6z On the t/ai'laus Effecfs produced hj^ 



particles are fo ft, the air is much more eafily decompofetl J 

 the ignition, of courfe,is more rapid : the defcent of the ma-* 

 terials is promoted beyond their proper ratio, and long be- 

 fore the carbonaceous matter has penetrated the ore, or 

 united to the metal, to conftitute fufibilitv. I (liall adduce 

 an example, as being moft illullrative of this doftrine. 



Siippoi'e a blaft-furnace, 3^ feet high, 11 feet wide at the 

 bolbes, properly burdened, and producing No. i, pig-iron. 

 Let the difcliarge of air be fuppofed equal to a prefllire 7,- 

 pounds upon the fquare inch, or equivalent to i-6th of the 

 atmofphcre, 01: 5 inches of mercury : under thefe circum- 

 ftances let it farther be fuppofed, that 1500 cubical feet of 

 air are difcharged in one minute; and that the diameter of 

 the difcharging-pipe is 2*625, the area of which is equal to 

 6'S<)o62'^ circular inches. Let the difcharging-pipe be in- 

 creafed tu 3 inches diameter, and let the fame quantity of 

 air be pallVd into the furnace; it is evident that as the area 

 of the difcharging-pipe is increafed to 9 circular inches, or 

 nearly i-3d more than formerly, the compreflion of air muft 

 be proportionally diminiflied. This alteration is foon per- 

 ceived by its eflerts ; the quantity of fcoria increafes from 

 the furnace, wliiKl; the confumption of the materials above 

 is alfo confiderably augmented. In a few hours the fcoria 

 will have undergone a complete change, from pure white, 

 enamelled with various blue {hades, to a green, brown, or 

 black colour, confiderably charged with the oxyd of iron *. 

 The fame eflc<fts will continue, in greater or lelTer degree, till 

 all the materials are reduced which were exiftino- in the fur- 



o 



nace at the period of diminiflied compreflion. The philo- 

 fophy of this fact may be accounted for in the following 

 manner : — 



While the juft aflociation of proportions remained, the air 

 was difcharged under fuch a degree of compreflion as to 

 excite proper combuftion : the decompofition of the air by 

 means of the igiiited fuel, was not cft'ccled in immediate con- 

 taft with the feparating metal, but had, by its uncommon 

 degree of denfity, refifted decompofition in the ignited paf- 



'■' The metal will hnve loft nearly all its carbon, and.havc become in- 

 f/rior in value 15 to 10 J>cr cent. 



