MUREXAN. 59 



Moreover, 



Alloxan = urea -f- Cg Og (see their respective formulae) ; 



therefore, 



Alloxan -\-0 =: urea + Cg Og = urea -\- 3 at. oxalic acid, 



and 



Alloxan -f 64:= urea + Cg 0,j = urea + 6 at. cai-bonic acid. 

 Also, 



Alloxan -j- Oj = parabauic acid + 2 HO + 2 CO, 

 = oxalui'ic acid -{- 2 at. carbonic acid. 

 Hence, 



Uric acid -f- 4 HO -f O3 = 2 at. urea + 3 at. oxalic acid. 



Uric acid + 2 HO + 0^== 2 at. urea -(- parabanic acid + 2 at. carl)onic acid. 

 Uric acid + 4 HO + 0^= 2 at. urea + oxalui-ic acid -j- 2 at. carbonic acid. 

 Uric acid -j- 4 HO -j- Og = 2 at. lu-ea + 6 at. carbonic acid. 



These formulse express laws of mucli importance in urinary 

 pathology ; they show us that if an abundant supply of oxygen 

 be given to the uric acid, carbonic acid and urea may be ob- 

 tained ; if a smaller quantity, oxalic acid and urea ; and if none 

 be given the acid remains unchanged. 



Murexid {Furpurate of ammonia^ The best method of exhi- 

 biting this substance is to evaporate a solution of uric acid in 

 dilute nitric acid, until it acquires a flesh-red colour : after it 

 has cooled to 160*^ a dilute solution of ammonia must be added, 

 till the presence of free ammonia is remarked by the odour. 

 The solution is then to be diluted with half its volume of boiling 

 water and allowed to cool : it crystallizes in short four-sided 

 prisms, two faces of Avhich reflect a green metallic lustre. 

 It is insoluble in alcohol; sparingly soluble in cold, but 

 more readily in boiling water, on the cooling of which it 

 crystallizes unchanged. It is soluble in caustic potash with a 

 beautiful indigo-blue colour, which disappears with the evolu- 

 tion of ammonia on the application of heat. The diflFerence 

 between the views of Prout and Liebig regarding this substance 

 is, that the latter considers it a distinct principle, while the 

 former regards it as a combination of a peculiar acid (purpuric) 

 with ammonia. Prout's view has been strongly confirmed by 

 the researches of Fritzsche, which are published in the Transac- 

 tions of the Academy of Sciences of St. Petersburgh, for 1839. 



The formula assigned to this substance by Liebig and Wohler 

 is C,, H^- N^ 0„. Fritzsche gives it the formula C,,. H, N,. O,,, or 



Murexan or purpuric acid is prepared by dissohdng murexid 

 in caustic potash by the aid of heat, which is to be applied till 



