Dr. BoUey on the Theory of Dyeing. 485 



red, and which, therefore, according to W. Cruni, has the cells 

 of its fibres completely filled, becomes black on being printed 

 with a blue dye, and orange with yellow ? By these objections 

 Persoz makes it plausible that the dye affects the surface 

 only. 



Dufay in 1737, and Bergmann in 1776, expressed an opinion 

 altogether opposite to the above, and they were followed by 

 Macquer (1 778), Berthollet, and finally by Chevreul. This entire 

 series of inquirers, among whom is to be found the most brilliant 

 talent of the period, regard the union of the pigment (and lake) 

 with the fibre as chemical. The property of wool to take colours 

 more readily than silk, and that again more readily than cotton 

 or flax, they attribute to the different degrees of chemical affinity 

 which these fibres have for dye stuffs. 



We must not neglect to examine more carefully into the views 

 and researches of Chevreul, which Persoz has altogether omitted 

 to mention. These are to be found in his treatise, entitled 

 " General Theory of the Art of Dyeing*." In the introduction 

 to this learned treatise, he maintains that the object of the dyer's 

 art is to apply to the diffei'ent fibres dyes which combine with 

 them by chemical affinity, and not by mechanical attraction. 



The portion of this treatise which touches on the subject under 

 consideration is divided into six parts, wherein numerous special 

 observations and experiments are cited. 



1. The behaviour of vegetable and animal fibres (as ternary 

 and quaternary combinations) to the elements is, as might be 

 expected, such that the latter unite with them unwillingly and 

 in small quantities. 



2. The acids, according to Chevreul, behave in the following 

 manner : — 



A liquid which contained 1 grm. of sulphuric acid diluted with 

 water to 10 cubic ceutims., gave up a portion of the acid to wool 

 and silk digested therein, the liquid poured off showing itself 

 less acid. Cotton produced an opposite effect; the fibres took 

 up the water and left a stronger acid. 



The behaviour of hydrochloric acid was only tried on wool ; a 

 mixture which in 10 cubic centims. contained 1*1628 gr. HCl, 

 gave up acid to wool. 



These acids could be extracted from the fibres again by long 

 washing. 



3. Of the bases, Chevreul states that magnesia and lime can 

 combine with wool, but nothing is said of the manner of effect- 

 ing the union. 



4. Salts brought into contact with fibres give four possible 

 results : — 



* Dictionnaire Technologique, vol. xxi. p. 365. 



