1'28 ACIDS. 



formerly made to the effect that citric acid was difficultly soluble 

 in ether. 



§ 217. Precipitation of Tartaric Add (§ 82).— As early as 1864, 

 Berthelot and de Fleurieu precipitated tartaric acid by converting 

 it into acid tartrate, and adding 5 volumes of ether-alcohol. ^ 

 Jokisch and Bolley^ have shown that acid tartrate of calcium may 

 be simultaneously thrown down. 



For the estimation of the total acid in must, see Pasteur. •' 



Martenson* precipitates tartaric acid from a 1 per cent, aqueous 

 solution of normal tartrate of potassium by the addition of chloride 

 of calcium and lime-water. The sides of the porcelain dish in 

 which the operation is performed should not be touched by the 

 stirring-rod. On standing for several hours, the calcium-salt 

 separates in crystals, and can be filtered off, washed with 80 to 

 85 per cent, spirit, dried at 100° and Aveighed ; its composition is 

 then CaCH.Oe, m.O. 



§ 218. Estimation of Tartaric and Citric Acid. — Fleischer recom- 

 mends the separation of the former as acid tartrate of potassium, 

 the precipitation being rendered complete by the addition to the 

 solution of twice its volume of 95 per cent, spirit. The acid 

 tartrate is filtered off", redissolved, and estimated by titration with 

 normal alkali (§ 82). 



The citric acid is i:)recipitated from the filtrate by neutral acetate 

 of lead, washed with spirit of about 45 to 50 per cent., liberated 

 by sulphuretted hydrogen, and estimated by titration with normal 

 alkali. 



This method is directly applicable if the acids are present in 

 the free state, or in comlünation with alkalies. '-^ 



^ Comptes rendus, Ixxvii. 394. 



- Dingler's polyt. Journ. clxxxiii. 47, 1867 (Amer. Jonrn. Pharm, xxxvi. 60). 

 See also Kissel, Zeitschr. f. anal. Chem. viii. 409, 1869. 



^ Zeitschr. f. anal. Chem. viii. 86, 1869. 



* Pharm. Zeitschr. f. llussland, viii. 23, 1868 (Amer. Journ. Pharm, xli. 335). 



•^ See also Schnitzer, Dinyler's polyt. Jonrn. clxiv. 132, 1862, on the sejiara- 

 tion of tartaric from citric acid as acid tartrate. 



Should it appear desirable to estimate the citric acid directly, after removal 

 of the tartaric as acid tartrate of potassium, the filtrate may be mixed vtiih 

 chloride of calcium and concentrated by boiling. The citrate of calcium that 

 separates after adding lime-water .should be filtered off hot, washed with boil- 

 ing water, dried and weighed (2.08 parts of the dried salt indicate 192 of citric 

 acid). See also Allen, Zeitschr. f. anal. Chem. xvi. S.^Jl, 1877. 



For distinctive characters of tartaric and citric acid, see Archiv d. Pharm, 

 clviii. 206, 18G1 ; Chapman and Smith, Laboratory, April, 1868 ; Wimmel, 

 Zeitschr. f. anal. Chem. vii. 411, 1868. 



