506 Dr. Bolley on the Theory of Dyeing. 



B. Witli regard to the nature of the force which connects the 

 fihre and the colouring matter. 



7. The attractive power of cotton for salts, diluted acids, &c., 

 is in all cases less than that of wool and silk. That tlie former, 

 however, has in anj^ case the opposite eft'cct to the latter is not 

 proved. (Chevreul, Thenard, and Roard state that silk and wool 

 weaken dilute sulphuric acid, while cotton, by abstracting the 

 water, concentrates the acid.) 



8. There is no sufficient reason for accepting the view prin- 

 cipally developed by Chevreul, that dyeing is a consequence 

 of chemical affinity. Neither the experiments made by him, and 

 before his time, on the power possessed by fibres of attracting 

 certain bodies from their solutions, nor even the observations 

 that have since been made, that certain fibres arc coloured by 

 penetration (infiltration), necessitate this view, to which indeed 

 there are important facts directly opposed. 



9. Mordants act by producing insoluble colours (lakes). 

 Their behaviour to colouring matter in solution must be ascribed 

 to chemical affinity, with which, however, the fibres themselves 

 have nothing to do. The so-called substantive dyes are those 

 which become insoluble from some cause other than the addition 

 of a mordant. 



10. The behaviour of fibres, whether towards dissolved salts 

 or colouring matter, or towards both applied simultaneously or 

 successively, belongs to that class of pheenomena which results 

 from the action of finely divided mineral or organic bodies (char- 

 coal for example) on such solutions. The considerations which 

 induced Persoz in his time to regard this view as inadmissible 

 fail, because they rest on the ]iy])othesis of a state of facts which 

 subsequent research has shown to be incorrect. 



Postscript. 



Since the greater part of the foregoing treatise was printed, 

 Nos. 7 and 8 for 1859 of the Journal fur Praktischc Chemie, 

 von 0. L. Erdmann and Werther, have come to hand. From 

 the first of these two Numbers I became acquainted with 

 a communication by Prof. Erdmann, " On the Operation of 

 Mordants, especially Alum, in Cotton Dyeing." I am obliged, 

 if only for the sake of completeness, shortly to notice this trea- 

 tise, which the able editor of this periodical has produced in con- 

 junction with one of his assistants, Mittenzwey, and to make the 

 following observations thereon. 



1. When, in the treatise, it is said " the phsenomena of dyeing 

 have hardly ever been the subject of accurate scientific examina- 

 tion," the industry of preceding writers seems very much under- 



