The determination of lignin

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Abstract
I. Certain sugars, particularly xylose and fructose, and, because of its fructose content, sucrose, to a slight extent arabinose, and polysaecharides containing pentose sugars, give an insoluble residue on standing with 72% H2SO4 and increase the apparent lignin figure when added to plant materials, the disturbance being small at 2 hrs. contact, but increasing with the time of contact. In plant materials the effect of the presence of xylose in the hemicellulose may be almost excluded by a hydrolytic pretreatment with dilute mineral acids, or minimized by reducing the time of contact to 2 hrs. The disturbance due to pentose is caused by the slow production of fur-furaldehyde and its condensation with lignin to form an insoluble phenol-furfuran resin.[long dash]II. Proteins alone give no precipitate on standing with 72% H2SO4 but added to plant materials, increase the apparent lignin content. The magnitude of the disturbance produced is different if the material is subjected to a hydrolytic pretreatment. If xylose and protein are treated together with 72% acid, insoluble precipitates are formed when the protein present is small in amt. Increasing quantities of protein give yields of precipitate diminishing to none. Small additions of protein cause a greater disturbance proportionately than do larger amts. The protein disturbance is probably due to the linkage of protein fission products with lignin. Direct linkage between protein and lignin is unlikely because the ratio (increment produced/N present) is very variable. Calculating the N in the lignin as protein and subtracting is useless, and in some cases likely to introduce a greater error.