1 84 Cellulose 



It is therefore established by these results that the furfural 

 yielding constituents of the wood-substance undergo very little 

 change with age. It is necessary to point out that De Chalmot 

 uses the term ' pentosan ' as identical with * furfural-yielding 

 compound,' but this requires some qualification. The forma- 

 tion of furfural is an empirical and an aggregate result, and, 

 while specially characteristic of the pentoses, is also a property 

 of certain oxidised derivatives of the hexoses, notably glycuronic 

 acid. It is probable that the furfural may be formed imme- 

 diately, in this case also from a C 5 derivative, a product of 

 resolution of the glycuronic acid a view which is supported by 

 the observation that the acid when boiled with hydrochloric 

 acid yields carbonic anhydride in quantity corresponding with 

 the equation 



C 6 H 8 O 6 = C 5 H 4 O 2 + CO 2 + 2H. 2 O, 



viz. 26-5 p.ct. CO 2 . The yield of furfural, on the other hand, 

 is only 15*3 p.ct. ; but this discrepancy may very well result 

 from secondary condensations of the C 5 aldose (Mann and 

 Tollens, loc. tit.), in consequence of which only the small pro- 

 portions are decomposed in the second stage according to the 

 equation. 



The import of these qualifying considerations is, perhaps, 

 rather physiological than chemical, showing that a number of 

 minor changes may be taking place in the furfural-yielding 

 groups without affecting their proportion to the lignocellulose 

 as measured in terms of this end-product of their decomposi- 

 tion. 



There is evidence that such changes do take place with age, 

 resulting in the formation of pentosans as such. The dicotyle- 

 donous woods all contain the body known as wood gum (Holz- 

 gummi), which appears to consist, for the most part, of xylaa 

 This substance is extracted by treatment of the ground wood 

 (sawdust) with solutions of sodium hydrate (2-5 p.ct. Na 2 O) in 



