OXALIC ACID. 933 



insoluble in alcohol. Binoxolate of potash, KO,C 2 O 3 -f HO,C 2 O 3 

 + 2HO, is sold under the name of salt of sorrel; it crystallizes 

 in oblique, diaphanous rhomboidal prisms, which are soluble in 40 

 parts of cold water, 6 parts of hot water, and insoluble in alcohol. 

 Quadroxalate of potash, KO,C 2 O 3 + HO,C 2 O 3 -f2(HO,C 2 O 3 

 -J-2HO), crystallizes in oblique octohedrons, of which two 

 angles are truncated. This salt appears to be a compound of 1 

 atom of binoxalate of potash, with 2 atoms of hydrated oxalic 

 acid ; the 4 atoms of water of crystallization, of the last men- 

 tioned constituent escape when the salt is heated to 262, 

 (page 172). Oxalate of soda, NaO,C 2 O 3 , is the only anhydrous 

 alkaline oxalate, and is the least soluble of the salts of soda. 

 There is also a binoxalate of soda. The oxalates of ammonia 

 correspond in number and composition with the salts of potash. 

 The neutral oxalate of ammonia, which is formed by neutralising 

 oxalic acid with carbonate of ammonia, is much used as a re- 

 agent, particularly to separate lime from magnesia, and generally 

 to precipitate lime. It is less soluble than oxalic acid. When 

 distilled in a glass retort, by a heat gradually increased, oxalate 

 of ammonia affords a dirty white sublimate of oxamide, C 2 O 2 

 -f-NH 2 (page 407), together with ammonia, carbonic acid, car- 

 bonic oxide, and cyanogen. 



Oxalate of lime, CaO,C 2 O 3 + 2HO is thrown down as a bril- 

 liant white precipitate, remarkable for its insolubility. It is 

 insoluble in acetic acid, but soluble in nitric and hydrochloric 

 acids. It leaves, when heated to incipient redness by a spirit 

 lamp, a white residue of carbonate of lime, from which the pro- 

 portion of oxalic acid, or of lime, maybe inferred. The oxalates 

 of magnesia, zinc, and manganese, have the same composition as 

 the oxalate of lime. The first mentioned possesses a small 

 degree of solubility, the others are insoluble. Oxalate of copper 

 forms a double salt with oxalate of ammonia, which corresponds 

 in composition with the binoxalate of ammonia. Oxalate of 

 barytes is expressed by BaO,C 2 O 3 + HO ; it is quite insoluble in 

 water. Oxalate of silver is an insoluble white powder, which is 

 anhydrous. (Phil. Trans. 1827, P- 47). 



The double oxalates of chronium, and the aluminous class, 

 have already been described (pages 519, 566, and 611). 



