URIC ACID. 



399 



a burette Liebig's mercuric nitrate solution, and test the mixture in a black glass plate with 

 dry sodic bicarbonate until a yellow speck remains. Multiply the number of c.c. of the burette 

 fluid used by - 04 (Pfliiger and Bohland). 



258. TJK.IC ACID = C 5 H 4 N 4 3 is the nitrogenous substance which, next to 

 urea, carries off most of the N from the body ; in twenty-four hours 0*5 grm. (7 

 to 10 grains) ; during hanger, 0*24 grm. (4 grains) ; after a strongly animal diet, 

 2*11 grm. (30 to 35 grains) are excreted. The proportion of urea to uric acid is 

 45 : 1. If a mammal be fed with uric acid, part of it becomes more highly oxidised 

 into urea, while the oxalic acid in the urine is also increased ( 260); in fowls, 

 feeding with leucin, glycin, or aspartic acid (v. Knieriem), or ammonia carbonate 

 (Schroeder), increases the amount of uric acid. When urea is administered to fowls, 

 it* is reduced chiefly to uric acid. 



It is the chief nitrogenous product in the urine of birds, reptiles, and insects, while it is 

 absent from herbivorous urine. 



Properties. It is dibasic, colourless, and crystallises in various forms (figs. 256 

 and 257), belonging to the rhombic system (1). When the angles are rounded, the 

 whetstone form (2) is produced, and if the long surfaces be flattened, six-sided tables 

 occur. Not unfrequently diabetic urine deposits spontaneously, large, yellow, 

 transparent rosettes (6, 8). If 20 c.c. of HC1, or acetic acid, be added to 1 litre of 

 urine, crystals (9) are deposited, like cayenne pepper, on the surface and sides of 

 the glass, after several hours. [The HC1 decomposes the urates, and liberates the 

 acid, which does not crystallise at once, owing to the presence of the phosphates in 

 the urine. Crystals of uric acid are usually yellowish in colour from the pigment 

 of the urine, and 

 they are soluble 

 in caustic pot- 

 ash.] 



Solubility. It is 



tasteless and odour- 

 less ; reddens lit- 

 mus ; is soluble in # 

 18,000 parts of cold 

 and in 15,000 of 

 boiling water, and 

 insoluble in alcohol 

 and ether. Hor- 

 baczewski prepared 

 it synthetically by 

 melting together 

 glycin, or, as it is 

 also called, glyco- 

 cin, and urea. It 

 is freely soluble in 

 alkaline carbonates, 

 borates, phosphates, 

 lactates, and ace- 

 tates, these salts at * * 256 



the same time re- Forms of uric acid. 1, Rhombic plates ; 2, whetstone forms ; 3, quadrate 

 movino- a part of forms ; 4, 5, prolonged into points; 6, 8, rosettes ; 7, pointed bundles; 

 thebas ; thus there 9, barrel forms precipitated by adding hydrochloric acid to urine, 

 are formed acid urates and acid salts from the neutral salts. It is soluble in concentrated sul- 

 phuric acid, from which it may be precipitated by the addition of water. 



Decomposition. During dry distillation it decomposes into urea, cyanuric acid, hydrocyanic 

 acid, and ammonium carbonate. Superoxide of lead converts it into urea, allantoin, oxalic 

 acid, and C0 2 ; while ozone forms the same substances, with the addition of alloxan. When it 

 is reduced by H in statu nascendi, as by sodium amalgam, it forms xanthin and sarkin. It is 

 a less oxidised metabolic product than urea, but it is by no means proved that uric acid is a 

 precursor of urea. 



Occurrence. Uric acid occurs dissolved in the urine in the form of acid urates 

 of soda and potash. These salts occur also in urinary calculi, gravel, and in gouty 



