100 Mr. Crum on tJve Manner in which Cotton unites with Colouring Matter. 



the extent of surface in proportion to the mass, as the measure of the 

 force which it exerts. On the other hand, Saussure, in his valuable 

 paper on the Absorption of Gases, informs us, that charcoal from box- 

 wood, in the solid state, absorbs twice as much common air as when 

 it is reduced to powder. Now, the effect of pulverization is certainly 

 not to diminish the extent of surface. Saussure accounts for it in 

 another way, and his explanation seems to connect many of the facts. 

 The condensation of gases in solid charcoal goes on, he conceives, in 

 the narrow cells of which it is composed, and is analogous to the rise 

 of liquids in capillary tubes. In both, he says, the power appears to 

 be in the inverse ratio of the size of the interior diameters of the pores 

 or tubes of the absorbing bodies. When we pulverize a body containing 

 such cells, we widen, open, and destroy them. Fir charcoal, whose 

 cells are wide, absorbs 4| times its bulk of common air, and boxwood 

 charcoal, with smaller pores, takes 7^. Charcoal from cork, with a 

 specific gravity of only O'l, absorbs no appreciable quantity. 



It appears to me that many of the operations of dyeing depend upon 

 this influence of the surface, or the capillary action described by Saus- 

 sure. The microscopic examination of the fibres of cotton by Mr. 

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

 parent glassy tubes, which, when unripe, are cylindrical ; 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. As 

 the sides of these tubes permit the passage of water, they also must be 

 porous ; but the form, or even the existence of such lateral perfora- 

 tions, cannot be detected by the most powerful microscope. 



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 decomposed, just as it would be, in similar cir- 

 cumstances, without the intervention of cotton. During the decom- 

 position of the 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 alumina act ; and, nearly 

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

 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, or of the invisible passages which lead to it. 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 enclosed. 



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

 inside with a metallic oxide, is subsequently dyed with madder or log- 

 wood, and becomes thereby red or black, the action is purely one of 

 chemical attraction between the mineral in the cloth, and the organic 



