64 Mr. Crum mi a Peculiar FiWe of Cotton incapable of being Dyed. 



subject, by M. Persoz, in his remarkable work, " Traite cle rirepression 

 des Tissus," of explaining, that I attribute to an attraction of surface 

 those cases of dyeing where pure cotton, by mere immersion, is enabled ' 

 to decompose the solid matters in solution, and to withdraw them from 

 the solvent. Such is the case with the solution of deoxidized indigo in 

 lime — with the plumbite of lime — with the various salts of tin, and many 

 other solutions. Cotton, as I have stated, acts in these cases like char- 

 coal and other porous bodies, and I have seen no reason to confine the 

 attraction in question to the internal surface of the cotton fibre. 



But I have not ranked the aluminous mordant among the class of 

 bodies so attracted, because cotton when immersed in a solution of acetate 

 of alumina, has not the power of separating its basis. That solution 

 must be applied to cotton and dried in it, and then the alumina only 

 adheres, or loses the power of being washed away, in proportion as the 

 acetic acid is removed by evaporation. I could see here no chemical 

 decomposition effected by the cotton-wool, for the same salt may be 

 decomposed by evaporation in a glass vessel. In this case I have repre- 

 sented the alumina as being held in the interior of the fibre, just as sand 

 may be held in a bag whose interstices are too narrow to allow its par- 

 ticles to pass. 



M. Persoz has remarked, however, that by evaporating a solution of 

 acetate of alumina in a glass vessel, we do not so thoroughly decompose 

 it as by drying the same substance upon calico. This I also have observed ; 

 and although I have been accustomed to ascribe the difference to the more 

 extensive division and exposure of the salt upon cotton, I have no proof, 

 and shall not deny that the presence of cotton at a particular stage of the 

 evaporation may accelerate the decomposition of the salt, and that its 

 fibres may thus attract a portion of alumina over their whole surface. If 

 this modification of the view I had given be correct, the action of the coton 

 mart proves at least that colouring matter adhering outside is not so 

 permanent as that which is held within the fibre of the matui'e cotton. 



Neither view gives any countenance to the chemical theory. Porous 

 bodies are well known to attract, and even to decompose, without chemi- 

 cally combining with the substances they precipitate. Accordingly, none 

 of the oxides are changed either in colour or in chemical character by their 

 union with cotton. The hydrated oxide of copper, for example, precipi- 

 tated upon calico, becomes carbonate, or arsenite when exposed to carbonic 

 or arsenious acid. The protoxide of iron changes speedily in the air into 

 the red sesquioxide, and that again may be converted into prussian blue, 

 or into a black or purple lake — every new compound, if it only be 

 insoluble, adhering firmly to the wool. 



Mr. Crum also reported upon some new facts in the Chemistry of 

 Digestion, and of Poisons. 



The Society then adjourned till the next Session. 



BULL AND BAI>', PKINTKKS, (JLASUOW. 



