^26 Phenomena ohferved in the Air- Vault 



the vault is to equalife the blaft, or render it uniform, which 

 it effefts more completely than any machinery ever yet con- 

 ftrived for the fame purpofe. The air is condufted from the 

 vault by the edu6lion-pipe, of 16 inches diameter, into an 

 iron box or wind-cheft, and from this it goes off to each 

 furnace in two fmaller pipes that terminate in nozzles, or 

 blow-pipes, of only 2[ to ^ inch diameter at the tweer of 

 the furnace. 



When the furnace was put iu blaft, after having been 

 filled with cokes, and gently heated for more than fix weeks, 

 the keepers allowed it to have but little blaft at firft, giving 

 it a fmall blow-pipe of about 2'^ inch diameter, and likewiie 

 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 fevcral months. From 

 the conftrutlion of this valve it was impoffible to ai'ccrtain 

 the exa6t proportion 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 ap- 

 peared in danger of choaking, or gobbing, as it is termed. 



After various experiments, tried in vain, by the keeper? 

 . 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 want- 

 ed,) they concluded that the air-vault was the caufe of the 

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

 had now difcovered that water was, in confiderable quan- 

 tities, driven out of the air-vault through the blow-pipe, 

 which cooled the furnace ; and they infifted, that the power 

 of the engine was fuch as to force water out of the folid rock ; 

 fo that this method of equalifing the blaft never would fuc- 

 ceed. The other managing partner was fo much alarmed 

 by thefe reprefer.tations, that he began to conlult with the 

 engineer, and others^ about finding a fubftitute for the air- 

 vault at any expence. 

 As the plan of the blowing apparatus had been adopted at 



my 



