03 J ACIDS DERIVED FROM CARBONIC OXIDE. 



RHODIZO^IC ACID. 



Formula of the acid supposed anhydrous : C 7 O 7 . Of the 

 salt of potash, 3 KO + C 7 O 7 ; of the salt of lead 3PbO + C 7 O 7 , 

 (Thaulow). 



This body, which derives its name from the red colour of its 

 salts, was first observed by L. Gmelin, and recognised as a 

 new acid by Heller. Potassium, gently heated in carbonic 

 oxide, absorbs that gas with avidity, fusing of a green tint, and 

 spreading over the sides of the vessel ; afterwards the oxicar- 

 buret becomes black and porous. Allowed to cool, it is dis- 

 solved with water, when a violent disengagement of combustible 

 gases occurs, and a red solution is formed, containing rhodizo- 

 nate of potash. The same oxicarburet of potassium is formed 

 in large quantity, as an accidental product in the preparation of 

 potassium from carbonate of potash and charcoal, being found 

 as a black mass in the neck of the retort, or in the receiver with 

 the potassium. The salt from the oxicarburet may be deprived 

 of the excess of caustic potash by alcohol, in which the rhodi- 

 zonate of potash is insoluble. 



Rhodizonic acid is apt to undergo decomposition in being 

 liberated from its salts, and has not been obtained in a state of 

 purity. All its salts are red, and in the dry state have a metallic 

 lustre, and reflect green. Its potash salt undergoes a remarkable 

 decomposition when its solution is heated, being converted into 

 free potash, oxalate of potash, and croconate of potash : 



3KO + C 7 O 7 =KO and KO-f C 2 O 3 and KO + C 5 O 4 . 



CROCONIC ACID. 



Formula of the acid supposed anhydrous, C 5 O 4 . 



This acid derives its name from the saffron colour of its salts ; 

 it was discovered by L. Gmelin. The croconate of potash is 

 deposited in long yellow and brilliant needles from a solution of 

 rhodizonate of potash, which has been decomposed by ebullition. 

 The acid may be obtained free, by decomposing croconate of 

 potash by hydrofluosilicic acid, and evaporating to dryriess. It 

 is strongly acid, crystallizes of a yellow colour easily, and is 

 soluble in alcohol. 



