712 MODIFICATIONS OF ORGANIC COMPOUNDS. 



taining nitrogen, give ammonia in the first period, and cyanogen 

 or hydrocyanic acid in the last. 



The decomposition of citric acid by heat, has been more 

 minutely investigated than any other, by M. Crasso, and is 

 particularly interesting from the variety of products it affords, 

 at different stages of the decomposition. After losing its water 

 of crystallization, the citric acid, C 12 H 5 O n , first undergoes a 

 decomposition, of which the products are a new and fixed 

 acid, aconitic acid, C 4 H 2 O 4 , also found in nature being the 

 acid of the aconitum napellus, together with one atom of acetone 

 C 3 H 3 O, four atoms of carbonic oxide C 4 O 4 , and one atom of 

 carbonic acid C O 2 . By a continuance of the heat, the fixed 

 aconitic acid itself is decomposed, three atoms of it C 12 H 6 O 12 , 

 affording two atoms of a volatile pyr-acid, named itaconic acid 

 2 (C 5 H 3 O 4 ), and two atoms of carbonic acid C 2 O 4 . The 

 itaconic acid again is decomposed when heated to its point of 

 ebullition, and gives a more volatile and stable acid, named 

 citraconic acid C 5 H 3 O 4 , which is consequently isomeric with 

 the preceding acid. It is believed, however, by Crasso, that the 

 last is the only monobasic acid in the series, and that the true 

 formulee of the hydrates of the three new acids produced by the 

 decomposition of citric acid by heat, are, with that of the ori- 

 ginal acid itself: 



Citric acid. . . . C 12 H 5 O u -f 3HO 



Aconitic acid. . . C 12 H 6 O 12 + 3HO 



Itaconic acid. . . C 10 H 6 O 8 +2HO 



Citraconic acid. . C 5 H 3 O 4 + HO* 



By the united action of heat and bases, other transformations 

 of acids have been effected. Thus malic acid is converted into 

 fumaric and equisetic acids, and citric acid into aconitic and 

 tartaric acids, when their compounds with oxide of antimony or 

 potash are heated so long as water is disengaged. 



ACTION OFOXYGRN EREMACAUSIS. 



Organic compounds when dry and in a state of purity 

 are generally capable of resisting the action of the air or 

 of free oxygen, at the usual temperature ; but a considerable 



* Annales ue Chimie et de Physique, 3me Srie, tome I, p. 311. 



