SS6 Mr. W. Crum on a peculiar Fibre of Cotton. 



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 be mechanical on the part of the cotton ; and the 

 adherence, as I shall endeavour to show, confined to the in- 

 terior 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 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 

 mineral constituent being previously connected with the cotton." 



To produce the purple dye of M. Koechlin's pattern, the 

 cloth has first to be impregnated with iron. For this purpose 

 it is made to imbibe a weak solution of proto-acetate of iron, 

 and afterwards dried. By exposure to the air for some days 

 the salt is decomposed. Its acetic acid evaporates, and the 

 oxide of iron, then become peroxide, remains in the fibre. 

 The cloth is afterwards subjected to severe washings in hot 

 and cold water, but its iron is not removed ; and the question 

 is. How is it retained in connexion with the cotton ? Mecha- 

 nically, as I maintain, and probably in the interior of its hollow 

 fibre, which it entered in a state of solution, and within which 

 it was precipitated. Others, as I have already stated, are of 

 opinion, after Bergman, that the combination is a chemical 

 one ; and so fully is that view carried out by my friend Pro- 

 fessor Runge of Oranienburg, in his ingenious and excellent 

 work on the Chemistry of Dyeing*, that he assumes coloured 

 cottons to be combinations of what he calls cottonic acid with 

 the various bases, in definite, and even in multiple proportions. 

 Thus a very pale shade of buff from oxide of iron is called 

 percottonate of iron ', a.no\hev \s c&WqA bicottonate of iron \ and 

 still deeper shades, cottonate and basic cottonate of iron. 



But the new fibre, by the same treatment, is incapable of 



retaining the iron mordant, and yet both fibres have the same 



chemical composition and the same ultimate structure. The 



only difference is, that one is shaped into tubes or bags capable 



♦ Farbenchemie. 2 vols. Berlin, 1832 and 1845. 



