234 DERIVATIVES OF URIC ACID. 



laminae of a mother-of-pearl lustre. From a solution 

 of the salt, the free acid is precipitated as a crystalline 

 powder by means of hydrochloric acid. It is soluble 

 in hot water, but only with decomposition and evolu- 

 tion of carbonic anhydride. 



Alloxan (Mesoxalylurea), C 4 H 2 N 2 4 = 

 CO 1 C0 ' This is P roduced b J tne action 



of concentrated, cold nitric acid on uric acid, urea 

 being formed at the same time. When uric acid is 

 added to nitric acid, alloxan is thrown down imme- 

 diately as a white crystalline powder, which, when 

 perfectly freed of acid, need only be recrystallized from 

 water. It is prepared most practically from alloxan- 

 tine. The latter is moistened with very concentrated 

 nitric acid, so as to form a thick, pasty mass, and then 

 allowed to stand for a few days, until, as may be 

 tested with a small portion, it dissolves readily and 

 completely in cold water. The mass is then allowed 

 to dry completely in the air, spread out on bricks, 

 and, after the removal of the last trace of nitric acid, 

 by heating over the water-bath, recrystallized from 

 hot water. 



On the cooling of the warm aqueous solution, it 

 crystallizes out with four molecules of water of crys- 

 tallization ; if the solution is evaporated by the aid of 

 heat, it crystallizes with only one molecule of water. 

 The former consists of large, shining, transparent, rhom- 

 bic crystals of the form of heavy spar ; effloresces in 

 the air and loses three molecules of water ; crystallized 

 with one molecule, it forms smaller, harder, monoclinic 

 crystals, which do not effloresce. It is easily soluble 

 in water ; the solution imparts to the skin a repulsive 

 odor, and colors it purple ; it tastes unpleasantly sour 

 and saltish ; shows an acid reaction ; is decomposed by 

 heating. It gives an indigo-blue color with salts of 

 iron suboxide. It unites with alkaline bisulphites by 

 heating, forming salts which can be obtained in large 

 crystals. 



The aqueous solution decomposes slowly at the ordi- 

 nary temperature, rapidly by boiling, into alloxantine, 



