Mr. Crum on a Peculiar Fibre of Cotton incapable of being Dyed. 63 



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 circum- 

 stances, without the intervention of cotton. During the decomposition 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 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, 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 

 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 Mr. 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 expo- 

 sure 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 connection with the cotton ? Mechanically, 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 Berg-man, that the combination is a 

 chemical one ; and so fully is that view carried out by my friend Professor 

 Runge of Oranienburg, in his ingenious and excellent work on the chem- 

 istry 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 bufi" from oxide of iron, 

 is called percottonate of iron; another is called 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 of holding all matters which are insoluble in 

 water — that is, all bodies that can be caught upon a filter, while the other 

 is possessed of no such inclosurc. 



I take this opportunity, in reply to a review of my first memoir on this 



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



