Me. George Thomson on Blast Furnaces. 



91 



45 feet high, worked with raw coal and hot blast; it produced 100 tons 

 a week, being blown with five twcres, of 3 inches diameter each. 



The cross pipes of the heating apparatus were four inches diameter, 

 and one apparatus supplied all the twe'res. 



The alteration was this — the number of heating pipes were increased, 

 the cross pipes increased in size from 4 inches diameter to 7 inches 

 diameter, and the main pipes also enlarged ; the top of the furnace 

 widened from 4 feet diameter to 7 feet diameter ; the number of 

 tweres increased from five to six, (two on each side and two at back,) 

 each of 3i inches diameter ; a new steam cylinder of greater power 

 was put to the blast engine, but the blast one was kept at same size. 



The consequence is, that more than 150 tons of iron have been pro- 

 duced at this furnace in one week, with an improvement of yield, and 

 the engine goes no more strokeSf showing that actually no more air is 

 forced into the furnace than when making only 100 tons a week, (two- 

 thirds of present quantity,) although with a much greater area of nozles. 



TABLE No. II. 



I give a short table of the pressure of blast, which shows that the 

 qnantity of blast bears no constant proportion to the capacity of for- 



