Yi] THE VEGETABLE ACIDS 85 



Glutaric and adipic acids have been detected in extracts from the 

 root of the Sugar Beet (Beta vulgaris var. Rapa). It is probable that 

 they also occur in other plants. The relationship of glutaric acid to 

 glutaminic acid is important (see p. 134). 



Of the monohydroxy-dibasic acids, malic acid is the best known. 



Malic acid. It should be noted that in constitution malic acid is a 

 hydroxy -succinic acid. It is widely distributed in plants, being found 

 in many fruits, such as those of the Apple, Pear, Cherry, etc. ; also in 

 leaves and vegetative parts, especially in some succulents (Crassulaceae, 

 Mesembryq^nthemum). 



Malic acid crystallizes in colourless needles which are very deli- 

 quescent and hence difficult to obtain. Its salts with the alkali metals 

 are soluble. Calcium malate is only precipitated from a very concentrated 

 solution of the acid (after neutralization) or of a soluble malate. Very 

 few well-defined tests can be made for malic acid. 



Bxpt. 84. Tests for malic acid. A. Take a 2 o/q solution of malic acid, neutralize 

 with caustic soda (or use a soluble malate) and make the following tests : 



(«) Add a few drops of 5 o/o calcium chloride solution. No precipitate is formed, 

 but the addition of an equal volume of 96 o/q alcohol will bring down a precipitate of 

 calcium malate. 



(6) Add a few drops of 5 % lead acetate solution. A white precipitate of lead 

 malate is formed. Add a little acetic acid and warm. The precipitate dissolves. 



B. Heat a little solid malic acid in a dry test-tube. It melts and then gives oflf 

 fumes of maleic acid which condense in white crystals on the cooler parts of the 

 tube. 



Expt. 85. Preparation of malic acid from apples. Take six apples (total weight 

 from 500-700 gms.). Cut them into thin slices and drop the slices as quickly 

 as possible into the minimum amount of boiling alcohol in a conical flask. In 

 this way the oxidizing enzymes are destroyed, and brown oxidation products are 

 avoided. After well boiling, filter through paper. Neutralize the filtrate to litmus 

 with sodium hydroxide solution, and add concentrated calcium chloride solution 

 until a precipitate ceases to be formed. Allow the precipitate of calcium malate to 

 settle and then add alternately a few drops of calcium chloride solution and a 

 little alcohol to ensure complete precipitation. Decant, and filter off the calcium 

 malate. Dissolve the malate in the minimum amount of hot water, filter and add 

 concentrated lead acetate solution until a precipitate of lead malate ceases to be 

 formed. Filter off the lead malate, suspend it in a minimum amount of water, and 

 pass in sulphuretted hydrogen until the malate is decomposed. Filter and concen- 

 trate in a crystallizing dish on a water-bath. Crystals of malic acid are deposited. 

 Test as in Expt. 84. 



