364 ISOPHTALIC ACID. 



1 part phtalic acid and 1 part crystallized sodium car- 

 bonate. Hard, tabular crystals ; difficultly soluble in 

 cold water and ether, more easily in hot water and in 

 alcohol ; fuses above 200, water being given oft' and 

 phtalic anhydride formed. Is decomposed when heated 

 with soda-lime, yielding benzene, hydrogen, and car- 

 bonic acid ; when fused with potassa, it yields benzoic 

 acid, hydrogen, and carbonic acid ; when it is gently 

 warmed with phosphorus chloride, it yields benzoyl 

 chloride, carbonic oxide, hydrochloric acid, and phos- 

 phorus oxichloride; when dissolved in concentrated 

 sulphuric acid, when bromine is allowed to act on its 

 aqueous solution, and when oxidized with dilute nitric 

 acid, it is converted into benzoic acid ; when its alco- 

 holic solution is saturated with hydrochloric acid gas, 

 ethyl benzoate is formed. 



Tetrahydrophtalic acid, C 8 H 10 4 . The anhydride 

 of this acid (C 8 H 8 3 , colorless laminae, fusing at 68) is 

 formed in the dry distillation of hydropyromellitic 

 acid. When this anhydride is heated with water, the 

 acid is generated. Easily soluble laminae; fuses at 

 96, being resolved at this temperature into water and 

 the anhydride. Bibasic acid. Bromine, when added 

 to its aqueous solution, converts it into brommalophtalic 

 acid, C 8 H 10 Br(OH)0 4 , which crystallizes in hard crusts, 

 and, when heated with baryta-water, is converted into 

 tartrophtalic acid, C 8 H 10 (OII) 2 4 (large, easily soluble 

 prisms). 



Hexahydrophtalic acid, C 8 H 12 4 . Is obtained 

 by heating tetrahydrophtalic acid with concentrated 

 hydriodic acid to 230 ; or, better, by heating hydro- 

 phtalic acid with concentrated hydriodic acid to 240- 

 250. Indistinct, small, hard crystals; fusing point, 

 203-205; somewhat difficultly soluble in water; bi- 

 basic. 



2. Isophtalic acid (Meta-phtalic acid), C 8 II 6 4 . Is 

 obtained by oxidizing meta-xylene (p. 283) and meta- 



