362 Mr Fenton, Oxidation in Presence of Iron. 



precipitation even with the sodium salts of strong acids, such as 

 sodium chloride or sulphate, and the precipitation is completed 

 by neutralization with ammonia or potassium carbonate ; but 

 since the dioxytartrates of ammonium and potassium are also 

 sparingly soluble, the best method was found in using a solution 

 of the potassium salt itself as precipitant. The latter is added in 

 excess to a neutral solution of the sodium salt to be estimated 

 and the mixture kept at 0° for about half an hour with occasional 

 stirring; under these conditions a complete precipitation of 

 sodium occurs. Instead of weighing the sodium dioxytartrate the 

 simplest method is to dissolve it in excess of dilute sulphuric 

 acid and titrate with potassium permanganate, the reaction being 

 sharp and definite at the ordinary temperature and taking place 

 according to the relation — 



C 4 H 6 8 + 30 = 4C0 2 + 3H 2 0. 



This volumetric method gives excellent results if carefully per- 

 formed. [Compare Sutton, Volumetric Analysis, 8th Edition, 

 p. 66.] 



Potassium dioxytartrate forms a most convenient and delicate 

 reagent for the qualitative detection of sodium and easily in- 

 dicates the presence of one part of sodium in about 2000 parts of 

 water. 



Glycollic Aldehyde or Diose. 



CH 2 OH 



I 

 CHO. 



[Trans. Chem. Soc. 1895. 774.] 



Dioxymaleic acid is, as above stated, sparingly soluble in cold 

 water ; it dissolves easily in warm water but the solution is very 

 unstable ; decomposition begins even at the ordinary temperature 

 and at 50 — 60° carbon dioxide is rapidly evolved. When the 

 decomposition is complete it is found that approximately two 

 molecules of carbon dioxide are evolved from one molecule of the 

 acid, and the resulting liquid has very powerful aldehydic 

 properties. It instantly restores the colour to Schiff's reagent, 

 gives a silver ' mirror' with ammoniacal silver nitrate, reacts with 

 phenylhydrazine and hydroxylamine and is easily oxidized by 

 bromine. The product of the action of phenylhydrazine is found 



CH : N 2 HPh 

 to be glyoxal osazone | and the product of oxidation 



CH : N 2 HPh 



