of Chemical Change* 



451 



Now since / varies inversely as the rate of change, by com- 

 paring the above three values the ratios are found to be 



115-1 : 131-9 : 201-3 = 100 : 100 + 14*6 : 100 + 5x14-9; 



showing that the amount of oxidation that takes 100 minutes 

 to be performed in the blank requires 114*6 minutes in the 

 presence of 1 gram MgS0 4 , and 174*9 minutes with 5 grams 

 of the salt ; or that the retardation is proportional to the 

 quantity of the salt added, and equal to about 14*7 per cent, 

 per gram. These three experiments are shown graphically in 

 the figure. 



Curves showing Retardation produced by 1 and 5 grams MgS0 4 . 

 Temp. 10° C. 



10 











8 



II 



c 6 

 o 



.2 



1 



a 

 Li A 



1 









1 



HGI^H^H 















H 4 







iM 





2 











120 



Time, minutes. 



The following table contains th e values of/ and g for equa- 

 tion (5), the mean in each case of several experiments, when 

 2 grams of the various sulphates were employed, the tempe- 

 rature being in every case 10° C. 



