ERYTHROGLUCIC ACID. 181 



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



Erythrogludc Add. 

 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, C n H 2n ~ 2 6 . 



1. Tartaric Add. 

 C 4 H 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 with 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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