Compound Celluloses 187 



Wood gum was first isolated and investigated by 

 T. Thomsen (J. Pr. Chem. [2], 19, 146), and Poumarede and 

 Figuier (Annalen, 64, 388). It is obtained from the woods of 

 the ash, elm, oak, beech, willow, cherry, &c., by digestion with 

 solutions of the alkaline hydrates as already described. The 

 following particulars of later investigations by Wheeler and 

 Tollens (Landw. Vers.-Stat. 39, 437) are noteworthy. After 

 extraction from beech wood, and precipitation by alcohol, the 

 product is purified by digestion with alcohol and hydrochloric 

 acid, and washing first with alcohol and then ether. It is ob- 

 tained thus as a white powder. In alkaline solution it exhibits 

 strong laevo-rotation (a)D = 6^'6. The yield is approxi- 

 mately 15 p.ct. of the wood. Hydrolysed with boiling acids it 

 gives a large yield of crystallisable xylose. Cherry wood under 

 the same treatment yields 12-13 P- ct - f tne product, also 

 yielding xylose as the chief product of acid hydrolysis. It is 

 noteworthy, on the other hand, that ' cherry gum,' the well- 

 known exudation from the tree, yields the isomeric pentaglucose 

 arabinose as the chief product of hydrolysis. 



The cereal straws also yield, under similar treatment, 14-17 

 p.ct. of the product, but retaining a large proportion of the in- 

 organic constituents of the straw, chiefly silica. This product 

 shows a stronger rotation, viz. (a) D = 84-1. With the aid of 

 heat in the alkaline digestion, a much larger yield of the pro- 

 duct (26 p.ct.) is obtained. 



Wood gum is insoluble in cold water, but slowly dissolves on 

 boiling with water ; on cooling, the solution is strongly opal- 

 escent ; but on the addition of alkali in small proportion, a per- 

 fectly clear solution is obtained. The compound is insoluble in 

 aqueous ammonia, and, in the process of isolating it, the raw 

 materials are therefore usually subjected to a preliminary diges- 

 tion with dilute ammonia, which removes colouring matters, &c. 



Numerous (elementary) analyses of wood gum have given 



