o2 
Uk* a very sliort time. It is malleable in 
every temperature, and its malleability in- 
creases in proportion as the temperature 
augments; but it cannot be hammered out 
nearly so thin as gold or silver, or even cop- 
per. Its ductility, however, is more perfect; 
tor it may be drawn out into wire as line at 
least as. a human hair. Its tenacity is such, 
that an iron wire 0.078 of an inch in diame- 
ter is capable of supporting 549.25 lbs. avoir- 
dupois without breaking. When heated to 
about 158" Wedgewood, it melts. Ibis 
temperature being nearly the highest to 
wnicli it can be raised, it has been impossible 
to ascertain the point at which this melted 
metal begins to bail and to evaporate. Nei- 
ther has the form of its crystals been ex- 
amined : but it is well known that the texture 
ot iron is fibrous ; that is, it appears when 
broken to be composed of a number of fibres 
or strings bundled together. 
V> lien exposed to the air, its surface is 
soon tarnished, and it is gradually changed 
into a brown or yellow powder, well known 
under the name of rust. This change takes 
•place more rapidly if the atmosphere is 
moist. It is occasioned by the gradual com- 
bination ot the iron with the oxygen of the 
atmosphere, for which it has a' very strong 
affinity. 
When iron filings are kept in water, pro- 
vided the temperature is not under 70°, they 
are gradually converted into a black powder, 
"'bile a quantity of hydrogen gas is emitted. 
r l his is occasioned by the slow decomposition 
or the water. The iron combines with its 
oxygen, while the hydrogen makes its escape 
under the form of gas. 
If the steam of water is made to pass 
through a red-hot iron tube, it is decom- 
posed instantly. The oxygen combines with 
the iron, and the hydrogen gas passes through 
the tube, and may be collected in proper 
vessels. This is one of the easiest methods of 
procuring pure hydrogen gas. 
These facts are sufficient to show that iron 
has a strong affinity for oxygen, since it is 
capable of taking it from air and water. It is 
capable' also of taking fire and burning with 
great rapidity. Twist a small iron wire into 
the form of a cork-screw, by rolling it round a 
cylinder; fix one end of it into a cork, and 
attach to the other a small bit of cotton thread 
dipt in melted tallow. Set fire to the cotton, 
and plunge it while burning into a jar filled 
with oxygen gas. The wire catches lire from 
the cotton, and burns with great brilliancy, 
•emitting very vivid sparks in all directions. 
For this very splendid experiment we are in- 
debted to Dr. Ingenhousz. During this 
combustion the iron combines with oxygen, 
and is converted into an oxide. Mr. Proust 
has proved that there are only two oxides 
of iron ; the protoxide has usually a black 
colour, but the peroxide is red. 
The protoxide of iron may be obtained by 
four different processes. 1 . By keeping iron 
filings a sufficient time in water at the tempe- 
rature of 70°. The oxide thus formed is a 
black powder, formerly much used in medi- 
cine under the name of martial ethiops, and 
jseems to have been first examined by Le- 
.meri ; but a better process is that of De 
Hoover. He exposes a paste formed of iron 
filings and water to the open air, in a stone- 
^ are vessel ; the paste becomes hot, and the 
IRON. 
water disappears. It is then • moistened 
again, and the process repeated till the whole 
is oxydized. The mass is then pounded, and 
the powder is heated in an iron vessel till it is 
perfectly dry, stirring it constantly. 2. By 
making steam pass through a red-hot iron 
tube, the iron is changed into a brilliant 
black brittle substance, which, when pounded, 
assumes (lie appearance of martial ethiops. 
This experiment was first made by Lavoisier. 
3. By burning iron wire in oxygen gas. The 
wire as it burns is melted, anil fails in drops 
to the boftom of the vessel, which ought to 
be covered with water, and to be of copper. 
These metallic drops are brittle, very hard, 
and blackish, but retain the metallic lustre. 
They were examined by Lavoisier, and found 
precisely the same with marthial ethiops. 
They owe their lustre to the fusion which 
they underwent. By dissolving iron in sul- 
phuric acid, and pouring potass into the so- 
lution. 4. A green powder falis to the bottom, 
which assumes the appearance of martial 
ethiops when dried quickly in close vessels. 
I his first oxide of iron, however formed, is 
always composed of 73 parts of iron and 27 of 
oxygen, as Lavoisier and Proust have de- 
monstrated. It is attracted by the magnet, 
and is often itself magnetic, ft is capable of 
crystallizing, and is often found native in that 
state. 
The peroxide or red oxide of iron may be 
formed by keeping iron filings red-hot in an 
open vessel, and agitating them constantly til! 
they are converted into a dark-red pow der. 
1 his oxide was formerly called saffron of Mars. 
