CHEMICAL ACTION AND MAGNETISM 299 



marked change when the constitution of one of the ingredi- 

 ents is altered: the atomic magnetism of trivalent iron is 

 25 per cent greater than that of the same element in the fer- 

 rous state. I resolved, therefore, to study the effect of mag- 

 netism upon the speed of oxidation and reduction of iron salts 

 in solution by reagents which showed but a feeble magnetism 

 by themselves. 



Two such reactions have already been studied under ordi- 

 nary conditions, and, inasmuch as the methods employed 

 seemed admirably suited to my purpose, I have followed them 

 in this investigation. 



Dr. J. J. Hood 1 determined the speed of the reaction 



6FeS04+KC103+3H 2 SO4=SFe 2 (SO 4 )3+KCl+3H 2 O, 



by estimating volumetrically with permanganate the amount 

 of ferrous salt remaining unaffected at different stages of the 

 process. 



Meyerhoffer 2 gives one series of observations upon the 



reaction 



2HI+2FeCl 3 =I 2 +2FeCl 2 +2HCl, 



in which case the iodine which had been set free could be 

 determined with starch paste and sodic thiosulphate. 



OXIDATION OF A FERROUS SALT 



I had at my disposal a large Ruhmkorff electro-magnet, 

 with cylindrical iron cores ten inches long and three inches 

 thick. [149] With the poles three inches apart, and with a 

 current from ten storage cells, the intensity of the magnetic 

 field was roughly determined at 10,000 c. g. s. per square- 

 centimeter. For my supply of electricity I am indebted to the 

 kindness of the director of the Physical Laboratory, Professor 

 A. A. Michelson. While ten cells were usually employed, I 



1 Philosophical Magazine, [5], 6, 371; 8, 121; 13, 419. 



2 Zeitschr. 2, 597. 



