266 



EIGHTH REPORT — 1838. 



our present knowledge on this interesting point, in which the 

 alloying metals are grouped according to their producing an 

 alloy more or less corrodible by oxidizing agents than iron 

 alone. 



The metals are here arranged according to their electrical 

 order, beginning with the most positive. In the first column 

 all above silver are positive to iron, and all below it, inclusive, 

 and in the second column, negative to it. It is obvious, how- 

 ever, that this gives us very defective information, as Faraday's 

 case of the platina alloy shows that mere difference in propor- 

 tion may wholly change the properties of the alloy in this re- 

 spect. An analogue to the peculiar action of the platina in this 

 case is found in the epigene crystals of native oxide of iron, 

 which are generally auriferous, and have the form of the bisul- 

 phuret of iron, whosa decomposition the electric agency of the 

 noble metal seems to have facilitated, though present in such 

 minute quantity in an uncombined state. 



34. Dr. Faraday also found that the alloys of pure iron vvere 

 less acted on by moist air than those of steel. It is also ex- 

 ceedingly remarkable, that in respect of corrodibility, the alloys 

 of steel follow a totally different order to those of wrought iron. 

 In the following table the first column shows the order of cor- 

 rodibility of various alloys with steel, compared with steel alone, 

 commencing with the less corrodible ; and the second column 

 shows the electric order of the metals with reference to iron, 

 beginning with the most positive. 



