LIGNIN 2IO 



better represented in the soft woods where they occur to 

 the extent of about 13 per cent, whereas 3-5 per cent is 

 the average for hard woods. Amongst the hexosans of the 

 gymnosperm are mannan, which varies very considerably in 

 amount averaging from 4'5-8 per cent, and galactan, which 

 varies from 8 up to as much as 17 per cent ; the occurrence 

 of a high percentage of galactan is characteristic of coniferous 

 wood, and actually this material has been commercially ex- 

 ploited as a source of mucic acid by oxidation with nitric acid.* 

 A method for the analysis of the various constituents of 

 wood mentioned above has been worked out by Dore.f 



CHEMISTRY OF LIGNIN. 



Lignification is easily detected by certain colour reactions 

 which readily distinguish lignified from unlignified tissue ; of 

 these the two following may be regarded as the most generally 

 useful : — 



(a) The yellow colour produced when lignified tissue is 

 treated with a solution of i per cent aniline sulphate or hydro- 

 chloride acidified with the corresponding acid. 



(b) The bright crimson produced on treatment of lignified 

 tissue with a dilute alcohoHc solution of phloroglucinol fol- 

 lowed by a little concentrated hydrochloric acid. 



The aniline employed in the first test may be replaced by 

 a great many other primary or secondary amines or even by 

 heterocyclic nitrogen bases such as pyrrol or indol, while the 

 phloroglucinol of the second test may be replaced by a number 

 of phenols both monohydric and di- or tri-hydric, but the 

 colours obtained are not all the same and vary in intensity. 



Some wood, notably that of the cherry, when moistened 

 with hydrochloric acid alone gives a red or violet colour ; 

 the fact that an aqueous extract of this wood gives with 

 lignified tissue a red colour on addition of acid, suggests 

 that cherry wood contains some phenolic substance capable 

 of replacing phloroglucinol in the test mentioned above ; it 



* Schorger and Smith : " J. Ind. Eng. Chem.," 1919, II, 556 ; 1920, 

 12, 264, 472, 476, 984. 



+ Dore : id., 1919, 1 1, 556; 1920, 12, 264, 472, 476, 984. 



