Mb. Crum on the Manner in which Cotton unites with Colouring Matter. 101 



matter in tho djo vessel, which, together, form the red or black com- 

 pound that results ; and there is no peculiarity of a chemical nature 

 from tho mineral constituent being previously connected with the 

 cotton. The process of cleansing in boiling liquids, and in the wash 

 wheel, to which cotton, printed with the various mordants, is subjected, 

 previous to being maddered, is to remove those portions of metallic 

 oxide which have been left outside the fibres, or got entangled between 

 them, and fastened there more or less firmly by the mucilage employed 

 to thicken the solution. 



The view I have now given is, in some respects, the old mechanical 

 theory of dyeing held by Macquer, Hellot, and le Pileur d*Apligny, 

 before the time of Bergman. Although unacquainted with the micros- 

 copic appearance of cotton, d'Apligny argued, that as no vegetable 

 substance in its growth can receive a juice without vessels proper for 

 its circulation, so the fibres of cotton must be hollow within. And of 

 wool, he says, the sides of the tubes must be sieves throughout their 

 length, with an infinity of lateral pores. We may gather, also, that 

 he conceived dyeing to consist, first, in removing a medullary substance 

 contained in the pores of the wool, and afterwards depositing in them 

 particles of a foreign colouring matter. 



But Bergman, in his Treatise on Indigo, in 1776, upset all this; 

 and attributed to cotton a power of elective attraction, by which all 

 the phenomena of dyeing were referred to purely chemical principles. 

 Macquer soon adopted the chemical theory, and it was keenly advanced 

 by Berthollet, who succeeded Dufay, Hellot, and Macquer, in the ad- 

 ministration of the arts connected with chemistry. Berthollet has 

 been followed by all, so far as I know, who have since that time written 

 on the subject, but nothing like evidence has ever been produced; and, 

 if we only consider that chemical attraction necessarily involves com- 

 bination, atom to atom ; and, consequently, disorganization of all 

 vegetable structure ; that cotton wool may be dyed without injury to 

 its fibre, and that that fibre remains entire, when, by chemical means, 

 its colour has again been removed, we shall find that the union of cotton 

 with its colouring must be accounted for otherwise than by chemical 

 affinity. In particular processes, as we shall afterwards see, attraction 

 is no doubt exerted, but it is an attraction connected with structure, 

 and therefore more mechanical than chemical. 



When we examine, with a powerful microscope, a fibre of cotton, 

 dyed either with indigo, with oxide of iron, chromate of lead, or tho 

 common madder red, the colour appears to be spread so uniformly 

 over the whole fibre that we cannot decide whether the walls of the 

 tube are dyed throughout, or that the colouring matter only lines their 

 internal surface. But the microscope shows that the collapsing which 

 occurs in raw and bleached cotton, is very considerably diminished in 

 tho dyed. 



The greater number of specimens of Turkey red which I have 



