TEREPHTALIC ACID. 365 



toluic acid (p. 338) with potassium bichromate and 

 dilute sulphuric acid. Is also formed by melting an 

 intimate mixture of potassium metabrom- or meta- 

 sulphobenzoate with sodium formate ; and by heating 

 hydropyromellitic and hydroprehnitic acids. Long 

 colorless, very fine crystals; almost insoluble in cold 

 water, difficultly soluble in boiling water, more easily 

 soluble in alcohol ; fuses above 300, and can be sub- 

 limed without undergoing decomposition. 



Barium isophtalate, C 8 H 4 4 Ba -f 3H 2 0. Crystal- 

 lizes in colorless, lustrous prisms; easily soluble in 

 water. 



Methyl isophtalate, C 6 H 4 (CO.O.CH 3 ) 2 . Colorless 

 needles, fusing at 64-65. The ethyl ether is a colorless 

 liquid, boiling at 285, and congealing at 0. 



Nitroisophtalic acid, C 6 H 3 (Fp 2 )(CO.qiI) 2 . By 

 heating isophtalic acid with fuming nitric acid. 

 Large, colorless, lustrous, thin laminse ; fusing point, 

 248-249 ; easily soluble in water and alcohol ; is con- 

 verted into amido-isophtalic acid, C 6 H 3 (NH 2 )(CO.OH) 2 , 

 by tin and hydrochloric acid. 



3. Terephtalic acid (Para-phtalic acid). Is pro- 

 duced from bodies belonging to the para-series : para- 

 xylene, ethylmethylbenzene, cymene, amylmethylben- 

 zene, cuminol, para-toluic acid, cuminic acid, ethyl- 

 benzoic acid, oil of turpentine, etc., by oxidizing them 

 with a mixture of potassium bichromate (2 parts) and 

 sulphuric acid (3 parts concentrated acid diluted with 

 three times its volume of water) ; by boiling paradi- 

 cyanbenzene (p. 256) with potassa-ley; and by melt- 

 ing a mixture of sodium parasulphobenzoate with 

 sodium formate. White powder; when allowed to 

 separate slowly it is crystalline; almost insoluble in 

 water, alcohol, and ether; freshly precipitated from a 

 solution of one of its salts, it is moderately easily 

 soluble in hot alcohol, and separates from this solution 



31* 



