486 Dr. Bolley on the Theory of Dyeing . 



(«) No effect ; a case left undiscussed, but of which it may be 

 doubted whether it ever really occurs. 



[b) The salt may unite as a lohole ■v{'\i\\ the fibre. Ferridcyan- 

 ide of potassium, separating from a dilute aqueous solution, 

 unites with wool and silk ; and from this behaviour it is inferred 

 that the same is the case with many other salts. The experi- 

 ment of Thenard and Roard is appealed to that alum unites with 

 fibres (what fibres?), and may be washed out again. 



(c) Another case is the separation of a basic from a neutral salt, 

 setting free an acid salt. 



A solution of persulphate of iron applied to silk tinges it of a 

 rust-colour, which results from the separation of a very insoluble 

 basic salt. Chevreul expressly maintains that these decomposi- 

 tions can only be ascribed to the chemical affinity of the silk for 

 the basic salt of iron. 



The power of silk to attract basic salts is greatest when the 

 salt solution is of one particular degree of concentration, less for 

 a more dilute solution ; when, however, the concentration is too 

 strong, the tendency of the basic salt to separate out again dimi- 

 nishes. Different salts of iron give up more or less basic salt, 

 according to their disposition to form such salts. 



{d) The last possible contingency is that one only of the two 

 constituents of the salt, the acid or the base, becomes fixed. 



Wool, according to Thenard and Roard, decomposes bitartrate 

 of potash, uniting with the tartaric acid and part of the unde- 

 composed salt, and setting free neutral tartrate. Cotton soaked 

 in acetate of alumina, dried and boiled, yields nothing but 

 alumina. 



5. As to the effect of fibres on the neutral binary, ternary, &c. 

 compounds other than salifiable 



Inorganic compounds which belong to this class are the me- 

 tallic sulphides, which are precipitated either from ammoniacal 

 solutions by the evaporation of the ammonia, or from solutions 

 in a fixed alkali by treating with an acid, or by soaking in a me- 

 tallic salt and passing through sulphide of potassium. 



Finally, organic dye stuffs are treated of in regard to their 

 behaviour on being bi'ought into immediate contact with fibres. 

 It would, however, be altogether useless to repeat the observa- 

 tions made on this subject. The discoveries which have been 

 made since the year 1833 (when the essay may have been written), 

 on the subject of organic colouiing matters, have effected so entire 

 a change in this branch of organic chemistry, that but the small- 

 est part of Chevreul's treatise is on a level with the present state 

 of our knowledge. 



As little important are the observations in part G of the trea- 

 tise, which relates to the behaviour oi fibres — bases, acids, or salt' 



