ELECTRO-CHEMICAL POSITIONS OF WROUGHT IRON, ETC. 209 



position; for instance, in the experiment with the plates, some of the steel 

 plates took a negative position compared with the wrought iron ; but afterwards 

 the position was reversed. 



This change of electro-chemical position is a fact of considerable interest, 

 and the author has therefore given as typical some of the full records of the 

 deflections observed in some of the experiments between steels, wrought iron, 

 cast metal, &c. 



These diagrams, &c, illustrate this tendency in detail. A reference to some 

 of the tables will also show that in many instances the interchange is greatly 

 varied and influenced by the nature of the solutions in which the steels, &c, 

 were immersed. When the steels, &c, were immersed in an acid solution 

 instead of one containing neutral salts, such as sea-water, a noticeable result 

 was, in some instances, an almost complete reversal of electro-chemical position. 

 (See table and diagram G, I, Plate XXXII.) 



Although the soft steel and Bessemer steel bars in table D are recorded 

 thereon as in the negative position compared with wrought iron, this is not 

 contradictory to the results of similar soft steels in table G, because the results 

 in table D are the first deflections, whereas those in table G indicate the same 

 negative position at the commencement of the experiment ; but the electro- 

 chemical position afterwards changes by prolonged exposure. 



An explanation of this change in the electro-chemical position of the soft 

 steels may be that, as the solution gradually penetrates and acts on the metal, 

 it meets with crystalline networks of higher carbides, &c, and other consti- 

 tuents of varying composition, which would probably offer varying resistance to 

 the action of the solution. 



This view of the case would appear to derive support from the observations 

 made " On the Microscopical Structure of Iron and Steel," by Henry Clifton 

 Sorby, Esq., LL.D., F.R.S., from which it would appear that iron or steel of 

 the finest manufacture cannot be regarded as of purely homogeneous composition. 



The experiments recorded in the following tables were made not only with 

 the object of endeavouring to ascertain the relative electro-chemical position of 

 wrought iron, steels, and cast metal, but also to throw light, if possible, on the 

 amount of galvanic action which takes place practically where these metals are 

 combined in marine or other structures. It will be seen, therefore, that the 

 observations are roughly arranged with this object. 



Amongst other experiments, measurements were not only taken using zinc, 

 copper, and wrought iron as standards in combination with iron and steel and 

 cast metal, &c, but it will be also observed that bars and plates covered with 

 magnetic oxide were employed, as practically the action of this oxide upon 

 wrought iron, steels, and cast metal in sea- water, &c, is frequently a source of 

 electrolytic disintegration, to ascertain the extent of which forms one object 

 of the following experiments : — 



