190 THE CONSTITUENTS OF PLANTS. IX. 



molecular weight is 1980, corresponding to the formula ahove 

 given. By the action of heat, inulin forms substances similar 

 to the dextrins. 



Levulin, (C (i H 10 5 ) n , occurs associated with inulin in dahlias 

 and artichokes. It is also found in immature grain, particularly 

 in rye and in oak bark. It is an amorphous, deliquescent sub- 

 stance, yielding a mixture of dextrose and levulose by treat- 

 ment with acid. 



Triticin is a similar substance found in couch-grass. Other 

 substances obtained from different sources havabeen described, 

 but their individuality is not very marked. 



Gums, (C r) H 10 5 ) n , are very widely distributed in plants. 

 They are amorphous and either dissolve in water or absorb it 

 and swell up when immersed in it. They are not coloured by 

 iodine, and by boiling with dilute acids they yield sugars, often 

 arabinose or xylose. 



Some of these substances are employed in the arts, e.g., 

 gum arable, the exudation from the bark of several species of 

 acacia. This substance contains 3 or 4% of ash (mainly lime), 

 and as its principal constituent arabin or arabic acid, a 

 white solid soluble in water, of highly complex constitution 

 (C 89 H 142 O 72 or C^HjaoOeg"). Very similar bodies are found in 

 nearly all vegetable tissue. Wood gum, the name given to 

 the substance occurring in wood, the straw of cereals, &c., is 

 a substance of this class. By boiling with dilute acids or 

 alkalies, some gums yield pentose sugars, arabinose, xylose, 

 or lyxose, C 5 H 10 5 . They, therefore, belong to the class of 

 bodies for which the name pentosan has been proposed, of the 

 composition (C 5 H 8 O 4 ) n . It appears! that the effect of boiling 

 arabin with dilute acid is to add gradually the elements of 

 water and to cause the splitting off of a sugar molecule, 

 leaving a residue known as arabinosic acid, which, by further 

 boiling, loses another sugar molecule, giving a lower acid 

 /3-arabinosic acid and so on, until finally an acid of the 

 formula C. 23 H as O 22 is left. 



* O'Sullivan. t O'Sullivan, Jour. Chem. Sue. 18S2, 41. 



