106 



partition method, for the iouization of tlie first hydrogen of Orthophos- 

 phoric Acid is fairlj- large. It does not accurately obey the Mass Action 

 Law : hence K^ has no defi ite meaning. However, the degree of disso- 

 ciation was determined from the values of the electrical conductivity of the 

 acid and its salts, and other known data, and the following values were ob- 

 tained, at 18° C : 



wherein C represents the concentration and r the degree of ionization. 

 Substituting the values of r we obtain, for the values of Kj at the different 

 concentrations ; 



Concentration. K. 



0.1 0.0114 



.05 .0104 



.01 .0091 



.002 .0087 



.0002 .0053 



and it is seen that the deviation from the law is marked. 



A comparison of the ionization constants of phosphoric acid with those 

 of some other acids is interesting. 



K X 101" 

 Acetic Acid, CjHjO, — H 180,000. 



Carbonic, HOO3 — H 3,040. 



Hydrosulphuric, HS — H 670. 



Boric. H0BO3 — H 17. 



*Pheuol, C,H,0 — H 1.3 



Phosphoric Acid, K, = H.PO, — H 100,000,000. (Approx.). 



" K2 = HPO'^4— H 2,090. 



" K, =P0'^'4— H 0.00556 



♦These values are taken from Walker, "Zeit Phys. Chem." S^, 137, 1900. 



