54 ORGANIC CONSTITUENTS. 



which contains a very large proportion of uric acid and urate of 

 ammonia. To powdered boa constrictor's excrement add an 

 equivalent proportion, or shght excess^ of caustic potash. (We 

 assume that the excrement is entirely urate of ammonia in this 

 calculation.) Boil in water (in the proportion of lib. of ex- 

 crement to 2 quarts of water) till the mass is reduced to dif- 

 fused gelatinous floccules, which speedily settle, leaving a dark- 

 brown supernatant fluid. Uemove this fluid by decantation or 

 filtration, and wash the urate of potash, which is collected, with 

 cold water. It must then be heated in water, and more caustic 

 potash must be added, till the solution becomes clear. While 

 still hot it must be poured into dilute hydrochloric acid, and 

 allowed to stand. In this manner pure crystals of uric acid 

 will be obtained.' The slight excess of caustic potash used in 

 the first instance seems to keep the colouring matter in solution. 



Uric acid is represented bythe empirical formida^ C,^ H„ N„ O^, 

 or C,„ H^ N^ O,, or C,„ H^ N^ O,; it is highly probable that 

 it contains one atom of water in this state, and may be consi- 

 dered as a hydrate, 0,^ N^ H3 0^-FHO. 



Uric acid crystaUizes in fine scales of a brilliant white colour 

 and silky lustre, is tasteless, inodorous, heavier than water, 

 almost insoluble in cold, and very slightly soluble in boiling 

 water.^ It is insoluble in alcohol and ether. It dissolves in 

 dilute nitric acid, with tlie evolution of equal volumes of car- 

 bonic acid and nitrogen : on evaporating the solution a pink 

 tint is produced, which, on the addition of ammonia in excess, 

 changes to a purple-red coloiu'. This is a characteristic test of the 

 presence of uric acid. Boiled with peroxide of lead in water it is 

 decomposed into oxalic acid and allantoin, and urea is separated. 



Several of the compounds of uric acid, with the alkalies and 

 alkaline earths, are of practical importance. 



Urate of potash is a frequent constituent of urinary calculi : 

 it may be obtained by boiling urate of ammonia with potash. 

 On cooling, the urate of potash pelds a mass of very minute aci- 



' The various forms uuder which uric acid crystallizes are noticed under the head 

 of Urinary sediments. 



' See Appendix I, Note 19. 



^ According to Liebig, uric acid requires 15,000 parts of cold, and 1,932 parts of 

 boiling water, for its perfect solution. It dissolves in all alkaline tluids, in solution 

 of phosphate of soda and of borax, but not in solutions of the bicarbonates of potash 

 or of ammonia. 



