IRON. 
gaged : for the quantity of this gas, in like 
circumstances, is proportional to that of 
the iron which is converted into oxide. 
There are considerable differences between 
the various products of the smelting fur- 
nace in these respects ; but it is found, 
that the white crude iron affords the least 
quantity of hydrogen in proportion to its 
bulk, and leaves a moderate portion of 
plumbago ; the grey crude iron affords 
more hydrogen, and more plumbago than 
the white ; and the softest bar iron affords 
most hydrogen of any, and little or no 
plumbago. The quantities of hydrogen 
gas, at a medium, by ounce measures, were 
sixty-two, afforded by one hundred grains 
of the white crude iron : seventy- one by 
the grey crude iron ; and seventy-seven by 
the malleable irop. 
Hence it may be inferred, that, in the 
white crude iron, the processes ot reduction 
and cementation are both carried to a less 
extent than in the grey crude iron, which is 
produced by means of /a stronger heat, 
excited with a larger quantity of fuel : and 
that the reduction of grey crude iron is 
still less perfect than that of the soft bar 
iron; though this last, by the refining in 
an open vessel, is so far from being more 
cemented, that it scarcely contains any 
plumbago at all. 
It must be admitted, however, that the 
solution in acids serves only to support 
these general conclusions, in conjunction 
with the facts observed in the dry pro- 
cesses; but cannot accurately show the 
quantities either of hydrogen or plumbago 
afforded by the several kinds of iron. For 
the plumbago, as it becomes disengaged, 
floats on the top of the sulphuric acid ; 
where it gradually disappears, though in- 
soluble in that acid. It must therefore be 
taken up by the hydrogen gas, and it is 
found that the volume of this air is dimi- 
nished by the absorption. Hence there is 
a double source of inaccuracy from the 
loss of plumbago, and the contraction of 
the hydrogen gas. 
On the whole then, since iron contains 
carburet in a state of combination, of which 
it may be deprived by heat with access 
of oxygen, which converts its carbon into 
the carbonic acid ; and since it recovers 
the plumbago by cementation with char- 
coal; there can be no question, but that 
this substance is originally afforded by the 
fuel. It appears also, that the reduction of 
the metallic oxide takes place first at a 
lower temperature ; and that the combina- 
tion of the carbon follows at a greater heat. 
Whence, in the refining of iron, the carbon 
is first burned, and the iron remains re- 
duced ; and in the cementation of bar iron, 
the metal is converted into steel, with 
blisters on its surface; which most pro- 
bably arise from carbonic acid, formed by 
the oxygen of some portions of unreduced 
oxide uniting with the acidifiable base from 
the charcoal. And lastly, as iron holds 
this acidifiable base, or carbon, in solution, 
so likewise it may not be separable from 
this metallic solvent, without carrying a 
portion with it; in the same manner as 
salts, which crystallize in water, always take 
up part of the solvent in the formation of 
their crystals. 
It would require many volumes to enu- 
merate the leading uses of iron. This most 
valuable of metals is applied to so many, 
and such important uses, that we cannot 
look round us without seeing its effects. 
When we contemplate the innumerable 
effects of human industry, and ask ourselves 
the simple question, Could this have been 
done without iron ? There is not a single 
instance, which will not immediately show 
its value. 
Iron is one of the principal ingredients, 
for dying black. The stuff is first pre- 
pared with a bath of galls and logwood, 
then with a similar bath to which verdegris 
is added, and lastly dyed in a similar bath 
with the addition of sulphate of iron. If it 
be wished, that the colour should be parti- 
cularly fine, the stuff should previously be 
dyed of a deep blue : otherwise a brown 
may be first given with the green husks of 
walnuts. Silk however must not be previ- 
ously blued with indigo, and sumach may 
be substituted instead of galls. Leather, 
prepared by tanning with oak bark, is 
blackened by a solution of sulphate of iron. 
Cotton has a very strong affinity for oxide 
of iron, so that, if it be immersed in a solu- 
tion of any salt of iron, it assumes a cha- 
mois colour, more or less deep, according 
to the strength of the solution. The action 
of the air on the oxide of iron deepens the 
colour ; and if the shade were at first deep, 
the texture of the stuff is liable to be cor- 
roded by it. To prevent this, the cotton 
should be immersed in the solution cold, 
carefully wrung, and immediately plunged 
into a ley of potash mixed with a solution of 
alum. After having lain in this four or 
five hours, it is to be wrung, washed, and 
dried. 
Mr. Brewer, to give a nankeen colour. 
