MELL1TIC ACID. 935 



Croconate of potash, KO,C 5 O 4 + 2HO, crystallizes in long 

 orange prisms of 6 or 8 sides, having a nitrous taste ; loses its 

 2 atoms of water at a moderate heat and becomes lemon yellow. 

 It is insoluble in alcohol, in common with all the salts of this 

 acid, except the croconate of ammonia which is soluble in 

 alcohol. 



Croconate of lead, PbO,C 5 O 4 -fHO, precipitates in golden 

 yellow micaceous plates, when a hot and dilute solution of 

 acetate of lead is added to a solution of croconate of potash con- 

 taining acetic acid. 



Hydrated croconic acid has been considered as a hydracid, 

 H 4- C 5 O 5 , that is, a compound of hydrogen, and a salt-radical ; 

 a constitution which is analogous, being assigned to mellitic 

 acid. 



The gas evolved when oxicarburet of potassium is dissolved 

 in water is not pure hydrogen, but contains carbon, and is dis- 

 tinguished, according to Mr. E. Davy, from all the other car- 

 burets of hydrogen, by the property it possesses of inflaming at 

 the ordinary temperature and depositing carbon, when mixed 

 with an equal volume of chlorine. 



MELLITIC ACID. 



Formula of the crystallized acid: H,C 4 O 4 , or HO + C 4 O 3 

 of the mellitates dried at 212, M,C 4 O 4 -f HO, or MO,C 4 O 3 

 + HO. 



This acid was discovered by Klaproth in a rare mineral, 

 meltite, which is the mellitate of alumina. The free acid is best 

 obtained, according to Woehler, by decomposing the mellitate of 

 lead by sulphuretted hydrogen ; it is a white crystalline pow- 

 der, soluble in water and alcohol ; from the last of which it 

 crystaUizes by slow evaporation in needles radiating from a 

 centre. The dry acid is not altered by a temperature of 572 

 (300 centig.), nor is it decomposed by boiling nitric or sulphuric 

 acid. 



Mellitates. Potash, soda and ammonia form acid besides 

 neutral mellitates. Nitrate of potash forms a remarkable double 

 salt with bimellitate of potash, KO,NO 5 4-4 (HO,M + KO,M) 

 + 6HO, described by Woehler. It is remarkable that the 

 nitrates particularly give rise to combinations in such propor- 



