:n2 



is diawii as a new axis of abscissae, the ciiive represents the excess 

 of aoiivitv of inidissocialed over dissociated urease. 



/^ IS 1^ II IX II 



Thus 



/c 



Fig. 4. 



^32 



ti = 



a 



^ {H) ^ (OH) 



The constant a, expressing- the proportionality between the activitj 

 as determined (in arbitrary nnits) and the undissociated fi-action, had 

 to he calculated from the experiments as well as the constants k„ 

 and kb- 



The term ^?, which appears to i>e about 18 from a provisional 

 survev of the curve, had, in point of fact, also to be determined 

 n)ore accurately in the same way. 



These calculations requii-ed the knowledge of the hydroxyl-ion 

 concentration (OH) as well as of the hydiogen-ion concentration (//). 



In w^ater or dilute solutions this value is in)mediately given by 

 the dissociation-equation of water: 



(H) (UH) = k,r 



Since an 87o phosphate solution, however, is not to be regarded 

 as a dilute solution, special determinations of the hydroxjl-ion 

 concentration were indispensable. 



The experiments, by which these were carried out, are described 

 in the last pait of this paper. 



The simplest method of calculation appeared to be giving- provi- 



