1891.] 



1 he Passive State of Iron and Steel. 



121 



Bunsen burner, and its temperature slowly raised, whilst the ice-tank 

 was kept full of powdered ice. A non-conductor of wood was put 

 between the ends of the two tanks so as to prevent the melting of 

 the ice ; the bottom or bent portion of the (J -tube was also enclosed 

 in a thick non-conductor of wood. A thermometer, T, was placed in 

 the water-tank. The bars were in circuit with the galvanometer, and 

 soon after immersing them in the nitric acid heat was applied to the 

 water-tank, and the temperature of the nitric acid in that limb of the 

 U -tube slowly raised to the temperatures required, whilst the acid in 

 the other limb of the U^ube was meanwhile maintained at a tem- 

 perature of 32 F. 



The arrangement will be understood on reference to fig. 3, and 

 the electro-chemical results obtained are graphically recorded on> 

 Diagram L 



FIG. 3. 



