Air ujed in the BlaJi^Ftirnacc. 63 



lage, and had been decompofed upon the cokes at a greater 

 elevation in the furnace. As a proof of this, we frcqiientiy 

 fee a tube formed throughout the whole breadth of the fur- 

 nace, quite black and apparently cold, formed of the fiifed 

 materials : when this is removed, a confiderable defcent mo- 

 mently takes place of cokes heated vilibly beyond the com- 

 mon pitch : thefe inflame rapidly, but are foon again cooled 

 to blacknefs by the incelTant difcharge of air upon them. 

 The defcending mixture of iron and lava are in like manner 

 cooled around the line of blaft; the tube is again formed, and, 

 if not removed, will remain for days together, while the fur- 

 nace will be otherways v/orking in the beft manner. 



When by accident or defign the compreflion and velocitv 

 of the blaft are dimini(hed, the tube begins to burn, and 

 throws off a great many red fiery- coloured fparks, the fides 

 and roof fail, and are carried before the blalt in all direc- 

 tions. Sometimes confiderable cloats of imperfect iron are 

 recoiled with fuch violence as to efcape the vortex of blall, 

 and iflfue from the tuvre-hole with fuch velocity as to inflani* 

 n\ the air, and fall down in the ftate of oxyd. In the end 

 the tuyre will appear to flame, and all the paflage inwards 

 fhews an aflonifiiins; degree of whitenefs. The decompo- 

 fition of the air is initantaneoufly eff'ecied upon its entering 

 the ignited palfage ; the iron by this means is expofed to ihci 

 oxygen that is difengaged ; and the vaft quantity of caloric 

 {et free, in confequence of its union with the iron and carbon, 

 produces the aftonilliing heat now vifiblc, but which formerly 

 took place at a more proper height in the furnace. 



From this it will appear, that although a greater apparent 

 degree of heat is vifiblv produced bv tlic fudden deconipo- 

 filion of the air, and a more rapid defcent of materials for 

 fome time is the confec'iuence, yet, as the quality of the iron 

 ie impaired, and as in the end the furnace will return to its 

 pld confumption of materials as to quantity, the eifecls of a 

 ioofe foft blafl: are conclufivclv pernicious. 



It fomctimes happens, that when a Ioofe blafl; is furcharged 

 with a confiderable portion of moiflure, or comes in contact 

 with cokes which had been wet when introduced into the 

 furiucc, tlie iafliimmatiou which taJ<es place at the tuyre i^ 



prodigious; 



