Year: 1877

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A very,important paper has lately been
read before the Society of Arts by Mr..
Barff, Professor of Chemistry to the
Royal Academy, upon method of pre-
serving iron from rust by coating it with
its own magnetic oxide. The facts which
Prof. Barff has brought forward, and the
such as to justify the belief that his dis
covery will prove to be one of enormous
value, and that it will, indeed, render all
all kinds of iron-work, however much ex-
posed to weather or to corrosive vapors
or liquids, practically indestructible and
everlasting.


When an iron surface is exposed to the
action of water, or of moist air. it speed
lily becomes covered by film of pro-
toxide, or ferrous oxide, which consists
of SO parts by weight of the metal to Is
parts of oxygen. The ferrous oxide
continues to attract oxygen from the
atmosphere, and is gradually con-
verted into another compound, the
sesquioxide, or ferric oxide, which is
composed of twice Sc parts by weight
of iron, and three times 16 parts by
weight of oxygen. The fer4ic oxide, in
its turn, gives up some of its oxygen to
the as vet unoxidized iron beneath it, and
the ferrous oxide thus formed is gradu-
ally converted into ferric oxide by the
access of air through the spongy layer of
superficial rust which covers it. In this
way the first formed film of rust exposes
to the atmosphere the surface which lies
below it and hence the rust becomes
carrier of oxygen to the deeper parts of
ba 1aft 10 OF alxy
corroded and worn through. Many at
tempts have been made to protect iron
surfaces by the application of some kind
of paint or varnish and these attempts
have, of course, been to some partial
extent successful. Such coatings, how
ever, have no real adhesion to the metal
on which they are placed, and are liable
to scale off or to perish in a variety of
ways. Even when the coating is gen.
orally sound, the smallest flaw in its con-
tinuity will give entrance to the enemy !;
for the rust from the exposed spot will
spread laterally under the coating, and
may be all the more dangerous and de-
structive from being partially concealed
from view.


1t is manifest that the evils incidental
to rusting are entirely due to the un-
stable character of the two oxides already
mentioned, which are formed spontane-
ously under ordinary climatic conditions.
There is, however, a third oxide which
possesses characteristics of totally diff
ferent kind, and which is uninhuenced,
not only by moist air, but even by acids
and other corrosive substances. This is
the magnetic or black oxide, which con-
sists of three times fifty-six parts by
weight of iron, and four times sixteen
parts by weight of oxygen. Prof. Barff
has discovered that if any iron article is
exposed, at high temperature, to the
action of superheated steam, it will be-
come covered by film of this black
oxide, of thickness which is determined
by the degree of temperature and by the
length of exposure. The oxide is harder
than the original iron, and adheres to it
even more firmly than the particles of
iron adhere to each other, 80 that there
is gain not only in chemical. but also in
mechanical resistance. If the operating
chamber is heated only to 500 degrees
Fahrenheit, and the exposure is con-
tinued for only five hours, a surface is
obtained which will resist emery-paper
for q considerable time, and which will
not rust within doors, or after any mod
crate degree of exposure to moisture. If
the oxidizing process is conducted at
1900 degrees Fahrenheit, and continued
for six or seven hours, the surface will
resist rasp and will bear any amount of
exposure to weather. The oxidation
does not affect the appearance of the sur
face in any other way than by turning it
black. Arough forging retains its rough
ness, and turned or polished surface
its smoothness. Ii there should be any
flaw in the coating, or if the black oxide
is designedly removed from part of the
surface, the common oxidation will occur
where the iron is thus left unprotected.
But such oxidation is strictly limited to
the unprotected portion, and has not the
smallest tendency either to spread later
ally under the black oxide or to detach
this from the subiacent parts.


Among the most valuable ana impor-
tant of the probable applications of the
invention will be the protection of steam
boilers and of the plates of iron ships;
and Prof. Barff hopes that by certain
arrangements it will be possible to
operate upon very large manufactured
articles without its being necessary to
provide heating-chamber large enough
to contain them. The applications seem
almost without number. The process
will be conducted at very small cost, and
it will probably be employed, at no dis
tant time, for iron goods of every de-
scription. Not only so, but it will extend
the applications of iron itself to several
purposes for which its liability to rust
hitherto rendered il unsuitable. Copper
vessels will no lenger possess any advan-
tages for cooking, and iron saucepans
will no longer need to be timed. Leaden
pipes for the conveyance of water will in
all probability be entirely superseded I;
and there can be no doubt that new uses
for incorrodible iron will every day sug-
gest themselves.