OXIDATION OF CANE SUGAR BY NITRIC ACID 599 



in the retort be then poured into a larger vessel, and upon 

 cooling small quadrilateral prismatic crystals are found adher- 

 ing together at an angle generally of about 45°. These, col- 

 lected and weighed on bibulous paper, weigh 109 grains." 



Apparently no more detailed account of the preparation 

 of oxalic acid by this method, or of the yield obtained, was 

 published until Thomson, some eighty years later, re-investi- 

 gated the action and described what he found to be the most 

 advantageous procedure. For nearly another eighty years 

 little further attention has been given to the subject, and 

 oxalic acid has been generally regarded as the sole end-product. 



It might have been thought, from the number of times 

 sugar has been oxidised for the preparation of oxalic acid 

 and from the number of chemists who at different times 

 have carried out the operation, that nothing remained to 

 be discovered regarding it. This, however, is not the case, 

 for recently it has been found that the comparatively little- 

 known mesoxalic acid is formed in considerable quantity in 

 the reaction, which in fact is the most convenient method of 

 obtaining this somewhat rare compound. 



Mesoxalic acid is easily recognised, being a ketonic acid 

 and forming a well-characterised hydrazone with any aromatic 

 hydrazine, and it can easily be isolated by taking advantage 

 of the very sparing solubility in water of its sodium salt. 

 About 10-12 grams of sodium mesoxalate are thus obtainable 

 from 100 grams of cane sugar. Other carbohydrates such as 

 dextrose, levulose, milk and malt sugars, and starch, also yield 

 large quantities of mesoxalic acid when similarly violently 

 oxidised by strong nitric acid. 



