74 Mr Fenton, Soluble forms of metallic dihydroxy tartrates. 



throwing further light upon this question and in the present 

 communication a short preliminary account is given of some 

 experiments which have been made with regard to the conditions 

 under which the salts can be formed. 



All the metallic dihydroxytartrates which have so far been 

 examined contain water of crystallization which is not expelled 

 when the salt is kept in a vacuum desiccator, and any attempt at 

 removal of the water by heat is attended with decomposition of 

 the salt. It appeared therefore to be a matter of interest to 

 ascertain the nature of the salts produced from solvents other 

 than water. 



When solutions of the free acid and sodium ethylate in 

 absolute alcohol are mixed together a semi-transparent gelatinous 

 precipitate is obtained which, when collected and washed with 

 alcohol, is very easily soluble in cold water. This result is re- 

 markable when it is remembered that the sodium salt prepared 

 from aqueous solutions is a heavy white crystalline powder almost 

 insoluble in water ; its solubility is in fact so slight that it serves 

 for the qualitative and quantitative estimation of sodium (Fenton, 

 loc. cit. 167). 



The aqueous solution of this soluble sodium salt after standing 

 for a few minutes begins to deposit the ordinary sparingly soluble 

 form of sodium dihydroxytartrate. By titration of the free acid 

 with sodium ethylate in absolute alcoholic solution it is found 

 that the ratio of acid to metal is the same in the soluble salt as 

 in the ordinary form, but it has not yet been found possible to 

 determine the composition of the soluble salt in the isolated 

 condition. When kept in a vacuum desiccator over sulphuric acid 

 it dries up to a white amorphous powder but at the same time 

 suffers a certain amount of decomposition ; it is still extremely 

 easily soluble in water but the aqueous solution effervesces with 

 dilute acids and gives a smaller yield of the insoluble salt on 

 standing. 



It was at first thought probable that the soluble form might 

 be a salt of the diketo-acid COOH . CO . CO . COOH, but analysis 

 shews that the dried product still contains hydrogen, the results 

 being 



C 2518, H 247, Na 24*2 per cent. 



The normal sodium salt of the diketo-acid would require 



C 25-26, Na 24-21 per cent. 



It is probable therefore that the dried product is a mixture of 

 this salt with some tartronate and carbonate. 



When dihydroxytartaric acid, or one of its soluble salts, is 

 mixed with calcium chloride in aqueous solution the mixture 

 almost immediately sets to a transparent colourless jelly, so that 



