246 DYEING 



I color, and loses this when washed. When silk and linen are 

 tested, it is found that the former behaves in a general way 

 as did wool, while the linen has more similarity to the cotton. 

 That vegetable fibers, such as cotton and linen, should act 

 differently toward coloring matter from animal fibers, such as 

 silk and wool, is not surprising when we consider that the 

 chemical nature of the two groups is very different ; vegetable 

 fibers contain only oxygen, carbon, and hydrogen, while ani- 

 mal fibers always contain nitrogen in addition, and in many 

 cases sulphur as well. 



227. The Selection of Dyes. When silk and wool, cotton and 

 linen, are tested in various dye solutions, it is found that the 

 former have, in general, a great affinity for coloring matter 

 and acquire a permanent color, but that cotton and linen, on 

 the other hand, have little affinity for dyestuffs. The color 

 acquired by vegetable fibers is, therefore, usually faint. 



There are, of course, many exceptions to the general state- 

 ment that animal fibers dye readily and vegetable fibers poorly, 

 because certain dyes fail utterly with woolen and silk material 

 and yet are fairly satisfactory when applied to cotton and 

 linen fabrics. Then, too, a dye which will color silk may not 

 have any effect on woo] in spite of the fact that wool, like 

 silk, is an animal fiber ; and certain dyestuffs to which cotton 

 responds most beautifully are absolutely without effect on 

 linen. 



The nature of the material to be dyed determines the color- 

 ing matter to be used; in dyeing establishments a careful ex- 

 amination is made of all textiles received for dyeing, and the 

 particular dyestuffs are then applied which long experience 

 has shown to be best suited to the material in question. 

 Where " mixed goods," such as silk and wool, or cotton and 

 wool, are concerned, the problem is a difficult one, and the 

 countless varieties of gorgeously colored mixed materials give 



