CHEMICAL SCIENCE. 213 



not been dyed with colors in a mere state of suspension, 1 seem to be impreg- 

 nated with the dye throughout their entire mass; while in the case of cotton, 

 by far the larger portion of the coloring matter adheres to the surface of the 

 fibre, the penetration of the cell-walls by the dye being either very slight or 

 altogether wanting. 



That the theory proposed by Mr. Crum, of England, that the tubular form 

 of the cotton fibres is an essential condition to their taking a dye, is unfound- 

 ed, appears from the fact that the amorphous cotton-gelatine precipitated 

 from its solution in cuprate of ammonia may be mordanted and dyed like 

 ordinary cotton. In like manner sulphate of baryta and other pulverulent 

 mineral bodies may be mordanted and dyed with decoctions of dycwoods. 



With regard to the nature of the force which binds the coloring matter to 

 the fibre, whether or no it be chemical attraction, Bollcy concludes that 

 there is no sufficient reason for accepting the view, principally developed by 

 Chevreul (and by Kuhlmarin, Coinptes Hendtts, Tomes xlii., xliii., et xliv.), 

 that dyeing is a direct consequence of chemical affinity. He believes that 

 the power possessed by fibres of attracting certain bodies whether salts 

 or coloring matters or both from their solutions, belongs to that class of 

 phenomena which results from the action of finely divided mineral or orga- 

 nic bodies (charcoal or bone-black, for example) on such solutions. The dis- 

 tinction between the action of charcoal and of fibres in thus removing saline 

 matters, or dyes, from their solutions, is one of degree only, the nature of the 

 operation being identical in either case. 



A Driven weight of well prepared animal charcoal can, as a rule, deprive a 

 larger quantity of liquid of its color than an equal weight of wool or silk. 

 Neither wool nor silk can remove all the color from a solution as charcoal 

 can, their effect extending only to a certain degree of dilution beyond which 

 the particles of coloring matter resist their attraction. Dyes which may have 

 been taken up without a mordant by wool, or especially by silk, may be 

 removed again by long washing in water, a fact which is not true in the case 

 of charcoal, or only to a very slight extent. The attraction of coloring mat- 

 ters for water is therefore more completely overcome by charcoal than by 

 animal fibre; but even the cleanest vegetable fibres, as unmordanted and 

 completely bleached cotton, possess a certain power of attracting coloring 

 matter. That cotton should have less effect in this matter than wool or silk 

 is not surprising, in view of the great difference in the structure of cotton 

 fibre as compared with that of the two substances last mentioned. It is 

 well known that wool and silk, in consequence of their physical constitution, 

 belong to the class of strongly absorbent or hygroscopic substances, i. (., in 

 consequence of a certain porosity or looseness of their particles they swell up 

 when moist and become easily penetrated by a liquid throughout their entire 

 mass; on the other hand the cell walls of cotton fibres are denser, less pene- 

 trable, and, at the same time, thinner, and therefore unable to contain the 

 same quantity of liquid. 



It has been often urged that since fibres, especially those of animal origin, 

 not only exert an attraction for salts, etc., but also possess the power of 

 decomposing some of them, their action must be chemical. But in this 

 respect the behavior of charcoal is similar to that of the fibres. So, too, with 

 regard to the increased attraction for color exhibited by mordanted cotton, 



1 In which case the coloring matter only adheres as a crust to the surface of the 

 fibre. 



