on the Altoijs of Steels 2^9 
tried, has produced voltaic action that was not first able to set 
a portion of the platina free bj dissolving out the iron. 
Other interesting' phenomena exhibited by the action of acids 
on these steels, are the differences produced when they are hard 
and when soft. Mr Daniel, in his interesting paper on the me- 
chanical structure of iron, published in the Journal of Science, 
has remarked, that pieces of hard and soft steel being placed in 
muriatic acid, the first required fivefold the time of the latter 
to saturate the acid ; and that when its surface was examined, 
it was covered with small cavities like worm-eaten wood, and 
was compact and not at all striated, and that the latter presented 
a fibrous and wavy texture. 
The properties of the platina alloy, have enabled us to ob- 
serve other differences between hard and soft steel equally strik- 
ing. When two portions of the platina alloy, one hard and one 
soft, are put into the same diluted sulphuric acid, and suffered 
to remain for a few hours, then taken out apjJ^j examined, the 
hard piece presents a covering of a metallic black carbonaceous 
powder, and the surface is generally slightly fibrous ; but the soft 
piece, on examination,, is found to be covered with a thick coat 
of grey metallic plumbaginous matter, soft to the touch, and 
which may be cut with a knife, and its quantity seven or eight 
times that of the powder on the hard piece : it does not appear 
as if it contained any free charcoal, but considerably resembles 
the plumbaginous powder Mr Daniel describes as obtained by 
the action of acid on cast iron. I 
The same difference is observed if pure steel be used, but it is 
not so striking ; because, being much less rapidly attacked by 
the acid, it has to remain longer in it, and the powder produced 
is still farther acted on. 
The powder procured from the soft steel or alloy in these ex- 
periments, when it has not remained long in the acid, exactly 
resembles finely divided plumbago, and appears to be a carbu- 
ret of iron, and probably of ' the alloying metal also. It is not 
acted on by water, but in the air the iron oxidates and discol- 
ours the substance. When it remains long in the acid, or is 
boiled in it,, it is reduced to the same state as the powder from, 
the bard steel or alloy, ^ 
A a 
o 
