136 THE CARBOHYDRATES 



treatment with potash is due to the presence of potassium 

 phellonate and not to cellulose, for, in addition, the coloration 

 does not take place if the corky tissue be subjected to the 

 action of boiling alcohol after treatment with potash. 



3. After treatment with cuprammonia, the chlorzinc iodide 

 gives a yellowish-brown colour ; this, according to Gilson, is 

 due to the alteration of potassium phellonate into the copper 

 salt, and not to the removal of cellulose, as had been supposed. 



Gilson separated from oak-cork suberic acid (Cj-Hgi^Oa) and 

 phloionic acid (CiiH2i04) in addition to phellonic acid. He 

 does not think that these occur as true glycerine esters, since 

 the suberin walls are insoluble in all fat-solvents, and do not 

 melt at a temperature below 290° C. 



These observations have been supported by Van Wisse- 

 lingh,* who finds that the suberin constituents are mostly 

 soluble in chloroform, and melt at a temperature below 

 100° C. He concludes that suberin consists of fatty substances 

 with glyceryl or other compound esters easily decomposed by 

 potash. 



CONSTITUTION OF CELLULOSE. 



The following characteristics of this substance throw some 

 light on the constitution of cellulose : — 



1. On hydrolysis it yields dextrose. 



2. On partial hydrolysis it sets free — CO groups which 

 are present in some suppressed form in ordinary unchanged 

 cellulose. 



3. The fact that on destructive distillation it yields acetic 

 acid and methyl alcohol points to the presence in the molecule 

 of a — CH2 — CO — ■ grouping. 



4. It is a very stable substance, which resists alkalis, 

 oxidizing agents, and, to some extent, acetylation, except in 

 the presence of a condensing agent, such as zinc chloride or 

 sulphuric acid. 



5. With strong acids it yields esters, e.g. nitrates, acetates, 

 and benzoates. 



6. It undergoes the thio-carbonate reaction by treating 



* Van Wisselingh: "Arch. Neerland.," 1893, 26. 



