448 Dr. J. J. Hood on Retardation 



that these substances, even in large quantity, influenced the 

 rate of the change comparatively little ; and that consequently 

 the term in (2) relating to the retarding or accelerating effects 

 of the products of the reaction could be neglected ; as indeed 

 the calculations from the experimental numbers showed to be 

 true, as is illustrated in the experiments with MgS0 4 given in 

 detail below. 



For part of the work relating to the retardation of sulphates 

 and influence of heat, the following equation w T as employed: — 



f = ~a !/ {(v x -l)A+y}{(v 2 -l)A+t,}, 



which, on integrating, gives 



/{fa-l)log„ y+( 7 1)A -^-l)log„ y+( 7 1)A }= g+l; (3) 



whilst in the experiments with chlorides the iron and chlorate 

 were in equivalent quantities, and the acid several multiples, 

 represented by the equation 



% = -af\(v 2 -l)A+y\, 

 which, on integrating, becomes 



/'{(n-l)A-^3log,„£±fc=i> A }=,(/ + ,). (4) 



Taking either of these equations (3) and (4), it is easy to 



see that -^ oc/ _1 , or that the time required to oxidize the 



iron from y f to y" is proportional to /; consequently in a 

 series of experiments in which everything is the same except- 

 ing the presence of inactive salts, by a comparison of the 

 values obtained for / with its value for an experiment in which 

 • no such extraneous salt is added, or a blank experiment, a 

 measure is obtained of the effect of such a salt on the rate of 

 the oxidation ; so also in the case of variations of temperature 

 a measure is obtained of the accelerating effect of heat on the 

 rate. 



Sulphates. 



The original design of this investigation was to determine 

 the retardation-effects of the various soluble chlorides. The 



