1891.] 



The Passive State of Iron and Steel. 



481 



II. " The Passive State of Iron and Steel. Part III." By 

 THOS. ANDREWS, F.R.SS.L. and E., M.Inst.C.E. Received 

 April 23, 1891. 



SERIES V, SET 1. 



Relative Passivity of Wrought-iron and various Steel Bars, and the 

 Influence of Chemical Composition and Physical Structure on their 

 Passive State in Cold Nitric Acid. 



. The author is not aware that any previous experiments have 

 hitherto been made showing the relative passivity of the various 

 kinds of steel compared with wroughb iron, or the influence of the 

 chemical composition and physical structure of such metals on their 

 passive condition in nitric acid. 



The passive state of iron or steel may have hitherto been regarded 

 by many as a sort of fixed property pertaining to iron and steel alike, 

 when immersed in cold, strong nitric acid. The following experi- 

 ments were made to investigate if the passivity was of an universally 

 static character, or whether it varied with the chemical composition 

 and general physical structure of the metal and, if so, to what extent. 

 For convenience, this part of the investigation was divided into two 

 parts, one portion of the observations, Set 1, being made on drawn 

 rods of metals of known chemical composition and structure, and the 

 other, Set 2, of experiments constituting a study of the relative 



FIG. 5. 



WROUGHT 



IRON BAR 



A 



