 



