ti6 On toe various 'Ejj'eds produced by 



of expanfive force, the following important ti'uths may hi 

 learned : That the quantity of oxygen which enters into our 

 atmofpheric compound is generally more fit for the manu- 

 farture of the fuperior qualities of crude iron than anv ^Tiix- 

 ture which may be furuillicd by the addition of water : that, 

 although the decompofition of water, by furnifliing a fuperior 

 quantity of oxygen, and bv throwing oif a relative proportion 

 of caloric, increafes the eflefts of combuftion immediately in 

 the vicinity of this chemical analyfis; yet, as the water had 

 previoufly abftrafted the heat neceflary to its decompofition 

 from the inferior flrata, a greater quantity by no means exifl.3 

 in the furnace. The water, in faft, only ferves as a medium 

 to convey the heat from one particular fpot, but, by attempt- 

 ing to fly off" with it, meets decompofition, and renders up 

 not only the abllra6led heat, but that which was contained 

 i-n the oxygen of its decompofitFon. 



4th, l^he comprefllion and velocity of the air difcharged. 

 into the furnace, confiderably afteft the refulls of the fmelt- 

 ing operations. In the eonfideratlon of this fubjeft, the va- 

 rious qualities of coals will be found to have an intimate 

 connexion with the area of the difeharging-pipe and the 

 coml^reffion of the blafl. It has already been more than 

 once obfefved, that a foft or mixed quality of coal is more 

 fufceptible of combuflion than either the fpllnt or clod-coal : 

 the confequoncc of this is, that, unlefs the neceflary com- 

 pi'eflion of air is rfed, decompofition is too early accom- 

 plifhed, and the cokes become oxygenated by combufi;ion in 

 a greater ratio than is proper for the carbonation of the me- 

 tal. To avoid this, the column of air ought to be difcharged, 

 in the cafe of foft coals being unavoidably ufed, under fuch a 

 degree of compreflion, as to refill entire decompofition in the 

 ignited paflage. In that cafe, the iron docs not fo immedi- 

 ately com€ into contact with oxygen, as the decompofition 

 is chiefly effeflcd in the luperior Itrata of the feparating ma- 

 terials. Under the former circumliaucc, of a loofc uncoii- 

 nefted ftream 'A' air being thrown upon cokes eafily com- 

 buftible, the quality of tlie metal, with the fame quantity of 

 fuel, becomes oxygenated, the tuyre becomes fiery, and fre- 

 quently emits fparks of metallic oxyd. The feparating iron 



may 



