ERYTHROGLUCIC ACID. 181 



B. MONOBASIC, TETRATOMIC ACIDS, C ?l H 2n 5 . 



Erythrogludc Acid. 

 C 4 H 8 5 = C 3 H 4 (OH) 3 CO.OH. 



Is produced when a solution of erythrite, to which 

 is added platinum black, is allowed to stand in contact 

 with the air for a long time ; and by the action of 

 nitric acid on erythrite. Crystalline, very deliquescent 

 mass. 



C. BIBASIC, TETRATOMIC ACIDS, OH 2n - 2 6 . 



1. Tartaric Acid. 

 OH 6 6 = C 2 H 2 (OH) 2 1 QO OH 



Occurrence and formation. Most particularly in 

 grape-juice. The crude tartar, which is deposited from 

 new wine, is potassium bitartrate. It is formed by 

 boiling several salts of dibromsuccinic acid, especially 

 the silver salt, with water ; and, in small quantity, by 

 the oxidation of the carbohydrates with nitric acid, in 

 company w T ith saccharic and mucic acids. 



Preparation. Purified tartar, in the form of a fine 

 powder, is mixed with one-quarter its weight of finely 

 pulverized chalk, and the mixture gradually thrown 

 into boiling water in small portions.- By this means 

 the tartar is decomposed, forming neutral potassium 

 tartrate, which remains in solution, and in calcium 

 tartrate, which is thrown down as a white insoluble 

 powder. By means of a solution of calcium chloride 

 the neutral potassium salt is, in its turn, converted 

 into calcium tartrate. From the calcium salt the tar- 

 taric acid is separated by digesting with dilute sul 

 phuric acid, the calcium sulphate filtered off, and the 

 solution of the acid evaporated to crystallization. 



Properties. It crystallizes in clear, oblique, rhombic 



prisms, of a strongly acid taste ; it is inodorous and 



easily soluble in water. Its solution rotates the plane 



of polarization towards the right ; the solution of the 



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