Common rust of iron is merelv this oxide 
combined with carbonic acid gas. T lie red 
oxide may be obtained also bv exposing for a 
long time a diluted solution of iron in sulphu- 
ric acid to the atmosphere, and then dropping 
into it an alkali, by which the oxide is preci- 
pitated. This oxide is also found native in 
great abundance. Proust proved it to be 
composed of 48 parts of oxygen and 52 of 
iron. Consequently the protoxide, when 
converted into red oxide, absorbs 0.40 of 
oxygen; or, which is the same thing, the 
red oxide is composed of 66.5 parts of black 
oxide and 33.5 parts of oxygen. One hun- 
dred parts of iron, when converted into a pro- 
toxide, absorb 37 parts of oxygen, and the 
oxide weighs 137 ; when converted intoper- 
oxide, it absorbs 52 additional parts of oxy- 
gen, and the oxide weighs 189. 
The peroxide cannot be decomposed by 
heat; but when heated along with its own 
weight of iron filings,' the w hole, as Vauque- 
lin first observed, is converted into black ox- 
ide. The reason of this conversion is evi- 
dent: The 100 parts of peroxide are com- 
posed of 52 parts of iron, combined with two 
different doses of oxygen : ] . With 14 parts, 
which, with the iron’ make 66 of protoxide: 
2. With 34 parts, which, with the protoxide, 
make up the 100 parts of peroxide. Now, 
the first ot these doses has a much greater af- 
finity for the iron than the second has. Con- 
sequently the 34 parts of oxygen, which con- 
stitute the second dose, being retained by a 
weak affinity, are easily abstracted by the 
100 parts of pure iron; and combining with 
the iron, the whole almost is converted into 
black oxide : for 100 parts of iron, to be con- 
verted into black oxide, require only 37 parts 
of oxygen. 
The peroxide of iron is not magnetic. It 
is converted into black oxide by sulphureted 
hydiogen gas and many other substances; 
which deprive it ot the second dose of oxy- 
gen, for which they have a stronger affinity, 
thougii they are incapable of decomposing 
the protoxide. Iron is capable ot combining 
with all the simple combustible bodies. 
. A small mixture of it constitutes that par- 
ticulai kind ot iron, known by the name of 
coal short iron, because it is brittle when 
cold-, though it is malleable when hot. 
Kin man has shewn that (he brittleness and 
bad qualities of cold short iron may be re-' 
moved by heating it strongly with limestone, 
and with this the experiments of Levavasseur 
correspond. 
i here are a great many varieties of iron,, 
which artists distinguish by particular names ; 
but all of them may be reduced under one or 
other of the three following classes: cast 
iron; wrought or soft iron; and steel. 
Cast iron, or pig iron, is the name of the 
metal when first extracted from its ores., 
I he ores from which iron is usually obtained 
are composed of oxide of iron and clay, lire 
object of the manufacturer is to reduce the 
oxide to the metallic state, and to separate 
all the clay with which it is combined. These 
two objects are accomplished at once, by 
mixing the ore reduced to small pieces with a 
certain portion of limestone and of charcoal, 
and subjecting the whole to a very violent 
heat in furnaces constructed for the purpose* 
I lie charcoal absorbs the oxigen of the oxide. 
Hies off in tire state of carbonic acid gas, and 
leaves the iron in the metallic state; the 
lime combines with the clay, and both toge- 
ther run into fusion, and form a kind of fluid 
glass ; the iron is also melted by the violence 
ot the heat, and being heavier than the glass, 
falis down, and is collected at the bottom of 
the furnace. Thus the contents of the fur- 
nace are separated into two portions; the 
glass swims at the surface, and the iron rests 
at the-bottom. A hole at the lower part of 
the furnace is now opened, and the iron al- 
lowed to flow out into nroulds prepared for its 
reception. 
I he cast iron thus obtained is distinguished 
by tire following properties: It is scarcely! 
malleable at any temperature. J t is generally 
so hard as to resist tire file. It can neither 
be hardened nor softened by ignition and 
cooling. It is exceedingly brittle. It melts 
at 130 Wedgewood. It is more sonorous 
than steel. For the most part it is of a dark- 
grey or blackish colour; but sometimes it is j 
whitish, and then it contains a quantity of 
phosphuret of iron, which considerably' im- 
pairs its qualities. A great number of uten- I 
sils are formed of iron in this state. 
r Io convert it into w rought iron, it is put 
into a furnace, and kept melted, by means of 
the flamg ot the combustibles, which is made 
to play upon its surface. While melted, it is 
constantly stirred by a workman, that every 
part of it may be exposed to the air. In 
about an hour the hottest part ot the mass 
begins to heave and swell, and to emit a lam- 
bent blue flame. This. continues nearly an 
hour ; and by that time the conversion is 
completed. The heaving is evidently pro- 
duced by the emission of an elastic fluid. As 
the process advances, the iron gradually ac- 
quires more consistency; and at last, not- 
withstanding the continuance of the heat, it 
10 
