Jir Vault of the Furnaces of the Devon Iron Works: at 



a partner and manager of thefe works, in order to increafe the produce of Uaft 

 furnaces. 



The two blaft furnaces at Devon are of large dimenfions, each being 44 feet high, 

 and about 13 feet wide in the boflies, or wideft part, and arc formed, on a fteep bank, by 

 two pits funk in a very folid flratum of coarfe grained freeftone. 



Thefe pits were afterwards fliaped and lined in the ufual manner of blaft furnaces, with 

 common bricks and fire bricks, and the hearth was laid with large blocks of the ftone 

 that had been dug out, and which ferve the purpofe of fire ftones. At the back of the two 

 furnaces, next the bank, the air vault is excavated, and formed by a mine drove in the 

 folid rock, diftant from the furnaces about 16 feet. The bottom of the air vault is only 

 about 4 feet higher than the level of the bottom of the furnaces. This vault has an 

 aperture at one end to receive the air from the blowing machine, and has two at the 

 ■ oppofite end, one of which receives the eduftion pipe, and the other is a door to give ad- 

 mittance occafionally into the vault. As the rock is extremely clofe and folid, the vault is 

 dry, except that a little water ouzes very gently from the fide next the bank in fmall drops, 

 and does not appear to exceed an Englilh pint in 24 hours. 



Thefe furnaces are provided with air, or blaft, as it is termed, by the means of a fire- 

 engine of the old, or Newcomen's conftruction. The diameter of the fteam cylinder is 

 -481 inches; and the fquare area of its pifton being about i866|^ fquare inches, the power 

 of this fort of engine cannot be rated at more than 7 lb. to the fquare inch, amounting in 

 all to about 13062 lb. This power was employed to work an air pump, or blowing 

 cylinder, of 78 inches diameter, and about 7 feet long. The number of fquare inches on 

 the pifton of the air pump is 4778, and therefore this area, being multiplied by a^-, will 

 produce 13139, being a refiftance that nearly balances the above-rated power, and fhows 

 that the air, which was expelled from the air pump, could not be condenfed more in the 

 ordinary way of working, than with a comprefiSng power of about 2| lb. on each fquare 

 inch; As the engine was not regulated, at firft, to make a longer ftroke than about 4 feet 

 8 Inches, only one furnace being ufed, the quantity of air expelled at each ftroke of the 

 machine was about 155 cubic feet, which it difcharged through a valve into the air vault, 

 about 16 times in a minute. When two furnaces afterwards were blown, the engine was 

 regulated to work much quicker, and with a longer ftroke. The air vault is 7a feet long, 

 14 feet wide, and 13 feet high; and contains upwards of 13,000 cubic feet, or above 80 

 times the contents of the air pump. The top, fides, and bottom of this vault, where the 

 leaft fifTure could be difcovered in the beds of the rock, were carefully caulked with 

 oakum, and afterwards plaftered, and then covered with pitch and paper. The intention 

 of blowing into the vault is to equalize the blaft, or render it uniform, which it effefts 

 more completely than any machinery ever yet contrived for the fame purpofe. The air is 

 conduced from the vault by the edudllon pipe, of 16 inches diameter, into an iron box 

 ot wind cheft, and from this it goes off to each furnace, in two fmaller pipes that terminate 

 in nozles, or yow-pipes, of only 2^ to 3I inch diameter, at the twcer of the furface. 



4 When 



