1010 CYANOGEN COMPOUNDS. 



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solution of carbonate of ammonia. This mixture has precisely 

 the proper temperature, and deposits very fine crystals of mu- 

 rexide. The experiment is not so successful on a large scale, 

 probably because the liquid, by remaining longer warm, under- 

 goes a partial change. It is best to try first a saturated solution 

 in cold water of carbonate of ammonia. If it do not yield good 

 crystals, add a little water, and try it again, and so on till a 

 solution of the carbonate is obtained, which gives a good result. 

 The difficulty is owing to the spontaneous formation of different 

 carbonates by the action of water on the carbonate of the shops ; 

 but when a proper solution is obtained, the experiment never 

 fails." (Turner's Chem. &c. p. 776). 



Murexide crystallizes in short four-sided prisms, of which 

 two faces, like the upper wings of cantharides, reflect a green me- 

 tallic lustre. The crystals are garnet-red by transmitted light ; 

 their powder is reddish brown, and acquires a green lustre 

 under the burnisher. Murexide is but slightly soluble in cold 

 water, but colours it of a magnificent purple ; it dissolves, how- 

 ever, readily in water at 158, and crystallizes again on the cool- 

 ing of its solution ; it is insoluble in alcohol, ether, or in water 

 saturated with carbonate of ammonia. But this substance can- 

 not be purified or obtained in crystals of large size, by crystal- 

 lizing it from boiling water. For on bailing murexide in a 

 small quantity of water for the time necessary to dissolve the 

 whole 5 the crystals become colourless, and upon cooling, a yel- 

 low gelatinous matter precipitates. Hence, probably, the slight 

 uncertainty which attends even the best process for the prepa- 

 ration of this substance. Murexide dissolves in solution of 

 potash, producing a superb indigo blue colour, which disappears 

 with the application of heat, ammonia being disengaged. All 

 the inorganic acids decompose murexide, precipitating from its 

 solution murexan in small brilliant plates. Sulphuretted hy- 

 drogen decomposes it immediately into alloxantin, dialuric 

 acid and murexan, while sulphur is set free. 



Murexan, C 6 N 2 H 4 O 5 , was named purpuric acid by Prout. It 

 is formed on dissolving murexide with heat in caustic potash, 

 heating till the blue colour disappears, and then adding an 

 excess of dilute sulphuric acid. It crystallizes in colourless 

 plates, which have a siiky lustre and are very brilliant, is inso- 

 luble in water and dilute acids ; it dissolves in ammonia and 



