URIC ACID. 
589 
does not completely express the chemical mechanism of uric-acid solution 
and precipitation. 1 
The mate deposit is amorphous, but on treatment with water it is 
found to decompose, part of its uric acid heing set free in crystalline 
form and part going into solution (Fig. 51). But this is a property which 
was stated above to he 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 hiurates. 
Eoberts' view is that the quadriurate is the only physiological type 
of uric acid salt, whether in blood or in urine. 
Fie 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) MHU + MH 2 P0 4 = MHU,H 2 U + M 2 HP0 4 . 
1 Roberts, loc. cit. 
