Mr Fenton, Oxidation in Presence of Iron. 361 



The stability of this acid is much greater than would be 

 expected from its remarkable constitution, and the dry substance 

 may be heated to 90° without loss of weight. 



Preparation of Tartronic Acid. 



An aqueous solution of dioxy tartaric acid when heated on a 

 water-bath to about 60 — 70° decomposes quantitatively into 

 tartronic acid and carbon dioxide 



C 4 H 6 8 = C 3 H 4 5 + H 2 + C0 2 , 



and after concentration of the solution by evaporation the acid is 

 obtained in a pure state in the form of long transparent prisms. 

 This reaction affords probably the simplest and most direct method 

 for the preparation of tartronic acid. 



The affinity-constant of tartronic acid as previously determined 

 was abnormal, being smaller than that of malonic acid ; but 

 Skinner [Trans. Chem. Soc. 1898. 489] taking advantage of this 

 new method of preparation, has redetermined the value and 

 obtains the number 0'5, that of malonic acid being 0'158. 



Salts of dioxytartaric acid and separation of the alkali metals. 



Hitherto the only metallic salt of this acid which was known 

 with certainty was that of sodium, the barium salt of Barth 

 [Sitz. Acad. Wien, 82. ii. 1024] being of doubtful composition. 

 Having now command of the free acid in quantity a further study 

 of the salts was undertaken. Especially interesting is a com- 

 parison of the solubilities of the alkali-metal dioxy tartrates, all of 

 which are easily obtained by neutralization of the free acid with 

 the respective carbonates. The ratio of the solubilities of these 

 at 0° is as follows — ■ 



Li : Na : K : Kb : Cs = 2 : 1 : 66 : 166 : 576, 



and it is evident therefore that the differences might be made use 

 of in separating the alkali metals. 



Calcium dioxytartrate, obtained by adding calcium chloride to 

 a soluble dioxytartrate, is a remarkable substance, being obtained 

 in the form of a perfectly colourless transparent jelly. 



Quantitative Estimation of Sodium. 



Sodium dioxytartrate is probably the least soluble sodium salt 

 known, its solubility at 0° being 0039. Since no direct method for 

 the quantitative estimation of sodium had hitherto been known, 

 experiments were made with a view of devising such a method 

 by the use of dioxytartaric acid. The free acid gives a partial 



