952 ORGANIC ACIDS. 



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The acid is now obtained by decomposing the malate of lead 

 diffused through water, by a stream of sulphuretted hydrogen, 

 the sulphuret of lead separated by filtration, and the liquid 

 evaporated, first by the naked fire, and afterwards by a water- 

 bath, to the consistence of a syrup. (Liebig). 



The hydrated acid forms granular crusts, of which the crys- 

 tallization is confused, and which are deliquescent. Its solu- 

 tion is very acid ; it reduces the salts of gold ; the dry acid 

 dissolves entirely in alcohol. The crystallized acid fuses at 

 266 or 284o (130 or 140 centig.), but when kept for some 

 time at that temperature, crystalline plates form in it, and gra- 

 dually increase in quantity ; these are fumaric acid, which is 

 sparingly soluble in cold water. By dry distillation, malic acid 

 affords water and afterwards a volatile and crystallizable acid, 

 named maleic acid by Pelouze. 



Malates. Malic acid forms both neutral and acid salts with 

 the alkaline and magnesian bases, the second atom of water in 

 the acid salts being water. The malate of peroxide of iron is 

 the only one which dissolves in alcohol.* 



Maleic acid (hydrated), 2HO + C 8 H 2 O 3 . This acid comes 

 over on the brisk distillation of malic acid. It crystallizes in 

 plates or in oblique prisms of a rhombic base, is very soluble in 

 water, alcohol and ether, its taste is acid and disagreeable. Dis- 

 tilled by a sharp heat it is decomposed, and resolved into water 

 and a white volatile matter, anhydrous maleic acid, fusible at 

 134.6, and boiling at 349. There exist both a neutral and 

 acid maleate of silver, the first containing 2 atoms of oxide of 

 silver, and the last, 1 atom of oxide of silver with 1 atom of 

 water as base, so that maleic acid is certainly bibasic. 



Fumaric acid, HO + C 4 HO 3 ; a monobasic acid, produced by 

 heating malic acid, and also existing in fumitory (Fumaria 

 officinalis), and in Iceland moss. The same acid is formed when 

 the malates of an alkaline base are exposed to a high tempe- 

 rature. Fumaric acid thus appears to be related to malic acid, 

 as pyrophosphoric acid is to phosphoric acid ; but Dr. Hagen 

 did not succeed in transforming fumaric acid again into malic, 

 by boiling a solution of the former. Fumaric acid crystallizes 



* Dr. Hagen on Malic Acid ; Memoirs of the Chemical Society of London, 

 vol. i, p. 28. 



