CITRIC ACID. 945 



crystallized citric acid is gently heated with 4 parts of oil of 

 vitriol, a considerable quantity of carbonic oxide is evolved, and 

 acetic acid is formed. When fused with an excess of hydrate 

 of potash, citric acid is decomposed into oxalic and acetic acids ; 

 1 atom of citric acid containing the elements of 2 atoms of 

 acetic acid, 2 atoms of oxalic acid and 2 atoms of water. 



Citrates. The neutral salts of citric acid, besides 3 atoms 

 of fixed base, carry along with them the atom of water of 

 acid hydrate A ; which water however they either abandon at the 

 ordinary temperature, like the citrate of silver, or at a high 

 temperature. In certain subcitrates this atom of water is re- 

 placed by an atom of metallic oxide, such as lime or oxide of 

 lead. The composition of these salts has received considerable 

 attention. The following are the formulae of the most re- 

 markable citrates : 



Citrates of potash : three salts exist containing as base res- 

 pectively, 3KO; 2KO + HO; and KO + 2HO. Citrates of 

 soda: salt A, 3NaO,C 12 H 5 O n + 1 1HO (Berzelius) ; loses 7HO 

 at 212, and the remaining 4 HO between 3/4 and 392 (190 

 and 200 centig.). Salt J5, 2NaO.HO,C 12 H 5 O n . Salt C, 

 NaO.2HO,C 12 H 5 O n . Citrate of barytes t 3BaO,C 12 H 5 O n + 

 7HO (Berzelius) ; loses 6HO at 302 and becomes anhydrous 

 at 374 . Another citrate of barytes appears to be a compound 

 of the preceding salt, with 2BaO.HO.C 12 H 5 O n , its empyrical 

 formula being 2C 12 H 5 O n + 5BaO + 8HO. Citrate of lime, 

 3CaO,C 12 H 5 O n +4HO (Berzelius) ; it loses 3HO at 212, and 

 the remaining HO at a higher temperature. The subcitrate of 

 lime lately mentioned loses HO at 212. Citrates of lead: 

 salt A, 3PbO,C 12 H 5 O n + HO. Salt JB, 2PbO.HO,C 12 H 5 O n 

 + 2HO. Salt C, 3PbO,C 12 H 5 O n +3PbO. Salt D, 3PbO, 

 C 12 H 5 O n + PbO,HO. Citrate of copper, 3CaO,C 12 H 5 O u -f 

 CaO. Citrate of silver, 3AgO,C 12 H 5 O n + HO ; loses HO 

 between 68 and 77 Citrate oi antimony and potash, 

 SbO y C lt2 VL 5 O ll +3KO ) C lt2 U 5 O u +5UO (Thaulow) 5 it crys- 

 tallizes in prisms of a brilliant whiteness which lose their 

 whole water of crystallization at 212. Citrate of ethyl 

 3EO,C 12 H 5 O U . (Liebig's Traite, ii, 45.) 



Aconitic acid, HO + C 4 H 2 O 3 . When crystallized citric acid 

 is heated, it fuses, gives off water, but undergoes no essential 

 change till inflammable gases are disengaged, and afterwards an 



2 Q Q 



