104 



The Ionization op the Successive Hydrogens of Ortho- 

 phosphoric Acid. 



George A. Abbott. 



T]je dissociation i-elations of polybasic acids are at present imperfectly 

 understood. Owing to tlie natural complexitj' of the compounds and the 

 experimental difiiculties due to hyrolysis, hydration, and possibly asso- 

 ciation in solution, few investigators have attempted to determine the dis- 

 sociation constants of the different hydrogens of these acids ; but the re- 

 cent development of physico-chemical methods of investigating the nature 

 of dissolved substances has made the solution of such problems appear en- 

 tirely practicable. Therefore an extended investigation was undertaken, 

 at the suggestion of Prof. A. A. Noyos, in the hope that an exhaustive study 

 of the dissociation relations of the phosphoric acids might contribute to- 

 ward a better understanding of their chemical behavior in inorganic re- 

 actions, 'i his investigation w as conducted in the Research Laboratory of 

 Physical Chemistry of the Mass. Inst, of Technologj\ 



In this paper I shall attempt to present briefly only a few results, in 

 the hope that they may ])rove sufficiently interesting to justify their presen- 

 tation. The method of measuring hydrolysis described in the previous pa- 

 per gives us at once a reliable means of determining the dissociation 

 constants of weak acids. When both acid and base are weak (slightly dis- 

 sociated), the following relation holds: 



h^ Kw 



(1— h) KaKb 



in which h denotes the degree of hydrolysis of the salt, and Kw, Ka and 

 Kb are the dissociation constants of water, the acid and the base, respect- 

 ively. They are defined by the following expressions of the Mass Action 

 Law: 



Kw = Ch X Coi 

 K^ = Ch X Ca. 



t/HA 



Kb ^ Cb X Cqh 



CnOR 



