REACTIONS AND IDENTIFICATION 349 solution. If A gives a marked yellow coloration compared with the control B (particularly when viewed down the length of the tube), then A contains the salt of an a-hydroxyacid (lactic, tartaric or citric): oxalates, however, give a very faint yellow coloration. Isolation of the acid from its salt. (i) If the salt is soluble in water, add cone. HCl to the solution. A pre-cipitate indicates an aromatic acid: filter, wash with cold water, and drain. If no precipitate is obtained, the acid must be aliphatic. (ii) If the salt is insoluble in water, boil with an excess of 10% aqueous Na 8 CO, solution for several minutes and then filter. The residue contains the original metal as carbonate and should be examined in the usual way. The filtrate contains the sodium salt of the acid and an excess of Na 2 CO 3 . Add dil. HCl until distinctly acid to litmus-paper and note any precipitate as in (i). The isolation of an aliphatic acid from its aqueous solution, particularly in
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