208 CONJUGATED ACIDS. 



mercury with 40 parts of water and a very small quantity of am- 

 monia; the purple-red fluid which is thus obtained must be 

 filtered, and after standing some time will deposit crystals of 

 murexide. This body may also be prepared by dissolving uric 

 acid in dilute nitric acid, and evaporating the fluid till it assumes 

 a reddish tint ; after it has cooled to 70 it must be saturated with 

 dilute ammonia, diluted with half its volume of water, and allowed 

 to stand. 



Murexide crystallises in, short four-sided prisms, tw r o of whose 

 surfaces present a cantharides-green, glistening appearance : in 

 refracted light these crystals present a garnet-red tint; when 

 pulverised it is of a brownish-red colour, and under the burnishing 

 rod presents a green, metallic lustre ; it is insoluble in alcohol and 

 ether, slightly soluble in cold, but freely in hot water, and it dis- 

 solves in a solution of potash, communicating an indigo-blue 

 colour to the fluid. It is decomposed by all the mineral acids. 



In the preparation of murexide from uramile and red oxide of 

 mercury , 2 atoms of uramile take up 3 atoms of oxygen from the 

 mercury, and form 1 atom of murexide, 1 atom of alloxanic acid 

 and 3 atoms of water ; (C 16 H 10 N 6 O 12 + 3O = C 12 H 6 N 5 O 8 + 

 C 4 HNO 4 + 3HO.) 



When uric acid is dissolved in dilute nitric acid, the principal 

 product is alloxantin, which by the action of the nitric acid during 

 evaporation is in part converted into alloxan, from which murexide 

 is formed on the addition of ammonia ; for 1 atom of alloxan, 2 

 atoms of alloxantin, and 4 atoms of ammonia, yield 2 atoms of 

 murexide and 14 atoms of water; (C 8 H 4 N 2 O 10 + C 16 H 10 N 4 O 20 

 + H 12 N 4 = C 24 H 12 N 10 16 + H 14 14 .) 



Murexan, C 6 H 4 N 2 O 5 , purpuric acid, is prepared by dissolving 

 murexide in a solution of potash, boiling, and supersaturating with 

 dilute sulphuric acid ; it crystallises in silky, glistening scales, is in- 

 soluble in water and in dilute acids, but dissolves unchanged in 

 concentrated sulphuric acid ; it likewise dissolves in the alkalies, 

 without, however, neutralising them. 



On treating murexide with alkalies or with acids, 2 atoms of 

 murexide take up 1 1 atoms of wafer, and are converted into 1 atom 

 of alloxan, 1 atom of alloxantin, 1 atom of murexan, 1 atom of 

 urea, and 2 atoms of ammonia; (G 24 H 1 . 2 N 10 O 16 -|-H 11 O 11 = 

 C 8 H 4 N 2 10 + C 8 H 5 N 2 10 + C 6 H 4 N 2 5 + C 2 H 4 N 2 O 2 + H 6 N 2 .) 



Preparation. The best method of preparing uric acid is that 

 given by.Bensch. The excrements of serpents or birds, or calculi 

 of uric acid, are boiled in a solution of I part of hydrate of potash 



