ON COLORING. 51 



more than the disposition or tendency which two or more sub- 

 stances have to unite and form a new compound, differing great- 

 ly in some of its qualities from the simple substances of which it 

 is composed ; one substance is therefore said to liave an affinity 

 for another when on being brought in contact it unites with and 

 assumes new appearances and qualities. For example, if iron 

 and sulphuric acid (oil of vitriol) be brought together they grad- 

 ually unite and form sulphate of iron (green vitriol or copperas) 

 but the sulphuric acid has a stronger affinity for lime than it has 

 for iron ; if, therefore, lime be brought into contact with sulphate 

 of iron, the sulphuric acid quits the iron, seizes on the lime, and 

 forms sulphate of lime (plaster of Paris.) Substances used in 

 dying possess an affinity for the fibres of the cloth and when dis- 

 solved in water or some other liquid, and brought into contact, 

 they unite, and change either the color of the fibres, or so 

 change their qualities, as to dispose them to unite with other col- 

 oring matter for which before they had no affinity. 



The art of dyeing then consists in combining a certain col- 

 oring matter with the fibres of the cloth. This process cannot 

 be well performed unless the dye-stuff be dissolved in some 

 liquid, and the particles so separated that their attraction for 

 each other becomes weaker than the attraction for them exerted 

 by the cloth. When the cloth is dipped into this solution, it 

 attracts the coloring matter, and from its stronger affinity takes 

 it from the solvent and fixes it upon itself The facility with 

 which cloth Imbibes a dye, depends on two circumstances, name- 

 ly, the affinity between the cloth and the dye-stuff, and the af- 

 finity between the dye-stuff and its solvent. It is of import- 

 ance to preserve a due proportion between these two affinities, 

 as upon that proportion much of the accuracy of dyeing depends. 

 If the affinity between the coloring matter and the cloth be too 

 great, compared with the affinity between the coloring matter 

 and the solvent, the cloth will take the dye too rapidly, and it 

 will be scarcely possible to prevent its color from being unequal. 

 On the other hand, if the affinity between the coloring matter 

 and the solvent be too great, compared with that between the 

 coloring matter and the cloth, it will either not take the color at 



