122 



Mr. T. Andrews. 

 DIAGRAM I. 



[Jan. 22, 



Current between two bright " passive " bars of the same composition, one in 

 warm, the other in cold, nitric acid sp. gr. 1*42. 



The electro-chemical position of the bar in the warm nitric acid was positive. 



I iM 



mi * S 



"* 



0-04 



! 



!! 

 I 



I 



I 



I 



! 



I 



I 



I 



\ys 

 iKSssssrr 



* 



mmmtm\ 

 '! 



mmmmmwmmmm* 



rin Miam 

 tin 



! 



I 



mA 



1PSHI 



(ft 



m 





IB 



IBUBI 



liBBiiiiiiii 



Difference of temperature between the nitric acid in Tubes A and B, 

 see Fig. 3, in degrees Fahrenheit. 



Curre A gives the E.M.F between two wrought iron bars, and Curve B gives 

 the E.M.F. between two cast steel bars under the conditions recorded. 



The above experiments indicate that the wrought iron was less passive in 

 wnrm nitric acid than the soft cast steel ; the average E.M.F. of 94 observations 

 with wrought iron was 0*030 volt ; whereas, in the case of the 94 observations on 

 cast steel, the average E.M.F. was only O'OIO volt. 



It will be seen from the above diagram that the behaviour of the steel, under the 

 conditions stated, was more irregular than that of the wrought iron. 



In the whole of the above series of experiments on Diagram I the 

 nitric acid was raised to a temperature of 175 F. ; the cold nitric acid 

 in the limb of the JJ-t-ube A remained perfectly colourless, and the 

 steel or iron therein absolutely passive ; but the steel or iron in the 

 warm nitric acid in tube A commenced to be gradually acted upon as 

 the temperature increased, a pale yellow tint beginning to appear in 



