100 
THE PRINCIPAL FLOOR. 
frequently stirred or rabbled. The operation is called 'puddling, 
and instead of relying entirely on the action of the air to 
remove the excess of carbon, a variable proportion of the 
oxide of iron or of maganese is commonly employed. As the 
carbon passes off as carbonic oxide the iron becomes less fusible, 
and ultimately breaks up into an incoherent granular mass 
like sand. The heat is then increased, the grains agglutinate, 
and being worked up into a ball, the mass is taken from 
the furnace and subjected to great pressure by machinery. The 
lump of malleable iron thus obtained is then passed through a 
succession of rollers, turned by a powerful steam engine, each 
pair of rollers having a smaller interval than the preceding ; by 
this means the mass is gradually elongated into a bar, and at 
the end of the rollers furthest from the furnace it passes out 
as the soft bar iron of commerce. Some fine examples of such 
iron will be found in the entrance hall. 
Whilst pig-iron is always brittle and exhibits a more or less 
crystalline structure, the puddled iron, after being duly ham- 
mered and rolled, is extremely malleable andjcresents on f racture 
a decidedly fibrous texture. Some specimens in Case 51 are 
interesting as illustrating a supposed alteration in the structure 
of wrought iron by vibration. 
A railway axle bent by an accident without breaking will be 
found in the Model Room A. 
Steel Manufacture. Table Case 11. — Steel may be regarded, 
in its typical form, as representing a condition intermediate 
between cast iron and wrought iron. The proportion of carbon 
which is present varies considerably in different varieties ; mild 
steel may not contain more than 0*2 per cent., or, when very 
soft, even less, whilst the harder tempers may contain ten times 
as much, or nearly 2 per cent. 
Steel is sometimes formed directly from the ore, as in the 
Catalan forge ; more frequently it is obtained by adding carbon 
to malleable iron, as in the old process of cementation ; whilst 
often again it is produced by the decarbonization of pig-iron, 
as in the Bessemer process, and in the basic process of Messrs. 
Thomas and Gilchrist ; or, finally, it may be obtained by the 
addition of oxidised iron ores, or of a malleable iron to pig-iron 
in an open hearth, as in the Siemens and Siemens-Martin 
processes. The old cementatian method of steel making is here 
illustrated by a series of specimens from Sheffield. 
Blister Steel probably owes its warty surface to the formation 
within the mass of a gaseous compound of carbon and oxygen, 
which occasions the formation of bubbles in the metal. 
The shear steel is made from blistered bars, by cutting them 
into lengths, fagotting several together, re-heating and welding 
the pile, and then hammering or rolling it into rods. 
In making the cast steel, shown here, blister bars are broken 
into small pieces and fused in a barrel-shaped crucible of Stour- 
bridge clay, and the molten steel is then poured into a mould. 
