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 0 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 4 mirror’ with ammoniacal silver nitrate, reacts with 
phenylhydrazine and hydroxylatnine and is easily oxidized by 
bromine. The product of the action of phenylhydrazine is found 
CH : N 2 HPh 
to be glyoxal osazone | 
CH : N 2 HPh 
and the product of oxidation 
