168 GLYCERIN. 



with nitric acid for a long time ; by heating citraconic 

 acid with concentrated hydriodic acid to 100, and by 

 heating citramonochlorpyrotartaric acid (p. 163) alone or 

 with water. Thin, lustrous prisms, which fuse at 208 

 and sublime at a slightly higher temperature without 

 decomposition. Difficultly soluble in cold water. Con- 

 ducts itself towards hydrogen, chlorine, etc., like ita- 

 conic acid. 



Paraconic acid, C 5 H 6 4 = C 3 H 4 (CO.OH) 2 , is formed, 

 together with itamalic acid (p. 178), by the decomposi- 

 tion of itamonochlorpyrotartaric acid with water, and 

 can be separated from the itamalic acid by preparing 

 the calcium salts and treating them with alcohol. From 

 a concentrated aqueous solution calcium itamalate is 

 precipitated by alcohol, whereas the paraconate remains 

 in solution. Silver paraconate is also formed by the 

 action of itachlorpyrotartaric acid on silver carbonate. 

 The free acid is crystalline, easily soluble ; fuses at 

 70 ; yields, when subjected to distillation, citraconic 

 anhydride ; combines with hydrobromic acid, forming 

 itamonobrompyrotartaric acid ; and is readily converted 

 into itamalic acid by treatment with bases. 



FIFTH GROUP. 

 A. TRIATOMIC ALCOHOLS, C n H 2n + 2 3 . 



These alcohols are derived from the hydrocarbons of 

 the marsh-gas series by the replacement of three atoms 

 of hydrogen by three hydroxyl groups. Only one of 

 these alcohols is known with any degree of exactness. 



Glycerin. 



CH 2 .OH 



C 3 H 8 3 = CH.OH 

 CH 2 .OH. 



Occurrence. !N"ot in a free state. In combination 

 with acids, as compound ethers, it forms most of the 



