50-1 Dr. Bolley on the Tlieonj of Dyeing. 



light on the behaviour of these bodies to sokitions of colouring 

 matter. 



1. Wool and silk are unable to deprive a solution of all its 

 colour, as charcoal can ; their effect only extends to a certain 

 degree of dilution, beyond which the particles of colouring mat- 

 ter resist their attraction. 



2. What we have already asserted concerning wool, and espe- 

 cially concerning silk, namely, that dyes which they have taken 

 without a mordant maybe removed again by long washing in water, 

 is not true in the case of charcoal, or only to a very slight degree. 



Both these observations show that the attraction of colouring 

 matter for water is more completely overcome by charcoal than 

 by animal fibre. 



Cotton, as we gather from the experiments above tabulated, 

 has less effect than wool and silk on salts and colouring matters 

 in solution; this, however, will not surprise us when we com- 

 pare the structure of cotton fibre with that of wool and silk, and 

 reflect that the latter substances, in consequence of their physical 

 constitution, belong (as has been long known) to the class of 

 strongly absorbent or hygroscopic bodies ; that is, bodies which, 

 in consequence of a certain porosity or looseness of their particles, 

 swell up when moist, and become easily penetrated by a liquid 

 throughout their entire mass. Similar to this (leaving the pe- 

 culiar property of surface attraction out of the question) is their 

 behaviour towards solutions, whether of salts or of dyes ; whereas, 

 on the other hand, the cell-walls of cotton fibres are denser, and 

 therefore less penetrable, and at the same time thinner, and there- 

 fore unable to contain the same quantity of liquid. Finally, if 

 it be contended that a fundamental difference must exist between 

 fibres of animal and vegetable origin, because the effect of the 

 latter is increased by a mordant base being united with them (by 

 being rendered insoluble), then we must call to mind the expe- 

 riments of Stenhouse, who considerably increased the decolorizing 

 power of wood-charcoal by precipitating alum on it. With 

 regard, therefore, to the power of diminishing the strength of 

 solutions, whether of salts or dyes, we can only admit a distinc- 

 tion between fibres and charcoal as to the degree, not as to the 

 nature of their operation. 



Fibres, however, especially those of an animal origin, not only 

 exert an attraction for the substances above mentioned, but they 

 also possess the power of decomposing some of them. Is not 

 this a ])roof of their chemical operation ? We learn from nume- 

 rous experiments, from the older ones of Payen, Bussy, Gra- 

 ham, Chevalier, and more recently from Filhol*, Weppenf; 



* Comptes Reiidus, vol. xxxiv. p. 247. 



t Ann. der Chetn. und Pharm. vol. Iv. p. 241. 



