IO 



ELECTROMOTIVE FORCE OF IRON AND OCCLUDED HYDROGEN. 



means of a siphon from the reservoir, and an inverted (J -tube and stopper 

 were inserted in the top to make connection with an open test-tube contain- 

 ing ferrous sulphate fastened alongside by means of a rubber band. In this 

 way the iron was kept for some time safe from oxidation, yet always open 

 to measurement. The arrangement is illustrated in figure 2. When the 

 end of the tube of the decinormal electrode (C in figure 2) was dipped into 

 this test-tube full of ferrous sulphate, the cell was complete and ready for 

 measurement. A large number of " iron electrodes " could be placed around 



w / 



w w 



Fig. 2. 



Fig. 3. 

 Receptacles for Iron Electrodes. 



Fig. 4. 



C. Tube leading to decinormal elec- 

 trode. 



F. Contains normal ferrous sulphate 

 solution. 



O. Protecting layer of paraffin oil. 



P. Hard paraffin. 

 V. Iron wire. 



W. Platinum wire and loop for holding 

 porous iron. 



the sides of the thermostat, all attached to one wire, and the change of con- 

 nection from one cell to another was made by simply lifting the iron stand 

 to which the decinormal electrode was attached and dipping the end of the 

 standard electrode's tube into the next test-tube. Thus a large number of 

 measurements could be taken with a minimum expenditure of time and 

 trouble, a very necessary matter in an investigation involving thousands of 

 measurements. The thermostat, electrically regulated and heated, in which 

 the electrode was immersed, was kept at 20.0 C. The normal ferrous 



