370 MELLITIC ACID. 



dride; with sodium-amalgam it yields hydromello- 

 phanic acid. 



h. Hexabasic Acids. 



Mellitic Acid. 

 C i2 H 6 i2 ^ C 6 (CO.OH) 6 . 



Occurrence and formation. In the mineral king- 

 dom; in honeystone or mellite (found in lignite), 

 which consists of aluminium mellitate crystallized in 

 yellow, quadratic octahedrons. The ammonium salt, 

 which crystallizes well, is prepared from this by boiling 

 with ammonium carbonate ; and from the ammonium 

 salt the insoluble barium or silver salt is prepared by 

 precipitation ; the salt thus obtained is decomposed by 

 dilute sulphuric or hydrochloric acid. It can be pre- 

 pared artificially by oxidizing pure carbon by means 

 of potassium hypermanganate in an alkaline solution. 



Properties. Fine needles of a silky lustre; easily 

 soluble in water and alcohol. When heated it melts ; 

 when distilled alone it is resolved into carbonic anhy- 

 dride, water, and pyromellitic anhydride ; when heated 

 with an excess of lime it yields carbonic acid and ben- 

 zene. Very stable acid ; is not decomposed by con- 

 centrated sulphuric, nitric, and hydriodic acids, nor 

 bromine even at an elevated temperature. 



Ammonium mellitate, C 12 12 (NH 4 ) 6 + 9H 2 0. Crys- 

 tallizes in large, colorless rhombic prisms. Barium 

 mellitate, C 12 12 Ba 3 + 3H 2 0, and Calcium mellitate are 

 precipitates, insoluble in water, rapidly becoming 

 crystalline. 



Methyl mellitate, C 6 (CO.O.CH 3 ) 6 , crystallizes in 

 colorless laminae, that fuse at 140. The Ethyl ether, 

 C^CO.O.OTP) 6 , forms lozenge-shaped crystals, that fuse 

 at 69. 



