Of the DEVON IRON WORKS. ^Z 



contents of the air punip. The top, fides, and bottom of this 

 vault, where the lead fiffure coald be difcovered in the beds ol" 

 the rock, were carefully caulked with oakum, and afterwards 

 plaflered, and then covered with pitch and paper. The inten- 

 tion of blowing into the vault is to equalize the blaft, or render 

 it uniform, which it efFecfls more completely than any machi- 

 nery ever yet contrived for the fame purpofe. The air is con- 

 duced from the vault by the edudlion pipe, of i6 inches dia- 

 meter, into an iron box or wind cheft, and from this it goes off 

 to each furnace, in two fmaller pipes that terminate in nozles, 

 or blow-pipes, of only 2 j to 2,-4 inch diameter, at the tweer of 

 the furnace. 



When the furnace was put in blafb, after having been filled 

 with coakes, and gently heated for more than fix weeks, the 

 keepers allowed it to have but little blafl: at firft, giving it a 

 fmall blow-pipe of about 2\ inch diameter, and likewife letting 

 off a very confiderable quantity of air, at the efcape, or fafety 

 valve on the top of the iron wind cheft, as it is a received 

 though erroneous opinion among them, that the blaft muft be 

 let on very gradually for feveral months. From the conftruc- 

 tion of this valve, it was impollible to afcertain the exadl propor- 

 tion of the blaft they thus parted with, but I believe it was very 

 confiderable. The confequence was, that the furnace, after it 

 had been in blaft for feveral days, never feemed to arrive at its 

 proper degree of heat, but was always black and cold about the 

 tweer in the hearth, and appeared in danger of choking, or gob- 

 bing, as it is termed. 



After various experiments tried in vain, by the keepers 

 and the Company's engineer, and others, (indeed they tried 

 every thing, except giving the furnace a greater quantity of 

 air, which, as I afterwards afcertained, was all that it wanted), 

 they concluded, that the air vault was the caufe of the whole 

 mifchief ; and, to confirm their opinion, they faid they had 



Part I. E now 



