318 SCIENCE PROGRESS 



so finely divided in the fabric that it now exhibits its proper 

 colours. 



Again, fluorescence is not restricted to solutions for many 

 solids, e.g. fluorspar and barium-platino-cyanide show this 

 property to a marked de'gree. Silk dyed with fluorescein 

 fluoresces, wool does not ; therefore, according to Witt's theory, 

 the dye-stuff exists in the former in solution, in the latter in the 

 free state. Silk, the surface of which has been injured by 

 mechanical treatment, no longer exhibits fluorescence when 

 dyed with these colouring matters ; and jute, finely bleached 

 before weaving, and fine Angora wool, exhibit fluorescence 

 when dyed with fluorescein, but on weaving lose this property. 

 The appearance of fluorescence on a dyed fabric is dependent 

 therefore, not on the state of aggregation of the colouring 

 matter, but on the condition of the surface or lustre of the 

 textile material. 



Again, if dyeing is a case of solution it should be a reversible 

 process, i.e. on treatment with water a dyed material should 

 give up its colour, which with many dye-stuffs is well known 

 not to be the case. Thus wool takes up the colour best at 

 ioo° C, and does not absorb it in the cold, i.e. according to Witt 

 the colour is more soluble in wool at ioo°C. than it is in water. 

 Consequently wool dyed at ioo°C. should give up its colour to 

 water at the ordinary temperature, which is contrary to all 

 experience. 



Georgevics favoured a mechanical view of the process, and 

 maintained that Vignon's experiments, although compatible with 

 a chemical explanation of the process of dyeing, did not prove 

 it, since many physical phenomena, such as capillarity and 

 surface tension, are influenced by the chemical character of the 

 active substance. The chemical theory must therefore be re- 

 jected until stoichiometrical relationships are definitely shown 

 to exist between the various factors of the dyeing process. 



Perhaps the strongest evidence against both the chemical 

 and more particularly the solid solution theory is that afforded 

 by an investigation of the partition co-efficients of various dyes 

 between water and the fibre employed. In the case of a solution, 

 when the molecular complexity of the solute is the same in both 

 solvents, the solute so distributes itself between them that at 

 any given temperature there is a definite ratio between the 

 concentrations of the two solutions when equilibrium is attained, 



