ALLOXAN. 57 



inodorous^ and exert no action on vegetable colours. They are 

 usually prisms of the right rhomboid system, have a glassy lustre, 

 and at 68° are soluble in 160 times their Aveight of cold, but 

 in a much less quantity of hot water : they dissolve in hot alco- 

 hol, but recrystallize as it cools. At a high temperature allan- 

 toin is converted by the caustic alkalies, and also by most concen- 

 trated acids (with the exception of nitric acid) into ammonia and 

 oxalic acid. This change may be illustrated by the formula 



2 At. Oxalic acid . . C^ Og 



2 A.t. Ammonia . . Hg N.^ 



C4 He N, O, 



If we compare the composition of allantoin with that of uric 

 acid and urea, we find that these substances bear a highly inte- 

 resting relation to each other ; if we add to one atom of uric 

 acid, one atom of urea and one atom of water, we obtain a 

 formula exactly corresponding with that of allantoin. 



1 At. Uric acid . . Cn, 11^ N^ Og 

 1 At. Urea . . . C, H^ N^ 0. 

 1 At. Water . . HO 



1 At. AUantoiu . . C^ H3 N^ O3 

 3 At. Water ... H3 O3 



C, H« N, 0« 



C,2H3NgOg = 3(C,H3N,03) 

 i. e. = 3 At. AUantoiu. 



" According to this," as Liebig observes, " it is evident that 

 the product of the secretion of the non-respiring fcetus of the 

 cow is, in a certain sense, identical with the products secreted 

 by the kidneys of the breathing animals. Urea represents 

 carbonate of ammonia from which the elements of two atoms 

 of water have separated; allantoin represents oxalate of am- 

 monia, from which the elements of three atoms of water have 

 separated." 



We now proceed to the consideration of a few of the most 

 important products of nitric acid with uric acid. 



Alloxan. One part of dry uric acid is gradually added to 

 four parts of nitric acid of spec. grav. l*-i2 — I'S, by which it 

 is dissolved with effervescence, and the production of heat. 

 The whole liquid is soon converted into a solid crystalline mass 

 of alloxan. Its formula is C^ H^ N„ O,^. It is very soluble 

 in water, reddens vegetable colours, and causes a pui'ple stain 

 on the skin. Its formation may be explained in the following 

 manner. We have already shown (see Urea,) that urea is con- 



