33 o SCIENCE PROGRESS 



nature of the fibre, but considerable support would be given to 

 the adsorption theory of dyeing if it could be shown that dye 

 solutions actually do lower the tension at the interface between 

 the solution and an inert liquid. This liquid must of course be 

 such that it excludes both chemical combination and solution. 

 For this purpose a hydrocarbon oil was used as the substance 

 to be dyed, and aqueous solutions of various concentrations of 

 Congo-red and methyl-orange were prepared. In each case it 

 was found that the interfacial tension was lowered, and that 

 the lowering was proportional to the concentration up to about 

 o'i per cent, solutions, at which point the tension remained 

 practically constant. On applying the equation it was found 

 to hold not in its theoretical form but with the anomaly it 

 shows in cases of ordinary " adsorption." This seems to show 

 that substantive dyeing must be more or less an adsorptive 

 process. In all probability the actual mechanism of dyeing 

 consists first in adsorption and afterwards fixation brought 

 about probably by " colloidal precipitation." In some cases 

 there may even be some degree of chemical combination which 

 varies with the nature of the dye, but whatever the nature of 

 this fixation, it is in a high degree probable that the first step in 

 the process of dyeing is an adsorption of dyestuff by the fibre 

 in accordance with Gibbs's theory of surface concentration. 



