on the alloys of steel. ' 263 
steel, either directly, or by producing a definite alloy, which 
is diffused through the rest of the steel ; in which case the 
whole mass would be a series of such voltaic combinations : 
or it may be occasioned by the liberation, on the first action of 
the acid, of particles which, if not pure platina, contain, as 
has been shown, a very large proportion of that metal, and 
which, being in close contact with the rest of the mass, form 
voltaic combinations with it in a very active state : or, in the 
third place, it may result from the iron being mechanically 
divided by the platina, so that its particles are more readily 
attacked by the acid, analogous to the case of proto-sulphuret 
of iron 
Although we have not been able to prove by such experi- 
ments, as may be considered strictly decisive, to which of 
these causes the action is owing, or how much is due to any 
of them, vet we do not hesitate to consider the second as al- 
most entirely, if not quite, the one that is active. The reasons 
which induce us to suppose this to be the true cause of the 
action, rather than any peculiar and previous arrangement of 
the particLs of steel and platina, or than the state of division 
of the steel, are, that the two metals combine in every propor- 
tion we have tried, and do not, in any case, exhibit evidences 
of a separation between them, like those, for instance, which 
steel and silver exhibit ; that when, instead of an acid, weaker 
agents are used, the alloy does not seem to act with them as 
if it was a series of infinitely minute voltaic combinations of 
steel and platina, but exactly as steel alone would do; that 
the mass does not render platina wire more negative than 
steel, as it probably in the third case would do ; that it does 
not rust more rapidly in a damp atmosphere ; and that when 
