OKGANIC CHEMISTRY. 75 



Oxalic Acid gives acidity to the leaf of the wood sorrel (Oxalis 

 acetoselld), and to some other vegetables and fruits. If w^ood be 

 treated with a larger proportion of nitric acid than was employed in 

 the formation of malic acid, and the digestion be protracted, crystal- 

 lized oxalic acid, or the acid of wood sorrel, results. Or if woody 

 fibre be moistened and treated with caustic potash, at a temperature 

 below that at which combustion takes place, hydrogen gas, nearly 

 pure, is evolved, and oxalate of potash is formed. 



Ulmic Acid. — In the common elm, a wound sometimes forms 

 which discharges, in considerable quantities, a thick, brown fluid, 

 containing a peculiar substance, which, from its combining with 

 alkaline and earthy bases, has been denominated ulmic acid. If the 

 last experiment be repeated, with less potash, and at a higher tem- 

 perature, the wood is converted into ulmic acid. 



Thus it appears that woody fibre is convertible, by the action of 

 heat, and other agents, into various acids, possessing very different 

 properties, most of them existing naturally in organized bodies, and 

 one of them as a production of the animal kingdom ; but, by adopt- 

 ing other processes, changes not less singular may be effected. 



Gum. — If dry saw-dust be triturated with concentrated sulphuric 

 acid added slowly, the fibre is gradually destroyed, and a mucilagi- 

 nous fluid is formed. If pure vegetable fibre, or linen, or cotton, 

 be substituted, no carbonization or discolouration ensues, and the 

 mucilage obtained is clear and transparent. The acid may be neu- 

 tralized by chalk, and water added, which will dissolve the gum, 

 and but a very small quantity of the sulphate of lime. The liquid, 

 on evaporation, affords a gum resembling that of the acacia, or gum 

 Arabic. 



Sugar. — If the gum formed in the last experiment be dissolved 

 in water slightly acidulated by sulphuric acid, and the mixture kept 

 at 212° for some hours, the gum will be wholly converted into 

 sugar. The acid may be removed, as in the former instance, by 

 chalk, and the colour by animal charcoal. The liquor being 

 then evaporated to the consistency of syrup, and set aside to 

 crystallize, will afford a crop of sugar exceeding, in weight, the 

 woody fibre employed. M. Raspail assures us that works are 

 established in France for manufacturing sugar by this process : 

 into the acidulated water, heated to the boiling point, starch is 

 thrown, and, in a few hours, is converted into sugar. By the sub- 

 stitution of starch, the conversion of fibre into gum is avoided ; a 

 process which, on the large scale, would be difficult, if not imprac- 

 ticable. 



