Compound Celluloses 115 



distinguished by a number of characteristic reactions. In 

 addition to those already described as admitting of quantitative 

 estimations, the following are the more important : 



(1) Salts of aniline (and many of the aromatic bases), in 

 aqueous solution, colour the fibre a deep golden yellow. 



(2) The Coal-tar dyes generally combine freely with theligno- 

 celluloses. In ' staining ' sections of plants and parts of plants 

 for microscopic observation, the lignocelluloses are dyed by 

 the majority of soluble coal-tar dyes. Their ' affinities ' for 

 colouring matters are, in fact, similar to those of the animal 

 fibres, silk and wool, although differing radically from them, 

 not only in constitution, but in containing no nitrogen (NH 2 

 groups). 



(3) Phlorogludnol) in hydrochloric acid, gives the deep 

 magenta colouration characteristic of the pentaglucoses. The 

 reagent is prepared by dissolving the phenol to saturation in 

 HClAq (ro6 sp.gr.). 



(4) Iodine is absorbed from its solutions in potassium 

 iodide in large quantity, colouring the fibre a deep brown. 



(5) Chlorine combines with the fibre with avidity, as already 

 described ; the chlorination is made evident by treatment 

 with sodium sulphite solution, which develops a deep magenta 

 colouration. This reaction is characteristic. Conversely, the 

 fibre-substance may be employed as a reagent for the identifi- 

 cation of chlorine, or may, in certain cases, be used for absorb- 

 ing the gas. 



(6) Ferric chloride colours the fibre- substance to a dark 

 greenish tint the reaction being due to traces of tannins. 



(7) Ferric ferricyanide the red solution obtained by mixing 

 together ferric chloride and potassium ferricyanide in equivalent 

 proportions gives a highly characteristic reaction (subsequently 

 described in detail), the fibre-substance rapidly decomposing 

 the compound to * Prussian blue,' the pigment being taken up 



I 2 



