§§ 215, 216. CITRIC ACID. 227 



takes advantage of the iusolulDÜity of the barium-salt in spirit. 

 To a neutral solution of the citrate a solution of acetate of barium 

 and 2 volumes of spirit are added. The precipitate is filtered 

 off, ignited, converted into sulphate by sulphuric acid, and weighed 

 as such. The composition of citrate of barium is said to be 

 BagCioHioOiv (Compare Zeitschr. f. anal, Chem. xi, 446, 1871.)^ 



Precipitation by barium had been previously recommended by 

 Kämmerer as a means of detecting citric acid. - If to a solution 

 of a citrate excess of acetate of barium is added, a voluminous 

 precipitate is obtained, which gradually becomes crystalline 

 (prisms) when heated for several houi's on the water-bath. The 

 presence of other fruit-acids does not interfere. If the solu- 

 tion is very dilute it must be concentrated after the addition of 

 the barium salt, as otherwise only acicular crystals are produced. 

 See further §§ 218 to 220. 



§ 216. Qualitative Reactions of Citric Acid. — Sarandinaki has 

 drawn attention to the fact that the triethylic ether of citric acid 

 decomposes when heated in sealed tubes to 110°, with separation 

 of a blue powder;^ and that an aqueous solution of citrate of 

 ammonium, similarly treated for six hours, also deposits a blue 

 decomposition-product on subsequent exposure to air and light in 

 a flat dish. Sabanin and Laskowsky^ have shown that neither 

 tartaric, malic, nor oxalic acid interferes with the reaction which 

 succeeds with O'Ol gram of citric acid. Aconitic acid comports 

 itself like citric. If the juice of a fruit or a vegetable infusion is 

 under examination, the citric acid can be precipitated as citrate of 

 lead, the latter converted into citrate of barium, and finally into 

 citrate of ammonium, which can be tested as above described. 



It may also be observed that an aqueous solution of citric acid 

 is optically inactive. According to Eoennefahrt, 100 parts of 

 ether dissolve 10 parts of the crystallized and 13 of the anhydrous 

 acid, and can remove as much as 3 "6 parts when shaken with an 

 aqueous solution ; facts scarcely in accordance with the statement 



^ For quantitative estimation of tartaric acid, see also Inette, Comptes 

 rendus, Ixvi. 417, 1868. 



" Annal. d. Chem. und Pharm, cxlviii. 294, and Zeitschr. f. anal. Chem. 

 viii. 298, 1869. 



^ Ber. d. d. chem. Ges. 1100, 1872. Compare also Kämmerer, ibid. 736, 

 1875 (Journ. Chem. Soc. xxix. 496, xxviii. 1178). 



^ Zeitschr. f. anal. Chem. xvii. 73, 1878 (Year-book Pharm. 165, 1878). 



15—2 



