64 On the various EffeBs produced hv 



prodigious: fine fire-clay will be- melted down and blown to 

 flag in a few minutes ; the fides of the furnace, compofed of 

 very infufible fire-llonc, is next attacked, and in a few 

 hours will be fo completely deftroyed as to ftop the work- 

 ins;, and require immediate repair. Effefts fimilar to thofe 

 now defcribed will be felt when blafl is improperly propor- 

 tioned to coal of a ftronger continuity of frafture and iuperior 

 quality. Bendes the efiocts produced by the ftiddcn decom- 

 pofition of iron, others of like nature are produced where a 

 foftcoal isufed, a fmall furnace, and a great difcharge of blaft. 



It has been found that crude iron, to be properly matured, 

 ought to remain in the blaft-furnace, according to circnm- 

 ftances, 48 to 60 hours ; that is, from the period that the 

 iron-ftone is introduced till fuch time as the metal begins to 

 occupy its place in the hearth in a ftate of perfeft feparation. 

 When the contrary is the cafe, the mixtures arrive at the 

 hotted parts of the furnace before the metal has taken up a 

 fufficient quantity of carbon from the fuel ; the acilion of 

 the blaft, and the immediate heat by which the ore is fur- 

 rounded, forces the iron from its connexions to the bottom 

 of the furnace. The quality is de- carbonated, and reduced 

 in its value : to reftore this again, the local portion of fuel is 

 increafedj this adds to the expence of manufaftiiring, and 

 ditiiiniflies, in fomc mcafurc, the fmclting of the furnace. 



When fplint-coal cokes are ufcd in the blaft-furnace, the 

 blaft admits of being thrown in under the higheft poffible 

 pitch of comprOffion ; the uncommon dcnfity of the charcoal 

 fuftains a very powerful difcharge of blaft before it is diflR- 

 patcd to facilitate the general defccnt. Moft frequently, large 

 niaftes of thcfe cinders pafs through the whole ignited cavity-, 

 and are thrown out below, poftefting all the acutenefs of their 

 original form and frafture. 



This quality of coal is ufed in all the Curfon blaft-furnaces, 

 where, to enfure a refpcftable produce, the air is difcharged 

 under a preflTure equal to ^'^ pounds upon the iquarc inch, or 

 6 5. inches of mercury. 



The fame quality of coal was ufed at the Devon iron- 

 works, where, at one time, having all the blaft of a 48 inch 

 eyiinder engine thrown into one furnace, the column of 

 8 nicrcary 



