Mercuric Chloride by Phosphorous Acid. 367 



Table VI. 



H<jCI 2 = 0-134 gram mols per liter = 2a 



H 3 P0 3 = 0-067 " " " " = a T — 25-2° 



HC1 =1-0 " " " " 



x = HgCl 



in hrs. 



in grams 



in mols 





Ki* 





K 2 f 



8'8 



0-1724 



0-0366 





0-159 





0-146 



21-6 



0-3280 



0-0694 





0-185 





0-149 



29-8 



0-3910 



0-0830 





0-204 





0-149 



48-0 



0-4782 



0-1015 





0-242 





0-147 



54-3 



0-4968 



0-1055 





0-254 





0-144 



a 



0-6311 



0-1340 











dX 7 /O 



— x) (a — \x) - 



= ik (2a — x) 



(2a- 



- x) = K, 



(2a 



— x)" 2 , whence 



X 



/finn Prmifij 



3n (1)). 











1 ~ 2a (2a - 



. , locc HiUUdlK 



x) t 





f Calculated from Equation 



(12). 











K, 



Summary. 



1. By Ostwald's " method of isolation " it is shown that the 

 reaction between mercuric chloride and phosphorous acid is of 

 the first order with respect to the mercuric chloride. 



2. The total reaction is of the second order and takes place 

 in two stages^ probably the following : 



(a) HgCl 2 + H.PO, = HC1 + HgCl + H 3 PO s 



(b) 2H.PO, + H 2 = H 3 P0 3 + H 3 P0 4 , 



reaction (b) being fairly rapid as compared with reaction (a) so 

 that the concentration of the H 3 P0 3 at any time t may be 

 denoted approximately by (b — -Ja?) instead of (b — x\ since for 

 every two molecules of H 3 P0 3 decomposed one molecule of 

 H 3 P0 3 is regenerated. 



3. Conclusive evidence is presented that the reaction is 

 accelerated by hydrogen ions. 



4. If no hydrochloric acid is present at the outset, the veloc- 

 ity coefficient K, calculated for a reaction of the second order, 

 goes through a minimum. This may be due partly to the 

 initial rate of the secondary reaction gradually increasing with 

 increase of the hydrogen ions, but is chiefly due to the forma- 

 tion of complexes between the HgCl 2 and the HC1 formed in 

 the reaction, and to their subsequent decomposition with 

 decrease in concentration of the mercuric chloride. 



