of Chemical Change. 

 Table II. 



453 



Temp. 0. 



Blank. 



2 grams MgS0 4 . 



/• 



9- 



f. 



c J- 



613 

 10 

 13 

 17 



366-7 

 256-4 

 193-7 

 134-3 



152-7 

 106-4 



80-7 

 563 



478-6 

 335-8 

 256-6 



178-7 



199-3 

 139-7 

 1069 



74-7 



The relations among these numbers are shown in the fol- 



lowing table : — j gives the retardation produced by 2 grams 



MgS0 4 at the different temperatures, or the time required to 

 oxidize the iron from y to y', being for the blank experiment 

 equal to 100. In column a the values for a for the blank 

 experiments are given, calculated on the assumption that the 

 relation between rate of change and temperature is p = fjLot d } 

 and in column b the values for a when the experiments are 

 retarded by magnesic sulphate. 



Table III. 



Temp. O. 



f 



f 



a. 



b. 



6-13 

 10 

 13 

 17 



130-5 

 130-9 

 132-4 

 1330 



1097 

 1-098 

 1-096 



1-096 

 1094 

 1-095 



Means 





1097 



1095 



From the above table it is seen that the retardation- 

 coefficient of MgS0 4 increases slightly with the temperature, 

 from 15-2 at 6°-13 O. to 16-5 at 17° 0., the rate of oxidation 

 between these limits of temperature increasing about three- 

 fold ; also that the rate increases in geometrical progression 

 with temperature both in the blank and in the retardation 

 experiments, the relation being in the former p=/^(l*097)^ 

 and in the latter p=///( 1*095)*. It has been shown* that 

 * Phil. Mag. October 1885. 



Phil Mag. S. 5. Vol. 20. No. 126. Nov. 1885. 2 K 



