454 



Dr. J. J. Hood on Retardation 



when ferrous sulphate is oxidized by chlorate, the same rela- 

 tion p = /i,(l-093)* holds good. 



Chlorides. 

 When the present experiments were undertaken, the prin- 

 cipal object in view was to determine the retardation- 

 coefficients of the different chlorides ; and it was conjectured 

 that, with the evidence obtained from former experiments, 

 these salts would be found to group themselves together as 

 regards retardation-effects, Such a grouping, however, has 

 not been found to exist. Indeed the anomalies that the expe- 

 riments exhibit are of a very striking character. For instance, 

 instead of a retardation, the presence of certain chlorides has 

 been found to produce a considerable acceleration on the rate 

 of oxidation ; whilst in another case, that of sodic chloride, 

 neither retardation nor acceleration occurs. 



Instead of employing quantities of iron, chlorate, and acid 

 in accordance with equation (5), it was found that, by using 

 only one molecule of chlorate and so rendering the rate much 

 slower, the effects of the chlorides, being comparatively small, 

 were better brought out. The acid being the same in amount 

 as in the experiments with sulphates, or v 2 = 5*425 and A=10'5, 

 inserting these values in (4), the equation becomes 



y + 46-46 ^ _ 



/(■ 



46-46- 



y 



4343 



log 



10' 



y 



=y(?+«). 



Salt, 

 5 grams. 



/. 



9- 



Time to oxidize 

 iron from y to y\ 



Blank 



49-36 

 49-72 

 60-30 

 51-70 

 44-44 

 40-65 

 4634 



136-3 

 136-9 

 166-3 

 142-2 

 121-9 

 111-9 

 127-5 



100 



1008 



122-2 



104-7 



90-0 



82-3 



93-9 



NaCl 



KC1 



AmCl 



ZnCl 2 



MgCl 2 



Cd01 a 



In the following table are given the values for /and g, the 

 means of several experiments, the temperature being 10° C. 



Table IV. 



From these numbers it will be seen that no two chlorides 

 give the same retardation-effects. Sodic chloride practically 

 produces no effect whatever, whilst the chlorides of magne- 

 sium, cadmium, and zinc produce an acceleration of the rate 



