LAWS OF ELECTROLYTIC DISSOCIATION 81 



ki = 2.3 X 10"" at 37°). Therefore, at any hydrion concentra- 

 tion (as long as it is not so small as to permit the uric acid, which 

 is dibasic, to begin the second dissociation stage) the solubility at 

 18° is: 



at 18° A = 1.40 X 10-^ (^^^^+1^1X^0-) 



Thus for example at the reaction of the blood, [H+] = 4.5 X 10~^, 



A = 4.77 X 10-3 



which is thirty times the value of A in iV HCl. 



A pure saturated solution of uric acid must have at 18° a hydrion 

 concentration according to (la) page 40. 



[H+] = Vl-o X 10-6 • 1.4 X 10-" = 1.45 X 10"^ 



The degree of dissociation of this solution is, according to (2), 

 page 42. 



1.5 X 10-6 



0.094 



1.5 X 10-6 + 1 45 X 10-5 



Paul and His found experimentally the value of a at 18° to be 

 0.095, and, moreover, conversely they derived the dissociation 

 constant from the above value of a. The verification of the theory 

 is then afforded by the fact that X and A are calculable from each 

 other. The solubility of uric acid calculated in the above manner 

 did not have the hoped for significance in physiology and pathology 

 because of the following two complications: 



The above considerations are valid only for the system in which 

 uric acid is the sohd phase. The presence of the alkali salt of the 

 weak acid did not enter into the derivation, for the alkali salts of 

 .aknost all acids are much more soluble than the acids themselves. 

 But in this respect uric acid forms an exception. The primary- 

 sodium urate is quite insoluble by itself, while in the presence 

 of NaCl it is an unusually insoluble salt. Furthermore, according 

 to Gudzent, the primary salt e.xists in two modifications, the lactam 

 .and the lactim forms, the solubilities of which are different. If, 

 therefore, one of these forms is present as the solid phase, then 

 the solubility of uric acid becomes a very complicated problem; 



