S6 ELEMENTARY AGRlCtJLTURAL CHEMISTRY 



Parchment paper is another product obtained from cellulose. 

 It is prepared by immersing unsized paper in strong sulphuric 

 acid and then washing it with water. The chief alteration 

 appears to be in the physical propeities. 



By long boiling with dilute sulphuric acid, cellulose — e.g., 

 filter paper, linen or cotton rags — is converted into dextrin and 

 dextrose. 



Similar in many respects to the starches are the bodies 

 known as pentosans, of which arahan and xijlan may be taken 

 as typical. These substances have the composition (C^HgO^)^,, 

 and by boiling with dilute acids yield arahinose or xylose, 

 C^Hj^jOj, sugar-like bodies known under the general name of 

 pentoses. The pentosans are very abundant in many plants, 

 especially in wood-gums (of which they constitute from 60 to 

 92 per cent.), in straw (lG-27 per cent.), bran (22-25 per 

 cent.), brewer's grains (27-31 per cent.), and meadow hay 

 (16-18 per cent.). The pentosans and pentoses are probably 

 not digestible. When treated with strong boiling hydrochloric 

 acid they yield furfurol, C^H^Og ; e.g., 



C^Hj^Oj = C.HgO.CHO + 3H,0. 



Arabinose Fuifurol Water 



Lignose or lignone is another ingredient in the stems 

 and woody portions of plants. It exists in association with 

 cellulose, from which it may be regarded as resulting by the 

 removal of water : 



2C,H,„0, = C,,H,30, + H,a 



Cellulose Ligno-ceilulcse 



The Pectin substances are bodies of unknown constitution 

 which exist as coagulable substances in fruit juices, stems, 

 roots, &c. They resemble the carbohydrates, though whether 

 the oxygen and hydrogen are in the ratio of exactly 8 to 1 

 seems somewhat uncertain. They readily pass into substances 

 which have the power of gelatinising. 



