TRANSACTIONS OF THE SECTIONS. 
609 
Having attentively examined this bridge during the progress 
of building,—having conversed with M. von Mitis on the sub¬ 
ject,—and being strongly impressed with the opinion that the 
employment of steel as a material for bridge suspension is of 
very great advantage, and forms a most important epoch in 
bridge-building,—I am very desirous of calling the attention 
of the scientific world, and particularly of civil engineers, to the 
serious consideration of the question,—How far ought iron to 
be hereafter used for suspension-bridges, since it is ascertained 
that a steel bridge can be built of equal strength, and superior 
durability, with one third or one fourth of the weight of an iron 
one, and at a much less expense, provided steel can be manu¬ 
factured in this country upon the same principles as that made 
in Styria? 
The only doubt of this being practicable on the large scale, 
arises from the circumstance, that in this country iron is made 
with mineral coal, but in Styria with charcoal of wood. 
It is well known that steel is made by decarbonizing cast 
iron, which is a compound of iron and carbon, down to the 
state of iron, (in which state it is wrought into bars); and re¬ 
carbonizing these bars up to the state of steel, in which state 
the iron is combined with a less proportion of carbon than was 
contained in it in the state of cast iron. 
Now the Austrian improvement consists in decarbonizing 
the cast iron down to the point at which the proportion of car¬ 
bon left in the iron is exactly sufficient to constitute steel, in 
which condition it is wrought into bars, which are found to 
be of a tougher quality than steel made in the ordinary way. 
It would appear that the carbon remains more uniformly com¬ 
bined with the iron, when the surplus quantity is removed, than 
when the new dose is given to it. 
Thus the expense is saved of the extra decarbonization and 
the whole of the recarbonization, and consequently the steel is 
produced at a much less cost than could be effected by the com¬ 
mon process. 
But whether or not this simple operation will be equally suc¬ 
cessful upon the large scale, with mineral coal, as with the char¬ 
coal of wood, is a problem which I would most earnestly call 
upon the iron-masters of the United Kingdom to lose no time 
in endeavouring to solve;—a problem of immense consequence 
to a large range of the manufactures of the country, and there¬ 
fore a high national object. The hope that this will be accom¬ 
plished is strengthened by the fact, that many small articles 
are now made of cast iron, and afterwards reduced down to 
steel. 
