226 ACIDS. 



thrown out of solution, softens on warming and aggregates to a 

 mass, Avhich becomes granular and crystalline on cooling. The 

 magnesia-reaction, mentioned by the same author as a new one, 

 consists in converting into malate of magnesia either by saturating 

 the acid with oxide or carbonate of magnesia, or by mixing a con- 

 centrated solution of an alkaline malate with chloride of mag- 

 nesium. The salt is precipitated b}'^ spirit from a hot solution, 

 as a tenacious mass hardening on cooling. (Citrate of magnesia 

 behaves in a similar manner.) 



Barfoed sejjarates onalic from oxalic (§ 219) and tartaric (§ 217) 

 acids by i^recipitating the last two from neutral solution by chloride 

 of calcium, and throwing out malate of calcium from the filtrate 

 by the addition of alcohol. If tartaric acid is present, it must be 

 remembered that the calcium-salt of this acid separates but slowly. 

 (See also §218.) 



In separating citric (§ 215) from malic acid the same chemist 

 takes advantage of the fact that citrate of calcium requires less 

 spirit for precipitation than malate. 



If malic acid is in solution with oxalic, tartaric, and citric acid, 

 Barfoed advises the precipitation of the last three as neutral am- 

 monium salts by the addition of 7 to 8 volumes of 98 per cent, 

 spirit ; after standing twelve to twenty-four hours the precipitate 

 is filtered off, and the malic acid thrown down in the filtrate with 

 acetate of lead. 



Succinic acid (§ 220) can be separated from 7naUc acid, according 

 to Bai'foed, by converting into neutral alkaline salts, precijiitating 

 with acetate of lead, dissolving the precipitate in acetate of ammonia 

 solution, and then separating the malate of lead by the addition 

 of 2 volumes of spirit ; or the concentrated aqueous solutions of 

 the neutral potassium, or sodium-salts, may be mixed with about 

 6 volumes of spirit, when the succinate remains in solution. 



For the separation of malic acid from gallotannic (§§ i9 et seq. 

 and IGo), gallic (§ 151), henzoic (§ 26), acetic and formic (§ 139), 

 acid, reference must be made to the original work. 



To remove sulphuric and 'phosphoric acids from solutions in which 

 malic acid is to be detected, Barfoed recommends separating the 

 first two by the addition of chloride of barium to the hot solution, 

 and precipitating the malate of barium from the filtrate by the 

 addition of alcohol. 



§ 215. Eslvmation of Citric Acid. — In estimating citric acid, Creuse 



