Dr. BoUey on the Theory of Dyeing. 503 



appears to the microscope uniform throughout. A clear solution 

 of gum behaves in precisely the same way. The observations of 

 Maschke only directly prove the power of animal fibres to absorb 

 solutions of colouring matter. 



We now come to the decision of the question whether, under 

 these circumstances, we are compelled to regard, or are justified 

 iu regarding, the union of all fibres with their dyes, whether 

 with or without a mordant, as chemical. 



Persoz maintains that there is a group of phsenomena well known 

 to chemistSjWhich possess great analogy to those in question, — the 

 attraction, namely, of charcoal and other finely divided solid bodies 

 for colouring matter and salts in solution. After detailing the 

 discoveries which had been made up to the time of the appear- 

 ance of his work on the power possessed by charcoal of attract- 

 ing and absorbing colouring matter (discoveries which have since 

 been considerably extended), he nevertheless comes to the con- 

 clusion that if a similar relation is to be assumed between fibres 

 and the particles of colouring matter, then the existence of che- 

 mical affinity must be denied ; and that nevertheless there is an 

 essential difi'erence between the attraction of charcoal for salt and 

 dyes in solution, and that of fibres for the same substances. He 

 entertained a settled opinion that the colouring process affected 

 only the surface of the fibre. This preconceived view compelled 

 him to suppose the existence of a species of cohesion between 

 solid bodies different from that between charcoal and dissolved 

 colom'ing matter; and he supported this view on the alleged 

 (and certainly erroneous) observation, that fibres (he does not 

 say which), if they possessed altogether the same properties as 

 charcoal, ought to deprive cochineal, weld, or madder baths of 

 colour just as charcoal docs; whereas the contrary is the fact, 

 since, he says, it is \.\\ovin ihvit fibres well cleaned from foreign 

 substances attract no colouring matter from solutions, whereas, the 

 trior e fatty matte)' or metallic oxide adheres to the fibre, the easier 

 does it take a dye. 



The behaviour of animal and vegetable fibres (well cleaned) 

 towards " liquid blue," and that of animal fibres towards decoc- 

 tions of cochineal, Campeachy, and Brazil wood, have been 

 mentioned; this, as well as the microscopic observations of 

 Maschke, and even the experience of dyers, that madder, 

 turmeric, yellow wood, and other colouring substances dye 

 unmordauted and completely bleached cotton, clearly shows that 

 the cleanest fibres do attract colom'ing matter. We will not, 

 however, deny that a given weight of well-i)repared animal 

 charcoal can, as a rule, deprive a larger quantity of liquid of 

 its colour than an equal weight of wool or silk : indeed, wc 

 can mention two complementary facts which throw a clear 



