361 
Mr Fenton, Oxidation in Presence of Iron. 
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 0 8 = C 3 H 4 0 5 + H 2 0 + 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 0T58. 
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. 
Haviug 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 : Rb : 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 dioxy tartrate, 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 0 039. 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 
