gh not always, more carbon is found in steel than in wrought iron. A
number of processes are in use, but nearly all the steel of commerce is
made by one of the two following methods.

[Illustration: Fig. 87]

1. _Bessemer process._ This process, invented about 1860, is by far the
most important. It is carried out in great egg-shaped crucibles called
converters (Fig. 87), each one of which will hold as much as 15 tons of
steel. The converter is built of steel and lined with silica. It is
mounted on trunnions T, so that it can be tipped over on its side for
filling and emptying. One of the trunnions is hollow and a pipe P
connects it with an air chamber A, which forms a false bottom to the
converter. The true bottom is perforated, so that air can be forced in
by an air blast admitted through the trunnion and the air chamber.

White-hot, liquid cast iron from a blast furnace is run into the
converter through its open necklike top O, the converter being tipped
over to receive it; the air blast is then turned on and the converter
rotated to a nearly vertical position. The elements in the iron are
rapidly oxidized, the silicon first and then the carbon. The heat
liberated in the oxidation, largely due to the combustion of silicon,
keeps the iron in a molten condition. When the carbon is practically all
burned out cast iron or spiegel iron, containing a known percentage of
carbon, is added and allowed to mix thoroughly with the fluid. The steel
is then run into molds, and the ingots so formed are hammered or rolled
into rails or other forms. By this process any desired percentage of
carbon can be added to the steel. Low carbon steel, which does not
differ much from wrought iron in composition, is now made in this way
and is replacing the more expensive wrought iron for many purposes.

~The basic lining process.~ When the cast iron contains
phosphorus and sulphur in appreciable quantities, the lining of
the converter is made of dolomite. The silicon and carbon burn,
followed by the phosphorus and sulphur, and the anhydrides of
acids so formed combine with the basic oxides of the lining,
forming a slag. This is known as the basic lining process.

2. _Open-hearth process._ In this process a furnace very similar to a
puddling furnace is used, but it is lined with silica or dolomite
instead of iron oxide. A charge consisting in part of old scrap iron of
any kind and in part of cast iron is melted i