441 
The difference between cast iron and malleable or wrought 
iron, is chiefly due to the presence in the former of a con- 
siderable quantity of carbon in combination with the iron. 
In order, therefore, to convert cast iron into malleable iron, 
it is requisite that we remove or drive off the carbon from 
the cast iron. This object is effected by exposing the 
surface of a quantity of molten cast iron as it lies in that 
state on the bottom of a suitable reverberatory furnace, to 
the action of a current of heated air, so that the oxygen 
of the air, as it passes over the surface of the molten cast 
iron, may combine with the carbon and carry it off in the 
form of carbonic acid and carbonic oxide gases. 
But as the naturally tranquil surface of the molten cast 
iron would not present sufficient surface of metal to the 
action of the air drawn over it by the draft of the furnace, 
and would, if left in a tranquil state, require a very long 
time to elapse ere the carbon was by the action of the air 
abstracted from the cast iron, it is found requisite to agitate 
the metal, so as to continually expose fresh surfaces to the 
decarbonising action of the air. 
This agitation is effected by raking the molten metal 
backward and forward by an iron rake or paddle called a 
" rabble," worked by the attendant at the furnace, who 
puddles amongst the molten iron with his rake to effect the 
agitation required — hence the term " puddling." As these 
iron rabbles have to be made of considerable strength and 
weight, and as the iron through which it is moved is 
somewhat stiff, although in a fluid state, the labour of 
this process of puddling is excessive, and it has in the 
ordinary system to be continued without interruption for 
upwards of thirty-five to forty minutes, the workman 
being all the while exposed to the violent heat of the 
surface of the furnace, distant only three to four feet from 
his person. 
