230 



ACIDS. 



Both tartaric and racemic acids are easily soluble in water and 

 alcohol. See also 219, 220. 



219. Separation of Oxalic Acid. Of the acids above referred 

 to, oxalic acid (81, 214, 216, 218) splits up, when heated, into 

 water, carbonic acid, and carbonic oxide without separation of 

 carbon. It undergoes a similar decomposition when warmed with 

 concentrated sulphuric acid. In addition to the reactions already 

 described, it must be observed that a neutral solution of an oxalate 

 throws down bright yellow crystalline ferrous oxalate, when warmed 

 or allowed to stand, with a solution of a ferrous salt. According 

 to Barfoed, 1 the precipitate is soluble in about 4,000 parts of cold 

 water, but tolerably easily in solutions of oxalates, tartrates, and 

 citrates of the alkalies. The reagent must therefore be added in 

 sufficient quantity to convert the whole of the vegetable acids 

 present into salts of iron. 



Tartaric acid, if present, might also yield a crystalline precipitate, 

 but the colour would be dirty-white and the crystals would be 

 distinguishable under the microscope ; it might be separated by 

 cold, very dilute hydrochloric acid, in which the oxalate is almost 

 insoluble. Citric acid delays the precipitation, and frequently 

 prevents the formation of characteristic crystals, which, however, 

 may be obtained by dissolving in a little warm hydrochloric acid 

 and neutralizing with ammonia. 



Oxalic acid can be isolated from oxalate of calcium ( 110) for 

 the purposes of further identification by dissolving in hydro- 

 chloric acid, and adding sufficient sulphuric acid to convert into 

 sulphate, which can then be completely precipitated by the 

 addition of an equal volume of spirit. Or the oxalate may be 

 dissolved in the smallest possible quantity of dilute nitric acid, pre- 

 cipitated with nitrate of lead, and liberated from the lead-salt by 

 sulphuretted hydrogen. (Of. 81, 218, 220, where the estimatioi 

 of oxalic acid is discussed.) Oxalic acid requires 10 parts of cold 

 water for solution, but only 2 parts of alcohol. 



220. Succinic Acid ( 214) is also one of those organic com- 

 pounds that are not blackened by concentrated sulphuric acid, 

 and leave no carbonaceous residue when heated on platinum foil, 

 or in a test-tube. In the latter case the major part is volatilized 

 without decomposition. It differs from oxalic acid in being less 

 soluble in cold water (about 1 in 15 at 20), and in being spar- 

 1 'Lehrb. d. org. qual. Analyse,' Copenhagen, 1880. 



