1891.] 



The Passive State of Iron and Steel. 



bars were cold drawn through a wortle, and were therefore different 

 in physical structure to the rolled plates used in the second series of 

 the experiments. An idea of their general properties will be obtained 

 on reference to Part II, Tables IV and V. A polished bar, 8 inches 

 long, 0'310 inch diameter, of the steel to be tested was placed in the 

 wooden stand W (fig. 5), along with a polished wrought-iron bar of 

 equal size, and the pair were then immersed in 1| fluid ounce of 

 nitric acid 1'42 sp. gr., contained in the JJ-tube, the bars being in 

 circuit with the galvanometer. The immersion was continued for 

 the periods stated, and with the electro-chemical results given on 

 Table VI. 



The wrought-iron bars used in each experiment were cut from one 

 longer polished rod, so as to afford a fair comparison of the relative 

 passivity of the various steels, compared with the wrought iron and 

 also with each other. The results are the average of numerous 

 experiments in each case. 



SERIES V, SET 2. 



Relative Passivity of Wrought-iron and various Steel Plates in Cold 

 Nitric Acid sp. gr. 1*42. 



In the following series of observations, the metals experimented 

 upon consisted of plates of rolled wrought iron, rolled steels made by 

 the Bessemer, Siemens-Martin, or crucible cast-steel processes, and 

 they were of the chemical composition given on Table VII. Each 

 plate was 3 inches square, by g inch thick, = total area of exposure, 

 19' 5 square inches including edges, brightly polished all over, and 

 had a long thin strip left on the top side (see fig. 6), for convenience 



Fia. 6. 



of attaching to the galvanometer connexions. The whole of the 

 wrought-iron plates, used as elements with the various steel plates, 



