Air njcd in the HI iijl~ Furnace. 6^ 



there is no method likely to be deyifed where heat •wonld not 

 be generated by the aftion of the particles of air upon each 

 other. When the bulb of a thermometer is held in the 

 middle of the current of biaft, as it ilfucs from the difcharg- 

 Jng-pipe, a temperature is indicated as much lower than the 

 temperature of the furrounding air, as the temperature of the 

 cylinder was higher ; and it is moft probable that a much 

 lower degree would be obtained, were it not for the previous 

 expreflion of fome heat in the blowing-cylinder. Upon the 

 whole, I think, tlie quality of the air obtained in this way 

 of blowing uniformly molt fit for combudion, provided the 

 numerous paufes and irregularities of the current of air were 

 done awav. 



Air forced into the furnace under water prcffure always 

 contains a coniiderable portion of moifture ; the blaft of 

 courfe is colder, as it iifues from the diicharging-pipe. The 

 temperature difl'ers fo much from that of the external air as to 

 fink the thermometer from 54° down to 28° and 30"^. Sucli 

 effefts are produced by air -coming into contaft with water, 

 that, although the temperature of tlie atmofphere is 60, 65^ 

 to 70, vet the blafl; at the orifice feldom rifcs above 38 : the 

 cold produced in this manner is much increafed if the air 

 is furcharged with fo much water as to be vil'ible in the ftate 

 of a fine fprav. The leading feature, therefore, of the water- 

 vault, as to its effects upon the fjuulity of the air, fcems to in- 

 dicate an almoft uniform degree of temperature in the blaft: 

 this can only be occafioued bv the warm air in fummer 

 faking up a greater portion of the water in folution, tl)e 

 efcape of which at a fmall orifice, and under a great dec;rce 

 of eomprelfion, produces the very great depreflion of the 

 thermometer. I have already hinted at the bad efiedils pro- 

 duced by moift blafts, and iball, in a proper place, more mi- 

 nutely attend to them. 



'J'he mod inferior quality of air ufcd in the blafi;-furnace 

 is that thrown into the air-vault, and afterwards exprefled 

 from thence by its own elafticily and the fucccffivc ftrokcs of 

 the engine. The capacity of fueh a building is from 60 to 

 70,000 cubical feet; this, wlien filled, generates a much fu- 

 j)erior degree of heal to that fcufible in the blowing-cvlindcr. 



As 



