76 ORGANIC AGRICULTURAL CHEMISTRY 



Tartaric Acid {Di-hydroxy-succinic acid) 



Just as we make malic acid from succinic acid through the 

 mono-brom-succinic acid so by converting succinic acid into 

 the symmetrical di-brom-succinic acid we obtain by means of 

 silver hydroxide, Ag(OH), tartaric acid which has, therefore 

 the constitution of symmetrical di-hydroxy-succinic acid. 



CH2-COOH CHBr-COOH CH(OH)-COOH 



I +2Br2^2HBr+ | +2Ag(0H)->| 



CH2 - COOH CHB r - COOH CH (OH) - COOH 



Succinic acid Sym. di-brom- Tartaric acid 



succinic acid Sym. di-hydroxy- 



succinic acid 



Tartaric acid is found naturally in the free condition and as 

 salts in certain fruits, especially in grapes. Being a dibasic 

 acid containing two carboxyl groups or two acid hydrogens, it 

 forms salts with either one or both of these hydrogens replaced 

 by metals. 



CH(OH) - COOH CH(OH) - COOK CH(OH) - COOK 



CH(OH) - COOH CH(OH) - COOH CH(OH) - COOK 



Tartaric acid Mono-potassium tartrate Di-potassium tartrate 



(Acid potassium tartrate) (Neutral potassium tartrate) 



The mono-potassium tartrate or (acid potassium tartrate) 

 is the form in which it occurs in grapes and from which source 

 it is commercially obtained. When grape juice is fermented 

 in preparing wine, there settles out an insoluble material con- 

 sisting largely of impure acid potassium tartrate and known as 

 argol or crude tartar, the purified acid potassium tartrate being 

 known as cream of tartar. The crude tartar is separated, re- 

 crystallized from hot water, converted into the wholly insoluble 

 calcium salt and then back into the free tartaric acid which is 

 then pure. Tartaric acid as thus obtained forms large trans- 

 parent crystals readily soluble in water or alcohol. Several 

 of the salts of tartaric acid are commonly in use either in cook- 

 ing or in medicine. They are as follows : 

 J Cream of Tartar, Acid Potassium Tartrate. — This salt of tar- 

 taric acid, the formula of which has just been given, is the form 



