LIGNIN 223 



this is conspicuously so, since the material isolated from the 

 so-called sulphite liquors contains sulphur and is, in fact, a 

 sulphonic acid derivative of lignin ; in the case of the alkaline 

 process, the lignin is less obviously altered. Most of the 

 attempts made to elucidate the constitution of lignin have been 

 carried out on material isolated by these two methods or else 

 by concentrated hydrochloric acid. At first sight it appears 

 strange that attempts to determine the constitution of such 

 a complex substance as lignin should be made upon material 

 which had undergone such drastic treatment, but this is 

 explained by the fact that as yet no gentler methods have 

 succeeded in separating lignin from cellulose. 



In spite of the considerable literature on the subject com- 

 paratively little is definitely known regarding the constitution 

 of this substance. The following facts are generally accepted : 

 the presence of hydroxyl methoxyl and acetyl group ; the 

 presence of an aldehyde or ketone group as is shown by the 

 ability to react with hydroxylamine, while evidence of un- 

 saturation is revealed by its ability to absorb iodine or bromine 

 and the readiness with which it is oxidized by ozone, nitric 

 acid ; furthermore, it appears fairly certain that some of the 

 methyl groups are attached to phenolic hydroxyl groups and 

 some are not. 



Lignin Isolated by the Bisulphite Process. 



Klason,* who worked on lignin isolated from wood by the 

 sulphite process, and which consequently contained more 

 or less combined sulphur, came to the conclusion that 

 lignin exists in two forms in spruce wood, namely a-lignin 

 which contains the acrolein group — CH = CH . CHO, and 

 jS-lignin which contains the corresponding acrylic acid group 

 — CH — CH . COOH in the proportions 63 : 37 per cent, 

 Klason has shown that a-lignin contains two methoxyl groups, 

 one phenolic and one alcoholic hydroxyl, and comes to the 

 conclusion that it has been formed from 2 molecules of 

 coniferyl aldehyde to produce a compound of the constitution 



* Klason : " Ber. deut. chem. Gesells.," 1923, 56, 300. 



