IRON. 
became perfectly hard. The heat in both plates in the nsual way, in which state they 
cases was a low red heat, proper for cast are brittle and warped: they then soften 
steel, which is not intended to be afterwards them by blazing, which consists in smearing 
annealed. We have very little doubt, but that the plate with oil or grease, and heating it 
alcohol and the essential oil of turpentine, till thick vapours are emitted, and burn off 
which are good conductors of heat and very with a blaze ; and after this they may be 
volatile, would render steel very hard, if hammered flat ; lastly, they blue them on a 
their inflammability, and the little necessity hot iron, which renders them stiff and elas- 
there is for using them, were not an impe- 
diment to their application. Various artists 
avail themselves of different substances for 
the immersion of ignited steel. Some use 
urine, others water charged with common 
salt, nitre, or sal ammoniac. Tallow and 
oil are used for such works as are not re- 
quired to be brittle, though very hard, the 
reason of which has just been mentioned ; 
but tallow differs from oil in the heat which 
becomes latent for its fusion ; and accord- 
ingly, solid tallow is an excellent material 
for hardening drills and other small articles. 
It has been found by Reaumur, that saline 
liquids produce rather more hardness than 
common water; and in particular, that 
aquafortis possesses this property in an 
eminent degree, probably from its conduct- 
ing power: the makers of files cover them 
with the grounds of beer and common salt, 
which assist their hardening, and keep the 
surface from scorifying. The mucilage of 
the beer supplies a coally matter; and the 
fused salt seems not only to form a varnish 
in the fire and defend the steel, but may 
also produce cold, by its sudden solution in 
the water at the time of immersion. Very 
small articles heated in a candle are found 
to be hardened perfectly by suddenly whirl- 
ing them in the cold air; and thin bars or 
plates of steel, such as the magnetic needle 
■of a compass, acquire a good degree of 
hardness by being ignited, then laid on a 
plate of cold lead, and suddenly covered with 
another plate. These would be unequally 
hai dened, and bend, if plunged in water. 
The bluing of steel appears to affect its 
elasticity in a manner not easily explained. 
Thte operation consists in exposing ateel, 
the surface of which has been first brighten- 
ed, to the regulated heat of a plate of, metal, 
or a charcoal fire, or the flame of a lamp, 
till the surface has acquired a blue colour. 
Now, if this blue coal be removed by grind- 
ing, the elasticity is completely destroyed, 
and may be restored by bluing the steel 
again. Rubbing with sand or emery-paper, 
glazing, or burnishing, equally impairs the 
elasticity in proportion as it destroys the 
blue coat. Saw-makers first harden their 
tic without altering their flatness. 
The Damascus sword blades have long 
been celebrated for their excellence, but it 
is not known how they are made. Mr. 
Stoddart took six small bars of good mal- 
leable iron, and the same number of sheer 
steel ; laid them alternately on each other ; 
welded them together ; forged them into a 
stout flat plate, which was twisted spirally 
into a cylinder, hammered flat, and again 
welded ; hammered this flat, doubled it 
throughout its length, inserted in the fold a 
slip of good steel to form the edge, and by 
another welding heat consolidated the 
whole into one mass. This being forged to 
a proper shape, cracked in different places 
on being cooled in water after heating : but 
Mr. Stoddart conceives, that by using more 
pieces, repeating the twisting, and not 
quenching in water, the process would 
succeed. 
Every species of iron is convertible into 
steel by cementation ; but good steel is not 
to be made except from iron of the best 
quality, which possesses a certain stiffness 
and hardness as well as malleability. Swe- 
dish iron, as we have before remarked, is 
the best for this purpose. M. Duhamel 
tried a great number of the irons of France, 
Sweden, and Spain. He found the second 
to be the best; but he likewise obtained 
excellent steel, superior to those of Styria 
and Carintbia, which are the best German 
steels, by using certain iron made in France. 
But this iron was selected without fault; 
and, in some instances, the loup or piece at 
the smelting furnace was fused and forged 
a second ti ne-f a process which, though 
attended with loss of weight and additional 
expense, he recommends as absolutely ne- 
cessary for making steel iron from ores of 
indifferent quality. The white spathose iron 
ores afforded him the best iron for the pur- 
pose of cementation ; and these also are the 
ores which afford the best steel by fusion in 
Styria, Carinthia, and Tyrol. He informs 
us that the English use no other cement 
than mere charcoal, which he also ’'finds 
perfectly adequate to the purpose ; and, 
moreover, that the quality of the steel is 
