THEORIES OF DYEING 317 



theory, but he noticed that exactly the same quantitative results 

 were obtained if, instead of dyeing fibres, he used broken porous 

 porcelain or glass beads, or even glass beakers, i.e. the colour 

 base was taken up and the HC1 left behind in the bath. The 

 chemical theory cannot hold here, and he therefore rejected 

 Knecht's explanation of the process and sought for another. 

 Obviously two alternatives present themselves, either the dye 

 is dissociated by the material of the glass or porcelain (which 

 is not likely since these two substances are chemically inert), 

 or else the dye is hydrolysed before it comes in contact with 

 the glass, i.e. magenta, methyl-violet, and chrysoidine are hydro- 

 lysed in aqueous solution. In support of this v. Georgevics 

 dipped one end of a tube containing a roll of filter paper in 

 a solution of magenta and allowed it to stand for some time ; 

 then the amounts of colouring matter and of HC1 in the paper 

 above the surface of the liquid were estimated. If hydrolysis 

 had occurred the two constituents would rise according to 

 their velocities of diffusion. As a matter of fact, the mole- 

 cular proportion of chlorine found was twenty times that ol 

 the magenta. He suggested therefore that on dissolving in 

 water the dye-stuff is hydrolysed, and if a substance for 

 which the colour base has an adhesive attraction be brought 

 into this solution, the base is taken up and a dyed body is 

 obtained. 



V. Georgevics next examined Witt's solution theory, and came 

 to the conclusion that, when all the properties of the dyed fabric 

 are taken into account, this theory is quite inadequate to explain 

 the facts, since not only the substance but the structure of the 

 fibre plays an important part in the process. Thus he found that 

 if magenta be powdered and mixed with chalk or other white 

 substance, the original green colour changes at once to red. 

 Similarly magenta or methyl-violet, when rubbed between 

 ground-glass plates, exhibits no longer the green colour char- 

 acteristic of the crystals, but are now red and violet respectively. 

 The colour of magenta and other crystals is not the colour of 

 the solid substance, but is due to abnormal dispersion of the 

 light at their surface ; such dispersion only taking place with 

 relatively thick layers. Also, if wool is dyed with a very 

 concentrated solution of magenta, the fabric shows the same 

 surface colours as the crystals — an effect known to dyers as 

 " bronzing " ; when dyed in the ordinary way the magenta is 



