168 DYEING 



produce chemical combination, or to get the dye or colour in such a minute state of 

 division as it will penetrate or enter into the fibre of the stuff. These preparations 

 embrace the formation of decoctions, extracts, and solutions, and also in some cases of 

 precipitation, previous to immersing the stuff into the bath. Stuffs, chemically 

 considered, have but a feeble attraction for other matters, so as to combine with them 

 chemically ; still that they do possess certain attractions is evident from various 

 phenomena observed in the dyeing processes, and that this attraction is possessed 

 with different degrees of intensity by the different fibres, is also evident from the ease 

 and permanence that woollen stuff will take up and retain dyes compared with 

 cotton ; and also, that certain dyes are retained and fixed within or upon one kind of 

 fibre and not at all in another. This may be determined by plunging the dry stuff 

 into solutions of the salts, and determining the density of the solution before the 

 immersion and after withdrawing the stuff. Wool abstracts alum from its solution, 

 but it gives it all out again to boiling water. The sulphates of iron, copper, and 

 zinc resemble alum in this respect. Silk steeped for some time in a solution of 

 protosulphate of iron, abstracts the oxide, and gets thereby dyed, and leaves the 

 solution acidulous. Cotton in nitrate of iron produces the same effect. Wool put in 

 contact with cream of tartar, decomposes a portion of it ; it absorbs the acid within its 

 pores, and leaves a neutral salt in solution in the liquor. Cotton produces no such 

 effect with tartar, showing by these different effects that there are certain attractions 

 between the stuff and dyes. This attraction, however, may be more what is termed 

 a catalytic influence, the fibres of the stuff producing a chemical action with the salt 

 or dye, with which it is in contact. This attraction or affinity of the fibre for the 

 dye-drug, does not produce a very extensive effect in the processes of dyeing. More 

 probably the power of imbibing and retaining colours possessed by the fibre is more 

 dependent upon a mechanical than a chemical influence. 



All dye-drugs must in the first instance be brought into a state of solution, in order 

 that the dye may be imbibed by the fibre ; but if the fibre exerts no attraction for the 

 colour so as to retain it, it is evident that so long as it remains capable of dissolving 

 in water, the stuffs being brought into contact with water, will soon lose their colour. 

 A colour thus formed does not constitute a dye, however strongly stained the stuffs 

 may appear to be, in or out of the dyeing solution ; in order to form a dye, the colour 

 must be fixed upon or within the stuff, in a condition insoluble in water. Hence 

 the mere immersion of the stuff into a solution of a colour will not constitute a dye, 

 except where the stuff really has an attraction for the colour and retains it, or causes 

 a decomposition by which an insoluble compound is fixed upon it, such as is referred to 

 by putting stuffs into solutions of iron. The abstraction of the colour from a solution 

 by the immersion of the stuff, is often the result of a mechanical attraction possessed 

 by porous substances, enabling them to absorb or imbibe certain colouring matters 

 from solutions that are held by a weak attraction by their solvents. On this principle, 

 a decoction of cochineal, logwood, brazil-wood, or a solution of sulphate of indigo, 

 by digestion with powdered bone-black, lose their colour, in consequence of the 

 colouring particles combining by a kind of capillary attraction with the porous carbon, 

 without undergoing any change. The same thing happens when well-scoured wool 

 is steeped in such coloured liquids ; and the colour which the wool assumes by its 

 attraction for the dye, is, with regard to most of the above coloured solutions, but 

 feeble and fugitive, since the dye may be again abstracted by copious washing with 

 simple water, whose attractive force therefore overcomes that of the wool. The aid 

 of a high temperature, indeed, is requisite for the abstraction of the colour from the 

 wool and the bone-black, probably by enlarging the size of the pores, and increasing 

 the solvent power of the water. 



Those dyes, whose colouring matter is of the nature of extractive, form a faster 

 combination with stuffs. Thus the yellow, fawn, and brown dyes, which contain 

 tannin and extractive, become oxygenated by contact of air, and insoluble in 

 by which means they can impart a durable dye. When wool is impregnated with 

 decoctions of that kind, its pores get charged by capillarity, and when the liquid 

 becomes oxygenated, they remain filled with a colour now become insoluble in water. 

 The fixation of iron oxide and several other bases also depends on the same change 

 within the pores or fibre ; hence all salts that have a tendency to pass readily into the 

 basic state are peculiarly adapted to act as a medium for fixing dyes ; however, this 

 property is not essential. 



In order to impart to the stuffs the power of fixing the colour in an insoluble form 

 upon it, recourse is had to other substances, which will combine with the soluble and 

 form with it an insoluble colour ; and it is not necessary that this new substance 

 should have an attraction for the stuff, or bo capable of passing into a basic form, any 

 more than the original colour, but it is necessary that it be rendered insoluble whilo 

 in contact with the stuff. 



