CARBOHYDRATES 71 



ing cellulose fibers, which by the way are much shorter 

 than cotton and linen fibers, are sized, loaded, and matted 

 into paper of various kinds. If unsized paper, that is, 

 pure, matted, cellulose fibers, are dipped in fairly strong 

 sulphuric acid for an instant and then plunged into water, 

 the cellulose assumes a tough, parchment-like texture, and 

 is used as a substitute for sheep skin. This material is 

 called "amyloid," since it is starch-like in character, giving 

 a blue color with iodine. 



59. Lignin and Pentosans. — These "encrusting sub- 

 stances" are derived from cellulose apparently, but differ 

 from it in chemical composition. Lignin contains less 

 oxygen than cellulose, and in addition has methyl (CH 3 ) 

 groups present. It is soluble with decomposition in hot 

 dilute alkali, acid sulphite, and some other solvents. It is 

 easily decomposed by chlorine and bromine. It forms a 

 large part of the woody fiber of trees, and hence its name, 

 lignin. Pentosans are compounds of the general formula 

 (C 5 H 8 04)n which are hydrolyzed by acids to pentoses, 

 C5H10O5. Xylan and araban, hydrolyzing to xylose and 

 arabinose, are examples. Pentosans form some 10 per cent 

 of the dry matter of coniferous trees and 20 per cent, of 

 deciduous trees. 



60. Inulin. — (CeHioCW This carbohydrate occurs natur- 

 ally as a storage form of carbohydrate in the roots of such 

 plants as dandelion, dahlia, and chicory. It is derived 

 undoubtedly as are the other anhydride forms of dextrose 

 by a dehydration process: 6C6H12O6 — 6H 2 = (CeHioOsV It 

 is a white, crystalline substance easily soluble in water, 

 insoluble in alcohol. It does not reduce Fehling's solution, 

 and is levorotatorv. It hvdrolvzes under the action of 

 dilute mineral acids and of the enzyme, inulase, to levulose. 

 It is not fermentable. 



61. Gums. — These are amorphous substances of unknown 

 composition, but are probably glucosides of organic acids. 

 They are soluble in water, or at least gelatinize in it, insoluble 

 in alcohol, and hydrolyze with acids to hexoses and pentoses. 

 Gum arable, used in making mucilage, and various wood 

 gums, are examples. 



