3 i2 SCIENCE "PROGRESS 



the fibre with water, and which then acts as a mordant, being 

 itself contained in the wool fibre in a state of solid solution. 



/ 'ig/ion next worked on the problem and found that by 

 introducing an amino-group into the cellulose molecule by 

 treating with strong ammonia at a high temperature, and under 

 a high pressure, the fibre readily took up acid dyes. This result 

 is interesting, and although it is only what might have been 

 expected, it shows that the chemical theory may possibly apply 

 to the dyeing of silk or wool, as both of these fibres contain 

 nitrogen. Such a theory, however, could hardly apply to the 

 dyeing of cotton, since cellulose contains no nitrogen. 



This chemical theory of dyeing received its most precise ex- 

 pression in the hands of Weber about 1894. Wool has the greatest 

 affinity for colouring matters of all kinds, and is capable of 

 decomposing the basic dyes into free acid and colour base ; the 

 latter then combining with the wool. It is also capable of 

 combining with the colour-acids of sulphonated dyes. In all 

 these cases the wool is dyed in shades identical with those of 

 the salts, or rather the " lakes," of these dyes. This double 

 function of the wool was shown by Knecht to be due to the 

 amino-acidic nature of the wool fibre, or to the lanuginic acid 

 contained in it. The process of dyeing can thus be expressed 

 in the form of an equation, e.g. : 



/NH 2 naphthol /NH 3 . O . S0 2 .C 6 H 4 . N = N.C 10 H 6 . OH 



x COOH orange XX)OH j 



/ 



NH 



a 



or with 

 magenta \C0.0- NH, = C.H. 



/C 6 H 4 . NH 2 



\: g h 4 . NH 2 



If this is so, then in the first example there is still a free 

 COOH group, and this ought to be able to combine with a basic 

 colouring matter in the same manner and degree as the undyed 

 wool. This is actually found to be the case. A skein of wool 

 dyed with " scarlet R " was washed and immersed in a bath of 

 magenta. At the same time a white skein of the same weight 

 was immersed in an exactly similar bath of magenta of the same 

 strength. It was found that both skeins absorbed the same 

 quantity of magenta. It may be urged against this that solutions 

 of all acid colouring matters precipitate solutions of all basic 

 colouring matters forming " lakes," which may therefore be 



