356 G. A. Lin hart — Rate of the Reduction of 









Table II. 







HgCl 2 



= 0*13 



2 gram 



mols 



per liter = 



a 



T = 60° 



H 3 P0 3 



= 0-0575 " 



n 



a u 



b 





t 

 in inin. 





x = HgCl 







in grams 





in mols 



K 



35 





0*1183 





0-02512 





0-1200 



87 





0-1902 





0-04038 





0-0911 



138 





0-2471 





0-05246 





0-0875 



183 





0-2891 





0-06138 





0-0884 



360 





0-4162 





0-08837 





0-1163 



00 





0-5417 





0-11500 







It will be clear from what follows that the initial falling off 

 and subsequent increase in the velocity coefficient K is due to 

 the effect of hydrochloric acid formed in the reaction. 



In order to determine this effect of hydrochloric acid a series 

 of experiments were carried out in which various amounts of 

 hydrochloric acid were present at the start. When the results 

 of these experiments were plotted, perfectly smooth curves 

 were obtained. See figs. I and II. Moreover, their relative 

 position shows clearly that the reaction is accelerated by hydro- 

 gen ions. 



It is, therefore, necessary to take the concentration of free 

 acid into account. Since the disappearance of phosphorous 

 acid results in the formation of an equivalent amount of phos- 

 phoric acid the effect of the hydrogen ions from these two 

 acids upon the velocity of the reaction is nearly constant, and 

 no serious error will be introduced by assuming the concentra- 

 tion of the hydrogen ions to be proportional to the concentra- 

 tion of hydrochloric acid, which may be represented by C + x, 

 w T here C denotes the initial concentration of the HC1 used.* 

 Introducing this value into equation (2) 



ctx 



— — k(a—x)(b — ix) (C + x). (5) 



Setting a = A, Hb = B, - = K, this becomes, 



— =-K (A - x) (B - x) (C + x), whence 



ctt 



2-3 

 (A - B) (ATC) (B + G)t 



(6) 



* Although some of the hydrochloric acid combines with the mercuric 

 chloride to form complexes, the catalytic effect of the hydrogen ions is not 

 impaired, as these complexes, according to Leblanc and Noyes, are dis- 

 sociated to the same extent as hydrochloric acid of equal molecular concen- 

 tration. — Zeitschr. phys. Chem., vi, 329. 



