158 THE CARBOHYDRATES 



and this substance, together with its potassium salt, gives a 

 red coloration with chlorzinc iodide. This suggests that the 

 coloration of suberized membranes with chlorzinc iodide after 

 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 sup- 

 posed. 



Gilson separated from oak-cork suberic acid (C 17 H 30 O 3 ) and 

 phloionic acid (C n H 2l O 4 ) 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 cork does not contain cellulose, and 

 that the suberin constituents are mostly soluble in chloro- 

 form, and melt at a temperature below 100 C. He concludes 

 that suberin consists of fatty substances with glycerol or 

 other compound esters easily decomposed by potash. 



Gilson's views also find support in the observations of 

 Schmidt,-f- who concludes that suberin and cutin are mixtures 

 of polymerized fatty acids and glycerine-esters. The matter, 

 however, cannot be considered as finally settled. 



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. 



*van Wisselingh: " Chem. Centr.," 1892, ii., 516. 



f Schmidt : " Monatshefte," 1910, 31, 347. 



JSee Cunningham: "J. Chem Soc.." 1918, 113, 173. 



