IRON 



949 



in which a metallic piston is exactly fitted as for a steam-engine, and made in the 

 same way. Towards the top and bottom of the blowing-cylinders orifices are left 

 covered with valves, which open inside when the vacuum is made with the cylinders, 

 and afterwards shut by their own weight. Adjutages conduct into the iron globe or 

 chest the air expelled by the piston, both in its ascent and descent, because these 

 blowing-machines have always a double stroke. 



The pressure of the air is made to vary through a very considerable range, according 

 to the nature of the fuel and the season of the year ; for as in summer the atmosphere 

 is more rarefied, it must be expelled with a compensating force. The limits are from 

 l to 3 Ibs. on the inch, the average in Staffordshire being 3lbs. The orifices, or 

 nose-pipes, through which the air issues, also vary with the nature of the coke and 

 the ore. 



In a blast-apparatus employed at the Cyfartha works, moved by a 90-horse 

 steam-power, the piston-rod of the blowing-cylinder is connected by a parallelogram 

 mechanism with the other end of the working-beam of the steam-engine. The cylinder 

 is 9 feet 4 inches in diameter, and 8 feet 4 inches high. The piston has a stroke 

 8 feet long, and it rises 13 times in the minute. By calculating the sum of the space 

 percursed by the piston in a minute, and supposing that the volume of the air ex- 

 pelled is equal to only 96 per cent, of that sum, we find that 12,588 cubic feet of air 



are propelled 

 every minute. 



* blowing -ma- 

 chines of this 



nature gives on an average 137 

 cubic feet of air per minute. 



At the establishment of Cyfartha 

 for blowing seven smelting fur- 

 naces, and the seven corresponding 

 fineries, three steam-engines are 

 employed, one of 90 horse-power, 

 another of 80, and a third of 40, 

 which constitute on the whole a 

 force of 210 horses, or 26 horses 

 and fth per furnace, supposing the 

 fineries to consume one-eighth of 

 the blast. In the whole of the 

 works of Messrs. Crawshay, the 

 proprietors of Cyfartha, the power 

 of about 340 horses is expended 

 in blowing 12 smelting furnaces 

 and their subordinate fineries ; 

 which gives from 25 to 26 horses 

 for each, allowing as before th for 

 the fineries. Each of the furnaces 

 consumes about 3,567 cubic feet of 

 air per minute. 



' As an example of the blowing 

 power used in Cleveland, the blast- 

 furnaces at Ayresome may be se- 

 lected. They are four in number : 

 each 18 feet high ; 25 feet width 

 of boshes; 15 feet broad at throat, 

 with cup and cone ; 10 feet 6 inches 

 broad. The hearth is 8 feet dia- 

 meter; 3 feet deep below tuyeres, 

 and 4 feet above them. There are 

 10 boilers for four furnaces, but 

 only 8 are in use at a time. They 

 are plain cylinders, 60 feet long, 

 and 4 feet in diameter. 



There are 3 blast-engines; but 

 2 only required to blow the four 



furnaces. They have 96-inch blast- and 40-inch steam-cylinders ; the steam-pressure 

 is 50 Ibs., and the blast 4| Ibs. in the engine house, equal to 4 Ibs. at the tuyeres. 



