in the Manufacture of Cast-Iron. 377 
The temperature of the air under blast had now been raised so 
as to melt lead, and sometimes zinc, and therefore was above 
600° Fahr., instead of being only 300°, as in the year 1830. 
The furnace had now become so much elevated in tempera- 
ture, as to require, around the nozzle of the blowpipes, a precau- 
tion borrowed from the finery-furnaces, wherein cast-iron is con- 
verted into malleable, but seldom or never employed where cast- 
iron is made by means of the cold blast. What is called the 
Tweer, is the opening in the furnace to admit the nozzle of the 
blowpipe. This opening is of a round funnel-shape, tapering 
inwards, and it used always to have a cast-iron lining, to protect 
the other building materials, and to afford them support. This 
cast-iron lining was just a tapering tube nearly of the shape of 
the blowpipe, but large enough to admit it freely. Now, un- 
der the changes I have been describing, the temperature of the 
furnace became so hot near the nozzles, as to risk the melting of 
the cast-iron lining, which, being essential to the twee7, is itself 
commonly called by that name. To prevent such an accident, 
an old invention called the water-tweer was made available. The 
peculiarity of this tweer consists in the cast-iron lining already 
described being cast hollow instead of solid, so as to contain wa- 
ter within, and water is kept there continually changing as it 
heats, by means of one pipe to admit the water cold, and ano- 
ther to let the water escape when heated. * 
During the first six months of the year 1833, when all these 
changes had been fully brought into operation, one ton of cast- 
iron was made by means of 2 tons 54 ewt. of coal, which had 
not previously to be converted into coke. Adding to this 8 cwt. 
of coal for heating, we have 2 tons 134 cwt. of coal required to 
make a ton of iron; whereas, in 1829, when the cold blast was 
im operation, 8 tons 14 ewt. of coal had to be used. This being 
* An incidental advantage attended the adoption of the water-tweers, inasmuch 
as these made it practicable to lute up the space between the blowpipe nozzle and 
the tweers, and thus prevent the loss of some air that formerly escaped by that 
space, and kept up a bellowing hiss, which, happily, is now no longer heard. 
