URIC ACID. 



589 



does not completely express the chemical mechanism of uric-acid solution 

 and precipitation. 1 



The urate deposit is amorphous, but on treatment with water it is 

 found to decompose, part of its uric acid being set free in crystalline 

 form and part going into solution (Fig. 51). But this is a property which 

 was stated above to be specially characteristic of the quadriurates, and 

 closer examination shows that the greater part of an amorphous urate 

 deposit does, in point of fact, consist of those hyperacid salts, and not 

 of ordinary biurates. 



Eoberts' view is that the quadriurate is the only physiological type 

 of uric acid salt, whether in blood or in urine. 



FIG. 51. Uric acid. In the lower half of the figure the crystals are 

 shown as they separate when a quadriurate deposit is decomposed 

 with water. 



In the normal acid urine, immediately after its secretion, all the uric 

 acid is in this form. But in aqueous solution the quadriurates are neces- 

 sarily in a state of unstable equilibrium, and tend at once to decompose 

 according to the equation 



(1) MHU,H 2 U = MHU + H 2 U; 



half the uric acid being precipitated and the other half remaining in 

 solution as biurates. But the latter are in the presence of acid phos- 

 phates, and this fact again involves a condition of unstable equilibrium; 

 the following change occurring 



(2) 



1 Roberts, loc. cit. 



