2i6 Cellulose 



C m H 3m O m . A second feature of distinction is that, while the 

 ^ 



former yield on hydrolysis hexoses and pentoses, the latter give 

 the series of pectic acids, this distinction corresponding with the 

 higher proportion of oxygen which characterises the group. It 

 is necessary to qualify these conclusions somewhat by pointing 

 out that the empirical formulae determined by the original in- 

 vestigators of these compounds viz. Fremy (Ann. Chim. Phys. 

 [3] 2 4> 5)> Chodnew (Ann. Chem. Pharm. 51, 355) have been 

 called in question by later observers. Thus Reichardt (Archiv 

 d. Pharm. [3] 10, 116) concludes that they are to be regarded 

 as gelatinisable carbohydrates (see Tollens, Kohlenhydrate, 



P- 243)- 



On the other hand it will be found that the pectocelluloses 

 differ from the celluloses by increased proportion of oxygen ; 

 and their acid character is further shown by their retaining 

 a relatively large proportion of basic mineral constituents 

 (ash). 



The general relationships of the group as determined by 

 the earlier observers are these : Pectose, the insoluble mother 

 substance of the group, occurs in mixture or union with the 

 cellulose of the parenchyma of fleshy fruits and roots, e.g. 

 apples, pears, turnips, &c. This is hydrolysed by boiling 

 dilute acids or alkalis, or by a ferment enzyme (pectase) 

 secreted in the tissue, to pectin (C 32 H 48 O 3 2, Fremy), the 

 solutions of which readily gelatinise. By continued hydro- 

 lysis (boiling water) this is further modified to parapectin, 

 and by alkalis to metapectin and parapectic acid and pectic 

 acid (C 32 H 44 O 3 o, Fremy ; C 12 H 16 O n , Regnault ; C 12 H 16 O 10 , 

 Mulder; C 14 H 22 O 14 , Chodnew). 



The final product of hydrolysis is metapectic acid. To 

 this acid Fremy assigned the formula C 8 H 14 O 9 . Later investi- 

 gations have established its general identity with arabic acid 



