ACTION OF HEAT UPON TARTARIC ACID. 949 



(Knapp). (3). A salt KO.SbO 3 ,2C 8 H 4 O 10 -f 7HO (Knapp), 

 formed by dissolving together 9 parts of tartar emetic, and 4 

 parts of crystallized tartaric acid, which is very soluble and crys- 

 tallizable. Tartrate of antimony and lead, PbO.SbO 3 ,C 8 H 4 O 10 

 (Dumas), the white precipitate which falls on adding a salt of 

 lead to a solution of tartar emetic, dried at 212. Heated to 

 392, it loses 2 HO, like tartar emetic. 



Action of heat upon tartaric acid. Tartaric acid fuses between 

 266 and 284, and becomes brown at 320. By the action of 

 heat it loses first one fourth, then one half, and finally the whole 

 of the water of its hydrate (Fremy), forming two new acids, 

 the relation of which to tartaric will be best seen by doubling 

 the formula of the latter : 



Anhydrous tartaric acid . . C 16 H 8 O 20 



Tartrelicacid C 16 H 8 O 20 + 2HO 



Tartralic acid C 16 H 8 O 20 3HO 



Crystallized tartaric acid . . C 16 H 8 O 20 + 4HO 



When the solutions of the modified acids are boiled, they are 

 quickly converted into ordinary tartaric acid.* Representing 

 anhydrous tartaric acid by C 4 H 2 O 5 , we have then, for the 

 modified acids, the following formula (Liebig) : 



2(C 4 H 2 O 5 )+2HO . . crystallized tartaric acid. 

 3(C 4 H 2 O 5 ) +2HO . . tartralic acid. 

 4(C 4 H 2 O 5 )+2HO . . tartrelic acid. 



The salts of tartralic and tartrelic acids with alkaline bases 

 are not crystallizable. Anhydrous tartaric acid is produced by 

 keeping the crystallized tartaric acid for some time in an oil 

 bath, at 302 (150 centig.) ; it is insoluble in cold water. 



Tartaric acid yields the two following acids by its destructive 

 distillation : 



Liquid pyrotartaric acid, HO,C 6 H 3 O 5 , which forms a mono- 

 basic ether and other salts. 



Solid pyrotartraric ac^/,HO,C 5 H 3 O 3 (Pelouze), is formed only 

 in small quantity by the distillation of tartaric acid, but in 



* Fremy ; Ann. de Chim. et de Phys. t. 68, p. 353. 



