in which Cotton unites with Colouring Matter. 243 



common air, and box-wood charcoal with smaller pores takes 

 7^. Charcoal from cork, with a specific gravity of only 0*1, 

 absorbs no appreciable quantity. 



It appears to me that many of the operations of dyeing de- 

 pend upon this influence of the surface, or the capillary action 

 described by Saussure. 



The microscopic examination of the fibres of cotton by Mr. 

 Thomson of Clitheroe, and Mr. Bauer, shows them to con- 

 sist of transparent glassy tubes, which when unripe are cylin- 

 drical, and in the mature state collapsed in the middle, from 

 end to end, giving the appearance of a separate tube on each 

 side of the flattened fibre. 



In many of the operations of dyeing and calico-printing 

 the mineral basis of the colour is applied to the cotton in a 

 state of solution in a volatile acid. This solution is allowed 

 to dry upon the cloth, and in a short time the salt is decom- 

 posed, just as it would be in similar circumstances without the 

 intervention of cotton. During the decomposition of this salt 

 its acid escapes, and the metallic oxide adheres to the fibre so 

 firmly as to resist the action of water applied to it with some 

 violence. In this way does acetate of alumine act, and nearly 

 in the same manner acetate of iron. The action here can only 

 be mechanical on the part of the cotton, and the adherence, 

 as I shall endeavour to show, confined to the interior of the 

 tubes of which wools consist. The metallic oxide permeates 

 these tubes in a state of solution, and it is only when its salt is 

 there decomposed and the oxide precipitated and reduced to 

 an insoluble powder, that it is prevented from returning 

 through the fine filter in which it is then inclosed. 



When the piece of cotton, which in this view consists of 

 bags lined inside with a metallic oxide, is subsequently dyed 

 with madder or logwood, and becomes thereby red or black, 

 the action is purely one of chemical attraction between the 

 mineral in the cloth and the organic matter in the dye vessel, 

 which together form the red or black compound that results ; 

 and there is no peculiarity of a chemical nature from the mi- 

 neral 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 por- 

 tions 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 me- 

 chanical theory of dyeing held by Macquer, Hellot, and Le 

 Pileur d'Apligny, before the time of Bergman. Although 



R2 



