Il8 On the EffeSts of Air f//>i in the BJaJl-Furnice. 



effeols arc produced with the clod coal, but in a more tvM^ 

 nent degree. Difcharging- pipes are ufed four inches in the: 

 diameter, and the comprcflinn only equal to two pounds ori 

 the fqaare inch ; yet the iame f;ita! efietls are not known as 

 in the nfe of foft coul, which, with fuch a cohmin of air, 

 would require the prellure to be equal to 3 1 pounds upon the 

 fquare inch at leaft. 



5tb, Upon the form and conftra-ilion of the difcharging- 

 pipe effects of more confiderable importance depend than i3 

 either generally allowed or even conceived. At fome iron- 

 works, no peculiar fliapc is adopted : if the tube is fufficicnt 

 to convey the air, and the mouth of it nearlv of tlie fize 

 wanted, the interior conftrutlion is cntirclv overlooked. This 

 indifference, however, is by no means general : varioully 

 conftruiled pipes are ufed at diflerent works, and at fome 

 places it is preferred to throw in the air from two pipes 

 whofe areas are only equal to one of the ufual fizc. 



The various (hapes mav, in point of the principle of their 

 conftruftion, be reduced to three. (See Plate V, Fig^ i, 2,3.) 



To underlland ])roperlv the objetlionable |)arts of the con- 

 flruftioii of nofe-nipes, it nuiit be recollected, that much 

 has j)ccn faid to depend upon the blali: reaching the oppofite 

 extremity of the furnace, as little impaired of the compaolncfs 

 and velocity of its original diicbarge as poffible. When it 

 is otherwife, the refults in the internal operations of the fur- 

 nace nudi. be confequentlv altered. If the comprcflion is 

 diminifhed ' or t when it reaches the oppolite wall, de- 

 compofilion in that portion mud be efl'ccled before the air 

 has attained its elevated fituation in tlie furnace. It is even 

 pollible to difperfe the whole column of air in fuch a manner 

 that the ignl.;.d materials of the oppofite fide may receive 

 little of its ctfcrts to promote combuftion. 



The difcharging-pipe Fig. i. is frequently ufed : its lenglh 

 is la inches or more; tiic diiciiarging aperture 3 inches, the 

 other end 5 inches; but thi:^ is arbitrary, depsndir;<j. upon 

 the fize of the adjoining pipe, Froni a pipe thus confirufted, 

 the air difpcrfcs or diverges" too fnddcHiy; and at a fmall dif- 

 tance from the oriiicc, a confiderable portion of it anfwers- 

 but imperfectly the purpofc^j^of conibuftion. Part of it is- 

 fpeedily decompofed. and the oxygen brought into immediate' 

 8 contact 



