in Ferric Salts and in Chromic Acid. 307 



the present case, than are the average values of their constants, 

 and will therefore be given the preference in comparing nickel 

 with the other metals. 



It should be noted that this process of extrapolation affords 

 a general method for correcting the observed reaction veloci- 

 ties for the effect of all disturbances which are initially absent 

 but are produced by the progress of the reaction. It will be 

 used in a number of the cases to follow. 



Tin. — Metallic tin was found to dissolve readily, retaining a 

 clean bright surface, in the ferric sulphate solutions used. The 

 results as recorded in Table IV were calculated by using for the 

 concentration of ferric salt the expression C — c — %(c — c ) 

 in which C and c are the initial concentrations of ferric and 

 ferrous salt respectively, and c is the titer of the solution at 









Table IV. 













Metal : 



Tin. 



E r Fe(S04) 2 , 



- 05 molar. 





No. of 



Exp. 







H2SO4 , 5 molar. 











1. C=62 



•oo 



Co - 2-46 











K 



v = 



580 



560 



540 520 



500 



480 



460 





At = 



10 



10 



10 10 



10 



10 



10 





c = 





5-91 9-48 13-00 16"53 20-13 2380 27 



•40 



fa = 



1-71 



1-75 



1-71 1-71 



1-75 



1-78 



1-72 





h = 



1-71 



1-74 



1-71 1-71 



1-75 



1-78 



1-72 



173 



2. k = 



1-76 



1-76 



l - 75 1-75 



1-71 



1-74 



1-71 



174 



3. h = 



1-75 



1-70 



1-73 1-69 



1-67 



1-71 



1-66 



170 









H 2 S04, 0-25 molar. 









4. k = 



4-07 



4-03 



4-09 4-10 



4-18 



4-22 



4-35 



415 



5. k = 



4-07 



4-04 



4-11 414 



4-28 



4-27 



436 



4-18 



Initial velocities by extrapolation : Exp. 4, 3'97; Exp. 5, 3*95. 



time t. This method of calculation is based on the reaction 

 2 Fe +++ + Sn = 2Fe ++ -f- Sn ++ , that is, it takes no account 

 of the possibility of oxidation beyond the stannous stage. 



The assumption here involved, that stannous sulphate is not 

 oxidized by the ferric sulphate, may seem at first sight to be 

 unwarranted, even as an approximation, for the reaction 

 between stannous chloride and ferric chloride, as shown by the 

 work of Kahlenberg* and of A. A. Noyes,f is fairly rapid and 

 practically complete, and is, moreover, accelerated by hydro- 

 chloric acid. We have found, however, that under the condi- 

 tions of our experiments the oxidation of stannous sulphate by 

 ferric sulphate is extremely slow. The following observations 



*Jour. Amer. Chem. Soc, xvi, 314, 1894. 

 f Zeitschr. phys. Chem., xvi, 550, 1895. 



