2 65 
on the alloys of steel. 
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 pro- 
duced is still farther acted on. 
The powder procured from the soft steel or alloy in these 
experiments, when it has not remained long in the acid, ex- 
actly resembles finely divided plumbago, and appears to be a 
carburet of iron, and probably of the alloying metal also. It 
is not acted on by water, but in the air the iron oxidates and 
discolours 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 hard steel or alloy. 
When any of these residua are boiled in diluted sulphuric 
or muriatic acid, protoxide of iron is dissolved, and a black 
powder remains unalterable by the farther action of the acid ; 
it is apparently in greater quantity from the alloys than from 
pure steel, and when washed, dried, and heated to 300* or 400° 
in the air, burns like pyrophorus, with much fume ; or if light- 
ed, burns like bitumen, and with a bright flame ; the residuum 
is protoxide of iron, and the alloying metal. Hence, during the 
action of the acid on the steel, a portion of hydrogen enters 
into combination with part of the metal and the charcoal, 
and forms an inflammable compound not acted upon by the 
acid. 
Some striking effects are produced by the action of nitric 
acid on these powders. If that from pure steel be taken, it is 
entirely dissolved ; and such is also the case if the powder be 
taken from an alloy, the metal of which is soluble in nitric 
acid ; but if the powder is from an alloy, the metal of which 
is not soluble in nitric acid, then a black residuum is left not 
mdcccxxii. M m 
