500 Dr. BoUey on the Theory of Dyeing. 



From B. That silk has the greatest attraction for indigo in 

 solution in sulphuric acid, charcoal next, and wool next to 

 that ; and lastly, that cotton has some, though a very slight 

 attraction for indigo under such circumstances. That, more- 

 over, animal fibres and charcoal, besides the iudigo, take up a 

 small portion of sulphuric acid, which is not the case with cotton. 



From C. That a solution of the yellow prussiate of potash of 

 the strength indicated is unaltered by digestion with fibres. 

 (Chevreul says that, with a much larger quantity of water than 

 is necessary for its solution, prussiate of potash does not unite 

 with silk and wool.) 



From D. That more of the component parts of bitartrate of 

 potash are absorbed by wool and silk (both raw and scoured) 

 than by cotton ; aud that the remaining liquid contains a consi- 

 derably greater amount of potash, as compared with the tartaric 

 acid, than there is in the tartar itself; and that, therefore, prin- 

 cipally tartaric acid, and very little or no potash, is taken up by 

 the fibre. 



From E. That a solution of sugar of lead gives up part of the 

 dissolved salt to wool and silk, but none to cotton. That, more- 

 over, fibres of animal origin partly decompose the salt by abs- 

 tracting from the solution more of the base than of the acid. 

 (This is very often the case (see below) when certain salts are 

 brought into contact with animal charcoal.) 



From F. That a solution of alum parts with a portion of the 

 dissolved salt to wool and silk, but with very little, if any, to 

 cotton ; and moreover, that more of the alumina is taken up 

 than of the sulphuric acid with which it is united : in all the 

 experiments the quantity of alumina in the solution was slightly 

 diminished, while that of the sulphuric acid was relatively some- 

 what increased*. (Thenard and Roard were of opinion that 

 alum was one of those salts which are indeed partly taken up 

 fi'om an aqueous solution by wool and silk, but without change 

 in their constitution ; and moreover, they held that alum could 

 be entirely removed again by washing.) 



Though the entire series of experiments A to F shows that 

 cotton has less effect than wool and silk, that, in fact, it has 

 little or no power of attraction (in the case at least of solutions 

 of the degrees of concentration experimented with), this must 

 not be held to contradict the well-known fact that concentrated 



* The decrease of base and relative increase of acid is indeed very slight ; 

 but as it was found universally in all solutions in nhich tibres had been di- 

 gestedj we cannot but attribute a decomposing power to the fibres, though 

 it must not be forgotten that the weakness of the solutions, and the influ- 

 ence of temperature on the small quantities taken for analysis, rendered 

 accurate estimation very difficult. 



