TBIMESIC ACID. 367 



excess of lime, it is resolved into carbonic acid and 

 toluene. 



2. Xylidinic acid (1:3: 4).* Is formed from 

 pseudocumene, xylylic, and paraxylylic acids by boil 

 ing them for a long time with dilute nitric acid. 

 Indistinct, colorless crystals ; fusing point, 280-283 ; 

 almost insoluble in cold water, very slightly in boiling 

 water, more easily in alcohol. 



3. Isuvitic acid. Is formed, together with phloro- 

 glucin, pyrotartaric, and acetic acids, by fusing gam 

 boge with caustic potassa. Short, thick, rhombic, 

 columnar crystals ; but slightly soluble in cold water, 

 more easily in hot water ; fuses at about 160. 



3. Acids, C W H = C 6 H 2 



Cumidinic acid. Is produced from durene and 

 durylic acid by continued boiling with dilute nitric 

 acid. Long, transparent prisms; almost insoluble in 

 water, even at the boiling temperature ; easily soluble 

 in hot alcohol ; sublimes at a high temperature in 

 plates, without previously fusing. 



/. Tribasic Acids. 



Benzenetricarbonic Acids. 

 C 9 IF0 6 = C 6 H 3 (CO.OH) 3 . 



1. Trimesic acid (1 : 3 : 5). Is obtained by oxidizing 

 mesitylenic and uvitic acids with potassium bichro 

 mate and dilute sulphuric acid; is also produced, 

 together with carbonic anhydride and benzenetetra- 

 carbonic acids, by heating hydro- and isohydromellitic 

 acids with concentrated sulphuric acid. Short, color 

 less prisms ; rather difficultly soluble in cold water, 

 easily soluble in hot water, in alcohol and ether; fuses 



* 1 and 4 indicate the position of the CO.OH groups; 3 that of the 

 group CH 3 . 



