DYEING. 245 



with, inasmuch as vegetable fabrics (such as cotton, linen, hemp, 

 and jute fibres, &c., and goods woven from them) are incapable of 

 so doing (except in the case of a comparatively small number of 

 dyestuffs, mostly artificial), and hence can only be permanently 

 dyed by other processes involving the use of a " mordant " or 

 substance acting as a kind of cement, fixing the colouring matter 

 firmly to the vegetable fibre (Expt. 291). 



Get a skein of white Berlin wool and wind part of it on a piece 

 of card about 6 or 8 inches long, so as to make a small hank of 

 some 10 or 12 turns ; tie the ends firmly with a small piece of 

 the same material to prevent the hank coming unwound, and 

 then immerse it in water tinted with a sufficient quantity of 

 the dyestuff employed ; these dyestuffs are now sold in small 

 quantities at a very cheap rate almost everywhere for general 

 household use. Instead of purchasing these artificial colours, 

 cochineal solution (such as is often used for tinting jellies and 

 sweetmeats) may be used; or the prepared indigo solution 

 described in Expt. 151. Stir the wool about in the dyeing liquid 

 with a glass rod or a stick, for some time ; it will gradually take 

 up the colouring matter and become dyed permanently. If too 

 much dye have not been added to the water in proportion to the 

 weight of the wool it will often happen that the wool will take 

 up almost the whole of the colouring matter, leaving the water 

 colourless or nearly so. By using different quantities of dyestuff 

 in different experiments (say 2 drops in one case, 4 in another, 8 

 in a third, 12 in a fourth, and so on), you will be able to dye 

 different hanks (all of about the same weight) various shades of 

 the same colour, and thus get a gradation of shaded wools vary- 

 ing in tint from a very light shade just perceptible up to the 

 deepest tones possible. 



Expt. 291. To dye Vegetable Cloths (Cotton, Linen, &c.). 

 In order that dyestuffs may adhere firmly to vegetable textile 

 fabrics, so as not to be removed by washing, it is in most cases 

 necessary to prepare the calico, &c., to be dyed by treating it with 

 certain materials termed mordants, which have the power of ad- 

 hering themselves firmly to the vegetable fibre, and also of causing 

 the colouring matter to adhere to, or combine with, themselves ; so 

 that mordants act somewhat as a cement, uniting together two things 

 that otherwise would not remain permanently associated together. 



The mordants most frequently employed are certain metallic 

 compounds, more especially those containing iron, aluminium, and 

 tin ; solutions of certain compounds of these metals are thickened 

 with gum or dextrin (converted starch, or British gum), and the 

 fluid thus obtained printed on to the goods to be dyed by means 



