70 CAEBOHYDRATES [ch. 



Although the best paper is made from cellulose, cheaper forms of 

 paper are manufactured from ligno-cellulose, and, as a result, they, give 

 reactions for lignin and are also turned yellow by exposure to light. 



Expt. 73, Reactions of lignin. 



One of the most striking reactions of lignin (due as it is supposed to a furfural 

 grouping) is the magenta-red coloration given by phloroglucinol in the presence of 

 concentrated hydrochloric acid. 



Soak the tissue to be experimented upon with an alcoholic solution of phloroglucinol 

 and then add a drop or two of strong hydrochloric acid. The magenta-red colour 

 will be produced. 



As material, practically any lignified tissue may be used. Shavings from twigs 

 of any tree or shrub, e.g. pith and wood from the Elder {Samhucus nigra), will be 

 found useful : also shavings from a match ; straw, bran, coarse string, cheap white 

 paper, such as newspaper or white and pale-coloured papers used for wrappings. 



Make the phloroglucinol test on good white writing paper. It should not give the 

 reaction since it is made from cellulose. 



Other phenols (resorcinol, orcinol, catechol, pyrogallol, etc.) and their derivatives 

 will also give colour reactions with lignin in the presence of hydrochloric acid, but the 

 colorations in most cases are not so much developed as with phloroglucinol (Czapek, 8). 



It should be noted that strong hydrochloric acid alone will sometimes 

 give a red colour with woody tissues: this is due to the presence of 

 phloroglucinol in the wood itself (see phloroglucinol, p. 102). 



Pecto-cellulose. The non-cellulose constituents in this case belong 

 to the class of pectic substances which have already been considered (see 

 p. Q^). Such celluloses occur in the cell-walls of the tissues of many fleshy 

 roots, stems and fruits. 



Adipo- or cuto-celluloses. These terms have been used for products 

 found in the walls of corky tissue (periderm) and cuticularized tissue 

 (cuticle). More correctly these substances should be termed respectively 

 suberin and cutin, and there is evidence (Priestley, 27) that cellulose is 

 absent from the actual layers of the cell-wall in which suberin and cutin 

 are present. Suberin may be regarded as an aggregate of various con- 

 densation products, or anhydrides, of certain organic acids (the suberogenic 

 acids), accompanied by small quantities of glycerides (true fats) of these 

 same acids. By saponification of the condensation products with alkali, 

 three suberogenic acids have been isolated in a more or less pure state, 

 i.e. phellonic acid, C22H43O3, phloionic acid, C22H40O7 and suberinic acid, 

 C17H30O3. The acids themselves are soluble in the usual solvents for 

 fats; phellonic acid or some of its salts may be soluble or have a tendency 

 to swell in water. The anhydrides, on the contrary, are insoluble in 

 solvents for fats and are totally unaffected by water. 



