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 tweer, 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 5^ cwt. of coal, which had 

 not previously to be converted into coke. Adding to this 8 cwt. 

 of coal for heating, we have 2 tons 13^ cwt. of coal required to 

 make a ton of iron ; whereas, in 1829, when the cold blast was 

 in operation, 8 tons 1£ cwt. 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. 



