DYEING. 



attraction by this means, they are also 

 caused to apply themselves more equally, 

 as every part of the stuff has thus un op- 

 portunity of attracting to itself the proper 

 quantity of colouring matter. 



The stuff receives the dye better, in 

 proportion to the degree of affinity which 

 the colouring matter has to it and to the 

 solvent relatively, for if its attraction to 

 the stuff is much more than to the sol* 

 vent, the stuff receives the dye too ra- 

 pidly, and it will be scarcely possible to 

 prevent Its being unequal : but if, on the 

 other hand, its attraction to the solvent 

 is too great, the stuff will either not take 

 the dye at all, or it will take it very 

 slowly and faintly. Wool has a stronger 

 attraction for colouring matters than silk, 

 silk than cotton, and this latter a stronger 

 than linen. Hence it is necessary to use 

 solvents for the dyes of the stuff's last 

 mentioned, which have a weaker affinity 

 for them than for those used in dyeing 

 wool. 



The essential circumstances in dyeing 

 are, to ascertain the affinities of the co- 

 louring substance ; first, to the solvents ; 

 secondly, to those substances which mo- 

 dify its colour, increase its bril ! iancy, and 

 strengthen its union with the stuff'; third- 

 ly, to the different agents, which may 

 change the colour, and principally to air 

 and light. 



The colouring matters possess chemi- 

 cal properties, that distinguish them from 

 all others : they have attractions peculiar 

 to themselves, by means of which they 

 unite with acids, alkalies, metallic oxides, 

 and some earths, particularly alumen. 

 They frequently precipitate oxides and 

 alumine from the acids which held them 

 in solution ; at other times they unite 

 with salts, and form supra-compounds, 

 which combine with the wool, silk, cot- 

 ton, or linen : and with these their union 

 is rendered much more close by means 

 of alumine, or a metallic oxide, than it 

 would be without their intervention. 



The qualities of the uncombined co- 

 louring particles are modified when they 

 unite with any substance ; and if this com- 

 pound unites with a stuff, it undergoes 

 new modifications. Thus the properties 

 of the colouring particles of cochineal 

 are modified by being combined with the 

 oxide of tin; and those of the substance 

 thence resulting are again modified by 

 their union with the wool or silk : and 

 all these modifications are analogous to 

 what is observed in other chemical com- 

 binations. 



Of Mordant*. 



The title of mordant is applied to those 

 substances which serve as intermedes be- 

 tween the colouring particles and the 

 stuff' to be dyed, either for the purpose 

 of facilitating, or of modifying their com- 

 bination ; and by their means, colours are 

 varied, brightened, made to strike, and 

 rendered more durable. 



\Vas it possible to procure a sufficient 

 number of colouring matters, having a 

 strong affinity to cloth, to answer all the 

 purposes of dyeing, that art would be 

 exceedingly simple and easy. But, ex- 

 cept indigo, there is scarcely a dye-stuff 

 which yields of itself a good colour, suffi- 

 ciently permanent to deserve the name 

 of a dye. This difficulty is obviated by 

 employing an intermediate substance, 

 which has a strong affinity both for the 

 stuff' and the colouring matter, and this 

 is the principal purpose for which the 

 mordant is used. 



A mordant is not always a simple agent; 

 new combinations are sometimes formed 

 by the ingredients which compose it: so 

 that the compounds resulting from the 

 mixture, and not the simple substances 

 that compose it, are the immediate agents 

 which produce the effect. 



Sometimes the mordant is mixed with 

 the colouring particles, sometimes the 

 stuff' is impregnated with it, and on other 

 occasions both those modes are united ; 

 and, finally, stuff's are dyed successively 

 with liquors containing different substan- 

 ces, the last of which only can act on that 

 with which the stuff is impregnated. 



The principal substances employed as 

 mordants are, aluminous salts, lime, me- 

 tallic oxides, some astringent substances, 

 and animal matters. 



Formerly sulphate of alumen was the 

 only species used as a mordant in dye- 

 ing; but of late years acetite of alumen 

 has been introduced with excellent ef- 

 fect, particularly for cottons or linens, 

 whose attraction to the a'umen being 

 weuk, they require it to be applied, com- 

 bined with a substance to which it has 

 not so strong an union as it has to sul- 

 phuric acid ; audits attraction to acetous 

 acid is found to be sufficiently inferior to 

 that for the cotton or linen, that it readily 

 quits the acetous acid to combine with 

 them. 



Acetite of alumen ispreparedby pour- 

 ing acetite of lead into a solution of alum, 

 in the proportion of one part of the ace- 

 tite of lead to three of the alum in weight, 



